Activation of coagulation is a common finding in patients with cancer, and is associated with an increased risk of venous thrombosis. As a hypoxic microenvironment is a common feature of solid tumors, we investigated the role of hypoxia in the regulation of tissue factor (TF) pathway inhibitor (TFPI) expression in breast cancer.Objectives:
To explore the transcriptional regulation of TFPI by hypoxia-inducible factor (HIF)-1α in breast cancer cells and their correlation in breast cancer tissues.Methods and results:
MCF-7 and SK-BR-3 breast cancer cells were cultured in 1% oxygen or treated with cobalt chloride (CoCl2) to mimic hypoxia. Time-dependent and dose-dependent downregulation of TFPI mRNA (quantitative RT-PCR) and of free TFPI protein (ELISA) were observed in hypoxia. Western blotting showed parallel increases in the levels of HIF-1α protein and TF. HIF-1α inhibitor abolished or attenuated the hypoxia-induced downregulation of TFPI. Luciferase reporter assay showed that both hypoxia and HIF-1α overexpression caused strong repression of TFPI promoter activity. Subsequent chromatin immunoprecipitation and mutagenesis analysis demonstrated a functional hypoxia response element within the TFPI promoter, located at −1065 to −1060 relative to the transcriptional start point. In breast cancer tissue samples, gene expression analyses showed a positive correlation between the mRNA expression of TFPI and that of HIF-1α.Conclusions:
This study demonstrates that HIF-1α is involved in the transcriptional regulation of the TFPI gene, and suggests that a hypoxic microenvironment inside a breast tumor may induce a procoagulant state in breast cancer patients.