Hypoxia inducible factor-1 mediates upregulation of urokinase-type plasminogen activator receptor gene transcription during hypoxia in cervical cancer cells.

Abstract

Hypoxia occurs during development of cervical cancer and is considered to correlate with its invasion. Hypoxia mediates tumor cells to have more invasive property in a variety of cancers. Urokinase plasminogen activator receptor (uPAR) which mediates invasion is considered to be induced by hypoxia. We sought to determine the regulators of uPAR expression during hypoxia in cervical cancer. We showed that cervical cancer cell lines, CaSki and CA, were more invasive under hypoxic condition (1% O2) than under normoxic condition (20% O2) by invasion assays. Using western blot analysis, hypoxia enhanced the endogenous hypoxia-inducible factor (HIF)-1α and uPAR protein expression. uPAR mRNA level was also upregulated by hypoxia using real-time RT-PCR. Overexpression of HIF-1α which is induced by hypoxia activated the transcriptional activity of the uPAR promoter by luciferase assays. HIF-1 protein bound the putative HIF-1 response element on the uPAR promoter using electrophoretic mobility shift analysis, and additional luciferase assays show that this is essential for uPAR transactivation by HIF-1. HIF-1 overexpression enhanced the endogenous uPAR expression and introduction of siRNA for HIF-1α diminishes uPAR expression during hypoxia. These results indicate the upregulation of uPAR by hypoxia in cervical cancer cells is mediated through HIF-1. In cervical cancer tissues, we also demonstrated that uPAR protein expression was detected in cervical cancer but not in normal cervix or cervical intraepithelial neoplasia (CIN) by immunohistopathological staining. Our results provide evidence that regulation of uPAR expression by HIF-1 represents a mechanism for cervical cancer invasion during hypoxia.