INVITED REVIEW
DNA damage and cell cycle checkpoints in hyperoxic lung
injury: braking to facilitate repair
Michael A.
O'Reilly
Department of Pediatrics (Neonatology), School of Medicine and
Dentistry, University of Rochester, Rochester, New York 14642
 |
ABSTRACT |
The beneficial use of supplemental oxygen
therapies to increase arterial blood oxygen levels and reduce tissue
hypoxia is offset by the knowledge that it injures and kills cells,
resulting in increased morbidity and mortality. Although many studies
have focused on understanding how hyperoxia kills cells, recent
findings reveal that it also inhibits proliferation through activation of cell cycle checkpoints rather than through overt cytotoxicity. Cell
cycle checkpoints are thought to be protective because they allow
additional time for injured cells to repair damaged DNA and other
essential molecules. During recovery in room air, the lung undergoes a
burst of proliferation to replace injured and dead cells. Failure to
terminate this proliferation has been associated with fibrosis. These
observations suggest that growth-suppressive signals, which inhibit
proliferation of injured cells and terminate proliferation when tissue
repair has been completed, may play an important role in the pulmonary
response to hyperoxia. Because DNA replication is coupled with DNA
repair, activation of cell cycle checkpoints during hyperoxia may be a
mechanism by which cells protect themselves from oxidant genotoxic
stress. This review examines the effect of hyperoxia on DNA integrity,
pulmonary cell proliferation, and cell cycle checkpoints activated by
DNA damage.
deoxyribonucleic acid; genotoxic stress; phosphorylation; proliferation; p53
 |
INTRODUCTION |
SINCE THEIR EVOLUTION 500-1,500
million years ago, aerobic cells have been paying a price for their
ability to obtain more energy from carbon sources compared with
anaerobic cells because cytotoxic reactive oxygen species (ROS) form
during aerobic respiration that can damage DNA, lipids and proteins.
These ROS include superoxide anion (O
·), hydrogen
peroxide (H2O2), hydroxyl radical (OH·), and
peroxynitrite (ONOO
). Because ROS are formed during
normal respiration, cells have developed enzymatic and nonenzymatic
antioxidant defense systems to reduce intracellular redox levels. The
enzymatic antioxidant systems include superoxide dismutases, catalase,
and glutathione peroxidase. Nonenzymatic systems include vitamins (A,
E, and C), selenium, and other nutritional molecules. These systems
usually provide adequate protection against the damaging effects of
normal oxygen metabolites (see Ref. 97 for a review).
Oxidative stress and damage occur when the balance of produced ROS
exceeds the capacity of the cell to detoxify.
A second line of defense against oxidant injury involves repair of
damaged molecules important for cellular function. Unfortunately, identifying enzymes that repair oxidant damage has been difficult because ROS can attack all molecules and organelles, resulting in cell
injury and death. Several excellent reviews (92, 96, 139)
have been written recently that focus on ROS and various signal
transduction pathways activated in response to oxidative stress. These
reviews, however, did not address in detail the cellular response to
oxidant DNA damage, which occurs when cells are injured by ionizing
radiation (IR), bleomycin, prooxidant particles, hydrogen peroxide,
hyperoxia, or any other chemical that oxidizes cells (13, 24,
73). Radical attacks on DNA produce nearly 100 lesions that
include oxidation of bases and sugars, depurination, depyrimidation,
and phosphodiester single- and double-strand breaks (42).
ROS can also oxidize lipids, which, in turn, damage DNA and contribute
to oxygen toxicity (23, 138). Although molecular oxygen is
inert when exposed directly to DNA (55), its genotoxic
effects on cells have been known for nearly 50 years (34).
Because hyperoxia produces free radicals (164), many
investigators use hydrogen peroxide as a surrogate for hyperoxia in
their studies. Even though hydrogen peroxide oxidizes DNA, it remains
questionable whether it exerts the same damage as hyperoxia. For
example, the genotoxic effects of hydrogen peroxide include mutagenic
single-strand breaks, whereas hyperoxia induces chromosome aberrations
and sister chromatid exchanges (56, 57, 59). Second, iron
chelators such as desferrioxamine have no effect on hyperoxia-induced
clonogenic survival, whereas they are protective to cells damaged by
hydrogen peroxide (58). It also takes several days for
oxygen to injure and kill cells, whereas hydrogen peroxide takes
immediate effect and has an extremely short half-life. Thus most
studies with hydrogen peroxide are likely studying repair. In contrast,
studies with hyperoxia are done under continuous exposure where repair
is compromised by continual damage. Even with these differences, ROS
such as those produced by hyperoxia or hydrogen peroxide clearly damage
genomic DNA.
Cells can repair DNA damage, fixate the mutation in their genome, or
die by apoptosis or necrosis. Because apoptosis is a swift and noninflammatory form of cell death compared with necrosis, one could argue that it is a beneficial method to deal with cells injured by ROS (121). However, it is also advantageous for
cells, especially stem cells such as alveolar type II cells, to undergo repair so that the tissue and organism are not compromised. Given that
nearly 10,000 nucleotides/nucleus are oxidized each day during normal
respiration (101), one must consider that DNA repair is as
important in the cellular response to superphysiological levels of
oxygen as programmed cell death. This paper discusses the genotoxic effect of oxygen on cell proliferation, with particular emphasis on the
lung, and concludes with a review of how cells sense DNA damage and
transduce this signal to growth-suppressive molecules.
 |
HYPEROXIA AND ITS EFFECTS ON PROLIFERATION |
Cell proliferation during hyperoxic exposure.
Detailed morphometric and ultrastructural studies in animal models have
been used over the past 30 years to understand how hyperoxia affects
cells. Adult rats, mice, and monkeys exposed to lethal levels of oxygen
(>90%) appear unaffected for the first 48 h, after which they
become lethargic and fail to eat or drink, with mortality between the
fourth and seventh days (2, 16, 80). One of the first
morphological signs of injury is focal cytoplasmic swelling of
microvascular endothelial cells and interstitial edema that is followed
by endothelial cell fragmentation. In contrast, the alveolar epithelium
is relatively unaffected until after 72 h of exposure when
cytoplasmic swelling and death of the type I epithelial cell occur.
Closer examination revealed that the death of endothelial and type I
epithelial cells was due to progressive swelling of cytoplasm, nuclei,
mitochondria, and cisternae of the endoplasmic reticulum that was
followed by disintegration of the plasma membrane. These morphological
signs of death are consistent with death by necrosis
(121). Although hyperoxia initially injured and killed
endothelial cells, survival was dependent on maintaining the structural
integrity of the type I epithelial cell (2, 37). Thus
hyperoxia initially injures and kills endothelial cells followed by
type I epithelial cells, with less of an effect on type II cells.
The effect of hyperoxia on proliferation in the adult lung is a
relatively understudied area of research, probably because the mitotic
index is very low. Mitotic labeling studies with
[3H]thymidine in adult mice revealed that lymphocytes are
the most proliferative cell type within the lung, albeit with only a
2% labeling index (17, 47). Microvascular endothelial
cells are the second most proliferative population, with type II
epithelial cells and macrophages representing a minor percentage.
Similar results were found in 3-wk-old rats where the mitotic index of type II cells was estimated at 0.25% (83). One of the
first studies on the toxic effects of oxygen in the rodent lung found that microvascular endothelial cells were injured at sublethal levels
of oxygen [fraction of inspired oxygen
(FIO2) <90%], whereas epithelial cells
appeared unaffected (48). Based on this finding and the
knowledge that endothelial cells had a higher mitotic index, Evans and
Hackney (48) argued that they would be more susceptible than epithelial cells to inhaled toxic pollutants. Crapo et
al. (37) reported similar findings in their studies with
rats exposed to FIO2 of 85%, which killed
endothelial cells without injuring epithelial cells. However, this
concentration of oxygen stimulated type II epithelial cells to undergo
one round of proliferation. Although higher concentrations of oxygen
typically inhibit proliferation and kill both endothelial and type I
cells (49), one study found that they also promoted ex
vivo proliferation of fibroblasts isolated from hyperoxic rats
(85). Because sublethal levels (<85%) of oxygen
generally stimulate proliferation while lethal levels (>90%) inhibit
it, growth cessation may be a response to cellular damage.
In contrast to the adult lung, the mitotic index of the postnatal lung
is significantly higher. At birth, rat lung fibroblasts and
microvascular endothelial cells have the highest labeling index
(83). Over the first few days of life, the labeling index of fibroblasts increases from 6.5 to 14% as the alveoli septate. Thereafter, proliferation of fibroblasts and endothelial cells decreases. Type II epithelial cells have the lowest mitotic index at
birth, but it increases over the first week of life to ~7% before
decreasing to the low level seen in the adult lung. During this time,
the type I cell population increases without significant label
retention. This was interpreted as evidence that type I cells originate
from type II cells (5). Like the adult lung, a
FIO2 > 95% inhibits proliferation
of the newborn lung. However, newborns are more resistant to the toxic
effects of oxygen, perhaps due to their greater level of antioxidant
enzymes (33, 53, 160). Although proliferation initially
decreases in newborns exposed to hyperoxia, it resumes after several
days even when continuously exposed (15, 104, 151). In
fact, the mitotic index increases significantly, as if the lung was
trying to "catch up" for the delay caused by the initial exposure.
The use of exogenous surfactant and steroids for the treatment of
respiratory distress and prevention of bronchopulmonary dysplasia has
revealed additional problems associated with lung prematurity that have
led some to suggest that it involves an arrest in alveolar and vascular
development (78). It remains unclear how much of this is
due to prematurity or lung injury caused by infection, supplemental
oxygen, and/or assisted ventilation. Thus the identification of
molecules that regulate pulmonary cell proliferation could provide
insight into these important questions.
A major question regarding the effects of oxygen on proliferation is
whether they reflect overt cytotoxicity or activation of specific cell
cycle checkpoints. If hyperoxia inhibited proliferation through general
toxicity, the cells would be expected to cease proliferation when the
rate-limiting molecules required for proliferation are compromised.
Several studies (11, 129, 130) have provided supportive
evidence that the inactivation of mitochondrial enzymes, mitochondrial
damage, and gradual respiratory failure occur in HeLa and Chinese
hamster ovary (CHO) cell lines and intact lungs in response to
hyperoxia. Hyperoxia also decreased ATP levels, consistent with the
loss of mitochondrial function (7, 60). Although these
findings suggest that changes in cell proliferation may be due to overt
cytotoxicity, other studies have discovered that hyperoxia
activates a G1 cell cycle checkpoint (36, 122, 132).
Cell cycle checkpoints as defined by Hartwell and Weinert
(69) represent specific events during the cell cycle where
cells cease proliferation to assess whether replication should
continue. These gaps in the cell cycle were identified by a number of
assays, including fusion of nuclei isolated from cells in various
stages of cell division. Cell replication can be divided into two
stages: the M phase where cell division occurs and the interphase, the time between M phases (Fig. 1). The
interphase consists of the S phase where DNA replication occurs and two
gap phases where cell cycle progression temporarily ceases. The first
gap phase, G1, is the interval between the M and S phases.
It is during this time that cells presumably decide whether conditions
are favorable for replication. The second interval, G2,
separates the S phase and the M phase. Here cells could ensure that DNA
had been faithfully replicated before cytokinesis occurred. Movement
through the cell cycle is regulated by kinases that have catalytic
partners called cyclins because their expression cycles during the cell
cycle (see Ref. 45 for a review). Early G1
cyclins include cyclins D1, D2, and D3 that complex with
cyclin-dependent kinases (Cdk) 4 or 6. Cyclin E is expressed in late
G1 and binds Cdk2. The S phase is regulated by cyclin A
interacting with Cdk2, and the G2 phase is regulated by
cyclin B associating with cdc2 (also called Cdk1). DNA replication
occurs when the G1 and S phase kinases phosphorylate the
retinoblastoma (Rb) gene product, resulting in release of the
transcription factor E2F that increases the transcription of genes like
thymidine kinase that are required for DNA synthesis. This is an
oversimplification because there are two other proteins (p107 and p130)
that are related to Rb and six E2F (E2F-1 through E2F-6) proteins. DNA
damage inhibits proliferation by activating signal transduction
pathways that block the G1, S, and G2 phases of
the cell cycle. For example, DNA damage increases expression of the
tumor suppressor p53, which inhibits proliferation in G1 by
increasing transcription of the G1 Cdk inhibitor
p21Cip1/WAF1/Sdi1 (hereafter p21) (44, 116,
146). This pathway is discussed in more detail later.

