DIFFERENTIAL REGULATION OF PROTEIN-TYROSINE PHOSPHATASES BY INTEGRIN ALPHA(IIB)BETA(3) THROUGH CYTOSKELETAL REORGANIZATION AND TYROSINE PHOSPHORYLATION IN HUMAN PLATELETS

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 re covered 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.