Department of Medicine, University of Melbourne, Western Hospital, Footscray 3011, Australia
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ABSTRACT |
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The use
of genetically engineered mice with both gain-of-function and
loss-of-function mutations has been particularly informative about the
normal and pathophysiological actions of a number of regulatory
peptides of the gastrointestinal tract. This review highlights some of
the major findings pertinent to the epidermal growth factor (EGF)
receptor and its ligands, particularly the major gut ligand
transforming growth factor-, as well as the trefoil peptides. Both
of these peptide families have important local actions in maintaining
tissue homeostasis and repair after injury, and when mechanisms
governing their regulation are disrupted they may contribute to disease
progression. Future applications of transgenic technology to these
areas are likely to be productive in furthering our understanding of
the biology of these peptides in health and disease.
epidermal growth factor receptor; transforming growth factor-; transgenic mice
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INTRODUCTION |
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THE ADVENT OF GENETIC ENGINEERING and advances in the application of molecular biology methods to problems in gastrointestinal physiology and disease have advanced our understanding of the underlying cellular processes of digestion, as well as mechanisms of ulceration and inflammation, in Crohn's disease, ulcerative colitis, and gastrointestinal cancer.
Maintenance of the normal physiological function of the
gastrointestinal mucosa is continually compromised by the harsh
extracellular (luminal) environment of the gut. As a result, there are
sophisticated reparative mechanisms in place that have the capacity to
rapidly restore mucosal integrity and digestive function. These include restitution, in which local epithelial cells migrate to cover denuded
areas, as well as increased mucus production and blood flow, followed
by proliferation and differentiation programs. The epidermal growth
factor (EGF) receptor (EGF-r) ligands [transforming growth factor
(TGF)-, EGF, amphiregulin, betacellulin, heparin-binding (HB)-EGF,
and epiregulin] and the trefoil peptides [TFF1 (pS2), TFF2
(spasmolytic polypeptide; SP), and TFF3 (intestinal trefoil factor;
ITF)] are two distinct families of polypeptides that are important cellular mediators of both normal tissue homeostasis and
repair. They act locally, are multifunctional in nature,
and when inappropriately expressed may contribute to cancer progression.
The relatively recent application of transgenic animal technology to investigation of the function of the EGF-r ligands and trefoil peptides has provided important new information about their normal physiological roles and specialized functions in gastrointestinal maturation and repair and in disease. This approach has been instructive despite the extensive functional redundancy exemplified by both polypeptide families, further underlining their biological importance. This article attempts to summarize what we have learned so far and where application of these models could be fruitful in the future.
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EGF-R LIGANDS IN THE GUT |
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The main endogenous ligand for the EGF-r in the gut is TGF-. TGF-
is expressed by gastric parietal cells, intestinal villus epithelial
cells, surface crypt epithelial cells of the colon, pancreatic ductular
cells, and hepatocytes (2). Betacellulin, a potent mitogen originally
isolated from conditioned medium of an insulinoma cell line derived
from the transgenic RIP-tag2 mouse is synthesized in the pancreas,
liver, and intestine (24). Epiregulin, characterized from a tumorigenic
fibroblast line (3T3/T7), is a low-affinity ligand for the EGF-r and is
weakly expressed in the small bowel and colon but strongly expressed by
many colon cancer cell lines (30). Amphiregulin is expressed mainly in the colon and pancreas and is a weak ligand for the EGF-r. EGF itself
is expressed only at low levels in the normal pancreas and small
intestine, and HB-EGF is not present at appreciable levels in the gut
(32). All these ligands bind the EGF-r, resulting in homodimerization
or heterodimerization with members of the erbB receptor family (erbB2,
-3, and -4) of which the EGF-r, or erbB1, is also a member. The natural
ligands for erbB3 and -4 particularly are the heregulins. Because the
erbB family are tyrosine kinases, ligand binding leads to
autophosphorylation followed by a well-characterized signaling cascade
via Ras and activation of mitogen-activated protein kinases to
transduce the functional signal.
