Transgenic mice that overexpress the human trefoil peptide pS2 have an increased resistance to intestinal damage

A paradoxical reduction in susceptibility to colonic injury upon targeted transgenic ablation of goblet cells

Goblet cells are the major mucus-producing cells of the intestine and are presumed to play an important role in mucosal protection. However, their functional role has not been directly assessed in vivo. In initial studies, a 5' flanking sequence of the murine intestinal trefoil factor (ITF) gene was found to confer goblet cell-specific expression of a transgene. To assess the role of goblet cells in the intestine, we generated transgenic mice in which approximately 60% of goblet cells were ablated by the expression of an attenuated diphtheria toxin (DT) gene driven by the ITF promoter; other cell lineages were unaffected. We administered 2 exogenous agents, dextran sodium sulfate (DSS) and acetic acid, to assess the susceptibility of mITF/DT-A transgenic mice to colonic injury. After oral administration of DSS, 55% of control mice died, whereas DT transgenic mice retained their body weight and less than 5% died. Similarly, 30% of the wild-type mice died after mucosal administration of acetic acid, compared with 3.2% of the transgenic mice. Despite the reduction in goblet-cell number, the total amount of ITF was increased in the mITF/DT-A transgenic mice, indicating inducible compensatory mechanisms. These results suggest that goblet cells contribute to mucosal protection and repair predominantly through production of trefoil peptides.

Metabolism of oral trefoil factor 2 (TFF2) and the effect of oral and parenteral TFF2 on gastric and duodenal ulcer healing in the rat

BACKGROUND

Trefoil factors (TFFs) are peptides produced by mucus-secreting cells in the gastrointestinal tract. A functional association between these peptides and mucus, leading to stabilisation of the viscoelastic gel overlying the epithelia, has been suggested. Both oral and parenteral administration of the peptides increase the resistance of the gastric mucosa.

AIM

To study the effect in rats of oral and parenteral porcine trefoil factor 2 (pTFF2) on the healing of gastric and duodenal ulcerations and to clarify the distribution and metabolism of orally administered pTFF2 in the gastrointestinal tract.

METHODS

Gastric ulcers were induced in female Sprague-Dawley rats by indomethacin and duodenal ulcers by mercaptamine. The rats were treated for up to seven days with oral or subcutaneous pTFF2. Ulcer size after treatment was assessed by stereomicroscopy after whole mount staining with periodic acid-Schiff stain. (125)I-labelled pTFF2 was given orally to rats, and tissues were investigated by gamma counting of samples and by autoradiography of paraffin embedded sections.

RESULTS

pTFF2 accelerated gastric ulcer healing after both oral and subcutaneous administration. Duodenal ulcers were aggravated by both treatments. After oral administration of (125)I-pTFF2, intact peptide was recovered from the superficial part of the mucus layer in the stomach; it passed through the small intestine but was degraded in the caecum. Only a minor part of the labelled pTFF2 entered the colon and was excreted in the faeces. Most of the label was excreted in the urine.

CONCLUSIONS

Oral as well as parenteral pTFF2 accelerates the healing of gastric ulceration and aggravates duodenal ulcers. Oral pTFF2 binds to the mucus layer of the stomach and the small intestine but does not reach the colonic mucosa.

Temporal changes in TFF3 expression and jejunal morphology during methotrexate-induced damage and repair

Trefoil factor TFF3 has been implicated in intestinal protection and repair. This study investigated the spatiotemporal relationship between TFF3 expression and morphological changes during intestinal damage and repair in a rat model of methotrexate-induced small intestinal mucositis. Intestinal tissues from rats with mucositis were collected daily for 10 days. Mucosal damage was characterized by an initial decrease in cell proliferation resulting in crypt loss, villus atrophy, and depletion of goblet cells, followed by hyperproliferation that lead to crypt and villus regeneration and mucous cell repopulation. TFF3 mRNA levels increased marginally during histological damage, and the cell population expressing TFF3 mRNA expanded from the usual goblet cells to include some nongoblet epithelial cells before goblet cell repopulation. TFF3 peptide, however, was depleted during histological damage and normalized during repair, mirroring the disappearance and repopulation of goblet cells. Although there is no temporal relationship between TFF3 levels and crypt hyperproliferation, confirming the nonmitogenic nature of TFF3, the coincidental normalization of TFF3 peptide with repopulation of goblet cells and mucin production after proliferative overshoot suggests that TFF3 may play a role in the remodeling phase of repair.

Intestinal overexpression of EGF in transgenic mice enhances adaptation after small bowel resection

The effect of direct intestinal overexpression of epidermal growth factor (EGF) on postresection adaptation has been investigated by the production of transgenic mouse lines. A murine pro-EGF cDNA construct was produced, and expression of the EGF construct was targeted to the small intestine with the use of the rat intestinal fatty acid-binding protein promoter. An approximately twofold increase in intestinal EGF mRNA and protein was detected in heterozygous mice. No changes in serum EGF levels were noted. Except for a slightly shortened small intestine, no other abnormal phenotype was observed. Intestinal adaptation (increases in body weight, DNA, protein content, villus height, and crypt depth) was markedly enhanced after a 50% proximal small bowel resection in transgenic mice compared with nontransgenic littermates. This transgenic mouse model permits the study of intestinal adaptation and other effects of EGF in the small intestine in a more physiological and directed manner than has been previously possible. These results endorse a direct autocrine/paracrine mechanism for EGF on enterocytes as a means to enhance adaptation.

