The regulation of uterine tissue factor by estrogen

Abstract

Tissue factor (TF) is a transmembrane protein that initiates coagulation and indirectly catalyzes the conversion of prothrombin to thrombin. We previously showed that treatment of immature rats with estradiol (E₂) stimulated a rapid increase in TF mRNA and protein in the uterus. Our current experiments usingin situ hybridization show that the increase in TF mRNA occurred primarily in the stromal cell layer. The effect of E₂ to increase TF mRNA occurred in uterine organ cultures but not in separated epithelial and stromal cellsin vitro. Thrombin and the phorbol ester, TPA, compounds which regulate TF expression in other cell types by activation of protein kinase C (PKC), increased TF mRNA in both uterine organ cultures and in separated uteriné cells. The 5′ regulatory region of the TF gene was examined for the presence of an estrogen response element (ERE) using a plasmid, pTFCAT, containing −740 to + 15 bp of the mouse TF promoter upstream of the chloramphenicol acetyltransferase (CAT) reporter gene. There was no response to E₂ in HeLa cells cotransfected with pTFCAT and a human ER construct, pHEO. In contrast, E₂ increased CAT activity in cells cotransfected with a positive-control plasmid, containing the consensus ERE cloned upstream of the thymidine kinase promoter-driven CAT gene, and pHEO. CAT activity was also increased by TPA in cells transfected with pTFCAT. In summary, E₂ induces TF mRNA in uterine organ culture indicating that systemic factors are not absolutely required for the effect. However, E₂ injection induces transudation of plasma prothrombin into the uterus where it may be converted to thrombin. Thus thrombin may contribute to E₂-induction of TF mRNAin vivo. An ERE was not identified in the 750 bp immediately 5′ to the transcription start site of the TF gene although a TPA-responsive element was present. It is postulated that E₂ may induce TF mRNA by multiple indirect pathways including stimulation of PKC and Jun and Fos transcription factors, and by generation of thrombin in the uterus.