SURFACE IGM-STIMULATED PROLIFERATION, INOSITOL PHOSPHOLIPID HYDROLYSIS, CA2-CELLS FROM P59(FYN-( FLUX, AND TYROSINE PHOSPHORYLATION ARE NOTALTERED IN B)-) MICE/

The surface immunoglobulin M (sIgM)-associated src family protein tyro sine kinases (PTKs) p55(blk), p59(fyn), and p53/56(lyn) become activat ed in B cells within seconds following sIgM cross-linking. Studies usi ng protein tyrosine kinase (PTK) inhibitors have demonstrated that PTK activity is crucial for downstream events such as calcium flux, inosi tol phospholipid hydrolysis, and cell cycle entry. The roles that the individual src family PTKs play in sIgM signaling are largely unknown, however. In order to determine whether p59(fyn) plays a distinct role in sIgM signal transduction, the signaling-capabilities of B cells is olated from fyn ''knockout'' mice were evaluated. We observed that in the absence of p59(fyn), there was no demonstrable compromise of the s IgM-coupled signaling events measured (tyrosine phosphorylation, inosi tol phospholipid hydrolysis, and Ca2+ flux). We propose that either p5 9(fyn) is not involved in coupling sIgM to these specific signaling pa thways or that other PTKs are able to compensate for the absence of p5 9(fyn), indicating redundancy in the sIgM signaling pathways.