3 Veterans Affairs Medical Center and Departments of 2 Medicine, 1 Pathology, and 4 Biochemistry and Molecular Biology and 5 Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, Michigan 48201
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ABSTRACT |
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Administration of pharmacological doses of epidermal
growth factor (EGF) or transforming growth factor- (TGF-
) in
young rats stimulates gastric mucosal proliferation, but, in aged rats, the same treatment inhibits proliferation. This may be due to enhanced
ligand-induced internalization of EGF receptor (EGFR). In support of
this, we demonstrated that although a single injection of EGF (10 µg/kg) or TGF-
(5 µg/kg) in young (4-6 mo old) rats greatly
increased membrane-associated EGFR tyrosine kinase activity, the same
treatment slightly inhibited the enzyme activity in aged (24 mo old)
rats. This treatment also produced a greater abundance of punctate
cytoplasmic EGFR staining in gastric epithelium of aged rats,
consistent with EGFR internalization. In vitro analyses demonstrated
that exposure of isolated gastric mucosal cells from aged but not young
rats to 100 pM TGF-
resulted in marked increases in intracellular
EGFR tyrosine kinase activity and that induction of EGFR tyrosine
kinase activity in mucosal membranes from aged rats occurred at doses
1,000-fold less than those required in young rats. Our data suggest
that aging enhances sensitivity of the gastric mucosa to EGFR ligands.
This may partly explain EGFR-mediated inhibition of gastric mucosal
proliferation in aged rats.
epidermal growth factor receptor; epidermal growth factor receptor internalization; cell proliferation; tyrosine kinase
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INTRODUCTION |
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WE AND OTHERS HAVE SHOWN that aging results in
increased gastrointestinal mucosal proliferative activity in Fischer
344 rats (2, 16, 17, 26, 28, 29). In gastric mucosa, this is also
associated with increased activity of several tyrosine kinases,
including the epidermal growth factor receptor (EGFR) (24, 32, 35, 41).
EGFR is a 170-kDa transmembrane glycoprotein (8) with ligands including
EGF, transforming growth factor- (TGF-
), amphiregulin, and
heparin-binding EGF (7, 8, 18, 42). Extracellular ligand binding leads
to EGFR dimerization, activation of the receptor's intrinsic tyrosine
kinase activity, and a signaling pathway resulting in cell
proliferation (7, 8, 18, 36, 42). Our observation that the age-related rise in gastric mucosal proliferative activity is accompanied by a
concomitant increase in mucosal EGFR tyrosine kinase suggests a role
for EGFR in regulating gastric mucosal proliferation during aging (41).
EGFR ligands, most notably EGF and TGF-, appear to be critically
involved in regulating mucosal proliferation in the gastrointestinal tract, including the stomach (3, 34). However, the mitogenic responsiveness of the gastric mucosa to EGF changes with aging (23). We
have demonstrated that although administration of pharmacological doses
of EGF stimulates epithelial proliferation in young rats, the same
treatment markedly inhibits epithelial proliferation in aged rats (23).
These changes were accompanied by parallel alterations in overall
tyrosine kinase activity and tyrosine phosphorylation of several
membrane proteins (23).
The underlying biochemical mechanisms for age-related alterations in
gastric mucosal response to exogenous EGF are not fully understood. We
hypothesized that aging may enhance mucosal sensitivity to EGFR ligands
so that low doses stimulate the EGFR-induced signal transduction
pathway and enhance mucosal epithelial proliferation, whereas high
doses inhibit these processes. To explore this, we evaluated
age-related changes in mitogenic responsiveness of the gastric mucosa
to TGF- in parallel with EGFR tyrosine kinase activation and
localization as well as EGFR internalization. The results are
consistent with age-dependent increases in ligand-induced EGFR
internalization, resulting in hypersensitivity to EGFR ligands in aged rats.
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MATERIALS AND METHODS |
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Animals and collection of tissues. Male Fischer 344 rats, 4 - 6 and 22-24 mo old, were used. The animals were purchased from the National Institute on Aging (Bethesda, MD) at least 1 mo before the experiment and were fed with Purina rat chow and water ad libitum before the experiment.
