ACTIVATION OF THE PROTEIN-KINASE-A INCREASES THE DNA-BINDING AND TRANSCRIPTIONAL ACTIVITY OF C-REL IN T-CELLS

Cyclic AMP (cAMP)-dependent protein kinase A (PKA) is known to have bo th negative and positive effects on the activation mechanisms of T lym phocytes. The authors have analysed the effect of increased cAMP on th e activation of NF-kappa B transcription factor. This factor controls the expression of several genes (e.g. IL-2 and IL-2 receptor) involved in the activation and proliferation of T cells. The authors found tha t elevation of intracellular cAMP in Jurkat T leukaemia cells activate d with phorbol ester (PDBu)/calcium ionophore (A23187) increased the D NA-binding of NF-kappa B as detected by the electrophoretic mobility s hift assay (EMSA). Analysis of the subunit composition of the DNA-bind ing complex indicated that the amount of c-Rel was enhanced while RelA was decreased. Analysis of the effect of elevated cAMP on the degrada tion of I kappa B-alpha and I kappa B-beta did not reveal an essential change in degradation kinetics of these inhibitor proteins. The eleva tion of cAMP did not increase the synthesis of c-Rel, but it enhanced the nuclear localization of this protein. Transfection of Jurkat cells with a plasmid kB/TK 10-CAT indicated that the increased DNA-binding of c-Rel containing complexes seen in EMSA was also functional. These data imply that the strong and long-lasting c-Rel nuclear localization and DNA-binding induced by protein kinase A is not due to increased c -Rel synthesis or enhanced degradation of the I kappa B inhibitors. Th erefore, a direct phosphorylation of the c-Rel protein is the most pla usible explanation for these observations. Taken together, these resul ts suggest that cAMP is able to regulate the expression of NF-kappa B- dependent genes in T cells by modifying the composition and subunit ac tivity of NF-kappa B.