THROMBIN-INDUCED REDISTRIBUTION OF PROTEIN-TYROSINE-PHOSPHATASES TO THE CYTOSKELETAL COMPLEXES IN HUMAN PLATELETS

Human platelets provide an attractive model for studying the regulatio n of tyrosine phosphorylations and cell-cell adhesion. Major non-recep tor tyrosine-kinases are suggested to be responsible for an increase i n protein tyrosine phosphorylation following platelet stimulation. Ago nist-induced platelet activation triggers also the reorganization of t he cytoskeleton with association of multiple signalling proteins. To u nderstand if protein-tyrosine-phosphatases (PTPs) were involved in pla telet aggregation, we have investigated the subcellular distribution o f these enzymes in resting and thrombin-stimulated platelets. A high l evel of PTP activity in human resting cells is distributed for 65% and 35%, respectively, in cytosolic and particular fractions. About 10% o f this activity are redistributed to the cytoskeletal network during p latelet activation. This translocation is dependent on actin polymeriz ation as proved by the disappearance of this phenomenon in cells pretr eated by cytochalasin D. Moreover, immunoblotting using anti-PTP polyc lonal antibodies indicates that two PTPs, SH-PTP1 and p58 related to H PTP beta, translocate from membranes to Triton X-100 insoluble fractio ns after platelet activation. This translocation is correlated with th e redistribution of several signalling proteins suggesting the possibl e regulation between these molecules and PTPs.