Regulation of insulin gene expression by dexamethasone, Ca2+ and a phorbol ester

The transcription of the insulin genes in rat pancreatic islets was determined in response to dexamethasone, cholera toxin and Ca2+. Furthermore, the contents of islet insulin mRNA after culture with the phorbol ester 4 beta-phorbol 12-myristate 13-acetate (TPA) were assayed by dot-blot analysis. Dexamethasone and cholera toxin stimulated the rates of insulin gene transcription, whereas the withdrawal of Ca2+ and addition of TPA exerted no effects on insulin gene expression. It is concluded that islet cAMP may be one factor regulating the transcription of the insulin gene in response to nutrient secretagogues, whereas Ca2+ and activation of protein kinase C do not serve such a function.