Identification of Estrogen-Related Receptor α Agonists in the Tox21 Compound Library

The estrogen-related receptor alpha (ERR alpha) is an orphan nuclear receptor (NR) that plays a role in energy homeostasis and controls mitochondrial oxidative respiration. Increased expression of ERR alpha in certain ovarian, breast, and colon cancers has a negative prognosis, indicating an important role for ERRa in cancer progression. An interaction between ERR alpha and peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1 alpha) has also recently been shown to regulate an enzyme in the beta-oxidation of free fatty acids, thereby suggesting that ERRa plays an important role in obesity and type 2 diabetes. Therefore, it would be prudent to identify compounds that can act as activators of ERRa. In this study, we screened; similar to 10,000 (8311 unique) compounds, known as the Tox21 10K collection, to identify agonists of ERR alpha. We performed this screen using two stably transfected HEK 293 cell lines, one with the ERR alpha-reporter alone and the other with both ERR alpha-reporter and PGC-1 alpha expression vectors. After the primary screening, we identified more than five agonist clusters based on compound structural similarity analysis (e.g., statins). By examining the activities of the confirmed ERR alpha modulators in other Tox21 NR assays, eliminating those with promiscuous NR activity, and performing follow-up assays (e.g., small interfering RNA knockdown), we identified compounds that might act as endocrine disrupters through effects on ERR alpha signaling. To our knowledge, this study is the first comprehensive analysis in discovering potential endocrine disrupters that affect the ERR alpha signaling pathway.