Most breast cancers express estrogen receptor (ER) where estrogen signaling plays an important role. Cancer contributes to activation of the coagulation system leading to an imbalance in the hemostatic system, and coagulation factor (F) V, which is a key regulator of blood coagulation, has been shown to be increased in breast tumors. Thus, the molecular association between estrogens and FV was explored. Stimulation with 17-β-estradiol (E2) or 17-β-ethinylestradiol (EE2) resulted in a time- and dose-dependent increase in F5 messenger RNA and FV protein in ERα-positive MCF-7 cells. Pretreatment with the ER antagonist fulvestrant or knockdown of ERα prior to stimulation with E2 counteracted this effect. Three ERα-binding half-sites were identified in the promoter region of the F5 gene in silico. Reporter gene analysis showed that all three half-sites were involved in the estrogen-induced gene regulation in vitro, as the effect was abolished only when all half-sites were mutated. High F5 levels in ER-positive breast tumors were associated with increased relapse-free survival of breast cancer patients.
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