Pancreatic spasmolytic polypeptide: first three-dimensional structure of a member of the mammalian trefoil family of peptides

Trefoil Factor Family Member 2: From a High-Fat-Induced Gene to a Potential Obesity Therapy Target

Obesity has its epidemiological patterns continuously increasing. With controlling both diet and exercise being the main approaches to manage the energy metabolism balance, a high-fat (HF) diet is of particular importance. Indeed, lipids have a low satiety potential but a high caloric density. Thus, focusing on pharmacologically targetable pathways remains an approach with promising therapeutic potential. Within this context, trefoil factor family member 2 (Tff2) has been characterized as specifically induced by HF diet rather than low-fat diet. TFF2 has also been linked to diverse neurological mechanisms and metabolic patterns suggesting its role in energy balance. The hypothesis is that TFF2 would be a HF diet-induced signal that regulates metabolism with a focus on lipids. Within this review, we put the spotlight on key findings highlighting this line of thought. Importantly, the hypothetical mechanisms pointed highlight TFF2 as an important contributor to obesity development via increasing lipids intestinal absorption and anabolism. Therefore, an outlook for future experimental activities and evaluation of the therapeutic potential of TFF2 inhibition is given. Indeed, its knockdown or downregulation would contribute to an antiobesity phenotype. We believe this work represents an addition to our understanding of the lipidic molecular implications in obesity, which will contribute to develop therapies aiming to manage the lipidic metabolic pathways including the absorption, storage and metabolism via targeting TFF2-related pathways. We briefly discuss important relevant concepts for both basic and clinical researchers.

Structure, Function, and Therapeutic Potential of the Trefoil Factor Family in the Gastrointestinal Tract

Trefoil factor family peptides (TFF1, TFF2, and TFF3) are key players in protecting, maintaining, and repairing the gastrointestinal tract. Accordingly, they have the therapeutic potential to treat and prevent a variety of gastrointestinal disorders associated with mucosal damage. TFF peptides share a conserved motif, including three disulfide bonds that stabilize a well-defined three-loop-structure reminiscent of a trefoil. Although multiple functions have been described for TFF peptides, their mechanisms at the molecular level remain poorly understood. This review presents the status quo of TFF research relating to gastrointestinal disorders. Putative TFF receptors and protein partners are described and critically evaluated. The therapeutic potential of these peptides in gastrointestinal disorders where altered mucosal biology plays a crucial role in the underlying etiology is discussed. Finally, areas of investigation that require further research are addressed. Thus, this review provides a comprehensive update on TFF literature as well as guidance toward future research to better understand this peptide family and its therapeutic potential for the treatment of gastrointestinal disorders.

The Double Face of Mucin-Type O-Glycans in Lectin-Mediated Infection and Immunity

Epithelial human blood group antigens (HBGAs) on O-glycans play roles in pathogen binding and the initiation of infection, while similar structures on secretory mucins exert protective functions. These double-faced features of O-glycans in infection and innate immunity are reviewed based on two instructive examples of bacterial and viral pathogens. Helicobacter pylori represents a class 1 carcinogen in the human stomach. By expressing blood group antigen-binding adhesin (BabA) and LabA adhesins that bind to Lewis-b and LacdiNAc, respectively, H. pylori colocalizes with the mucin MUC5AC in gastric surface epithelia, but not with MUC6, which is cosecreted with trefoil factor family 2 (TFF2) by deep gastric glands. Both components of the glandular secretome are concertedly up-regulated upon infection. While MUC6 expresses GlcNAc-capped glycans as natural antibiotics for H. pylori growth control, TFF2 may function as a probiotic lectin. In viral infection human noroviruses of the GII genogroup interact with HBGAs via their major capsid protein, VP1. HBGAs on human milk oligosaccharides (HMOs) may exert protective functions by binding to the P2 domain pocket on the capsid. We discuss structural details of the P2 carbohydrate-binding pocket in interaction with blood group H/Lewis-b HMOs and fucoidan-derived oligofucoses as effective interactors for the most prevalent norovirus strains, GII.4 and GII.17.