Two in vivo experiments were performed. In the first set of experiments, groups of three young (4-6 mo old) and three aged (22-24 mo old) rats were implanted with subcutaneous osmotic mini-pumps (Alza, Palo Alto, CA) that delivered either TGF-Mucosal histology. Formalin-fixed gastric tissues were dehydrated in graded alcohol and embedded in paraffin to yield full-thickness mucosal sections. Serial sections (4 µm thick) were stained with hematoxylin and eosin.
Determination of proliferating cell nuclear antigen immunoreactivity. Serial sections (4 µm thick) were deparaffinized and incubated at ambient temperature with anti- proliferating cell nuclear antigen (PCNA; monoclonal antibody, Glostrup) for 30 min at 1:50 dilution. The avidin-biotin technique was then performed with matched components (secondary biotinylated antibody and avidin-peroxidase complex) from the DAKO labeled streptavidin-biotin system (Carpinteria, CA) according to the manufacturer's suggested protocol. Amino ethyl carbazole was used as chromagen to localize PCNA-positive cells. All slides were lightly counterstained with Harris' hematoxylin and examined by a pathologist blinded to sample coding. At least 10 well-oriented crypts on each slide and 5 slides from each sample were examined under high power. At least 750 cells/slide were counted using a ×40 objective.
Immunofluorescent staining of EGFR.
Serial sections (4 µm thick) of gastric tissues were collected on
poly-L-lysine-coated slides. After deparaffinization and rehydration, sections were blocked with 10% chick serum, 10% porcine serum, and 0.5% BSA in PBS for 1 h at room temperature. After being
washed with PBS twice, the slides were incubated overnight at 4°C
with 2 µg/ml polyclonal rabbit anti-EGFR antibody (Santa Cruz
Biotechnology, Santa Cruz, CA). Rabbit -globulin (Sigma Chemical,
St. Louis, MO) in PBS was used as a negative control. After extensive
washing in PBS, the slides were incubated with 20 µg/ml
FITC-conjugated-F(ab')2 fragment of anti-rabbit IgG
(Jackson Immunolabs, West Grove, PA) for 1 h at room temperature. After being washed in PBS, slides were mounted with Vectashield mounting medium (Vector Laboratories, Burlingame, CA). The slides were examined
using a Zeiss LSM 310 imaging system.
Tyrosine kinase activity of EGFR.
Tyrosine kinase activity was determined in the surface membrane and
intracellular fractions as previously described (20, 27). Briefly,
aliquots of frozen mucosal scrapings or freshly isolated gastric
mucosal cells were homogenized in homogenizing buffer [HEPES, pH
7.4, 150 mM NaCl, 1 mM phenylmethylsulfonyl fluoride (PMSF), 1 mM
Na3VO4, 10 µg/ml leupeptin, 1 µg/ml
aprotinin, and 1 mM 1,10-phenanthroline] and centrifuged at
30,000 g for 30 min to obtain crude membrane (30,000 g
pellet) and intracellular (30,000 g supernatant) fractions. The
surface membrane fraction was resuspended in homogenizing buffer. After
determination of protein content using the Bio-Rad standard protein
assay kit (Hercules, CA), aliquots of surface membrane and
intracellular fractions containing 350 µg of protein were diluted
with an equal volume of radioimmunoprecipitation assay (RIPA) buffer
(20 mM sodium phosphate, pH 7.4, 1% Triton X-100, 0.1% SDS, 0.5%
sodium deoxycholate, 0.5% Nonidet P-40, 50 mM NaCl, 5 mM EDTA, 1 mM
PMSF, 1 mM Na3VO4, 10 µg/ml leupeptin, 1 µg/ml aprotinin, and 1 mM 1,10-phenanthroline). The samples were
incubated overnight at 4°C with 1 µg of polyclonal antibody to
EGFR (UBI, Lake Placid, NY). The immune complexes were precipitated
with heat-denatured Pansorbin, washed several times with
RIPA/homogenizing buffer. The immunoprecipitates were resuspended in 30 µl of homogenizing buffer containing 0.1% Triton X-100 and assayed
for tyrosine kinase activity by measuring 32P incorporation
from [-32P]ATP into acid-denatured enolase
(20, 27). In all immunoprecipitation studies, protein concentration was
standardized among the samples.