The trefoil peptides TFF2 and TFF3 are expressed in rat lymphoid tissues and participate in the immune response

Members of the trefoil factor (TFF) family are mucin-associated polypeptides that are expressed along the entire length of the gastrointestinal tract. TFFs have been proposed to play a role in mucosal defence through both protective and reparative mechanisms. The potential relationship between TFFs and mucins in non-gut glycoprotein-secreting epithelia has not been fully explored. In the present study we identified TFF2 and TFF3 mRNA and peptide in rat lymphoid tissues, demonstrated that TFF peptide expression in rat spleen increased 1.5- to 3-fold following experimental induction of the immune response, and showed that hTFF2 and hTFF3 (1-5 mg/ml) stimulated migration of human monocytes. Our data suggest that TFFs may in part be involved in the repair of injury through the modulation of the inflammatory response.

The trefoil peptide TFF1 inhibits the growth of the human gastric adenocarcinoma cell line AGS

TFF1 is a 60-amino acid peptide produced in normal gastric mucosa which forms dimers spontaneously. Tumours of patients with gastric cancer usually have reduced TFF1 levels and disruption of the TFF1 gene causes animals to develop gastric adenomas and carcinomas. The effect of normal sequence human recombinant TFF1 and an analogue (Cys(58)-->Ser(58)), which is unable to dimerize, on the proliferation and morphology of the human gastric adenocarcinoma cell line AGS was therefore investigated. Proliferation, assessed by total cell number and [methyl-(3)H]thymidine incorporation, was reduced by dimeric TFF1 in a dose-dependent manner. Monomeric TFF1 also reduced proliferation but was less potent than the dimeric form. It is concluded that TFF1 may be an important controller of gastric cell proliferation, that dimerization of TFF1 is important in this effect, and that the reduced levels of TFF1 seen in gastric cancer may be of clinical relevance.

Trefoil peptides and surgical disease

BACKGROUND

Trefoil peptides are a family of small proteins that are expressed in a site-specific fashion by certain epithelial tissues. These peptides appear to be important in mucosal healing processes and in neoplastic disease.

METHODS

This manuscript reviews the relevant literature obtained by an extensive text word search of the Medline database and a manual search of references from the articles identified.

RESULTS AND CONCLUSION

Trefoil peptides are aberrantly expressed by a wide range of human carcinomas and gastrointestinal inflammatory conditions. They impart protection from injury to the gastrointestinal mucosa by possible interaction with mucin glycoproteins. Trefoil peptides influence epithelial cell migration and mucosal restitution following injury. In the future, serum levels of trefoil peptides might be used as markers for both neoplastic and inflammatory diseases. In addition, novel therapies based on such peptides might be used for gastrointestinal inflammatory conditions and to accelerate repair of the gastrointestinal mucosa after surgery.

Intestinal trefoil factor binds to intestinal epithelial cells and induces nitric oxide production: priming and enhancing effects of mucin

Intestinal trefoil factor (ITF or TFF3), NO and epithelium-associated mucin have important roles in sustaining mucosal integrity in the gastrointestinal tract. In the present study we examined ITF-binding molecules on IEC-18 cells (an intestinal epithelial cell line) with the use of flow cytometry and localized these molecules on the cell surface by confocal microscopy. Furthermore, we studied the interaction of mucin and ITF and their co-operative effect on NO production by the epithelium. Stimulation of cells with mucin (5 mg/ml) for 90 min resulted in a 5-fold increase in ITF binding. Treatment of IEC-18 cells with actinomycin D or cycloheximide attenuated mucin-enhanced ITF binding. Ligand blot analysis confirmed the induction of ITF-binding protein in IEC-18 cells by mucin. These results indicate that transcriptional and translational mechanisms are involved in the effect of mucin. Treatment with ITF overnight resulted in a low level of nitrite production by the cells, a 5-fold increase over control, in a concentration-dependent manner. ITF-induced NO production was attenuated by 1400W, a selective type II nitric oxide synthase (NOS2) inhibitor. By immunoblotting we found that NOS2 was up-regulated by ITF treatment. Priming IEC-18 cells with mucin for 90 min enhanced the effect of ITF on NO production, suggesting that the up-regulation of ITF-binding molecules by mucin might be physiologically relevant. Taken together, these observations indicate (1) that ITF-binding molecules that are up-regulated by mucin exist on the intestinal epithelial surface, and (2) that ITF modulates epithelial NO production via the NOS2 pathway, which is enhanced by mucin.

