CD38-mediated signaling events in murine pro-B cells expressing human CD38with or without its cytoplasmic domain

To elucidate the signaling mechanism of CD38 (a transmembrane molecule high ly expressed in immature hemopoietic cells), we transfected Ba/F3 murine pr o-B cells with a cDNA encoding human CD38, CD38 ligation with anti-CD38 Abs caused rapid, transient, dose-dependent tyrosine phosphorylation of severa l proteins, including the tyrosine kinase TEC and the adaptor molecule CBL, and association of tyrosine-phosphorylated proteins with phosphatidylinosi tol 3-kinase p85, Exposure to anti-CD38 Abs or their F(ab')(2) and Fab also induced tight aggregation of CD38-transfected Ba/F3 cells, which appeared to be Ca2+ and Mg2+ independent and did not involved LFA-1, Aggregation was abrogated by addition of the tyrosine kinase inhibitor herbimycin A and wa s delayed by the phosphatidylinositol 3-kinase inhibitor wortmannin, sugges ting a link between biochemical events and cellular effects induced by CD38 , Cell aggregation was accompanied by a decrease in cell recovery. After 3 days of culture on bone marrow-derived stroma, the mean (+/-SD) cell recove ry in the presence of anti-CD38 (T16) was 10.5 +/- 9.2% (n = 7) of that in parallel cultures with an isotype-matched nonreactive Ab, Finally, CD38 lig ation in Ba/F3 cells expressing a mutant human CD38 lacking the cytoplasmic domain induced tyrosine phosphorylation with intensity and kinetics simila r to those seen with the entire protein. It also induced cell aggregation a nd decreased cell recovery. We conclude that CD38 triggers remarkably simil ar signaling pathways in human and murine immature B cells. This signaling is independent of the CD38 cytoplasmic domain, suggesting the existence of accessory transmembrane molecules associated with CD38.