Identification and functional characterization of a polymorphic oestrogen response element in the human coagulation factor IX gene promoter

The liver expressed procoagulant factor IX (FIX) shows inter-individual variation in levels, some of which is heritable. Raised levels of FIX are associated with a thrombotic tendency. This study demonstrated that, in females but not males, part of this variation in FIX levels is due to polymorphic genotype at a locus in the factor IX gene (F9) promoter 698 bp upstream of the major transcription initiation site (-698C/T). The -698C allele (associated with higher FIX level) shows closer homology to a canonical ORE sequence and a higher binding affinity for oestrogen receptor alpha than the -698T allele. Reporter gene vectors were constructed with elements spanning residues -738 to +50 of the F9 promoter corresponding to wild type -698C and -698T alleles. A related series of vectors comprising three copies of the F9 ORE driving expression of a minimal synthetic promoter were also created. Transfection into the liver-derived HepG2 and erythroleukaemic K562 cell lines demonstrated increased levels of expression in the presence of oestrogenic factors when compared to those found in their absence; this stimulation was more pronounced in the non-liver derived K562 cell line and from the reporter vectors containing promoter elements corresponding to the -698C allele.