Hypoxia-Inducible Factor-1 Expression of Tissue Factor in Glioblastoma Multiforme Early Growth Response Gene-1 Regulates Hypoxia-Induced

Hypoxia strongly up-regulates tissue factor and promotes plasma clotting by glioblastoma multiforme, but transcriptional mechanisms remain undefined. Here, we investigated the potential roles of early growth response gene-1 (Egr-1), Sp1, nuclear factor-KB (NF-KB), activator protein-1 (AP-1), and hypoxia-inducible factor-1 (HIF-1) in the hypoxic regulation of tissue factor by glioblastoma multiforme cells in vitro. Hypoxia (1% O2) strongly induced Egr-1 mRNA within 1 hour and led to nuclear localization of Egr-1 protein. Using luciferase reporter plasmids in glioma cells, we found that hypoxia dramatically increased luciferase activity in cells with constructs containing Egr-1-binding sites but not in cells with constructs containing AP-1or NF-KB-binding sites. Electrophoretic mobility shift assays revealed hypoxia-induced Egr-1, but not Sp1, binding to oligonucleotides containing the Egr-1/ Sp1 motif of tissue factor gene promoter. Using an expression vector containing the minimal tissue factor promoter ( 111 to +14 bp) and small interfering RNA (siRNA) directed at Egr-1 and Sp1 mRNAs, we found that Egr-1 was required for maximal hypoxic induction of promoter activity. Forced overexpression of Egr-1 but not Sp1 by cDNA transfection caused up-regulation of tissue factor in glioma cells under normoxia (21% O2), whereas siRNA directed at Egr-1 strongly attenuated hypoxia-induced tissue factor expression. To examine the effects of HIF-1A on tissue factor expression, we used glioma cells stably transfected with a HIF-1a siRNA expression vector and found that HIF-1a mRNA silencing did not affect tissue factor expression under hypoxia. We conclude that hypoxic up-regulation of tissue factor in glioblastoma multiforme cells depends largely on Egr-1 and is independent of HIF-1. (Cancer Res 2006; 66(14): 7067-74)