High salt diet can down-regulate TFF2 expression level in gastric mucosa of MGs after H. pylori infection

This study aimed to elucidate the effect of Helicobacter pylori (H. pylori) and high salt diet on Trefoil factor 2 (TFF2) expression level of Mongolian gerbils (MGs) gastric mucosa. The results of H. pylori identification and histopathology showed that H. pylori infected MGs model was built successfully. According to the immunohistochemical staining results, 25% (4/16) of H. pylori infected MGs with high salt diet showed high TFF2 expression, which was significantly lower than H. pylori infection group 61% (11/18)(P = 0.045). The results suggested that High salt diet could down-regulated TFF2 expression level of MGs gastric mucosa induced by H. pylori infection.

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.

Trefoil factor family domains represent highly efficient conformational determinants for N-linked N,N'-di-N-acetyllactosediamine (LacdiNAc) synthesis

The disaccharide N,N'-di-N-acetyllactose diamine (LacdiNAc, GalNAcβ1-4GlcNAcβ) is found in a limited number of extracellular matrix glycoproteins and neuropeptide hormones indicating a protein-specific transfer of GalNAc by the glycosyltransferases β4GalNAc-T3/T4. Whereas previous studies have revealed evidence for peptide determinants as controlling elements in LacdiNAc biosynthesis, we report here on an entirely independent conformational control of GalNAc transfer by single TFF (Trefoil factor) domains as high stringency determinants. Human TFF2 was recombinantly expressed in HEK-293 cells as a wild type full-length probe (TFF2-Fl, containing TFF domains P1 and P2), as single P1 or P2 domain probes, as a series of Cys/Gly mutant forms with aberrant domain structures, and as a double point-mutated probe (T68Q/F59Q) lacking aromatic residues within a hydrophobic patch. The N-glycosylation probes were analyzed by mass spectrometry for their glycoprofiles. In agreement with natural gastric TFF2, the recombinant full-length and single domain probes expressed nearly exclusively fucosylated LacdiNAc on bi-antennary complex-type chains indicating that a single TFF domain was sufficient to induce transfer of this modification. Contrasting to this, the Cys/Gly mutants showed strongly reduced LacdiNAc levels and instead preponderant LacNAc expression. The probe with point mutations of two highly conserved aromatic residues in loop 3 (T68Q/F59Q) revealed that these are essential determinant components, as the probe lacked LacdiNAc expression. The structural features of the LacdiNAc-inducing determinant on human TFF2 are discussed on the basis of crystal structures of porcine TFF2, and a series of extracellular matrix-related LacdiNAc-positive glycoproteins detected as novel candidate proteins in the secretome of HEK-293 cells.

Human trefoil factor 2 is a lectin that binds α-GlcNAc-capped mucin glycans with antibiotic activity against Helicobacter pylori

Helicobacter pylori infection is the major cause of gastric cancer and remains an important health care challenge. The trefoil factor peptides are a family of small highly conserved proteins that are claimed to play essential roles in cytoprotection and epithelial repair within the gastrointestinal tract. H. pylori colocalizes with MUC5AC at the gastric surface epithelium, but not with MUC6 secreted in concert with TFF2 by deep gastric glands. Both components of the gastric gland secretome associate non-covalently and show increased expression upon H. pylori infection. Although blood group active O-glycans of the Lewis-type form the basis of H. pylori adhesion to the surface mucin layer and to epithelial cells, α1,4-GlcNAc-capped O-glycans on gastric mucins were proposed to inhibit H. pylori growth as a natural antibiotic. We show here that the gastric glycoform of TFF2 is a calcium-independent lectin, which binds with high specificity to O-linked α1,4-GlcNAc-capped hexasaccharides on human and porcine stomach mucin. The structural assignments of two hexasaccharide isomers and the binding active glycotope were based on mass spectrometry, linkage analysis, (1)H nuclear magnetic resonance spectroscopy, glycan inhibition, and lectin competition of TFF2-mucin binding. Neoglycolipids derived from the C3/C6-linked branches of the two isomers revealed highly specific TFF2 binding to the 6-linked trisaccharide in GlcNAcα1-4Galβ1-4GlcNAcβ1-6(Fucα1-2Galβ1-3)GalNAc-ol(Structure 1). Supposedly, lectin TFF2 is involved in protection of gastric epithelia via a functional relationship to defense against H. pylori launched by antibiotic α1,4-GlcNAc-capped mucin glycans. Lectin-carbohydrate interaction may have also an impact on more general functional aspects of TFF members by mediating their binding to cell signaling receptors.