View larger version (26K):
[in this window]
[in a new window]
|
Fig. 1.
Overview of the cell cycle depicting separation between
interphase and mitosis (M). Interphase can be further divided into
G1, S, and G2 phases. Each phase is regulated
by the activities of cyclin-dependent kinases (Cdk) that bind catalytic
cyclin proteins (A, B, D, and E). DNA damage inhibits progression at
G1, S, and G2 phases through unique molecular
signals.
|
|
If hyperoxia were activating cell cycle checkpoints, one would expect
to see changes in the expression of molecules that regulate cell
proliferation. And, in fact, hyperoxia does alter the expression of
mitogens and antimitogens. For example, the mitogen basic fibroblast growth factor and insulin-like growth factor I increased in adult rat
lungs exposed to 85% oxygen (19, 66). As shown in a
newborn rabbit model of oxygen injury, hyperoxia increased expression of keratinocyte growth factor, which stimulates proliferation of
epithelial cells, principally type II cells (27, 142).
Sublethal levels of oxygen in rats stimulated type II cell
proliferation and decreased expression of parathyroid hormone, which
inhibits type II cell proliferation (70). Because lethal
levels of oxygen inhibit proliferation, one would predict that they
also induce growth-inhibitory proteins that could counteract the
growth-promoting effects of mitogens expressed at lower levels. This is
also true because exposure of adult rodents to 100% oxygen increased
expression of transforming growth factor (TGF)-
, which is a potent
inhibitor of epithelial cell proliferation (21, 99, 106).
TGF-
expression decreased on recovery in room air when proliferation
occurs. Similarly, hyperoxia increased expression of p21 in adult and
newborn mice (95, 109). Like TGF-
, p21 expression also
decreased during recovery in room air. Perhaps the most compelling
argument for activation of cell cycle checkpoints is the recent
observation that hyperoxia did not inhibit proliferation in
p21-deficient mice even though it still caused morbidity and
mortality (111).
Several in vitro cell line models have also been used to understand how
hyperoxia alters cell proliferation at the molecular level. Changes in
cell proliferation are one of the earliest signs that hyperoxia has
affected cell function and were first described in HeLa cells by
Rueckert and Mueller (128) in 1960. The toxic effects of oxygen were not due to secretion of cell poisons because medium collected from oxygen-exposed cultures did not kill normoxic cells (137). Using a rat type II epithelial cell line that
was immortalized with SV40, Clement et al. (32)
showed that 95% oxygen inhibited proliferation and decreased
translation of histone and thymidine kinase mRNAs, which are required
for DNA replication. Subsequent studies revealed that hyperoxia also
increased mRNA levels of the cytokine TGF-
and its receptors,
consistent with in vivo studies in rodents (26, 36). It
also increased expression of p21, which inhibited G1 cyclin
E-dependent kinase activity, consistent with activation of a
G1 checkpoint that prevented DNA replication. Based on the
finding that neutralizing antibodies to TGF-
increased cyclin
E-dependent kinase activity, the authors concluded that
hyperoxia inhibits proliferation in G1 through p21 that was
induced by TGF-
. However, this concept was not uniformly held in
other in vitro models because Rancourt et al. (123)
demonstrated that hyperoxia does not inhibit proliferation of Mv1Lu
mink lung adenocarcinoma cells through TGF-
signaling. In this
model, Mv1Lu cells were shown to growth arrest predominantly in the S
phase of the cell cycle, whereas TGF-
inhibits proliferation at the G1/S boundary. Using A549 lung adenocarcinoma and HCT116
colon carcinoma epithelial cells that lacked p21, Rancourt et al.
(122) further showed that hyperoxia inhibits proliferation
in the G1 and S phases of the cell cycle, whereas p21
mediates the G1 arrest. The finding that Mv1Lu cells
arrested in the S phase and not in the G1 was due to the
inability of hyperoxia to induce p21 in these cells. An additional
study (132) revealed that hyperoxia inhibited
proliferation of bronchial smooth muscle airway cells in the
G1 and S phases along with induction of p21. A similar study (14) was performed in the human breast carcinoma
cell line T47D-H3. Approximately 40% of these cells accumulated in the
S phase when exposed to hyperoxia, without p21 binding to the
G1 and S phase Cdk2. Although this study differed from
other studies in that hyperoxia did not increase p21 protein levels, it
confirmed that hyperoxia induces a p21-independent S phase arrest. In
summary, these studies all show that hyperoxia inhibits proliferation
through a p21-dependent G1 arrest and a presently uncharacterized S phase arrest. Because little is known about S phase
checkpoints, it will be interesting to discern whether growth arrest in
the S phase is mediated by activation of a novel checkpoint or overt cytotoxicity.
Cell proliferation during recovery in room air.
Normal repair during recovery in room air is dependent on the rapid and
balanced proliferation of fibroblasts and endothelial and epithelial
cells (1, 141). In addition to terminating growth-inhibitory signals like TGF-
and p21, growth-stimulatory signals are likely to be expressed because proliferation exceeds the
basal level typically observed before exposure. Pulse-chase labeling
studies (1, 80) with [3H]thymidine in mice
and monkeys showed that type II epithelial cells proliferate and
differentiate into type I cells. Although it remains to be determined
how endothelial cells are replaced, proliferating type II cells
isolated from adult rabbits were found to transiently express high
levels of the potent endothelial cell mitogen vascular endothelial
growth factor (91). Thus type II cells play a major role
in the normal homeostasis and repair of the lung because they express
pulmonary surfactant, act as stem cells for type I cells, and may
participate in proliferation of endothelial cells by expressing
vascular endothelial growth factor. In addition, mitogens that are
expressed during exposure, like basic fibroblast growth factor,
keratinocyte growth factor, and insulin-like growth factor I, could
potentially stimulate proliferation during recovery when
growth-inhibitory signals decrease (19, 27, 31).
Fibroblasts also produce presently unidentified growth-stimulatory molecules for alveolar type II cells exposed to 100% oxygen
(50). Although it remains unknown whether these mitogens
affect cell proliferation during recovery, increased G1 and
S phase cyclin kinase activity has been reported in recovering rat
lungs, consistent with reactivation of the cell cycle machinery
(22).
An imbalance between proliferation of type II cells and fibroblasts can
lead to chronic inflammation and fibrosis. Although inflammation and
collagen production are likely to be important during the remodeling
phases, failure to terminate these processes can be catastrophic. This
is most evident in the bleomycin-induced model of pulmonary fibrosis
where continued proliferation of type II cells is observed
(3). Modest septal thickening and increased interstitial
collagen have been reported in lungs recovering from lethal levels of
oxygen or in lungs exposed for long periods of time to sublethal
levels, consistent with modest fibrosis (4, 99, 151). One
study (4) using an explant model to recapitulate fibrosis
after hyperoxic injury observed that fibroblast proliferation exceeded
epithelial cell proliferation due to epithelial cell necrosis. However,
attenuation of fibroblast proliferation with proline analogs to block
collagen production failed to inhibit fibrosis (18). This
study also discovered that normal repair involves interactions between
fibroblasts and the epithelium because epithelial cell proliferation
was affected by the drugs too. Another study (20) found
that cultured type II cells isolated from rat lungs exposed to
hyperoxia undergo apoptosis even though they are thought to be
resistant to oxidant damage. In summary, injured and dead cells are
replaced during recovery through increased proliferation and
differentiation. Normal repair is dependent on the balanced
proliferation of both epithelial and mesenchymal cells. Given that
controlled proliferation is beneficial during and after oxidant injury,
let us examine how cell cycle progression is regulated.
 |
CELL CYCLE AND CHECKPOINTS |
G1 checkpoints.
As described in Cell proliferation during hyperoxic
exposure, the cell cycle can be divided into discreet time
periods where G1 represents the first phase of interphase.
During this time, Hartwell and Weinert (69) argued, cells
could ensure that the conditions for DNA replication were favorable.
Cyclin D and E kinases phosphorylate the Rb gene product, resulting in
release of the transcription factor E2F, which increases transcription of the genes required for DNA replication and S phase progression (Fig.
2). Growth arrest is achieved through
multiple pathways that inhibit G1 and S phase cyclin
kinases. Two families of proteins have been identified that inhibit
cell proliferation in G1. One group of proteins comprises
the cyclin- or kinase-inhibitory proteins (Cip/Kip) p21, p27, and p57.
These proteins share an amino-terminal domain that binds to cyclin D-
and E-Cdk complexes and inhibits their activity (29, 68, 87, 117,
159). A second group of proteins comprises the INK4 family, so
named because it binds and inhibits Cdk4. This family includes p15,
p16, p18, and p19, which exert their effects by binding Cdk4 and
displacing the associated cyclin (65). They all contain a
fourfold repeated ankyrin-like sequence that bares no homology to the
Cip/Kip family. Thus any pathway that impinges on Cip/Kip or INK4
proteins will activate G1 growth arrest.

View larger version (25K):
[in this window]
[in a new window]
|
Fig. 2.
DNA damage G1 cell cycle checkpoint. DNA
damage stabilizes p53 and increases transcription of p21. Increased
levels of p21 inhibit cyclin D and E kinase activities for
retinoblastoma (Rb)-E2F complexes, resulting in G1 growth
arrest. Similarly, transforming growth factor (TGF)- increases p15
that inhibits cyclin D kinase or p21 that inhibits cyclin D and E
kinase activities. S phase progression resumes on phosphorylation (P)
of Rb by G1 cyclins, causing release of E2F, which
increases transcription of genes required for DNA synthesis. Some
representative genes required for DNA synthesis include thymidine
kinase (TK), thymidine synthase (TS), dihydrofolate reductase (DHFR),
E2F-1, and DNA polymerase (POL). Kip, kinase-inhibitory protein.
|
|
The tumor suppressor protein p53 is a major regulator of the
G1 checkpoint after DNA damage. Cells typically express low
levels of p53 that is phosphorylated when DNA damage occurs, resulting in increased stability and its accumulation. In fact, elegant studies
showed that p53 accumulates within hours after exposure to IR,
ultraviolet (UV) light, or alkylating agents or even after transfection with nicked plasmid DNA or DNase (82, 103).
p53 binds to the p21 promoter ~2.4 kb 5' of the transcription
initiation site, resulting in increased levels of p21 mRNA and protein
(43, 44). Additional sites with less binding affinity have
been identified closer to the TATA box. Thus DNA damage induces p53,
resulting in increased levels of p21 that prevent entry into the S
phase. A kinetic study (44) with an inducible p53
construct demonstrated that p21 and growth arrest occurred only after
p53 levels increased. Interestingly, hydrogen peroxide and other
molecules that increase intracellular ROS induce expression of p21
independent of p53 (46, 120). TGF-
- and
interleukin-6-type cytokines can also induce p53-independent expression
of p21 (12, 38). The growth-inhibitory activities of p21
have been localized to two domains (90). The amino-terminal portion of p21 inhibits cell cycle progression in
G1/S by binding and inhibiting G1 and S phase
kinase activities (127, 159). The carboxy terminus
inhibits DNA replication by binding to proliferating cell nuclear
antigen (PCNA) and blocking recruitment of DNA polymerase
(145). These two domains can act separately from each
other to exert growth arrest. As mentioned above, only the
amino-terminal domain is found in the related kinase inhibitors p27 and
p57 (29, 68, 159).
