Yan-Shi Guo

Regulation of growth of human gastric cancer by gastrin and glycine-extended progastrin

BACKGROUND & AIMSnGastrin (G-17) stimulates the growth of certain gastric and colon cancers mostly through gastrin/cholecystokinin (CCK)-B receptors. Glycine-extended gastrin (Gly-G) stimulates growth of a rat pancreatic acinar cell line; however, the effect of Gly-G on human gastric cancers is not known. The purpose of this study was to characterize the trophic effect of G-17 and Gly-G on two human gastric cancer cell lines, AGS and SIIA.nnnMETHODSnBinding analyses were performed, and cell growth was assessed by counting cells over a time course.nnnRESULTSnG-17 stimulated growth of both AGS and SIIA cells. In AGS cells, gastrin/CCK-B receptor antagonists inhibited the effect of G-17 and competitively antagonized 125I-G-17 binding, whereas the CCK-preferring (CCK-A) receptor antagonists had no effect. In contrast, CCK-A receptor antagonists inhibited the stimulatory effect of G-17 in SIIA cells, whereas CCK-B receptor antagonists had no effect. Gly-G stimulated the growth of AGS and SIIA cells; neither the CCK-B nor the CCK-A receptor antagonists blocked this effect.nnnCONCLUSIONSnG-17 stimulates proliferation of AGS cells through the CCK-B receptor; however, G-17-mediated growth of SIIA acts through a CCK-A-like receptor. Furthermore, Gly-G stimulates growth of human gastric cancer cell lines, possibly through a receptor other than the CCK-B or CCK-A receptor.

Effect of Peptide YY on Cephalic, Gastric, and Intestinal Phases of Gastric Acid Secretion and on the Release of Gastrointestinal Hormones

The objective of this study was to investigate the effects of a novel gut peptide, peptide YY (PYY), on the cephalic, gastric, and intestinal phases of gastric acid secretion and to explore the mechanisms involved. The cephalic phase of gastric acid secretion, stimulated by the intravenous injection of 2-deoxyglucose (75 mg/kg), was found to be inhibited by intravenous PYY (100, 200, 400 pmol/kg X h) in a dose-related fashion. Peptide YY (200 and 400 pmol/kg X h) also resulted in a significant dose-dependent inhibition of the gastric phase of acid secretion. On the other hand, PYY (400 pmol/kg X h) failed to affect the intestinal phase of gastric acid output. Serum gastrin levels were increased on infusion of 10% liver extract into stomach, but were unaffected on instillation of liver extract into duodenum. Peptide YY did not inhibit the release of gastrin in either the gastric or intestinal phase studies. Furthermore, PYY had no significant effect on either the basal release of secretin, gastric inhibitory polypeptide, pancreatic polypeptide, or neurotensin, or on the stimulated release of pancreatic polypeptide by 2-deoxyglucose. The specific binding of gastrin to its receptors on the fundic mucosa was also unaffected by PYY. These results indicate that PYY inhibits the cephalic and gastric phases of acid secretion independently, and that its actions are not mediated by either a negative effect on gastrin release or a positive effect on the release of some of the known acid inhibitors, or by an inhibition of gastrin binding to its receptors on the fundic cells. Our present findings (in combination with our previous findings of inhibition of pentagastrin- and bethanechol-stimulated gastric acid secretion by PYY, independent of the vagal cholinergic mechanism) indicate that the action of PYY is either direct on the parietal cells or is mediated by yet another, unidentified, inhibitor.

Effect of peptide YY on insulin release stimulated by 2-deoxyglucose and neuropeptides in dogs.