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TREFOIL PEPTIDES IN THE GUT |
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The trefoil peptides are a family of abundant 7- to 14-kDa polypeptides, which are secreted by mucus cells predominantly of the gut. There are three mammalian members of the family: a gastric peptide TFF1 (alternative nomenclature pS2), expressed by surface and pit mucus cells; TFF2/SP, a gastric peptide found in mucous neck and glandular mucus cells as well as Brunner's glands of the proximal duodenum; and TFF3/ITF, expressed by goblet cells of the intestine and colon. Individual peptides have homology in cysteine-rich regions of 38 or 39 amino acids known as trefoil motifs, in which the component cysteine residues form disulfide bonds in an invariable 1-5, 2-4, 3-6 design that results in a compact triple-loop or trefoil structure (28). TFF-1 and -3 have a single trefoil motif and form bioactive homodimers linked by a disulfide bond, whereas TFF-2 has two motifs. The trefoil motif is extremely stable and is the basis for the extraordinary resistance of these peptides to acid hydrolysis and proteolysis, making them well suited for action in the harsh luminal environment of the gut.
It is now well established that trefoil peptides are cytoprotective and promote healing in response to gastrointestinal damage. Both oral and subcutaneous TFF2/SP or TFF3/ITF can protect the gastric epithelium from a variety of damaging agents and/or processes including ethanol, nonsteroidal anti-inflammatory drugs, and restraint stress, and luminal application of TFF2/SP in a rat model of inflammatory bowel disease was shown to accelerate healing and reduce inflammation (31). However, the cellular mechanisms by which TFF2/SP and TFF3/ITF accomplish this are unclear, as is whether their effects are receptor mediated. Primarily in vitro evidence supports a role for the trefoil peptides in both extracellular and intracellular actions, including stimulation of cell migration, inhibition of apoptosis in certain cells, and increasing the barrier function of mucus; all of these are commensurate with a role in protection and repair. Of interest is the large body of evidence that trefoils are also ectopically expressed in many epithelial cancers (although not in others), and it is possible that their inappropriate expression under these circumstances may contribute to the inhibition of programmed cell death and metastatic capacity of these cells.
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APPLICATION OF TRANSGENIC MOUSE MODELS TO DETERMINATION OF TREFOIL PEPTIDE FUNCTION |
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Before the development of the first loss-of-function or gain-of-function trefoil peptide transgenics, the evidence for a direct role for these peptides in injury repair was circumstantial. The separate publication of descriptions of mouse phenotypes lacking TFF1/pS2 (16) and TFF3/ITF (19), as well as the TFF1/pS2 gain-of-function phenotype (21), showed that the trefoil peptides were essential for normal wound repair and that they also have likely roles in gastrointestinal cell migration and maturation programs. To date, TFF2/SP transgenics have not been described. However, given the demonstrable importance of TFF2/SP in repair programs of the stomach and the colon, the gastric localization of this trefoil peptide to the developmentally pivotal mucous neck/antral gland/Brunner's gland cell, and the instructive TFF1/pS2 and TFF3/ITF transgenic phenotypes, it is likely that TFF2/SP transgenic animals will also be informative about trefoil function.
Trefoil peptides are essential for normal gastrointestinal wound
repair.
Generation of TFF3/ITF /
mice showed that they were
phenotypically identical to wild-type animals and developed normally but were extremely sensitive to otherwise mildly damaging
concentrations of ingested dextran sulfate given in drinking water, so
that 50% of treated mice died and others showed high morbidity with
diarrhea and rectal bleeding. Histology confirmed a marked colitis.
Moreover, the severity of colitis, when induced by the topical irritant acetic acid could be reduced by intracolonic application of recombinant TFF3/ITF (19). Further application of this model (3) to the clinical
problem of intestinal mucositis brought about by chemotherapy or
radiotherapy showed that animals lacking TFF3/ITF had more severe
symptoms (bloody diarrhea, weight loss, and intestinal permeability)
than wild-type controls and that these symptoms could be reduced by
giving oral ITF.
Trefoil peptides participate in gastrointestinal maturation.
TFF1/pS2 /
mice exhibit an increased mitotic index, with
reduced migration to other glandular compartments, resulting in elongated gastric pits lacking mucus in the foveolar cells (16). TFF3/ITF
/
mice also have an expanded stem
cell/proliferative zone so that normal migration and cell turnover
patterns from crypt to villus are disrupted (19). These observations
suggest that the trefoil peptides participate in maturation events
including cell migration, differentiation, and possibly apoptosis.
Experiments using in vitro systems confirmed that trefoils act as weak
motogens for epithelial cells (9) and inhibit apoptosis in cancer cell lines (26). They also show a late and sustained induction of expression
in the regenerating gastrointestinal mucosa in in vivo models of repair
(1, 7), temporally commensurate with the differentiation and cell
positioning programs of many epithelial cell types (15). Experiments in
cell lines in which differentiation pathways are defined and that are
amenable to transfection with trefoil peptide constructs, treatment of
late-gestation fetal gut explants with recombinant peptides, or
antisense constructs and antisera may help to clarify trefoil
regulation of differentiation pathways. This approach, or the
development of triple mutants (TFF1/pS2, TFF2/SP, and TFF3/ITF null
mice) is required to overcome the overlapping expression and function
of trefoil genes in the maturation of the gastrointestinal mucosa.
Trefoil peptide and EGF-r ligand expression are functionally linked.
There appears to be an important link between the expression of the
trefoil peptides and the main EGF-r ligands of the gut, particularly
TGF- in the regenerating gastrointestinal tract. It has been
proposed (35) that epithelial rebuilding takes place as a consequence
of the induction of a new cell lineage (ulcer-associated cell lineage;
UACL) that arises at the periphery of the ulcerated mucosa. EGF-r
ligands and all three trefoil peptides have been proposed to be
expressed sequentially, with the latter being induced by the former and
presumably both contributing to the overall reepithelialization.
Support for this hypothesis has come from in vitro and in vivo studies
demonstrating synergy between EGF and TFF3/ITF in promoting cell
migration and in protecting the stomach against
indomethacin/restraint-induced injury (6, 21) and from unpublished data
demonstrating increased sequential protein expression of TGF-
and
then TFF2/SP and TFF3/ITF in the stomach during restitution and
glandular reepithelialization after deep ulceration. An added dimension
to this relationship comes from the observation that trefoil peptides
are able to transactivate the EGF-r (27) and perhaps other members of
the erbB family.
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APPLICATION OF TRANSGENIC MODELS TO DETERMINATION OF FUNCTION OF EGF-R AND ITS LIGANDS IN THE GUT |
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The application of transgenic models to the determination of function
of EGF-r ligands in the gut (as opposed to other organs) has mainly
been restricted to overexpressing TGF- under the control of
promoters that allow tissue-specific and temporal regulation. In
particular, the metallothionein promoter/enhancer (MT)-TGF-
mouse,
in which the transgene can be activated by application of cadmium or
zinc salts in adult life, has been very useful in elucidating and
confirming much of the physiology and pathophysiology of TGF-
. This
has been particularly instructive for understanding liver disease and
regeneration, the latter being the subject of a previous review in this
series (13).
Mice engineered to be TGF- null, or mutants found to be so by
genetic analysis after comparison of coat phenotype with TGF-
knockouts (10), were initially thought to be relatively uninformative with respect to gut function. However, careful analysis of the gastrointestinal repair phenotype has revealed some unexpected insights.
TGF- regulates differentiation and repair programs.
Ectopic TGF-
expression in the stomach has been reported in the
MT-TGF-
mouse (8, 23). A major consequence of this is that the
fundic surface mucous cell compartment is greatly expanded, effectively
increasing the length of the pits and compressing the progenitor zone
to the gland bases. This process has been termed "antralization,"
presumably because of the phenotypic and structural similarity of the
glands to the gastric antrum (14), and appears to be brought about by a
block in the terminal differentiation of parietal and chief/zymogen
cells once gastric TGF-
reaches a certain threshold level of
expression. Expansion of the foveolar compartment also results in an
increase in TFF1/pS2 (14) but also TFF2/SP (23) expression, suggesting
either that foveolar cells have a mixed phenotype or that a metaplastic
repair phenotype (UACL-like) has been induced. The extent of expression
of TFF3/ITF in this model would help resolve the issue and would also
better define the relationship between TGF-
and trefoil gene expression.
Menetrier's disease: a consequence of inappropriate expression of
TGF-?
The gastric phenotype of MT-TGF-
transgenic mice is very similar to
that of human Menetrier's disease, a relatively uncommon precancerous
condition marked by foveolar hyperplasia, hypochlorhydria (lack of
HCl), and increased mucus synthesis and secretion. Menetrier's patients have high TGF-
expression (8), and this along with the
characteristic morphology makes it likely that increased TGF-
, or
inappropriate induction of expression in conjunction with other cofactors, might contribute to the pathogenesis of this disease.
