title: The SH2 domain containing tyrosine phosphatase-1 down-regulates activation of Lyn and Lyn-induced tyrosine phosphorylation of the CD19 receptor in B cells.
abstract: SHP-1 is a cytosolic tyrosine phosphatase implicated in down-regulation of B cell antigen receptor signaling. SHP-1 effects on the antigen receptor reflect its capacity to dephosphorylate this receptor as well as several inhibitory comodulators. In view of our observation that antigen receptor-induced CD19 tyrosine phosphorylation is constitutively increased in B cells from SHP-l-deficient motheaten mice, we investigated the possibility that CD19, a positive modulator of antigen receptor signaling, represents another substrate for SHP-1. However, analysis of CD19 coimmunoprecipitable tyrosine phosphatase activity in CD19 immunoprecipitates from SHP-1-deficient and wild-type B cells revealed that SHP-1 accounts for only a minor portion of CD19-associated tyrosine phosphatase activity. As CD19 tyrosine phosphorylation is modulated by the Lyn protein-tyrosine kinase, Lyn activity was evaluated in wild-type and motheaten B cells. The results revealed both Lyn as well as CD19-associated Lyn kinase activity to be constitutively and inducibly increased in SHP-1-deficient compared with wild-type B cells. The data also demonstrated SHP-1 to be associated with Lyn in stimulated but not in resting B cells and indicated this interaction to be mediated via Lyn binding to the SHP-1 N-terminal SH2 domain. These findings, together with cyanogen bromide cleavage data revealing that SHP-1 dephosphorylates the Lyn autophosphorylation site, identify Lyn deactivation/dephosphorylation as a likely mechanism whereby SHP-1 exerts its influence on CD19 tyrosine phosphorylation and, by extension, its inhibitory effect on B cell antigen receptor signaling.
authors.affiliation: Department of Medicine, University of Toronto, the Samuel Lunenfeld Research Institute, Mount Sinai Hospital and the University Health Network Research Institute, Toronto, Ontario M5G 1X5, Canada.
authors.forename: A K
authors.initials: AK
authors.lastname: Somani
authors.forename: K
authors.initials: K
authors.lastname: Yuen
authors.forename: F
authors.initials: F
authors.lastname: Xu
authors.forename: J
authors.initials: J
authors.lastname: Zhang
authors.forename: D R
authors.initials: DR
authors.lastname: Branch
authors.forename: K A
authors.initials: KA
authors.lastname: Siminovitch
mesh_terms: D000818:Animals; D018941:Antigens, CD19 / Q000378:metabolism*; D001402:B-Lymphocytes / Q000378:metabolism*; D002384:Catalysis; D015536:Down-Regulation; D004789:Enzyme Activation; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism*; D018909:src Homology Domains; D019061:src-Family Kinases / Q000378:metabolism*
chemical_list: D018941:Antigens, CD19; D014443:Tyrosine; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases