Department of Medicine, University of Minnesota, Minneapolis, Minnesota 55455
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The Na+
pump, Na+-K+-ATPase, along with the
Na+ channel is essential for the
removal of alveolar solute and fluid perinatally. Because
Na+-pump mRNA and activity
increase before birth and maternal glucocorticoids (GCs) influence
Na+-K+-ATPase
mRNA expression in fetal rat lung, we hypothesized that GCs increased
Na+-K+-ATPase
gene expression in a fetal lung epithelial cell line. After 24 h of
exposure, dexamethasone increased the steady-state levels of
Na+-K+-ATPase
1 and
1 mRNA in a fetal rat lung
epithelial cell line in a dose-dependent fashion
(10
7 to
10
5 M). The maximal
increase in mRNA levels was 3.8-fold for
1 and 2.8-fold for
1. The increase in mRNA was
detected as early as 6 h for the
1-subunit and 18 h for the
1-subunit, and both peaked at
24 h. This gene upregulation was not due to increased mRNA stability
based on mRNA half-life determination after actinomycin D inhibition.
Transfection experiments with
1
and
1 promoter-reporter constructs demonstrated 3.2 ± 0.5- and 2.6 ± 0.4-fold
increases, respectively, in promoter activity, consistent with
transcriptional activation of the promoter-reporter construct. These
findings, increased promoter activity with no change in stability,
indicate that GCs increased
Na+-K+-ATPase
transcription in a fetal lung epithelial cell line.
sodium-potassium-adenosine 5'-triphosphatase; promoter
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
LATE IN GESTATION, the fetal air space epithelium
changes from primarily secreting
Cl and fluid to
predominantly absorbing Na+ and
water in preparation for normal gas exchange after birth (4, 27). This
vectoral transport of Na+ across
the alveolus occurs primarily through the apically located Na+ channel and basolateral
Na+-K+-ATPase
(11, 12, 32).
Na+-K+-ATPase
or the Na+ pump is a
heterodimeric, transmembrane enzyme composed of a large catalytic
-subunit and smaller glycosylated
-subunit (14, 23). In cells
specialized for vectoral Na+
transport, such as alveolar type II cells,
Na+-K+-ATPase
is abundant because it is the major site of
Na+ transport on the basolateral
membrane of the cells (20, 32).
During normal lung development, both the
Na+ channel and
Na+-K+-ATPase
gene expression increase just before birth (14, 24-26). The exact
mechanisms that promote this increased expression are incompletely
defined. During this stage in development, many changes in the fetal
hormonal state also occur. Several hormones, including aldosterone,
catecholamines, thyroid hormones, and glucocorticoids (GCs), increase
late in gestation and potentially augment the expression of
Na+-K+-ATPase
and/or the Na+ channel (2, 10, 13,
24, 25). This upregulation is specific to the type of tissue and
developmental stage; for example, GCs increase
Na+-K+-ATPase
1 and
1 transcription and activity in
the neonatal rat kidney but not in adult rat kidneys (6, 36).
Ingbar et al. (13) have previously reported that maternal GC treatment upregulated expression of fetal lung Na+-K+-ATPase mRNA in a complex manner that was dependent on GC dosing, duration, and fetal age. However, the exact cells in which the increased expression occurred and the mechanism of induction were not defined. We demonstrated that GCs upregulated Na+-K+-ATPase gene expression via activation of transcription in a fetal lung epithelial cell line in both physiological and supraphysiological doses. Understanding the mechanisms and characteristics by which GCs regulate gene expression in fetal distal lung epithelial cells may permit therapeutic manipulation of the Na+ pump and speed the resolution of pulmonary edema in premature neonates.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Cell cultures. A rat pre-type ll cell
line (FD18; gift from Dr. Gary W. Hunninghake, University of Iowa, Iowa
City; 18) was obtained from rat fetal lungs at gestational
days
18-19 and
immortalized with the adenoviral 12S E1A gene product. These cells
retained many of the ultrastructural features that are typical of
pre-type ll cells in primary culture, such as absence of lamellar
bodies, abundant stores of glycogen, expression of cytokeratin
filaments, and binding of the lectin Maclura
pomifera (18). The cells were maintained in Waymouth
medium containing 10% fetal bovine serum (FBS) and antibiotics (100 U/ml of penicillin, 100 µg/ml of streptomycin, and 2.5 µg/ml of
amphotericin B; GIBCO BRL, Life Technologies). Dexamethasone
(Dex)-treated cells were cultured in medium containing 10% FBS in
which endogenous GCs were previously removed by mixing serum with a
resin slurry (5 g resin/100 ml serum; Bio-Rad AG 1-X8) as previously
described by Samuels et al. (29). The serum was treated with resin
three times (one 4-h and two overnight washes) and filtered each time
to remove resin. The elimination of GCs was confirmed by the
elimination of [3H]Dex
tracer, with <0.01% of tracer detected after the third wash (29).
Cells at ~40-50% confluence were exposed to various
concentrations of Dex (107
to 10
4 M) and incubated in
5% CO2-95% air at 37°C for
various time intervals. The cells continued to divide in all
concentrations of Dex and became confluent after 24-48 h of
culture, with no observable cell death.
RNA isolation and Northern analysis.
Total cellular RNA was extracted and isolated by the guanidinium method
as previously published (5, 37). The purity and concentration of RNA
were assessed from the 260- to 280-nm absorbance ratio, and Northern analysis was performed with 20 µg of total RNA loaded onto 1% agarose formaldehyde gels and electrophoresed in MOPS buffer (22, 37).
RNA was transferred to nylon membranes in 10× saline-sodium citrate (SSC; 3.0 M NaCl and 0.3 M sodium citrate) overnight, and the
membranes were heat fixed at 80°C for 2 h. The membranes were
prehybridized in 10% dextran sulfate, 50% formamide, 1% SDS, 10%
Denhardt's solution, 20% salmon sperm DNA, and 1 M NaCl
at 42°C for 2 h. After prehybridization for a minimum of 6 h, the blots were hybridized with random primer
32P-labeled full-length rat cDNA
probes for
Na+-K+-ATPase
1 and
1 mRNAs (gifts from Dr. E. Benz, Johns Hopkins University, Baltimore, MD) and a cDNA probe coding
for
-actin for 18 h at 42°C. The membranes were washed two times
in each of the following conditions: 5 min at room temperature with
2× SSC, 20 min at 50°C with 2× SSC-1% SDS, and 1 h at
68°C with 0.1× SSC-0.1% SDS. Transcripts were visualized
with standard autoradiography or phosphorimaging (Bio-Rad) and
quantitated. The integrated optical density (IOD) of the RNA bands was
determined with Densitometry Image software (Molecular Analyst). Both
transcripts of the
1 mRNA were
included in the IOD for the
1-subunit. All RNA densitometry values were normalized to actin. The experiments were performed at
least in triplicate.
RNA stability. Stability of Na+-K+-ATPase mRNA was measured as previously described (7, 37). To inhibit mRNA synthesis, 10 µg/ml of actinomycin D (Act D) were added for various time intervals during the final portion of the 24-h incubation in cells treated with Dex or under control conditions. Twenty-four hours of Dex treatment was chosen because the maximal increase in steady-state Na+-K+-ATPase mRNA levels was seen at this time. Preliminary data showed that 12 h of Act D treatment resulted in <20% of the original Na+-K+-ATPase mRNA being present; therefore, the cells were treated with Act D for 0, 2, 4, 6, 8, 10, 12, and 14 h. To calculate the half-life of each subunit, RNA was isolated and Northern blots were performed as described in RNA isolation and Northern analysis. The densitometry of each time point was divided by time 0 in that specific (control or Dex) condition and plotted on a log scale with previously described methods (7, 37). Therefore, mRNA levels were 100% at time 0 for each condition to enable half-life determination despite Dex-treated cells having higher initial mRNA levels. All experiments were performed at least in triplicate.
Promoter-reporter constructs. Genomic
cloning of the
Na+-K+-ATPase
1-subunit was carried out by
following standard procedures (28), with minor modifications (1).