TGF- overexpression results in pancreatic fibrosis
and transdifferentiation and may contribute to multistage
carcinogenesis.
In the MT-TGF-
transgenic mouse TGF-
is highly expressed in
pancreatic acini, and early studies showed a progressive pancreatic enlargement with age caused by interstitial fibrosis along with a
redifferentiation of acinar to ductular cells and, ultimately, tubular
complexes (4). Subsequent work in the EL-TGF-
-hGF transgenic line
demonstrated that there is progressive dysplasia in the tubular
structures accompanied by increases in EGF-r and p53 expression (33)
and that 20% of mice over 1 yr old had cystic papillary tumors. Acinar
cell carcinomas have also been induced in double-transgenic mice
expressing oncogenes of either viral (SV40 T antigens) or cellular
(c-myc) origin and TGF-
. In these animals the TGF-
transgene alone was not oncogenic; however, its presence accelerated
the development of tumors produced by either oncogene (22). The results
from these experiments, which could not have been carried out in any
other system, point to a role for TGF-
in promoting multistage
carcinogenesis in conjunction with accumulated mutations as well as
tumor growth. It is likely that future multiple transgenics based on
TGF-
and known facilitators of tumor development such as Ras will
also be informative in this respect.
Multiple EGF-r ligand knockouts emphasize importance of redundancy in EGF-r signaling. To circumvent the compensatory mechanisms involved in EGF-r activation, a gene targeting strategy in which the three main upper gut EGF-r ligands were knocked out was carried out (17). Surprisingly, there were no morphological abnormalities in the gut, although the triple-null mutant neonates did not thrive and showed growth retardation, compared with wild-type animals, because of an inadequate milk supply. However, the fact that most mutants reached sexual maturity and exhibited apparently normal gut function suggests that further redundancy in EGF-r ligand binding or transactivation via other erbB receptors exists, either by known or uncharacterized EGF-r ligands.
Contributions from EGF-r null mutant and conditionally immortalized mice and derived cell lines. The importance of the EGF-r in transducing signaling by a multiplicity of ligands involved in proliferation, differentiation, and migration is underscored by the fact that EGF-r null mice invariably die either in utero because of defects in placentation or early in postnatal life because of multiorgan failure, depending on the genetic background (20, 25, 29). Mouse mutants bred on a CD-1 or C57 background had impaired gut proliferation with a reduced stem cell zone and disorganized mucosal architecture. The C57 background phenotype was most severe, exhibiting hemorrhagic lesions and villus destruction characteristic of the premature human infant gut condition necrotizing enterocolitis (20).
Unlike EGF-r null animals, waved-2 mice with a naturally occurring mutation in the tyrosine kinase domain of the EGF-r that results in impaired signaling (10) are viable and have apparently normal gut morphology. This suggests that even attenuated EGF-r function is sufficient to maintain tissue homeostasis or that transactivation by other ligands assumes greater importance under these circumstances. Because conditional EGF-r knockouts have not yet been reported and EGF-r null mice do not live until sexual maturity, it has not been possible to fully assess the contribution of this pivotal receptor in gastrointestinal function. However, the establishment of a conditionally immortalized transgenic mouse strain (H-2Kb-tsA58) in which the SV40 tsA58 thermolabile transgene is driven by an interferon- ![]() |
THE FUTURE FOR GENETICALLY ENGINEERED MICE IN TREFOIL AND EGF-R/LIGAND FUNCTION |
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In the last five years, the use of genetically engineered mice has confirmed the pivotal role that the trefoil peptides play in gastrointestinal repair and the likelihood that this is brought about in part by their motogenic actions and ability to promote differentiation during the extensive mucosal rebuilding after ulceration. An unexpected finding was the specific and potentially detrimental adenoma-carcinoma progression at the gastric pylorus in TFF1/pS2 null animals, suggesting an otherwise unpredicted inhibitory role for this peptide. This must be followed up, possibly in conjunction with the generation of a TFF2/SP-only null mouse, especially because 70% of null TFF1/pS2 mutants also lack gastric but not pancreatic TFF2/SP (16).
