INVITED REVIEW
Physiology and pathophysiology of apoptosis in epithelial cells of
the liver, pancreas, and intestine
Blake A.
Jones and
Gregory J.
Gores
Center for Basic Research in Digestive Diseases, Division of
Gastroenterology, Mayo Clinic, Medical School, and Foundation,
Rochester, Minnesota 55905
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ABSTRACT |
Cell death of
gastrointestinal epithelial cells occurs by a process referred to as
apoptosis. In this review, we succinctly define apoptosis and summarize
the role of apoptosis in the physiology and pathophysiology of
epithelial cells in the liver, pancreas, and small and large intestine.
The physiological mediators regulating apoptosis in gastrointestinal
epithelial cells, when known, are discussed. Selected
pathophysiological consequences of excessive apoptosis and inhibition
of apoptosis are used to illustrate the significance of apoptosis in
disease processes. These examples demonstrate that excessive apoptosis
may result in epithelial cell atrophy, injury, and dysfunction, whereas
inhibition of apoptosis results in hyperplasia and promotes malignant
transformation. The specific cellular mechanisms responsible for
dysregulation of epithelial cell apoptosis during pathophysiological
disturbances are emphasized. Potential future areas of physiological
research regarding apoptosis in gastrointestinal epithelia are
highlighted when appropriate.
cholestasis; colon cancer; transforming growth factor-
; pancreatitis
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INTRODUCTION |
APOPTOSIS, a morphologically and biochemically distinct
form of cell death, is an important physiological process in epithelial cell biology. Cell death by apoptosis is a highly conserved
evolutionary process for deleting senescent, damaged, redundant, and
deleterious cells from the organism. In addition, rates of apoptosis
are paired with rates of mitosis so that epithelial cell numbers remain
constant and tissue homeostasis is maintained (54). Given the
widespread and critical role of apoptosis in physiology, it is not
surprising that dysregulation of apoptosis occurs frequently during
pathophysiological disturbances. Indeed, several key concepts have
recently emerged with respect to the dysregulation of apoptosis in
pathophysiological processes, making a review focused on
gastrointestinal epithelial cells timely and topical. First, tissue
hyperplasia and atrophy can result from inhibition or potentiation of
apoptosis, respectively. Second, pathophysiological processes can
trigger the cellular apoptotic machinery leading to rapid and extensive
cell death and tissue dysfunction. Finally, failure of apoptosis to
delete genetically altered cells appears to contribute to malignant
transformation. The therapeutic corollaries of these concepts are that
1) inhibition of apoptosis may
prevent tissue injury and/or promote tissue regeneration and
restitution, 2) induction of
apoptosis of dysplastic and transformed cells may be useful in
preventing and treating malignant diseases, and
3) conversion of necrotic
inflammatory injury to an apoptotic noninflammatory process may
ameliorate disease processes (see below). Indeed, enhanced
and/or deregulated apoptosis has already been implicated in
several diseases (Table 1). Although
several reviews on apoptosis are available (6, 177, 178), especially regarding the intracellular mechanisms regulating apoptosis (20, 36,
88, 108, 139), this review provides an update on the physiology and
pathophysiology of apoptosis as it relates to gastrointestinal epithelial cells. Because mechanisms of apoptosis are best studied when
they are exaggerated or disturbed during pathological events, we
frequently use pathophysiological paradigms to illustrate the mechanisms regulating apoptosis of gastrointestinal epithelia. We first
review, succinctly, key general concepts on the cell physiology of
apoptosis, followed by a more in-depth review of apoptosis in
the liver, pancreas, and small and large intestine. The lack of
information on apoptosis in the esophagus and stomach precludes a
review of apoptosis in these tissues. We also highlight those areas of
apoptosis that deserve further investigative attention by the
physiologist.
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CELL PHYSIOLOGY OF APOPTOSIS |
Apoptosis is characterized by stereotypical morphological features
including cell shrinkage, the disappearance of microvilli, the
formation of cell surface blebs containing organelles, nuclear chromatin condensation and margination, and nuclear fragmentation (Fig.
1). Ultimately, the cell
separates into intact, discrete, membrane-bound bodies, referred to as
apoptotic bodies. These morphological changes of apoptosis are
currently the "gold standard" for identifying apoptosis.
Apoptotic bodies are phagocytosed in vivo by neighboring epithelial
cells and professional phagocytic cells (mononuclear
cells). Indeed, phagocytosis of apoptotic bodies has been
observed in both hepatocytes and intestinal epithelial cells (111A,
126). Apoptosis is difficult to detect in tissues because the changes
of apoptosis occur rapidly (over 2-4 h) and the apoptotic bodies
are rapidly phagocytosed and removed from the tissue. Indeed,
identifying apoptotic cells in tissues has been likened to counting
meteors in the night sky (23). The intact plasma membrane of the
apoptotic body and its rapid phagocytosis are thought to limit release
of intracellular constituents into the extracellular space. Because
release of intracellular constituents into the extracellular space is
limited, the inflammatory response to the dead cell is postulated to be
nonexistent. However, apoptosis may not be as "silent" as
presumed. For example, hepatocyte apoptosis is associated with the
appearance of hepatocyte intracellular enzymes in the circulation (102,
104, 146). Furthermore, the mediators of apoptosis, such as
transforming growth factor-
1 (TGF-
1), may have other consequences
(e.g., tissue fibrogenesis). Current dogma suggests that isolated cell
apoptosis also occurs without a disruption of the epithelial cell
permeability barrier. However, few functional data exist to support
this morphological observation, and enhanced rates of apoptosis may
potentially alter the transmembrane resistance of epithelia, leading to
alterations in absorption and secretion.

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Fig. 1.
Morphological features and identification of apoptosis.
A: schematic representation of the
morphological features of apoptosis. Normal cell at far
left exhibits a uniformly distributed chromatin in the
nucleus, and phosphatidylserine (lollipops) is restricted to the inner
leaflet of the plasmalemma. Early morphological features of apoptosis
include blebbing of the plasma membrane and condensation and
margination of nuclear chromatin (second cell). Externalization of
phosphatidylserine occurs at this early stage. Subsequently the nucleus
becomes fragmented (third cell), and the cell separates into
membrane-bound apoptotic bodies containing intact organelles (fourth
cell). Apoptotic bodies are phagocytosed by neighboring cells.
B: representative approaches for the
identification of apoptotic cells are demonstrated.
Left: fluorescein-conjugated annexin V
binds to phosphatidylserine on the external membrane leaflet of the
plasmalemma of 2 early apoptotic hepatocytes.
Middle: fluorescence photomicrograph
showing nuclear fragmentation identified using the fluorescent DNA
binding dye 4',6'-diamidino-2-phenylindole.
Right: DNA fragmentation of apoptotic
cells assessed by DNA agarose gel electrophoresis. The "ladder"
pattern of DNA cleavage results from internucleosomal cleavage.
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The biochemical features of apoptosis identified to date include
changes in the plasma membrane phospholipid orientation, alterations of
intracellular ion homeostasis, activation of proteases and
endonucleases with cleavage of proteins and DNA, respectively, intracellular generation of ceramide via sphingomyelinase, and activation of transglutaminase (21, 36, 108, 140). The precise roles of
each of these events and their relationship to each other is a topic of
current investigation. Phosphatidylserine is located predominantly on
the inner or cytoplasmic face of the plasma membrane in healthy cells.
However, early in apoptosis, phosphatidylserine is translocated to the
outer leaflet of the plasma membrane, presumably for phagocytic
recognition (32). The externalization of phosphatidylserine can be
readily detected using fluorescently labeled annexin V, which has a
strong affinity for phosphatidylserine. Assays employing fluorescently
labeled annexin V are frequently used to identify apoptotic cells
experimentally (Fig. 1) (73). Increases in cytosolic free calcium and
magnesium and decreases in cytosolic pH and potassium have been
implicated as mechanisms contributing to apoptosis (10, 42, 89, 106,
127). Despite the widespread recognition of cell volume changes and
disturbances of ion homeostasis in apoptosis, this facet of apoptosis
has received little attention by transport physiologists and is a
neglected but potentially fruitful area of investigation. A variety of
proteases have been implicated in apoptosis, including members of the
caspase family (previously known as the interleukin-1
-converting
enzyme family of proteases), calpains, cathepsins, and the
proteasome (108). In particular, caspases (cysteine proteases
recognizing aspartate in the P1 position of the substrate) have been
strongly implicated in apoptosis. Caspase protease cascades analogous
to the coagulation protease cascade have been suggested as a mechanism
leading to the structural changes of apoptosis. Endonuclease activation
with DNA cleavage follows protease activation in apoptosis. DNA is
initially cleaved into fragments of 300,000 and/or 50,000 base
pairs. This type of DNA cleavage appears to be universal
in apoptosis and can be detected by pulse-field gel electrophoresis or
field inversion gel electrophoresis of DNA. The large-order DNA
cleavage is often, but not always, followed by internucleosomal DNA
cleavage into fragments of 180-200 base pairs (the so-called
"ladder" pattern of DNA cleavage) (Fig. 1).
Different endonucleases are thought to mediate the two types of DNA
cleavage. Detection of DNA cleavage in extracted DNA by gel
electrophoresis techniques or in situ using cytochemical and
histochemical techniques is frequently employed to confirm and identify
apoptosis (39, 102). Activation of either neutral or acidic
sphingomyelinase occurs in many models of apoptosis, leading to the
generation of ceramide from sphingomyelin; ceramide activates a
proapoptotic cell signaling cascade (56). Cross-linking of proteins by
transglutaminase, which catalyzes the formation of
e-(
-glutamyl)lysine peptide bonds between appropriate substrates,
keeps the apoptotic bodies intact during the fragmentation of the cell
(34).
The intracellular signaling pathways for apoptosis have not yet been
completely delineated. However, the Fas receptor/Fas ligand pathway of
apoptosis has been elucidated more fully and remains the best
characterized model of apoptosis (Fig. 2).
In this model of apoptosis, binding of the Fas ligand to the Fas receptor results in trimerization of the receptor (98). The trimerized
receptor then recruits the binding protein FADD/MORT1 to its death
domain. The binding of FADD to the death domain results in the
recruitment of caspase 8 to the resulting death-inducing signaling
complex (77). Via as yet unknown mechanisms, the interaction of caspase
8 with the death-inducing signaling complex leads to caspase 8 activation. After caspase 8 activation mitochondrial dysfunction
occurs, leading to the release of cytochrome
c and perhaps also apoptosis-inducing
factor (AIF) into the cytosol (77). Either cytochrome
c or AIF can potentiate caspase 3 activation, a key protease causing the structural changes of apoptosis.

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Fig. 2.
Intracellular signaling cascade for apoptosis after Fas ligation.
Binding of Fas ligand to Fas receptor results in trimerization of the
receptor, leading to formation of a multiprotein complex involving the
receptor and cytosolic proteins, referred to as the death-inducing
signaling complex (98). Via an as yet unknown mechanism, interaction of
caspase 8 with the death-inducing signaling complex leads to caspase 8 activation. After caspase 8 activation, mitochondrial dysfunction
occurs, again by unclear mechanisms. Mitochondrial dysfunction results
in release of cytochrome c and perhaps
also apoptosis-inducing factor (AIF) into the cytosol (77). Either
cytochrome c or AIF can potentiate
caspase 3 activation, a key protease causing the structural changes of
apoptosis.