Briefly, a rat liver genomic library contained in Lambda Dash II phage
(Stratagene, San Diego, CA) was screened by hybridization with a DNA
probe carrying a predetermined promoter sequence of the
1 gene that spanned from
817 to
40 bp of the
1 promoter (17). The probe was
generated via PCR with two oligonucleotides
(5'-GAATTCTACAGTATAGGGTAGGGG-3' and
5'-CACCATCCGTAGCTCCGCCTACCG-3') and was
labeled with 32P. Approximately 1 million plaques were screened, and one positive clone that hybridized
to the probe was isolated and plaque purified. Phage DNA was isolated
by the liquid lysate method (28). Genomic fragments of this clone were
mapped with restriction enzymes and subcloned into a pBluescript vector
(Stratagene) for further analysis. DNA-sequencing analysis of genomic
fragments was performed on an Applied Biosystems 373A automated
sequencer (API, Foster City, CA) with the Sanger dideoxy method (30),
with fluorescent-tagged dye terminators. Oligonucleotides for
sequencing were synthesized on a Beckman 1000M synthesizer with
phosphoramidite chemistry. Sequence assembly was carried out with a GCG
software package (Wisconsin Package version 9.1)
The promoter-reporter plasmid was constructed with a -galactosidase
reporter plasmid, p
gal-Basic (Clontech) because luciferase and
chloramphenicol acetyltransferase reporters are poorly expressed in
FD18 cells (data not shown). A Kpn
I-Sal I fragment carrying a sequence
of the
1 promoter from
817 to +151 bp was isolated from pXP1-
1 (luciferase reporter
vector; 17) and then ligated to the
Kpn
I-Xho I-digested p
gal-Basic vector.
To create a promoter-reporter vector with a larger promoter sequence, a
fragment carrying a 5'-flanking sequence from
3.5 kb to
818 bp was isolated from the pBluescript clone
described above and ligated in the p
gal-Basic vector at
817
bp, creating a chimeric gene now designated
1-g303. Therefore, the
1-g303 construct contained a continuous sequence from
3.5 to
+151 bp, obtained from our new clone (
3.5 kb to
818 bp)
and pXP1-
1 (
817 to +151 bp), linked to a
-galactosidase reporter gene.
The 1-g1576 construct was created by subcloning the
1-subunit promoter (pA1lF-1;
39), which spanned from
1,576 to +262 bp, into a
-galactosidase expression vector (p
gal-Basic, Clontech).
DNA transfection experiments.
Transfection experiments were performed on the second day of culture in
FD18 cells plated at a density of 8 million cells/35-mm plate in
Waymouth medium with 10% FBS. Preliminary studies demonstrated the
optimal DNA and Superfect (Qiagen) concentrations for transfection in
FD18 cells to be 2.0 µg DNA and 60 µl Superfect/35-mm plate.
Transfection was carried out following the manufacturer's
recommendation for a total of 3 h in antibiotic-free Waymouth medium
containing 10% FCS with the constructs 1-g303 and
1-g1576. After
4 h of transfection in serum-free medium, the cells were incubated for
48 h in medium plus 10% FBS with and without Dex
(10
6 M). The cells were
lysed and then assayed for
-galactosidase activity (Clontech) in a
luminometer (Berthold LB 9501) and protein concentration (bicinchoninic
acid assay, Pierce). In the
1-subunit transfection
experiments, lysates were heat treated to eliminate endogenous
-galactosidase activity (40). In the
1-subunit transfection
experiments, the cells were transfected with the promoterless
p
gal-Basic vector and then treated with and without Dex. The
activity of the promoterless vector represented background
-galactosidase activity and was subtracted from the
-galactosidase activity of the control and Dex-treated cells treated
with promoter-reporter vectors. Dex treatment did not
affect background
-galactosidase activity [145.2 ± 10.2 (SE) for control cells; 153.5 ± 4.5 for Dex-treated
cells].
Statistical analysis. Results are reported as means ± SE of three to four experiments. Paired evaluations were made for the experimental and control conditions within each experiment, and significance was determined by Student's t-test. For the Northern experiments performed with multiple concentrations of Dex, an ANOVA was performed. The threshold of significance was considered to be P < 0.05, and trends were reported with 0.05 < P < 0.10.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Effects of Dex on
Na+-K+-ATPase
mRNA steady-state levels.
