RECIPROCAL REGULATION OF MESSENGER-RNA 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 regu lation of cAMP-dependent protein kinase subunits during cAMP-mediated inhibition of Reh cell proliferation. Human Reh cells express mRNAs fo r the RIalpha and Calpha subunits of cAK at high levels and are practi cally devoid of cAMP-dependent protein kinase type II Treatment with i soproterenol, forskolin, or a cAMP analog increased RIalpha mRNA in a time- and concentration-dependent manner (maximal, 4-fold, at 4-8 h). Messenger RNA for Calpha was also stimulated by cAMP, although with sl ower kinetics (maximal, 2-fold, at 16-24 h). Nuclear run-on assays sho wed a 2-fold increase in RIalpha gene transcription, whereas that of C alpha was unchanged. In spite of the stimulatory effects of cAMP on mR NAs for both RIalpha and Calpha phosphotransferase activity and specif ic [H-3]cAMP binding decreased rapidly after treatment with either cAM P or forskolin. Interestingly, the decrease in R and C activity preced ed the increase in RIalpha and Calpha mRNA levels, raising the questio n whether increased mRNA levels may be secondary to the decrease in RI alpha or Calpha protein. The finding that the protein synthesis inhibi tor cycloheximide gave changes in RIalpha and Calpha mRNA similar to c AMP and that co-treatment with cycloheximide and cAMP resulted in addi tive effects tend to support this notion.