Statistical analysis. Where applicable, results were evaluated with Student's t-test for unpaired samples.
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RESULTS |
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EGF and TGF- induce proliferation in gastric mucosa
of young rats but not aged rats.
We have previously shown (23) that supraphysiological doses of EGF
inhibit epithelial proliferation in the gastric mucosa of aged rats. To
determine whether this effect was specific to EGF or could be
reproduced with other EGFR ligands, rats were treated with TGF-
by
continuous infusion over 4 days. Unlike EGF, which is primarily
synthesized in the salivary gland, TGF-
is synthesized in the
gastric mucosa (3). Thus TGF-
may be a more physiologically relevant
ligand for gastric mucosal EGFR. The effect of TGF-
is similar to
that previously reported for EGF (23). In young rats, infusion of
TGF-
markedly increased proliferative activity in the gastric
mucosa, as evidenced by a 65% increase in PCNA-immunoreactive cells
relative to controls (P < 0.001; Fig.
1). In contrast, TGF-
induced a 64%
decline in PCNA-immunoreactive gastric mucosal cells in aged rats
(P < 0.001; Fig. 1). In the absence of TGF-
treatment,
aged rats demonstrated a 50% increase in PCNA-immunoreactive gastric
epithelial cells relative to young rats (P < 0.001; Fig. 1).
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EGF and TGF- induce distinct patterns of EGFR
redistribution in gastric mucosa of young and aged rats.
We considered the possibility that the age-related change in mitogenic
response to EGF and TGF-
could be due to increased internalization
or degradation of EGFR in gastric epithelium of aged rats. We evaluated
this hypothesis both morphologically and biochemically. Because
ligand-induced activation and subsequent internalization of EGFR are
early events in the EGFR signaling cascade (10, 42), gastric mucosa was
evaluated 30 min after a single injection of EGF or TGF-
(Fig.
2). Immunolocalization of EGFR of control
young rats showed that the majority of EGFR was localized to the apical
membrane (Fig. 2A). The overall EGFR immunostaining appeared to
be less intense than in the control aged rats. Administration of EGF or
TGF-
to young rats induced the appearance of EGFR-containing
punctate vesicular structures in the basal cytoplasm. Additionally,
TGF-
induced the appearance of diffuse apical cytoplasmic EGFR
staining. In control aged rats (Fig. 2B) the overall EGFR
staining intensity was increased relative to young rats.
EGFR was localized to the apical membrane and to basal cytoplasmic
vesicular structures. These cytoplasmic structures were similar to
those seen in EGF- or TGF-
-treated young rats. However, the staining
intensity, number, and size of these basal structures was greater than
that seen in control or EGF- or TGF-
-treated young rats.
Administration of EGF or TGF-
to aged rats induced marked increases
in EGFR detected within these basal vesicular structures. These data
support the hypothesis that internalization of EGFR occurs at an
increased basal level in the gastric mucosa of aged rats as opposed to
young rats. The data also suggest that ligand-induced internalization
of EGFR is more rapidly triggered in aged rats relative to young rats.
We considered the possibility that these changes might be due to
altered cell composition in the oxyntic mucosa of young and aged
animals, but no significant differences in relative density of
foveolar, chief, or parietal cells were apparent on examination of
hematoxylin and eosin-stained sections.
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Response of gastric epithelial EGFR tyrosine kinase activity to in
vivo EGF and TGF- is greater in young than in aged
rats.
To determine whether the apparent ligand-induced EGFR internalization
correlated with altered activation, EGFR tyrosine kinase activity was
measured in membrane preparations from gastric epithelium of young and
aged rats 30 min after administration of EGF or TGF-
. In control
rats, total EGFR tyrosine kinase activity of aged rats was 417% of
that in young controls (Fig. 3).
