Nrf2 regulates thromboxane synthase gene expression in human lung cells.

Area of Science:

• Molecular Biology
• Gene Regulation
• Biochemistry

Background:

• Thromboxane A(2) synthase (TXAS) produces thromboxane A(2), crucial for vasoconstriction and platelet aggregation.
• TXAS expression varies by cell type, being high in hematopoietic cells and low in nonhematopoietic cells.
• Previous work identified p45 NF-E2 as a TXAS promoter activator in hematopoietic cells.

Purpose of the Study:

• To investigate the regulatory mechanisms of TXAS gene expression in lung cells.
• To identify the specific transcription factors responsible for TXAS activation in nonhematopoietic cells.
• To elucidate the role of the NF-E2 binding site in TXAS regulation across different cell types.

Main Methods:

• Transient and stable transfection assays in A549 and WI-38 lung cells.
• Site-directed mutagenesis of the TXAS promoter NF-E2 binding site.
• Ectopic expression of NF-E2 related factors (Nrf1, Nrf2, Nrf3, Bach1).
• Chromatin immunoprecipitation (ChIP) assays.
• Analysis of p300 coactivator effects.

Main Results:

• The NF-E2 binding site (-86/-77) is critical for TXAS promoter activity in lung cells, similar to hematopoietic cells.
• Mutation of the NF-E2 site drastically reduced TXAS promoter activity (to 0.25% of wild-type in stable transfections).
• Nrf2, but not other tested factors, dose-dependently activated the TXAS promoter.
• ChIP assays confirmed in vivo binding of Nrf2 to the TXAS NF-E2 site.
• p300 upregulated TXAS expression, an effect dependent on the NF-E2 site.

Conclusions:

• The TXAS gene uses a conserved cis-acting element (NF-E2 site) but distinct trans-acting factors (Nrf2 in lung cells) for cell-preferential expression.
• Nrf2 is a key activator of TXAS in lung cells.
• The p300 coactivator enhances TXAS transcription via the NF-E2 site.