Quantitative measurements of trefoil factor family peptides: possibilities and pitfalls

The trefoil factor family (TFF) peptides TFF1, TFF2, and TFF3 are produced and secreted by mucous membranes throughout the body. Their importance for the protection and repair of epithelial surfaces is well established, and the three peptides are present in various amounts in mucosal secretions as well as in the circulation. They have been linked to both inflammatory diseases and to various types of cancer, and serum concentrations of TFF3 show a more than 47-fold increase during pregnancy. Several both commercial and in-house immunoassays exist, but a number of methodological issues remain unresolved. This review describes methodological challenges in the measurement of the peptides in humans, and summarizes current knowledge concerning the occurrence and possible significance of the peptides in human health and disease.

Short toxin-like proteins abound in Cnidaria genomes

Cnidaria is a rich phylum that includes thousands of marine species. In this study, we focused on Anthozoa and Hydrozoa that are represented by the Nematostella vectensis (Sea anemone) and Hydra magnipapillata genomes. We present a method for ranking the toxin-like candidates from complete proteomes of Cnidaria. Toxin-like functions were revealed using ClanTox, a statistical machine-learning predictor trained on ion channel inhibitors from venomous animals. Fundamental features that were emphasized in training ClanTox include cysteines and their spacing along the sequences. Among the 83,000 proteins derived from Cnidaria representatives, we found 170 candidates that fulfill the properties of toxin-like-proteins, the vast majority of which were previously unrecognized as toxins. An additional 394 short proteins exhibit characteristics of toxin-like proteins at a moderate degree of confidence. Remarkably, only 11% of the predicted toxin-like proteins were previously classified as toxins. Based on our prediction methodology and manual annotation, we inferred functions for over 400 of these proteins. Such functions include protease inhibitors, membrane pore formation, ion channel blockers and metal binding proteins. Many of the proteins belong to small families of paralogs. We conclude that the evolutionary expansion of toxin-like proteins in Cnidaria contributes to their fitness in the complex environment of the aquatic ecosystem.

Stability analysis of recombinant human TFF2 and its therapeutic effect on burn-induced gastric injury in mice

The trefoil factor family 2 (TFF2), a member of the trefoil factor family, plays a critical role in maintaining homeostasis throughout the gastrointestinal tract. In the present study, we expressed recombinant human TFF2 by Escherichia coli expression system with the purity above 95%. In an in vitro simulated gastrointestinal environment, rhTFF2 was shown to exhibit resistance to proteases, heat, acid and alkali. In addition, in mouse burn-induced gastric injury models, rhTFF2 was demonstrated to accelerate the healing of gastric mucosal lesions. This study provides a new way to treat burn-induced gastric injury.

Trefoil factor family-1 mutations enhance gastric cancer cell invasion through distinct signaling pathways

BACKGROUND & AIMS

Trefoil factor family-1 (TFF1) is a key gastric tumor-suppressor gene. TFF1 knockout mice develop multiple gastric adenomas and carcinomas, and human gastric cancers typically lack TFF1 expression. Recently, TFF1 mutations have been found in human gastric cancer. The purpose of this study was to determine the functionality of these mutants.

METHODS

Recombinant wild-type TFF1 and the gastric cancer-associated TFF1 mutants (A10D and E13K) were produced and tested for their effect on gastric cancer cell proliferation, apoptosis, and invasion. Molecular modeling was used to guide the choice of mutants and to evaluate structure-function relationships.

RESULTS

Molecular modeling suggested that A10D and E13K altered the surface charge of the loop 1 region of TFF1 without disturbing protein stability. Recombinant wild-type TFF1 significantly inhibited cell growth; A10D and E13K lost this tumor-suppressive property along with the ability to block etoposide-induced apoptosis. Although wild-type TFF1 promoted cell invasion, A10D and E13K were even more pro-invasive. Invasion induced by both mutants was blocked by inhibiting PI3-kinase or phospholipase-C, but inhibiting Rho-associated kinase (ROCK) blocked only E13K-induced invasion.

CONCLUSIONS

The loss of tumor-suppressor activity and gain of invasiveness from single point mutations constitute evidence for a functional role of TFF1 mutations in gastric cancer. These site-directed mutagenesis experiments provide the tools for continued probing of signal transduction mechanisms and structural elements responsible for TFF1 functions.

The diurnal rhythm of the cytoprotective human trefoil protein TFF2 is reduced by factors associated with gastric mucosal damage: ageing, Helicobacter pylori infection, and sleep deprivation

OBJECTIVES

To determine if the normal TFF2 diurnal rhythm is disrupted in those with increased risk of gastric morbidity. Trefoil proteins protect the gastrointestinal mucosa from damage and aid its repair. TFF2 is considered the major cytoprotective gastric trefoil protein. There is a marked circadian variation in gastric luminal TFF2 in young healthy volunteers with peak levels present during the night.

METHODS

Gastric juice was aspirated at two hourly intervals over a 24-h period via a nasogastric tube. TFF2 was measured by quantitative western transfer analysis. Helicobacter pylori (H. pylori) status was measured by C13 urea breath test and by serology. The effects of H. pylori infection, sleep deprivation, and ageing, which cause increased gastric morbidity, on the TFF2 circadian rhythm were tested.

RESULTS

H. pylori infection attenuated the increase in TFF2 that occurs during the night. The TFF2 diurnal rhythm was reduced in older people and both the TFF2 level reached and the time at which the maximum TFF2 concentration occurs were associated inversely with age (p < 0.005). Sleep deprivation delayed the normal night time increase in gastric TFF2 and resulted in an overall reduction in TFF2 secretion.

CONCLUSIONS

H. pylori infection, ageing, and sleep deprivation cause a reduction in the TFF2 diurnal rhythm. The demonstration that the TFF2 rhythm is impaired in cohorts of individuals known to suffer gastric symptoms suggests that interventions to restore the normal TFF2 rhythm in those with poor mucosal protection could reduce morbidity.

High-level expression of human TFF3 in Escherichia coli

A strategy for expression and purification of recombinant N-terminal human trefoil factor family-domain peptide 3 (hTFF3) in Escherichia coli was established. The gene of hTFF3 was synthesized to substitute the low-usage condons with corresponding high-usage synonymous condons. At the same time, the signal peptide of DsbC was added to the N-terminus of the hTFF3 gene. The mature recombinant hTFF3 was located in the periplasm of E. coli, which can be released by sonication. The protein was further purified by a two-step cation exchange chromatography mentod. The yield is about 14-15 mg/l of culture. The biological activity of purified hTFF3 was analyzed by cell-based apoptosis assay, which shows that the recombinant hTFF3 is biologically active.

TFF2 (trefoil family factor2) inhibits apoptosis in breast and colorectal cancer cell lines

We have recently demonstrated that human TFF2 inhibits apoptosis in the non-TFF2 expressing breast adenocarcinoma cell line MCF-7. In this study we examined the impact of TFF2 and an anti-TFF2 antibody (hSP3) on the survival of other human adenocarcinoma cell lines; TFF2-positive (LS174T and SW480) and TFF2-negative (MCF-7 and T47D). Addition of TFF2 protected the (TFF2-) lines but had no effect on those constitutively expressing TFF2. Blocking with hSP3 significantly increased apoptosis in the (TFF2+) cell lines with minimal effect on the (TFF2-) cells. Our results show that the cytoprotective effect of TFF2 seen in MCF-7 cells is not cell line-specific and can be abrogated by inhibition of its expression.

