Target specificities of estrogen receptor-related receptors: analysis of binding sequences and identification of Rb1-inducible coiled-coil 1 (Rb1cc1) as a target gene.

Estrogen receptor-related receptors (ERRs) are orphan members of the nuclear receptor superfamily. A single AGGTCA sequence element preceded by three conserved nucleotides has been identified as a specific recognition motif of ERRs. Here we performed systematic analyses of target sequences on all three ERR subtypes, alpha, beta and gamma. In electrophoretic gel-mobility shift assay and transcriptional reporter assays, they exhibited similar patterns of recognition specificities, showing extremely broad ranges of target sequences. We searched a mouse promoter database for a gene carrying possible ERR-binding sequences. The Rb-1 inducible coiled-coil 1 (Rb1cc1) gene was found to contain two putative ERR binding elements, named response element (RE)-1 and RE-2, in the promoter region. In gene reporter assays, RE-2, but not RE-1, functioned as an effective cis-regulatory element for transactivation by ERRalpha in the presence of a coactivator, peroxisome proliferator-activated receptor gamma coactivator-1alpha. Mutational analyses suggested that RE-2 is recognized by ERRalpha partly as a monovalent element, but also as a direct repeat motif separated by four spacer nucleotides. In vivo binding of ERRalpha to the Rb1cc1 promoter region was confirmed by the chromatin immunoprecipitation assay. Thus, Rb1cc1 is a target gene of ERRalpha, driven by a novel type of recognition sequence.