Inhibition of anti-IgM-induced translocation of protein kinase C βI inhibits ERK2 activation and increases apoptosis

Expression of the COOH-terminal residues 179-330 of the LSP1 protein in the LSP1(+) B-cell line W10 increases anti-IgM- or ionomycin-induced apoptosis, suggesting that expression of this LSP1 truncate (B-LSP1) interferes with a Ca2+-dependent step in anti-IglM signaling. Here we show that inhibition of Ca2+-dependent conventional protein kinase C (cPKC) isoforms with Go6976 increases anti-IgM-induced apoptosis of W10 cells and that expression of B-LSP1 inhibits translocation of PKC betaI but not of PKC beta II or PKC alpha to the plasma membrane. The increased anti-IgM-induced apoptosis is partially reversed by overexpression of PKC betaI, This shows that the B-LSP1-mediated inhibition of PKC betaI leads to increased anti-IgM-induced apoptosis, Expression of constitutively active PKC betaI protein in W10 cells activates the mitogen-activated protein kinase ERK2, whereas expression of B-LSP1 inhibits anti-IgM-induced activation of ERK2, suggesting that anti-IgM-activated PKC betaI is involved in the activation of ERK2 and that inhibition of ERK2 activation contributes to the increased anti-IgM-induced apoptosis, Pull-down assays show that LSP1 interacts with PKC betaI but not with PKC beta II or PKC alpha in W10 cell lysates, while in vitro LSP1 and B-LSP1 bind directly to PKC betaI, Thus, B-LSP1 is a unique reagent that binds PKC betaI and inhibits anti-IgM-induced PKC betaI translocation, leading to inhibition of ERK2 activation and increased apoptosis.