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 to 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 primary murine splenic B cells and was unchanged in nuclear extracts obtained from B cells stimulated in a variety of ways. This activity was shown to be specific by competition analysis and to represent CREB or a closely related molecule on the basis of a "supershift" in the mobility of the nucleoprotein complex induced by anti-CREB antiserum. The function of B cell CREB was assessed by transient transfection of the murine B lymphoma cell line, BAL-17, with a CRE-dependent chloramphenicol acetyl-transferase (CAT) construct that contains a portion of the somatostatin promoter. Cross-linking of the surface Ig receptors of transfected BAL-17 B cells produced a threefold induction of CAT activity. Forskolin, which markedly induced CAT expression in PC12 cells transfected with the CRE-dependent construct, failed to stimulate CAT activity in transfected BAL-17 B cells despite an increase in cAMP. However, anti-Ig was found to act in synergy with forskolin to produce enhanced CAT activity. A phosphoprotein of appropriate molecular size for CREB was immunoprecipitated from anti-Ig plus forskolin treated BAL-17 B cells. These results suggest that CREB is present in primary B cells and that CRE-dependent gene expression is regulated by surface Ig either alone or in synergy with cAMP; the latter implies cross-talk between intracellular signaling pathways acting at the level of CREB.
Xie
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Department of Microbiology, Boston University Medical Center, MA 02118.
Chiles
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Rothstein
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D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis / Q000494:pharmacology*; D017362:Cyclic AMP Response Element-Binding Protein / Q000032:analysis / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D005786:Gene Expression Regulation; D007106:Immune Sera / Q000276:immunology; D016393:Lymphoma, B-Cell / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D016716:PC12 Cells; D010750:Phosphoproteins / Q000276:immunology; D051381:Rats; D011947:Receptors, Antigen, B-Cell / Q000276:immunology*; D017452:Receptors, IgG / Q000378:metabolism; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
D017362:Cyclic AMP Response Element-Binding Protein; D007106:Immune Sera; D010750:Phosphoproteins; D011947:Receptors, Antigen, B-Cell; D017452:Receptors, IgG; D005576:Colforsin; D000242:Cyclic AMP