Intestinal trefoil factor binds to intestinal epithelial cells and induces nitric oxide production: priming and enhancing effects of mucin

Intestinal trefoil factor (ITF or TFF3), NO and epithelium-associated mucin have important roles in sustaining mucosal integrity in the gastrointestinal tract. In the present study we examined ITF-binding molecules on IEC-18 cells (an intestinal epithelial cell line) with the use of flow cytometry and localized these molecules on the cell surface by confocal microscopy. Furthermore, we studied the interaction of mucin and ITF and their co-operative effect on NO production by the epithelium. Stimulation of cells with mucin (5 mg/ml) for 90 min resulted in a 5-fold increase in ITF binding. Treatment of IEC-18 cells with actinomycin D or cycloheximide attenuated mucin-enhanced ITF binding. Ligand blot analysis confirmed the induction of ITF-binding protein in IEC-18 cells by mucin. These results indicate that transcriptional and translational mechanisms are involved in the effect of mucin. Treatment with ITF overnight resulted in a low level of nitrite production by the cells, a 5-fold increase over control, in a concentration-dependent manner. ITF-induced NO production was attenuated by 1400W, a selective type II nitric oxide synthase (NOS2) inhibitor. By immunoblotting we found that NOS2 was up-regulated by ITF treatment. Priming IEC-18 cells with mucin for 90 min enhanced the effect of ITF on NO production, suggesting that the up-regulation of ITF-binding molecules by mucin might be physiologically relevant. Taken together, these observations indicate (1) that ITF-binding molecules that are up-regulated by mucin exist on the intestinal epithelial surface, and (2) that ITF modulates epithelial NO production via the NOS2 pathway, which is enhanced by mucin.

Bovine colostrum is a health food supplement which prevents NSAID induced gut damage

BACKGROUND

Non-steroidal anti-inflammatory drugs (NSAIDs) are effective for arthritis but cause gastrointestinal injury. Bovine colostrum is a rich source of growth factors and is marketed as a health food supplement.

AIMS

To examine whether spray dried, defatted colostrum or milk preparations could reduce gastrointestinal injury caused by indomethacin.

METHODS

Effects of test solutions, administered orally, were examined using an indomethacin restraint rat model of gastric damage and an indomethacin mouse model of small intestinal injury. Effects on migration of the human colonic carcinoma cell line HT-29 and rat small intestinal cell line RIE-1 were assessed using a wounded monolayer assay system (used as an in vitro model of wound repair) and effects on proliferation determined using [3H]thymidine incorporation.

RESULTS

Pretreatment with 0.5 or 1 ml colostral preparation reduced gastric injury by 30% and 60% respectively in rats. A milk preparation was much less efficacious. Recombinant transforming growth factor beta added at a dose similar to that found in the colostrum preparation (12.5 ng/rat), reduced injury by about 60%. Addition of colostrum to drinking water (10% vol/vol) prevented villus shortening in the mouse model of small intestinal injury. Addition of milk preparation was ineffective. Colostrum increased proliferation and cell migration of RIE-1 and HT-29 cells. These effects were mainly due to constituents of the colostrum with molecular weights greater than 30 kDa.

CONCLUSIONS

Bovine colostrum could provide a novel, inexpensive approach for the prevention and treatment of the injurious effects of NSAIDs on the gut and may also be of value for the treatment of other ulcerative conditions of the bowel.

Intestinal trefoil factor binds to intestinal epithelial cells and induces nitric oxide production: priming and enhancing effects of mucin

Intestinal trefoil factor (ITF or TFF3), NO and epithelium-associated mucin have important roles in sustaining mucosal integrity in the gastrointestinal tract. In the present study we examined ITF-binding molecules on IEC-18 cells (an intestinal epithelial cell line) with the use of flow cytometry and localized these molecules on the cell surface by confocal microscopy. Furthermore, we studied the interaction of mucin and ITF and their co-operative effect on NO production by the epithelium. Stimulation of cells with mucin (5 mg/ml) for 90 min resulted in a 5-fold increase in ITF binding. Treatment of IEC-18 cells with actinomycin D or cycloheximide attenuated mucin-enhanced ITF binding. Ligand blot analysis confirmed the induction of ITF-binding protein in IEC-18 cells by mucin. These results indicate that transcriptional and translational mechanisms are involved in the effect of mucin. Treatment with ITF overnight resulted in a low level of nitrite production by the cells, a 5-fold increase over control, in a concentration-dependent manner. ITF-induced NO production was attenuated by 1400W, a selective type II nitric oxide synthase (NOS2) inhibitor. By immunoblotting we found that NOS2 was up-regulated by ITF treatment. Priming IEC-18 cells with mucin for 90 min enhanced the effect of ITF on NO production, suggesting that the up-regulation of ITF-binding molecules by mucin might be physiologically relevant. Taken together, these observations indicate (1) that ITF-binding molecules that are up-regulated by mucin exist on the intestinal epithelial surface, and (2) that ITF modulates epithelial NO production via the NOS2 pathway, which is enhanced by mucin.

Growth factors in inflammatory bowel disease

The pathogenesis of both ulcerative colitis and Crohn's disease is unknown but these forms of inflammatory bowel disease (IBD) may be associated with an inability of the intestinal mucosa to protect itself from luminal challenges and/or inappropriate repair following intestinal injury. Numerous cell populations regulate these broad processes through the expression of a complex array of peptides and other agents. Growth factors can be distinguished by their actions regulating cell proliferation. These factors also mediate processes such as extracellular matrix formation, cell migration and differentiation, immune regulation, and tissue remodeling. Several families of growth factors may play an important role in IBD including: epidermal growth factor family (EGF) [transforming growth factor alpha (TGF alpha), EGF itself, and others], the transforming growth factor beta (TGF beta) super family, insulin-like growth factors (IGF), fibroblast growth factors (FGF), hepatocyte growth factor (HGF), trefoil factors, platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and others. Collectively these families may determine susceptibility of IBD mucosa to injury and facilitate tissue repair.