It is the unique carboxy-terminal PCNA binding domain by which p21 can
participate in DNA repair (54). p21 bound to PCNA inhibits
binding of DNA endonucleases, such as flap endonuclease (FEN)-1
(35, 135). The PCNA-p21 complex binds to sites of DNA damage, at which point repair is thought to commence when p21 dissociates from PCNA. These biochemical findings were confirmed at the
cellular level with HCT116 colon carcinoma cells in which p21 was
deleted through homologous recombination. With these and other cell
line models, it was shown that p21-deficient cells are
sensitive to DNA damage caused by exposure to cisplatin, nitrogen mustard, or UV radiation (51, 94, 131). Furthermore,
p21-deficient cells are unable to repair damaged DNA as
shown by their inability to restore reporter activity to a transfected
plasmid damaged by the alkylating agent methylmethane sulfonate or UV
light. Damage caused by IR appears to be less affected by
p21 deficiency; however, this concept was disputed in H1299
pulmonary adenocarcinoma cells containing a regulatable p21 transgene
(148). Interestingly, p21-deficient mice show
increased sensitivity to hyperoxia as assessed by rapid necrosis of
alveolar cells and a 40% reduction in mean survival time
(111). Even though hyperoxia failed to inhibit
proliferation in these mice, one must consider that the protective
effects of p21 may extend beyond simple growth regulation because the
mitotic index of the adult lung is very small.
Although TGF-
is not directly regulated by DNA damage or p53, some
studies (26, 36) have argued that hyperoxia inhibits proliferation through TGF-
signaling. This scenario is possible because TGF-
increases p53-independent transcription of p21 in keratinocytes (39, 88). TGF-
signals by binding cell
surface receptors that lead to activation of intracellular
transcription factors called SMADs (see Ref. 71 for a
review). The SMAD binding site in the p21 promoter is adjacent to Sp1
sites and is distinct from the p53-binding site (112). The
effects of TGF-
to exert G1 growth arrest appear to be
cell-type specific because it does not inhibit proliferation only
through p21. For example, TGF-
inhibits proliferation of Mv1Lu
adenocarcinoma cells by elevating the INK4 protein p15 that displaces
p27 from G1 cyclin complexes (125). The
increased levels of free p27 can bind tightly to an S phase cyclin
A-Cdk2 complex, thereby further preventing phosphorylation of Rb.
Although p27 levels are thought to remain relatively constant throughout the cell cycle, they increased in SV40-immortalized type II
cells exposed to hyperoxia (36). These findings reveal that hyperoxia activates a G1 checkpoint involving Cip/Kip
family members, principally p21. The role of other members of this
family, as well as the INK4 family, remains to be examined in
oxygen-arrested cells.
S phase checkpoints.
There is very little that is known about S phase checkpoints, and it is
thought that arrest during this period is catastrophic for cells. In
the absence of the G1 checkpoint, damaged cells typically
progress through the S phase and arrest in G2. For example, IR induces p21 that inhibits proliferation in G1. Cells
lacking p21, such as p21-deficient mouse embryo fibroblasts
or HCT116 cells, progress through the S phase and growth arrest in
G2 (41, 146). The cells then continue to
replicate their DNA without undergoing cytokinesis and eventually die
by apoptosis (147). Thus it is highly intriguing
that the same HCT116 cells lacking p21 growth arrest in the S phase
when exposed to hyperoxia (122). There are, however,
several studies that implicate the existence of S phase checkpoints.
For example, low levels of alkylating agents slow S phase
progression in Saccharomyces cerevisiae through a mechanism
that involves Mec-1, a yeast homolog of the ataxia telangiectasia
mutant (ATM), and several other DNA damage checkpoint proteins
(113, 114). This decrease in S phase progression did not
appear to be dependent on DNA lesions because
mec-1-deficient cells rapidly traversed the S phase. Another
study (6) demonstrated that nucleotide deficiency could
promote S phase arrest that required p53 but not p21. As shown by
Neades et al. (102), multiple doses of low levels of UV
radiation to mouse keratinocytes induce S phase growth arrest
associated with increased Cdk2 kinase activity. This study also showed
that p21 was not required for S phase arrest. Interestingly, in another
study (14), hyperoxia induced a p21-independent S phase
arrest in T47D breast carcinoma cells along with increased Cdk2 kinase
activity similar to that in the study by Neades et al.
(102). Although there is some evidence that S
phase checkpoints may exist and may be activated by hyperoxia, one must
also consider that failure to complete the S phase may be due to
overall genotoxic stress.
G2 checkpoints.
DNA damage also activates a G2 checkpoint through targeting
cyclin B and cdc2 kinase activity (Fig.
3). Cyclin B-dependent kinase is
the major regulator that moves cells from G2 into mitosis. As cyclin B levels increase in the G2 phase, it binds to
cdc2, enters the nucleus, and promotes entry into the M phase. However, this complex remains inactive because of inhibitory phosphorylation on
cdc2 at threonine-14 and tyrosine-15. The relative levels of the cdc25
phosphatase and wee1/mik1 kinase maintain this inhibitory phosphorylation. Cells in G2 have higher levels of wee1,
whereas cells entering the M phase have higher levels of cdc25.
Activated cdc2 kinase phosphorylates cdc25c, resulting in greater
phosphatase activity for cdc2 and amplification of cell cycle
progression toward mitosis. DNA damage inhibits G2
progression through several pathways. One pathway inhibits activating
phosphorylation on cdc25, thereby resulting in decreased cdc25
phosphatase activity (105). Phosphorylated cyclin B-cdc2
complexes are retained in the cytoplasm where they cannot stimulate
G2 to M phase progression. A second pathway involves
p53-dependent degradation of cyclin B (74). A third
pathway involves association of growth arrest and DNA damage (GADD45)
with cdc2, leading to disruption of the complex (161).
These latter observations were significant because they provided
evidence for p53 to inhibit G2 directly by regulating cyclin B expression or indirectly through expression of GADD45 that
regulated cdc2 activity.

View larger version (17K):
[in this window]
[in a new window]
|
Fig. 3.
DNA damage G2 cell cycle checkpoint. Progression
through G2 phase is dependent on dephosphorylation of cdc2
kinase by the phosphatase cdc25c. Active cyclin B/cdc2 kinase
phosphorylates cdc25c, resulting in increased phosphatase activity for
cdc2. DNA damage inhibits G2 progression by blocking
phosphorylation of cdc25c, increasing growth arrest and DNA damage
(GADD45) that binds and inactivates cdc2 or increasing degradation of
cyclin B. T14, threonine-14; Y15, tyrosine-15.
|
|
To date, there is no direct evidence that hyperoxia activates a
G2 cell cycle checkpoint (14, 122).
G2 growth arrest is also not observed when oxygen-exposed
cells are allowed to recover in room air (unpublished
observations). There are, however, several suggestive studies
that implicate G2 checkpoints. For example, bronchial
smooth muscle cells exposed to 40% oxygen had more cells in
G2 than cultures exposed to 100% oxygen, which accumulated in the G1 and S phases (132). This suggests
that cells exposed to lower levels of oxygen were able to complete the
S phase and arrest in G2. Another line of evidence comes
from a study that showed that hyperoxia increases
p53-independent expression of GADD45 in bronchiolar
epithelial and type II cells of adult mice (110). GADD45
was initially identified as an inducible mRNA transcript in CHO cells
exposed to a variety of DNA damaging agents (52). It may
participate in the G2 checkpoint because it disrupts cyclin B-cdc2 interactions (161). It may also function in DNA
repair because antisense expression in cell lines leads to enhanced
killing by UV light and cisplatin (136). Because hyperoxia
induces GADD45 in type II cells, which are relatively resistant to
hyperoxia, one can only speculate at this time about its role in
regulating their proliferation.
In summary, there is abundant evidence that hyperoxia alters cell
proliferation. Recent studies reveal that part of its
growth-arresting properties come from active expression of
growth-suppressive molecules including p53, p21, and TGF-
(26,
36, 122, 132). The expression of p21 is probably derived from a
response to oxidant DNA damage and expression of p53
(122). We therefore examine evidence for oxygen to damage
DNA and how cells sense and activate growth suppression.
 |
HYPEROXIA AND DNA FRAGMENTATION IN THE LUNG |
Although the clastogenic effects of hyperoxia have been described
extensively in cultured cells like HeLa and CHO cells (34, 56), less is known about its genotoxic effects in the lung. Recent studies (10, 108, 152) in rodent models of
hyperoxic lung injury have argued that hyperoxia kills cells by
apoptosis because intense terminal deoxynucleotidyltransferase
dUTP nick end labeling (TUNEL)-positive cells, indicative of
apoptosis, are detected throughout terminal bronchiolar
epithelium and parenchyma. Apoptotic cells undergo orderly DNA
fragmentation that may be detected as TUNEL-positive staining and DNA
laddering by gel electrophoresis. One paradox with these studies is
that DNA laddering has been extremely difficult to detect even though
nearly 60% of parenchymal cells exposed to hyperoxia are TUNEL
positive. In addition, TUNEL-positive cells are readily detected in
bronchiolar epithelial cells that are believed to be more resistant to
cell death than parenchymal cells (108). Some studies
(10, 150) have attempted to link TUNEL staining with
morphological signs of apoptosis and expression of members of
the Bcl-2 gene family, which regulate cell survival and death. However,
no correlation was found between TUNEL staining, ultrastructural
evidence of apoptosis, and expression of the proapoptotic Bax and antiapoptotic Bcl-XL genes (107).
Moreover, p53-deficient mice, which failed to induce Bax,
showed comparable levels of injury as assessed by TUNEL staining and
wet-to-dry lung ratios as in wild-type mice (10, 110).
Nevertheless, it is important to recognize that TUNEL staining
identifies DNA that contains a break in the phosphodiester backbone of
the double helix (8, 62). An alternative hypothesis is
that TUNEL staining during hyperoxia reflects DNA damage that either is
repaired or will lead to cell death by apoptosis or necrosis.
As shown in Fig. 4, TUNEL-positive cells
are not easily detected in the lungs of mice exposed to room air. In
contrast, faint TUNEL-positive cells are detected throughout the
terminal bronchioles and parenchyma after only 12 hours of exposure to
a FIO2 > 95%. Because cell death is
not observed for an additional 2 days of exposure, one could conclude
that TUNEL staining represents DNA strand breaks that need to be
repaired or the cells will die.

View larger version (131K):
[in this window]
[in a new window]
|
Fig. 4.
Terminal
deoxynucleotidyltransferase dUTP nick end labeling (TUNEL) staining in
adult mouse lungs exposed to hyperoxia. Adult mice were exposed to room
air (A) or 100% fraction of inspired oxygen for 12 h
(B), and their lungs were stained for free 3'-hydroxyl ends
of DNA as previously described (108). TUNEL-positive
nuclei (solid arrows) stained brown, whereas TUNEL-negative nuclei
(open arrows) stained blue due to the methyl green
counterstain.
|
|
A second paradox was the findings of Kazzaz et al. (84),
who demonstrated that hyperoxia does not induce TUNEL staining in
cultured A549 pulmonary adenocarcinoma cells. Similar findings were
reported later in the mink lung adenocarcinoma cell line Mv1Lu
(123). In fact, vital dyes revealed that both cell lines died by necrosis. In contrast, hyperoxia induces TUNEL staining in the
mouse RAW 264.7 macrophage cell line (115). The
single-cell gel electrophoresis or comet assay is a highly sensitive
method to discriminate different types of DNA fragmentation caused by genotoxic compounds (13). As shown in Fig.
5, genomic DNA of A549 pulmonary
adenocarcinoma cells exposed to room air is intact as shown by the
brightly fluorescent nucleus. In contrast, cells exposed to hyperoxia
develop a distinct comet tail, consistent with older studies
demonstrating the clastogenic nature of hyperoxia (24, 56, 57,
59). Although it remains unclear why TUNEL staining is not
detected in most cell lines exposed to hyperoxia, the positive comet
and clastogenic effects demonstrating DNA damage are indisputable.

View larger version (55K):
[in this window]
[in a new window]
|
Fig. 5.
Single-cell gel electrophoresis (comet) assay. A549 cells
were exposed to room air-5% CO2 or 95% O2-5%
CO2 (hyperoxia) for 48 h before being embedded in
agarose. DNA was separated by electrophoresis, stained with Syber gold,
and visualized under fluorescence microscopy. Note the intact nuclear
DNA in the room air sample compared with the fragmented DNA that
appears like a comet in the sample exposed to hyperoxia.
|
|
Given that hyperoxia fragments DNA in cells and lungs, one should be
able to detect changes in the expression of genes such as the tumor
suppressor p53, which increases in cells that have DNA damage
(82, 103). In fact, p53 does increase in cell lines like
A549 and newborn and adult lungs exposed to hyperoxia (10, 20,
95, 108). These observations were important because p53 regulates transcription of genes that determine whether injured cells
cease proliferation and repair DNA damage or undergo apoptosis. Interestingly, one of the first papers to examine the effects of
hyperoxia on cell function documented that it altered proliferation of
HeLa cells (128). Because molecules that participate in
DNA replication are also involved in DNA repair, one can envision that
growth arrest promotes repair.
 |
DNA DAMAGE RECOGNITION AND RESPONSES |
Although many of the genes that regulate cell cycle progression
have been identified, less is known about how cells recognize and
activate the DNA damage response. This may be because DNA can be
damaged in many different ways, especially within the context of
oxidant-induced injury. Studies that will now be presented have revealed that the response to DNA damage is complex and involves genes that recognize DNA damage and transduce the signal to p53, which
effects the cellular response by inhibiting proliferation, stimulating
repair, or inducing apoptosis (Fig.
6).

View larger version (22K):
[in this window]
[in a new window]
|
Fig. 6.
DNA damage-response pathway involves genes that sense DNA
damage, genes that transduce this signal, and the p53 effector that
regulates the cellular response. p53 levels are decreased when it
associates with murine double minute (mdm) 2, which is regulated by DNA
damage and oncogenic signals. Elevated levels of p53 regulate the
expression of genes that inhibit proliferation or promote repair or
apoptosis. DNA-PK, DNA-dependent protein kinase; PARP,
poly(ADP-ribose) polymerase; PCNA, proliferating cell nuclear antigen;
ATM, ataxia telangiectasia mutant; ATR, ATM-Rad3 related.
|
|
Sensors.
One of the major unsolved questions in DNA damage signaling today is
how cells recognize DNA damage. Initial studies suggested that the
DNA-dependent protein kinase (DNA-PK) and poly(ADP-ribose) polymerase
(PARP) sensed DNA damage because they bind single-strand DNA. However,
genetic evidence has argued that these proteins are not the only
players in sensing DNA damage and perhaps are not the major players
either. For example, studies have provided evidence for (134,
155) and against (77, 124) the role of DNA-PK to
signal p53-dependent growth arrest after IR-induced DNA damage. PARP is
a nuclear zinc finger protein that detects single-strand DNA and
catalyzes the transfer of ADP-ribose from respiratory coenzyme
NAD+ to histones and replication proteins.
Poly(ADP-ribosylated) proteins lose their affinity for DNA, which is
thought to allow access to DNA. Studies in PARP-deficient mice and
cells revealed that PARP participates in base excision repair of DNA
that is damaged by IR or alkylating agents such as methylmethane
sulfonate (40, 93, 149). As predicted, PARP deficiency
does not alter the sensitivity of cells to UV radiation-induced damage,
which is repaired by nucleotide excision repair. Recent studies in
Saccharomyces pombe have identified other proteins that are
structurally related to PCNA that may act as global DNA damage sensors.
The proteins Rad1, Rad9, and Hus1 form a heterotrimer around the DNA
helix similar to the homotrimer of PCNA (143). Based on
the activities of PCNA, which slides along the DNA as it replicates,
one can envision that this complex slides along DNA to identify sites of damage. The observation that Hus1-deficient embryonic
fibroblasts are sensitive to damage caused by hydroxyurea or UV light
supports the yeast data that these genes may also function as damage
sensors in mammalian cells (153). An additional study
(100) has suggested that the breast cancer gene BRCA1 can
sense double-strand DNA breaks. BRCA1 complexes with a group of
proteins, including the mismatch repair enzymes MSH2/6 and MLH2 that
are involved in DNA repair and ATM, which transduces the damage
response. Collectively, these findings suggest that multiple sensors
exist, which complicate studies in ROS-induced damage that produce
dozens of different types of damage. For example, PARP may sense
hydrogen peroxide-induced damage because inhibitors of PARP can protect
myocytes and fibroblasts from hydrogen peroxide-induced death
(63). In contrast, hyperoxia does not alter NAD levels,
suggesting that PARP, which consumes NAD, may not be a sensor for
hyperoxia-induced damage (60).
Transducers.
Two major groups of proteins have been identified as transducing the
signal to downstream regulators such as p53. The first group includes
ATM, the ATM-Rad3-related (ATR) gene, and DNA-PK based on their
relatedness to the phosphatidylinositol 3-kinase superfamily. Unlike
phosphatidylinositol 3-kinase that phosphorylates lipids, these kinases
phosphorylate proteins. Because these proteins have weak affinity for
DNA, it remains unclear how DNA damage leads to their activation. In
response to double-strand DNA breaks such as those caused by IR, ATM
phosphorylates p53, murine double mutant (mdm) 2, and Chk2, thereby
activating and amplifying additional signals in the DNA damage response
(9, 86). It, however, is not the only effector of the
damage response because IR still phosphorylates p53 in
ATM-deficient cell lines, albeit at a slower rate
(25). Interestingly, ATM-deficient cells are
highly sensitive to IR-induced damage but not UV radiation or
alkylating agents. In contrast, ATR mediates the UV radiation response
by phosphorylating p53 (140). It also phosphorylates Chk1
in response to UV radiation, suggesting that DNA damage response may be
specified, in part, by their selective activation (89).
Thus DNA damage may signal initially through ATM or ATR that can
amplify the signal by phosphorylating Chks or by directly activating
the DNA sensor p53.
The serine/threonine Chk1 and Chk2 kinases comprise a second group of
transducer proteins. These proteins are also phosphorylated by DNA
damage and, in turn, phosphorylate p53. For example, ATM phosphorylates
Chk2, and it, in turn, can phosphorylate p53 at multiple sites
(133). Phosphorylation of serine-20 by Chk1 is thought to
be especially important for stabilizing p53 levels in cells. Similar
results were observed in another study (89), which showed that Chk1-deficient embryonic stem cells
display a G2 cell cycle checkpoint defect in response to
IR. IR, UV light, and hydroxyurea also phosphorylated Chk1 through an
ATR-dependent mechanism (89). Because nothing is known
about the effects of hyperoxia on DNA damage transducers, this remains
an open field of study.
Effectors.
The tumor suppressor protein p53 is the major effector of the DNA
damage response because it decides whether injured cells live or die by
regulating transcription of the genes involved in cell cycle
progression and apoptosis (see Ref. 61 for a
review). Although many pulmonary studies focus on p53 mutations
associated with lung cancer (reviewed in Ref. 72), their
role in lung injury is less studied. The p53 protein may be
structurally segregated into three domains. The
amino-terminal domain regulates stability and is a
transcriptional coactivator, the central domain binds cis-acting elements of gene promoters, and the carboxy
terminus regulates transcriptional activity and oligomerization. Under normal conditions, p53 levels are extremely low and the p53 response pathway is considered "off." DNA damage, hypoxia, nucleotide
depletion, telomerase erosion, or uncontrolled growth caused by
oncogene activation increases p53 expression. p53 levels remain low in cells because it binds the oncoprotein mdm2 that exports it from the
nucleus to the cytoplasm where it is ubiquitinated and degraded by the
proteasome (79, 134) (Fig. 6). mdm2 expression is
upregulated by p53, thereby creating a feedback loop by which p53
downregulates its own expression (156). mdm2 is also
negatively regulated by p19ARF (p14ARF in the
human; p19ARF in the mouse), an alternatively spliced gene
encoded within the Cdk p16 gene (118, 163). Thus pathways
that alter interactions between p53 and mdm2 or mdm2 with
p19ARF regulate p53 expression.
Recent studies suggest that at least three independent
pathways regulate p53 levels, of which two pathways lead to
site-specific phosphorylation on p53 (81, 103, 126). In
fact, a multitude of posttranslational modifications to p53, including
phosphorylation of serine-6, -9, -15, -20, -33, -37, and -392, dephosphorylation of serine-376, and acetylation of lysine-320, -373, and -382, have been reported. Although entire review articles have been devoted to this topic (e.g., Ref. 119), only a few key
examples are described. The DNA damage transducers involving ATM or
Chk2 kinases phosphorylate the amino terminus of p53 at serine-15, consistent with the notion that this blocks association with mdm2. One
site by itself is not responsible for stabilizing p53 because IR still
induced expression of a mutant form of p53 where serine-15 was
converted to alanine (25). However, this mutant failed to elicit p53-dependent apoptosis. Recently, phosphorylation on
serine-20 was shown to stabilize p53 through Chk1 and independent of
ATM or ATR (28, 133). A second pathway involves
ATR-dependent activation of p53 by UV light and chemotherapeutic drugs.
ATR phosphorylates serine-15, -37, and -392 (392 in humans; 389 in
mice) in response to UV radiation (67, 81).
Interestingly, ATR phosphorylates serine-15 and -392, whereas ATM
phosphorylates serine-15 but not serine-392. Thus the UV radiation
response has overlapping and distinct effects on p53 phosphorylation.
Oncogene-dependent cell growth represents a third pathway to regulate
p53 as shown by a recent study demonstrating that activation of Ras
induced the Raf/mitogen-activating protein kinase
kinase/mitogen-activating protein kinase pathway, resulting in
increased mdm2 transcription and p53 degradation (126).
Although hyperoxia increases p53 in vivo and in vitro, little is known
about how this occurs. A recent study (122) showed that
hyperoxia activates p53-dependent transcription and phosphorylates p53
on serine-15, consistent with a DNA damage response involving ATM
and/or ATR kinases. Additional studies that examine whether hyperoxia
phosphorylates other sites on p53 are needed to provide insight into
signal transduction pathways activated by oxygen-induced DNA damage.
In addition to regulating p53 abundance, additional changes must occur
before it can mediate transcriptional activity. A major unresolved
question in the field is how cell growth and apoptosis are
discriminated by p53. Vousden (144) has recently proposed two models. A "smart p53" model argues that specific types of damage activate unique pathways, leading to site-specific
phosphorylation or other posttranslational modifications on p53 that
result in response specificity. This model is consistent with a recent
study (25) showing that mutations, which lack the ability
to phosphorylate serine-15, attenuate the p53 response that leads to
apoptosis. It is also consistent with another study
(30) showing that low levels of p53 caused cell growth
arrest through induction of p21, whereas higher levels induced
apoptosis. The "dumb p53" model proposes that p53 always
activates growth arrest and apoptosis. The outcome is dependent
on additional signals that augment or block one pathway. Vousden
(144) argues that the convergence of oncogenic signals
that promote both growth and apoptosis will kill cells with
p53-induced signals.
Once p53 levels have increased in cells, its ability to bind
cis-acting elements on DNA can be inhibited by oxidation or
metal chelators (64). This can be counteracted by
interactions with Ref-1, which reduces oxidized transcription factors
like p53, activator protein-1, nuclear factor-
B, and
hypoxia-inducible factor 1, thereby restoring DNA binding activity
(76, 157). Interestingly, Ref-1 is also AP endonuclease,
an enzyme that functions in base excision DNA repair
(158). p53 can also bind single-strand DNA, suggesting
that it can block DNA replication directly at sites of damage
(75, 98). The role of p53 in hyperoxic lung injury
presently remains unclear. Although it is required for the induction of
p21 in adult mouse lungs exposed to 92% oxygen (95),
another study (111) showed that it was not necessary when
exposed to 100% oxygen. Some of the differences observed between these
studies may be due to the amount of oxygen used. Intriguingly, p53 is
necessary for hyperoxia to increase p21 levels in a number of cultured
cell lines (122; unpublished observations). p53 was necessary
for hyperoxia to induce Bax (107). However, because
p53 deficiency did not modify lung injury, it remains unclear whether p53-dependent induction of Bax is important for oxygen-induced cell death. In contrast, hyperoxia induced GADD45 in
bronchiolar epithelial and alveolar type II cells independent of p53
(110). This observation is intriguing because UV light induces p53-independent expression of GADD45, whereas the induction of
GADD45 by IR required p53 (162). Does this mean that
hyperoxia mimics UV radiation-induced damage? These types of questions
emphasize that we have much to learn about signal transduction pathways activated during pulmonary oxygen toxicity.
 |
FUTURE DIRECTIONS |
The past few years have provided strong evidence that in vitro
cultured cells and intact lungs exposed to lethal levels of oxygen have
fragmented DNA and express growth-inhibitory molecules. Although the
relationship between growth arrest and DNA repair remains murky, the
finding that the same proteins are involved suggest that these
processes are related. Given that hyperoxia inhibits proliferation
through activation of cell cycle checkpoints, how does this occur and
does it really protect cells from hyperoxia? This question may seem
strange when one considers that the mitotic index of the endothelial
cell is extremely small and the type I cell is terminally senescent.
