Trefoil peptides

TFF2, a MUC6-binding lectin stabilizing the gastric mucus barrier and more (Review)

The peptide TFF2 (formerly 'spasmolytic polypeptide'), a member of the trefoil factor family (TFF) containing two TFF domains, is mainly expressed together with the mucin MUC6 in the gastric epithelium and duodenal Brunner's glands. Pathologically, TFF2 expression is observed ectopically during stone diseases, chronic inflammatory conditions and in several metaplastic and neoplastic epithelia; most prominent being the 'spasmolytic polypeptide-expressing metaplasia' (SPEM), which is an established gastric precancerous lesion. TFF2 plays a critical role in maintaining gastric mucosal integrity and appears to restrain tumorigenesis in the stomach. Recently, porcine TFF2 has been shown to interact with the gastric mucin MUC6 and thus stabilize the gastric mucus barrier. On the one hand, TFF2 binds to MUC6 via non-covalent lectin interactions with the glycotope GlcNAcα1→4Galβ1→R. On the other hand, TFF2 is probably also covalently bound to MUC6 via disulfide bridges. Thus, implications for the complex multimeric assembly, cross-linking, and packaging of MUC6 as well as the rheology of gastric mucus are discussed in detail in this review. Furthermore, TFF2 is also expressed in minor amounts in the immune and nervous systems. Thus, similar to galectins, its lectin activity would perfectly enable TFF2 to form multivalent complexes and cross-linked lattices with a plethora of transmembrane glycoproteins and thus modulate different signal transduction processes. This could explain the multiple and diverse biological effects of TFF2 [e.g., motogenic, (anti)apoptotic, and angiogenic effects]. Finally, a function during fertilization is also possible for TFF domains because they occur as shuffled modules in certain zona pellucida proteins.

Mucin production and mucous cell metaplasia in otitis media

Otitis media (OM) with mucoid effusion, characterized by mucous cell metaplasia/hyperplasia in the middle ear cleft and thick fluid accumulation in the middle ear cavity, is a subtype of OM which frequently leads to chronic OM in young children. Multiple factors are involved in the developmental process of OM with mucoid effusion, especially disorders of mucin production resulting from middle ear bacterial infection and Eustachian tube dysfunction. In this review, we will focus on several aspects of this disorder by analyzing the cellular and molecular events such as mucin production and mucous cell differentiation in the middle ear mucosa with OM. In addition, infectious agents, mucin production triggers, and relevant signaling pathways will be discussed.

Effects of recombinant human intestinal trefoil factor on trinitrobenzene sulphonic acid induced colitis in rats

Intestinal trefoil factor (ITF) has been proved to be effective in treatment of ulcerative colitis. However, the mechanisms of it remain unclear. In this study, we observed the effects of combined treatment with 5-aminosalicylic acid (5-ASA) and recombinant human ITF (rhITF) on the expression of Myeloperoxidase (MPO), nuclear factor-κB (NF-κB) and epidermal growth factor (EGF) in trinitrobenzene sulphonic acid (TNBS) induced colitis in rats. Forty Sprague-Dawley (SD) male rats which were induced to distal colitis by the colonic administration of TNBS, were randomly divided into four groups and colonically treated with normal saline (A), 5-ASA (B), rhITF (C), respectively. The macroscopic and histological changes of the colon, activities of MPO, expressions of serum EGF and tissue NF-κB were detected. The results showed that manifestation, colonic damage score and MPO activities of the rats treated with 5-ASA or/and rhITFs were improved, serum EGF production was augmented and expression of tissue NF-κB was down-regulated. Single usage of 5-ASA or rhITF had no significant difference, but combined using of them had more significant and noticeable effects compared to any single treatment. It could be concluded that topical treatment with 5-ASA and rhITF had beneficial effects in treating TNBS-induced colitis of rats and combined treatment was better than single treatment. It was possibly related to suppression of neutrophil infiltration, down-regulation expression of NF-κB and up-regulation expression of EGF.