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The cellular threshold for apoptosis is also highly regulated,
especially by members of the Bcl-2 family of proteins. Multiple mammalian members of this family have been reported to date, including Bcl-2, Bax, Bcl-x, Bcl-w, Bak, Bad, A1, NR-13, and Mcl-1 (37). These
proteins (except for Bad) are integral membrane proteins localized
predominantly to the nuclear membrane, endoplasmic reticulum, and outer
mitochondrial membranes. Members of this family can be antiapoptotic
[Bcl-2, Bcl-xL (long),
Bcl-w, A1, Mcl-1, NR-13] and proapoptotic
[Bcl-xS (short), Bax,
Bad]; however, the pro- or antiapoptotic function of these
proteins may also depend on the cell type, the apoptotic stimuli, the
cellular context (e.g., cell cycle dependence of the process), and the
cellular environment (e.g., presence or absence of growth factors). The
mechanism by which these proteins modulate apoptosis is unclear, but
these proteins appear to regulate each other by forming homo- and
heterodimers. The crystal structure of Bcl-x has been reported; this
protein appears to have a channel configuration similar to diphtheria toxin, and anion-transporting activity has been observed (96). Thus
these proteins may modulate apoptosis by altering the electrochemical responses of cells to pathophysiological processes.
Rates of epithelial cell apoptosis, as with other cells, can be
controlled by the presence of growth factors. Because growth factors
often inhibit apoptosis by paracrine mechanisms, Raff (115) has
suggested that apoptosis is a socially regulated process in that cells
need each other to survive. This concept has four important conceptual
ramifications. First, the default response of a cell may be to die by
apoptosis unless it is kept alive by cell survival signals originating
from other cells. The social control of apoptosis may be important in
maintaining tissue homeostasis with regard to cell number. Second, the
dependence on neighboring cells for cell survival is a strong stimulus
to prevent cell metastases. Third, therapeutic administration of growth
factors may block apoptosis in disease processes. Finally, inhibition
of apoptotic programs may be required for cell growth.
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LIVER |
Physiology of apoptosis in the liver.
There are two epithelial cell types in the liver, hepatocytes and
cholangiocytes (bile duct epithelial cells). Because much of what we
know about apoptosis in the liver is based on studying hepatocytes, in
this review we primarily discuss hepatocyte apoptosis. Where
information is available, we also discuss what is known regarding the
physiology of cholangiocyte apoptosis. Characterization of apoptosis
rates in epithelial tissues such as the liver with low rates of cell
turnover is problematic due to the transient nature of recognizable
apoptotic events. Indeed, even in a tissue undergoing 50% involution
in 3 days by steady-state apoptosis, at any given time point only 9%
of the cells would be identified as apoptotic (6). In the liver,
it is estimated that only 2-4 cells per 10,000 will be
detected as apoptotic given the low cell turnover of both hepatocytes
and cholangiocytes under physiological conditions (126). Despite the
low endogenous rates of apoptosis in the liver, the importance of
apoptosis in regulating liver volume is underscored by two
observations. First, the nongenotoxic, peroxisome-proliferating drugs
lead to increases in liver cell volume by inhibiting apoptosis (7) and
the Fas knockout mouse has substantial liver cell hyperplasia (3).
Second, segmental liver atrophy occurring during portal vein ligation
results from enhanced hepatocyte apoptosis (70). We believe a better
understanding of epithelial cell apoptosis in tissues with low turnover
rates will require new and different methods for identifying apoptotic cells.
Physiological mediators of apoptosis: growth factors, cytokines, and
Fas receptor/Fas ligand.
Although primary cultures of hepatocytes do not appear to require
growth factors for survival, this observation is confounded by the
extremely rapid dedifferentiation of hepatocytes in culture, which
precludes an assessment of their dependence on growth factors for
survival. Hepatocyte growth factor (HGF) is a potent mitogen for
hepatocytes in primary culture and appears to provide a key physiological growth stimulus after partial hepatectomy (91). After
chronic treatment of hepatocytes in vitro with HGF, acute withdrawal of
the growth factor induces hepatocyte apoptosis. These observations
suggest that in vivo, where growth factors are continually present,
hepatocytes may be dependent on growth factors for their survival (24).
HGF is able to prevent apoptosis induced by treatment of murine
hepatocytes with interferon-
(95). The HGF receptor associates with
the antiapoptotic protein BAG-1, providing a mechanism for inhibition
of apoptosis by HGF (6b). Indeed, the HGF receptor when expressed as a
constitutively active form blocks apoptosis and permits hepatocyte
immortalization (5). Likewise, epidermal growth factor, also a hepatic
mitogen, inhibits hepatocyte apoptosis induced by TGF-
(31). Growth
factors may potentially inhibit apoptosis by enhancing expression of
the antiapoptotic members of the Bcl-2 family of proteins. For example,
liver regeneration after partial hepatectomy is associated with
increases in the mRNA transcript for
Bcl-xL, suggesting that inhibition
of the apoptotic machinery by this protein promotes liver regeneration (76). Interleukin-6 (IL-6), also a potent growth factor in the regenerating liver, upregulates
Bcl-xL expression in myeloma
cells, preventing apoptosis (129). Liver failure from extensive cell death, presumably by apoptosis, occurs after a partial hepatectomy in
IL-6-deficient mice (25).
The proapoptotic response of hepatocytes to the injurious growth factor
TGF-
1 and the toxic cytokine tumor necrosis factor-
(TNF-
) has
been more extensively studied. Physiological regression of the liver to
baseline volumes after cessation of treatment with hepatomitogens
occurs by induction of hepatocyte apoptosis (18, 43, 125). Hepatocyte
apoptosis is accompanied by expression of TGF-
1 in apoptotic cells
(103). Another line of evidence supporting a role for TGF-
1 in
hepatocyte apoptosis includes the induction of apoptosis in rat liver
by activin, a member of the TGF-
1 family (128). Although TGF-
1
expression in the liver is abnormal in a variety of disease states
(45), the role of TGF-
1 in hepatocyte apoptosis in disease processes
requires further documentation. Escape from TGF-
1-induced apoptosis
may contribute to hepatocarcinogenesis. Indeed, the development of
resistance to TGF-
1, with a consequent loss of growth inhibition and
apoptosis, was shown to contribute to the spontaneous transformation of
rat liver epithelial cells to a malignant phenotype (62) and
hepatocellular cancer in vivo (31a).
TGF-
1 may also provide an important link between apoptosis and
fibrogenesis in the liver (Fig. 3). In
addition to being synthesized by hepatocytes and causing hepatocyte
apoptosis, TGF-
1 is also produced by and activates stellate cells,
which mediate hepatic fibrogenesis. Thus hepatocyte apoptosis and
fibrogenesis could potentially be coupled by one of several possible
mechanisms through TGF-
1 (Fig. 3). In one potential scenario,
hepatocyte apoptosis may be the primary event. Secretion of TGF-
1 by
apoptotic hepatocytes may lead to stellate cell activation. The
TGF-
1-activated stellate cells would then synthesize and secrete
collagen. In an alternative model, stellate cell activation would be
the primary event. Secretion of TGF-
1 by activated stellate cells
would then cause apoptosis of neighboring hepatocytes. Indeed,
coculture of hepatocytes with activated stellate cells, which produce
TGF-
1, results in enhanced hepatocyte apoptosis (46). Hepatocyte
apoptosis induced by activated stellate cells is reduced when a
recombinant soluble receptor to TGF-
1 is included in the cell
culture medium, suggesting TGF-
1 is responsible for hepatocyte
apoptosis (46). Given the importance of both apoptosis and fibrogenesis
in liver diseases, the relationship between the two is an important
physiological puzzle requiring further delineation.

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Fig. 3.
Mechanisms interrelating hepatocyte apoptosis and fibrogenesis.
Apoptotic cells secreting transforming growth factor- 1
(TGF- 1) may be the driving force for hepatic fibrogenesis.
Stellate cells exposed to TGF- 1 originating from apoptotic
hepatocytes become activated (myofibroblasts) and contribute to liver
fibrogenesis by proliferating and increasing collagen deposition.
Alternatively, pathophysiological events may lead to direct activation
of stellate cells. Activated stellate cells (myofibroblasts) secrete
TGF- 1, inducing apoptosis of neighboring hepatocytes.
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TNF-
, a cytokine primarily produced by macrophages, cholangiocytes,
and Kupffer cells, is capable of producing a wide range of effects in
vivo, including hepatotoxicity (35). It is now appreciated that TNF-
causes liver injury by inducing hepatocyte apoptosis (82, 104, 109).
TNF-
may mediate hepatocyte apoptosis occurring during Kupffer cell
activation by lipopolysaccharide (LPS) and ischemia-reperfusion
injury, the cytokine syndromes associated with septic shock, and
ethanol-mediated liver injury (141). Indeed, TNF-
peripheral serum concentrations are increased in alcoholic hepatitis
and may contribute to the hepatocyte injury observed in this syndrome
(13). Induction of apoptosis of mouse hepatocytes by TNF-
requires
transcriptional arrest but functional translation, implicating protein
synthesis as a necessary component of the pathway (81, 82). Translation
of proapoptotic proteins from preformed RNA or the activation of an
immediate-early gene response (with preformed transcriptional
machinery) may thus be inferred to be apoptotic mechanisms mediating
the signaling cascade distal to TNF-
receptor ligation. In both
TNF-
and LPS models of hepatocyte apoptosis the production of nitric
oxide (NO) by increased expression of inducible nitric oxide synthase
(iNOS) has been suggested as a cytoprotective mechanism; prevention of iNOS upregulation was thus suggested to be a candidate mechanism by
which transcriptional inhibition sensitizes hepatocytes to undergo
apoptosis (82). However, subsequent investigations have demonstrated
that NO generated by increased iNOS expression may itself be a toxic
mediator enhancing hepatocyte death (78). Further work is required to
clarify the potential cytoprotective and injurious actions of iNOS and
NO in hepatocyte apoptosis.
Fas receptor/Fas ligand interactions are also important inducers of
apoptosis in hepatocytes (38). The Fas receptor is a member of the
nerve growth factor receptor family. Binding of the receptor by Fas
ligand results in apoptosis of the cell expressing the Fas receptor.
Unlike many ligands, Fas ligand is predominantly cell bound and it is
expressed in high numbers of cytotoxic T lymphocytes (68). Hepatocytes
constitutively express Fas receptor and may upregulate expression of
this receptor in a variety of liver diseases, including viral hepatitis
and alcohol-induced liver disease (38, 60, 92). For example,
immunohistochemical studies demonstrate Fas receptor expressed on
hepatocytes attached to infiltrating lymphocytes near the regions of
"piecemeal necrosis" in hepatitis C-positive patients, suggesting
that hepatocyte apoptosis occurs via a T cell-mediated Fas pathway in
this viral liver disease (60). In a model of fulminant hepatic failure,
intraperitoneal injection of agonistic anti-Fas antibody leads to
massive hepatocyte apoptosis and liver failure (104). In
pathophysiological processes, hepatocytes may also express Fas ligand,
raising the possibility that a Fas ligand-positive hepatocyte may
induce apoptosis in a Fas receptor-positive neighbor, an example of
fratricide (38). Because Fas ligand is constitutively expressed on
cytotoxic lymphocytes (CTL), cell-mediated immunity, a common process
contributing to hepatocyte apoptosis in autoimmune and viral hepatitis,
likely occurs via Fas-dependent pathways (68). CTL-induced apoptosis of
target cholangiocytes occurring in allograft rejection, graft vs. host
disease, and primary biliary cirrhosis may also occur via Fas-mediated
pathways (11, 75). Table 2 provides a
summary of the physiological mediators and inhibitors of
apoptosis.
Cholestasis as a pathophysiological model of liver cell apoptosis.
Cholestasis is a common but complex pathophysiological process in human
liver disease leading to impaired bile formation, which affects both
hepatocytes and cholangiocytes. As a pathophysiological process, it
provides a useful model to study apoptosis in both cell types. The
prominence of hepatocyte-derived acidophilic (apoptotic) bodies and
cell dropout rather than extensive necrosis in cholestatic liver biopsy
specimens is testimony to the role of hepatocyte apoptosis in
cholestasis (107). Retention and accumulation of toxic bile salts
during cholestasis is thought to trigger hepatocyte apoptosis. Indeed,
exposure of hepatocytes in primary culture to toxic, hydrophobic bile
salts has been demonstrated to directly cause apoptosis of hepatocytes
(106). The mechanism of apoptosis by toxic bile salts has been
partially clarified in recent years (Fig.
