STAT-3-dependent cytosolic phospholipase A2 expression is required for thrombin-induced vascular smooth muscle cell motility

Vascular smooth muscle cell (VSMC) migration from media to intima and its multiplication in intima is a contributing factor in the pathogenesis of atherosclerosis and restenosis after angioplasty. Previously, we have demonstrated that STAT-3-dependent cytosolic phospholipase A, (cPLA,) expression is needed for VSMC motility induced by platelet-derived growth factor-BB, a receptor tyrosine kinase agonist (Neeli et aL (2005) J. BioL Chem. 279, 46122-46128). In order to learn more about the STAT-3-cPLA(2) axis in motogenic signaling, here we have studied its role in VSMC motility in response to a G protein-coupled receptor (GPCR) agonist, thrombin. Thrombin induced VSMC motility in a dose-dependent manner with a maximum effect at 0.5 units/ ml. Thrombin activated STAT-3 as measured by its tyrosine phosphorylation and translocation from the cytoplasm to the nucleus. Forced expression of a dominant negative mutant of STAT-3 reduced thrombin-induced STAT-3 tyrosine phosphorylation and its translocation from the cytoplasm to the nucleus. Thrombin stimulated STAT-3-DNA binding and reporter gene activities in VSMC, and these responses were blocked by FS3DM, a dominant negative mutant of STAT-3. FS3DM also attenuated thrombin-induced VSMC motility. Thrombin induced the expression of cPLA(2) in a time- and STAT-3-dependent manner. In addition, pharmacological inhibition of cPLA(2) blocked thrombin-induced VSMC motility. Furthermore, exogenous addition of arachidonic acid rescued thrombin-induced VSMC motility from inhibition by blockade of STAT-3 activation. Forced expression of cPLA(2) also surpassed the inhibitory effect of dominant negative STAT-3 on thrombin-induced VSMC motility. Together, these results show that thrombin-induced VSMC motility requires STAT-3-dependent induction of expression of cPLA(2).