Identification of a 70-kDa gastrin-binding protein on DLD-1 human colorectal carcinoma cells

Gastrin17gly acts as a growth factor for the colonic mucosa. Studies of the receptor involved have generally been restricted to its binding properties, and no investigation of the structure of gastrin17gly receptors on human colorectal carcinoma cell lines has yet been reported. The aim of this study was to optimise the conditions for binding of gastrin17gly to the human colorectal carcinoma cell line DLD-1, and to investigate the structure of the receptor responsible. Binding of 125I[Met15]gastrin17gly to DLD-1 cells was measured in competition experiments with increasing concentrations of either gastrin17gly or gastrin17, or with single concentrations of gastrin receptor antagonists. The molecular weights of the gastrin17gly binding proteins were determined by gel electrophoresis and autoradiography after covalent cross-linking of 125I[Nle15]gastrin2,17gly to cells or membranes with disuccinimidyl suberate. The IC50 value for binding of gastrin17gly to DLD-1 cells was 2.1+/-0.4 microM. Binding was inhibited by the non-selective gastrin/cholecystokinin receptor antagonists proglumide and benzotript, but not by the cholecystokinin-A receptor antagonist L364,718, or the gastrin/cholecystokinin-B receptor antagonist L365,260. The molecular weight of the major gastrin binding protein on DLD-1 cells or membranes was 70,000. We conclude that the major gastrin17gly binding site on the human colorectal carcinoma cell line DLD-1 is clearly distinct from the cholecystokinin-A and gastrin/cholecystokinin-B receptors, but is similar in some respects to the gastrin/cholecystokinin-C receptor.