ESTROGEN INDUCTION AND CONTACT PHASE ACTIVATION OF HUMAN FACTOR-XII

This paper reviews data reported in the literature and results of our experiments on the transcriptional control of Factor XII by estrogens and on the activation of Factor XII in the plasma. Coagulation Factor XII (Hageman factor, FXII) is a serine protease secreted by the liver and activated by negative charged surfaces to play roles in fibrinolys is, coagulation, and inflammation. Multiple effects on hemostasis invo lving these processes via Hageman factor have been reported in relatio n to estrogen therapy. The nucleotide sequence of 3,174 base pair (bp) DNA at the 5' end of the Factor XII gene indicates that the Factor XI I promoter is typical of TATA-less, liver-specific, and serine proteas e-type eukaryotic genes involved in clotting. In addition the Factor X II promoter contains at position -44/-31 a palindrome similar but not identical, to an estrogen-responsive element (ERE) together with four hemisite EREs between positions -1314 and -608. These promoter regions may underlie the mechanism by which estrogens enhance Factor XII conc entration in plasma. In vivo, a 6-fold stimulation of FXII gene transc ription by 17 beta-estradiol was observed in ovariectomized rats. In v itro a 230-bp promoter fragment of Factor XII (-181/+49) confers a str ong 17 beta-estradiol responsiveness onto a chlorampenicol acetyltrans ferase reporter when transiently co-transfected with the human estroge n receptor. The domain structure of Factor XII allows identification o f those parts of the protein with particular functions. cDNA construct s, in which sequences coding for selected domains were deleted, were u sed to produce recombinant deleted Factor XII proteins in a vaccinia v irus expression system. To identify the domain(s) responsible for cont act phase activation, these recombinant proteins were tested for their capacity to bind to negatively charged substrates, to become activate d by kallikrein, and to sustain blood clotting and amidolytic activity . In addition to the N-terminal domain, the growth factor and kringle domains and, to a lesser extent, the polyproline region also interact with negatively charged surfaces and presumably thus contribute to act ivation.