Expression and motogenic activity of TFF2 in human breast cancer cells

The expression of TFF2 in breast cancer cells and the effect of recombinant TFF2 on breast cancer cell migration were assessed. TFF2 expression was detected by PCR in estrogen receptor-negative and at lower levels in estrogen receptor-positive breast cancer cells. TFF2 expression was detected in nine out of 10 primary breast tumors but its expression was not related to that of the estrogen receptor. Focal expression was observed in normal and tumor cells by immunohistochemistry. TFF2 stimulated the migration of estrogen-responsive MCF-7 and non-responsive MDA-MB231 cells. We conclude that TFF2 is expressed in normal and malignant breast epithelial cells and that it stimulates the migration of breast cancer cells.

Cell type specific expression of secretory TFF peptides: colocalization with mucins and synthesis in the brain

The "TFF domain" is an ancient cysteine-rich shuffled module forming the basic unit for the family of secretory TFF peptides (formerly P-domain peptides and trefoil factors). It is also an integral component of mosaic proteins associated with mucous surfaces. Three mammalian TFF peptides are known (i.e., TFF1-TFF3); however, in Xenopus laevis the pattern is more complex (xP1, xP4.1, xP4.2, and xP2). TFF peptides are typical secretory products of a variety of mucin-producing epithelial cells (e.g., the conjunctiva, the salivary glands, the gastrointestinal tract, the respiratory tract, and the uterus). Each TFF peptide shows an unique expression pattern and different mucin-producing cells are characterized by their specific TFF peptide/secretory mucin combinations. TFF peptides have a pivotal role in maintaining the surface integrity of mucous epithelia in vivo. They are typical constituents of mucus gels, they modulate rapid mucosal repair ("restitution") by their motogenic and their cell scattering activity, they have antiapoptotic effects, and they probably modulate inflammatory processes. Pathological expression of TFF peptides occurs as a result of chronic inflammatory diseases or certain tumors. TFF peptides are also found in the central nervous system, at least in mammals. In particular, TFF3 is synthesized from oxytocinergic neurons of the hypothalamus and is released from the posterior pituitary into the bloodstream.

Effect of trefoil factors on the viscoelastic properties of mucus gels

BACKGROUND

Trefoil peptides (TFFs) are expressed and secreted in a tissue-specific manner in the gastrointestinal tract. Evidence of coexpression of trefoil peptides and mucins has been demonstrated in most mucus-producing cells in the gastrointestinal tract. The expression of trefoil peptides is up-regulated in gastric ulceration and colitis. It is believed that TFF peptides interact with mucin to increase viscosity but this has never been confirmed. The aims of the present study were to elucidate the direct effect of trefoil peptides on mucus gel formation.

MATERIALS AND METHODS

The viscosity of mucin solutions was measured by means of a rotational rheometer after adding three mammalian trefoil peptides: TFF1, TFF2, and TFF3.

RESULTS

Adding TFF2 (0.3%) to the mucin solutions (8%) resulted in more than a factor 10 increase in viscosity and elasticity, and the mucin solution was transformed into a gel-like structure with serpentine-like complexes between the mucin and TFF2. The dimer form of TFF3 also increased viscosity but resulted in a spider's web-like structure. The monomer forms of TFF1 and TFF3 had very little effect on the viscosity and elasticity of the mucin solutions.

CONCLUSIONS

The addition of TFF2 to mucin solutions results in significantly increased viscosity and elasticity, under which the mucin solutions are transformed into a gel-like state. The ability of some trefoil peptides to catalyse the formation of stable mucin complexes may be one of the ways by which these peptides exert their protective and healing functions.