Growth factors in inflammatory bowel disease

The pathogenesis of both ulcerative colitis and Crohn's disease is unknown but these forms of inflammatory bowel disease (IBD) may be associated with an inability of the intestinal mucosa to protect itself from luminal challenges and/or inappropriate repair following intestinal injury. Numerous cell populations regulate these broad processes through the expression of a complex array of peptides and other agents. Growth factors can be distinguished by their actions regulating cell proliferation. These factors also mediate processes such as extracellular matrix formation, cell migration and differentiation, immune regulation, and tissue remodeling. Several families of growth factors may play an important role in IBD including: epidermal growth factor family (EGF) [transforming growth factor alpha (TGF alpha), EGF itself, and others], the transforming growth factor beta (TGF beta) super family, insulin-like growth factors (IGF), fibroblast growth factors (FGF), hepatocyte growth factor (HGF), trefoil factors, platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and others. Collectively these families may determine susceptibility of IBD mucosa to injury and facilitate tissue repair.

Modes of epithelial cell death and repair in Sjögren's syndrome (SS)

We evaluated possible modes of epithelial cell destruction and restoration in minor salivary gland biopsies from patients with SS. Minor salivary gland biopsies from 10 primary Sjögren's syndrome (pSS) patients and eight control individuals were evaluated by immunohistochemical staining for the expression of apoptosis-related molecules, substances released by activated cytotoxic T cells, as well as proteins involved in epithelial cell repair. The results were analysed by computer screen analysis and they were expressed as average percentages. Apoptosis-promoting molecules, Fas antigen and Fas ligand were observed in ductal and acinar epithelial cells as well as in infiltrating mononuclear cells of minor salivary glands from SS patients in comparison with control biopsies. Bax protein, which acts as a death-promoter message, was expressed in the ductal and acinar epithelial cells and in mononuclear infiltrating cells of SS patients compared with control individuals, while Bcl-2, an inhibitor of apoptosis, was primarily found in the lymphocytic infiltrates. In situ DNA fragmentation assay (TUNEL) revealed that epithelial cells were apoptotic in patients with SS compared with control subjects. Immunohistochemical staining for perforin and granzyme B, released from granules of activated cytotoxic lymphocytes, revealed their presence in lymphocytic infiltrates of patients with SS compared with control biopsies. pS2, a member of the trefoil protein family which functions as promoter of epithelial cell repair and cell proliferation, was expressed in epithelial cells in biopsies from SS patients. These studies suggest that the functional epithelium of minor salivary glands in patients with SS appears to be influenced by both intrinsic and extrinsic mechanisms of destruction, while a defensive mechanism of epithelial restoration seems to be active.

Osmotic changes and ethanol modify TFF gene expression in gastrointestinal cell lines

The gastrointestinal tract is exposed to environmental insult as a result of food intake or in pathological conditions such as diarrhoea, and is therefore protected by the mucus layer. As part of it, trefoil peptides (TFFs) are able to modify the visco-elastic properties of the mucus, protect against experimental ulceration, and promote repair of the epithelia. We investigated, using transient reporter gene assays and RT-PCR in the gastric carcinoma cell line MKN45 and colon carcinoma cell lines LS174T and HT29, whether ethanol and osmotic changes can modify transcriptional activity of TFFs. In a mild hypotonic environment (200 mosmol/l) all three TFF genes were up-regulated by at least a factor of 2. In hypertonic medium (400 mosmol/ll), TFF1 and TFF3 were down-regulated, whereas TFF2 was up-regulated by elevated concentrations of sodium or chloride in MKN45. Raising the osmolality by ethanol resulted in an up-regulation of TFF3 in both colon cell lines but not in the gastric cell line. We conclude that alteration in TFF gene expression is a response of gut epithelia to deal with osmotic forces and ethanol.

Future trends in the development of safer nonsteroidal anti-inflammatory drugs

Gastrointestinal (GI) adverse events, ranging from mild to life-threatening, are well-recognized sequelae to nonsteroidal anti-inflammatory drug (NSAID) use. Recent improvements in our knowledge of the mechanisms responsible for NSAID-associated gastropathy have enabled several experimental approaches to decreasing the risk of these events. Whereas such strategies as preassociation of NSAIDs to zwitterionic phospholipids to prevent NSAID-mucosal interactions and concomitant administration of trefoil peptides to stimulate mucosal defense pathways represent novel approaches, their clinical feasibility remains to be determined. Other strategies that appear more immediately promising in the reduction of NSAID-associated GI toxicity are the coupling of NSAIDs to nitric oxide (NO)-releasing compounds and the introduction of NSAIDs that are preferential or specific for cyclo-oxygenase-2 (COX-2), the isoform implicated in the inflammatory response. Clinical trials of several specific COX-2 inhibitors, as well as European clinical data for a preferential COX-2 inhibitor, meloxicam, suggest that COX-2 inhibitors provide an advantage over standard NSAIDs in terms of GI tolerability. However, as recent observations have implicated COX-2 as an integral component in the maintenance of physiologic homeostasis, careful scrutiny of both the beneficial and the deleterious effects of the selective COX-2 inhibitors is requisite before their approval and widespread use. Furthermore, based on the physiologic importance of COX-2, the preferential inhibitors may ultimately prove to represent the optimal compromise for the treatment of various arthritides.

Growth factors and the gastrointestinal tract

This paper reviews areas of interest in gut mucosal growth factor physiology. Several epidermal growth factor (EGF)-like peptides (EGF, transforming growth factor [TGF]-alpha, heparin-binding EGF-like peptide, amphiregulin, and betacellulin) have been identified in the gut, EGF is produced by the salivary glands and is present in milk. It may act on the mucosa from the lumen as a surveillance peptide promoting mucosal repair. A stem-cell-derived "ulcer-associated cell lineage" develops adjacent to ulcers and produces EGF, which may play a role in ulcer healing. TGF-alpha is expressed by villus enterocytes and may have an important role in mucosal healing. The Trefoil peptides (pS2, spasmolytic polypeptide, intestinal trefoil factor) are protease resistant molecules secreted by mucin cells throughout the gut, with a role in mucosal healing. The TGF-beta family inhibit cell proliferation, and promote cell differentiation. TGF-beta has a gradient of expression along the crypt villus axis, with maximum production at the villus tip. It is suspected that it may prevent cell proliferation and support differentiation of villus enterocytes. Hepatocyte growth factor is a multifunctional growth factor expressed in many tissues, including the gastrointestinal tract. It has a role in organogenesis. Intestinal adaptation is highly dependent on enteral nutrition, and it is likely that growth factors are involved in adaptation. Little is known, however, about interactions between nutrients and growth factors. Milk contains a range of potentially important growth factors. Their biological significance is uncertain, and this is an area of active research.

Molecular cloning and characterization of murine Mpgc60, a gene predominantly expressed in the intestinal tract

We have isolated from mouse intestine a full-length cDNA clone that encodes an 86-amino acid precursor protein containing a 26-amino acid signal sequence. As deduced from its sequence, the mature 60-aa protein named MPGC60 belongs to the Kazal type of secreted trypsin inhibitors. The MPGC60 peptide has 58% homology with the PEC-60 peptide isolated from pig intestine. In the gut of adult mice, an increasing rostrocaudal gradient in MPGC60 mRNA levels was observed by Northern analysis. In situ hybridization analysis demonstrated strong Mpgc60 expression in Paneth cells and in a subset of goblet cells in the differentiated gut. During postnatal differentiation of the gut, a strong increase in Mpgc60 expression was detected in both small and large intestine. However, in small intestine activation of the Mpgc60 gene occurred earlier than in the large intestine. Apart from the intestinal tract, MPGC60 mRNA was also detectable in the mesenchyme surrounding the uterine epithelium and in endothelia of some blood vessels. However, in contrast to the situation observed in pig, no Mpgc60 expression was detectable by Northern, in situ and reverse transcriptase polymerase chain reaction (RT-PCR) analysis in cells of the immune system, that is, in monocytes, macrophages, peripheral blood and in spleen. Northern blot analysis on mRNA isolated from porcine and murine intestine showed a single transcript in mouse, but several transcripts in pig. Southern blot and fluorescent in situ hybridisation (FISH) analysis demonstrated the presence of a single gene situated in band A of chromosome 4. This region is syntenic with human chromosome regions 6q, 8q and 9p. The gene responsible for human hereditary mixed polyposis syndrome has been localized to human 6q. This raises the possibility that Mpgc60 is a candidate gene for this human disorder.

The pS2/TFF1 trefoil factor, from basic research to clinical applications

pS2/TFF1 trefoil factor is normally expressed in the stomach, and is found ectopically in gastrointestinal inflammatory disorders and in various carcinomas. It is involved in stomach ontogenesis and in the maintenance of the integrity of the mucosa, and may represent a pharmacological tool for prevention and healing of gastrointestinal ulcerations. In breast cancer, it can be used to select patients suitable for hormone therapy. pS2/TFF1 is a pleiotropic factor involved in mucin polymerization, cell motility, cell proliferation and/or differentiation, and possibly in the nervous system.

Distribution and metabolism of intravenously administered trefoil factor 2/porcine spasmolytic polypeptide in the rat

BACKGROUND

Trefoil peptides are secreted by mucus producing cells in the gastrointestinal tract and are supposed to be involved in oligomerisation processes of the mucin glycoproteins in the lumen. Endocrine functions have also been suggested.

AIMS

To target possible binding sites for iodine-125 labelled porcine spasmolytic polypeptide (pSP) in an in vivo rat model.

METHODS

125I-pSP was given by intravenous injection to female Sprague-Dawley rats. The distribution of 125I-pSP was assessed by gamma counting of samples of organs and by autoradiography of paraffin wax embedded sections. The degradation of 125I-pSP was studied by trichloroacetic acid precipitation, and the saturability of binding by administration of excess unlabelled peptide.

