Tyrosine phosphorylation of an SH2-containing protein tyrosine phosphatase is coupled to platelet thrombin receptor via a pertussis toxin-sensitive heterotrimeric G-protein.

Abstract

Corresponding author SH-PTP1 is a protein tyrosine phosphatase (PTP) predominantly expressed in haematopoietic cells and containing two src homology-2 (SH2) domains. Here we report that SH-PTP1 is phosphorylated on both serine and tyrosine residues in response to thrombin or phorbol myristate acetate (PMA), which increased by 60 and 40%, respectively, SH-PTP1 activity. Thrombin-induced phosphorylation of SH-PTP1 is an early signalling event (maximal within 10 s) involving neither integrin signalling, nor calcium, nor release of ADP or thromboxane A2. Moreover, in contrast with PMA, the effect of thrombin on the tyrosine phosphorylation of SH-PTP1 was hardly affected by GF109203X, a specific protein kinase C (PKC) inhibitor. Finally, phosphorylation of SH-PTP1 could be provoked in permeabilized platelets by thrombin or GTPyS. This was abolished by pertussis toxin, the specificity of this effect being verified with the megakaryocytic cell line Dami cell. Our data thus identify SH-PTP1 as an in vivo substrate of a putative protein tyrosine kinase linked to the thrombin receptor by a G; protein. This might offer some clue to unravel the mechanism of thrombin not only in platelets but also in nucleated cells, where its mitogenic effect is known to involve pertussis toxin-sensitive G-proteins, tyrosine phosphorylation and the ras pathway.

Association of the protein tyrosine phosphatase PTP1C with the protein tyrosine kinase c‐Src in human platelets

“…In the present report, we showed that PTP1C was phosphorylated on tyrosine after platelet activation [23,24], thereby forming a binding site to the c-Src SH2 domain.…”

“…A Cell lysate ti ~n [23,24]. The migration in SDS-PAGE of PTP1C corresponded to the migration of the prominent tyrosine protein of 64 kDa [29].…”

“…Regulation of signalling proteins by their phosphorylation i,, a general feature. Increase in phosphatase activity upon t~rosine phosphorylation has been reported for PTP1C in p atelets [24] and for CD45 in T lymphocytes [30,31]. Tyrosine pilosphorylation also allows interactions with SH2 domains [I 8,19] or phosphotyrosine interaction domains [32,33].…”

“…In platelets, it is not clearly established whether this phosphatase plays a role in an early signalling event or in an aggregationdependent mechanism. Indeed, PTP1C phosphorylation occurs within the first seconds of stimulation [23,24]. However, depending on the reports, this phosphorylation follows platelet aggregation [23] or does not [24].…”

“…Indeed, PTP1C phosphorylation occurs within the first seconds of stimulation [23,24]. However, depending on the reports, this phosphorylation follows platelet aggregation [23] or does not [24]. Moreover, translocation of c-Src and PTP1C to the platelet cytoskeleton has been described, but up to now there is no evidence of any interaction between the two molecules.…”