4). The induction of
apoptosis by toxic bile salts appears to proceed through activation of
protein kinase C (PKC) (67). Activation of PKC appears to cause
magnesium influx into the cell, activating magnesium-dependent
endonucleases that cleave DNA (66, 106). Through a process that is not
yet clear, PKC activity is also associated with activation of cathepsin
B, which appears to function as a key effector protease in this model
of apoptosis (67, 118).

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Fig. 4.
Mechanisms of induction of apoptosis by toxic bile salts (BS) during
cholestasis. High intracellular concentrations of toxic hydrophobic BS
activate protein kinase C (PKC).
Mg2+ influx from the cell exterior
results from increased PKC activity and increases activity of
Mg2+-dependent endonucleases,
leading to DNA cleavage. PKC activity also leads to cathepsin B
activation and translocation to the nucleus, resulting in cleavage of
nuclear proteins.
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Mechanical obstruction of the bile duct (i.e., obstructive cholestasis)
induces hyperplasia of cholangiocytes, presumably due to a growth
stimulus. Release of the mechanical obstruction with loss of the growth
stimulus results in regression of cholangiocyte numbers by apoptosis
(12). Interestingly, the apoptotic cholangiocytes are shed into the
biliary lumen, where they appear in bile (12). Cholangiocyte apoptosis
in this model likely represents the classic paradigm of epithelial cell
apoptosis on withdrawal of a growth factor.
In contrast to this model of extrahepatic restriction to bile flow,
loss of cholangiocytes and consequent ductopenia characterize the
cholestasis observed in the majority of chronic cholestatic liver
diseases, such as primary biliary cirrhosis, primary sclerosing cholangitis, and biliary atresia. This loss of biliary epithelium appears to be mediated by apoptosis induced by CTL in these presumed autoimmune syndromes (11). Indeed, cholangiocytes are known to express
Fas receptor, supporting this hypothesis (38).
Dysregulation of apoptosis and hepatobiliary malignancy.
Development of a malignant clone may be conceptualized as proceeding in
a stepwise manner. Among the requirements for successful establishment
as a malignancy may be the sequential accumulation of mutations
necessary to block apoptosis. For example, dysregulation of apoptosis
may be necessary to promote growth, prevent elimination by CTL, and
allow survival despite detachment from the substratum during metastases
(8). These tenets do not mean that neoplastic cells do not undergo
apoptosis, because apoptosis is common in neoplastic tissues (19).
However, the mechanisms of apoptosis appear to be altered during cell
dedifferentiation and malignant transformation.
p53 mutations are common in hepatocellular carcinoma. The p53 gene
product acts as a genetic sentinel, acting to initiate the apoptotic
process if excessive DNA damage occurs (79). A defective copy of p53
behaves as a dominant negative, resulting in a cell that is resistant
to undergoing many forms of apoptosis (84). In regions of the world
where both chronic hepatitis B virus infection and dietary aflatoxin
B1 exposure are widely prevalent, hepatocellular carcinoma is frequently accompanied by mutation of p53
(57). Moreover, the protein product of the hepatitis X gene binds to
p53 and abrogates p53-mediated apoptosis (144).
A novel mechanism to escape immune recognition by neoplastic cells is
loss of Fas receptor expression and the development of Fas ligand
expression by the cancer (53, 93). Expression of the Fas ligand results
in apoptosis of Fas-receptor-expressing CTL as they attempt to attack
the neoplastic cell; loss of Fas receptor by the neoplastic cell
ensures its survival despite recognition by the CTL. Indeed,
hepatocellular cancers do not express Fas receptor and frequently
express Fas ligand, apparently to escape immune surveillance (134).
Similar observations have been made in colon cancers (93).
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PANCREAS |
Physiology of apoptosis in the pancreas.
The pancreas contains two epithelial cell types, acinar cells and
pancreatic ductal cells. Analogous to the epithelial cells in the
liver, the turnover of both acinar and ductal cells in the pancreas is
limited. Under basal conditions, tritiated thymidine uptake by cells in
the pancreas is only 0.1-0.2% (40). Assuming basal cell
proliferation is matched to apoptosis, rates of apoptosis in the normal
pancreas should be equally as low. Unfortunately there is a lack of
information regarding the physiological mediators of pancreatic cell
apoptosis in either health or disease. Most of what we know about
apoptosis in the pancreas is derived from studies of pathophysiological
models of pancreatitis.
Pathophysiology of pancreatitis and apoptosis.
Pancreatitis results from acinar cell injury and can be characterized
as either acute or chronic. Acute pancreatitis is associated with
extracellular release of digestive enzymes, which further propagate the
inflammatory injury. In various animal models of acute pancreatitis,
including pancreatic duct ligation, infusing supramaximal stimulating
concentrations of caerulein, and feeding a choline-deficient,
ethionine-supplemented diet, the severity of pancreatitis is directly
related to the magnitude of acinar cell necrosis and inversely related
to the magnitude of acinar cell apoptosis (69). The extent of the
inflammation and necrosis appears to be dependent on the recruitment of
neutrophils to the pancreas (48). Neutrophils may convert the process
of acinar cell death from apoptosis to necrosis (122). Thus the
pathophysiological form of cell death during pancreatic injury may be
apoptosis, with neutrophils acting as an exogenous necrotic trigger.
These data have led to the concept that potentiation of acinar cell death by apoptosis instead of necrosis may ameliorate disease severity
during pancreatitis (Fig. 5) (48, 69).
Indeed, feeding mice a raw soy diet to stimulate pancreatic growth
followed by a switch to a normal chow diet to induce involutional
acinar cell apoptosis protects against caerulein-induced apoptosis
(121). Thus purposefully inducing acinar cell apoptosis may reduce the severity of pancreatitis in humans. The concept of pharmacological induction of pancreatic apoptosis during the early stages of acute pancreatitis provides a new therapeutic strategy for the treatment of
this disease. To our knowledge, this is one of the few examples in
which intentional induction of apoptosis in a benign disease would be
of potential therapeutic benefit. Potential pharmacological approaches
would include prevention of neutrophilic infiltration of the pancreas
(122).

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Fig. 5.
Apoptosis of pancreatic acinar cells reduces tissue damage in acute
pancreatitis. Acinar cell apoptosis during pancreatic injury is
associated with mild inflammation. In contrast, neutrophilic
infiltration and acinar cell necrosis during pancreatic injury lead to
severe pancreatic inflammation (see text for details).
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In contrast to acute pancreatitis, chronic pancreatitis is
characterized by acinar cell atrophy and replacement of the gland architecture with fibrotic tissue. Acinar cell atrophy likely occurs
through an apoptotic process (142). Indeed, chronic obstruction of the
pancreatic duct, feeding a copper-deficient diet, and ethionine administration have also been shown to lead to apoptosis of pancreatic acinar cells in the rat, with resultant pancreatic atrophy (72, 142,
143). Acinar cell atrophy by apoptosis may also contribute to the
transdifferentiation of ductular epithelial cells to hepatocytes in the
copper-deficient pancreas by altering the cellular communications in
their microenvironment (117). The acinar cells of the splenic lobe of
mouse pancreas also undergo apoptosis after selective ductal ligation
as a model of chronic pancreatitis, suggesting that this is the
predominant form of cell death leading to atrophy of the exocrine
pancreas in this condition (145). Apoptosis of acinar cells has also
been identified in rodents fed ethanol plus a low-protein diet, in a
model perhaps more germane to human chronic pancreatitis. TGF-
is
capable of inducing fibrogenesis in pancreatic tissue, and conceivably
replacement of acinar tissue by fibrous scarring is in part mediated by
the apoptotic clearance of pancreatic acinar cells (124). The role of
TGF-
in inducing acinar cell apoptosis as well as fibrous scarring
in vivo remains unknown. However, overexpression of the
TGF-
-regulated zinc finger encoding gene, TIEG, induces apoptosis in
pancreatic epithelial cells (135a). Thus it is highly likely that
TGF-
can induce pancreatic cell apoptosis.
Dysregulation of apoptosis and pancreatic malignancy.
Pancreatic adenocarcinoma is an extremely aggressive cancer with an
accordingly poor prognosis. Current concepts suggest pancreatic cancers
arise primarily from the ductal epithelial cells in the pancreas. To
date, studies investigating dysregulation of apoptosis as a mechanism
of pancreatic ductal cell carcinogenesis have focused on p53, the
adenomatous polyposis coli (APC) gene, and members of the Bcl-2 family
of proteins. p53 null mice heterozygous for the APC gene lose their
remaining copy of wild-type APC through a somatic mutation. A high
proportion of pancreatic cells in this model exhibit a range of
pancreatic abnormalities, including dysplasia and preneoplastic foci
(61%) and adenocarcinoma (22%) (22). In humans, the p53 gene is
mutated in the majority of pancreatic adenocarcinomas and may
contribute to the clinical aggressiveness of these tumors (27). The
antiapoptotic oncoprotein Bcl-xL
is also strongly expressed in human pancreatic adenocarcinomas (64). The enhanced expression of Bcl-xL
suggests that an altered threshold for the induction of apoptosis (in
addition to the mutation of p53 observed in most pancreatic cancers)
has permitted clonal expansion of the cancer (85, 132). Finally, it is
interesting to note that the tumor supressor gene first identified in
pancreatic cancer, DPC4, is a downstream signaling factor for TGF-
and is now referred to as smad4 (88a). This observation suggests that inhibition of TGF-
-induced pancreatic apoptosis may be important in
pancreatic carcinogenesis. Although these observations suggest that
dysregulation of apoptosis may occur in pancreatic carcinogenesis, this
concept has not been adequately tested and remains a hypothesis.
 |
SMALL AND LARGE INTESTINE |
Physiology of apoptosis in the small and large intestine.
Both the small and large intestine have rapid cell turnover rates
(3-6 days), suggesting that rates of apoptosis are equally high to
provide a counterbalance to the increased cell division (110, 130).
Apoptosis of cells at villus tips in the small intestine and luminal
surface of the colon is an attractive hypothesis to help explain the
high rates of epithelial cell turnover in these organs. However,
documentation of enhanced rates of apoptosis in the villus tips and
luminal surface of the small and large intestine has proved
surprisingly controversial (39, 54, 90). Cells at the villus tip have
been noted to be positive for DNA strand breaks with the use of the
terminal dideoxynucleotide transferase (TdT) labeling technique,
suggesting the cells are apoptotic (39, 54). In contrast, other
investigators using the same technique did not identify labeling of
cells on the villus tips (90). The controversy resulting from these
disparate studies centers on the technique of TdT labeling of
3'-OH ends of DNA as a marker for apoptosis. This technique
relies on digestion of tissue with proteinase K before the enzymatic
labeling step. It is now apparent that the duration of proteinase K
digestion and the use of diethyl pyrocarbonate-treated water influence
which and how many cells are labeled using this technique (133). TdT
labeling should be combined with complementary morphological techniques
before it can be considered a marker for apoptosis. Furthermore, the
TdT-based technique is not specific for apoptosis and can also be
observed in cell death by necrosis (44). In the small intestine, TdT will label approximately four times as many cells as would be detected
by morphology in the villus tip with the use of electron microscopy
(130). Nonetheless, apoptosis occurs rapidly in vivo and
may therefore appear underrepresented in histological sections, and
kinetic analysis suggests that apoptosis rather than shedding from the
luminal surface accounts for a large proportion of the cells lost (54).