RESULTS

125I-pSP was taken up in the kidneys and the gastrointestinal tract and was excreted almost unmetabolised in the urine. In the stomach, it could be displaced by unlabelled pSP in a dose dependent manner. Autoradiography showed grains in mucous neck cells, parietal cells, the mucus layer, and the pyloric glands of the stomach; in Brunner's glands and the Paneth cells in the small intestine; and in cells in the lower part of the crypts in the colon.

CONCLUSIONS

125I-pSP from the circulatory system is taken up by mucus producing cells in the gastrointestinal tract. The binding can be displaced by non-radioactive pSP, suggesting the presence of a receptor.

Dimerization of human pS2 (TFF1) plays a key role in its protective/healing effects

Human pS2 (trefoil factor family 1, TFF1), a 60-amino acid member of the trefoil peptide family, forms dimers via Cys58 and may stimulate gut repair. The effects of dimeric pS2-TFF1 and monomeric pS2-TFF1 (Cys58 replaced by Ser58) were compared in models of wound healing. Rats given dimeric pS2-TFF1 at 25 and 50 micrograms/kg per h had 50 per cent and 70 per cent reduction in gastric damage induced respectively by indomethacin (20 mg/kg subcutaneously) and restraint (P < 0.01). Monomeric pS2-TFF1, at the same doses, was significantly less effective at reducing injury (about half the amount of protection, P < 0.01 vs. same doses of dimeric). The rate of migration of cells at the leading edge of wounded monolayers of the human colonic cell line HT29 was increased by addition of dimeric or monomeric forms of pS2-TFF1 (0.65-325 micrograms/ml). Dimeric pS2-TFF1 had a greater effect than the monomeric form at all doses tested (P < 0.05). Cell migration induced by pS2-TFF1 was blocked by a pS2-TFF1 antibody, but not by a transforming growth factor beta neutralizing antibody. pS2-TFF1 did not influence cell proliferation as assessed by thymidine incorporation. The increased biological effects of dimeric pS2-TFF1 might be due to direct interaction of Cys58 with a putative trefoil receptor or, more likely, dimerization of pS2-TFF1 might stabilize the interaction with its receptor. This may involve a bivalent interaction of residues on the surfaces of the two trefoil domains.

Mice lacking secretory phospholipase A2 show altered apoptosis and differentiation with Helicobacter felis infection

BACKGROUND & AIMS

Infection with Helicobacter pylori uniformly leads to a chronic superficial gastritis that may progress to atrophic gastritis, a premalignant process. A mouse model of Helicobacter felis infection was used to study possible genetic determinants of the response to infection.

METHODS

Three inbred mouse strains with known secretory phospholipase A2 (sPLA2) genotypes [BALB/c (+/+), C3H/HeJ (+/+), and C57BL/6 (-/-)] were orally infected with H. felis and examined longitudinally using routine histology, immunocytochemistry, electron microscopy, proliferating cell nuclear antigen, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling, and Northern and Western blot studies.

RESULTS

Only the C57BL/6 strain showed increased gastric fundic proliferation and apoptosis in response to infection. In addition, the C57BL/6 mouse showed a marked loss of parietal and chief cells, along with a marked expansion of an aberrant gastric mucous cell lineage that stained positive for spasmolytic polypeptide. In contrast, no significant change in these cell types was observed in BALB/c and C3H/HeJ strains. Increased expression of sPLA2 was observed in BALB/c and C3H/HeJ after H. felis infection, whereas sPLA2 expression was absent in C57BL/6 mice.

CONCLUSIONS

H. felis infection leads to increased apoptosis and altered cellular differentiation in the C57BL/6 mouse, a strain that lacks gastric sPLA2 expression. Because sPLA2 has been identified recently as the MOM1 (modifier of MIN) locus that influences polyp formation in the colon, these studies suggest that sPLA2 may also influence the gastric epithelial response to Helicobacter infection.

Oral human spasmolytic polypeptide protects against aspirin-induced gastric injury in rats

Spasmolytic polypeptide (SP) is a member of the trefoil peptide family; gut peptides that participate in the protection and repair of the gastric mucosa. Previous studies have failed to agree on the mode of action of human SP (hSP). We investigated the effect of orally administered human SP on the protection and repair of rat gastric mucosa in an established in vivo model of damage induced by the non-steroidal anti-inflammatory drug aspirin (ASA). The integrity of the gastric mucosa was quantified in four ways: the temporal change in transmucosal potential difference (PD), area of macroscopic damage by planimetry, relative area of microscopic damage by histological morphometry, and the number of deep erosions per centimetre of mucosa sectioned. Human SP (200 micromol/L) administered orally before, or in combination with ASA significantly reduced the fall in PD, the area of microscopic damage, and the number of deep erosions (P < 0.05). The area of macroscopic damage was significantly reduced only in rats where hSP (200 micromol/L) was given in conjunction with ASA (P < 0.05). Human spasmolytic polypeptide (70 or 200 micromol/L) administered after ASA failed to hasten the re-establishment of PD or stimulate the repair of the gastric mucosa in the 90 min following injury (P > 0.05, compared with ASA alone). We conclude that hSP prevents gastric mucosal damage by its topical actions, probably by a rapid interaction with luminal mucins or epithelial cells, but fails to stimulate early restitution in the injured gastric mucosa.

