Gut hormones, growth and malignancy

The role of peptide YY in gastrointestinal diseases and disorders (review)

Peptide YY (PYY) is affected in several gastrointestinal diseases and disorders. Changes in PYY appear to be an adaptive response to alterations in pathophysiological conditions caused by the disease. This applies to gastrointestinal diseases/disorders such as irritable bowel syndrome, inflammatory bowel disease, celiac disease, systemic sclerosis, and post-intestinal resection. By contrast, the changes in PYY in chronic idiopathic slow transit constipation (CST) seem to be of a primary nature, and may be one etiological factor of the disease. Abnormalities in PYY seem to contribute to the development of symptoms present in irritable bowel syndrome, inflammatory bowel disease, gastroenteropathy in long-standing diabetes and CST. The changes in PYY could, however, be favorable in some gastrointestinal disorders such as celiac disease, systemic sclerosis and post-intestinal resection state. Investigating changes in PYY in gastrointestinal diseases/disorders could be beneficial in clinical practice, where a receptor agonist or an antagonist can be used as a drug, depending on the condition. Similar to other neuroendocrine peptides/amines of the gut, PYY has broad physiological/pharmacological effects: it can bind to and activate several receptors with independent actions. Thus, in order to use PYY as a drug, receptor-specific agonists or antagonists need to be developed.

The murine gastrin promoter is synergistically activated by transforming growth factor-beta/Smad and Wnt signaling pathways

The transforming growth factor-beta (TGF-beta) and Wnt/wingless pathways play critical roles in the specification of cell fate during development and also contribute to cancer formation and progression. Whereas Wnt signaling is clearly pro-oncogenic, TGF-beta signaling is cell- and context-dependent, manifesting both inhibitory and proliferative effects. The growth factor, gastrin, has previously been shown to be a downstream target of the Wnt pathway and a promoter of gastrointestinal cancer. In this study, we show that the mouse gastrin promoter is regulated synergistically by TGF-beta/Smads and beta-catenin/T-cell factor (TCF). Co-transfection of Smad3/Smad4 and beta-catenin expression constructs synergistically activated mouse gastrin promoter activity 30-60-fold in AGS cells with minimal effect seen with either construct alone. This activation was further potentiated by TGF-beta1 treatment. Mutating either the TCF binding site or the Smad-binding element (SBE) diminished the activation of gastrin expression by Smad3/Smad4 and beta-catenin and led to a loss of gastrin promoter responsiveness to TGF-beta1 treatment. Wnt and TGF-beta regulated endogenous gastrin mRNA levels in AGS cells in a similar fashion, as revealed by small interference RNA studies or overexpression of Smads and TCF4/beta-catenin. Electrophoretic mobility shift assays and DNA affinity precipitation assays showed that the putative SBE and T-cell factor (TCF) sites were able to bind a complex containing Smads and beta-catenin/TCF4. In addition, the synergy between Smads and beta-catenin/TCF4 was dependent on CREB-binding protein (CBP)/P300, as demonstrated by overexpression of CBP or E1A. Moreover, by using a heterogeneous promoter reporter system, we showed that this complex containing Smads/TCF4/beta-catenin complex was able to up-regulate transcription at isolated SBE or TCF sites. Thus, the Wnt signaling pathway is able to activate some target genes through its actions as a co-activator at non-TCF sites and has the potential to profoundly alter transcriptional responses to TGF-beta signaling.

Expression of TGF-alpha in neuroendocrine tumours of the distal colon and rectum

AIM

Transforming growth factor alpha (TGF-alpha) has been localized in neuroendocrine L-cells of the colon and rectum in previous studies. We examined whether neuroendocrine tumours with L-cell differentiation express TGF-alpha.

EXPERIMENTAL DESIGN

Immunohistochemistry was performed for proglucagon- and pro-pancreatic polypeptide derivatives, as well as for TGF-alpha, and epidermal growth factor receptor (EGFR) using paraffin sections from 16 neuroendocrine tumours of the colon and rectum. Also, in situ hybridization for TGF-alpha and proglucagon was carried out.