Similarly, if growth arrest is beneficial, why do newborn lungs resume
proliferation during continuous exposure without fixation of mutations
in their genome? Once repair has been completed, what are the molecular
signals that stimulate reentry into the cell cycle and how does the
repaired lung terminate proliferation so as to not become fibrotic?
Another question is whether hyperoxia-induced cell injury can prevent
or promote cell injury caused by another agent. The rationale for this
thought is that both hyperoxia and carcinogens target p53.
Interestingly, studies have shown that hyperoxia or ozone can modify
the pulmonary response to carcinogens (see Ref. 154 for a
review). Answers to these and other related questions may provide novel
insights into the cellular response to oxidant injury caused by
hyperoxia as well as by IR, bleomycin, ozone, nitrogen dioxide,
particles, inflammation, and ischemia-reperfusion. Given the
relevance of oxygen toxicity to produce ROS, the role of which in
signal transduction processes has recently been appreciated by the
entire scientific community, I anticipate that studies on the cellular
response to hyperoxia will be quite prolific in the future!
 |
ACKNOWLEDGEMENTS |
Because no review can cover the myriad of studies related to one
topic, I apologize for those that were not included due to space
constraints. I am extremely grateful to the members of my laboratory,
especially Rhonda Staversky, and my colleagues who have contributed to
the research presented in this review article.
 |
FOOTNOTES |
This work was supported in part by National Heart, Lung and Blood
Institute Grant HL-58774.
Address for reprint requests and other correspondence: M. A. O'Reilly, Dept. of Pediatrics, Division of Neonatology, Box 777, Children's Hospital at Strong, The Univ. of Rochester, 601 Elmwood Ave., Rochester, NY 14642 (E-mail:
michael_oreilly{at}urmc.rochester.edu).
 |
REFERENCES |
1.
Adamson, IY,
and
Bowden DH.
The type 2 cell as progenitor of alveolar epithelial regeneration. A cytodynamic study in mice after exposure to oxygen.
Lab Invest
30:
35-42,
1974[ISI][Medline].
2.
Adamson, IY,
Bowden DH,
and
Wyatt JP.
Oxygen poisoning in mice. Ultrastructural and surfactant studies during exposure and recovery.
Arch Pathol
90:
463-472,
1970[ISI][Medline].
3.
Adamson, IY,
Hedgecock C,
and
Bowden DH.
Epithelial cell-fibroblast interactions in lung injury and repair.
Am J Pathol
137:
385-392,
1990[Abstract].
4.
Adamson, IY,
Young L,
and
Bowden DH.
Relationship of alveolar epithelial injury and repair to the induction of pulmonary fibrosis.
Am J Pathol
130:
377-383,
1988[Abstract].
5.
Adamson, IYR,
and
Bowden DH.
Derivation of type 1 epithelium from type 2 cells in the developing rat lung.
Lab Invest
32:
736-745,
1975[ISI][Medline].
6.
Agarwal, ML,
Agarwal A,
Taylor WR,
Chernova O,
Sharma Y,
and
Stark GR.
A p53-dependent S-phase checkpoint helps to protect cells from DNA damage in response to starvation for pyrimidine nucleotides.
Proc Natl Acad Sci USA
95:
14775-14780,
1998[Abstract/Free Full Text].
7.
Allen, CB,
and
White CW.
Glucose modulates cell death due to normobaric hyperoxia by maintaining cellular ATP.
Am J Physiol Lung Cell Mol Physiol
274:
L159-L164,
1998[Abstract/Free Full Text].
8.
Ansari, B,
Coates PJ,
Greenstein BD,
and
Hall PA.
In situ end-labelling detects DNA strand breaks in apoptosis and other physiological and pathological states.
J Pathol
170:
1-8,
1993[ISI][Medline].
9.
Banin, S,
Moyal L,
Shieh S,
Taya Y,
Anderson CW,
Chessa L,
Smorodinsky NI,
Prives C,
Reiss Y,
Shiloh Y,
and
Ziv Y.
Enhanced phosphorylation of p53 by ATM in response to DNA damage.
Science
281:
1674-1677,
1998[Abstract/Free Full Text].
10.
Barazzone, C,
Horowitz S,
Donati YR,
Rodriguez I,
and
Piguet PF.
Oxygen toxicity in mouse lung: pathways to cell death.
Am J Respir Cell Mol Biol
19:
573-581,
1998[Abstract/Free Full Text].
11.
Bassett, DJ,
Elbon CL,
and
Reichenbaugh SS.
Respiratory activity of lung mitochondria isolated from oxygen-exposed rats.
Am J Physiol Lung Cell Mol Physiol
263:
L439-L445,
1992[Abstract/Free Full Text].
12.
Bellido, T,
O'Brien CA,
Roberson PK,
and
Manolagas SC.
Transcriptional activation of the p21(WAF1,CIP1,SDI1) gene by interleukin-6 type cytokines. A prerequisite for their pro- differentiating and anti-apoptotic effects on human osteoblastic cells.
J Biol Chem
273:
21137-21144,
1998[Abstract/Free Full Text].
13.
Benitez-Bribiesca, L,
and
Sanchez-Suarez P.
Oxidative damage, bleomycin, and gamma radiation induce different types of DNA strand breaks in normal lymphocytes and thymocytes. A comet assay study.
Ann NY Acad Sci
887:
133-149,
1999[Abstract/Free Full Text].
14.
Bilodeau, JF,
Faure R,
Piedboeuf B,
and
Mirault ME.
Hyperoxia induces S-phase cell-cycle arrest and p21(Cip1/Waf1)-independent Cdk2 inhibition in human carcinoma T47D-H3 cells.
Exp Cell Res
256:
347-357,
2000[ISI][Medline].
15.
Bonikos, DS,
Bensch KG,
Ludwin SK,
and
Northway WH, Jr.
Oxygen toxicity in the newborn. The effect of prolonged 100 per cent O2 exposure on the lungs of newborn mice.
Lab Invest
32:
619-635,
1975[ISI][Medline].
16.
Bowden, DH,
Adamson IY,
and
Wyatt JP.
Reaction of the lung cells to a high concentration of oxygen.
Arch Pathol
86:
671-675,
1968[ISI][Medline].
17.
Bowden, DH,
Davies E,
and
Wyatt JP.
Cytodynamics of pulmonary alveolar cells in the mouse.
Arch Pathol
86:
667-670,
1968[ISI][Medline].
18.
Bowden, DH,
Young L,
and
Adamson IY.
Fibroblast inhibition does not promote normal lung repair after hyperoxia.
Exp Lung Res
20:
251-262,
1994[ISI][Medline].
19.
Buch, S,
Han RN,
Liu J,
Moore A,
Edelson JD,
Freeman BA,
Post M,
and
Tanswell AK.
Basic fibroblast growth factor and growth factor receptor gene expression in 85% O2-exposed rat lung.
Am J Physiol Lung Cell Mol Physiol
268:
L455-L464,
1995[Abstract/Free Full Text].
20.
Buckley, S,
Barsky L,
Driscoll B,
Weinberg K,
Anderson KD,
and
Warburton D.
Apoptosis and DNA damage in type 2 alveolar epithelial cells cultured from hyperoxic rats.
Am J Physiol Lung Cell Mol Physiol
274:
L714-L720,
1998[Abstract/Free Full Text].
21.
Buckley, S,
Bui KC,
Hussain M,
and
Warburton D.
Dynamics of TGF-
3 peptide activity during rat alveolar epithelial cell proliferative recovery from acute hyperoxia.
Am J Physiol Lung Cell Mol Physiol
271:
L54-L60,
1996[Abstract/Free Full Text].
22.
Bui, KC,
Buckley S,
Wu F,
Uhal B,
Joshi I,
Liu J,
Hussain M,
Makhoul I,
and
Warburton D.
Induction of A- and D-type cyclins and cdc2 kinase activity during recovery from short-term hyperoxic lung injury.
Am J Physiol Lung Cell Mol Physiol
268:
L625-L635,
1995[Abstract/Free Full Text].
23.
Burcham, PC.
Genotoxic lipid peroxidation products: their DNA damaging properties and role in formation of endogenous DNA adducts.
Mutagenesis
13:
287-305,
1998[Abstract].
24.
Cacciuttolo, MA,
Trinh L,
Lumpkin JA,
and
Rao G.
Hyperoxia induces DNA damage in mammalian cells.
Free Radic Biol Med
14:
267-276,
1993[ISI][Medline].
25.
Canman, CE,
Lim DS,
Cimprich KA,
Taya Y,
Tamai K,
Sakaguchi K,
Appella E,
Kastan MB,
and
Siliciano JD.
Activation of the ATM kinase by ionizing radiation and phosphorylation of p53.
Science
281:
1677-1679,
1998[Abstract/Free Full Text].
26.
Cazals, V,
Mouhieddine B,
Maitre B,
Le Bouc Y,
Chadelat K,
Brody JS,
and
Clement A.
Insulin-like growth factors, their binding proteins, and transforming growth factor-beta 1 in oxidant-arrested lung alveolar epithelial cells.
J Biol Chem
269:
14111-14117,
1994[Abstract/Free Full Text].
27.
Charafeddine, L,
D'Angio CT,
Richards JL,
Stripp BR,
Finkelstein JN,
Orlowski CC,
LoMonaco MB,
Paxhia A,
and
Ryan RM.
Hyperoxia increases keratinocyte growth factor mRNA expression in neonatal rabbit lung.
Am J Physiol Lung Cell Mol Physiol
276:
L105-L113,
1999[Abstract/Free Full Text].
28.
Chehab, NH,
Malikzay A,
Stavridi ES,
and
Halazonetis TD.
Phosphorylation of Ser-20 mediates stabilization of human p53 in response to DNA damage.
Proc Natl Acad Sci USA
96:
13777-13782,
1999[Abstract/Free Full Text].
29.
Chen, IT,
Akamatsu M,
Smith ML,
Lung FD,
Duba D,
Roller PP,
Fornace AJ, Jr,
and
O'Connor PM.
Characterization of p21Cip1/Waf1 peptide domains required for cyclin E/Cdk2 and PCNA interaction.
Oncogene
12:
595-607,
1996[ISI][Medline].
30.
Chen, X,
Ko LJ,
Jayaraman L,
and
Prives C.
p53 levels, functional domains, and DNA damage determine the extent of the apoptotic response of tumor cells.
Genes Dev
10:
2438-2451,
1996[Abstract].
31.
Chetty, A,
Faber S,
and
Nielsen HC.
Epithelial-mesenchymal interaction and insulin-like growth factors in hyperoxic lung injury.
Exp Lung Res
25:
701-718,
1999[ISI][Medline].
32.
Clement, A,
Edeas M,
Chadelat K,
and
Brody JS.
Inhibition of lung epithelial cell proliferation by hyperoxia. Posttranscriptional regulation of proliferation-related genes.
J Clin Invest
90:
1812-1818,
1992[ISI][Medline].
33.
Clerch, LB,
and
Massaro D.
Rat lung antioxidant enzymes: differences in perinatal gene expression and regulation.
