A mitogen-activated protein kinase-dependent signaling pathway in the activation of platelet integrin alpha IIbbeta3.

Zhenyu Li,Xiaoping Du,Xiaodong Xi

doi:10.1074/jbc.m106129200

Abstract

We have recently shown that the platelet integrin alpha(IIb)beta(3) is activated by von Willebrand factor (vWF) binding to its platelet receptor, glycoprotein Ib-IX (GPIb-IX), via the protein kinase G (PKG) signaling pathway. Here we show that GPIb-IX-mediated activation of integrin alpha(IIb)beta(3) is inhibited by dominant negative mutants of Raf-1 and MEK1 in a reconstituted integrin activation model in Chinese hamster ovary (CHO) cells and that the integrin-dependent platelet aggregation induced by either vWF or low dose thrombin is inhibited by MEK inhibitors PD98059 and U0126. Thus, mitogen-activated protein kinase (MAPK) pathway is important in GPIb-IX-dependent activation of platelet integrin alpha(IIb)beta(3). Furthermore, vWF binding to GPIb-IX induces phosphorylation of Thr-202/Tyr-204 of extracellular signal-regulated kinase 2 (ERK2). GPIb-IX-induced ERK2 phosphorylation is inhibited by PKG inhibitors and enhanced by overexpression of recombinant PKG. PKG activators also induce ERK phosphorylation, indicating that activation of MAPK pathway is downstream from PKG. Thus, our data delineate a novel integrin activation pathway in which ligand binding to GPIb-IX activates PKG that stimulates MAPK pathway, leading to integrin activation.

Highlights

The integrin ␣IIb␤3 mediates platelet adhesion, spreading, and aggregation and plays a critical role in thrombosis and hemostasis [1]
Activation of extracellular signal-regulated kinases (ERKs) Pathway Is Downstream from protein kinase G (PKG) in the glycoprotein Ib-IX (GPIb-IX)-mediated Integrin Activation in Platelets—To further investigate whether activation of mitogen-activated protein kinase (MAPK) is downstream from PKG in the GPIb-IX-signaling pathway in platelets, we examined the effects of PKG activators and inhibitors on the phosphorylation of extracellular signal-regulated kinase 2 (ERK2) in platelets
In this study we found that 1) ligand binding to GPIb-IX activates ERK pathway, which is important in mediating GPIb-IX-induced activation of integrin ␣IIb␤3, and 2) the ERK pathway is downstream from PKG in the GPIb-IX-induced integrin activation

Summary

Introduction

The integrin ␣IIb␤3 mediates platelet adhesion, spreading, and aggregation and plays a critical role in thrombosis and hemostasis [1]. We show that GPIb-IX-mediated activation of integrin ␣IIb␤3 is inhibited by dominant negative mutants of Raf-1 and MEK1 in a reconstituted integrin activation model in Chinese hamster ovary (CHO) cells and that the integrindependent platelet aggregation induced by either vWF or low dose thrombin is inhibited by MEK inhibitors PD98059 and U0126.

Results

Conclusion