MAIN RESULTS

A strong expression of TGF-alpha at the protein level can be shown for neuroendocrine tumours of the hindgut. In one third of our cases we found a strong hybridization signal and in two thirds a moderate signal for TGF-alpha. The immunohistological phenotype concerning gut hormones is highly heterogeneous. Glucagon-like peptide 2 (GLP2) in our series was the most sensitive immunohistological hormone marker.

MAJOR CONCLUSIONS

The immunophenotype of colorectal neuroendocrine tumours regarding hormone markers is heterogeneous. The expression of TGF-alpha corresponds to the immunohistological profile of normal L-cells. TGF-alpha, especially in the neuroendocrine L-cells, most probably acts as a multifunctional trophic factor responsible for cellular integrity and survival, and not as an oncogenic growth factor.

Peptide YY in gastrointestinal disorders

The changes in PYY in several gastrointestinal disorders and their possible clinical implications are reviewed. The changes in PYY seem to be an adaptive response to alterations in the patho-physiological condition caused by the disease. This becomes evident in gastrointestinal disorders such as diabetes gastroenteropathy, inflammatory bowel diseases, celiac disease, systemic sclerosis and post-intestinal resection state. On the other hand, changes in PYY in chronic idiopathic slow transit constipation appear to be primary and could be one of the etiologic factors of the disease. PYY does not seem to be involved in colorectal carcinoma. Although gastrointestinal dysmotility in neuro-muscular diseases is evident, PYY is not affected. The changes in PYY in gastrointestinal disorders could be beneficial in clinical practice. Thus, in cases where an increase or decrease in PYY is desirable, a diet that increases or decreases PYY synthesis and release can be followed, or a receptor agonist or antagonist can be utilized.

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.

HGF regulates tight junctions in new nontumorigenic gastric epithelial cell line

The regulation of intercellular adhesion by hepatocyte growth factor (HGF) was examined on a novel nontumorigenic gastric epithelial cell line (IMGE-5) derived from H-2Kb-tsA58 transgenic mice. IMGE-5 cells constitutively expressed cytokeratin 18 and HGF receptors. Under permissive conditions (33 degrees C + interferon-gamma), IMGE-5 cells proliferated rapidly but did not display membrane expression of adherens and tight junction proteins. Under nonpermissive conditions, their proliferation was decreased and they displayed a strong, localized membrane expression of E-cadherin/beta-catenin and occludin/ZO-1. HGF treatment largely prevented the targeting of ZO-1 to the tight junction and induced a significant decrease of the transepithelial resistance measured across a confluent IMGE-5 cell monolayer. HGF rapidly increased the tyrosine phosphorylation of ZO-1 and decreased its association with occludin in a phosphatidylinositol 3-kinase (PI 3-kinase)-dependent manner. PI 3-kinase was also involved in HGF-induced migration of IMGE-5 cells. Our results demonstrate that 1) HGF prevents the appearance of ZO-1 in the membrane during epithelial cell differentiation; 2) HGF causes partial relocalization of ZO-1 to the cytoplasm and nucleus and concomitantly stimulates cell dissociation and migration; and 3) IMGE-5 cells offer a useful model for the study of gastric epithelial cell differentiation.

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.

Altered enteroendocrine cell expression in T cell receptor alpha chain knock-out mice

Mice lacking T cell receptor alpha chain (TCRalpha(-/-)) develop inflammation of the colon. We have examined the effect of this inflammation on the colonic epithelium by studying markers of epithelial cuff, enteroendocrine, and immune cell differentiation. Using immunohistochemical techniques, colons were compared in normal C57/BL6 and murine TCR alpha(-/-) mice aged 2 and 3 weeks and 3-11 months. TCR alpha(-/-) mice aged 3-11 months had histologic evidence of inflammation with increased expression of CD45, CD4+, CD8+, and B220+ cells and a decrease in expression of IgA+ cells. There was a decrease in the number of cholecystokinin, serotonin, and neurotensin enteroendocrine expressing cells in the colon of TCR alpha(-/-) mice. These changes were not present in 2-3-week-old suckling/weaning mice. In contrast, peptide tyrosine tyrosine (PYY), glucagon-like peptide-1, and gastrin expression did not change and small intestinal enteroendocrine cells remained unaltered. The change in colonic enteroendocrine cell expression appears to be a specific response, since only a subset of these cells was altered, and the epithelium was intact by histologic analysis. The absence of functional T cells in TCR alpha(-/-) colon has a marked effect on differentiation of a specific subpopulation of enteroendocrine cells, prior to loss of integrity of the epithelium.

