Effect of hypoxia on tissue factor pathway inhibitor expression in breast cancer

Essentials A hypoxic microenvironment is a common feature of tumors that may influence activation of coagulation. MCF‐7 and SK‐BR‐3 breast cancer cells and breast cancer tissue samples were used. The results showed transcriptional repression of tissue factor pathway inhibitor expression in hypoxia. Hypoxia‐inducible factor 1α may be a target for the therapy of cancer‐related coagulation and thrombosis. Summary Background 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.