Functional independence and interdependence of the Src homology domains ofphospholipase C-gamma 1 in B-cell receptor signal transduction

B-cell receptor (BCR)-induced activation of phospholipase C-gamma 1 (PLC ga mma 1) and PLC gamma 2 is crucial for B-cell function, While several signal ing molecules have been implicated in PLC gamma activation, the mechanism c oupling PLC gamma to the BCR remains undefined. The role of PLC gamma 1 SH2 and SH3 domains at different steps of BCR-induced PLC gamma 1 activation w as examined by reconstitution in a PLC gamma-negative B-cell line. PLC gamm a 1 membrane translocation required a functional SH2 N-terminal [SH2(N)] do main, was decreased by mutation of the SH3 domain, but was unaffected by mu tation of the SH2(C) domain. Tyrosine phosphorylation did not require the S H2(C) or SH3 domains but depended exclusively on a functional SH2(N) domain , which mediated the association of PLC gamma 1 with the adapter protein, B LNK. Forcing PLC gamma 1 to the membrane via a myristoylation signal did no t bypass the SH2(N) domain requirement for phosphorylation, indicating that the phosphorylation mediated by this domain is not due to membrane anchori ng alone. Mutation of the SH2(N) or the SH2(C) domain abrogated BCR-stimula ted phosphoinositide hydrolysis and signaling events, while mutation of the SH3 domain partially decreased signaling. PLC gamma 1 SH domains, therefor e, have interrelated but distinct roles in BCR-induced PLC gamma 1 activati on.