Membrane IgM cross-linking is not coupled to protein kinase C translocation in WEHI-231 B lymphoma cells.
The early molecular events involved in the process of signal transduction via membrane immunoglobulins (mIg) include phosphatidyl inositol metabolism, intracellular Ca2+ mobilization, and protein kinase C (PKC) activation. Anti-mIg antibodies exert either stimulating or inhibitory effects depending on the activation state and/or the differentiation stage of B cells. WEHI-231 is a murine B lymphoma that becomes inactivated upon anti-mIg treatment. This lymphoma has an immature B cell phenotype and is considered as a model for tolerance induction in B lymphocytes. In this study, we have investigated the relationship between mIg triggering, Ca2+ elevation, PKC translocation, and growth inhibition in WEHI-231 cells. Monoclonal antibodies to mu and kappa chains of the mIgM receptor promoted a rapid increase in intracytoplasmic Ca2+ and were potent inhibitors of cell growth. Ca2+ elevation and PKC translocation have been previously shown to be associated in B lymphocytes. To study the subcellular distribution of PKC in WEHI-231 cells, we used enzymatic assays and immunodetection methods. Although phorbol 12-myristate 13-acetate induced a rapid and almost complete redistribution of cytosolic PKC to the membrane fraction, anti-mIg treatment failed to modify the compartmentalization of PKC. These findings extend recent observations suggesting that B cell triggering through mIg receptors may involve additional pathways independent from PKC activation. PKC activation in normal B cells is also believed to provide a regulatory signal which limits the magnitude of the early signals produced by anti-mIg. Such a regulatory control is unlikely in WEHI-231 cells, due to the dissociation between Ca2+ mobilization and PKC translocation. Our findings therefore suggest that the sensitivity of immature B cells such as WEHI-231 to the inhibitory effects of anti-mIg antibodies may result in part from alterations of the phosphoinositide signal transduction pathway.
Sarthou
P
P
Unité d'Immunochimie Analytique, Département d'Immunologie, Institut Pasteur, Paris, France.
Henry-Toulmé
N
N
Cazenave
P A
PA
D000818:Animals; D000937:Antigen-Antibody Reactions; D001402:B-Lymphocytes / Q000502:physiology*; D015153:Blotting, Western; D002118:Calcium / Q000502:physiology; D002451:Cell Compartmentation / Q000187:drug effects; D002455:Cell Division; D007108:Immune Tolerance; D007075:Immunoglobulin M / Q000502:physiology*; D066298:In Vitro Techniques; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000276:immunology; D051379:Mice; D011493:Protein Kinase C / Q000378:metabolism*; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D007075:Immunoglobulin M; D011947:Receptors, Antigen, B-Cell; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium