THE REGULATION OF UTERINE TISSUE FACTOR BY ESTROGEN

Tissue factor (TF) is a transmembrane protein that initiates coagulati on and indirectly catalyzes the conversion of prothrombin to thrombin. We previously showed that treatment of immature rats with estradiol ( E(2)) stimulated a rapid increase in TF mRNA and protein in the uterus . Our current experiments using in situ hybridization show that the in crease in TF mRNA occurred primarily in the stromal cell layer. The ef fect of E(2) to increase TF mRNA occurred in uterine organ cultures bu t not in separated epithelial and stromal cells in vitro. Thrombin and the phorbol ester, TPA, compounds which regulate TF expression in oth er cell types by activation of protein kinase C (PKC), increased TF mR NA in both uterine organ cultures and in separated uterine cells. The 5' regulatory region of the TF gene was examined for the presence of a n estrogen response element (ERE) using a plasmid, pTFCAT, containing - 740 to + 15 bp of the mouse TF promoter upstream of the chlorampheni col acetyltransferase (CAT) reporter no response to E(2) in HeLa cells co-transfected with pTFCAT and a human ER construct, pHEO. In contras t, E(2) increased CAT activity in cells cotransfected with a positive- control plasmid, containing the consensus ERE cloned upstream of the t hymidine kinase promoter-driven CAT gene, and pHEO. CAT activity was a lso increased by TPA in cells transfected with pTFCAT. In summary, E(2 ) induces TF mRNA in uterine organ culture indicating that systemic fa ctors are not absolutely required for the effect. However, E(2) inject ion induces transudation of plasma prothrombin into the uterus where i t may be converted to thrombin. Thus thrombin may contribute to E(2)-i nduction of TF mRNA in vivo. An ERE was not identified in the 750 bp i mmediately 5' to the transcription start site of the TF gene although a TPA-responsive element was present. It is postulated that E(2) may i nduce TF mRNA by multiple indirect pathways including stimulation of P KC and Jun and Fos transcription factors, and by generation of thrombi n in the uterus.