Spatio-temporal expression of trefoil peptide following severe gastric ulceration in the rat implicates it in late-stage repair processes

BACKGROUND

The trefoil peptide (TFF1) is a member of a family of mucin-associated regulatory peptides that are widely distributed in gastrointestinal tissues and have been implicated in the maintenance of the gastric mucosa. The role of TFF1 in gastric mucosal repair was examined by analysis of the spatio-temporal expression of TFF1 following gastric ulceration in the rat.

METHODS

Gastric ulcers were induced in rats by application of glacial acetic acid to the serosa of the fundus. At various time points post injury (0-28 days), macroscopic and microscopic examination of the gastric mucosa was performed. In addition, the spatio-temporal expression of TFF1 protein and proliferating cell nuclear antigen were identified by immunohistochemistry, TFF1 message by in situ hybridization, and acidic/neutral secreting mucins by Alcian blue-periodic acid-Schiff staining.

RESULTS

In normal rat gastric tissue, TFF1 peptide and mRNA were expressed in mucosal cells of the superficial epithelium. Trefoil peptide and mRNA were significantly induced between 4 and 28 days post ulceration, with expression extending beyond the superficial epithelium and being localized to acidic mucin-producing cells deep within the repairing mucosa.

CONCLUSIONS

Spatio-temporal expression of TFF1 mRNA and peptide following macroscopic repair implicates TFF1 as a potential mediator of late stage-repair processes. Whether this is through direct stimulation of cellular differentiation or the enhancement of mucosal protective properties through an interaction with gastric mucins remains to be elucidated.

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.

The solution structure of the disulphide-linked homodimer of the human trefoil protein TFF1

The trefoil factor family protein, TFF1, forms a homodimer, via a disulphide linkage, that has greater activity in wound healing assays than the monomer. Having previously determined a high-resolution solution structure of a monomeric analogue of TFF1, we now investigate the structure of the homodimer formed by the native sequence. The two putative receptor/ligand recognition domains are found to be well separated, at opposite ends of a flexible linker. This contrasts sharply with the known fixed and compact arrangement of the two trefoil domains of the closely related TFF2, and has significant implications for the mechanism of action and functional specificity of the TFF of proteins.

Isolation and characterization of putative trefoil peptide receptors

Mammalian trefoil factors (TFFs) constitute a group of three peptides (TFF1, TFF2 and TFF3) widely distributed in the gastrointestinal tract. Although a mucosal protection/healing effect of these peptides is well documented the mechanism of action is still unknown. A mucosal membrane extract was prepared from porcine stomach scrapings and incubated with a gel containing immobilized porcine TFF2. The affinity gel material was specifically eluted with a neutral buffer containing a high concentration of the ligand (porcine TFF2). A subsequent SDS-gel electrophoresis showed one protein with a MW of approximately 220 kDa and three proteins with MW around 140 kDa. The proteins were analyzed by trypsin digestion followed by mass spectrometric sequencing of tryptic fragments. In this way a 140-kDa beta subunit of fibronectin receptor and a 224-kDa CRP-Ductin gene product were identified. The CRP-Ductin gene product (also named MUCLIN), which is expressed in the intestinal crypts, is characterized by being a membrane protein with a short cytoplasmic region, a transmembrane domain and a large extracellular region. This protein thus fulfils some of the criteria for being a TFF receptor or a TFF binding protein.

pS2/TFF1 interacts directly with the VWFC cysteine-rich domains of mucins

BACKGROUND & AIMS

Trefoil factors (TFFs) are secreted gastrointestinal proteins that have been shown to protect and promote healing of the gastrointestinal tract. Moreover, pS2/TFF1 is essential for normal differentiation of the gastric mucosa because deficient mice develop antropyloric adenomas. To date, it is unclear how TFFs mediate their functions.

METHODS

Using the yeast 2-hybrid system, we attempted to identify murine TFF1 interacting proteins by screening a stomach and duodenum complementary DNA (cDNA) expression library.

RESULTS

Four positive clones were isolated. Sequence and expression studies showed that they corresponded to the murine counterpart of human cDNA sequences encoding carboxy-terminal fragments of mMuc2 (489 residues) and mMuc5AC (427, 430, and 894 residues) mucin proteins. Mutagenesis experiments showed that TFF1 interacts with the 2 mucins through binding with their VWFC1 and VWFC2 (von Willebrand factor C) cysteine-rich domains.

