The transcriptional coactivator PPARγ coactivator-1α (PGC-1α) has been characterized as a broad regulator of cellular energy metabolism. Although PGC-1α functions through many transcription factors, the PGC-1α partners identified to date are unlikely to account for all of its biologic actions. The orphan nuclear receptor estrogen-related receptor α (ERRα) was identified in a yeast two-hybrid screen of a cardiac cDNA library as a novel PGC-1α-binding protein. ERRα was implicated previously in regulating the gene encoding medium-chain acyl-CoA dehydrogenase (MCAD), which catalyzes the initial step in mitochondrial fatty acid oxidation. The cardiac perinatal expression pattern of ERRα paralleled that of PGC-1α and MCAD. Adenoviral-mediated ERRα overexpression in primary neonatal cardiac mycoytes induced endogenous MCAD expression. Furthermore, PGC-1α enhanced the transactivation of reporter plasmids containing an estrogen response element or the MCAD gene promoter by ERRα and the related isoform ERRγ. In vitro binding experiments demonstrated that ERRα interacts with PGC-1α via its activation function-2 homology region. Mutagenesis studies revealed that the LXXLL motif at amino acid position 142-146 of PGC-1α (L2), necessary for PGC-1α interactions with other nuclear receptors, is not required for the PGC-1α-ERRα interaction. Rather, ERRα binds PGC-1α primarily through a Leu-rich motif at amino acids 209-213 (Leu-3) and utilizes additional LXXLL-containing domains as accessory binding sites. Thus, the PGC-1α-ERRα interaction is distinct from that of other nuclear receptor PGC-1α partners, including PPARα, hepatocyte nuclear factor-4α, and estrogen receptor α. These results identify ERRα and ERRγ as novel PGC-1α interacting proteins, implicate ERR isoforms in the regulation of mitochondrial energy metabolism, and suggest a potential mechanism whereby PGC-1α selectively binds transcription factor partners.
ASJC Scopus subject areas