Am J Physiol Lung Cell Mol Physiol
263:
L466-L470,
1992[Abstract/Free Full Text].
34.
Conger, A,
and
Fairchild L.
Breakage of chromosomes by oxygen.
Proc Natl Acad Sci USA
38:
289-299,
1952[ISI].
35.
Cooper, MP,
Balajee AS,
and
Bohr VA.
The C-terminal domain of p21 inhibits nucleotide excision repair in vitro and in vivo.
Mol Biol Cell
10:
2119-2129,
1999[Abstract/Free Full Text].
36.
Corroyer, S,
Maitre B,
Cazals V,
and
Clement A.
Altered regulation of G1 cyclins in oxidant-induced growth arrest of lung alveolar epithelial cells. Accumulation of inactive cyclin E-DCK2 complexes.
J Biol Chem
271:
25117-25125,
1996[Abstract/Free Full Text].
37.
Crapo, JD,
Barry BE,
Foscue HA,
and
Shelburne J.
Structural and biochemical changes in rat lungs occurring during exposures to lethal and adaptive doses of oxygen.
Am Rev Respir Dis
122:
123-143,
1980[ISI][Medline].
38.
Datto, MB,
Li Y,
Panus JF,
Howe DJ,
Xiong Y,
and
Wang XF.
Transforming growth factor beta induces the cyclin-dependent kinase inhibitor p21 through a p53-independent mechanism.
Proc Natl Acad Sci USA
92:
5545-5549,
1995[Abstract].
39.
Datto, MB,
Yu Y,
and
Wang XF.
Functional analysis of the transforming growth factor beta responsive elements in the WAF1/Cip1/p21 promoter.
J Biol Chem
270:
28623-28628,
1995[Abstract/Free Full Text].
40.
De Murcia, JM,
Niedergang C,
Trucco C,
Ricoul M,
Dutrillaux B,
Mark M,
Oliver FJ,
Masson M,
Dierich A,
LeMeur M,
Walztinger C,
Chambon P,
and
de Murcia G.
Requirement of poly(ADP-ribose) polymerase in recovery from DNA damage in mice and in cells.
Proc Natl Acad Sci USA
94:
7303-7307,
1997[Abstract/Free Full Text].
41.
Deng, C,
Zhang P,
Harper JW,
Elledge SJ,
and
Leder P.
Mice lacking p21CIP1/WAF1 undergo normal development, but are defective in G1 checkpoint control.
Cell
82:
675-684,
1995[ISI][Medline].
42.
Dizdaroglu, M.
Measurement of radiation-induced damage to DNA at the molecular level.
Int J Radiat Biol
61:
175-183,
1992[ISI][Medline].
43.
El-Deiry, WS,
Harper JW,
O'Connor PM,
Velculescu VE,
Canman CE,
Jackman J,
Pietenpol JA,
Burrell M,
Hill DE,
Wang Y,
Wiman KG,
Mercer WE,
Kastan MB,
Kohn KW,
Elledge SJ,
Kinzler KW,
and
Vogelstein B.
WAF1/CIP1 is induced in p53-mediated G1 arrest and apoptosis.
Cancer Res
54:
1169-1174,
1994[Abstract].
44.
El-Deiry, WS,
Tokino T,
Velculescu VE,
Levy DB,
Parsons R,
Trent JM,
Lin D,
Mercer WE,
Kinzler KW,
and
Vogelstein B.
WAF1, a potential mediator of p53 tumor suppression.
Cell
75:
817-825,
1993[ISI][Medline].
45.
Elledge, SJ.
Cell cycle checkpoints: preventing an identity crisis.
Science
274:
1664-1672,
1996[Abstract/Free Full Text].
46.
Esposito, F,
Cuccovillo F,
Vanoni M,
Cimino F,
Anderson CW,
Appella E,
and
Russo T.
Redox-mediated regulation of p21(waf1/cip1) expression involves a post-transcriptional mechanism and activation of the mitogen-activated protein kinase pathway.
Eur J Biochem
245:
730-737,
1997[Abstract].
47.
Evans, MJ,
and
Bils RF.
Identification of cells labeled with tritiated thymidine in the pulmonary alveolar walls of the mouse.
Am Rev Respir Dis
100:
372-378,
1969[ISI][Medline].
48.
Evans, MJ,
and
Hackney JD.
Cell proliferation in lungs of mice exposed to elevated concentrations of oxygen.
Aerospace Med
43:
620-622,
1972[ISI].
49.
Evans, MJ,
Hackney JD,
and
Bils RF.
Effects of a high concentration of oxygen on cell renewal in the pulmonary alveoli.
Aerospace Med
40:
1365-1368,
1969[ISI].
50.
Everett, MM,
King RJ,
Jones MB,
and
Martin HM.
Lung fibroblasts from animals breathing 100% oxygen produce growth factors for alveolar type II cells.
Am J Physiol Lung Cell Mol Physiol
259:
L247-L254,
1990[Abstract/Free Full Text].
51.
Fan, S,
Chang JK,
Smith ML,
Duba D,
Fornace AJ, Jr,
and
O'Connor PM.
Cells lacking CIP1/WAF1 genes exhibit preferential sensitivity to cisplatin and nitrogen mustard.
Oncogene
14:
2127-2136,
1997[ISI][Medline].
52.
Fornace, AJ, Jr,
Nebert DW,
Hollander MC,
Luethy JD,
Papathanasiou M,
Fargnoli J,
and
Holbrook NJ.
Mammalian genes coordinately regulated by growth arrest signals and DNA-damaging agents.
Mol Cell Biol
9:
4196-4203,
1989[ISI][Medline].
53.
Frank, L,
Bucher JR,
and
Roberts RJ.
Oxygen toxicity in neonatal and adult animals of various species.
J Appl Physiol
45:
699-704,
1978[Abstract/Free Full Text].
54.
Gary, R,
Ludwig DL,
Cornelius HL,
MacInnes MA,
and
Park MS.
The DNA repair endonuclease XPG binds to proliferating cell nuclear antigen (PCNA) and shares sequence elements with the PCNA-binding regions of FEN-1 and cyclin-dependent kinase inhibitor p21.
J Biol Chem
272:
24522-24529,
1997[Abstract/Free Full Text].
55.
Gilbert, D,
Gerschman R,
Cohen J,
and
Sherwood W.
The influence of high oxygen pressures on the viscosity of solutions of sodium desoxyribonucleic acid and of sodium algenate.
J Am Chem Soc
79:
5677-5680,
1957[ISI].
56.
Gille, JJ,
and
Joenje H.
Chromosomal instability and progressive loss of chromosomes in HeLa cells during adaptation to hyperoxic growth conditions.
Mutat Res
219:
225-230,
1989[ISI][Medline].
57.
Gille, JJ,
Mullaart E,
Vijg J,
Leyva AL,
Arwert F,
and
Joenje H.
Chromosomal instability in an oxygen-tolerant variant of Chinese hamster ovary cells.
Mutat Res
219:
17-28,
1989[ISI][Medline].
58.
Gille, JJ,
van Berkel CG,
and
Joenje H.
Effect of iron chelators on the cytotoxic and genotoxic action of hyperoxia in Chinese hamster ovary cells.
Mutat Res
275:
31-39,
1992[ISI][Medline].
59.
Gille, JJ,
van Berkel CG,
and
Joenje H.
Mutagenicity of metabolic oxygen radicals in mammalian cell cultures.
Carcinogenesis
15:
2695-2699,
1994[Abstract].
60.
Gille, JJ,
van Berkel CG,
Mullaart E,
Vijg J,
and
Joenje H.
Effects of lethal exposure to hyperoxia and to hydrogen peroxide on NAD(H) and ATP pools in Chinese hamster ovary cells.
Mutat Res
214:
89-96,
1989[ISI][Medline].
61.
Gotz, C,
and
Montenarh M.
p53: damage DNA, repair DNA, and apoptosis.
Rev Physiol Biochem Pharmacol
127:
65-95,
1996[ISI][Medline].
62.
Grasl-Kraupp, B,
Ruttkay-Nedecky B,
Koudelka H,
Bukowska K,
Bursch W,
and
Schulte-Hermann R.
In situ detection of fragmented DNA (TUNEL assay) fails to discriminate among apoptosis, necrosis, and autolytic cell death: a cautionary note.
Hepatology
21:
1465-1468,
1995[ISI][Medline].
63.
Ha, HC,
and
Snyder SH.
Poly(ADP-ribose) polymerase is a mediator of necrotic cell death by ATP depletion.
Proc Natl Acad Sci USA
96:
13978-13982,
1999[Abstract/Free Full Text].
64.
Hainaut, P,
and
Milner J.
Redox modulation of p53 conformation and sequence-specific DNA binding in vitro.
Cancer Res
53:
4469-4473,
1993[Abstract].
65.
Hall, M,
Bates S,
and
Peters G.
Evidence for different modes of action of cyclin-dependent kinase inhibitors: p15 and p16 bind to kinases, p21 and p27 bind to cyclins.
Oncogene
11:
1581-1588,
1995[ISI][Medline].
66.
Han, RN,
Han VK,
Buch S,
Freeman BA,
Post M,
and
Tanswell AK.
Insulin-like growth factor-I and type I insulin-like growth factor receptor in 85% O2-exposed rat lung.
Am J Physiol Lung Cell Mol Physiol
271:
L139-L149,
1996[Abstract/Free Full Text].
67.
Hao, M,
Lowy AM,
Kapoor M,
Deffie A,
Liu G,
and
Lozano G.
Mutation of phosphoserine 389 affects p53 function in vivo.
J Biol Chem
271:
29380-29385,
1996[Abstract/Free Full Text].
68.
Harper, JW,
Adami GR,
Wei N,
Keyomarsi K,
and
Elledge SJ.
The p21 Cdk-interacting protein Cip1 is a potent inhibitor of G1 cyclin-dependent kinases.
Cell
75:
805-816,
1993[ISI][Medline].
69.
Hartwell, LH,
and
Weinert TA.
Checkpoints: controls that ensure the order of cell cycle events.
Science
246:
629-634,
1989[ISI][Medline].
70.
Hastings, RH,
Berg JT,
Summers-Torres D,
Burton DW,
and
Deftos LJ.
Parathyroid hormone-related protein reduces alveolar epithelial cell proliferation during lung injury in rats.
Am J Physiol Lung Cell Mol Physiol
279:
L194-L200,
2000[Abstract/Free Full Text].
71.
Heldin, CH,
Miyazono K,
and
ten Dijke P.
TGF-beta signalling from cell membrane to nucleus through SMAD proteins.
Nature
390:
465-471,
1997[ISI][Medline].
72.
Hollstein, M,
Sidransky D,
Vogelstein B,
and
Harris CC.
p53 mutations in human cancers.
Science
253:
49-53,
1991[ISI][Medline].
73.
Imlay, JA,
Chin SM,
and
Linn S.
Toxic DNA damage by hydrogen peroxide through the Fenton reaction in vivo and in vitro.
Science
240:
640-642,
1988[ISI][Medline].
74.
Innocente, SA,
Abrahamson JL,
Cogswell JP,
and
Lee JM.
p53 regulates a G2 checkpoint through cyclin B1.
Proc Natl Acad Sci USA
96:
2147-2152,
1999[Abstract/Free Full Text].
75.
Jayaraman, J,
and
Prives C.
Activation of p53 sequence-specific DNA binding by short single strands of DNA requires the p53 C-terminus.
Cell
81:
1021-1029,
1995[ISI][Medline].
76.
Jayaraman, L,
Murthy KG,
Zhu C,
Curran T,
Xanthoudakis S,
and
Prives C.
Identification of redox/repair protein Ref-1 as a potent activator of p53.
Genes Dev
11:
558-570,
1997[Abstract].
77.
Jimenez, GS,
Bryntesson F,
Torres-Arzayus MI,
Priestley A,
Beeche M,
Saito S,
Sakaguchi K,
Appella E,
Jeggo PA,
Taccioli GE,
Wahl GM,
and
Hubank M.
DNA-dependent protein kinase is not required for the p53-dependent response to DNA damage.
