THE INSULIN GENE CONTAINS MULTIPLE TRANSCRIPTIONAL ELEMENTS THAT RESPOND TO GLUCOSE

The beta cells in the pancreatic islets of L,angerhans increase insuli n gene transcription in response to increased glucose concentration. W e have mapped sequences within the rat insulin I gene 5'-fIanking DNA (rInsI promoter) that direct this transcriptional response to glucose. When linked to chloramphenicol acetyltransferase and expressed in cul tured beta cells, no single mutation of the rInsI promoter removes its ability to respond to glucose, although several mutations cause marke d reductions in basal chloramphenicol acetyltransferase expression. A 50-bp sequence isolated from the rInsI promoter, the Far-FLAT minienha ncer, can confer glucose responsiveness to nonresponsive promoters. Fi ne mapping of this minienhancer further localizes a glucose response t o the sequence GGCCATCTGGCC, or the Far element. Nuclear extracts from islets grown in various glucose concentrations demonstrate a glucose- stimulated increase in a protein complex that binds the Far element an d contains the transcription factors Pan-1 and Pan-2. Overexpression o f intact or partially deleted Pan-1 ablates the Far-directed transcrip tional response to glucose. We conclude that the full glucose response of the insulin promoter involves the interaction of multiple sequence elements. Part of this response, however, results from activation of a complex binding at the Far element.