Reciprocal regulation of mRNA and protein for subunits of cAMP-dependent protein kinase (RI alpha and C alpha) by cAMP in a neoplastic B cell line (Reh).

The present study examines the activity, levels of expression and regulation of cAMP-dependent protein kinase subunits during cAMP-mediated inhibition of Reh cell proliferation. Human Reh cells express mRNAs for the RI alpha and C alpha subunits of cAK at high levels and are practically devoid of cAMP-dependent protein kinase type II. Treatment with isoproterenol, forskolin, or a cAMP analog increased RI alpha mRNA in a time- and concentration-dependent manner (maximal, 4-fold, at 4-8 h). Messenger RNA for C alpha was also stimulated by cAMP, although with slower kinetics (maximal, 2-fold, at 16-24 h). Nuclear run-on assays showed a 2-fold increase in RI alpha gene transcription, whereas that of C alpha was unchanged. In spite of the stimulatory effects of cAMP on mRNAs for both RI alpha and C alpha, phosphotransferase activity and specific [3H]cAMP binding decreased rapidly after treatment with either cAMP or forskolin. Interestingly, the decrease in R and C activity preceded the increase in RI alpha and C alpha mRNA levels, raising the question whether increased mRNA levels may be secondary to the decrease in RI alpha or C alpha protein. The finding that the protein synthesis inhibitor cycloheximide gave changes in RI alpha and C alpha mRNA similar to cAMP and that co-treatment with cycloheximide and cAMP resulted in additive effects tend to support this notion.