Estrogen-related receptor α1 up-regulates endothelial nitric oxide synthase expression

The human estrogen-related receptor alpha1 (ERRalpha1) is a member of an orphan receptor family closely related to the estrogen receptor. It has been demonstrated that estrogen modulates endothelial nitric oxide synthase (eNOS) expression through the estrogen receptor in endothelial cells. However, little is known about the relationship between ERRalpha1 and eNOS. In this study, we show that ERRalpha1 activates the estrogen response element (ERE) and eNOS promoter-dependent luciferase activity in COS-7 cells and bovine pulmonary artery endothelial cells. The endogenous ligand for ERRalpha1 has not been identified, but we show that these actions are dependent on serum constituents because ERRalpha1 fails to stimulate eNOS promoter-dependent luciferase activity in charcoal-treated serum. Furthermore, through the use of truncated eNOS promoter luciferase constructs, we demonstrate that the activation of eNOS transcription by ERRalpha1 is mediated via three regions: base pairs -1001 to -743, base pairs -743 to -265, and downstream from base pair -265 on the eNOS promoter. In addition, ERRalpha1 upregulates eNOS mRNA and protein expression and stimulates eNOS activity in bovine pulmonary artery endothelial cells. These results suggest that ERRalpha1 has a potential role in the regulation of eNOS expression and may stimulate NO production by endothelial cells, which may in turn result in a protective effect against atherosclerosis.