Regulatory effect and mechanism of gastrin and its antagonists on colorectal carcinoma

AIM: To explore the effect and mechanism of gastrin and its an tagonists proglumide and somatostatin on colorectal carcinoma and their clinical significance.

METHODS: A model of transplanted human colonic carcinoma was established from SW480 cell line in gymnomouse body. The volume and weight of transplanted carcinoma was observed under the effect of pentagatrin (PG), proglumide (PGL) and octapeptide somotostatin (SMS201-995, SMS). The cAMP content of carcinoma cell was determined by radioimmunoassay and the DNA, protein content and cell cycle were determined by flow-cytometry. The amount of viable cells was determined by MTT colorimetric analysis, IP₃ content was determined by radioimmuno assay, Ca²⁺ concentration in cell by fluorometry and PKC activity by isotopic enzymolysis. The expression of gastrin, c-myc, c-fos and rasP21 in 48 case s of colorectal carcinoma tissue was detected by the immuno-cytochemistry SP method. Argyrophilia nucleolar organizer regions was determined with argyrophilia stain.

RESULTS: The volume, weight, cAMP, DNA and protein content in carcinoma cell, cell amount and proliferation index of S and G₂M phase in PG group were all significantly higher than those of control group. When PG was at the concentration of 25 mg/L, the amount of viable cells, IP₃ content and Ca²⁺ concentration in cell and membrane PKC activity in PG group were significantly higher than those in control group; when PGL was at a concentration of 32 mg/L, they dropped to the lowest level in PG (25 mg/L) + PGL group, but without significant difference from the control group. The positive expression rate of gastrin, c-myc, c-fos and rasP21 in carcinoma tissue was 39.6%, 54.2%, 47.9% and 54.2% respectively and significantly higher than that in mucosa 3 cm and 6 cm adjacent to carcinoma tissue and normal colorectal mucosa. The positive expression rate of gastrin of highly-differentiated adenocarcinoma group was significantly higher than that of poorly-differentiated and mucinous adenoc arcinoma groups. The AgNORs count of carcinoma tissue was significantly higher than that in mucosa 3 cm and 6 cm adjacent to carcinoma tissue and norm al colorectal mucosa; and the positive expression of c-myc and c-fos and the A gNORs count in gastrin-positive group was significantly higher than those in gastrin-negative group.

CONCLUSION: Pentagastrin has a promoting effect on the growth of transplanted human colonic carcinoma from SW480 cell line. PGL has no obvious effect on the growth of human colonic carcinoma SW480 cell line, but could inhibit the growth promoting effect of PG on transplanted carcinoma. Somatostatin can not only inhibit the growth of transplanted human colonic carcinoma from SW480 cell line directly but also depress the growth-promoting effect of gastrin on the transplanted carcinoma. Some colorectal carcinoma cells can produce and secrete gastrin through autocrine, highly-differentiated adenocarcinoma express the highest level gastrin. Endogenous gastrin can stimulate the cell division and proliferation of carcinoma cell and promote the growth of colorectal carcinoma regulating the expression of oncogene c-myc, c-fos. Our study has provided experimental basis for the adjuvant treatment using gastrin antagonist such as PGL, so matostatin of patients with colorectal carcinoma.

Postnatal development of intestinal endocrine cell populations in the water buffalo

The frequency and distribution of 11 endocrine cell populations were studied in the intestine of differently aged buffalo, grouped on the basis of diet: 2-d-olds (suckling), 5-mo-olds (weaning) and 5-y-olds (ruminant adult diet). The endocrine cell populations were identified immunocytochemically using antisera against 5-hydroxytryptamine (5-HT), somatostatin, gastrin, cholecystokinin (CCK), COOH-terminal octapeptide of gastrin/CCK, neurotensin, motilin, gastric inhibitory polypeptide (GIP), secretin, glucagon/glicentin (GLU/GLI) and polypeptide YY (PYY). In adult buffalos the regional distribution of endocrine cells is similar to that of other adult ruminants. During postnatal development, these cell types showed the following changes in their frequency and distribution: (1) 5-HT, neurotensin and gastrin/CCK immunoreactive cells (i.c.) showed a decrease in frequency with age; (2) somatostatin i.c. frequency remained stable with age; (3) motilin, GIP, secretin and CCK i.c. showed a slight increase in frequency with age; (4) GLU/GLI and PYY i.c. decreased in frequency with age in the small intestine, caecum and proximal colon and an increase in frequency in the rectum. It was hypothesised that the endocrine cell types, whose presence and localisation is substantially stable in all examined ages, probably contain substances that are strictly necessary for intestinal function. In contrast the hormones contained in the cell populations that decreased with age, are probably involved in physiological needs during the milk and weaning diet or play a role in intestinal growth.

Growth factors and gut function

Growth factors play a key role in maintaining gut integrity and in stimulating repair. By understanding their physiological function we can use this information to apply to the treatment of conditions in which mucosal homeostasis has broken down.

Proliferating cell nuclear antigen as a marker of cell kinetics in aberrant crypt foci, hyperplastic polyps, adenomas, and adenocarcinomas of the human colon

BACKGROUND

One of the first steps in multistage colonic carcinogenesis is increased cell proliferation and an upward shift of the proliferation zone of colonic crypts. In the present study, progression in cell kinetics was followed up at all sequential stages of colonic carcinogenesis, starting with aberrant crypt foci (ACF), the earliest putative preneoplastic lesions, hyperplastic and dysplastic polyps, and invasive carcinomas.

MATERIALS AND METHODS

Colonic tissue and tumor specimens were prospectively obtained from 65 patients treated at our hospital for adenocarcinoma or malignant polyps. For identification of ACFs, dissected mucosal strips obtained from patients with colorectal cancer were stained with 0.1% methylene blue and scanned under dissecting microscope. Paraffin-embedded ACFs and macroscopic lesions were serially sectioned, deparaffinized, and stained with a monoclonal antiproliferating cell nuclear antigen (PCNA) antibody. The PCNA-labelling index (PCNA-LI), expressed as a ratio of positively stained nuclei to total nuclei counted, was calculated separately for basal, middle, and upper colonic crypt compartments. A comparison of the PCNA-LI was made for each compartment in normal mucosa, and hyperplastic and dysplastic lesions.

RESULTS

A stepwise increase in the PCNA-LI was observed during neoplastic progression of colonic lesions. The two most important variables of increased cell proliferation, expressed as PCNA-LI per crypt compartment, were the presence of dysplasia and the size of dysplastic lesions.

CONCLUSIONS

In colorectal carcinogenesis, hyperproliferation with upward expansion of proliferative compartment is a characteristic feature at all stages of malignant progression.

Effect of carboxypeptidase E deficiency on progastrin processing and gastrin messenger ribonucleic acid expression in mice with the fat mutation

Proforms of gastrointestinal peptides are cleaved at paired basic residues into intermediate forms. Paired basic residues at the C-terminal then are excised by carboxypeptidases before the peptide is amidated. An obese mouse, called Cpe(fat)/Cpe(fat), has a missense mutation in carboxypeptidase E (CPE) with no pancreatic CPE activity and a reduced processing of pancreatic proinsulin to insulin. The purpose of this study was 1) to look for the presence of CPE in the antrum of the stomach, duodenum, and colon in the Cpe(fat)/Cpe(fat) mouse; 2) to determine whether CPE is involved in the processing of progastrin (Pro-G) to its carboxyl-terminal amidated form; and 3) to determine whether a decrease in amidated gastrin results in an up-regulation of stomach gastrin messenger RNA (mRNA) levels. In Cpe(fat)/Cpe(fat) mice, CPE activity was absent in the antrum and colon. In Cpe(fat)/Cpe(fat) mice, amidated gastrin levels were reduced significantly. Levels of the precursor for amidated gastrin (gastrin-Gly-Arg-Arg) were markedly elevated. Gastrin mRNA levels were increased approximately 2-fold over the levels in Cpe(fat)/Cpe(fat) mice. These results indicate that CPE is needed for processing progastrin to gastrin in the stomach and that amidated gastrin exerts an inhibitory feedback effect on gastrin mRNA levels.

