Glucose and forskolin regulate IAPP gene expression through different signal transduction pathways

Molecular mechanisms for the regulation of islet amyloid polypeptide (IAPP) gene expression remain unclear. In the present study, we investigated the effects of glucose and forskolin on IAPP gene regulation in the INS-1 islet beta -cell line. Both glucose and forskolin increased the level of express ion of this gene, as measured by Northern blot analysis, and increased IAPP gene transcription in a time- and concentration-dependent manner, as demon strated in a reporter gene assay. Although inhibition of protein kinase A a ctivity with H-89 eliminated the effect of forskolin on this gene, the gluc ose effect was unaffected. This supported the predominant use of a protein kinase A-independent signaling pathway for glucose regulation of the IAPP g ene. Electrophoretic mobility shift assay further indicated that glucose an d forskolin regulated expression of this gene by targeting different elemen ts of the promoter. Mutation of the cAMP regulatory element flanking the IA PP coding region resulted in the loss of most of the forskolin-stimulated I APP gene promoter activity, whereas glucose-enhanced IAPP gene transcriptio n was unaffected. These results demonstrate parallel and distinct regulator y pathways involved in glucose- and forskolin-induced IAPP gene expression in this model beta -cell system.