Trefoil peptides: mitogens, motogens, or mirages?

Healing of mucosal damage occurs in two phases: restitution of mucosal integrity followed by remodeling with recreation of mucosal architecture. Models of these phenomena include cryoprobe-induced ulcers, NSAID lesions, and surgical anastomosis. Three trefoil peptides are expressed constitutively by epithelial cells in specific regions of the GI tract: pS2 (gastric), spasmolytic polypeptide (SP, gastric and Brunner's glands), and intestinal trefoil factor (ITF, goblet cells). Altered expression occurs in reparative epithelium and adjacent mucosa. In cryoprobe ulceration, rSP mRNA abundance doubles within 2 h, with rITF mRNA becoming detectable after 2-3 days. TGF-alpha and EGF mRNAs do not increase as rapidly as rSP or to the same extent as rITF. Indomethacin lesions of gastric mucosa show increased SP immunoreactivity deep in damaged glands within hours. Surgical anastomotic damage increases rITF mRNA levels at the ulcer edge and sometimes rSP mRNA and peptide in para-anastomotic crypts. Initially, trefoil peptides were viewed as mitogens. However, they are in fact motogens, able to promote cell migration, and may possibly be morphogens. Interactions occur between trefoils and other wound healing peptides (FGFs and EGF). Trefoil peptides appear to be of considerable importance to mucosal healing and might constitute a biologic target of therapeutic relevance.

Homodimerization and hetero-oligomerization of the single-domain trefoil protein pNR-2/pS2 through cysteine 58

The single-domain human trefoil proteins [pNR-2/pS2 and human intestinal trefoil factor (hITF)] have seven cysteine residues, of which six are involved in maintaining the structure of the trefoil domain. The seventh does not form part of the trefoil domain and is located three residues from the C-terminus. The ability of the pNR-2/pS2 single trefoil domain protein to dimerize was examined by using recombinant protein with either a cysteine or a serine residue at this position by equilibrium ultracentrifugation, laser-assisted desorption MS, gel filtration and PAGE. pNR-2/pS2 Cys58 formed dimers, whereas pNR-2/pS2 Ser58 did not. Experiments in which the dimer was treated with thiol agents demonstrated that the dimer was linked via a disulphide bond and that the intermolecular disulphide bond was more susceptible to reduction than the intramolecular disulphide bonds. To examine whether dimeric pNR-2/pS2 was secreted by oestrogen-responsive breast cancer cells, which are known to express pNR-2/pS2 mRNA, conditioned medium was separated on non-denaturing polyacrylamide gels, transferred to PVDF membrane and reacted with antiserum against pNR-2/pS2. Monomeric and dimeric pNR-2/pS2 were detected but the majority of the protein reactivity was associated with a larger protein. Treatment of this protein with thiol agents suggested that it is an oligomer containing pNR-2/pS2 linked to another protein by a disulphide bond. These studies suggest that the biological action of pNR-2/pS2 single-domain trefoil protein might involve the formation of homodimers or oligomers with other proteins.

Trefoil proteins: their role in normal and malignant cells

The three human trefoil proteins pS2, human intestinal trefoil factor (hITF), and human spasmolytic polypeptide (hSP) are expressed principally in the mucosa of the gastrointestinal tract. They are also expressed in a variety of other normal tissues and tumours. This review discusses the pattern of expression of trefoil proteins in cancer, current views on the biological functions of trefoil proteins, and the way in which the expression of trefoil proteins may influence the behaviour of cancer cells.

Characterization of a putative receptor for intestinal trefoil factor in rat small intestine: identification by in situ binding and ligand blotting

Intestinal trefoil factor (ITF), a small peptide secreted by intestinal goblet cells, maintains mucosal integrity and promotes epithelial wound healing. Although ITF has been cloned, the detailed mechanism by which ITF interacts with intestinal epithelium remains elusive. In the present study, we expressed mature rat ITF (rITF) with pXa (a prokaryotic expression vector) in Escherichia coli to generate a biotinylated rITF fusion protein (bTag-ITF). By using bTag-ITF probe, we identified ITF binding cells in the crypts of the small intestine and mucous cells of the region of gastric glands. Using a ligand blotting technique, we further characterized a 50 kDa glycosylated protein from the membrane fraction of the small intestine, which bound to bTag-ITF. Our data suggest that this 50 kDa membrane glycoprotein is a putative receptor for ITF in the gastrointestinal tract.

Expression of human intestinal trefoil factor in malignant cells and its regulation by oestrogen in breast cancer cells

Human intestinal trefoil factor (hITF) is a small cysteine-rich protein expressed in the gastrointestinal (GI) tract. Its sequence is related to that of other trefoil peptides including the pNR-2/pS2 protein, which is regulated by oestrogen in breast cancer. This study was designed to investigate whether hITF is expressed in human carcinoma cells. cDNA was obtained by reverse transcription-polymerase chain reaction (RT-PCR) of gastric mucosal RNA and sequenced, establishing that this mRNA is expressed in the stomach. Expression of hITF was detected in a proportion of cell lines derived from malignancies of the GI tract, in hepatocellular carcinoma cells, and at highest levels in a small cell lung carcinoma cell line. Amongst breast cancer cell lines, it was expressed in all the oestrogen-responsive but in none of the oestrogen-nonresponsive breast cancer cell lines. The possibility that hITF expression in breast cells is controlled by oestradiol was then tested. Oestradiol treatment increased hITF expression between three- and ten-fold in the oestrogen-responsive breast cancer cell lines, demonstrating that, like pNR-2/pS2, hITF is regulated by oestrogen in breast cancer cells. Tamoxifen inhibited the induction of hITF expression by oestradiol but tamoxifen alone was a partial oestrogen agonist for hITF expression. These results show that hITF is expressed, sometimes ectopically, in several human malignancies, which suggests that trefoil peptides may have a more general role in tumourigenesis than hitherto appreciated. That the expression of hITF is regulated by oestrogen in breast cancer cells suggests that hITF expression may provide a novel marker for oestrogen responsiveness in breast cancer.

Rolling in the clover: trefoil factor family (TFF)-domain peptides, cell migration and cancer

Trefoil factor family (TFF)-domain peptides 1-3 are mucin-associated molecules, largely found in epithelia of gastrointestinal tissues. Structurally similar, resistant to enzymatic degradation, they are up-regulated around areas of epithelial damage such as ulcers. Transgenic expression or exogenous peptide ameliorates or prevents gastric mucosal damage due to indomethacin and some are rapidly up-regulated after cryogenic burns. A role in promoting cell migration is strongly suggested. Knockout mice lacking TFF1 or TFF3 show significant pathology, with the former developing gastric tumours. A recent Conference Philippe Laudat agreed upon a new nomenclature for these peptides.

Involvement of DNA methylation in the control of the expression of an estrogen-induced breast-cancer-associated protein (pS2) in human breast cancers

pS2 gene has been used to investigate the relationship between alterations of DNA methylation patterns in human tumors and gene expression. The expression of pS2, which is transcriptionally controlled by estrogens in breast cancer cell lines, is restricted to estrogen-receptor-rich human breast tumors. We found that the CCGG site within the promoter/enhancer sequence of pS2 was hypomethylated in estrogen-receptor-rich breast tumors expressing this gene. The amount of DNA molecules unmethylated at this site was related to the amount of pS2 mRNA detected in the samples. The demethylation of this region, which contains the estrogen responsive element, was confirmed by genomic sequencing. Transient expression of functional human estrogen receptors stimulated the expression of the endogenous pS2 in HeLa cells, but failed, in BT-20 cells, to stimulate expression of this gene. Since the promoter/enhancer region of pS2 is unmethylated in HeLa cells and methylated in BT-20 cells, these data also support the hypothesis that DNA methylation might be involved in the control of pS2 expression.

High-resolution solution structure of human pNR-2/pS2: a single trefoil motif protein

pNR-2/pS2 is a 60 residue extracellular protein, which was originally discovered in human breast cancer cells, and subsequently found in other tumours and normal gastric epithelial cells. We have determined the three-dimensional solution structure of a C58S mutant of human pNR-2/pS2 using 639 distance and 137 torsion angle constraints obtained from analysis of multidimensional NMR spectra. A series of simulated annealing calculations resulted in the unambiguous determination of the protein's disulphide bonding pattern and produced a family of 19 structures consistent with the constraints. The peptide contains a single "trefoil" sequence motif, a region of about 40 residues with a characteristic sequence pattern, which has been found, either singly or as a repeat, in about a dozen extracellular proteins. The trefoil domain contains three disulphide bonds, whose 1-5, 2-4 and 3-6 cysteine pairings form the structure into three closely packed loops with only a small amount of secondary structure, which consists of a short alpha-helix packed against a two-stranded antiparallel beta-sheet. The structure of the domain is very similar to those of the two trefoil domains that occur in porcine spasmolytic polypeptide (PSP), the only member of the trefoil family whose three-dimensional structure has been previously determined. Outside the trefoil domain, which forms the compact "head" of the molecule, the N and C-terminal strands are closely associated, forming an extended "tail", which has some beta-sheet character for part of its length and which becomes more disordered towards the termini as indicated by (15)N{(1)H} NOEs. We have considered the structural implications of the possible formation of a native C58-C58 disulphide-bonded homodimer. Comparison of the surface features of pNR-2/pS2 and PSP, and consideration of the sequences of the other human trefoil domains in the light of these structures, illuminates the possible role of specific residues in ligand/receptor binding.

Gastric mucosa abnormalities and tumorigenesis in mice lacking the pS2 trefoil protein

To determine the function of the pS2 trefoil protein, which is normally expressed in the gastric mucosa, the mouse pS2 (mpS2) gene was inactivated. The antral and pyloric gastric mucosa of mpS2-null mice was dysfunctional and exhibited severe hyperplasia and dysplasia. All homozygous mutant mice developed antropyloric adenoma, and 30 percent developed multifocal intraepithelial or intramucosal carcinomas. The small intestine was characterized by enlarged villi and an abnormal infiltrate of lymphoid cells. These results indicate that mpS2 is essential for normal differentiation of the antral and pyloric gastric mucosa and may function as a gastric-specific tumor suppressor gene.