Although further studies will be necessary to prove or disprove the
hypothesis that apoptosis is responsible for shedding of cells from the
villus tips in the small intestine or luminal surface of the colon, the
observation that Bcl-2 is expressed in the proliferation compartment of
colonic crypts, whereas Bax is expressed near the lumen, supports this
hypothesis in the colon (61, 74, 111a).
Stem cells in the large and small intestine also appear to undergo
apoptosis (112). The proportion of stem cells in the small intestinal
crypt that undergo apoptosis under physiological conditions has been
estimated to be 10% (113). The spontaneous apoptosis of stem cells not
exposed to exogenous insults may represent detection and deletion of
defective cells (i.e., random genetic defects), as well as control of
cell number per se (111). p53 null mice exhibit normal levels of
spontaneous apoptosis in the intestinal crypts (28). This suggests
either that p53 is not involved in the detection of genetic flaws in
recent progeny of stem cells or that the prime function of induction of
apoptosis is regulation of cell number. The low incidence of small
intestinal tumors despite rapid cellular division in contrast to the
relatively high rate of neoplasia in the colon implies more effective
eradication of malignant precursor lesions via apoptosis in the small
vs. large intestine. The absence of Bcl-2 expression and the presence
of the proapoptotic Bax protein in the small intestinal crypt would favor a proapoptotic threshold helping to facilitate apoptosis of
genetically altered stem cells (74, 90). In contrast, stem cells in the
colon do express the antiapoptotic Bcl-2 protein favoring cell survival
despite genetic damage. These observations provide insight into the
mechanisms contributing to the high rates of colon cancer in the large
intestine compared with the low rates of cancer in the small intestine
(80, 87, 119).
Expression of Fas ligand has been described as a feature of "immune
privileged" sites. Cells expressing Fas ligand can produce apoptosis
of Fas receptor-expressing immune effector cells, thereby conferring an
immune privilege (47). The Paneth cells of the small intestine express
Fas ligand at a high level under normal circumstances (94). The reason
for this unique status of Paneth cells is currently unclear. Normal
colonic epithelial cells also constitutively express Fas receptor and
undergo apoptosis on Fas ligation. Based on these observations it has
been proposed that the Fas system contributes to epithelial cell injury
in ulcerative colitis and graft vs. host disease (120a, 134a).
Physiological mediators of apoptosis: growth factors and dietary
factors.
As we have discussed, TGF-
directly induces apoptosis in most
epithelial cells, including colonic epithelial-derived cell lines (6c).
Immunohistochemical studies have shown that, in the small bowel,
TGF-
1 is localized primarily in the villus tip (6a, 6c).
In colonic tissue, TGF-
1 is expressed predominantly in
nonreplicating cells at the top of the colonic crypts (6a). Positive
expression of TGF-
and the absence of Bcl-2 expression by
the cells at the top of the crypts would appear to prime these cells
for apoptosis (54).
Sodium butyrate, a fermentation product of dietary fiber in the colon,
has been shown to induce apoptosis in human colonic cancer cell lines
independent of p53 (51). Butyrate-induced apoptosis of colonic
epithelial cells is associated with increased expression of
p21WAF-1/cip1 (a tumor suppressor
protein that inhibits various cyclin-dependent kinases).
p21WAF-1/cip1 expression induces
apoptosis and cell cycle arrest in a variety of cells and also likely
mediates butyrate-induced apoptosis of colonic epithelial cells (41,
65). Of note is the apparent structural specificity for a four-carbon
acyl chain for butyrate-induced apoptosis; acetate, proprionate, and
isobutyrate (which is branched) appear to be much less effective (50,
59). In contrast, acute butyrate deprivation induces apoptosis in
tissue sheets from guinea pig proximal colon by inducing Bax, a model
more relevant to in vivo conditions than the use of cell lines (58).
The differences between the survival effects of butyrate in vivo and
its apoptotic effects on cell lines remain unclear but have been
comprehensively discussed in a recent editorial (52). Nonetheless, it
appears that dietary products that are metabolized by luminal bacteria can regulate apoptosis of colonic epithelia.
Dysregulation of apoptosis and colorectal cancer.
Although there are scant data on apoptosis as a mechanism of tissue
injury in the small and large intestine, dysregulation of apoptosis as
a mechanism contributing to colon carcinogenesis has received
considerable attention (Fig. 6). Studies in
the colon on dysregulation of apoptosis as a mechanism of
carcinogenesis are providing fundamental, pioneering observations
highly relevant to the broad field of carcinogenesis in general.
Therefore, instead of the the pathophysiological consequences of
excessive apoptosis in the intestine, this portion of the review
focuses on dysregulation of apoptosis as a cellular mechanism of colon
carcinogenesis. Bcl-2, an antiapoptotic oncogene product first
implicated in the pathogenesis of follicular lymphoma, has been
implicated in the genesis of the adenoma/carcinoma sequence of events
in colon carcinogenesis. In normal colon, Bcl-2 protein is expressed
only in the base and the lower third of the epithelial column (26).
However, increased expression of Bcl-2 was found in most dysplastic,
adenomatous, and early adenocarcinomatous lesions (16, 90). Although
Bcl-2 may not be expressed in advanced, anaplastic cancers, it is
expressed in virtually 100% of adenomas, suggesting that Bcl-2
contributes to the early stages of neoplastic transformation by
blocking apoptosis during the transformation process of genetically
altered cells (15, 16). These observations suggest that impaired
induction of apoptosis due to aberrant Bcl-2 expression facilitates the development of colonic neoplasia.

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|
Fig. 6.
Development of a colon cancer by dysregulation of apoptosis. Escape
from an apoptotic fate may be essential for a malignant clone's
survival, as depicted for a colonic adenocarcinoma. Early in the course
of progression, a somatic mutation may increase Bcl-2 expression; the
resultant increase in resistance to apoptosis may permit further
mutations. Loss of functional TGF- type II receptor occurs
frequently in patients with microsatellite instability and prevents
this cytokine from inducing apoptosis. p53 mutations prevent activation
of apoptosis despite DNA damage. In familial adenomatous polyposis coli
(APC) patients, the APC protein is truncated and presumably
nonfunctional, thereby disrupting pathways of apoptosis dependent on
APC. Tumor cells may additionally express Fas ligand (FasL), thereby
escaping tumor surveillance by cytotoxic lymphocytes (CTL). COX-2,
cyclooxygenase-2.
|
|
One of the most convincing examples of dysregulation of apoptosis as a
mechanism of carcinogenesis is in the hereditary nonpolyposis colorectal cancer (HNPCC) syndromes. Individuals with HNPCC syndrome have defects in the base-base mismatch repair pathway of DNA repair, leading to frameshift mutations (1, 147). Colon cancers from these
individuals frequently exhibit insertions or deletions of one or two
adenine base pairs in the gene for the TGF-
type II receptor (4,
86). The resulting frameshift mutations in the gene for this receptor
encode truncated proteins that lack transmembrane and cytoplasmic
domains for the receptor (86). The truncated protein is inactive in
cell signaling and prevents TGF-
-mediated apoptosis of colonic
epithelium (86). Failure of TGF-
-mediated apoptosis interrupts a key
physiological mediator of apoptosis in the colon and likely contributes
to colon carcinogenesis in this syndrome. Indeed, mutation of the
TGF-
type II receptor occurs in 90% of colon cancers displaying
microsatellite instability, a phenotypic marker for defects in the
base-base mismatch repair enzymes (2, 63, 86, 105, 137). Recently,
frameshift mutations in the bax gene
have also been identified in colon cancers from patients with this
syndrome (116). Loss of Bax function by this mutation would alter the
apoptotic threshold. How failure of TGF-
- or Bax-mediated apoptosis
of colonic epithelium leads to colon carcinogenesis remains unclear;
however, failure of apoptosis likely helps to prolong cell survival
during the multiple mutations involved in the multistep stages of colon
carcinogenesis.
Alterations in eicosanoid production within colonic epithelium may also
promote colon carcinogenesis by blocking apoptosis. Most colon cancers
overexpress prostaglandin endoperoxide synthase 2, commonly referred to
as cyclooxygenase-2 (COX-2) (123). Intestinal epithelial
cells overexpressing COX-2 increase expression of Bcl-2, decrease
expression of retinoblastoma kinase, cyclin D1, and TGF-
receptors,
and enhance cellular adherence to matrix proteins such as
E-cadherin (29, 30, 138). These phenotypic alterations lead
to a cellular phenotype resistant to butyrate-induced apoptosis (138).
The resistance to apoptosis can be reversed by nonsteroidal anti-inflammatory drugs (NSAIDs), which inhibit the enzymatic activity
of COX-2, suggesting that enhanced eicosanoid production leads to the
altered phenotype. Compared with histologically normal mucosa, tissue
from human colon cancers showed a 2.3-fold increase of prostaglandin
E2 and a 3.5-fold decrease of
prostaglandin I2 levels, with
unaltered levels of thromboxanes and leukotrienes (representing
products of the 5-lipoxygenase pathway of arachidonic acid metabolism)
(114). However, leukotriene B4 and
12-(R)-hydroxyeicosapentaenoic acid
have also been shown to increase the rate of proliferation of colon
cancer cells in vitro, suggesting that at least some metabolites from
the lipoxygenase and cytochrome P-450
pathways may also be responsible for increased proliferation in colon
cancer (14). These exciting studies provide insight into the resolution of colonic adenomas, which have been reported in patients taking NSAIDs. The use of specific COX-2 inhibitors currently under
development may prove efficacious in the chemoprevention of human
colonic neoplasia. However, it should be noted that induction of
apoptosis by NSAIDs may be independent of blocking eicosanoid pathways. For example, induction of apoptosis cannot be prevented by the addition
of exogenous prostaglandins, and these compounds induce apoptosis in
HCT-15 cells, which lack both COX-1 and COX-2 transcripts (55). The NSAID sulindac and its metabolite sulindac sulfide reduce
the level and activity of multiple cyclin-dependent kinases and induce
expression of p21WAF-1/cip1.
Multiple cellular mechanisms may lead to apoptosis by these pharmacological agents (41, 131).
Finally, alterations in the APC gene, which lead to colon
carcinogenesis, may also regulate apoptosis. The protein product of
this gene is expressed in the nonproliferating, differentiated cell in
the upper half of the crypt. Patients with germline mutations of this
gene produce a truncated protein that presumably has loss of function
(17, 71, 101). APC has been reported to associate with
- and
-catenin, proteins that associate with E-cadherin, suggesting that
APC is involved in cell adhesion (120, 135). Recent data suggest APC
may be involved in the apoptotic pathway, and loss of function could
inhibit apoptosis, promoting an expansion of the proliferative zone in
the colon crypt, or could conceivably facilitate metastasis (17).
Expansion of the proliferating zone and prolonged cell survival may
provide the cellular substrate for the enhanced mutagenesis and the
early development of colon cancers observed in affected individuals.
 |
SUMMARY |
Recent knowledge regarding cell death by apoptosis has markedly altered
our concepts of the physiology and pathophysiology of gastrointestinal
epithelial cells. We now realize that enhanced apoptosis can lead to
tissue injury during vascular, inflammatory, infectious, metabolic, and
drug-induced disease processes. Dysregulation or inhibition of
apoptosis appears to be important in cell proliferation, tissue
hyperplasia, and malignant transformation of gastrointestinal epithelia. Nonetheless, we believe much remains to be learned regarding
the role of apoptosis in gastrointestinal diseases. Two fundamental
questions remain: 1) What are the
initiators and regulators of apoptosis in gastrointestinal epithelia?
and 2) What are the intracellular
pathways culminating in apoptosis in gastrointestinal epithelial cells?