Administration of EGF and TGF-
to young rats induced 483% and
1,100% increases, respectively, in total EGFR tyrosine kinase activity
(Fig. 3). In contrast, EGF had no effect and TGF-
produced a 21%
decrease in total EGFR tyrosine kinase activity in aged rats (Fig. 3). These data are consistent with increased basal activation of EGFR in
aged rats. The data also support the hypothesis that ligation of EGFR
in aged rats results in downregulation of membrane receptor kinase
activity, perhaps via internalization, whereas receptor ligation
induces activation of EGFR tyrosine kinase activity in young rats.
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Isolated gastric epithelial cells from aged rats internalize EGFR
tyrosine kinase activity more rapidly than gastric epithelial cells
from young rats.
To further characterize the proposed enhanced internalization of EGFR
in aged rats, surface membrane and intracellular fractions were
isolated from gastric epithelial cells stimulated in vitro. When
epithelial cells isolated from young rats were exposed to 100 pM
TGF-, EGFR tyrosine kinase activity increased steadily between 5 and
20 min, both in surface membrane and intracellular fractions. Fifty
percent of total EGFR kinase activity was present in the intracellular
fraction at 5 min after TGF-
stimulation. This increased to 69% and
67% of total EGFR kinase activity after 10 and 20 min of stimulation,
respectively (Fig. 4). In
contrast, although total EGFR tyrosine kinase activity increased at
each interval in epithelial cells from aged rats, the intracellular fraction of EGFR kinase activity was 73%, 71%, and 84% at 5, 10, and
20 min, respectively (Fig. 4). Thus at each interval after TGF-
stimulation the intracellular fraction of EGFR tyrosine kinase activity
was greater in aged than in young rats. These data support the
hypotheses that gastric epithelial cells from aged rats have increased
basal EGFR activation compared with cells from young rats and that a
greater fraction of EGFR is intracellular in aged rats after TGF-
stimulation.
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Gastric mucosal membranes from aged rats are more sensitive to
TGF- stimulation than those from young rats.
To determine whether aging enhances responsiveness of the gastric
mucosa to the EGF family of peptides, we examined age-related changes
in EGFR tyrosine kinase activity in mucosal membrane preparations from
young and aged rats in response to increasing concentrations of
TGF-
. As shown in Fig. 5, EGFR tyrosine
kinase activity in mucosal membranes from aged rats was maximally
stimulated with a dose of 10 pM TGF-
. Doses above 10 pM inhibited
the maximal stimulatory action of the peptide. The results show a
biphasic response of the gastric mucosa of aged rats to TGF-
.
However, no such biphasic response was observed in young rats. In fact, EGFR tyrosine kinase activity in mucosal membranes from young rats was
not significantly affected until the TGF-
concentration was elevated
to 1 nM, a dose that was 1,000-fold greater than the lowest dose (1 pM)
that significantly stimulated EGFR tyrosine kinase in mucosal membranes
from aged rats. Our current results show that gastric mucosal
sensitivity to TGF-
is considerably higher in aged than young rats.
This is consistent with in vivo "priming" of EGFR in aged
animals.
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DISCUSSION |
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Cells of the gastrointestinal mucosa undergo a constant process of renewal. In normal adults, this reflects a balance between exfoliation of surface cells and proliferation of precursor cells. However, the proliferative rate is not constant throughout life. In fact, accumulating data suggest that gastrointestinal epithelial cells undergo age-dependent changes in their proliferative rate (26, 28, 29, 34). For example, we have shown that DNA synthesis and thymidine kinase activity, as measures of gastric epithelial proliferative activity, are elevated during the first 2 wk of life and then decrease dramatically over the next 2-3 wk (30). More recently, we and others have shown that gastric (24, 28, 35), small intestinal (16, 17), and large intestinal (15) mucosal proliferative activity increase with advancing age. The observation reported herein that more PCNA-immunoreactive cells are present in the gastric mucosa of aged rats than in young rats also supports the contention that aging is associated with increased gastric mucosal proliferative activity.
