Thrombin-induced redistribution of protein-tyrosine-phosphatases to the cytoskeletal complexes in human platelets.

Human platelets provide an attractive model for studying the regulation of tyrosine phosphorylations and cell-cell adhesion. Major non-receptor tyrosine-kinases are suggested to be responsible for an increase in protein tyrosine phosphorylation following platelet stimulation. Agonist-induced platelet activation triggers also the reorganization of the cytoskeleton with association of multiple signalling proteins. To understand if protein-tyrosine-phosphatases (PTPs) were involved in platelet aggregation, we have investigated the subcellular distribution of these enzymes in resting and thrombin-stimulated platelets. A high level of PTP activity in human resting cells is distributed for 65% and 35%, respectively, in cytosolic and particular fractions. About 10% of this activity are redistributed to the cytoskeletal network during platelet activation. This translocation is dependent on actin polymerization as proved by the disappearance of this phenomenon in cells pretreated by cytochalasin D. Moreover, immunoblotting using anti-PTP polyclonal antibodies indicates that two PTPs, SH-PTP1 and p58 related to HPTP beta, translocate from membranes to Triton X-100 insoluble fractions after platelet activation. This translocation is correlated with the redistribution of several signalling proteins suggesting the possible regulation between these molecules and PTPs.