INDUCTION OF CREB ACTIVITY VIA THE SURFACE IG RECEPTOR OF B-CELLS

The regulation and function of CREB was examined in B cells to begin t o elucidate the role of cAMP-derived signals in B cell activation. CRE -binding activity detected by the electrophoretic mobility shift assay was found to be constitutively expressed in nuclear extracts of prima ry murine splenic B cells and was unchanged in nuclear extracts obtain ed from B cells stimulated in a variety of ways. This activity was sho wn to be specific by competition analysis and to represent CREB or a c losely related molecule on the basis of a ''supershift'' in the mobili ty of the nucleoprotein complex induced by anti-CREB antiserum. The fu nction of B cell CREB was assessed by transient transfection of the mu rine B lymphoma cell line, BAL-1 7, with a CRE-dependent chloramphenic ol acetyltransferase (CAT) construct that contains a portion of the so matostatin promoter. Cross-linking of the surface Ig receptors of tran sfected BAL-17 B cells produced a threefold induction of CAT activity. Forskolin, which markedly induced CAT expression in PC12 cells transf ected with the CRE-dependent construct, failed to stimulate CAT activi ty in transfected BAL-17 B cells despite an increase in cAMP. However, anti-Ig was found to act in synergy with forskolin to produce enhance d CAT activity. A phosphoprotein of appropriate molecular size for CRE B was immunoprecipitated from anti-Ig plus forskolin treated BAL-17 B cells. These results suggest that CREB is present in primary B cells a nd that CRE-dependent gene expression is regulated by surface Ig eithe r alone or in synergy with cAMP; the latter implies cross-talk between intracellular signaling pathways acting at the level of CREB.