Transcription factor FOXP3: A repressor of the TFPI gene?

Single nucleotide polymorphisms (SNPs) may play an important role in the risk of certain diseases. We have previously shown that the -287T/C SNP of the tissue factor pathway inhibitor (TFPI) gene promoter region exerts differential impact on TFPI mRNA expression; the C allele being associated with higher TFPI expression, which in turn is associated with reduced risk of thrombosis. In the present study, we aimed to reveal the underlying molecular mechanisms using human embryonic kidney 293 (HEK293) and Michigan Cancer Foundation-7 (MCF7) cells that both express TFPI. Transfecting the cells with luciferase reporter gene constructs containing the TFPI promoter with either the T or the C allele of -287T/C resulted in increased luciferase activity with the C allele relative to the T allele. Three potential candidate transcription factors for binding to the two -287 alleles were predicted using the ALGGEN PROMO software, and results from electrophoretic mobility shift assays indicated that forkhead box protein 3 (FOXP3), initially identified as a functional marker of T regulator cells, bound more specifically to the T allele compared with the C allele. By chromatin immunoprecipitation assays analysis it was confirmed that FOXP3 was able to bind to the DNA region that contains the SNP. Knockdown or overexpression of FOXP3 resulted in increased or decreased TFPI levels, respectively, in both cell types. In conclusion, this study indicates that FOXP3 most likely is involved in the increased levels of TFPI observed with the -287C allele and also that FOXP3 might be a repressor for TFPI expression.