B Cell Receptor-induced cAMP-response Element-binding Protein Activation in B Lymphocytes Requires Novel Protein Kinase

The cAMP-response element-binding protein (CREB) is activated by phosphorylation on Ser-133 and plays a key role in the proliferative and survival responses of mature B cells to B cell receptor (BCR) signaling. The signal link between the BCR and CREB activation depends on a phorbol ester (phorbol 12-myristate 13-acetate)-sensitive protein kinase C (PKC) activity and not protein kinase A or calmodulin kinase; however, the identity and role of the PKC(s) activity has not been elucidated. We found the novel PKC (nPKC ) activator bistratene A is sufficient to induce CREB phosphorylation in murine splenic B cells. The pharmacological inhibitor Gö6976, which targets conventional PKCs and PKC , has no effect on CREB phosphorylation, whereas the nPKC inhibitor rottlerin blocks CREB phosphorylation following BCR cross-linking. Bryostatin 1 selectively prevents nPKC depletion by phorbol 12-myristate 13-acetate when coapplied, coincident with protection of BCR-induced CREB phosphorylation. Ectopic expression of a kinase-inactive nPKC blocks BCR-induced CREB phosphorylation in A20 B cells. In addition, BCR-induced CREB phosphorylation is significantly diminished in nPKC -deficient splenic B cells in comparison with wild type mice. Consistent with the essential role for Bruton’s tyrosine kinase and phospholipase C 2 in mediating PKC activation, Bruton’s tyrosine kinaseand phospholipase C 2-deficient B cells display defective CREB phosphorylation by the BCR. We also found that p90 RSK directly phosphorylates CREB on Ser-133 following BCR cross-linking and is positioned downstream of nPKC . Taken together, these results suggest a model in which BCR engagement leads to the phosphorylation of CREB via a signaling pathway that requires nPKC and p90 RSK in mature B cells.