Over the past three decades, numerous reports have appeared suggesting
that gastrointestinal hormones and peptides, most notably gastrin,
bombesin, EGF, and TGF-, regulate mucosal proliferation throughout
the gastrointestinal tract, including the stomach, both in vivo
and in vitro (3-6, 11-14, 18, 22, 30, 37-40, 43).
However, increases in gastric mucosal proliferative activity in aged
rats cannot be attributed to increased responsiveness to any of these
hormones and peptides. In fact, aging is associated with a loss of
gastric mucosal responsiveness to the trophic activities of both
gastrin and bombesin (25, 31), and EGF inhibits mucosal proliferative
activity in aged rats (23). Our current observation that
pharmacological doses of TGF-
, which stimulate gastric epithelial proliferation in young rats, inhibit gastric epithelial proliferation in aged rats is analogous to our previous observations using EGF (23).
Clearly, these results suggest that large doses of either EGF or its
structural and functional analog TGF-
inhibit gastric epithelial
proliferation in aged rats. Similar observations have been reported for
the human breast cancer cell line MDA-MB-468 and the human epidermoid
carcinoma cell line A431, each of which overexpresses EGFR (1, 9, 19).
Interestingly, aging is also associated with increased expression of
EGFR in the gastric mucosa (41). Together, the results suggest an
inverse relationship between overexpression of EGFR and mitogenic
response to EGF and TGF-
. On the basis of these observations, we
postulated that the inhibition of gastric mucosal proliferative
activity in aged gastric mucosa in response to pharmacological doses of
EGF or TGF-
could be the result of increased ligand-induced
internalization or degradation of EGFR. Our current data appear to
support such a contention. We have observed that in aged rats, but not
in young rats, a single injection of a pharmacological dose of either
EGF or TGF-
produced a marked rise in the relative abundance and intensity of basal vesicular cytoplasmic EGFR staining within the
gastric epithelium. This result suggests that the gastric epithelium of
aged rats responds to pharmacological doses of EGFR ligands with an
increased internalization response relative to young rats. We
considered the possibility that differential distribution of exogenous
EGF or TGF-
could explain the differences between young and old rats
but concluded that this was unlikely since similar differential
responses were noted in vitro. Although we did not evaluate the
extent of EGFR-ligand complex degradation biochemically, the
progressive increases in intracellular EGFR tyrosine kinase activity
observed in vitro also support the conclusion that the internalization
response in aged rats is exaggerated. The in vitro studies also
demonstrated that 100 pM TGF-
induced much greater and more rapid
increases in intracellular EGFR tyrosine kinase activity in gastric
epithelial cells from aged rats than did similar stimulation of gastric
epithelial cells from young rats. Although the regulatory mechanisms
for the increased internalization of EGFR in the gastric mucosa of aged
rats in response to exogenous EGF or TGF-
remain to be elucidated,
our data suggest that aging may be associated with increased
sensitivity of the EGFR to its ligands. It is also possible that some
of the differences may be due to altered cytoskeletal responsiveness of
epithelial cells from young and aged rats, as polyamine depletion has
been recently reported to alter both actin structure and EGFR function
in the IEC-6 cell line (33). Consistent with this, we showed that the concentration of TGF-
needed to induce maximal in vitro
stimulation of EGFR tyrosine kinase activity in gastric mucosal
membranes from aged rats was 1,000-fold less than that required in
young rats.
In conclusion, the data presented in this study demonstrate that aging
is associated with altered responsiveness of gastric mucosal epithelium
to pharmacological doses of the EGFR ligands EGF and TGF-. These
peptides stimulate proliferative activity in gastric epithelial cells
from young rats but cause inhibition of proliferation in aged rats. The
greater extent of EGFR internalization observed in the gastric mucosa
of aged rats as opposed to that seen in young rats suggests that rapid
internalization of the ligand-receptor complex may partly contribute to
the inhibition of mucosal proliferative activity in aged rats. Thus
altered responses of the gastric epithelial EGFR occur with aging and
may, in part, explain age-related changes in epithelial proliferation
and responses to peptide growth factors.