Nature
400:
81-83,
1999[ISI][Medline].
78.
Jobe, AJ.
The new BPD: an arrest of lung development.
Pediatr Res
46:
641-643,
1999[ISI][Medline].
79.
Kamijo, T,
Weber JD,
Zambetti G,
Zindy F,
Roussel MF,
and
Sherr CJ.
Functional and physical interactions of the ARF tumor suppressor with p53 and Mdm2.
Proc Natl Acad Sci USA
95:
8292-8297,
1998[Abstract/Free Full Text].
80.
Kapanci, Y,
Weibel ER,
Kaplan HP,
and
Robinson FR.
Pathogenesis and reversibility of the pulmonary lesions of oxygen toxicity in monkeys. II. Ultrastructural and morphometric studies.
Lab Invest
20:
101-118,
1969[ISI][Medline].
81.
Kapoor, M,
and
Lozano G.
Functional activation of p53 via phosphorylation following DNA damage by UV but not gamma radiation.
Proc Natl Acad Sci USA
95:
2834-2837,
1998[Abstract/Free Full Text].
82.
Kastan, MB,
Onyekwere O,
Sidransky D,
Vogelstein B,
and
Craig RW.
Participation of p53 protein in the cellular response to DNA damage.
Cancer Res
51:
6304-6311,
1991[Abstract].
83.
Kauffman, SL,
Burri PH,
and
Weibel ER.
The postnatal growth of the rat lung. II. Autoradiography.
Anat Rec
180:
63-76,
1974[ISI][Medline].
84.
Kazzaz, JA,
Xu J,
Palaia TA,
Mantell L,
Fein AM,
and
Horowitz S.
Cellular oxygen toxicity. Oxidant injury without apoptosis.
J Biol Chem
271:
15182-15186,
1996[Abstract/Free Full Text].
85.
Kelleher, MD,
Naureckas ET,
Solway J,
and
Hershenson MB.
In vivo hyperoxic exposure increases cultured lung fibroblast proliferation and c-Ha-ras expression.
Am J Respir Cell Mol Biol
12:
19-26,
1995[Abstract].
86.
Khosravi, R,
Maya R,
Gottlieb T,
Oren M,
Shiloh Y,
and
Shkedy D.
Rapid ATM-dependent phosphorylation of MDM2 precedes p53 accumulation in response to DNA damage.
Proc Natl Acad Sci USA
96:
14973-14977,
1999[Abstract/Free Full Text].
87.
Lee, MH,
Reynisdottir I,
and
Massague J.
Cloning of p57KIP2, a cyclin-dependent kinase inhibitor with unique domain structure and tissue distribution.
Genes Dev
9:
639-649,
1995[Abstract].
88.
Li, CY,
Suardet L,
and
Little JB.
Potential role of WAF1/Cip1/p21 as a mediator of TGF-beta cytoinhibitory effect.
J Biol Chem
270:
4971-4974,
1995[Abstract/Free Full Text].
89.
Liu, Q,
Guntuku S,
Cui XS,
Matsuoka S,
Cortez D,
Tamai K,
Luo G,
Carattini-Rivera S,
DeMayo F,
Bradley A,
Donehower LA,
and
Elledge SJ.
Chk1 is an essential kinase that is regulated by Atr and required for the G(2)/M DNA damage checkpoint.
Genes Dev
14:
1448-1459,
2000[Abstract/Free Full Text].
90.
Luo, Y,
Hurwitz J,
and
Massague J.
Cell-cycle inhibition by independent CDK and PCNA binding domains in p21Cip1.
Nature
375:
159-161,
1995[ISI][Medline].
91.
Maniscalco, WM,
Watkins RH,
Finkelstein JN,
and
Campbell MH.
Vascular endothelial growth factor mRNA increases in alveolar epithelial cells during recovery from oxygen injury.
Am J Respir Cell Mol Biol
13:
377-386,
1995[Abstract].
92.
Mantell, LL,
and
Lee PJ.
Signal transduction pathways in hyperoxia-induced lung cell death.
Mol Genet Metab
71:
359-370,
2000[ISI][Medline].
93.
Masutani, M,
Nozaki T,
Nishiyama E,
Shimokawa T,
Tachi Y,
Suzuki H,
Nakagama H,
Wakabayashi K,
and
Sugimura T.
Function of poly(ADP-ribose) polymerase in response to DNA damage: gene-disruption study in mice.
Mol Cell Biochem
193:
149-152,
1999[ISI][Medline].
94.
McDonald, ER, III,
Wu GS,
Waldman T,
and
El-Deiry WS.
Repair defect in p21 WAF1/CIP1 -/- human cancer cells.
Cancer Res
56:
2250-2255,
1996[Abstract].
95.
McGrath, SA.
Induction of p21WAF/CIP1 during hyperoxia.
Am J Respir Cell Mol Biol
18:
179-187,
1998[Abstract/Free Full Text].
96.
Merker, MP,
Pitt BR,
Choi AM,
Hassoun PM,
Dawson CA,
and
Fisher AB.
Lung redox homeostasis: emerging concepts.
Am J Physiol Lung Cell Mol Physiol
279:
L413-L417,
2000[Abstract/Free Full Text].
97.
Michiels, C,
Raes M,
Toussaint O,
and
Remacle J.
Importance of Se-glutathione peroxidase, catalase, and Cu/Zn-SOD for cell survival against oxidative stress.
Free Radic Biol Med
17:
235-248,
1994[ISI][Medline].
98.
Miller, SD,
Farmer G,
and
Prives C.
p53 inhibits DNA replication in vitro in a DNA-binding-dependent manner.
Mol Cell Biol
15:
6554-6560,
1995[Abstract].
99.
Moore, AM,
Buch S,
Han RN,
Freeman BA,
Post M,
and
Tanswell AK.
Altered expression of type I collagen, TGF-
1, and related genes in rat lung exposed to 85% O2.
Am J Physiol Lung Cell Mol Physiol
268:
L78-L84,
1995[Abstract/Free Full Text].
100.
Moynahan, ME,
Chiu JW,
Koller BH,
and
Jasin M.
Brca1 controls homology-directed DNA repair.
Mol Cell
4:
511-518,
1999[ISI][Medline].
101.
Nakamura, J,
Walker VE,
Upton PB,
Chiang SY,
Kow YW,
and
Swenberg JA.
Highly sensitive apurinic/apyrimidinic site assay can detect spontaneous and chemically induced depurination under physiological conditions.
Cancer Res
58:
222-225,
1998[Abstract].
102.
Neades, R,
Cox L,
and
Pelling JC.
S-phase arrest in mouse keratinocytes exposed to multiple doses of ultraviolet B/A radiation.
Mol Carcinog
23:
159-167,
1998[ISI][Medline].
103.
Nelson, WG,
and
Kastan MB.
DNA strand breaks: the DNA template alterations that trigger p53-dependent DNA damage response pathways.
Mol Cell Biol
14:
1815-1823,
1994[Abstract].
104.
Northway, WH, Jr,
Rezeau L,
Petriceks R,
and
Bensch KG.
Oxygen toxicity in the newborn lung: reversal of inhibition of DNA synthesis in the mouse.
Pediatrics
57:
41-46,
1976[Abstract].
105.
O'Connor, PM,
Ferris DK,
Hoffmann I,
Jackman J,
Draetta G,
and
Kohn KW.
Role of the cdc25C phosphatase in G2 arrest induced by nitrogen mustard.
Proc Natl Acad Sci USA
91:
9480-9484,
1994[Abstract/Free Full Text].
106.
O'Reilly, MA,
Staversky RJ,
Flanders KC,
Johnston CJ,
and
Finkelstein JN.
Temporal changes in expression of TGF-
isoforms in mouse lung exposed to oxygen.
Am J Physiol Lung Cell Mol Physiol
272:
L60-L67,
1997[Abstract/Free Full Text].
107.
O'Reilly, MA,
Staversky RJ,
Huyck HL,
Watkins RH,
LoMonaco MB,
D'Angio CT,
Baggs RB,
Maniscalco WM,
and
Pryhuber GS.
Bcl-2 family gene expression during severe hyperoxia induced lung injury.
Lab Invest
80:
1845-1854,
2000[ISI][Medline].
108.
O'Reilly, MA,
Staversky RJ,
Stripp BR,
and
Finkelstein JN.
Exposure to hyperoxia induces p53 expression in mouse lung epithelium.
Am J Respir Cell Mol Biol
18:
43-50,
1998[Abstract/Free Full Text].
109.
O'Reilly, MA,
Staversky RJ,
Watkins RH,
and
Maniscalco WM.
Accumulation of p21(Cip1/WAF1) during hyperoxic lung injury in mice.
Am J Respir Cell Mol Biol
19:
777-785,
1998[Abstract/Free Full Text].
110.
O'Reilly, MA,
Staversky RJ,
Watkins RH,
Maniscalco WM,
and
Keng PC.
p53-independent induction of GADD45 and GADD153 in mouse lungs exposed to hyperoxia.
Am J Physiol Lung Cell Mol Physiol
278:
L552-L559,
2000[Abstract/Free Full Text].
111.
O'Reilly MA, Staversky RJ, Watkins RH, Reed CK, de Mesy Jensen KL,
Finkelstein JN, and Keng PC. The cyclin-dependent kinase inhibitor
p21 protects the lung from oxidative stress. Am J Respir
Cell Mol Biol. In press.
112.
Pardali, K,
Kurisaki A,
Moren A,
ten Dijke P,
Kardassis D,
and
Moustakas A.
Role of smad proteins and transcription factor Sp1 in p21Waf1/Cip1 regulation by transforming growth factor-beta.
J Biol Chem
275:
29244-29256,
2000[Abstract/Free Full Text].
113.
Paulovich, AG,
and
Hartwell LH.
A checkpoint regulates the rate of progression through S phase in S. cerevisiae in response to DNA damage.
Cell
82:
841-847,
1995[ISI][Medline].
114.
Paulovich, AG,
Margulies RU,
Garvik BM,
and
Hartwell LH.
RAD9, RAD17, and RAD24 are required for S phase regulation in Saccharomyces cerevisiae in response to DNA damage.
Genetics
145:
45-62,
1997[Abstract/Free Full Text].
115.
Petrache, I,
Choi ME,
Otterbein LE,
Chin BY,
Mantell LL,
Horowitz S,
and
Choi AM.
Mitogen-activated protein kinase pathway mediates hyperoxia-induced apoptosis in cultured macrophage cells.
Am J Physiol Lung Cell Mol Physiol
277:
L589-L595,
1999[Abstract/Free Full Text].
116.
Petrocelli, T,
Poon R,
Drucker DJ,
Slingerland JM,
and
Rosen CF.
UVB radiation induces p21Cip1/WAF1 and mediates G1 and S phase checkpoints.
Oncogene
12:
1387-1396,
1996[ISI][Medline].
117.
Polyak, K,
Lee MH,
Erdjument-Bromage H,
Koff A,
Roberts JM,
Tempst P,
and
Massague J.
Cloning of p27Kip1, a cyclin-dependent kinase inhibitor and a potential mediator of extracellular antimitogenic signals.
Cell
78:
59-66,
1994[ISI][Medline].
118.
Pomerantz, J,
Schreiber-Agus N,
Liegeois NJ,
Silverman A,
Alland L,
Chin L,
Potes J,
Chen K,
Orlow I,
Lee HW,
Cordon-Cardo C,
and
DePinho RA.
The Ink4a tumor suppressor gene product, p19Arf, interacts with MDM2 and neutralizes MDM2's inhibition of p53.
Cell
92:
713-723,
1998[ISI][Medline].
119.
Prives, C,
and
Hall PA.
The p53 pathway.
J Pathol
187:
112-126,
1999[ISI][Medline].
120.
Qiu, X,
Forman HJ,
Schonthal AH,
and
Cadenas E.
Induction of p21 mediated by reactive oxygen species formed during the metabolism of aziridinylbenzoquinones by HCT116 cells.
J Biol Chem
271:
31915-31921,
1996[Abstract/Free Full Text].
121.
Raffray, M,
and
Cohen GM.
