Early growth response gene-1 and hypoxia-inducible factor-1α affect tumor metastasis via regulation of tissue factor

Background. Hypoxia up-regulated expression of tissue factor (TF) may facilitate tumor cell metastasis, but transcriptional mechanisms remain undefined. Material and methods. To verify the role of Egr-1 in hypoxia-induced TF expression in breast cancer cells, quantitative PCR and Western blot analysis were performed. The secretion of VEGF under hypoxia was detected by enzyme-linked immunosorbent assay (ELISA). Egr-1 and HIF-1 alpha siRNA were transiently transfected into breast cancer cells to evaluate their specific roles. Results. The increased Egr-1 expression occurring in hypoxic breast cancer cells can up-regulate TF expression and stimulating protein 1(Sp1) was not responsible for the hypoxia-induced expression of TF. HIF-1 alpha mediated the hypoxia-induced up-regulation of TF expression through vascular endothelial growth factor (VEGF). The regulatory effects of Egr-1 on TF under hypoxia were independent of HIF-1 alpha. Either Egr-1 or HIF-1 alpha was responsible for hypoxic induction of tumor cells adhesion. HIF-1 alpha, but not Egr-1, had a pivotal role in human breast cancer cells invasion. Both Egr-1 and HIF-1 alpha were critical to angiogenesis induced by hypoxic conditions in MDA-MB-231 and HUVEC co-cultures. In nude mice, both Egr-1 and HIF-1 alpha small interfering RNA (siRNA) could decrease extravasation of MDA-MB-435 cells in the lung after tail vein injection. Conclusions. Hypoxia-induced expression of TF in human breast cancer cells depends on Egr-1 and HIF-1 alpha, and both of these proteins may play an important role in breast cancer metastasis, either directly or indirectly through the TF pathway.