Recovery of responsiveness to ACTH and cAMP in a protein kinase-defective adrenal cell mutant following transfection with a protein kinase gene.

The cause and effect relationship between mutations in cAMP-dependent protein kinase activity and resistance of adrenocortical tumor cells to ACTH and cAMP was evaluated by transfection with cloned cDNAs encoding subunits of the mouse cAMP-dependent protein kinase. Protein kinase defective, Kin 8 adrenocortical tumor cells were transfected with pRev [an expression vector encoding the regulatory subunit of the type 1 cAMP-dependent protein kinase (RI)] or with pC alpha ev [an expression vector encoding the catalytic subunit of cAMP-dependent protein kinase (C)]. The pC alpha ev transformant recovered cAMP responsive protein kinase activity, whereas the pRev transformant recovered cAMP-binding activity, but did not recover cAMP responsive protein kinase activity. The pC alpha ev transformant concomitantly recovered steroidogenic and morphologic responsiveness to ACTH- and 8-bromo-cAMP, whereas the pRev transformant remained resistant to these effects of the hormone and cyclic nucleotide. Since Kin 8 cells recovered their responsiveness to ACTH and 8-bromo-cAMP following transfection with pC alpha ev we suggest that the defect in cAMP-dependent protein kinase activity is directly responsible for the ACTH- and cAMP-resistant phenotype of the Kin 8 mutant.