FUNCTION OF THE HUMAN INSULIN PROMOTER IN PRIMARY CULTURED ISLET CELLS

Pancreatic islet beta cells regulate the rate of insulin gene transcri ption in response to a number of nutrients, the most potent of which i s glucose. To test for its regulation by glucose, the promoter sequenc e was isolated from the human insulin gene. When linked to chloramphen icol acetyltransferase and transfected into primary islet cultures, th e human insulin promoter is activated by glucose. In parallel islet tr ansfections, glucose also activates the L-pyruvate kinase and islet am yloid polypeptide promoters and represses the branched chain ketoacid dehydrogenase E1a promoter, but it does not affect the beta cell gluco se kinase promoter. Using deletion and substitution mutations of the p roximal human insulin promoter, we mapped a metabolic response element to the E box, E1, at -100 base pairs relative to the transcription st art site. Although the isolated E1 element responds to glucose, inclus ion of either of two AT-rich sequences, A1 or A2/Cl on either side of E1, results in dramatic synergistic activation. Inclusion of A2/Cl als o increases the response to glucose. The A2-E1-A1 region alone, howeve r, does not explain all of the activity of the human insulin promoter in cultured islets, and other transcriptionally important elements lik ely contribute to the glucose response as well.