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ACKNOWLEDGEMENTS |
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We thank Linda Mayernik for expert assistance with confocal microscopy.
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FOOTNOTES |
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This study was supported by the National Institute on Aging and the Department of Veterans Affairs (A. P. N. Majumdar) and National Institute of Diabetes, Digestive, and Kidney Diseases Grants DK-02503 and DK-56121 (J. R. Turner) and Institute of Chemical Toxicology of Wayne State University Grant NIH P30-ES06639.
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: A. P. N. Majumdar, Research Service-151, Veterans Affairs Medical Center, 4646 John R, Detroit, MI 48201 (E-mail: a.majumdar{at}wayne.edu).
Received 15 September 1999; accepted in final form 2 December 1999.
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REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Armstrong, DK,
Kaufmann SH,
Ottaviano YL,
Furuya Y,
Buckley JA,
Isaacs JT,
and
Davidson NE.
Epidermal growth factor-mediated apoptosis of MDA-MB-468 human breast cancer cells.
Cancer Res
54:
5280-5283,
1994[Abstract].
2.
Atillasoy, E,
and
Holt PR.
Gastrointestinal proliferation and aging.
J Gerontol B Psychol Sci Soc Sci
48:
B43-B49,
1993.
3.
Barnard, JA,
Beauchamp RD,
Russell WE,
Dubois RN,
and
Coffey RJ.
Epidermal growth factor-related peptides and their relevance to gastrointestinal pathophysiology.
Gastroenterology
108:
564-580,
1995[ISI][Medline].
4.
Chen, MC,
Lee AT,
and
Soll AH.
Mitogenic response of canine fundic epithelial cells in short-term culture to transforming growth factor and insulinlike growth factor I.
J Clin Invest
87:
1716-1723,
1991[ISI][Medline].
5.
Comoglio, PM,
Di Renzo MF,
Gaudino G,
Ponzetto C,
and
Prat M.
Tyrosine kinase and control of cell proliferation.
Am Rev Respir Dis
142:
S16-S19,
1990[ISI][Medline].
6.
Dethloff, LA,
Barr BM,
and
Bestervelt LL.
Inhibition of gastrin-stimulated cell proliferation by the CCK-B/gastrin receptor ligand CI-988.
Food Chem Toxicol
37:
105-110,
1999[ISI][Medline].
7.
Dignass, AU,
and
Podolsky DK.
Cytokine modulation of intestinal epithelial cell restitution: central role of transforming growth factor .
Gastroenterology
105:
1323-1332,
1993[ISI][Medline].
8.
Earp, HS,
Dawson TL,
Li X,
and
Yu H.
Heterodimerization and functional interaction between EGF receptor family members: a new signaling paradigm with implications for breast cancer research.
Breast Cancer Res Treat
35:
115-132,
1995[ISI][Medline].
9.
Filmus, J,
Pollak MN,
Cailleau R,
and
Buick RN.
MDA-468, a human breast cancer cell line with a high number of epidermal growth factor (EGF) receptors, has an amplified EGF receptor gene and is growth inhibited by EGF.
Biochem Biophys Res Commun
128:
898-905,
1985[ISI][Medline].
10.
Futter, CE,
and
Hopkins CR.
Subfractionation of the endocytic pathway: isolation of compartments involved in the processing of internalised epidermal growth factor-receptor complexes.
J Cell Sci
94:
685-694,
1989[Abstract].
11.
Goodlad, RA,
and
Wright NA.
Peptides and epithelial growth regulation.
Experientia
43:
780-784,
1987[ISI][Medline].
12.
Goodlad, RA,
and
Wright NA.
Peptides and epithelial growth regulation.
Experientia Suppl
56:
180-191,
1989.
13.
Hakanson, R,
Oscarson J,
and
Sundler F.
Gastrin and the trophic control of gastric mucosa.
