Regulation of gene expression by transfected subunits of cAMP-dependent protein kinase

cAMP regulates the expression of several genes by activation of a promoter consensus sequence which functions as a cAMP-response element. Evidence indicated that this is accomplished via cAMP dissociation of cAMP-dependent protein kinase into its regulatory (R) and catalytic (C) subunits. Our investigations of the role of these two subunits in gene expression provide direct and quantitative evidence that the C subunit is required for cAMP stimulation of the cAMP-response element in the vasoactive-intestinal-peptide gene in rat pheochromocytoma cells. After cotransfection of a metallothionein-regulated C-subunit expression vector (pCEV) and a vasoactive-intestinal-peptide--chloramphenicol acetyltransferase construct containing a cAMP-response element, we could demonstrate expression of transfected C-alpha-subunit mRNA (truncated size 1.7 kb) by Northern blot and a concentration-dependent C subunit stimulation of chloramphenicol acetyltransferase activity. Basal activity was stimulated 12- and 50-fold by pCEV (30 micrograms), in the absence and presence, respectively, of Zn2+. Metallothionein-regulated expression of C was demonstrated by results that showed a 2-4-fold increase in chloramphenicol acetyltransferase activity in the presence versus the absence of 90 microM Zn2+. In contrast, overexpression of the R-II beta regulatory subunit did not stimulate chloramphenicol acetyltransferase activity, and R-II beta transfected together with C (ratio 2:1 and 4:1) inhibited the stimulation by the C subunit 70% and 90% respectively. Our results indicate that transfection of cAMP-dependent protein kinase subunits results in functional expression of both C-alpha and R-II beta subunits. Expression of the C subunit mediated cAMP-regulated gene expression but this expression could be inhibited by cotransfected R-II beta subunit, indicating intracellular reconstitution of the inactive holoenzyme of cAMP-dependent protein kinase.