Trefoil factor family (TFF) peptides and cancer progression

TFF peptides are involved in mucosal maintenance and repair through motogenic and antiapoptotic activities. These peptides are overexpressed during inflammatory processes and cancer progression. They also function as scatter factors, proinvasive and angiogenic agents. Such a divergence is related to the pathophysiological state of tissues submitted to persistent aggressive situations during digestive processes in the normal gastrointestinal tract, inflammatory and neoplastic diseases. In agreement with this model, TFF peptides are connected with multiple oncogenic pathways. As a consequence, the TFF signaling pathways may serve as potential targets in the control of chronic inflammation and progression of human solid tumors.

Preventive effect of hydrotalcite on gastric mucosal injury in rats induced by taurocholate

AIM: To study the preventive effect of hydrotalcite on gastric mucosal injury in rat induced by taurocholate, and to investigate the relationship between the protective mechanism of hydrotalcite and the expression of trefoil factor family 2 (TFF2) mRNA and c-fos protein.

METHODS: Forty five male Wistar rats were randomly divided into hydrotalcite group, ranitidine group and control group. Gastric mucosal injury was induced by introgastric acidified taurocholate. OD value of TFF2 mRNA expression in gastric mucous cells was determined by hybridization and computer image analysis system. OD value of c-fos protein expression in gastric mucous cells was measured by immunohistochemistry and computer image analysis system.

RESULTS: The gross mucosal injury index in hydrotalcite group was significantly lower than that in ranitidine group and control group (8.60 ± 2.20 vs 16.32 ± 4.27, 29.53 ± 5.39; P < 0.05, P < 0.01). The expression level of TFF2 mRNA in hydrotalcite group was markedly higher than that in ranitidine group and control group (0.56 ± 0.09 vs 0.30 ± 0.05, 0.28 ± 0.03, P < 0.05). The OD value of c-fos protein in hydrotalcite group was higher than that in ranitidine group and control group (0.52 ± 0.07 vs 0.31 ± 0.04, 0.32 ± 0.05, P < 0.05).

CONCLUSION: Hydrotalcite can protect gastric mucosal injury in rats induced by taurocholate, which may be related to the increased expression of TFF2 and c-fos protein.

Peptide growth factors in the intestine

A continuously increasing number of regulatory peptides has been demonstrated to be expressed in the intestine and to modulate several functional properties of various intestinal cell populations, including the intestinal epithelium and lamina propria cell populations. These regulatory peptides include members of the epidermal growth factor (EGF) family, the transforming growth factor beta (TGF-beta) family, the insulin-like growth factor (IGF) family, the fibroblast growth factor (FGF) family, the trefoil factor (TFF) family, the colony-stimulating factor (CSF) family, and a few other seemingly unrelated regulatory peptides, such as hepatocyte growth factor (HGF), platelet-derived growth factor (PDGF), and various interleukins, interferons and tumour necrosis factor-related proteins. In addition to the well-known effects on cell proliferation, these regulatory peptide factors regulate several other functional properties of epithelial and other cell populations, such as differentiation, migration, and extracellular matrix deposition and degradation. This review is designed not to discuss all the identified factors in detail but to highlight some of the basic principles of growth factor action in the intestine. It focuses mainly on classical growth factors rather than interleukins and interferons.

Ulcer associated cell lineage glands expressing trefoil peptide genes are induced by chronic ulceration in ileal pouch mucosa

BACKGROUND

Chronic ulcerative conditions in the gastrointestinal tract result in the appearance of the ulcer associated cell lineage (UACL). The glands of this new cell lineage secrete epidermal growth factor, transforming growth factor alpha, and the trefoil factor family (TFF) peptides, which are known to participate in repair processes. Pouchitis is the most frequent complication of ileal pouch-anal anastomosis.

AIM

Our aim was to determine whether the mucosal ulceration present in pouchitis can induce the development of UACL glands.

METHODS

Biopsies from ileal pouches with pouchitis (n=10), healthy pouches (n=5), and normal terminal ileum (n=5) were studied. Expression of TFF mRNA was assessed by in situ hybridisation. TFF1 and TFF2 proteins were localised by immunochemistry.

RESULTS

UACL glands containing TFF1 and TFF2 were observed in six patients with pouchitis. In some glands, there was TFF3 mRNA as has been reported for Crohn's UACL. None of the biopsies from ileal reservoirs without pouchitis showed UACL glands (p<0.05). Neither TFF1 nor TFF2 expression was detected in ileal reservoirs without pouchitis.