Peptide YY (PYY) is a hormone released from gut after a meal. The objective of this study was to determine the effect of PYY on insulin release stimulated by either 2-deoxyglucose (2-DG) or neuropeptides in conscious dogs with gastric and duodenal fistulas. In control experiments dogs received either 2-DG (75 mg/kg i.v. bolus) or atropine (25 μg/kg bolus followed by 20 μg/kg/h i.v.) plus 2-DG (75 mg/kg i.v.) or bethanechol (80 μg/kg/h i.v.1 or vasoactive intestinal peptide (VIP, 4 μg/kg i.v. bolus) or gastrin-releasing peptide (GRP, 400 pmol/kg/h i.v.) or tetragastrin (G4, 100 μg/dog, i.v. bolus). On separate days, PYY was also infused intravenously in combination with one of the above stimulants. Given intravenously, PYY (200, 400 pmol/kg/h) significantly inhibited 2-DG stimulated-insulin secretion in a dose-dependent fashion. This inhibitory effect also existed in the presence of atropine. Peptide YY (400 pmoYkg/h) depressed the insulin levels in response to GRP or G4 but failed to inhibit bethanechol- and VIP-stimulated insulin release. After administration of the above stimulants, PYY did not modify the blood sugar concentrations. These results demonstrated that PYY might inhibit the cephalic phase of insulin release from dogs triggered by 2-DG and by the neuropeptides GRP and G4. Thus, PYY may play a negative feedback regulatory role on insulin release.

Peptide YY and gallbladder contraction

Abstract The purpose of this study was to examine the effect of peptide YY on contraction of the gallbladder in vivo and in vitro and on contraction of the sphincter of Oddi in vitro. In conscious dogs that were prepared with strain-gauge force transducers implanted in the gallbladder wall, peptide YY (400 ng/kg, bolus; 800 pmol/kg · h, infusion) did not affect the resting contractile pattern of the gallbladder, nor did it inhibit cholecystokinin-octapeptide (CCK-8)-stimulated gallbladder contraction. In contrast, the cholecystokinin antagonist proglumide (5, 10, 20, 40, or 80 mg/kg), given in vivo, inhibited CCK-8-stimulated gallbladder contraction in a dose-related manner. The highest dose of proglumide (80 mg/kg) completely abolished contraction of the gallbladder stimulated by CCK-8. In vitro studies showed that peptide YY (0.25, 0.5, or 1 μg/ml) did not affect the resting tension of rabbit gallbladder strips, and it did not inhibit CCK-8-stimulated contraction of gallbladder strips. Proglumide (0.4, 0.8, 1.6, or 3.2 mg/ml) inhibited CCK-8-stimulated tension of gallbladder strips in a dose-related manner. Peptide YY and CCK-8 had no effect on the motility of the canine sphincter of Oddi in vitro, whereas acetylcholine caused contraction and adrenergic agonists caused relaxation. These results suggest that peptide YY and pancreatone (a peptidelike substance, extracted from ileal and colonic mucosa, that inhibits CCK-8-stimulated gallbladder contraction in vivo) do not appear to be identical.

In vivo mitogenic effects of estradiol on colon cancers: Role of gastrin and gastrin receptors

We have previously reported mitogenic effects of gastrin on a mouse colon cancer (MC-26) cell line in vivo. The present studies were undertaken to determine if gonadal hormones can influence the mitogenic response of MC-26 cells to gastrin. The female gonadal hormone, estradiol (E2), was determined to be as mitogenic as pentagastrin (PG) for the growth of MC-26 tumors in mice; the mitogenic effects of E2 and PG were not additive. Female gonadal hormones were furthermore as effective as PG in maximally up-regulating gastrin receptor (GR) concentrations on MC-26 tumor membranes, which was confirmed in autoradiographic studies. Since PG and E2 had similar and non-additive trophic effects it was hypothesized that gastrin may be mediating the trophic effects of E2. Serum gastrin concentrations were significantly increased in E2 treated ovariectomized mice that correlated with an increase in tumor weights; E2 however was ineffective in stimulating the release of gastrin from perfused rat stomachs indicating that the increase in serum gastrin concentration on long-term treatment with E2 was mediated by some other mechanism. Saturable high-affinity E2 binding sites were not measured in MC-26 cells and tumors, supporting the possibility that mitogenic effects of E2 were probably mediated via indirect mechanisms. In summary our results indicate that both E2 and PG are equally mitogenic for colon cancer cells in vivo which may explain the sex- and age-related discrepancy in the incidence of human colon cancers.

