CROSS-LINKING OF SURFACE IGM ACTIVATES NF-KAPPA-B IN LYMPHOCYTE-B

In B lymphocytes, cross-linking of surface IgM activates changes in both the cell cycle and differentiation. In normal B cells and B cell tumors, many stimuli induce the activation of NF-chi-B and its translocation from the cytoplasm to the nucleus. In this study we sought to determine if cross-linking of surface IgM led to the activation of NF-chi-B. Our results show that activation of B cells by cross-linking anti-IgM antibodies activated NF-chi-B in the murine B lymphoid cell lines 70Z/3 and M12, and in the dense fraction of splenic cells. The activation of NF-chi-B required optimal doses of anti-IgM antibodies and took 5 to 10 min to reach maximal levels. Cross-linking of IgM has also been shown to activate protein kinases including protein kinase C (PKC). To test wether PKC activation was required for NF-chi-B translocation, we treated 70Z/3 cells for 18 h with phorbol 12-myristate 13-acetate, a procedure which depletes these cells of functional PKC. This treatment did not abrogate the nuclear translocation of NF-chi-B following anti-IgM cross-linking. These results indicate that the nuclear translocation of NF-chi-B is rapidly induced by surface IgM cross-linking and that this activation appears to use a pathway which does not require PKC.