CONCLUSIONS

These results show that the gastrointestinal protective effect of TFF1, and presumably of the other TFFs, is caused at least partially by their participation, via mucin binding, in the correct organization of the mucous layer that protects the apical side of the mucosa from deleterious luminal agents.

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 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.

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.

Molecules involved in mammalian sperm-egg interaction

To achieve fertilization, sperm and egg are equipped with specific molecules which mediate the steps of gamete interaction. In mammals, the first interaction between sperm and egg occurs at an egg-specific extracellular matrix, the zona pellucida (zp). The three glycoproteins, ZP1, ZP2, and ZP3, that comprise the zp have been characterized from many species and assigned different roles in gamete interaction. A large number of candidate-binding partners for the zp proteins have been described; a subset of these have been characterized structurally and functionally. Galactosyltransferase, sp56, zona receptor kinase, and spermadhesins are thought to participate in the primary binding between sperm and zp and may initiate the exocytotic release of hydrolytic enzymes in the sperm head, the acrosome reaction. Digestion of the zp by these enzymes enables sperm to traverse the zp, at which time the proteins PH20, proacrosin, sp38, and Sp17 are thought to participate in secondary binding between the acrosome-reacted sperm and zp. Once through the zp, sperm and egg plasma membranes meet and fuse in a process reported to involve the egg integrin alpha 6 beta 1 and the sperm proteins DE and fertilin. These molecules and the processes involved in gamete interaction are reviewed in this chapter within a physiological context.

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.

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.

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.

Structure and distribution of modules in extracellular proteins

It has become standard practice to compare new amino-acid and nucleotide sequences with existing ones in the rapidly growing sequence databases. This has led to the recurring identification of certain sequence patterns, usually corresponding to less than 300 amino-acids in length. Many of these identifiable sequence regions have been shown to fold up to form a ‘domain’ structure; they are often called protein ‘modules’ (see definitions below). Proteins that contain such modules are widely distributed in biology, but they are particularly common in extracellular proteins.

Effects of pancreatic spasmolytic Polypeptide (PSP) on epithelial cell function

Trefoil peptides are expressed near endodermal ulcerations and may modulate epithelial repair. The trefoil pancreatic spasmolytic polypeptide (PSP) was tested for growth activity in vitro on epithelial cells and in vivo following intragastric or intravenous infusion in parenterally fed intact rats. Ion transport was assessed as changes in short-circuit current in rat intestine and adenocarcinoma cells in Ussing chambers. PSP stimulated growth of MCF-7 and Colo-357 cells, but only in the presence of extracellular glutathione (GSH). The effect was attenuated by GSH depletion with buthionine sulphoximine, even in GSH-containing media. When GSH-reduced PSP was carboxymethylated with iodoacetic acid, it still depended on extracellular GSH for its growth effect. Intestinal epithelial proliferation in rats was not affected by either intravenous or intraluminal infusion. PSP had no effect on basal or stimulated ion flux in rat jejunum or epithelial monolayers. The peptide did not compete with 125I-labeled epidermal growth factor for its receptor. [14C]Iodoacetamide treatment of PSP, followed by prolonged tryptic digestion yielded predominantly a 14C-labeled tetrapeptide fragment containing Cys1O4, with a lesser quantity of a 14C-labeled 15-amino-acid peptide containing Cys95 (molar ratio 15:1). GSH may predominantly reduce the Cys6-Cys1O4 terminal disulphide bond in PSP. We conclude that some epithelia may exhibit a growth response to PSP if extracellular GSH is present. Reduction of PSP by GSH is not necessary for this response, suggesting that the trefoil receptor or its signal transduction is GSH sensitive. PSP could assist wound healing by interactions with epithelial cells exposed concurrently to a local high GSH concentration.

pS2 transfection of murine adenocarcinoma cell line 410.4 enhances dispersed growth pattern in a 3-D collagen gel