Scand J Gastroenterol Suppl
118:
18-30,
1986[Medline].
14.
Hansen, OH,
Pedersen T,
Larsen JK,
and
Rehfeld JF.
Effect of gastrin on gastric mucosal cell proliferation in man.
Gut
17:
536-541,
1976[Abstract].
15.
Holt, PR,
and
Yeh KY.
Colonic proliferation is increased in senescent rats.
Gastroenterology
95:
1556-1563,
1988[ISI][Medline].
16.
Holt, PR,
and
Yeh KY.
Small intestinal crypt cell proliferation rates are increased in senescent rats.
J Gerontol B Psychol Sci Soc Sci
44:
B9-B14,
1989.
17.
Holt, PR,
Yeh KY,
and
Kotler DP.
Altered controls of proliferation in proximal small intestine of the senescent rat.
Proc Natl Acad Sci USA
85:
2771-2775,
1988[Abstract].
18.
Kato, K,
Chen MC,
Nguyen M,
Lehmann FS,
Podolsky DK,
and
Soll AH.
Effects of growth factors and trefoil peptides on migration and replication in primary oxyntic cultures.
Am J Physiol Gastrointest Liver Physiol
276:
G1105-G1116,
1999
19.
Kawamoto, T,
Mendelsohn J,
Le A,
Sato GH,
Lazar CS,
and
Gill GN.
Relation of epidermal growth factor receptor concentration to growth of human epidermoid carcinoma A431 cells.
J Biol Chem
259:
7761-7766,
1984
20.
Khan, AJ,
Fligiel SE,
Liu L,
Jaszewski R,
Chandok A,
and
Majumdar APN
Induction of EGFR tyrosine kinase in the gastric mucosa of diabetic rats.
Proc Soc Exp Biol Med
221:
105-110,
1999[Abstract].
21.
Kinoshita, Y,
Nakata H,
Hassan S,
Asahara M,
Kawanami C,
Matsushima Y,
Naribayashi-Inomoto Y,
Ping CY,
Min D,
Nakamura A,
and
Chiba T.
Gene expression of keratinocyte and hepatocyte growth factors during the healing of rat gastric mucosal lesions.
Gastroenterology
109:
1068-1077,
1995[ISI][Medline].
22.
Koh, TJ,
Goldenring JR,
Ito S,
Mashimo H,
Kopin AS,
Varro A,
Dockray GJ,
and
Wang TC.
Gastrin deficiency results in altered gastric differentiation and decreased colonic proliferation in mice.
Gastroenterology
113:
1015-1025,
1997[ISI][Medline].
23.
Majumdar, APN,
and
Arlow FL.
Aging: altered responsiveness of gastric mucosa to epidermal growth factor.
Am J Physiol Gastrointest Liver Physiol
257:
G554-G560,
1989
24.
Majumdar, APN,
Edgerton EA,
and
Arlow FL.
Gastric mucosal tyrosine kinase activity during aging and its relationship to cell proliferation in rats.
Biochim Biophys Acta
965:
97-105,
1988[ISI][Medline].
25.
Majumdar, APN,
Edgerton EA,
Dayal Y,
and
Murthy SN.
Gastrin: levels and trophic action during advancing age.
Am J Physiol Gastrointest Liver Physiol
254:
G538-G542,
1988
26.
Majumdar, APN,
Fligiel SE,
and
Jaszewski R.
Gastric mucosal injury and repair: effect of aging.
Histol Histopathol
12:
491-501,
1997[ISI][Medline].
27.
Majumdar, APN,
and
Goldenring JR.
Localization and significance of pp55, a gastric mucosal membrane protein with tyrosine kinase activity.
Am J Physiol Gastrointest Liver Physiol
274:
G863-G870,
1998
28.
Majumdar, APN,
Jasti S,
Hatfield JS,
Tureaud J,
and
Fligiel SE.
Morphological and biochemical changes in gastric mucosa of aging rats.
Dig Dis Sci
35:
1364-1370,
1990[ISI][Medline].
29.