When interpreting data from the next generation of trefoil null mice in which multiple trefoil genes are inactivated simultaneously, it will be important to ask questions not just about wound healing in the gut but also about the implications of a lack of active trefoil expression in other tissues like the lung, uterus, kidney, and eye in which mucus secretion occurs and in which trefoil expression has been detected. In addition, we have recently shown (6a) that a population of unidentified immunocytes present in spleen, thymus, lymph node, and bone marrow synthesize TFF2/SP and TFF3/ITF, raising the possibility that they may be involved in some general aspect of immune regulation. Because application of recombinant trefoils can reduce inflammatory indexes in animal models of colitis and TFF1/pS2 knockout mice have intestinal inflammation it is possible that this is an important function for these peptides and one that requires a whole animal response to be tested. This could be accomplished by inducing experimental inflammation in trefoil loss-of-function and gain-of-function transgenics and comparing and quantifying the inflammatory response in a tissue-specific way.
Because EGF-r null mice usually die in utero or in early postnatal life, the elucidation of EGF-r function using transgenic animals has been less informative. What is now required is the production of conditional knockouts so that the contribution of EGF-r and other members of the erbB family to gut homeostasis can be fully assessed. This can be accomplished in several ways, including use of the Cre/loxP site-specific recombination system, in which mice expressing the enzyme Cre recombinase driven by a tissue-specific promoter are crossed with mutants expressing the gene of interest engineered with flanking loxP sites. Cre cleaves at the loxP sites, resulting in gene deletion only where it is expressed. This means that target genes can be knocked out in a cell-, tissue-, or time-dependent manner, allowing exact definition of gene function. This system is especially useful for genes that are normally widely expressed or those that are developmentally lethal.
Unlike the situation with the EGF-r, the broad gut organ expression of
TGF- and its contribution to differentiation, repair, and multistage
carcinogenesis in a tissue-specific pattern when conditionally
overexpressed in adult tissues have been very instructive. The
contribution to these processes by other EGF-r ligands expressed in the
gut such as betacellulin, amphiregulin, and epiregulin now must be addressed.
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ACKNOWLEDGEMENTS |
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A. S. Giraud was supported by grants from the National Health and Medical Research Council of Australia.
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FOOTNOTES |
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* Tenth in a series of invited articles on Lessons From Genetically Engineered Animal Models.
Address for reprint requests and other correspondence: A. S. Giraud, Dept. of Medicine, Univ. of Melbourne, Western Hospital, Footscray 3011, Australia (E-mail: ag{at}medicine.unimelb.edu.au).
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REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Alison, MR,
Chinery R,
Poulsom R,
Ashwood P,
Loncroft JM,
and
Wright NA.
Experimental ulceration leads to sequential expression of spasmolytic polypeptide, intestinal trefoil factor, epidermal growth factor and transforming growth factor- mRNAs in rat stomach.
J Pathol
175:
405-414,
1995[ISI][Medline].
2.
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].
3.
Beck, PL,
and
Podolsky DK.
Intestinal trefoil factor reduces the severity of chemotherapy and radiotherapy-induced intestinal mucositis (Abstract).
Gastroenterology
116:
G2133,
1999.
4.
Bockman DE and Merlino G. Cytological changes in the
pancreas of transgenic mice overexpressing transforming growth factor
. Gastroenterology 103: 1883-1892.
5.
Calnan, DP,
Westley BR,
May REB,
Floyd DN,
Marchbank T,
and
Playford RJ.
The trefoil peptide TFF1 inhibits the growth of the human gastric adenocarcinoma cell line AGS.
J Pathol
188:
312-317,
1999[ISI][Medline].
6.
Chinery, R,
and
Playford RJ.
Combined intestinal trefoil factor and epidermal growth factor is prophylactic against indomethacin-induced gastric damage in the rat.
Clin Sci (Colch)
88:
401-403,
1995[ISI][Medline].
6a.
Cook, GA,
Familari M,
Thim L,
and
Giraud AS.
The trefoil peptides TFF2 and TFF3 are expressed in rat lymphoid tissues and participate in the immune response.
FEBS Lett
456:
155-159,
1999[ISI][Medline].
7.
Cook, GA,
Yeomans ND,
and
Giraud AS.