Ingbar et al. (13) previously demonstrated that GCs increased
Na+-K+-ATPase
in fetal rat whole lungs after maternal injections of Dex. We
hypothesized that the increase in whole lung
Na+-K+-ATPase
was due, at least in part, to increased
Na+-K+-ATPase
mRNA in pre-type II cells. To study this, we treated a rat fetal lung
pre-type ll cell line, FD18, with various concentrations of Dex
(107 to
10
4 M) for 24 h and
measured steady-state levels of
Na+-K+-ATPase
1- and
1-subunit mRNAs (Fig.
1). The doses of Dex ranged from high
physiological to therapeutic levels. Significant increases were
detected in both
1 and
1 mRNA expression at a
physiological Dex concentration
(10
7 M) compared with that
in control samples. The mRNA steady-state levels increased in a
dose-dependent manner over the range of 10
7 to
10
5 M, and the maximal
induction, 3.8- and 2.8-fold, was detected at a supraphysiological
concentration of Dex (10
5
M) in the
1- and
1-isoforms, respectively. The
increased mRNA steady-state levels dropped off at Dex concentrations > 10
5 M. These changes in
Dex concentration were significant (P = 0.02 by ANOVA) for the
1-subunit, and there was a
trend toward significance (P = 0.08 by
ANOVA) for the
1-subunit.
|
|
Effects of Dex on
Na+-K+-ATPase
mRNA half-life.
The effects of steroid hormones on gene expression are generally
thought to occur through specific steroid-receptor proteins that
activate transcription. However, some gene upregulation by steroid
hormones is due to increased mRNA stability (38). We investigated
whether increased mRNA steady-state levels of the 1- and
1-subunits were related to
changes in mRNA half-life by treating cells with Act D to inhibit
transcription and measuring the mRNA half-life.
|
Effects of Dex on
Na+-K+-ATPase
promoter activity.
To measure promoter activation and transcription, FD18 cells were
transiently transfected with expression vector constructs containing
either the 1 or
1 promoter linked to a
-galactosidase reporter gene with and without
10
6 M Dex. Transfection
experiments revealed 3.2 ± 0.5- and 2.6 ± 0.4-fold increases in
promoter activity of the
1 and
1 promoters, respectively, in
Dex-treated cells compared with that in control cells (Fig.
4). The increased promoter activity,
accompanied by the lack of significant increases in mRNA stability,
indicated that Dex increased transcription of the
1- and
1-subunits.
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Several hormones such as GCs, aldosterone, catecholamines, and thyroid hormone, which influence the expression of a variety of genes, are upregulated in the fetal circulation before birth. In the lung, GCs upregulate multiple genes that are crucial for normal homeostasis, such as creating a dry alveolus, maintaining low surface tension, and protecting against a new, oxidizing environment. Specifically, GCs upregulate the gene expression of surfactant, Na+-K+-ATPase, Na+ channel, aquaporin 3, and several antioxidant genes such as catalase and superoxide dismutase (9, 16, 25, 31, 34, 35). Previous studies (6, 13, 35) demonstrated that maternally administered GCs increased fetal lung Na+-K+-ATPase expression in a manner dependent on fetal stage and duration of hormonal exposure. However, the specific cell type responsible for this induction and the mechanism involved were not defined. In this study, we identified that GCs increased Na+-K+-ATPase mRNA expression in a rat fetal distal lung epithelial cell line in both a time- and dose-dependent manner. In addition, mRNA stability and promoter-reporter transfection experiments indicated that GCs induced transcription as a mechanism of increased gene expression in this fetal lung epithelial cell line.
Although we used a transformed cell line in our experiments, this system had advantages over whole lung studies. First, there are no changes in confounding hormones such as thyroid hormone and epinephrine, which occur in whole lung experiments due to the stress of maternal hormone injections. Both of these hormones have been implicated in Na+-K+-ATPase gene regulation (10). Second, we tested the response of one specific cell type, i.e., pre-type II cells, which is not possible in whole lung studies because they contain many cell types. Therefore, using this cell line allowed us to identify epithelial cells as a source of Na+-K+-ATPase upregulation and explore the mechanism of induction by GCs.
