Differential expression of the protein kinase A regulatory subunit (RIα) in pancreatic endocrine cells

A PCR-based subtractive cloning procedure was used to identify genes expressed at higher levels in the pancreatic beta cell line beta TC1, as compared to the pancreatic alpha cell line alpha TC1. One of the clones isolated by this procedure corresponded to the regulatory subunit (RI alpha) of protein kinase A (PKA). Using antibodies directed against RI alpha, we now demonstrate both by immunoblot and immunofluorescence that RI alpha protein is present at higher levels in cultured beta cells as compared to alpha cells. In vitro PICA assays revealed high basal PKA activity in alpha TC1 extracts, which changed little on addition of exogenous cAMP. On the other hand, extracts from beta cells showed very low basal activity of PICA, which was elevated upon addition of cAMP. A similar trend was observed in vivo using transfected luciferase constructs bearing multiple copies of a CRE element: in alpha TC1 cells, no induction by forskolin was observed, whereas in beta TC1 cells, forskolin produced a 9-fold increase in activity, Therefore, the results indicate that RI alpha of PW is selectively ex-pressed in pancreatic beta cells as compared to alpha cells: this selective expression is associated with major differences in the properties of the PICA signal transduction pathway, Differential expression of the regulatory subunit may play a role in determining the patterns of gene expression and signal transduction characteristic of alpha and beta cells. (C) 1998 Federation of European Biochemical Societies.