Although the role of Fas receptor and Fas ligand pathways of apoptosis
(a pathway fully elucidated in lymphocytes) needs to be further
explored in gastrointestinal diseases, many of the initiators and
regulators of apoptosis in the gastrointestinal tract will not be
shared by lymphocytes (i.e., private pathways of apoptosis). In
particular, characterization of the expression of the Bcl-2 family
members of proteins and their role in promoting or preventing apoptosis
as well as their regulation by cytokines, dietary factors,
neuroendocrine peptides, and neurotransmitters needs further
delineation. In contrast, the intracellular pathways of apoptosis
(e.g., caspase activation, mitochondrial dysfunction) are likely to be
shared between lymphocytes and gastrointestinal epithelial cells.
Investigators interested in intracellular mechanisms of apoptosis in
epithelial cells will need to compare and contrast differences and
similarities between the intracellular mechanisms known in lymphocytes
and those of epithelial cells. As new knowledge becomes available, the
purposeful, therapeutic regulation of apoptosis should prove useful in
disease processes.
 |
ACKNOWLEDGEMENTS |
We gratefully acknowledge the superb secretarial assistance of Sara
Erickson.
 |
FOOTNOTES |
This work was supported by National Institute of Diabetes and Digestive
and Kidney Diseases Grant DK-41876, by the Gainey Foundation, St. Paul,
MN, and by the Mayo Foundation, Rochester, MN.
Address for reprint requests: G. J. Gores, Mayo Medical School, Clinic,
and Foundation, 200 First St. SW, Rochester, MN 55905.
 |
REFERENCES |
1.
Aaltonen, L. A.,
P. Peltomäki,
F. S. Leach,
P. Sistonen,
L. Pylkkänen,
J.-P. Mecklin,
H. Järvinen,
S. M. Powell,
J. Jen,
S. R. Hamilton,
G. M. Peterson,
K. W. Kinzler,
B. Vogelstein,
and
A. de la Chapelle.
Clues to the pathogenesis of familial colorectal cancer.
Science
260:
812-816,
1993[Medline].
2.
Aaltonen, L. A.,
P. Peltomäki,
J.-P. Mecklin,
H. Järvinen,
J. R. Jass,
J. S. Green,
H. T. Lynch,
P. Watson,
G. Tallquist,
M. Juhola,
P. Sistonen,
S. R. Hamilton,
K. W. Kinzler,
B. Vogelstein,
and
A. de la Chapelle.
Replication errors in benign and malignant tumors from hereditary nonpolyposis colorectal cancer patients.
Cancer Res.
54:
1645-1648,
1994[Abstract].
3.
Adachi, M.,
S. Suematsu,
T. Kondo,
J. Ogasawara,
T. Tanaka,
N. Yoshida,
and
S. Nagata.
Targeted mutation in the Fas gene causes hyperplasia in peripheral lymphoid organs and liver.
Nat. Genet.
11:
294-300,
1995[Medline].
4.
Akiyama, Y.,
R. Iwanaga,
K. Saitoh,
K. Shiba,
K. Ushio,
E. Ikeda,
T. Iwama,
T. Nomizu,
and
Y. Yuasa.
Transforming growth factor
type II receptor gene mutations in adenomas from hereditary nonpolyposis colorectal cancer.
Gastroenterology
112:
33-39,
1997[Medline].
5.
Amicone, L.,
F. M. Spagnoli,
G. Späth,
S. Giordano,
C. Tommasini,
S. Bernardini,
V. De Luca,
C. Della Rocca,
M. C. Weiss,
P. M. Comoglio,
and
M. Tripodi.
Transgenic expression in the liver of truncated Met blocks apoptosis and permits immortalization of hepatocytes.
EMBO J.
16:
494-503,
1997.
6.
Arends, M. J.,
and
A. H. Wyllie.
Apoptosis: mechanisms and roles in pathology.
Int. Rev. Exp. Pathol.
32:
223-254,
1991[Medline].
6a.
Avery, A.,
C. Paraskeva,
P. Hall,
K. C. Flanders,
M. Sporn,
and
M. Moorghen.
TGF-
expression in the human colon: differential immunostaining along crypt epithelium.
Br. J. Cancer
68:
137-139,
1993[Medline].
6b.
Bardelli, A.,
P. Longati,
D. Albero,
S. Goruppi,
C. Schneider,
C. Ponzetto,
and
P. M. Comoglio.
HGF receptor associates with the anti-apoptotic protein BAG-1 and prevents cell dealth.
EMBO J.
15:
6205-6212,
1996[Abstract].
6c.
Barnard, J. A.,
R. D. Beauchamp,
R. J. Coffey,
and
H. L. Moses.
Regulation of intestinal epithelial-cell growth by transforming growth factor type
.
Proc. Natl. Acad. Sci. USA
86:
1578-1582,
1989[Abstract].
7.
Bayly, A. C.,
R. A. Roberts,
and
C. Dive.
Suppression of liver cell apoptosis in vitro by the non-genotoxic hepatocarcinogen and peroxisome proliferator nafenopin.
J. Cell Biol.
125:
197-203,
1994[Abstract].
8.
Bedi, A.,
P. J. Pasricha,
A. J. Akhtar,
J. P. Barber,
G. C. Bedi,
F. M. Giardiello,
B. A. Zehnbauer,
S. R. Hamilton,
and
R. J. Jones.
Inhibition of apoptosis during development of colorectal cancer.
Cancer Res.
55:
1811-1816,
1995[Abstract].
9.
Bedossa, P.,
T. Poynard,
P. Mathurin,
G. Lemaigre,
and
J. C. Chaput.
Transforming growth factor
1: in situ expression in the liver of patients with chronic hepatitis C treated with
interferon.
Gut
34:
S146-S147,
1993[Medline].
10.
Benson, R. S. P.,
S. Heer,
C. Dive,
and
A. J. M. Watson.
Characterization of cell volume loss in CEM-C7A cells during dexamethasone-induced apoptosis.
Am. J. Physiol.
270 (Cell Physiol. 39):
C1190-C1203,
1996[Abstract/Free Full Text].
11.
Bernuau, D.,
G. Feldman,
C. Degott,
and
C. Gisselbrecht.
Ultrastructural lesions of bile ducts in primary biliary cirrhosis. A comparison with the lesions observed in graft versus host disease.
Hum. Pathol.
12:
782-793,
1981[Medline].
12.
Bhathal, P. S.,
and
J. A. M. Gall.
Deletion of hyperplastic biliary epithelial cells by apoptosis following removal of the proliferative stimulus.
Liver
5:
311-325,
1985[Medline].
13.
Bird, G. L. A.,
N. Sheron,
A. K. J. Goka,
G. J. Alexander,
and
R. S. Williams.
Increased plasma tumor necrosis factor in severe alcoholic hepatitis.
Ann. Intern. Med.
112:
917-920,
1990[Medline].
14.
Bortuzzo, C.,
R. Hanif,
K. Kashfi,
L. Staiano-Coico,
S. J. Shiff,
and
B. Rigas.
The effect of leukotriene B and selected HETEs on the proliferation of colon cancer cells.
Biochim. Biophys. Acta
1300:
240-246,
1996[Medline].
15.
Bosari, S.,
L. Moneghini,
D. Graziani,
A. K. C. Lee,
J. J. Murray,
G. Coggi,
and
G. Viale.
bcl-2 Oncoprotein in colorectal hyperplastic polyps, adenomas, and adenocarcinomas.
Hum. Pathol.
26:
534-540,
1995[Medline].
16.
Bronner, M. P.,
C. Culin,
J. C. Reed,
and
E. E. Furth.
The bcl-2 proto-oncogene and the gastrointestinal epithelial tumor progression model.
Am. J. Pathol.
146:
20-26,
1995[Abstract].
17.
Browne, S. J.,
A. C. Williams,
A. Hague,
A. J. Butt,
and
C. Paraskeva.
Loss of APC protein expressed by human colonic epithelial cells and the appearance of a specific low-molecular-weight form is associated with apoptosis in vitro.
Int. J. Cancer
59:
56-64,
1994[Medline].
18.
Bursch, W.,
B. Dürsterburg,
and
R. Schulte-Hermann.
Growth, regression and cell death in rat liver as related to tissue levels of the hepatomitogen cyproterone acetate.
Arch. Toxicol.
59:
221-227,
1986[Medline].
19.
Bursch, W.,
S. Paffe,
B. Putz,
G. Barthel,
and
R. Schulte-Hermann.
Determination of the length of the histological stages of apoptosis in normal liver and in altered hepatic foci of rats.
Carcinogenesis
11:
847-853,
1990[Abstract].
20.
Chinnaiyan, A. M.,
and
V. M. Dixit.
Cytotoxic T-cell-derived granzyme B activates the apoptotic protease ICE-LAP3.
Curr. Biol.
6:
555-562,
1996[Medline].
21.
Chinnaiyan, A. M.,
K. Orth,
K. O'Rourke,
H. Duan,
G. G. Poirier,
and
V. M. Dixit.
Molecular ordering of the cell death pathway. Bcl-2 and Bcl-xL function upstream of the CED-3-like apoptotic proteases.
J. Biol. Chem.
271:
4573-4576,
1996[Abstract/Free Full Text].
22.
Clarke, A. R.,
M. C. Cummings,
and
D. J. Harrison.
Interaction between murine germline mutations in p53 and APC predisposes to pancreatic neoplasi but not to increased intestinal malignancy.
Oncogene
11:
1913-1920,
1995[Medline].
23.
Colucci, W. S.
Apoptosis in the heart.
N. Engl. J. Med.
335:
1224-1226,
1996[Free Full Text].
24.
Columbano, A.,
G. M. Ledda-Columbano,
P. Coni,
G. Faa,
C. Liguori,
G. Santacruz,
and
P. Pani.
Occurrence of cell death (apoptosis) during the involution of liver hyperplasia.
Lab. Invest.
52:
670-675,
1985[Medline].
25.
Cressman, D. E.,
L. E. Greenbaum,
R. A. Deangelis,
G. Ciliberto,
E. E. Furth,
V. Poli,
and
R. Taub.
Liver failure and defective hepatocyte regeneration in interleukin-6-deficient mice.
Science
274:
1379-1383,
1996[Abstract/Free Full Text].
26.
Crider, B. P.,
X. S. Xie,
and
D. K. Stone.
Bafilomycin inhibits proton flow through the H+ channel of vacuolar proton pumps.
J. Biol. Chem.
269:
17379-17381,
1994[Abstract/Free Full Text].
27.
Digiuseppe, J. A.,
M. S. Redston,
C. J. Yeo,
S. E. Kern,
and
R. H. Hruban.
p53-independent expression of the cyclin-dependent kinase inhibitor p21 in pancreatic carcinoma.
Am. J. Pathol.
147:
884-888,
1995[Abstract].
28.
Donehower, L. A.,
M. Harvey,
B. L. Slagle,
M. J. McArthur,
C. A. Montgomery, Jr.,
J. S. Butel,
and
A. Bradley.
Mice deficient for p53 are developmentally normal but susceptible to spontaneous tumors.
Nature
356:
215-221,
1992[Medline].
29.
DuBois, R. N.,
A. Radhika,
B. S. Reddy,
and
A. J. Entingh.
Increased cyclooxygenase-2 levels in carcinogen-induced rat colonic tumors.
Gastroenterology
110:
1259-1262,
1996[Medline].
30.
DuBois, R. N.,
J. Shao,
M. Tsujii,
H. Sheng,
and
R. D. Beauchamp.
G1 delay in cells overexpressing prostaglandin endoperoxide synthase-2.
Cancer Res.
56:
733-737,
1996[Abstract].
31.
Fabregat, I.,
A. Sanchez,
A. M. Alvarez,
T. Nakamura,
and
M. Benito.
Epidermal growth factor, but not hepatocyte growth factor, suppresses the apoptosis induced by transforming growth factor-
in fetal hepatocytes in primary culture.
FEBS Lett.
384:
14-18,
1996[Medline].
