Molecular Basis for the Constitutive Activity of Estrogen-related Receptor α-1

Abstract

Some orphan nuclear receptors, including estrogen-related receptor α-1 (ERRα-1), can activate gene transcription in a constitutive manner. Little is known about the molecular basis of the constitutive activity of these receptors. Our results from site-directed mutagenesis experiments have revealed that Phe-329 (analogous to Ala-350 in estrogen receptor α (ERα)) is responsible for the constitutive activity of ERRα-1. The ERRα-1 mutant F329A lost the transactivation activity and acted as a dominant negative mutant. The mammalian cell transfection experiments revealed that the ERRα-1 mutant F329A, like wild-type ERα, recognized toxaphene (an organochlorine pesticide) as an agonist. This compound was previously shown to be an antagonist of wild-type ERRα-1. On the other hand, like wild-type ERRα-1, the ERa mutant A350F was found to be constitutively active (as demonstrated by mammalian cell transfection and yeast two-hybrid assays). These results indicate that Phe-329 in ERRα-1 and Ala-350 in ERα play important roles in both ligand binding and transactivation function.