| The estrogen receptor-related receptor alpha (ERRalpha) is an orphan member of the nuclear receptor superfamily of ligand-activated transcription factors. While structurally related to steroid receptors, no ligand is necessary to activate ERRalpha. ERRalpha binds to response elements of target genes and interacts with cofactors in the absence of ligand. Recent studies suggest ERRalpha may be a therapeutic target in the treatment of breast cancer, diabetes, and osteoporosis. However, without pharmacological agents to regulate ERRalpha activity, the role of this receptor and its signal transduction pathway have been difficult to define. The objective of this dissertation research is to elucidate the physiological roles of ERRalpha by (a) isolating novel cofactors, (b) characterizing the molecular interactions with cofactors, and (c) identifying target genes and signaling pathways regulated as a result of these interactions.; ERRalpha activates transcription through interactions with cofactors. To identify ERRalpha cofactors, a T7 phage display cDNA library was screened for novel ERRalpha binding partners. We identified RIP140 as a repressor of ERRalpha activity, and two known ERRalpha coactivators, PGC-1alpha and SRC2, validating this approach to identify novel nuclear receptor cofactors.; The molecular determinants governing the interaction between ERRalpha and its coactivators were defined by mutation analyses. Two coactivators, PGC-1alpha and SRC2, have different amino acid requirements. SRC2 depends on a charge clamp in the ERRalpha AF2 domain, while PGC-1alpha does not. This difference could be exploited to develop pharmaceutical agents selecting for functional differences by facilitating one ERR:cofactor interaction over another.; The identification of target genes is critical to determining the biological function of ERRalpha. To modulate ERRalpha activity, we developed approaches to positively and negatively regulate ERRalpha activity in target cells. Selective peptide antagonists were generated that block cofactor binding and inhibit activity. "Customized" coactivators that selectively activate ERRalpha transcriptional activity were developed by replacing the interaction domain of PGC-1alpha with the selective peptide. With the "customized" coactivator, microarray technology, and RNA interference, we defined ERRalpha target genes involved in energy metabolism. Cumulatively, these studies have elucidated the regulatory partners, molecular interactions, and biological function of ERRalpha. |