31a.
Factor, V. M.,
C.-Y. Kao,
E. Santoni-Rugiu,
J. T. Woitach,
M. R. Jensen,
and
S. S. Thorgeirsson.
Constitutive expression of mature transforming growth factor
1 in the liver accelerates hepatocarcinogenesis in transgenic mice.
Cancer Res.
57:
2089-2095,
1997[Abstract].
32.
Fadok, V. A.,
D. R. Voelker,
P. A. Campbell,
and
P. M. Henson.
Exposure of phosphatidylserine on the surface of apoptotic lymphocytes triggers specific recognition and removal by macrophages.
J. Immunol.
148:
2207-2216,
1992[Abstract/Free Full Text].
33.
Fausto, N.,
and
J. E. Mead.
Biology of disease. Regulation of liver growth: protooncogenes and transforming growth factors.
Lab. Invest.
60:
4-13,
1989[Medline].
34.
Fesus, L.,
V. Thomazy,
and
A. Falus.
Induction and activation of tissue transglutaminase during programmed cell death.
FEBS Lett.
224:
104-108,
1987[Medline].
35.
Fiers, W.
Tumor necrosis factor: characterization at the molecular, cellular, and in vivo level.
FEBS Lett.
285:
199-212,
1991[Medline].
36.
Fraser, A.,
and
G. Evan.
A license to kill.
Cell
85:
781-784,
1996[Medline].
37.
Gajewski, T. F.,
and
C. B. Thompson.
Apoptosis meets signal transduction: elimination of a BAD influence.
Cell
87:
589-592,
1996[Medline].
38.
Galle, P. R.,
W. J. Hofmann,
H. Walczak,
H. Schaller,
G. Otto,
W. Stremmel,
P. H. Krammer,
and
L. Runkell.
Involvement of the CD95 (APO-1/Fas) receptor and ligand in liver damage.
J. Exp. Med.
182:
1223-1230,
1995[Abstract].
39.
Gavrieli, Y.,
Y. Sherman,
and
S. A. Ben-Sasson.
Identification of programmed cell death in situ via specific labeling of nuclear DNA fragmentation.
J. Cell Biol.
119:
493-501,
1992[Abstract].
40.
Githens, S.
Differentiation and development of the pancreas in animals.
In: The Pancreas: Biology, Pathobiology, and Disease, edited by V. L. W. Go,
E. P. DiMagno,
J. D. Gardner,
E. Lebenthal,
H. A. Reber,
and G. A. Scheele. New York: Raven, 1993, p. 21-55.
41.
Goldberg, Y.,
I. I. Nassif,
A. Pittas,
L.-L. Tsai,
B. D. Dynlacht,
B. Rigas,
and
S. J. Shiff.
The anti-proliferative effect of sulindac and sulindac sulfide on HT-29 colon cancer cells: alterations in tumor suppressor and cell cycle-regulatory proteins.
Oncogene
12:
893-901,
1996[Medline].
42.
Gottlieb, R. A.
Cell acidification in apoptosis.
Apoptosis
1:
40-48,
1996.
43.
Grasl-Kraupp, B.,
W. Bursch,
B. Ruttkay-Nedecky,
A. Wagner,
B. Lauer,
and
R. Schulte-Hermann.
Food restriction eliminates preneoplastic cells through apoptosis and antagonizes carcinogenesis in rat liver.
Proc. Natl. Acad. Sci. USA
91:
9995-9999,
1994[Abstract/Free Full Text].
44.
Grasl-Kraupp, B.,
H. Ruttkay-Nedecky,
K. Koudelka,
K. Bukowska,
W. Bursch,
and
R. Schulte-Hermann.
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[Medline].
45.
Gressner, A. M. Hepatic fibrogenesis: the puzzle
of interacting cells, fibrogenic cytokines, regulatory loops, and
extracellular matrix molecules (Review). Zeitschrift
Gastroenterol. 30, Suppl. 1: 5-16,
1992.
46.
Gressner, A. M.,
B. Polzar,
B. Lahme,
and
H.-G. Mannherz.
Induction of rat liver parenchymal cell apoptosis by hepatic myofibroblasts via transforming growth factor
.
Hepatology
23:
571-581,
1996[Medline].
47.
Griffith, T. S.,
T. Brunner,
S. M. Fletcher,
D. R. Green,
and
T. A. Ferguson.
Fas ligand-induced apoptosis as a mechanism of immune privilege.
Science
270:
1189-1192,
1995[Abstract].
48.
Gukovskaya, A. S.,
P. Perkins,
V. Zaninovic,
D. Sandoval,
R. Rutherford,
T. Fitzsimmons,
S. J. Pandol,
and
S. Poucel-Hatton.
Mechanisms of cell death after pancreatic duct obstruction in the opossum and the rat.
Gastroenterology
110:
875-884,
1996[Medline].
49.
Gunthert, A. R.,
J. Strater,
U. Vonreyher,
C. Henne,
S. Joos,
K. Koretz,
P. H. Krammer,
and
P. Moller.
Early detachment of colon carcinoma cells during cd95(apo-1/fas)-mediated apoptosis. I. De-adhesion from hyaluronate by shedding of cd44.
J. Cell Biol.
134:
1089-1096,
1996[Abstract].
50.
Hague, A.,
D. J. E. Elder,
D. J. Hicks,
and
C. Paraskeva.
Apoptosis in colorectal tumor cells: induction by the short chain fatty acids butyrate, proprionate, and acetate and by the bile salt deoxycholate.
Int. J. Cancer
60:
400-406,
1995[Medline].
51.
Hague, A.,
A. M. Manning,
K. A. Hanlon,
L. I. Huschtscha,
D. Hart,
and
C. Paraskeva.
Sodium butyrate induces apoptosis in human colonic tumour cell lines in a p53-independent pathway: implications for the possible role of dietary fibre in the prevention of large-bowel cancer.
Int. J. Cancer
55:
498-505,
1993[Medline].
52.
Hague, A.,
B. Singh,
and
C. Paraskeva.
Butyrate acts as a survival factor for colonic epithelial cells: further fuel for the in vivo versus in vitro debate.
Gastroenterology
112:
1036-1040,
1997[Medline].
53.
Hahne, M.,
D. Rimoldi,
M. Schroter,
P. Romero,
M. Schreier,
L. E. French,
T. Bornand,
A. Fontana,
D. Lienard,
J. C. Cerottini,
and
J. Tschopp.
Melanoma cell expression of Fas(APO-1/CD95) ligand
implications for tumor immune escape.
Science
274:
1363-1366,
1996[Abstract/Free Full Text].
54.
Hall, P. A.,
P. J. Coates,
B. Ansari,
and
D. Hopwood.
Regulation of cell number in the mammalian gastrointestinal tract: the importance of apoptosis.
J. Cell Sci.
107:
3569-3577,
1994[Abstract/Free Full Text].
55.
Hanif, R.,
A. Pittas,
Y. Feng,
M. I. Koutsos,
L. Qiao,
L. Staiano-Coico,
S. I. Shiff,
and
B. Rigas.
Effects of nonsteroidal anti-inflammatory drugs on proliferation and on induction of apoptosis in colon cancer cells by a prostaglandin-independent pathway.
Biochem. Pharmacol.
52:
237-245,
1996[Medline].
56.
Hannun, Y. A.,
and
L. M. Obeid.
Ceramide: an intracellular signal for apoptosis.
Trends Biochem. Sci.
20:
73-77,
1995[Medline].
57.
Harris, C. C.,
and
M. Hollstein.
Clinical implications of the p53 tumor-suppressor gene.
N. Engl. J. Med.
329:
1318-1327,
1993[Free Full Text].
58.
Hass, R.,
R. Busche,
L. Luciano,
E. Reale,
and
W. V. Engelhardt.
Lack of butyrate is associated with induction of Bax and subsequent apoptosis in the proximal colon of guinea pig.
Gastroenterology
112:
875-881,
1997[Medline].
59.
Heerdt, B. G.,
M. A. Houston,
and
L. H. Augenlicht.
Potentiation by specific short-chain fatty acids of differentiation and apoptosis in human colonic carcinoma cell lines.
Cancer Res.
54:
3288-3294,
1994[Abstract].
60.
Hiramatsu, N.,
N. Hayashi,
K. Katayama,
K. Mochizuki,
Y. Kawanishi,
A. Kasahara,
H. Fusamoto,
and
T. Kamada.
Immunohistochemical detection of Fas antigen in liver tissue of patients with chronic hepatitis C.
Hepatology
19:
1354-1359,
1994[Medline].
61.
Hockenberry, D. M.,
M. Zutter,
W. Hickey,
M. Nahm,
and
S. Korsmeyer.
BCL2 protein is topographically restricted in tissues characterized by apoptotic cell death.
Proc. Natl. Acad. Sci. USA
88:
6961-6965,
1991[Abstract].
62.
Huggett, A. C.,
P. A. Ellis,
C. P. Ford,
L. L. Hampton,
D. Rimoldi,
and
S. S. Thorgeirsson.
Development of resistance to the growth inhibitory effects of transforming growth factor
1 during the spontaneous transformation of rat liver epithelial cells.
Cancer Res.
51:
5929-5936,
1991[Abstract].
63.
Ionov, Y. M.,
A. Peinado,
S. Malkhosyan,
D. Shibata,
and
M. Perucho.
Ubiquitous somatic mutations in simple repeated sequences reveal a new mechanism for colon carcinogenesis.
Nature
363:
558-561,
1993[Medline].
64.
Janiak, F.,
B. Leber,
and
D. W. Andrews.
Assembly of Bcl-2 into microsomal and outer mitochondrial membranes.
J. Biol. Chem.
269:
9842-9849,
1994[Abstract/Free Full Text].
65.
Jiang, H.,
J. Lin,
Z.-Z. Su,
F. R. Collart,
E. Huberman,
and
P. B. Fisher.
Induction of differentiation in human promyelocytic HL-60 leukemia cells activates p21, WAF1/CIP1, expression in the absence of p53.
Oncogene
9:
3397-3406,
1994[Medline].
66.
Jones, B. A.,
T. C. Patel,
S. F. Bronk,
R. T. Stravitz,
and
G. J. Gores.
Protein kinase C (PKC) promotes Mg2+ influx in bile salt-induced apoptosis of cultured rat hepatocytes (Abstract).
Gastroenterology
112:
1295,
1997.
67.
Jones, B. A.,
R. T. Stravitz,
Y.-P. Rao,
and
G. J. Gores.
Bile salt-induced apoptosis of hepatocytes involves activation of protein kinase C.
Am. J. Physiol.
272 (Gastrointest. Liver Physiol. 35):
G1109-G1115,
1997[Abstract/Free Full Text].
68.
Kagi, D.,
F. Vignaux,
B. Ledermann,
K. Burki,
V. Depraetere,
S. Nagata,
H. Hengartner,
and
P. Goldstein.
Fas and perforin pathways as major mechanisms of T-cell mediated cytotoxicity.
Science
265:
528-530,
1994[Medline].
69.
Kaiser, A. M.,
A. K. Saluja,
A. Sengupta,
M. Saluja,
and
M. L. Steer.
Relationship between severity, necrosis, and apoptosis in five models of experimental acute pancreatitis.
Am. J. Physiol.
269 (Cell Physiol. 38):
C1295-C1304,
1995[Abstract/Free Full Text].
70.
Kerr, J. F. R.
Shrinkage necrosis: a distinct mode of cellular death.
J. Pathol.
105:
13-20,
1971[Medline].
71.
Kinzler, K. W.,
M. C. Nilbert,
L. K. Su,
B. Vogelstein,
T. M. Bryan,
D. B. Levy,
K. J. Smith,
A. C. Preisinger,
P. Hedge,
D. McKechnie,
R. Finniear,
A. Markham,
J. Groffen,
M. S. Boguski,
S. F. Altschul,
A. Horii,
H. Ando,
Y. Miyoshi,
O. Miko,
I. Nishishu,
and
Y. Nakamura.
Identification of FAP locus genes from chromosome 5q21.
