Insulinotropic hormone glucagon-like peptide-I(7-37) stimulation of proinsulin gene expression and proinsulin biosynthesis in insulinoma βTC-1 cells

Abstract

Glucagon-like peptide-I(7-37) [GLP-I(7-37)] is an intestinal peptide hormone that is released in response to oral nutrients and that potently augments glucose-mediated insulin secretion. GLP-I(7-37) has potent insulin-releasing activities in vivo in response to oral nutrients, in situ in the isolated perfused pancreas, and in vitro in cultured pancreatic B-cells. As such GLP-I(7-37) is a potent hormonal mediator in the enteroinsular axis involved in the regulation of glucose homeostasis. We now show that in addition to stimulating the release of insulin, GLP-I(7-37) stimulates proinsulin gene expression at the levels of gene transcription and cellular levels of proinsulin messenger RNA as well as the translational biosynthesis of proinsulin. These findings of the positive anabolic actions of GLP-I(7-37) on the synthesis of insulin in B-cells support the notion that GLP-I(7-37) may be of therapeutic use in stimulating the production of insulin in patients with noninsulin-dependent diabetes mellitus and that overproduction of insulin with subsequent hypoglycemia will not occur in response to the administration of GLP-I(7-37). Furthermore, these positive actions of GLP-I(7-37) on insulin production obviate the possibility of B-cell exhaustion in response to such a potent secretagogue.