Thrombin activates the hypoxia-inducible factor-1 signaling pathway in vascular smooth muscle cells role of the p22(phox)-containing NADPH oxidase

The heterodimeric transcription factor hypoxia-inducible factor-1 (HIF-1) i s activated under hypoxic conditions, resulting in the upregulation of its target genes plasminogen activator inhibitor-1 (PAI-1) and vascular endothe lial growth factor (VEGF). PAI-1 and VEGF are also induced in response to v ascular injury, which is characterized by the activation of platelets and t he coagulation cascade as well as the generation of reactive oxygen species (ROS), However, it is not known whether HIF-1 is also stimulated by thromb otic factors. We investigated the role of thrombin, platelet-associated gro wth factors, and ROS derived from the p22(phox)-containing NADPH oxidase in the activation of HIF-1 and the induction of its target genes PAI-1 and VE GF in human vascular smooth muscle cells (VSMCs), Thrombin, platelet-derive d growth factor-AB (PDGF-AB), and transforming growth factor-beta (1) (TGF- beta (1)) upregulated HIF-1 a protein in cultured and native VSMCs, This re sponse was accompanied by nuclear accumulation of HIF-1 alpha as well as by increased HIF-1 DNA-binding and reporter gene activity. The thrombin-induc ed expression of HIF-1 alpha, PAI-1, and VEGF was attenuated by antioxidant treatment as well as by transfection of p22(phox) antisense oligonucleotid es. Inhibition of p38 mitogen-activated protein kinase and phosphatidylinos itol-3-kinase significantly decreased thrombin-induced HIF-1 alpha, PAI-1, and VEGF expression. These findings demonstrate that the HIF-1 signaling pa thway can be stimulated by thrombin and platelet-associated growth factors and that a redox-sensitive cascade activated by ROS derived from the p22(ph ox)-containing NADPH oxidase is crucially involved in this response.