Science
253:
661-665,
1991[Medline].
72.
Kishimoto, S.,
S. Iwamoto,
S. Matstani,
R. Yamamoto,
T. Jo,
F. Saji,
N. Terada,
Y. Sasaki,
S. Imaoka,
and
T. Sugiyama.
Apoptosis of acinar cells in the pancreas of rats fed on a copper-depleted diet.
Exp. Toxicol. Pathol.
45:
489-495,
1994[Medline].
73.
Koopman, G.,
C. P. M. Reutelingsperger,
G. A. M. Kuijten,
R. M. J. Keehnen,
S. T. Pals,
and
M. H. J. van Oers.
Annexin V for flow cytometric detection of phosphatidylserine expression on B cells undergoing apoptosis.
Blood
84:
1415-1420,
1994[Abstract/Free Full Text].
74.
Krajewski, S.,
M. Krajewska,
A. Shabaik,
T. Miyashita,
H. G. Wang,
and
J. C. Reed.
Immunohistochemical determination of in vivo distribution of Bax, a dominant inhibitor of Bcl-2.
Am. J. Pathol.
145:
1323-1336,
1994[Abstract].
75.
Krams, S. M.,
H. Egawa,
M. B. Quinn,
J. C. Villanueva,
R. Garcia-Kennedy,
and
O. M. Martinez.
Apoptosis as a mechanism of cell death in liver allograft rejection.
Transplantation
59:
621-625,
1995[Medline].
76.
Kren, B. T.,
J. H. Trembley,
S. Krajewski,
T. W. Behrens,
J. C. Reed,
and
C. J. Steer.
Modulation of apoptosis-associated genes bcl-2, bcl-x and bax during rat liver regeneration.
Cell Growth Differ.
7:
1633-1642,
1996[Abstract].
77.
Kroemer, G.,
N. Zamzami,
and
S. A. Susin.
Mitochondrial control of apoptosis.
Immunol. Today
18:
44-51,
1997[Medline].
78.
Kurose, I.,
S. Miura,
H. Higuchi,
N. Watanabe,
Y. Kamegaya,
M. Takaishi,
K. Tomita,
D. Fukumura,
S. Kato,
and
H. Ishii.
Increased nitric oxide synthase activity as a cause of mitochondrial dysfunction in rat hepatocytes: roles for tumor necrosis factor
.
Hepatology
24:
1185-1192,
1996[Medline].
79.
Lane, D. P.
p53, Guardian of the genome.
Nature
358:
15-16,
1992[Medline].
80.
Laws, H. L.,
S. Y. Jhan,
and
J. S. Aldrete.
Malignant tumors of the small bowel.
South. Med. J.
77:
1087-1090,
1984[Medline].
81.
Leist, M.,
F. Gantner,
I. Bohlinger,
P. G. Germann,
G. Tiegs,
and
A. Wendel.
Murine hepatocyte apoptosis induced in vitro and in vivo by TNF-
requires transcriptional arrest.
J. Immunol.
153:
1778-1788,
1994[Abstract/Free Full Text].
82.
Leist, M.,
F. Gantner,
S. Jilg,
and
A. Wendel.
Activation of the 55 kDa TNF receptor is necessary and sufficient for TNF-induced liver failure, hepatocyte apoptosis, and nitrite release.
J. Immunol.
154:
1307-1316,
1995[Abstract/Free Full Text].
83.
Leist, M.,
F. Gantner,
H. Naumann,
H. Bluethmann,
K. Vogt,
R. Brigelius-Flohé,
P. Nicotera,
H.-D. Volk,
and
A. Wendel.
Tumor necrosis factor-induced apoptosis during the poisoning of mice with hepatotoxins.
Gastroenterology
112:
923-934,
1997[Medline].
84.
Lowe, S. W.,
H. E. Ruley,
T. Jacks,
and
D. E. Housman.
p53 dependent apoptosis modulates the cytotoxicity of anticancer agents.
Cell
74:
957-967,
1993[Medline].
85.
Lumadue, J. A.,
C. A. Griffin,
M. Osman,
and
R. H. Hruban.
Familial pancreatic cancer and the genetics of pancreatic cancer.
Surg. Clin. North Am.
75:
845-855,
1995[Medline].
86.
Markowitz, S. D.,
J. Wang,
L. Myeroff,
R. Parsons,
L. Sun,
J. Lutterbaugh,
R. S. Fan,
E. Zborowska,
K. W. Kinzler,
B. Vogelstein,
M. Brattain,
and
J. K. W. Willson.
Inactivation of the type II TGF-
receptor in colon cancer cells with microsatellite instability.
Science
268:
1336-1338,
1995[Medline].
87.
Martin, R. G.
Malignant tumors of the small intestine (Abstract).
Surg. Clin. North Am.
66:
779,
1986[Medline].
88.
Martin, S. J.,
and
D. R. Green.
Protease activation during apoptosis: death by a thousand cuts?
Cell
82:
349-352,
1995[Medline].
88a.
Massague, J.,
A. Hata,
and
F. Lin.
TGF-
signaling through small pathways.
Trends Cell Biol.
7:
187-192,
1997.
89.
McConkey, D. J.,
S. Orrenius,
and
M. Jondal.
Cellular signalling in programmed cell death (apoptosis).
Immunol. Today
11:
120-121,
1990[Medline].
90.
Merritt, A. J.,
C. S. Potten,
A. J. M. Watson,
D. Y. Loh,
K.-I. Nakayama,
K. Nakayama,
and
J. A. Hickman.
Differential expression of bcl-2 in intestinal epithelia. Correlation with attenuation of apoptosis in colonic crypts and the incidence of colonic neoplasia.
J. Cell Sci.
108:
2261-2271,
1995[Abstract/Free Full Text].
91.
Michalopoulos, G. K.
Hepatocyte growth factor (HGF) and its receptor (Met) in liver regeneration, neoplasia, and disease.
In: Liver Regeneration and Carcinogenesis: Molecular and Cellular Mechanisms, edited by R. L. Jirtle. San Diego: Academic, 1995, p. 27-49.
92.
Mita, E.,
N. Hayashi,
S. Iio,
T. Takehara,
T. Hijioka,
A. Kasahara,
H. Fusamoto,
and
T. Kamada.
Role of Fas ligand in apoptosis induced by hepatitis C virus infection.
Biochem. Biophys. Res. Commun.
204:
468-474,
1994[Medline].
93.
Moller, P.,
K. Koretz,
F. Leithauser,
S. Bruderlein,
C. Henne,
A. Quentmeier,
and
P. H. Krammer.
Expression of APO-1 (CD95), a member of the NGF/TNF receptor superfamily, in normal and neoplastic colon epithelium.
Int. J. Cancer
57:
371-377,
1994[Medline].
94.
Moller, P.,
H. Walczak,
S. Riedl,
J. Strater,
and
P. H. Krammer.
Paneth cells express high levels of CD95 ligand transcripts
a unique property among gastrointestinal epithelia.
Am. J. Pathol.
149:
9-13,
1996[Abstract].
95.
Morita, M.,
Y. Watanabe,
and
T. Akaike.
Protective effect of hepatocyte growth factor on interferon-
-induced cytotoxicity in mouse hepatocytes.
Hepatology
21:
1585-1593,
1995[Medline].
96.
Muchmore, S. W.,
M. Sattler,
H. Liang,
R. P. Meadows,
J. E. Harlan,
H. S. Yoon,
D. Nettesheim,
B. S. Chang,
C. B. Thompson,
S. L. Wong,
S. C. Ng,
and
S. W. Fesik.
X-ray and NMR structure of human Bcl-x(L), an inhibitor of programmed cell death.
Nature
381:
335-341,
1996[Medline].
97.
Nagasue, N.,
L. Q. Yu,
M. Yamaguchi,
H. Kohno,
M. Tachibana,
and
H. Kubota.
Inhibition of growth and induction of TGF-
(1) in human hepatocellular carcinoma with androgen receptor by cyproterone acetate in male nude mice.
J. Hepatol.
25:
554-562,
1996[Medline].
98.
Nagata, S.
Apoptosis by death factor.
Cell
88:
355-365,
1997[Medline].
99.
Nakamura, N.,
Y. Shidoji,
H. Moriwaki,
and
Y. Muto.
Apoptosis in human hepatoma cell line induced by 4,5-didehydrogeranylgeranoic acid (acyclic retinoid) via down-regulation of transforming growth factor-
.
Biochem. Biophys. Res. Commun.
219:
100-104,
1996[Medline].
100.
Ni, R.,
Y. Tomita,
K. Matsuda,
A. Ichihara,
K. Ishimura,
J. Osagawara,
and
S. Nagata.
Fas-mediated apoptosis in primary cultured mouse hepatocytes.
Exp. Cell Res.
215:
332-337,
1994[Medline].
101.
Nishisho, I.,
Y. Nakamura,
Y. Miyoshi,
Y. Miki,
H. Ando,
A. Horii,
K. Koyama,
J. Utsunomiya,
S. Baba,
and
P. Hedge.
Mutations of chromosome 5q21 genes in FAP and colorectal cancer patients.
Science
253:
665-669,
1991[Medline].
102.
Oberhammer, F. A.,
W. Bursch,
R. Tiefenbacher,
G. Fröschl,
M. Pavelka,
T. Purchio,
and
R. Schulte-Hermann.
Apoptosis is induced by transforming growth factor-
1 within 5 hours in regressing rat liver without significant fragmentation of the DNA.
Hepatology
18:
1238-1246,
1993[Medline].
103.
Oberhammer, F. A.,
M. Pavelka,
S. Sharma,
R. Tiefenbacher,
A. F. Purchio,
W. Bursch,
and
R. Schulte-Hermann.
Induction of apoptosis in cultured hepatocytes and in regressing liver by transforming growth factor
1.
Proc. Natl. Acad. Sci. USA
89:
5408-5412,
1992[Abstract].
104.
Ogasawara, J.,
R. Watanabe-Fukunaga,
M. Adachi,
A. Matsuzawa,
T. Kasugai,
Y. Kitamura,
N. Itoh,
T. Suda,
and
S. Nagata.
Lethal effect of the anti-Fas antibody in mice.
Nature
364:
806-809,
1993[Medline].
105.
Parsons, R.,
L. L. Myeroff,
B. Liu,
J. K. V. Willson,
S. D. Markowitz,
K. W. Kinzler,
and
B. Vogelstein.
Microsatellite instability and mutations of the transforming growth factor
type II receptor gene in colorectal cancer.
Cancer Res.
55:
5548-5550,
1995[Abstract].
106.
Patel, T.,
S. F. Bronk,
and
G. J. Gores.
Increases of intracellular magnesium promote glycodeoxycholate-induced apoptosis in hepatocytes.
J. Clin. Invest.
94:
2183-2192,
1994[Medline].
107.
Patel, T.,
and
G. J. Gores.
Apoptosis and hepatobiliary disease.
Hepatology
21:
1725-1741,
1995[Medline].
108.
Patel, T.,
G. J. Gores,
and
S. H. Kaufmann.
The role of proteases during apoptosis.
FASEB J.
10:
587-597,
1996[Abstract/Free Full Text].
109.
Pfeffer, K.,
T. Matsuyama,
T. M. Kündig,
A. Wakeham,
K. Kishihara,
A. Shahinian,
K. Wiegmann,
P. S. Ohashi,
M. Krönke,
and
T. W. Mak.
Mice deficient for the 55 kD tumor necrosis factor receptor are resistant to endotoxic shock, yet succumb to L. monocytogenes infection.
Cell
73:
457-467,
1993[Medline].