CONCLUSION

UACL glands arise de novo in ileal pouch mucosa of patients with pouchitis and express all three TFF peptide genes. Chronic inflammation alone, present in healthy pouches, is not enough to stimulate the growth of the UACL, and additional stimuli consequent on ulceration may be needed.

Dramatic diurnal variation in the concentration of the human trefoil peptide TFF2 in gastric juice

BACKGROUND

TFF2, a member of the trefoil factor family of proteins, is a glycosylated protein of 106 amino acids. It is secreted by gastric antral and pyloric glands and by Brunner's glands of the duodenum. TFF2 is found in high concentrations around sites of ulceration. It stimulates cell motility and is probably the principal cytoprotective trefoil peptide in the stomach.

AIMS

To determine if production of TFF2 follows a circadian rhythm and to measure changes in secretion of TFF2 in response to food intake and during sleep.

SUBJECTS

Young healthy adults were recruited. They were asymptomatic and were not receiving medication. The 24 hour regimen was designed to allow normal stimulation of gastric secretion in response to food intake and sleep. Gastric juice was collected two hourly via a nasogastric tube.

METHODS

Glycosylated and non-glycosylated TFF2 proteins were measured by quantitative western transfer analysis. The results were analysed statistically using SPSS software.

RESULTS

There was a dramatic diurnal variation in the concentration of TFF2. The mean concentration was lowest in the early evening (0.29 microg/ml), increased gradually during the evening, and then sharply during the night to reach 7.9 microg/ml. The ratio of glycosylated to non-glycosylated TFF2 varied and was higher during the night than in the afternoon. pH, total protein, and pepsin concentrations in gastric juice did not vary significantly over 24 hours.

CONCLUSION

The data suggest that diurnal variations in TFF2 secretion occur independently of pepsin and gastric acid secretion. The concentration of glycosylated TFF2 in the gastric lumen falls in response to food intake. TFF2 secretion increases during inactivity and sleep. These results suggest that secretion of TFF2 in the stomach is highest during the night and that the cytoprotective effects of TFF2 on the gastric mucosa occur mainly during sleep.

Mechanisms and modulation of intestinal epithelial repair

The mucosal epithelium of the alimentary tract represents a crucial barrier to a broad spectrum of noxious and immunogenic substances within the intestinal lumen. An impairment of the integrity of the mucosal epithelial barrier is observed in the course of various intestinal disorders including inflammatory bowel diseases (IBD), celiac disease, intestinal infections, and various other diseases. Furthermore, even under physiologic conditions temporary damage of the epithelial surface mucosa may be caused by proteases, residential flora, dietary compounds, or other factors. Generally, the integrity of the intestinal mucosal surface barrier is rapidly reestablished even after extensive destruction because of an enormous regenerative capability of the mucosal surface epithelium. Rapid resealing of the surface epithelium is accomplished by epithelial cell migration, also termed epithelial restitution, epithelial cell proliferation, and differentiation. Healing of the intestinal surface epithelium is regulated by a complex network of highly divergent factors, among them a broad spectrum of structurally distinct regulatory peptides that have been identified within the mucosa of the intestinal tract. These regulatory peptides, conventionally designated as growth factors and cytokines, play an essential role in regulating differential epithelial cell functions to preserve normal homeostasis and integrity of the intestinal mucosa. In addition, a number of other peptide molecules such as extracellular matrix factors and blood clotting factors, and also nonpeptide molecules including phospholipids, shortchain fatty acids, adenine nucleotides, trace elements, and pharmacological agents, have been demonstrated to modulate intestinal epithelial repair mechanisms. Some of these molecules may be released by platelets, adjacent stromal cells, inflammatory cells, or injured epithelial and nonepithelial cells and may play an important role in the modulation of intestinal injury. Repeated damage and injury of the intestinal surface are key features of various intestinal disorders including IBD and require constant repair of the epithelium. Enhancement of intestinal repair mechanisms by regulatory peptides or other modulatory factors may provide future approaches for the treatment of diseases that are characterized by injuries of the epithelial surface.

