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.

The effects of partial retro-inverso modifications of selected peptide bonds of the N-terminal tetrapeptide of gastrin have been studied. In some of the synthesized compounds, the phenylalanyl residue has been replaced by the (R,S)-2-benzylmalonyl, 3-phenylpropionyl, benzylcarbamoyl, or benzyloxycarbonyl moieties. All pseudopeptides showed affinity for the gastrin receptor, in vitro, with potencies varying from IC50 = 10(-7) to IC50 = 10(-4) M. These compounds exhibited little or no activity on acid secretion in the anesthetized rat but were able to antagonize the action of gastrin. Among the most potent were Boc-Trp-Leu-gAsp-CO-CH2CH2C6H5 (20) (ED50 = 0.15 microM/kg), Boc-Trp-Leu-gAsp-m(R,S)Phe-NH2 (3) (ED50 = 0.15 microM/kg), and Boc-Trp-gLeu-D-Asp-m(R,S)Phe-NH2 (7) (ED50 = 0.3 microM/kg).

Pseudo-peptide analogues of the C-terminal tetrapeptide of gastrin, in which a peptide bond has been replaced by a CH2-NH bond, i.e. (tert-butyloxycarbonyl)-L-tryptophyl-psi (CH2-NH)-L-leucyl-L-aspartyl-L-phenylalanine amide (8), (tert-butyloxycarbonyl)-L-tryptophyl-L-leucyl-psi (CH2-NH)-L-aspartyl-L-phenylalanine amide (13), (tert-butyloxycarbonyl)-L-tryptophyl-L-leucyl-L-aspartyl-psi (CH2NH)-L-phenylalanine amide (20), were synthesized. The pseudo-peptides 8 and 13 were shown to have the same affinity as (tert-butyloxycarbonyl)-L-tryptophyl-L-leucyl-L-aspartyl-L-phenylalanine amide (21) for the gastrin receptor on isolated mucosal cells. The pseudo-peptide 20 exhibited lower affinity (IC50 congruent to 10(-5) M). The biological activity of these pseudo-peptides was studied on acid secretion in the anesthetized rat. Compound 8 stimulated acid secretion, identically with that of 21. Compound 13 did not exhibit any agonist activity but was able to antagonize the action of gastrin (ED50 = 0.3 mg/kg). Compound 20 did not show any agonist activity but was able to inhibit gastrin-induced acid secretion, with lower potency (ED50 = 15 mg/kg). The importance of the peptide bonds in the mode of action of gastrin is discussed, and a hypothetical approach of the mechanism of action is presented.

Glicentin (proglucagon 1-69 GLIC) and oxyntomodulin (proglucagon 33-69 or OXM) are two peptide hormones that are co-released from ileum and large intestine during digestion. They modulate in vivo gastric acid secretion and the gastro-pyloro-duodenal activity. The specificity of their effects is linked to the presence of their C-terminal octapepide. As yet, no isolated target cell that responds specifically to this family of peptides has been described. The present report describes the in vitro effect of human synthetic GLIC, OXM and octapeptide-bearing fragments on smooth muscle cells isolated from the rabbit antrum. GLIC or OXM decreased the mean length of the cells by: 13.9 +/- 0.8% and 15.5 +/- 0.9%, respectively - GLIC being 16 times more potent than OXM (respective EC50 values: 5 and 83 pM). The C-terminal fragments OXM(19-37) and OXM(30-37) were as efficient as GLIC or OXM. Their potencies were OXM = OXM(19-37)>>OXM(30-37). Glucagon, which corresponds to OXM without the C-terminal octapeptide, or glucagon-like peptide-1 (7-36 amide) did not have any effect. The response to OXM was not influenced by antagonists to muscarinic, cholecystokinin or substance P receptors. In conclusion, our studies demonstrate for the first time an isolated target cell that responds specifically to GLIC, OXM and other octapeptide-bearing peptides.