Differential transcriptional regulation by the alpha- and gamma-catalytic subunit isoforms of XXXX -dependent protein kinase.

@entity268 @entity1 @entity18774 @entity573 @entity25449 @entity3419
The C gamma and C alpha isoforms of the @entity268 -dependent protein kinase (PKA) share 83% identity including all critical catalytic and substrate-binding residues defined to date. Compared to C alpha, C gamma has a different substrate specificity and a selective pseudosubstrate specificity, exhibiting inhibition by regulatory subunits, but not by the protein kinase inhibitor. In these studies, C gamma-mediated gene transcription regulation was compared with that of C alpha in four cell lines using transient transfection/dual luciferase assays. As compared to C gamma, C alpha more efficiently activated a @entity268 -response element (CRE)-regulated fragment of the @entity1 alpha-glycoprotein hormone promoter which was coupled to a firefly luciferase reporter gene (pGH alpha-fluc). This occurred in Cos7, Y1, and Kin8 adrenal cells by 23-, 6.5-, and 1.4-fold, respectively. In contrast, C gamma, but not C alpha, activated the Sp1RE-regulated herpes simplex virus thymidine kinase promoter which was coupled to a Renilla luciferase reporter ( @entity25449 -rluc). In @entity3419 -deficient Sf9 cells, pGH alpha-fluc expression was maintained for both isoforms, but cotransfection with an @entity3419 expression plasmid was necessary and sufficient for activation of @entity25449 -rluc expression by C gamma. In all cell lines, cotransfection with a @entity18774 expression plasmid enhanced the transcriptional activation of both C alpha and C gamma (1.5- to 3-fold), while a catalytically inactive @entity18774 mutant (PDK. @entity573 ) did not. These results suggest that both C alpha and C gamma can activate CRE-responsive genes; however, C alpha does so with better efficiency than C gamma. In contrast to C alpha, C gamma activates transcription of genes containing @entity25449 -like Sp1RE sites. Activation of different C subunit isoforms can provide a means to diversify @entity268 -mediated transcription, possibly affecting cell phenotype.