Overexpression of ZBP-89, a zinc finger DNA binding protein, in gastric cancer

ZBP-89 is a Krüppel-type zinc finger protein that binds to the gastrin EGF response element (gERE). Sp1 binds to the same DNA element and transactivates gastrin promoter activity, whereas ZBP-89 competes for Sp1 binding and prevents EGF induction. Both transcription factors mediate growth factor signals originating from the EGF receptor and thus were studied in normal and neoplastic tissues or cell lines. When compared to normal tissue from the same patient, ZBP-89 protein expression was increased in neoplastic tissue from the stomach antrum and in malignant cell lines. RT-PCR analysis of ZBP-89 mRNA correlated with protein overexpression. Immunocytochemical studies confirmed that ZBP-89 expression is elevated in neoplastic tissue and chronic gastritis, whereas Sp1 expression was nearly unchanged. These results suggest that the transcription factor ZBP-89, like Sp1, may be a marker for neoplastic transformation in some gastric cancers.

Gastrin receptor antagonist CI-988 inhibits growth of human colon cancer in vivo and in vitro

BACKGROUND

Whilst gastrin has been found to be trophic for some colorectal cancer cell lines, and gastrin receptor antagonists are able to block this phenomenon, their potency has been modest.

METHODS

The effect of a new, potent and selective CCK B receptor antagonist, CI-988 on the growth of LoVo, a human colon cancer cell line both in vitro and in vivo was instigated.

RESULTS

Basal growth of LoVo in vitro was inhibited by up to 58.93 +/- 7.30% with concentrations of CI-988 as low as 1 X 10(-11) mol/L whereas the addition of gastrin (G17) at 0.5 nmol/L had no effect. LoVo was also grown in vivo for 10 days in nude mice subsequently treated with CI-988 at 10 mg/kg per day orally for 20 days. CI-988 inhibited the growth of xenografts by 53%.

CONCLUSION

This was the first study in cancer with this potent gastrin receptor antagonist, CI-988. The results suggest that CI-988 may be of use in inhibiting the growth of colorectal cancer.

Epidermal growth factor (EGF)

Despite the wealth of information concerning EGF and its related peptides, its precise role in the control of gastrointestinal functions is still not fully resolved. However, there is no doubt that it can have some very potent effects on the gastrointestinal tract. These may be related to the control of growth and development and to the regular control of cell renewal. Nevertheless, in the adult, EGF may only be active in response to luminal damage and repair, and furthermore this may also only occur if the luminal EGF is protected from proteolytic degradation. Notwithstanding this, 'EGF'-like responses may be evoked in the gut by intestinal TGF-alpha. The possible therapeutic use of EGF and members of its family in ulcer therapy will be discussed in later Chapters of this volume, other potential uses are in the control of necrotising enteritis and in the alleviation of the mucositis associated with cancer treatment.

Transforming growth factor-beta in GI neoplasia, wound healing and immune response

The last decade has been marked by tremendous advances in the biochemical and functional characterization of TGF-betas and their receptors in normal and transformed cells. TGF-betas have been shown to modulate proliferation, differentiation and motility of different cell types in a number of in vitro model systems and in some cases with some intriguing results. It is obvious that there is no simple pattern that explains the TGF-betas biological activity in vitro and their effects on cell behaviour need to be assessed in the context of an appropriate physiological cellular environment. Cell-cell and cell-matrix interactions, the differentiating status of the cell together with the functional activity of other soluble growth factors can influence how TGF-betas modulate cell behaviour. However, the overwhelming interest in this field shown by clinicians and basic scientists is rapidly increasing our understanding of how growth factors such as TGF-betas regulate the homeostasis of the GI mucosa and their role in gastrointestinal carcinogenesis.