INDUCTION OF PHOSPHATIDYLINOSITOL TURNOVER AND EGR-1 MESSENGER-RNA EXPRESSION BY CROSS-LINKING OF SURFACE IGM AND IGD IN THE HUMAN B-CELL LINE-B104

We have previously shown that a human B lymphoma cell line, B104, expr essed surface IgM (sIgM) and surface IgD (sIgD), and that crosslinking of sIgM and sIgD by anti-IgM antibody (Ab) and anti-IgD Ab, respectiv ely, induced Ca2+ influx to almost the same degree, whereas only sIgM- crosslinking caused B104 cell death. Here, we investigated the accumul ation of cyclic AMP (cAMP), the hydrolysis of inositol phosphates, pro tein kinase C (PKC) activity and the induction of Egr-1 and c-fos mRNA expression by sIgM- and sIgD-crosslinking to examine differences in t he signals mediated through sIgM and sIgD in B104 cells. Both sIgM- an d sIgD-crosslinking with antibodies induced elevation of cAMP levels, phosphatidylinositol turnover, PKC activation and expression of Egr-1 and c-fos mRNA, although sIgM-crosslinking was more effective than sIg D-crosslinking, presumably due to the higher expression of sIgM than o f sIgD. Egr-1 mRNA expression induced by sIgM- and sIgD-crosslinking w as inhibited by H7, erbstatin and genistein, but not by HA1004. Erbsta tin and genistein inhibited the sIg-crosslinking-induced Egr-1 mRNA ex pression in a dose-dependent manner parallel to that observed in the i nhibition of sIg-crosslinking-induced protein tyrosine phosphorylation . Phorbol myristate acetate induced Egr-1 mRNA expression but forskoli n and dibutyryl cyclic AMP did not. These findings suggest that the Eg r-1 mRNA activating signals through sIgM and sIgD are protein tyrosine kinase- and PKC-dependent, but protein kinase A-independent. Cyclospo rin A (CsA) and FK506 rescued B104 cells from death induced by anti-Ig M Ab, but did not affect the expression of Egr-1 and c-fos mRNA, showi ng that CsA and FK506 affect signal transducers differently from or do wnstream to these molecules. The difference in signals transduced thro ugh sIgM and sIgD in B104 cells is discussed.