10nM siRNA, more than 50% transfected cells

INTRODUCTION: Oestrogens influence the pathophysiology and development of hormone-sensitive cancers, such as breast cancer. Tissue factor pathway inhibitor (TFPI) is a serine protease inhibitor of the extrinsic coagulation pathway and has recently been associated with breast cancer cell development. Moreover, reduced TFPI levels have been reported in plasma of healthy post-menopausal women receiving hormone replacement therapy, indicating a possible link between oestrogen and TFPI. In our study, we aimed to examine the effects of oestrogen and oestrogen analogues on TFPI expression in breast cancer cells and to identify underlying mechanism(s). METHODS: Oestrogen receptor alpha (ERalpha) positive MCF7 and negative MDA-MB-231 cells were treated with 17-beta-oestradiol, 17-beta-ethinyloestradiol, raloxifene and fulvestrant. TFPI mRNA and protein was measured using qRT-PCR and ELISA, respectively. Transient ERalpha knockdown was achieved using siRNA. RESULTS: In ERalpha expressing MCF7 cells, but not in MDA-MB-231 cells, the TFPI mRNA and protein levels were significantly downregulated by more than 50% after four or six hours of incubation with 17-beta-ethinyloestradiol and 17-beta-oestradiol, respectively. Moreover, a significant increase in FXa generation was detected in response to oestrogens. Breast tissue ER antagonists, raloxifene and fulvestrant, did not affect TFPI mRNA, however, fulvestrant blocked oestrogen mediated reduction of TFPI mRNA. Transient knockdown of ERalpha abolished the oestrogenic effect on TFPI and co-treatment of MCF7 cells with the protein synthesis inhibitor cycloheximide and 17-beta-oestradiol also led to reduction of TFPI mRNA. CONCLUSION: Our data establish a direct and time dependent regulation of TFPI expression by oestrogens through the ERalpha at the transcriptional level.