Majumdar, APN,
Jaszewski R,
and
Dubick MA.
Effect of aging on the gastrointestinal tract and the pancreas.
Proc Soc Exp Biol Med
215:
134-144,
1997[Abstract].
30.
Majumdar, APN,
and
Johnson LR.
Gastric mucosal cell proliferation during development in rats and effects of pentagastrin.
Am J Physiol Gastrointest Liver Physiol
242:
G135-G139,
1982
31.
Majumdar, APN,
and
Tureaud J.
Role of tyrosine kinases in bombesin regulation of gastric mucosal proliferative activity in young and aged rats.
Peptides
13:
795-800,
1992[ISI][Medline].
32.
Majumdar, APN,
Tureaud J,
Relan NK,
Kessel A,
Dutta S,
Hatfield JS,
and
Fligiel SE.
Increased expression of pp60c-src in gastric mucosa of aged rats.
J Gerontol B Psychol Sci Soc Sci
49:
B110-B116,
1994.
33.
McCormack, SA,
Blanner PM,
Zimmerman BJ,
Ray R,
Poppleton HM,
Patel TB,
and
Johnson LR.
Polyamine deficiency alters EGF receptor distribution and signaling effectiveness in IEC-6 cells.
Am J Physiol Cell Physiol
274:
C192-C205,
1998
34.
McCormack, SA,
and
Johnson LR.
Role of polyamines in gastrointestinal mucosal growth.
Am J Physiol Gastrointest Liver Physiol
260:
G795-G806,
1991
35.
Relan, NK,
Fligiel SE,
Dutta S,
Tureaud J,
Chauhan DP,
and
Majumdar APN
Induction of EGF-receptor tyrosine kinase during early reparative phase of gastric mucosa and effects of aging.
Lab Invest
73:
717-726,
1995[ISI][Medline].
36.
Rusch, V,
Mendelsohn J,
and
Dmitrovsky E.
The epidermal growth factor receptor and its ligands as therapeutic targets in human tumors.
Cytokine Growth Factor Rev
7:
133-141,
1996[Medline].
37.
Rutten, MJ,
Dempsey PJ,
Solomon TE,
and
Coffey RJ, Jr.
TGF-alpha is a potent mitogen for primary cultures of guinea pig gastric mucous epithelial cells.
Am J Physiol Gastrointest Liver Physiol
265:
G361-G369,
1993
38.
Sakamoto, C,
Matsuda K,
Nakano O,
Konda Y,
Matozaki T,
Nishisaki H,
and
Kasuga M.
EGF stimulates both cyclooxygenase activity and cell proliferation of cultured guinea pig gastric mucous cells.
J Gastroenterol
29 Suppl7:
73-76,
1994[ISI][Medline].
39.
Sharp, R,
Babyatsky MW,
Takagi H,
Tagerud S,
Wang TC,
Bockman DE,
Brand SJ,
and
Merlino G.
Transforming growth factor alpha disrupts the normal program of cellular differentiation in the gastric mucosa of transgenic mice.
Development
121:
149-161,
1995
40.
Tsukimi, Y,
and
Okabe S.
Changes in gastric function and healing of chronic gastric ulcers in aged rats.
Jpn J Pharmacol
68:
103-110,
1995[ISI][Medline].
41.
Tureaud, J,
Sarkar FH,
Fligiel SE,
Kulkarni S,
Jaszewski R,
Reddy K,
Yu Y,
and
Majumdar APN
Increased expression of EGFR in gastric mucosa of aged rats.
Am J Physiol Gastrointest Liver Physiol
273:
G389-G398,
1997
42.
Ullrich, A,
and
Schlessinger J.
Signal transduction by receptors with tyrosine kinase activity.
Cell
61:
203-212,
1990[ISI][Medline].
43.
Van Nieuwenhove, Y,
De Backer T,
Chen D,
Hakanson R,
and
Willems G.
Gastrin stimulates epithelial cell proliferation in the oesophagus of rats.
Virchows Arch
432:
371-375,
1998[ISI][Medline].