Estrogen-related receptor-gamma and peroxisome proliferator-activated receptor-gamma coactivator-1alpha regulate estrogen-related receptor-alpha gene expression via a conserved multi-hormone response element.

The expression of estrogen-related receptor-alpha (ERRalpha) is stimulated by estrogen in selective tissues. Recently, a correlation between ERRalpha expression and the induction of peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) in the liver of fasting animals and in cold-stressed brown-fat tissues and skeletal muscle was shown. To explore the molecular mechanisms of ERRalpha regulation by diverse signals, the promoter of the human ERRalpha gene was cloned and characterized. Mutation and deletion analyses revealed that a 53 bp region containing repeated core element AGGTCA motifs of the ERRalpha gene serves as a multi-hormone response element (MHRE) for several nuclear receptors in transient co-transfection studies of human endometrial carcinoma (HEC-1B) cells. Among the nuclear receptors tested, ERRgamma bound to and robustly stimulated the transcription of reporters containing at least two AGGTCA motifs. Ectopic expression of PGC-1alpha in HEC-1B cells strongly activated the reporter containing the MHRE, presumably via the endogenous nuclear receptor binding to the element. Reducing the endogenous level of ERRgamma by small interfering RNA, and increasing the ERRgamma level by ectopic expression, substantially decreased and increased respectively the transactivation capability of PGC-1alpha. The activation function 2 domain of the ERRgamma and the L2 and L3 motifs of PGC-1alpha were essential to transactivate the MHRE. Additionally, PGC-1alpha increases the amount of endogenous ERRgamma bound to the MHRE region as determined by a chromatin immunoprecipitation assay. The present study demonstrates that the MHRE of the ERRalpha gene is a target for ERRgamma transactivation, which is enhanced by PGC-1alpha.