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 considered to be responsive to elevation of cAMP through the activity of protein 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 shown to result in trans-activation of a cAMP response element (CRE)-dependent promoter to which bound B cell CREB. In this study, we explored the mechanism underlying this unexpected linkage between sIg and CREB. We found that sIg cross-linking results in phosphorylation of CREB at Ser133. Although this phosphorylation step is mediated by PKA in pheochromocytoma cells, it depends on protein kinase C (PKC) in B lymphocytes. This conclusion is based on abrogation of sIg-induced CREB Ser133 phosphorylation by long-term phorbol-ester treatment to deplete PKC, and mimicking of sIg-induced CREB phosphorylation and CRE-dependent gene expression by short-term PKC agonism. Furthermore, CD40 ligand (CD40L) and LPS, two PKC-independent forms of B cell stimulation, failed to induce phosphorylation of CREB Ser133. These results suggest that CREB responds to specific surface-receptor signals in B cells and that this response is mediated by PKC. Interestingly, forskolin failed to induce phosphorylation of CREB Ser133 in B cells, although it did so in PC12 pheochromocytoma cells. Taken together with PKC mediation of CREB Ser133 phosphorylation in B cells, these results suggest that the dominant mode of CREB regulation is cell-type specific.
Department of Microbiology, Evans Memorial Department of Clinical Research, Boston University Medical Center, MA 02118.
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D000818:Animals; D001402:B-Lymphocytes / Q000201:enzymology / Q000276:immunology*; D023201:CD40 Ligand; D002467:Cell Nucleus / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000502:physiology*; D016393:Lymphoma, B-Cell / Q000473:pathology; D008562:Membrane Glycoproteins / Q000494:pharmacology; D051379:Mice; D008807:Mice, Inbred BALB C; D016716:PC12 Cells / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D011493:Protein Kinase C / Q000819:agonists / Q000502:physiology*; D011499:Protein Processing, Post-Translational; D051381:Rats; D011947:Receptors, Antigen, B-Cell / Q000276:immunology*; D014407:Tumor Cells, Cultured
D017362:Cyclic AMP Response Element-Binding Protein; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D011947:Receptors, Antigen, B-Cell; D023201:CD40 Ligand; D010768:Phosphoserine; D005576:Colforsin; D000242:Cyclic AMP; D011493:Protein Kinase C