TYROSINE PHOSPHORYLATION OF MB-1, B29, AND HS1 PROTEINS IN HUMAN B-CELLS FOLLOWING RECEPTOR CROSS-LINKING

Recent studies of murine and human B lymphocytes have shown that crosslinking of surface IgM (sIgM) and sIgD stimulates tyrosine phosphorylation of a set of proteins involved in signal transduction. We investigated tyrosine phosphorylation of the sig-associated proteins MB-1 and B29, and p75(HS1) (HS1), and the association of HS1 with MB-1/B29 heterodimers in normal human B cells and a human B lymphoma cell line, B104. Using immunoprecipitation with anti-phosphotyrosine antibodies (Abs) followed by immunoblotting with anti-MB-1 Abs, anti-B29 Abs or anti-HS1 Abs, we demonstrated that MB-1, B29 and HS1 were tyrosine-phosphorylated after sIgM or sIgD crosslinking. Immunoprecipitation with anti-B29 Abs followed by anti-HS1 Abs immunoblotting revealed that HS1 was associated with MB-1/B29 heterodimers after sIgM or sIgD crosslinking. The results showed that HS1 may play an important role in signal transduction through sIgM and sIgD on human B cells.