Examination of B lymphoid cell lines for membrane immunoglobulin-stimulated tyrosine phosphorylation and src-family tyrosine kinase mRNA expression.

Crosslinking of membrane immunoglobulin (mIg) on B cells induces two signal transduction pathways: protein tyrosine phosphorylation and phosphoinositide turnover. A panel of murine and human B cell-lines, representing different stages of B cell development, was examined for the presence of anti-immunoglobulin-induced protein tyrosine phosphorylation. Of 10 B cell lines examined, only one, the human Raji cell line, had no detectably induced protein tyrosine phosphorylation. The pattern of proteins that were phosphorylated on tyrosine in response to mIg crosslinking differed somewhat in cell lines representing different stages of B cell development. Differences in the levels of constitutive phosphorylation of proteins were also observed between the cell lines. The identity of the tyrosine kinase(s) activated by membrane immunoglobulin ligation is not known. However, members of the src family of intracellular tyrosine kinases have been implicated as signal transduction molecules. As the tyrosine phosphorylation of proteins is a general phenomenon of signal transduction by membrane immunoglobulin, the tyrosine kinase(s) activated by it might be expected to be present in all cell lines in which the tyrosine phosphorylation signalling occurs. Therefore we examined these B cells for expression of mRNAs encoding the eight known src-like tyrosine kinases. Surprisingly, all eight kinase mRNAs were expressed in at least some of the B cell lines examined. The expression pattern of the fyn, hck, and lck genes suggests that expression of these kinases may be developmentally regulated in the B cell lineage. Three of the kinases, p55blk, p53/p56lyn and p60src, were detected in all 10 B cell lines. Whereas the src gene shows a ubiquitous pattern of expression, the expression of the blk and lyn genes is mostly restricted to cells of hematopoietic origin, and more especially B lymphoid cells. Thus, p55blk and p53/p56lyn may be particularly good candidates for the membrane immunoglobulin-activated tyrosine kinase.