Nrf2 Regulates Thromboxane Synthase Gene Expression in Human Lung Cells

Abstract

Thromboxane A₂ synthase (TXAS) converts prostaglandin H₂ to thromboxane A₂, a potent inducer of vaso-constriction and platelet aggregation. TXAS expression level is cell type preferential; high in hematopoietic cells and low in nonhematopoietic cells. We previously showed that p45 NF-E2 activated the TXAS promoter in hematopoietic cells via binding to the nucleotides -86/-77 from the transcriptional start site [Yaekashiwa and Wang (2002) J. Biol. Chem. 277, 22497-22508]. We reported here that, by transient transfection analysis, this region was also critical for TXAS trans-activation in the A549 and WI-38 lung cells. Mutation of the NF-E2 site greatly reduced TXAS promoter activity in these two types of cells. Using stably transfected A549 cells, we showed that an NF-E2 mutation retained only 0.25% of the wild-type promoter activity. Ecotopic expression of NF-E2 related factors showed that Nrf2, but not Nrf1, Nrf3, or Bach1, activated TXAS promoter in a dose-dependent manner. Furthermore, chromatin immunoprecipitation assay using the stably transfected A549 cells demonstrated that Nrf2 bound the TXAS NF-E2 site in vivo. TXAS gene thus utilizes the same cis-acting element but different trans-acting factors to confer cell-preferential expression. We also showed that forced expression of p300 upregulated TXAS gene in a dose-dependent manner. Mutation of NF-E2 site, but not TATA or initiator site, abolished the p300-mediated activation of TXAS gene.