c-Myc is essential for urokinase plasminogen activator expression on hypoxia-induced vascular smooth muscle cells

The purpose of this study was to investigate whether c-Myc regulates expression of urokinase plasminogen activator (uPA) on hypoxia-induced vascular smooth muscle cells (VSMCs). VSMCs were isolated from thoracic aorta of wild-type (WT), tissue plasminogen activator (tPA) and uPA-deficient mice. Gene and protein expression levels were examined by reverse-transcription PCR and Western blotting, respectively. c-Myc and uPA transcriptional activity were determined by luciferase analysis. Zymography analysis was used to test the activity of matrix metalloproteinases (MMPs), tPA, and uPA. Hypoxia significantly promoted WT and tPA-/- VSMC migration and invasion. However, uPA-/- severely decreased hypoxia-induced VSMC migration and invasion. Hypoxia increased uPA and MMP-2 activity, while uPA-/- decreased hypoxia-induced MMP-2 activity. c-Myc expression and transcriptional activity were increased in response to hypoxia, and silenced c-Myc abolished hypoxia-induced uPA and MMP-2 activity. In addition, hypoxia-induced Bcl2 expression and Bcl2 binding to c-Myc led to enhanced c-Myc-mediated uPA and MMP-2 activity in response to hypoxia. The results show that c-Myc was essential for hypoxia-induced uPA expression and activity, resulting in VSMC migration and invasion. In addition, Bcl2 enhanced the c-Myc-mediated uPA/MMP-2 pathway.