Receptor type protein tyrosine phosphatase, RPTPbeta on the surface of platelets:relationship to the Helicobacter pylori-related disease

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Helicobacter pylori is reportedly related to gastric ulcer/cancer, idiopathic thrombocytopenic purpura, and ischemic heart disease. We hypothesized that one of the causes of pylori-related diseases is VacA-stimulated platelet activation through interaction with RPTPbeta. The aim of this study in 2007 is to prove that VacA stimulates platelets by interacting with RPTPbeta using RPTPbeta-deficient mice and that in 2007 is to investigate signal transduction pathway mediated through RPTPbeta. In 2006, we failed to prove that VacA stimulates platelets by interacting with RPTPbeta and lost opportunity to use RPTPbeta-deficient mice. Therefore, we sought to identify another VacA receptor in platelets. MS/MS analysis revealed a macromolecule that is stored in the platelet alpha granule (named protein X) as one of the proteins associated with VacA-coated beads. We confirmed the binding between VacA and GST-protein X fusion protein using Biacore. We are now investigating VacA binding site in pro … More tein X. In other cells, an adapter protein, Git 1 is reported to undergo tyrosine phosphorylation downstream of RPTPbeta upon stimulation with VacA. Although VacA did not stimulate tyrosine phosphorylation of Git 1 in platelets, it is tyrosine-phosphorylated by outside-in signals downstream of integrin αIIbβ3. Since there has been no report about Git 1 expression in platelets, we decided to investigate regulation of Git 1 in platelets. We found that GIT 1 was abundantly expressed in platelets and underwent tyrosine phosphorylation downstream of integrin αIIbβ3, which was inhibited by the Src kinase inhibitor PP2. Furthermore, GIT1 constitutively associated with betaPlX, a guanine nucleotide exchange factor for Rac. The GIT1/betaPIX complex associated with allbp3, concomitantly with GIT1 tyrosine phosphorylation. Moreover, both GIT1 and αIIbβ3 rapidly translocated to the cytoskeletal fraction during platelet aggregation, which was not observed in the absence of aggregation. These results suggest that tyrosine phosphorylation of GIT1 by Src kinases may regulate cytoskeletal reorganization downstream of αIIbβ3 by bringing the Rac GEF betaPlX to the vicinity of the integrin. Less