title: Association of p72syk with the src homology-2 (SH2) domains of PLC gamma 1 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.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104, USA.
authors.forename: A L
authors.initials: AL
authors.lastname: Sillman
authors.forename: J G
authors.initials: JG
authors.lastname: Monroe
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism*; D004792:Enzyme Precursors / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D010716:Phosphatidylinositols / Q000378:metabolism; D051966:Phospholipase C gamma; D017434:Protein Structure, Tertiary; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011947:Receptors, Antigen, B-Cell / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D000072377:Syk Kinase; D010738:Type C Phospholipases / Q000378:metabolism*
chemical_list: D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D010716:Phosphatidylinositols; D011947:Receptors, Antigen, B-Cell; D011993:Recombinant Fusion Proteins; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D010738:Type C Phospholipases; D051966:Phospholipase C gamma