Somatic mutations of the trefoil factor family 1 gene in gastric cancer

BACKGROUND & AIMS

There is increasing evidence that trefoil factor family 1 (TFF1) is a stabilizer of the mucous gel overlying the gastrointestinal mucosa that provides a physical barrier against various noxious agents. TFF1 knockout mice developed multiple gastric adenomas and carcinomas, suggesting that TFF1 is a gastric-specific tumor-suppressor gene.

METHODS

We analyzed the somatic mutations and loss of heterozygosity (LOH) of the TFF1 gene using an intragenic polymorphic marker in 61 gastric tumors. The expression pattern of TFF1 was also examined by immunohistochemistry.

RESULTS

We detected a total of 8 somatic mutations-1 (5.5%) of 18 adenomas and 7 (16.3%) of 43 carcinomas-that were all missense mutations confined to the loop I and loop II structure of TFF1. We detected LOH in 5 (1 in adenoma and 4 in cancer) of 30 (16.7%) informative gastric tumors with an intragenic polymorphic marker -2 base pairs (bp) upstream of the coding region of the TFF1 gene. Although 2 cases were noninformative, the 7 gastric cancers with mutation seemed to show the loss of the remaining allele except in 1 case, suggesting that TFF1 is a tumor-suppressor gene. We found loss of TFF1 expression in 44.2% of the gastric carcinomas, but there is no correlation between immunoreactivity and genetic alterations of the TFF1 gene.

CONCLUSIONS

These results indicate that genetic alterations of TFF1 may lead to gastric mucosal barrier defects and contribute to the pathogenesis of gastric cancer.

Patterns of expression of trefoil peptides and mucins in gastric polyps with and without malignant transformation

The expression of two trefoil peptides (TFF1 and TFF2) and four mucins (MUC1, MUC2, MUC5AC, and MUC6) was evaluated by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR) in 29 gastric polyps, 10 hyperplastic and 19 adenomatous, eight of which displayed malignant transformation. The aims of this study were to characterize the expression profile of these molecules in each type of polyp and to investigate possible modifications of the profile during the process of malignant transformation. All hyperplastic polyps displayed immunoreactivity for TFF1, MUC5AC, and MUC1 in more than 75 per cent of the cells. In adenomatous polyps, three main phenotypes could be identified: complete gastric phenotype (co-expression of TFF1 and MUC5AC)-nine cases (47.4 per cent); incomplete gastric phenotype (TFF1-positive and MUC5AC-negative)-seven cases (36.8 per cent); non-gastric (intestinal) phenotype (no expression of TFF1 or MUC5AC)-three cases (15.8 per cent). Data yielded by immunohistochemistry and RT-PCR showed a good correlation for both TFF1 and TFF2. One hyperplastic and seven adenomatous polyps with villous architecture displayed foci of diffuse and intestinal-type carcinoma, respectively; in all of these cases, MUC1 expression and signs of gastric differentiation were observed in both the non-malignant and the carcinomatous component. It is concluded that gastric differentiation is a feature of hyperplastic polyps and of a subset of adenomatous polyps which is shared by early carcinomas arising in some of these polyps, regardless of the histological type of polyp and of carcinoma.

Increased expression of HGF and c-met in rat small intestine during recovery from methotrexate-induced mucositis

Chemotherapy or radiotherapy often cause mucosal damage in the gut (gut mucositis) in cancer patients. As a step to investigate mechanisms underlying subsequent intestinal repair, we have examined the expression profiles of hepatocyte growth factor (HGF) and its receptor c-met, two molecules previously implicated in tissue repair, in comparison to the histopathological and proliferative changes in a rat model of methotrexate-induced small intestinal mucositis. Histological analysis of the intestinal specimens revealed crypt loss and villus atrophy with damage maximal on day 5 after methotrexate injection, and normalization of mucosal structure commencing on day 6. Crypt cell proliferation was decreased dramatically on day 3, normalized on day 4 and up-regulated on days 5 and 6. HGF and c-met protein/mRNA expression was up-regulated between days 4 and 7, with the mRNA co-localizing to the crypt and lower villus epithelium. Therefore, following methotrexate injection, a decrease in crypt cell proliferation preceded histological damage, and conversely, crypt cell hyperproliferation preceded mucosal regeneration. Up-regulation of HGF and c-met coincided with crypt hyperproliferation and mucosal recovery, suggesting a role for HGF in intestinal repair following acute injury. The crypt epithelial localization of HGF and c-met implies an autocrine or paracrine mechanism of HGF action.

