title: Collagen induces tyrosine phosphorylation of Wiskott-Aldrich syndrome protein in human platelets.
abstract: Wiskott-Aldrich syndrome (WAS) and X-linked thrombocytopenia (XLT) are caused by mutations of the WAS protein (WASP) gene. All hematopoietic stem cell-derived lineages, including platelets, express WASP. Platelets from WAS patients are smaller than their normal counterparts and defects in platelet aggregation and actin polymerization have been reported. To determine if WASP is important for normal platelet function, we examined its role in signal transduction. We found that collagen but not thrombopoietin or thrombin induces a rapid and robust increase in tyrosine phosphorylation of platelet-associated WASP. Collagen-induced tyrosine phosphorylation of WASP was inhibited by cytochalasin D and wortmannin, respectively, suggesting that actin polymerization and phosphatidylinositol 3-kinase (PI3-kinase) play a role in the induction of tyrosine phosphorylation of WASP. Binding of glutathion S-transferase (GST)-Grb2 to WASP was seen in the lysate of resting platelets. The binding was reduced when lysates from collagen-stimulated platelets were incubated with GST-Grb2, suggesting that tyrosine phosphorylation of WASP may directly or indirectly modulate the adapter function of WASP. Although thrombin- and thrombopoietin-induced increase in tyrosine phosphorylation of WASP is negligible or marginal, WASP from thrombin-activated platelets became incorporated into the Triton X-100-insoluble 10, 000g sedimentable residue in an aggregation-dependent manner, suggesting that it may have a regulatory role in platelet cytoskeletal processes during aggregation. Lastly, we found that WASP is cleaved in response to activation of calpain, a protease that may have a role in postaggregation signaling processes. Our data suggest that collagen specifically induces an increase in tyrosine phosphorylation of WASP and that WASP is involved in signaling during thrombin-induced aggregation by its redistribution to the cytoskeleton and its cleavage during aggregation.
authors.affiliation: Division of Hematology, Department of Internal Medicine, and the Blood Center, Keio University, Tokyo, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Oda
authors.forename: H D
authors.initials: HD
authors.lastname: Ochs
authors.forename: B J
authors.initials: BJ
authors.lastname: Druker
authors.forename: K
authors.initials: K
authors.lastname: Ozaki
authors.forename: C
authors.initials: C
authors.lastname: Watanabe
authors.forename: M
authors.initials: M
authors.lastname: Handa
authors.forename: Y
authors.initials: Y
authors.lastname: Miyakawa
authors.forename: Y
authors.initials: Y
authors.lastname: Ikeda
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000730:Androstadienes / Q000494:pharmacology; D001792:Blood Platelets / Q000378:metabolism*; D003094:Collagen / Q000037:antagonists & inhibitors / Q000097:blood / Q000502:physiology*; D003599:Cytoskeleton / Q000378:metabolism; D051380:GRB2 Adaptor Protein; D005982:Glutathione Transferase / Q000097:blood; D006801:Humans; D010766:Phosphorylation / Q000187:drug effects; D010974:Platelet Aggregation; D011485:Protein Binding; D011506:Proteins / Q000187:drug effects / Q000378:metabolism*; D014443:Tyrosine / Q000097:blood*; D014923:Wiskott-Aldrich Syndrome / Q000097:blood*; D051316:Wiskott-Aldrich Syndrome Protein; D000077191:Wortmannin
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000730:Androstadienes; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; D011506:Proteins; C495767:WAS protein, human; D051316:Wiskott-Aldrich Syndrome Protein; D014443:Tyrosine; D003094:Collagen; D005982:Glutathione Transferase; D000077191:Wortmannin