Glycine-extended gastrin acts as an autocrine growth factor in a nontransformed colon cell line

Abstract

Background and Aims: The hypothesis that progastrin-derived peptides act as autocrine growth factors for colorectal carcinomas has generated considerable interest. However, the influence of autocrine gastrins on nontumorigenic colonic cells has not been investigated. This study tested the above hypothesis in the nontumorigenic, conditionally immortalized mouse colon cell line YAMC. Methods: The effects of expression of antisense or sense gastrin messenger RNA, treatment with antibodies against progastrin- derived peptides, or treatment with gastrin receptor antagonists on YAMC cell proliferation were measured. Results: YAMC clones expressing antisense gastrin messenger RNA had reduced levels of immunoreactive progastrin- derived peptides and a reduced rate of proliferation, relative to vector only-transfected cells. Glycine-extended gastrin17, but not amidated gastrin17, reversed the antisense-induced inhibition of proliferation and stimulated the proliferation of sense- or vector only-transfected cells. YAMC cells bound 125I-glycine-extended gastrin17 (K(d), 0.36 nmol/L, 1810 sites/cell), but not 125I-amidated gastrin17, and binding was unaffected by gastrin receptor antagonists including benzotript. Proliferation of all YAMC clones was partially inhibited either by an antibody selective for glycine-extended gastrin or by preincubation with benzotript, and the inhibitory effects were additive. Conclusions: YAMC cells use nonamidated progastrin-derived peptides as autocrine growth factors, partly through binding to an extracellular receptor selective for glycine-extended gastrin, and partly through an intracellular mechanism.