Ligation of membrane IgM stimulates a novel c-Jun amino-terminal domain kinase activity in Daudi human B cells.
Stress-activated protein kinases (SAPK; also known as JNK for c-Jun N-terminal kinase) phosphorylate Ser63 and Ser73 in the amino-terminus of the c-Jun protein and potentiate its transcriptional activity. We have analysed phosphorylation of GST fusion proteins containing the c-Jun N-terminal domain by lysates of Daudi human B lymphoblastoid cells stimulated with medium or anti-IgM. Crosslinking membrane IgM (mIgM) results in an increase in phosphorylation of GST-c-Jun (5-89) in an antibody dose-dependent manner. The kinase activity specifically phosphorylates the c-Jun N-terminal domain since it does not phosphorylate GST or GST-JunB. The activity preferentially phosphorylates the substrate that contains the sites for in vivo phosphorylation by SAPK/JNK and requires the delta domain of c-Jun, which is also required for SAPK/JNK activity. However, the c-Jun N-terminal kinase activity induced by mIgM ligation is not precipitatable with anti-SAPK/JNK antibodies. In addition, unlike SAPK/JNKs, the mIgM-dependent c-Jun N-terminal kinase activity is not detectable in assays for renaturable kinase activity (in-gel assay) or in assays that test activities that bind to c-Jun (solid-phase assay). The increased phosphorylation of c-Jun N-terminal domain in response to mIgM ligation is unlikely to be due to mIgM-activated ERKs as it was not suppressed by a selective MEK inhibitor. Thus, the mIgM-induced activity is distinct from the known SAPK/JNKs and may represent a novel mechanism for c-Jun phosphorylation in response to mIgM engagement in human B cells.
Li
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Department of Medicine, University of Alabama at Birmingham 35294, U.S.A.
Franklin
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CC
Kraft
A S
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Carter
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RH
D001402:B-Lymphocytes / Q000201:enzymology* / Q000276:immunology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000096:biosynthesis / Q000378:metabolism*; D004789:Enzyme Activation / Q000276:immunology; D004790:Enzyme Induction / Q000276:immunology; D006801:Humans; D007075:Immunoglobulin M / Q000378:metabolism* / Q000502:physiology; D048031:JNK Mitogen-Activated Protein Kinases; D016393:Lymphoma, B-Cell; D020928:Mitogen-Activated Protein Kinases; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism* / Q000502:physiology; D014407:Tumor Cells, Cultured
D007075:Immunoglobulin M; D011947:Receptors, Antigen, B-Cell; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases