PROTEIN-KINASE-C MEDIATES ACTIVATION OF NUCLEAR CAMP RESPONSE ELEMENT-BINDING PROTEIN (CREB) IN B-LYMPHOCYTES STIMULATED THROUGH SURFACE IG

The cAMP response element-binding protein (CREB) is generally consider ed to be responsive to elevation of cAMP through the activity of prote in kinase A (PKA). Although it is well known that cAMP-raising agents can strongly influence B cell stimulation, the regulation of CREB has been little studied. Recently, cross-linking of surface Ig (sIg) was s hown to result in trans-activation of a cAMP response element (CRE)-de pendent promoter to which bound B cell CREB. In this study, we explore d the mechanism underlying this unexpected linkage between sIg and CRE B. We found that sIg cross-linking results in phosphorylation of CREB at Ser(133). Although this phosphorylation step is mediated by PKA in pheochromocytoma cells, it depends on protein kinase C (PKC) in B lymp hocytes. This conclusion is based on abrogation of sIg-induced CREB Se r(133) phosphorylation by long-term phorbol-ester treatment to deplete PKC, and mimicking of sIg-induced CREB phosphorylation and CRE-depend ent gene expression by short-term PKC agonism. Furthermore, CD40 ligan d (CD40L) and LPS, two PKC-independent forms of B cell stimulation, fa iled to induce phosphorylation of CREB Ser(133). These results suggest that CREB responds to specific surface-receptor signals in B cells an d that this response is mediated by PKC. Interestingly, forskolin fail ed to induce phosphorylation of CREB Ser(133) in B cells, although it did so in PC12 pheochromocytoma cells. Taken together with PKC mediati on of CREB Ser(133) phosphorylation in B cells, these results suggest that the dominant mode of CREB regulation is cell-type specific.