Association of p72 with the src Homology-2 (SH2) Domains of PLCγ1 in B Lymphocytes

Abstract

Phospholipase C gamma-catalyzed inositol phospholipid hydrolysis, a critical step in B cell antigen receptor signaling leading to second messenger generation and proliferation, depends upon tyrosine kinase activation. The B cell antigen receptor-associated tyrosine kinases p53/56lyn, p59fyn, p55blk, and p72syk are assumed to participate in receptor-initiated signaling. It is unknown, however, which of these kinases is involved in the tyrosine phosphorylation and resulting activation of phospholipase C gamma in response to antigen receptor cross-linking. We have used a fusion protein containing the tandem src homology-2 (SH2) domains of phospholipase C gamma 1 (PLC gamma 1) to identify B cell kinases which associate with PLC gamma 1. Using an in vitro kinase assay, we demonstrate SH2-dependent association of tyrosine kinase activity from anti-mu-stimulated B cells. The PLC gamma 1 SH2 domains associate with a prominent 70-72-kDa tyrosine phosphoprotein from anti-mu-stimulated, but not resting, B cells. Immunoblotting and secondary immunoprecipitation studies definitively identify this protein as p72syk. These results imply a physical interaction between PLC gamma 1 and p72syk in antigen receptor-stimulated B cells. This conclusion is confirmed by our ability to co-immunoprecipitate p72syk and PLC gamma 1 from lysates of anti-mu-stimulated B cells. These results implicate p72syk in the activation of phospholipase C gamma 1 during B cell antigen receptor signaling.

Cooperation of Tyrosine Kinases P72syk and P53/56lyn Regulates Calcium Mobilization in Chicken B Cell Oxidant Stress Signaling

“…Substitution of pheuylalanine at Tyr783 of PLCyl also eliminates PtdIns hydrolysis after platelet-derived growth factor stimulation [36]. The cross-linking of B cell receptors promotes the association of ~7 2 "~ with PLCyl [37]. Abrogation of InsP, production in both syk-negative and lyn-negative cells, therefore, may be due to the upstream transducer PLCy that is not activated under the conditions of the ~7 2 " '~ or p53/56"" defect.…”

Syk Is Required for BCR-mediated Activation of p90Rsk, but Not p70S6k, via a Mitogen-activated Protein Kinase-independent Pathway in B Cells

“…In one study, anti-Ig-induced activation of PLC-␥, a direct substrate of Syk (39,40), was unaffected in a Lyn-deficient cell line, DT40Lyn Ϫ , but abolished in a Syk-deficient cell line, DT40Syk Ϫ (26). This result suggested that the anti-Ig-induced activation of PLC-␥ required Syk activation but could occur in the absence of Lyn.…”

Normal Syk protein level but abnormal tyrosine phosphorylation in B-CLL cells

“…A good illustration is the enzymes of the PLC␥ family. These molecules probably associate with tyrosine-phosphorylated Syk in activated B cells through a SH2-type interaction 19 and are potential substrates tein deficiency might be found in a much larger panel of patients, given the great heterogeneity of this malignancy, but no clear relationship between the level of Syk protein in cell Shc, 21,22 could also account for most of the band at 145 kDa in Syk precipitates. Whether it is the inositol polyphosphate 5-extracts and the responding or non-responding nature of the cell was found here.…”