title: The protein-tyrosine phosphatase SHP-1 regulates the phosphorylation of alpha-actinin.
abstract: Platelet activation triggers integrin alpha(IIb)beta(3)-dependent signals and the induction of tyrosine phosphorylation of the cytoskeletal protein alpha-actinin. We have previously reported that alpha-actinin is phosphorylated by the focal adhesion kinase (FAK). In this study, a phosphatase of 68 kDa that dephosphorylated alpha-actinin in vitro was isolated from platelet lysates by three sequential chromatography steps. The phosphatase was identified as SHP-1 by electrospray tandem mass spectrometry. alpha-Actinin was dephosphorylated in vitro by recombinant SHP-1 and by SHP-1 immunoprecipitated from unstimulated or thrombin-stimulated platelet lysates. SHP-1 immunoprecipitated from lysates of platelets adherent to fibrinogen, however, failed to dephosphorylate alpha-actinin. In contrast, the activity of SHP-1 against a synthetic substrate was not affected by the mode of platelet activation. The robust and sustained phosphorylation of alpha-actinin detected in platelets adherent to fibrinogen thus correlates with a decrease in the activity of SHP-1 toward it. Tyrosine phosphorylation of alpha-actinin is seen in vanadate-treated COS-7 cells that are co-transfected with alpha-actinin and wild type FAK. Triple transfection of the cells with cDNAs encoding for alpha-actinin, FAK, and wild type SHP-1 abolished the phosphorylation of alpha-actinin. The phosphorylation of FAK, however, was barely affected by the expression of wild type SHP-1. Both alpha-actinin and FAK were phosphorylated in cells co-expressing alpha-actinin, FAK, and a catalytic domain mutant (C453S) of SHP-1. These findings establish that SHP-1 can dephosphorylate alpha-actinin in vitro and in vivo and suggest that SHP-1 may regulate the tethering of receptors to the cytoskeleton and/or the extent of cross-linking of actin filaments in cells such as platelets.
authors.affiliation: Department of Surgery, Robert Wood Johnson Medical School-University of Medicine and Dentistry of New Jersey and the Cancer Institute of New Jersey, New Brunswick, New Jersey 08903, USA.
authors.forename: Siang-Yo
authors.initials: SY
authors.lastname: Lin
authors.forename: Shital
authors.initials: S
authors.lastname: Raval
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Zhang
authors.forename: Michele
authors.initials: M
authors.lastname: Deverill
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Siminovitch
authors.forename: Donald R
authors.initials: DR
authors.lastname: Branch
authors.forename: Beatrice
authors.initials: B
authors.lastname: Haimovich
mesh_terms: D000185:Actinin / Q000378:metabolism*; D000818:Animals; D001792:Blood Platelets / Q000201:enzymology; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D008810:Mice, Inbred C57BL; D010766:Phosphorylation; D010973:Platelet Adhesiveness; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000502:physiology
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D000185:Actinin; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; C496051:Ptk2 protein, mouse; C509249:PTPN6 protein, human; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; C509248:Ptpn6 protein, mouse