MULTIPLE PROTEIN-KINASE A-REGULATED EVENTS ARE REQUIRED FOR TRANSCRIPTIONAL INDUCTION BY CAMP

The second messenger cAMP stimulates the expression of numerous genes via the protein kinase A-mediated phosphorylation of the cAMP response element-binding protein (CREB) at Ser-133. Ser-133 phosphorylation, i n turn, appears to induce target gene expression by promoting interact ion between CREB and CBP, a 265-kDa nuclear phosphoCREB-binding protei n. It is unclear, however, whether Ser-133 phosphorylation per se is s ufficient for CREB-CBP complex formation and for target gene induction in vivo. Here we examine CREB activity in Jurkat T cells after stimul ation of the T-cell receptor (TCR), an event that leads to calcium ent ry and diacylglycerol production, Triggering of the TCR stimulated Ser -133 phosphorylation of CREB with high stoichiometry, but TCR activati on did not promote CREB-CBP complex formation or target gene induction unless suboptimal doses of cAMP agonist were provided as a costimulus . Our results demonstrate that, in addition to mediating Ser-133 phosp horylation of CREB, protein kinase A regulates additional proteins tha t are required for recruitment of the transcriptional apparatus to cAM P-responsive genes.