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  • Title: Differential regulation of protein-tyrosine phosphatases by integrin alpha IIb beta 3 through cytoskeletal reorganization and tyrosine phosphorylation in human platelets.
    Author: Ezumi Y, Takayama H, Okuma M.
    Journal: J Biol Chem; 1995 May 19; 270(20):11927-34. PubMed ID: 7538126.
    Abstract:
    The major platelet integrin alpha IIb beta 3 (glycoprotein IIb-IIIa) has been implicated in the regulation of tyrosine phosphorylation and dephosphorylation in activated platelets. To investigate the mechanisms of the alpha IIb beta 3-dependent tyrosine dephosphorylation, normal platelets or thrombasthenic platelets lacking alpha IIb beta 3 were stimulated with thrombin and fractionated into Triton X-100-soluble or -insoluble subcellular matrices. We then examined the kinetics of the tyrosine-phosphorylated proteins and distribution of protein-tyrosine phosphatases in these fractions and whole cell lysates. First, alpha IIb beta 3-dependent tyrosine dephosphorylation was recovered mainly in the cytoskeleton with similar kinetics to the whole cell lysate. Second, protein-tyrosine phosphatase (PTP) 1B and its cleaved 42-kDa form were associated with the cytoskeleton in an aggregation-dependent manner, whereas association of PTP1C with the cytoskeleton was regulated differentially both by thrombin stimulation and by alpha IIb beta 3-mediated aggregation. Several calpain inhibitors did not affect either tyrosine phosphorylation and dephosphorylation or relocation of PTP1B, but they did inhibit cleavage of PTP1B. Cytochalasin D blocked relocation of both PTP1B and PTP1C but not PTP1B cleavage. SH-PTP2 was distributed in the other fractions than the cytoskeleton and showed no relocation on thrombin stimulation. Finally, the cytoskeleton-associated PTP1C became tyrosine-phosphorylated in an alpha IIb beta 3-mediated aggregation-dependent manner. Thus, integrin alpha IIb beta 3 was involved differentially in the regulation of PTP1B and PTP1C.
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