Cloning of rat betacellulin and characterization of its expression in the gastrointestinal tract

Betacellulin (BTC) is relatively a more recently discovered member of the EGF family of growth factors. As a prelude to its expression and functional studies in rat models of gut damage/repair, we have cloned rat BTC and examined its expression in the gastrointestinal tract. Rat BTC was found to be nearly identical to mouse betacellulin. A single 3 kb mRNA species was detected by Northern blotting, and ribonuclease protection analysis showed that its expression was ubiquitous but low in abundance throughout the gut. BTC mRNA and protein were found expressed in the gastric surface and upper pit epithelium as well as in some cells of gastric glands. In the jejunum, BTC mRNA and protein were localised to the crypt epithelium and in villous goblet cells. In the colon, BTC mRNA and protein were found produced in crypt and surface epithelium as well as in goblet cells. Taken together, the wide spread expression in the gut epithelium and in mucous cells in particular suggests an important and unique role for BTC in the gastrointestinal tract.

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.

Cell proliferation in gastrointestinal mucosa

Gastrointestinal cell proliferation plays an important role in the maintenance of the integrity of the gastrointestinal system. The study of gastrointestinal proliferation kinetics allows a better understanding of the complexity of the system, and also has important implications for the study of gastrointestinal carcinogenesis. Gastrointestinal stem cells are shown to be pluripotential and to give rise to all cell lineages in the epithelium. Carcinogenesis in the colon occurs through sequential mutations, possibly occurring in a single cell--the stem cell.

Patterns of expression of trefoil peptides and mucins in gastric polyps with and without malignant transformation

The expression of two trefoil peptides (TFF1 and TFF2) and four mucins (MUC1, MUC2, MUC5AC, and MUC6) was evaluated by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR) in 29 gastric polyps, 10 hyperplastic and 19 adenomatous, eight of which displayed malignant transformation. The aims of this study were to characterize the expression profile of these molecules in each type of polyp and to investigate possible modifications of the profile during the process of malignant transformation. All hyperplastic polyps displayed immunoreactivity for TFF1, MUC5AC, and MUC1 in more than 75 per cent of the cells. In adenomatous polyps, three main phenotypes could be identified: complete gastric phenotype (co-expression of TFF1 and MUC5AC)-nine cases (47.4 per cent); incomplete gastric phenotype (TFF1-positive and MUC5AC-negative)-seven cases (36.8 per cent); non-gastric (intestinal) phenotype (no expression of TFF1 or MUC5AC)-three cases (15.8 per cent). Data yielded by immunohistochemistry and RT-PCR showed a good correlation for both TFF1 and TFF2. One hyperplastic and seven adenomatous polyps with villous architecture displayed foci of diffuse and intestinal-type carcinoma, respectively; in all of these cases, MUC1 expression and signs of gastric differentiation were observed in both the non-malignant and the carcinomatous component. It is concluded that gastric differentiation is a feature of hyperplastic polyps and of a subset of adenomatous polyps which is shared by early carcinomas arising in some of these polyps, regardless of the histological type of polyp and of carcinoma.

Primary mucinous carcinomas of the skin express TFF1, TFF3, estrogen receptor, and progesterone receptors

Mucinous carcinoma may present at various sites, including the breast and the gastrointestinal tract. Rarely, such tumors arise within the skin. Comparatively, breast lesions are relatively common and usually associated with a good prognosis. When pure, they are typically estrogen (ER) and progesterone receptor (PR) positive and responsive to tamoxifen. The authors studied 12 mucinous carcinomas of the skin and compared the morphology with that of typical mammary lesions. The authors also evaluated for expression of estrogen receptor, progesterone receptor, and the mucus-associated peptides of the trefoil factor family (TFF), TFF1 (formerly pS2) and TFF2 (formerly SP), using immunohistochemistry. The localization of mRNAs for TFF1, TFF2, and TFF3 (formally ITF) was also studied in a subset of three tumors, using in-situ hybridization with S35 labeled riboprobes. The Grimelius stain was used to look for evidence of neuroendocrine differentiation. Eight resembled type A mucinous carcinomas of the breast, two resembled type B, and one had composite features. The 12th was a papillary neoplasm. The two type B tumors exhibited argyrophilia. All showed strong nuclear staining with the estrogen receptor antibody but a more varied pattern with antibodies to progesterone receptor and TFF1. None labeled for TFF2. The detection of TFF1 in mammalian skin is a novel finding. Cutaneous mucinous carcinoma shows strong similarities to its mammary counterpart, including expression of estrogen receptor, TFF1, and TFF3 mRNA. These observations suggest that some mucinous carcinomas of the skin might respond to antiestrogenic therapies.

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.

Aspects of the biology of regeneration and repair in the human gastrointestinal tract

The main pathways of epithelial differentiation in the intestine, Paneth, mucous, endocrine and columnar cell lineages are well recognized. However, in abnormal circumstances, for example in mucosal ulceration, a cell lineage with features distinct from these emerges, which has often been dismissed in the past as 'pyloric' metaplasia, because of its morphological resemblance to the pyloric mucosa in the stomach. However, we can conclude that this cell lineage has a defined phenotype unique in gastrointestinal epithelia, has a histogenesis that resembles that of Brunner's glands, but acquires a proliferative organization similar to that of the gastric gland. It expresses several peptides of particular interest, including epidermal growth factor, the trefoil peptides TFF1, TFF2, TFF3, lysozyme and PSTI. The presence of this lineage also appears to cause altered gene expression in adjacent indigenous cell lineages. We propose that this cell lineage is induced in gastrointestinal stem cells as a result of chronic mucosal ulceration, and plays an important part in ulcer healing; it should therefore be added to the repertoire of gastrointestinal stem cells.

Intestinal trefoil factor induces inactivation of extracellular signal-regulated protein kinase in intestinal epithelial cells

Intestinal trefoil factor (ITF), a small, compact protease-resistant peptide, is abundantly expressed in goblet cells of large and small intestine. Although several biological activities of ITF have been identified, including promotion of wound healing, stimulation of epithelial cell migration, and protection of intestinal epithelial barrier, little is known about signaling events through which ITF mediates its physiological function. In this study, the effects of exogenous ITF on mitogen-activated protein kinase (MAPK) signaling cascades were examined in IEC-6 cells, a nontransformed intestinal epithelial cell line that does not express endogenous trefoil peptides. Stimulation with ITF resulted in rapid decrease in extracellular signal-related protein kinase (ERK) activity and concomitant reduced ERK tyrosine phosphorylation. ITF also decreased activation of ERK activity induced by either transforming growth factor-alpha, which links extracellular stimuli to the Ras/Raf/MEK/ERK pathway via the epidermal growth factor receptor, or phorbol 12-myristate 13-acetate, which activates Raf through protein kinase C. ITF-induced inhibition of ERK activity was blocked by an inhibitor of tyrosine and dual-specific phosphatases, sodium orthovanadate. In summary, ITF leads to inhibition of ERK and the MAPK pathway through activation of tyrosine or dual-specific phosphatase.

Characterization of dopuin, a polypeptide with special residue distributions

A 62-residue polypeptide, dopuin, has been isolated from pig small intestine. It is distinguished by an N-terminal part with a high content of proline (7 in a 26-residue segment), a C-terminal part with a high proportion of histidine (3 in a 9-residue segment), and six half-cystine residues in three intrachain disulphide bridges (connecting positions 22-25, 23-54 and 35-44). The Cys and Pro distributions suggest a tight and special conformation. In contrast to PEC-60 and somatostatin, it has no established inhibitory effect on insulin secretion. At 10 nM concentration, a weak inhibitory tendency is less than half of that of the other two peptides. Like gastrointestinal trefoil peptides, dopuin has three disulphide bridges, Ala-Pro segments, and many charged residues, but they are differently distributed and dopuin belongs to a separate, apparently novel family. However, dopuin is similar to a peptide corresponding to an expressed-sequence-tag cDNA of human fetal liver and spleen, establishing the nature of the mature form of the product of this cDNA, and showing a general tissue, age, and species distribution of this peptide. A truncated form of vimentin, composed of its C-terminal 37 residues, vimentin-C37, was also purified and structurally characterized. These two peptides increase the complexity of known intestinal polypeptides and at least dopuin has properties compatible with specific biofunctions.