Molecular cloning and cell-specific expression of newly discovered subunits of cAMP-dependent protein kinases. Implications for different cellular responses to cAMP.

In recent years a multiplicity in isoforms of cAMP-dependent protein kinases has been revealed. Gene products for four different regulatory subunits (RI alpha, RI beta, RII alpha, RII beta) and two different catalytic subunits (C alpha, C beta) have been identified. We hereby present the molecular cloning of rat cDNAs for RII beta, as well as full-length human cDNAs for RII beta and RI alpha. The amino acid sequences deduced from the cDNAs of the regulatory subunits, revealed dissimilarities which were primarily confined to the N-terminal part of the protein. Based on the vital role in testicular function played by gonadotropin-induced activation of cAMP-dependent protein kinases, mRNA levels for the various subunits of cAMP-dependent protein kinase have been studied in rat testis. A clear pattern of cellular localization of mRNAs for the various subunits of cAMP-dependent protein kinase has been demonstrated. Furthermore, stimulation of Sertoli cells by FSH and cAMP elicited a differential response in mRNA levels for various subunits. A dramatic increase (30-40 fold) in the mRNA for RII beta (3.2 kb) was seen with cAMP stimulation, whereas such treatment had minor effects on mRNAs for RI alpha, RII alpha and C alpha. A distinct pattern of expression for various subunits of cAMP-dependent protein kinase was observed during germ cell differentiation. RI alpha and RI beta were expressed at high levels at early stages of spermatogenesis, whereas unique mRNAs for RII alpha and RII beta appeared in post-meiotic germ cells. Altogether, the present results demonstrate specific expression of mRNAs for different subunits of cAMP-dependent protein kinase in different cell types, during hormonal stimulation and during cellular differentiation. This indicates that the individual subunits may confer specific functional properties to the cAMP-dependent protein kinase holoenzyme and to the cAMP signal pathway of the cell.