In our study, Dex increased
Na+-K+-ATPase
mRNA levels in FD18 cells in a dose-dependent manner for both subunits
over a wide range of concentrations, both physiological and
supraphysiological. This wide dose response to GCs had been
demonstrated in other cell systems such as vascular smooth muscle cells
(19). GCs increased
Na+-K+-ATPase
expression in vascular smooth muscle cells starting at a concentration
of 1010 M and peaking at a
concentration of 10
6 M,
similar to our results (19). Our results have two implications. First,
this may represent the mechanism by which
Na+-K+-ATPase
expression increases before birth when maternal GC levels are
increasing concomitantly. Second, we demonstrated that
supraphysiological doses of GCs further augment the increases in
Na+-K+-ATPase.
The exact mechanism by which GCs increased lung
Na+-K+-ATPase
gene expression has not been fully elucidated. GCs can increase gene
expression by increasing mRNA stability such as that of fatty acid
synthase in the fetal rat lung (38). In our system, neither subunit had
a change in mRNA stability that could account for the increased mRNA
levels. The 1-subunit had a
slightly shorter half-life in Dex-treated cells, whereas the
1 half-life was unchanged. Usually, a shorter half-life would decrease mRNA steady-state levels
unless there was a concomitant increase in transcription. Wang et al.
(36) demonstrated that GC increased
1- and
1-subunit transcription in the
infant rat kidney. In our studies, transient transfection experiments
with promoter-reporter constructs of the
Na+-K+-ATPase
subunits demonstrated that GCs increased
-galactosidase levels via
promoter activation and active transcription of the reporter gene for
both subunits. These data, along with the mRNA stability results,
indicated that GCs induced transcription of the
Na+-K+-ATPase
subunits as a mechanism of increasing mRNA steady-state levels in these
fetal distal lung epithelial cells.
GCs commonly increase transcription through a GC receptor that
functions as a transcription factor. These receptors are very abundant
in the lung throughout development and bind to a glucocorticoid response element (GRE), which consists of an imperfect, inverted hexanucleotide repeat separated by 3-10 nucleotides (15). The promoter for the 1-subunit
contains two half-motifs that exhibit a five of six match to the GRE,
and the
1-subunit contains six putative half-sites and one imperfect inverted GRE separated by 10 nucleotides at positions
629 to
609 bp (Table
1) (17, 39). This site at
629 bp is homologous to a functional GRE and mineralocorticoid
responsive element on the human
1 promoter (8). In our
experiments, the
1-subunit was
upregulated within 6 h of GC treatment, consistent with direct
activation of the GRE as a mechanism. Direct activation of a GRE
through a hormone receptor seemed less likely for the
1-subunit, which required 18 h
for significant mRNA levels to be obtained. Therefore, activation of
the
1 promoter may be through
indirect mechanisms other than direct activation of the GRE through a
hormone receptor. Because GCs can activate transcription through
non-GC-receptor mechanisms, direct assessment of the promoter elements
required for
Na+-K+-ATPase
activation by GCs need to be identified.
|
Regulation of
Na+-K+-ATPase
gene expression is complex. In a previous study, Ingbar et al. (13)
demonstrated that fetal lung 1
mRNA increased 24-72 h after maternal GC treatment; however, there
was no induction in
1 mRNA. In
similar experiments, Celsi et al. (6) demonstrated that both subunits
increased when shorter time periods were studied; however,
1 induction did not persist in
the postnatal period. In adult type ll cells, Barquin et al. (3)
demonstrated increased
Na+-K+-ATPase
1 mRNA within 6 h of GC
exposure without upregulation of the
1-subunit. This discrepancy in
1 expression may reflect differences between fetal regulation of
Na+-K+-ATPase
and regulation in adult cells. Therefore, regulation of lung
Na+-K+-ATPase
by GCs is dependent on the developmental stage and duration after GC treatment.
The effects of GCs on the fetal lung have important therapeutic implications. Antenatal steroids decrease premature infant morbidity and mortality according to the National Institutes of Health Consensus Statement (21). The indication for antenatal steroids has been to augment the surfactant system; however, maturation of ion transport likely plays an important role as well. Because both the Na+ pump and channel respond to GCs in a complex manner dependent on fetal age and duration of therapy, understanding the exact mechanism and timing of this response is important. In our experiments, we demonstrated that GCs increased Na+-K+-ATPase gene expression in a rat fetal lung epithelial cell line via induction of transcription. Understanding the mechanisms by which GCs influence fetal lung gene expression, exact timing, and dosing relationships may be important in optimizing treatment of premature infants by maternal GCs.
![]() |
FOOTNOTES |
---|
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Address for reprint requests and other correspondence: C. H. Wendt, Dept. of Medicine, Box 276, Univ. of Minnesota Hospital and Clinics, 420 Delaware St. SE, Minneapolis, MN 55455 (E-mail: wendt005{at}gold.tc.umn.edu).
Received 7 May 1998; accepted in final form 11 March 1999.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Argaud, D.,
Q. Zhang,
W. Pan,
S. Maitra,
S. J. Pilkis,
and
A. J. Lange.
Regulation of rat liver glucose-6-phosphatase gene expression in different nutritional and hormonal states: gene structure and 5'-flanking sequence.
Diabetes
45:
1563-1571,
1996[Abstract].
2.
Barker, P. M.,
L. B. Strang,
and
D. V. Walters.
The role of thyroid hormones in maturation of the adrenaline-sensitive lung liquid reabsorptive mechanism in fetal sheep.
J. Physiol. (Lond.)
424:
473-485,
1990[Abstract].
3.
Barquin, N.,
D. E. Ciccolella,
K. M. Ridge,
and
J. I. Sznajder.
Dexamethasone upregulates the Na-K-ATPase in rat alveolar epithelial cells.
Am. J. Physiol.
273 (Lung Cell. Mol. Physiol. 17):
L825-L830,
1997[Medline].
4.
Bland, R. D.,
and
C. A. Boyd.
Cation transport in lung epithelial cells derived from fetal, newborn, and adult rabbits.
J. Appl. Physiol.
61:
506-515,
1986.
5.
Carter, E. P.,
S. E. Duvick,
C. H. Wendt,
J. Dunitz,
L. Nici,
O. D. Wangensteen,
and
D. H. Ingbar.
Hyperoxia increases active alveolar Na+ resorption in vivo and type II cell Na,K-ATPase in vitro.
Chest
105:
75S-78S,
1994[Medline].
6.
Celsi, G.,
Z.-M. Wang,
G. Akusjarvi,
and
A. Aperia.
Sensitive periods for glucocorticoids' regulation of Na+,K+-ATPase mRNA in the developing lung and kidney.
Pediatr. Res.
33:
5-9,
1993[Abstract].
7.
Chambers, S. K.,
M. Gilmore-Hebert,
B. M. Kacinski,
and
E. J. Benz.
Changes in Na,K-ATPase gene expression during granulocytic differentiation of HL60 cells.
Blood
80:
1559-1564,
1992[Abstract].
8.
Derfoul, A.,
N. M. Robertson,
J. B. Lingrel,
D. J. Hall,
and
G. Litwack.
Regulation of the human Na/K-ATPase 1 gene promoter by mineralocorticoid and glucocorticoid receptors.
J. Biol. Chem.
273:
20702-20722,
1998
9.
Deterding, R. R.,
H. Shimizu,
J. H. Fisher,
and
J. M. Shannon.
Regulation of surfactant protein D expression by glucocorticoids in vitro and in vivo.
Am. J. Respir. Cell Mol. Biol.
10:
30-37,
1994[Abstract].
10.
Ewart, H. S.,
and
A. Klip.
Hormonal regulation of Na+-K+-ATPase: mechanisms underlying rapid and sustained changes in pump activity.
Am. J. Physiol.
269 (Cell Physiol. 38):
C295-C311,
1995
11.