110.
Potten, C. S.
Extreme sensitivity of some intestinal crypt cells to X and
irradiation.
Nature
169:
518-521,
1977.
111.
Potten, C. S.
The significance of spontaneous and induced apoptosis in the gastrointestinal tract of mice.
Cancer Metastasis Rev.
11:
179-195,
1992[Medline].
111a.
Potten, C. S.
Epithelial cell growth and differentiation. II. Intestinal apoptosis.
Am. J. Physiol.
273 (Gastrointest. Liver Physiol. 36):
G253-G257,
1997[Free Full Text].
112.
Potten, C. S.,
and
M. Loeffler.
Stem cells: attributes, cycles, spirals, pitfalls and uncertainties. Lessons for and from the crypt.
Development
110:
1001-1020,
1990[Abstract].
113.
Potten, C. S.,
A. Merritt,
J. Hickman,
P. Hall,
and
A. Faranda.
Characterization of radiation-induced apoptosis in the small intestine and its biological implications.
Int. J. Radiat. Biol.
65:
71-78,
1994[Medline].
114.
Qiao, L.,
V. Kozoni,
G. J. Tsioulias,
M. I. Koutsos,
R. Hanif,
S. J. Shiff,
and
B. Rigas.
Selected eicosanoids increase the proliferation rate of human colon carcinoma cell lines and mouse colonocytes in vivo.
Biochim. Biophys. Acta
1258:
215-223,
1995[Medline].
115.
Raff, M. C.
Social control on cell survival and cell death.
Nature
356:
397-400,
1992[Medline].
116.
Rampino, N.,
H. Yamamoto,
Y. Ionov,
Y. Li,
H. Sawai,
J. C. Reed,
and
M. Perucho.
Somatic frameshift mutations in the BAX gene in colon cancers of the microsatellite mutator phenotype.
Science
275:
967-969,
1997[Abstract/Free Full Text].
117.
Rao, M. S.,
and
J. K. Reddy.
Hepatic transdifferentiation in the pancreas.
Sem. Cell Biol.
6:
151-156,
1995[Medline].
118.
Roberts, L. R,
H. Kurosawa,
S. F. Bronk,
W.-T. Leung,
F. Mao,
and
G. J. Gores.
Cathepsin B mediates bile salt-induced hepatocytes apoptosis.
Gastroenterology
113:
1714-1726,
1997[Medline].
119.
Ross, R. K.,
N. M. Hartnett,
L. Bernstein,
and
B. E. Hendersen.
Epidemiology of adenocarcinomas of the small intestine: is bile a small bowel carcinogen?
Br. J. Cancer
63:
143-145,
1991[Medline].
120.
Rubinfeld, B.,
B. Souza,
I. Albert,
O. Müller,
S. H. Chamberlain,
F. R. Masiarz,
S. Munemitsu,
and
P. Polakis.
Association of the APC gene product with
-catenin.
Science
262:
1731-1734,
1993[Medline].
120a.
Sakai, T.,
Y. Kimura,
K. Inagaki-Ohara,
K. Kusagami,
D. H. Lynch,
and
Y. Yoshikai.
Fas-mediated cytotoxicity by intestinal intraepithelial lymphocytes during acute graft vs. host disease in mice.
Gastroenterology
113:
168-174,
1997[Medline].
121.
Saluja, A.,
B. Hofbauer,
Y. Yamaguchi,
K. Yamanaka,
and
M. Steer.
Induction of apoptosis reduces the severity of caerulein-induced pancreatitis in mice.
Biochem. Biophys. Res. Commun.
220:
875-878,
1996[Medline].
122.
Sandoval, D.,
A. Gukovskaya,
P. Reavey,
S. Gukovsky,
A. Sisk,
P. Braquet,
S. J. Pandol,
and
S. Poucelhatton.
The role of neutrophils and platelet-activating factor in mediating experimental pancreatitis.
Gastroenterology
111:
1081-1091,
1996[Medline].
123.
Sano, H.,
Y. Kawahito,
R. L. Wilder,
A. Hashiramoto,
S. Mukai,
K. Asai,
S. Kimura,
H. Kato,
M. Kondo,
and
T. Hla.
Expression of cyclooxygenase-1 and -2 in human colorectal cancer.
Cancer Res.
55:
3785-3789,
1995[Abstract].
124.
Sanvito, F.,
P.-L. Herrera,
J. Huarte,
A. Nichols,
R. Montesano,
L. Orci,
and
J.-D. Vassali.
TGF-
1 influences the relative development of the exocrine and endocrine pancreas in vitro.
Development
120:
3451-3462,
1994[Abstract/Free Full Text].
125.
Schulte-Hermann, R.
Two-stage control of cell proliferation induced in rat liver by
-hexachlorocyclohexane.
Cancer Res.
37:
166-171,
1977[Abstract].
126.
Schulte-Hermann, R.,
W. Bursch,
and
B. Grasl-Kraupp.
Active cell death (apoptosis) in liver biology and disease.
In: Progress in Liver Diseases, edited by J. L. Boyer,
and R. K. Ockner. Philadelphia: Saunders, 1995, vol. 13, p. 1-34.
127.
Schulz, J. B.,
M. Weller,
and
T. Klockgether.
Potassium deprivation-induced apoptosis of cerebellar granule neurons: a sequential requirement for new mRNA and protein synthesis, ICE-like protease activity, and reactive oxygen species.
J. Neurosci.
16:
4696-4706,
1996[Abstract/Free Full Text].
128.
Schwall, R. H.,
K. Robbins,
P. Jardieu,
L. Chang,
C. Lai,
and
T. G. Terrell.
Activin induces cell death in hepatocytes in vivo and in vitro.
Hepatology
18:
347-356,
1993[Medline].
129.
Schwarze, M. M.,
and
R. G. Hawley.
Prevention of myeloma cell apoptosis by ectopic bcl-2 expression or interleukin 6-mediated up-regulation of bcl-xL.
Cancer Res.
55:
2262-2265,
1995[Abstract].
130.
Shibihara, T.,
N. Sato,
S. Waguri,
T. Iwanaga,
A. Nakahara,
H. Fukutomi,
and
Y. Uchiyama.
The fate of effete epithelial cells at the villus tips of the human small intestine.
Arch. Histol. Cytol.
58:
205-219,
1995[Medline].
131.
Shiff, S. J.,
L. Qiao,
L.-L. Tsai,
and
B. Rigas.
Sulindac sulfide, an aspirin-like compound, inhibits proliferation, causes cell cycle quiescence, and induces apoptosis in HT-29 colon adenocarcinoma cells.
J. Clin. Invest.
96:
491-503,
1995[Medline].
132.
Simon, B. R.,
R. Weinel,
M. Hohne,
J. Watz,
J. Schmidt,
G. Kortner,
and
R. Arnold.
Frequent alterations of the tumor suppressor genes p53 and DCC in human pancreatic carcinoma.
Gastroenterology
106:
1645-1651,
1994[Medline].
133.
Stähelin, B. J.,
U. Marti,
M. Solioz,
H. Zimmermann,
and
J. Reichen.
False positive staining in TUNEL assay is due to release of endogenous DNAse and inhibited by diethyl-pyrocarbonate (DEPC) in liver tissue (Abstract).
Hepatology
24:
368A,
1996.
134.
Strand, S.,
W. J. Hofmann,
H. Hug,
M. Müller,
G. Otto,
D. Strand,
S. M. Mariani,
W. Stremmel,
P. H. Krammer,
and
P. R. Galle.
Lymphocyte apoptosis induced by CD95 (APO-1/Fas) ligand-expressing tumor cells
a mechanism of immune evasion?
Nat. Med.
2:
1361-1366,
1996[Medline].
134a.
Sträter, J.,
I. Wellisch,
S. Kiedl,
H. Walczak,
K. Koretz,
A. Tandara,
P. H. Krammer,
and
P. Möller.
CD95 (APD-1/Fas)-mediated apoptosis in colon epithelial cells: a possible role in ulcerative colitis.
Gastroenterology
113:
160-167,
1997[Medline].
135.
Su, L.-K.,
B. Vogelstein,
and
K. W. Kinzler.
Association of the APC tumor suppressor protein with catenins.
Science
262:
1734-1737,
1993[Medline].
135a.
Tachibana, I.,
M. Imoto,
P. N. Adjei,
G. J. Gores,
M. Subramanian,
T. C. Spelsberg,
and
R. Unutia.
Overexpression of the TGF-
-regulated zinc finger protein encoding gene, TIEG, induces apoptosis in pancreatic epithelial cells.
J. Clin. Invest.
99:
2365-2374,
1997[Abstract/Free Full Text].
136.
Tamura, T.,
N. Aoyama,
H. Saya,
H. Haga,
S. Futami,
M. Miyamoto,
T. Koh,
T. Ariyasu,
M. Tachi,
M. Kasuga,
and
R. Takahashi.
Induction of Fas-mediated apoptosis in p53-transfected human colon carcinoma cells.
Oncogene
11:
1939-1946,
1995[Medline].
137.
Thibodeau, S. N.,
G. Bren,
and
D. Schaid.
Microsatellite instability in cancer of the proximal colon.
Science
260:
816-819,
1993[Medline].
138.
Tsujii, M.,
and
R. DuBois.
Alterations in cellular adhesion and apoptosis in epithelial cells overexpressing prostaglandin endoperoxide synthase-2.
Cell
83:
1452-1457,
1995.
139.
Vaux, D. L.,
G. Haecker,
and
A. Strasser.
An evolutionary perspective on apoptosis.
Cell
76:
777-779,
1994[Medline].
140.
Vaux, D. L.,
and
A. Strasser.
The molecular biology of apoptosis.
Proc. Natl. Acad. Sci. USA
93:
2239-2244,
1996[Abstract/Free Full Text].
141.
Waage, A.
Presence and involvement of TNF in septic shock.
In: Tumor Necrosis Factors: The Molecules and Their Emerging Role in Medicine, edited by B. Beutler. New York: Raven, 1993, p. 275-283.
142.
Walker, N. I.,
C. M. Winterford,
and
J. F. R. Kerr.
Ultrastructure of the rat pancreas after experimental duct ligation. II. Duct and stromal cell proliferation, differentiation, and deletion.
Pancreas
7:
420-434,
1992[Medline].
143.
Walker, N. I.,
C. M. Winterford,
R. M. Williamson,
and
J. F. R. Kerr.
Ethionine-induced atrophy of rat pancreas involves apoptosis of acinar cells.
Pancreas
8:
443-449,
1993[Medline].
144.
Wang, X. W.,
M. K. Gibson,
W. Vermeulen,
H. Yeh,
K. Forrester,
H.-W. Stürzbecher,
J. H. J. Hoeijmakers,
and
C. C. Harris.
Abrogation of p53-induced apoptosis by the hepatitis B virus X gene.
Cancer Res.
55:
6012-6016,
1995[Abstract].
145.
Watanabe, S.,
K. Abe,
Y. Anbo,
and
H. Katoh.
Changes in the mouse exocrine pancreas after pancreatic duct ligation
a qualitative and quantitative histologic study.
Arch. Histol. Cytol.
58:
365-374,
1995[Medline].
146.
Watanabe, Y.,
M. Morita,
and
T. Akaike.
Concanavalin A induces perforin-mediated but not Fas-mediated hepatic injury.
Hepatology
24:
702-710,
1996[Medline].
147.
Wu, C.,
Y. Akiyama,
K. Imai,
S. Miyake,
H. Nagasaki,
M. Oto,
S. Okabe,
T. Iwama,
K. Mitamura,
H. Masumitsu,
T. Nomizu,
S. Baba,
K. Maruyama,
and
Y. Yuasa.
DNA alterations in cells from hereditary nonpolyposis colorectal cancer patients.
Oncogene
9:
991-994,
1994[Medline].
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