Abstract
Angioinvasion is critical for metastasis with urokinase-type plasminogen activator receptor (uPAR) and tumor hypoxia-activated hypoxia-inducible factor 1 (HIF-1) as key players. Transcriptional control of uPAR expression by HIF has never been reported. The aim of the present study, therefore, was to test whether tumor hypoxia-induced HIF expression may be linked to transcriptional activation of uPAR and dependent angioinvasion. We used human pancreatic cancer cells and a model of parental and derived HIF-1beta-deficient mouse liver cancer cell lines and performed Northern blot analysis, nuclear runoff assays, electrophoretic mobility shift assay, polymerase chain reaction-generated deletion mutants, luciferase assays, Matrigel invasion assays, and in vivo angioinvasion assays in the chorioallantoic membrane of fertilized chicken eggs. Urokinase-type plasminogen activator receptor promoter analysis resulted in four putative HIF binding sites. Hypoxia strongly induced de novo transcription of uPAR mRNA. With sequential deletion mutants of the uPAR promoter, it was possible to identify one HIF binding site causing a nearly 200-fold increase in luciferase activity. Hypoxia enhanced the number of invading tumor cells in vitro and in vivo. In contrast, HIF-1beta-deficient cells failed to upregulate uPAR expression, to activate luciferase activity, and to invade on hypoxia. Taken together, we show for the first time that uPAR is under transcriptional control of HIF and that this is important for hypoxia-induced metastasis.