Goodman, B. E.,
R. S. Fleischer,
and
E. D. Crandall.
Evidence for active Na+ transport by cultured monolayers of pulmonary alveolar epithelial cells.
Am. J. Physiol.
245 (Cell Physiol. 14):
C78-C83,
1983
12.
Gross, I.
Regulation of fetal lung maturation.
Am. J. Physiol.
259 (Lung Cell. Mol. Physiol. 3):
L337-L344,
1990
13.
Ingbar, D. H.,
S. Duvick,
S. K. Savik,
D. E. Schellhase,
R. Detterding,
J. D. Jamieson,
and
J. M. Shannon.
Developmental changes of fetal rat lung Na-K-ATPase after maternal treatment with dexamethasone.
Am. J. Physiol.
272 (Lung Cell. Mol. Physiol. 16):
L665-L672,
1997
14.
Ingbar, D. H.,
C. B. Weeks,
M. Gilmore-Hebert,
E. Jacobsen,
S. Duvick,
R. Dowin,
and
J. D. Jamieson.
Developmental regulation of Na,K-ATPase in rat lung.
Am. J. Physiol.
270 (Lung Cell. Mol. Physiol. 14):
L619-L629,
1996
15.
Kalinyak, J. E.,
C. A. Griffin,
R. W. Hamiltion,
J. G. Bradshaw,
A. J. Perlman,
and
A. R. Hoffman.
Developmental and hormonal regulation of glucocorticoid receptor messenger RNA in the rat.
J. Clin. Invest.
84:
1843-1848,
1989[Medline].
16.
Keeney, S. E.,
M. J. Mathews,
and
D. K. Rassin.
Antioxidant enzyme responses to hyperoxia in preterm and term rats after prenatal dexamethasone administration.
Pediatr. Res.
33:
177-180,
1993[Abstract].
17.
Liu, B.,
and
G. Gick.
Characterization of the 5' flanking region of the rat Na+/K+-ATPase 1 subunit gene.
Biochim. Biophys. Acta
1130:
336-338,
1992[Medline].
18.
Mallampalli, R. K.,
C. S. Floerchinger,
and
G. W. Hunninghake.
Isolation and immortalization of rat pre-type II cell lines.
In Vitro Cell. Dev. Biol.
28A:
181-187,
1992.
19.
Muto, S.,
J. Nemoto,
A. Ohtaka,
Y. Watanabe,
M. Yamaki,
K. Kawakami,
K. Nagano,
and
Y. Asan.
Differential regulation of Na+-K+-ATPase gene expression by corticosteroids in vascular smooth muscle cells.
Am. J. Physiol.
270 (Cell Physiol. 39):
C731-C739,
1996
20.
Nici, L.,
R. Dowin,
M. Gilmore-Hebert,
J. D. Jamieson,
and
D. H. Ingbar.
Upregulation of rat lung Na-K-ATPase during hyperoxic injury.
Am. J. Physiol.
261 (Lung Cell. Mol. Physiol. 5):
L307-L314,
1991
21.
NIH Consensus Development Panel on the Effect of Corticosteroids for Fetal Maturation on Perinatal Outcomes.
Effect of corticosteroids for fetal maturation on perinatal outcomes.
JAMA
273:
413-418,
1995[Abstract].
22.
Nogee, L. M.,
J. R. Wispe,
J. C. Clarke,
T. E. Weaver,
and
J. A. Whitsett.
Increased expression of pulmonary surfactant proteins in oxygen-exposed rats.
Am. J. Respir. Cell Mol. Biol.
4:
102-107,
1991[Medline].
23.
O'Brodovich, H.
Epithelial ion transport in the fetal and perinatal lung.
Am. J. Physiol.
261 (Cell Physiol. 30):
C555-C564,
1991
24.
O'Brodovich, H.,
C. Canessa,
J. Ueda,
B. Rafii,
B. C. Rossier,
and
J. Edelson.
Expression of the epithelial Na+ channel in the developing rat lung.
Am. J. Physiol.
265 (Cell Physiol. 34):
C491-C496,
1993
25.