Temporal expression of trefoil peptides in the TGF- knockout mouse after gastric ulceration.
Am J Physiol Gastrointest Liver Physiol
272:
G1540-G1549,
1997
8.
Dempsey, PJ,
Goldenring JR,
Soroka CJ,
Modlin IM,
McClure RW,
Lind CD,
Alquist DA,
Pittelkow MR,
Lee DC,
Sandgren EP,
Page DL,
and
Coffey RJ.
Possible role of transforming growth factor TGF- in the pathogenesis of Menetrier's disease: supportive evidence in humans and transgenic mice.
Gastroenterology
103:
1950-1963,
1992[ISI][Medline].
9.
Dignass, A,
Lynch-Devaney K,
Kindon H,
Thim L,
and
Podolsky DK.
Trefoil peptides promote epithelial migration through a transforming growth factor--independent pathway.
J Clin Invest
94:
376-383,
1994[ISI][Medline].
10.
Dunn, AR,
Mann GB,
Fowler KJ,
Grail D,
Hibbs ML,
Alexander WS,
Walker F,
and
Burgess AW.
Insights into the physiology of TGF and signalling through the EGF receptor revealed by gene targeting and acts of nature.
Princess Takamatsu Symp
24:
276-89,
1994[Medline].
11.
Egger, B,
Procaccino F,
Lakshmanan J,
Reinshagen M,
Hoffmann P,
Patel A,
Reuben W,
Gnanakkan S,
Liu L,
Barajas L,
and
Eysselein VE.
Mice lacking transforming growth factor have an increased susceptibility to dextran-sulfate-induced colitis.
Gastroenterology
113:
825-832,
1997[ISI][Medline].
12.
Egger, B,
Carey HV,
Procaccino F,
Chai NN,
Sandgren EP,
Lakshmanan J,
Buslon VS,
French SW,
Buchler MW,
and
Eysselein VE.
Reduced susceptibility of mice overexpressing transforming growth factor to dextran sodium sulfate induced colitis.
Gut
43:
64-70,
1998
13.
Fausto, N.
Lessons From Genetically Engineered Animal Models. V. Knocking out genes to study liver regeneration: present and future.
Am J Physiol Gastrointest Liver Physiol
277:
G917-G921,
1999
14.
Goldenring, JR,
Poulsom R,
Ray GS,
Wright N,
Meise KS,
and
Coffey RJ.
Expression of trefoil peptides in the gastric mucosa of transgenic mice overexpressing transforming growth factor-.
Growth Factors
13:
111-119,
1996[ISI][Medline].
15.
Karam, SM,
and
Leblond CP.
Dynamics of epithelial cells in the corpus of the mouse stomach. III. Inward migration of neck cells followed by progressive transformation into zymogenic cells.
Anat Rec
236:
297-313,
1993[ISI][Medline].
16.
Lefebvre, O,
Chenard M-P,
Masson R,
Linares J,
Dierich A,
Lemeur M,
Wendling C,
Tomasetto C,
Chambon P,
and
Rio M-C.
Gastric mucosa abnormalities and tumorigenesis in mice lacking the pS2 protein.
Science
274:
259-262,
1996
17.
Luetteke, NC,
Qiu TH,
Fenton SE,
Troyer KL,
Riedel RF,
Chang A,
and
Lee DC.
Targeted inactivation of the EGF and amphiregulin genes reveals distinct roles for EGF receptor ligands in mouse mammary gland development.
Development
126:
2739-2750,
1999
18.
Marchbank, T,
Cox H,
Goodlad R,
Giraud AS,
Moss S,
Wright NA,
and
Playford RJ.
Transgenic mice overexpressing TFF3 (rat intestinal trefoil factor) within the jejunum have an increased regional resistance to intestinal damage, but no difference in cell migration or apoptosis (Abstract).
Gastroenterology
116:
G4000,
1999.
19.
Mashimo, H,
Wu D-C,
Podolsky DK,
and
Fishman MC.
Impaired defense of intestinal mucosa in mice lacking intestinal trefoil factor.
Science
274:
262-265,
1996
20.
Miettinen, PJ,
Berger JE,
Meneses J,
Phung Y,
Pederson RA,
Werb Z,
and
Derynck R.
Epithelial immaturity and multiorgan failure in mice lacking epidermal growth factor receptor.