Apoptosis and necrosis in toxicology: a continuum or distinct modes of cell death?
Pharmacol Ther
75:
153-177,
1997[ISI][Medline].
122.
Rancourt, RC,
Keng PC,
Helt CE,
and
O'Reilly MA.
The role of p21Cip1/WAF1 in growth of epithelial cells exposed to hyperoxia.
Am J Physiol Lung Cell Mol Physiol
280:
L617-L626,
2001[Abstract/Free Full Text].
123.
Rancourt, RC,
Staversky RJ,
Keng PC,
and
O'Reilly MA.
Hyperoxia inhibits proliferation of Mv1Lu epithelial cells independent of TGF-
signaling.
Am J Physiol Lung Cell Mol Physiol
277:
L1172-L1178,
1999[Abstract/Free Full Text].
124.
Rathmell, WK,
Kaufmann WK,
Hurt JC,
Byrd LL,
and
Chu G.
DNA-dependent protein kinase is not required for accumulation of p53 or cell cycle arrest after DNA damage.
Cancer Res
57:
68-74,
1997[Abstract].
125.
Reynisdottir, I,
Polyak K,
Iavarone A,
and
Massague J.
Kip/Cip and Ink4 Cdk inhibitors cooperate to induce cell cycle arrest in response to TGF-beta.
Genes Dev
9:
1831-1845,
1995[Abstract].
126.
Ries, S,
Biederer C,
Woods D,
Shifman O,
Shirasawa S,
Sasazuki T,
McMahon M,
Oren M,
and
McCormick F.
Opposing effects of Ras on p53: transcriptional activation of mdm2 and induction of p19ARF.
Cell
103:
321-330,
2000[ISI][Medline].
127.
Rousseau, D,
Cannella D,
Boulaire J,
Fitzgerald P,
Fotedar A,
and
Fotedar R.
Growth inhibition by CDK-cyclin and PCNA binding domains of p21 occurs by distinct mechanisms and is regulated by ubiquitin-proteasome pathway.
Oncogene
18:
4313-4325,
1999[ISI][Medline].
128.
Rueckert, RR,
and
Mueller GC.
Effect of oxygen tension on HeLa cell growth.
Cancer Res
20:
944-949,
1960[ISI].
129.
Schoonen, WG,
Wanamarta AH,
van der Klei-van Moorsel JM,
Jakobs C,
and
Joenje H.
Hyperoxia-induced clonogenic killing of HeLa cells associated with respiratory failure and selective inactivation of Krebs cycle enzymes.
Mutat Res
237:
173-181,
1990[ISI][Medline].
130.
Schoonen, WG,
Wanamarta AH,
van der Klei-van Moorsel JM,
Jakobs C,
and
Joenje H.
Respiratory failure and stimulation of glycolysis in Chinese hamster ovary cells exposed to normobaric hyperoxia.
J Biol Chem
265:
1118-1124,
1990[Medline].
131.
Sheikh, MS,
Chen YQ,
Smith ML,
and
Fornace AJ, Jr.
Role of p21Waf1/Cip1/Sdi1 in cell death and DNA repair as studied using a tetracycline-inducible system in p53-deficient cells.
Oncogene
14:
1875-1882,
1997[ISI][Medline].
132.
Shenberger, JS,
and
Dixon PS.
Oxygen induces S-phase growth arrest and increases p53 and p21(WAF1/CIP1) expression in human bronchial smooth-muscle cells.
Am J Respir Cell Mol Biol
21:
395-402,
1999[Abstract/Free Full Text].
133.
Shieh, SY,
Ahn J,
Tamai K,
Taya Y,
and
Prives C.
The human homologs of checkpoint kinases Chk1 and Cds1 (Chk2) phosphorylate p53 at multiple DNA damage-inducible sites.
Genes Dev
14:
289-300,
2000[Abstract/Free Full Text].
134.
Shieh, SY,
Ikeda M,
Taya Y,
and
Prives C.
DNA damage-induced phosphorylation of p53 alleviates inhibition by MDM2.
Cell
91:
325-334,
1997[ISI][Medline].
135.
Shivji, MK,
Ferrari E,
Ball K,
Hubscher U,
and
Wood RD.
Resistance of human nucleotide excision repair synthesis in vitro to p21Cdn1.
Oncogene
17:
2827-2838,
1998[ISI][Medline].
136.
Smith, ML,
Kontny HU,
Zhan Q,
Sreenath A,
O'Connor PM,
and
Fornace AJ, Jr.
Antisense GADD45 expression results in decreased DNA repair and sensitizes cells to u.v.-irradiation or cisplatin.
Oncogene
13:
2255-2263,
1996[ISI][Medline].
137.
Spitz, DR,
Elwell JH,
Sun Y,
Oberley LW,
Oberley TD,
Sullivan SJ,
and
Roberts RJ.
Oxygen toxicity in control and H2O2-resistant Chinese hamster fibroblast cell lines.
Arch Biochem Biophys
279:
249-260,
1990[ISI][Medline].
138.
Sullivan, SJ,
Oberley TD,
Roberts RJ,
and
Spitz DR.
A stable O2-resistant cell line: role of lipid peroxidation byproducts in O2-mediated injury.
Am J Physiol Lung Cell Mol Physiol
262:
L748-L756,
1992[Abstract/Free Full Text].
139.
Thannickal, VJ,
and
Fanburg BL.
Reactive oxygen species in cell signaling.
Am J Physiol Lung Cell Mol Physiol
279:
L1005-L1028,
2000[Abstract/Free Full Text].
140.
Tibbetts, RS,
Brumbaugh KM,
Williams JM,
Sarkaria JN,
Cliby WA,
Shieh SY,
Taya Y,
Prives C,
and
Abraham RT.
A role for ATR in the DNA damage-induced phosphorylation of p53.
Genes Dev
13:
152-157,
1999[Abstract/Free Full Text].
141.
Tryka, AF,
Witschi H,
Gosslee DG,
McArthur AH,
and
Clapp NK.
Patterns of cell proliferation during recovery from oxygen injury. Species differences.
Am Rev Respir Dis
133:
1055-1059,
1986[ISI][Medline].
142.
Ulich, TR,
Yi ES,
Longmuir K,
Yin S,
Biltz R,
Morris CF,
Housley RM,
and
Pierce GF.
Keratinocyte growth factor is a growth factor for type II pneumocytes in vivo.
J Clin Invest
93:
1298-1306,
1994[ISI][Medline].
143.
Volkmer, E,
and
Karnitz LM.
Human homologs of Schizosaccharomyces pombe rad1, hus1, and rad9 form a DNA damage-responsive protein complex.
J Biol Chem
274:
567-570,
1999[Abstract/Free Full Text].
144.
Vousden, KH.
p53. Death star.
Cell
103:
691-694,
2000[ISI][Medline].
145.
Waga, S,
Hannon GJ,
Beach D,
and
Stillman B.
The p21 inhibitor of cyclin-dependent kinases controls DNA replication by interaction with PCNA.
Nature
369:
574-578,
1994[ISI][Medline].
146.
Waldman, T,
Kinzler KW,
and
Vogelstein B.
p21 is necessary for the p53-mediated G1 arrest in human cancer cells.
Cancer Res
55:
5187-5190,
1995[Abstract].
147.
Waldman, T,
Lengauer C,
Kinzler KW,
and
Vogelstein B.
Uncoupling of S phase and mitosis induced by anticancer agents in cells lacking p21.
Nature
381:
713-716,
1996[ISI][Medline].
148.
Wang, Y,
Blandino G,
and
Givol D.
Induced p21waf expression in H1299 cell line promotes cell senescence and protects against cytotoxic effect of radiation and doxorubicin.
Oncogene
18:
2643-2649,
1999[ISI][Medline].
149.
Wang, ZQ,
Auer B,
Stingl L,
Berghammer H,
Haidacher D,
Schweiger M,
and
Wagner EF.
Mice lacking ADPRT and poly(ADP-ribosyl)ation develop normally but are susceptible to skin disease.
Genes Dev
9:
509-520,
1995[Abstract].
150.
Ward, NS,
Waxman AB,
Homer RJ,
Mantell LL,
Einarsson O,
Du Y,
and
Elias JA.
Interleukin-6-induced protection in hyperoxic acute lung injury.
Am J Respir Cell Mol Biol
22:
535-542,
2000[Abstract/Free Full Text].
151.
Warner, BB,
Stuart LA,
Papes RA,
and
Wispe JR.
Functional and pathological effects of prolonged hyperoxia in neonatal mice.
Am J Physiol Lung Cell Mol Physiol
275:
L110-L117,
1998[Abstract/Free Full Text].
152.
Waxman, AB,
Einarsson O,
Seres T,
Knickelbein RG,
Warshaw JB,
Johnston R,
Homer RJ,
and
Elias JA.
Targeted lung expression of interleukin-11 enhances murine tolerance of 100% oxygen and diminishes hyperoxia-induced DNA fragmentation.
J Clin Invest
101:
1970-1982,
1998[Abstract/Free Full Text].
153.
Weiss, RS,
Enoch T,
and
Leder P.
Inactivation of mouse Hus1 results in genomic instability and impaired responses to genotoxic stress.
Genes Dev
14:
1886-1898,
2000[Abstract/Free Full Text].
154.
Witschi, H.
Effects of oxygen and ozone on mouse lung tumorigenesis.
Exp Lung Res
17:
473-483,
1991[ISI][Medline].
155.
Woo, RA,
McLure KG,
Lees-Miller SP,
Rancourt DE,
and
Lee PW.
DNA-dependent protein kinase acts upstream of p53 in response to DNA damage.
Nature
394:
700-704,
1998[ISI][Medline].
156.
Wu, X,
Bayle JH,
Olson D,
and
Levine AJ.
The p53-mdm-2 autoregulatory feedback loop.
Genes Dev
7:
1126-1132,
1993[Abstract].
157.
Xanthoudakis, S,
and
Curran T.
Identification and characterization of Ref-1, a nuclear protein that facilitates AP-1 DNA-binding activity.
EMBO J
11:
653-665,
1992[Abstract].
158.
Xanthoudakis, S,
Miao G,
Wang F,
Pan YC,
and
Curran T.
Redox activation of Fos-Jun DNA binding activity is mediated by a DNA repair enzyme.
EMBO J
11:
3323-3335,
1992[Abstract].
159.
Xiong, Y,
Hannon GJ,
Zhang H,
Casso D,
Kobayashi R,
and
Beach D.
p21 is a universal inhibitor of cyclin kinases.
Nature
366:
701-704,
1993[ISI][Medline].
160.
Yam, J,
Frank L,
and
Roberts RJ.
Oxygen toxicity: comparison of lung biochemical responses in neonatal and adult rats.
Pediatr Res
12:
115-119,
1978[Abstract].
161.
Zhan, Q,
Antinore MJ,
Wang XW,
Carrier F,
Smith ML,
Harris CC,
and
Fornace AJ, Jr.
Association with Cdc2 and inhibition of Cdc2/Cyclin B1 kinase activity by the p53-regulated protein Gadd45.
Oncogene
18:
2892-2900,
1999[ISI][Medline].
162.
Zhan, Q,
Bae I,
Kastan MB,
and
Fornace AJ, Jr.
The p53-dependent gamma-ray response of GADD45.
Cancer Res
54:
2755-2760,
1994[Abstract].
163.
Zhang, Y,
Xiong Y,
and
Yarbrough WG.
ARF promotes MDM2 degradation and stabilizes p53: ARF-INK4a locus deletion impairs both the Rb and p53 tumor suppression pathways.
Cell
92:
725-734,
1998[ISI][Medline].
164.
Zweier, JL,
Duke SS,
Kuppusamy P,
Sylvester JT,
and
Gabrielson EW.
Electron paramagnetic resonance evidence that cellular oxygen toxicity is caused by the generation of superoxide and hydroxyl free radicals.
FEBS Lett
252:
12-16,
1989[ISI][Medline].
Am J Physiol Lung Cell Mol Physiol 281(2):L291-L305
1040-0605/01 $5.00
Copyright © 2001 the American Physiological Society