Novel role for STAT-5B in the regulation of Hsp27-FGF-2 axis facilitating thrombin-induced vascular smooth muscle cell growth and motility

Previously, we have demonstrated that STAT-3 plays a role in thrombin-induced VSMC motility. To learn more about the role of STATs in the mitogenic and chemotactic signaling events of thrombin, here we have studied the role of STAT-5. Thrombin activated STAT-5 as measured by its tyrosine phosphorylation, DNA binding, and reporter gene activity. Inhibition of STAT-5B, but not STAT-5A, by adenovirus-mediated expression of its respective dominant-negative mutants suppressed thrombin-induced VSMC growth and motility. Thrombin induced the expression of Hsp27 and FGF-2 in a time- and STAT- 5B - dependent manner in VSMC. In addition, small interfering RNA - directed depletion of Hsp27 levels or adenovirus-mediated expression of its dominant-negative mutant attenuated thrombin-induced FGF-2 expression, growth, and motility of VSMC. An increased association of STAT- 5B with STAT- 3 occurred in response to thrombin and adenovirus-mediated expression of dnSTAT-3 suppressed thrombin-induced Hsp27 and FGF-2 induction, DNA synthesis and motility in VSMC. Together, these results indicate that thrombin-induced VSMC growth and motility require STAT- 5B/STAT-3-dependent expression of Hsp27 and FGF-2. These observations also suggest that STAT- 5B/STAT-3/Hsp27/FGF-2 signaling via its involvement in the regulation of VSMC growth and motility may play an important role in the pathogenesis of vascular diseases such as restenosis after angioplasty.