Nature
376:
337-341,
1995[ISI][Medline].
21.
Playford, RJ,
Marchbank T,
Goodlad RA,
Chinery RA,
Poulsom R,
Hanby AM,
and
Wright NA.
Transgenic mice that overexpress the human trefoil peptide pS2 have an increased resistance to intestinal damage.
Proc Natl Acad Sci USA
93:
2137-2142,
1996
22.
Sandgren, EP,
Luetteke NC,
Qui TH,
Palmiter RD,
Brewster RL,
and
Lee DC.
Transforming growth factor dramatically enhances oncogene-induced carcinogenesis in transgenic mouse pancreas and liver.
Mol Cell Biol
13:
320-330,
1993[Abstract].
23.
Sharp, R,
Babyatsky MW,
Takagi H,
Tagerud S,
Wang TC,
Bockman DE,
Brand SJ,
and
Merlino G.
Transforming growth factor disrupts the normal program of cellular differentiation program in the gastric mucosa of transgenic mice.
Development
121:
149-161,
1995
24.
Shing, Y,
Christofori G,
Hanahan D,
Ono Y,
Sasada R,
Igarashi K,
and
Folkman J.
Betacellulin: a mitogen from pancreatic cell tumors.
Science
259:
1604-1607,
1993[ISI][Medline].
25.
Sibilia, M,
and
Wagner EF.
Strain-dependent epithelial defects in mice lacking the EGF receptor.
Science
269:
234-238,
1995[ISI][Medline].
26.
Taupin, DR,
Kinoshita K,
and
Podolsky DK.
The trefoil peptide ITF regulates colonic epithelial apoptosis and tumor cell resistance to chemotherapy (Abstract).
Gastroenterology
116:
G2269,
1999.
27.
Taupin, D,
Wu D-C,
Jeon W-K,
Devaney K,
Wang TC,
and
Podolsky DK.
The trefoil peptide gene family are coordinately expressed immediate-early genes: EGF receptor- and MAP kinase-dependent interregulation.
J Clin Invest
103:
R31-R38,
1999
28.
Thim, L.
Trefoil peptides: a new family of gastrointestinal molecules.
Digestion
55:
353-360,
1994[ISI][Medline].
29.
Threadgill, DW,
Dlugosz AA,
Hansen LA,
Tennenbaum T,
Lichti U,
Yee D,
LaMantia C,
Mourton T,
Herrup K,
Harris RC,
Barnard JA,
Yuspa SH,
Coffey RJ,
and
Magnuson T.
Targeted disruption of mouse EGF receptor: effect of genetic background on mutant phenotype.
Science
269:
230-234,
1995[ISI][Medline].
30.
Toyoda, H,
Komurasaki T,
Uchida D,
and
Morimoto S.
Distribution of mRNA for human epiregulin, a differentially expressed member of the epidermal growth factor family.
Biochem J
326:
69-75,
1997[ISI][Medline].
31.
Tran, CP,
Cook GA,
Yeomans ND,
Thim L,
and
Giraud AS.
Trefoil peptide TFF2 (spasmolytic polypeptide) potently accelerates healing and reduces inflammation in a rat model of colitis.
Gut
44:
636-642,
1999
32.
Vaughan, TJ,
Pascall JC,
and
Brown KD.
Tissue distribution of mRNA for heparin-binding epidermal growth factor.
Biochem J
287:
681-684,
1992[ISI][Medline].
33.
Wagner, M,
Luhrs H,
Kloppel G,
Adler G,
and
Schmid RM.
Malignant transformation of duct-like cells originating from acini in transforming growth factor transgenic mice.
Gastroenterology
115:
1254-1262,
1998[ISI][Medline].
34.
Whitehead, RH,
VanEeden PE,
Noble MD,
Ataliotis P,
and
Jat PS.
Establishment of conditionally immortalized epithelial cell lines from both colon and small intestine of adult H-2Kb-tsA58 transgenic mice.
Proc Natl Acad Sci USA
90:
587-591,
1993[Abstract].
35.
Wright, NA,
Pike C,
and
Elia G.
Induction of a novel epidermal growth factor-secreting cell lineage by mucosal ulceration in gastrointestinal stem cells.
Nature
343:
82-85,
1990[ISI][Medline].