O'Brodovich, H.,
O. Staub,
B. C. Rossier,
K. Geering,
and
J. P. Kraehenbuhl.
Ontogeny of 1- and
1-isoforms of Na+-K+-ATPase in fetal distal rat lung epithelium.
Am. J. Physiol.
264 (Cell Physiol. 33):
C1137-C1143,
1993
26.
Orlowski, J.,
and
J. B. Lingrel.
Tissue-specific and developmental regulation of rat Na,K-ATPase catalytic isoform and
subunit mRNAs.
J. Biol. Chem.
263:
10436-10442,
1988
27.
Rao, A. K.,
and
G. R. Cott.
Ontogeny of ion transport across fetal pulmonary epithelial cells in monolayer culture.
Am. J. Physiol.
261 (Lung Cell. Mol. Physiol. 5):
L178-L187,
1991
28.
Sambrook, J.,
E. F. Fritsch,
and
T. Maniatis.
Analysis and cloning of eukaryotic genomic DNA.
In: Molecular Cloning: A Laboratory Manual. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory, 1989, p. 9.31-9.58.
29.
Samuels, H. H.,
F. Stanley,
and
J. Casanova.
Depletion of L-3,5,3'-triiodothyronine and L-thyroxine in euthyroid calf serum for use in cell culture studies of the action of thyroid hormone.
Endocrinology
105:
80-85,
1979[Abstract].
30.
Sanger, F.,
S. Nicklen,
and
A. R. Coulson.
DNA sequencing with chain-terminating inhibitors.
Biotechnology
24:
104-108,
1992[Medline].
31.
Schellhase, D. E.,
and
J. M. Shannon.
Effects of maternal dexamethasone on expression of SP-A, SP-B, and SP-C in the fetal rat lung.
Am. J. Respir. Cell Mol. Biol.
4:
304-312,
1991[Medline].
32.
Schneeberger, E. E.,
and
K. M. McCarthy.
Cytochemical localization of Na+-K+-ATPase in rat type II pneumocytes.
J. Appl. Physiol.
60:
1584-1589,
1986
34.
Tanaka, M.,
N. Inase,
K. Fushimi,
K. Ishibashi,
M. Ichioka,
S. Sasaki,
and
F. Marumo.
Induction of aquaporin 3 by corticosteroid in a human airway epithelial cell line.
Am. J. Physiol.
273 (Lung Cell. Mol. Physiol. 17):
L1090-L1095,
1997
35.
Tchepichev, S.,
J Ueda,
C. Canessa,
B. C. Rossier,
and
H. O'Brodovich.
Lung epithelial Na channel subunits are differentially regulated during development and by steroids.
Am. J. Physiol.
269 (Cell Physiol. 38):
C805-C812,
1995[Abstract].
36.
Wang, Z.-M.,
M. Yasui,
and
G. Celsi.
Differential effects of glucocorticoids and mineral-corticoids on the mRNA expression of colon ion transporters in infant rats.
Pediatr. Res.
38:
164-168,
1995[Abstract].
37.
Wendt, C. H.,
H. Towle,
R. Sharma,
S. Duvick,
K. Kawakami,
G. Gick,
and
D. H. Ingbar.
Regulation of Na-K-ATPase gene expression by hyperoxia in MDCK cells.
Am. J. Physiol.
274 (Cell Physiol. 43):
C356-C364,
1998
38.
Xu, Z.-X.,
and
S. A. Rooney.
Glucocorticoids increase fatty acid synthase mRNA stability in fetal rat lung.
Am. J. Physiol.
272 (Lung Cell. Mol. Physiol. 16):
L860-L864,
1997
39.
Yagawa, Y.,
K. Kawakami,
and
K. Nagano.
Cloning and analysis of the 5'-flanking region of rat Na+/K+-ATPase 1 subunit gene.
Biochim. Biophys. Acta
1049:
286-292,
1990[Medline].
40.
Young, D. C.,
S. D. Kingsley,
K. A. Ryan,
and
F. J. Dutko.
Selective inactivation of eukaryotic -galactosidase in assays for inhibitors of HIV-1 TAT using bacterial
-galactosidase as a reporter enzyme.
Anal. Biochem.
215:
24-30,
1993[Medline].