Interplay between estrogen-related receptor alpha (ERRalpha) and gamma (ERRgamma) on the regulation of ERRalpha gene expression.

Estrogen-related receptor alpha (ERRalpha) modulates estrogen receptor (ER)-mediated activity and is participating in the energy homeostasis by regulation of downstream target genes. The ERRalpha gene itself is proposed to be regulated by peroxisome proliferator-activated receptor gamma coactivator (PGC-1alpha) through an autoregulatory loop under physiological stimulation. We have previously shown that the close family member ERRgamma is a positive regulator of ERRalpha gene expression. ERRalpha and ERRgamma are coexpressed in metabolically active tissues such as heart, kidney and muscle, yet the physiological role of ERRgamma and its relationship with ERRalpha in gene regulation are currently unknown. The present study examined the interplay of ERRgamma and ERRalpha in regulation of ERRalpha gene expression. Using real-time PCR analyses we found that ERRgamma, like the ERRalpha and PGC-1alpha is induced in mouse liver during fasting. Overexpression of ERRgamma in the HEC-1B cells robustly stimulated the multi-hormone response element (MHRE) of the ERRalpha gene promoter and this activity was repressed by increasing expression of ERRalpha. The two ERRs bind MHRE simultaneously in electrophoretic mobility shift assay (EMSA) and they were detected as multimeric complexes in cells by coimmunoprecipitation. Although ERRalpha and ERRgamma share high sequence identity, they differ in biochemical and molecular characteristics as examined by trypsin digestion, reporter activation and coactivator interaction and utilization. Using chromatin immunoprecipitation (ChIP) assay, we showed that ectopic expression of both ERRalpha and ERRgamma modifies chromatin structure at the MHRE region while ectopic expression of PGC-1alpha in HEC-1B cells promotes ERRgamma but not ERRalpha occupancy at the MHRE region of the ERRalpha gene promoter and enhances the recruitment of coactivator SRC1. These data suggested that ERRalpha and ERRgamma regulate ERRalpha gene expression with different molecular mechanisms.