Synergistic induction of cyclooxygenase-2 by gastrin and EGF in intestinal epithelial cells

Cyclooxygenase-2 (COX-2) is aberrantly overexpression in gastrointestinal cancers and has been implicated in carcinogenesis and cancer progression; but the regulation of COX-2 expression has not been well defined. EGF is an inducer of COX-2 expression. We recently reported that gastrin stimulates the expression of COX-2 mRNA, protein and its promoter activity in intestinal epithelial cells (Guo et al, J Binl Chem 2002, in press). The purpose of this study was to determine whether gastrin collaborates with EGF to synergistically induce COX-2 gene expression in RIE/CCKBR cells, and if so, what mechanisms are involved. METHODS. RIE/CCKBR cell line, denved from rat intestine epithelial cells (RIE1), possesses native EGF receptor (EGFR) and was stably transfected with CCK-B receptor. The COX-2 mRNA, protein and promoter activity were determined by Northern blot, Western blot and luciferase analyses, respectively. The phnsphorylation of extracellular signal-regulated kinase (ERK) was examined using anti-active ERK1/2 antibody. Tyrnsine phosphorylation of EGER was determined by immunoprecipitating with anti-EGFR and blotting with anti-phosphotyrosine antibodies. RESULTS. Gastrin (100 nM) or EGF (20 ng/ml) alone induced a timedependent increase of COX-2 protein levels (3 to 5 folds) in RIE/CCKBR cells. The combination of both peptides synergistically stimulated the COX-2 protein expression (10 to 30 folds), and increased the COX-2 mRNA abundance and COX-2 promoter activity. The synergistic effect was significantly suppressed by AG-1478, a selective inhibitor of EGFR tyrosine kinase activity; whereas gastrin induced a EGF-independent phnsphorylation of EGFR. The synergistic induction of COX-2 also was partially blocked by donnnant negative Src construct and the selective Src inhibitor PP2. Moreover, the combination of gastrni and EGF elicited a synergistic increase of ERK1/2 phosphorylation, whereas PD98059, a specific inhibitor of MEK/ERK pathway, significantly inhibited the induction of COX-2 in response to combined gastrin and EGF. CONCLUSION. Gastrin may collaborate with EGF to synergistically induce COX-2 expression in intestinal epithelial cells. The synergistic induction of COX-2 requires the gastrin-mediated transactivation of EGFR, and the activation of Src and ERK kinases. These findings provide a better understanding of the regulating mechanisms of COX-2 in intestinal epithelial cells.

Insulin-Like Growth Factors and Their Receptors and Binding Proteins in the Gastrointestinal System

Insulin-like growth factor I and II (IGF-I, and IGF-II) are single chain peptides with around 70% sequence homology and 50% homology with proinsulin The IGFs were first identified in 1956 and were originally named sulfation factors or somatomedins (1, 2). IGF circulating in the blood at concentrations of 20–80 nM is mainly produced by the liver; whereas tissue IGF is produced, in great part, locally. The expression of IGF-I and, to a lesser degree, of IGF-II in the human liver is under the control of growth hormone (GH). IGF-I can mimic most, but probably not all, the effects of GH. IGFs, their receptors and their binding proteins, constitute a family of cell modulators that play essential roles in the regulation of growth and development. The IGFs interact with specific receptors designated as type I and type II IGF receptors, as well as with insulin receptors. Most, if not all, of the mitogenic effects of IGFs are mediated via type I IGF receptors. The biological roles of IGFs are modulated by a family of at least six binding proteins (IGFBPs) that are found in the circulation, and in extracellular compartments and produced by most tissues (3–6).