We describe the first model system employing human pS2 gene transfer and expression in a non-pS2-expressing cell line, mouse mammary adenocarcinoma 410.4, in order to analyse the potential effect of human trefoil peptide pS2 in glandular epithelium. Two selected clones, AA4 and AD4, were established and shown to have incorporated the pS2 cDNA sequence into the genome, express pS2 containing transcript and produce the pS2 peptide. When grown in 3-D collagen gels both transfectants show striking morphological changes compared to the vector control clone (VA5). VA5 forms large cohesive spherical aggregates with rare coarse spicular outgrowths, accompanied by prominent hyalinised extracellular matrix deposition. pS2 transfectants form poorly cohesive, stellate colonies with very little or no matrix deposition, radiating long cords composed of single elongated cells, an effect previously observed in other cell lines with hepatocyte growth factor. pS2 transfection had no demonstrable effect on proliferation and this is not a morphogenetic phenomenon, as tubulogenesis is not seen. Motility assays suggest that the pS2 ‘dispersant’ effect in collagen gels is due to an increase in cell motility. There were no measurable alterations in either E-cadherin expression or E-cadherin-dependent cell-cell aggregation. pS2 may play a role in maintenance and restitution of mucosal integrity by accelerating migration/dispersion.

NMR-based structural studies of the pNR-2/pS2 single domain trefoil peptide. Similarities to porcine spasmolytic peptide and evidence for a monomeric structure

NMR spectroscopy measurements have been used to obtain structural information about the pNR-2/pS2 single-domain trefoil peptide. NMR data from 2D (two dimensional) double-quantum-filtered correlation spectroscopy (DQF-COSY), total correlation spectroscopy (TOCSY), NOE spectroscopy (NOESY), rotating frame NOE spectroscopy (ROESY) and 2D 13C-1H heteronuclear single-quantum coherence (HSQC) and 13C-1H HSQC-TOCSY spectra have been analysed to provide essentially complete 1H and 13C sequence-specific assignments for the pNR-2/pS2 protein. From a consideration of the NOE intensities, 3J(NH-alpha CH) coupling constants, 1H and 13C chemical shifts of backbone atoms and amide-proton exchange rates, the pNR-2/pS2 was found to contain two short antiparallel beta-strands (32-35 and 43-46), a short helix (25-30) and a type I beta-turn (11-15). These elements of secondary structure are very similar to those found in the two trefoil domains of pSP for which detailed structural information is already available. Similar 1H chemical shifts were noted for several conserved residues in pNR-2/pS2 and pSP and a characteristic Phe residue with a slowly flipping ring was found in the pNR-2/pS2 variant and in both domains of pSP. The tertiary structures of the domains therefore appear to be very similar in the two proteins and it is likely that the pNR-2/pS2 has the same pattern of disulphide bonds (1-5, 2-4, 3-6) as pSP. Correlation time measurements derived from 1H-1H NOE measurements indicate that the Cys58-->Ser form of the pNR-2/pS2 protein used in this study is monomeric in solution at approximately 2 mM.

Characterisation of the single copy trefoil peptides intestinal trefoil factor and pS2 and their ability to form covalent dimers

A bacterial recombinant expression system was established to produce biologically active rat Intestinal Trefoil Factor (rITF). Characterisation of purified rITF shows that both monomers and dimers can be observed under reducing and non-reducing conditions, respectively. Site-directed mutagenesis studies show that Cys57 is necessary for rITF dimer formation. Samples of human gastrointestinal tissue following biopsy also demonstrated the presence of reducible human pS2 and ITF covalent dimers. Three-dimensional models for pS2 and ITF support the hypothesis that both pS2 and ITF can exist as disulphide-linked dimers in vivo and that any proposed function for these peptides must take dimer formation into account.

Trefoil peptides. Coming up clover

Now that information on trefoil domain structure is available from X-ray crystallographic and nuclear magnetic resonance spectroscopy studies, we can begin to understand the functions of these unusual protein motifs.