ABSTRACT
Vertebrate members of the nuclear receptor NR5A subfamily, which includes steroidogenic factor 1 (SF-1) and liver receptor homolog 1 (LRH-1), regulate crucial aspects of development, endocrine homeostasis, and metabolism. Mouse LRH-1 is believed to be a ligand-independent transcription factor with a large and empty hydrophobic pocket. Here we present structural and biochemical data for three other NR5A members-mouse and human SF-1 and human LRH-1-which reveal that these receptors bind phosphatidyl inositol second messengers and that ligand binding is required for maximal activity. Evolutionary analysis of structure-function relationships across the SF-1/LRH-1 subfamily indicates that ligand binding is the ancestral state of NR5A receptors and was uniquely diminished or altered in the rodent LRH-1 lineage. We propose that phospholipids regulate gene expression by directly binding to NR5A nuclear receptors.
Subject(s)
DNA-Binding Proteins/chemistry , DNA-Binding Proteins/metabolism , Phosphatidylinositols/metabolism , Receptors, Cytoplasmic and Nuclear/chemistry , Receptors, Cytoplasmic and Nuclear/metabolism , Transcription Factors/chemistry , Transcription Factors/metabolism , Animals , Binding Sites/physiology , Cell Line, Tumor , Crystallography, X-Ray , Evolution, Molecular , Homeodomain Proteins , Humans , Ligands , Mice , Models, Molecular , Phosphatidylinositol Phosphates/chemistry , Phosphatidylinositol Phosphates/metabolism , Phosphatidylinositols/chemistry , Phylogeny , Protein Binding/physiology , Protein Structure, Tertiary/physiology , Signal Transduction/physiology , Steroidogenic Factor 1ABSTRACT
Structural analysis of nuclear receptor subfamily V orphan nuclear receptors suggests that ligand-independent mechanisms must regulate this subclass of receptors. Here, we report that steroidogenic factor 1 (SF-1) and liver receptor homolog 1 are repressed via posttranslational SUMO modification at conserved lysines within the hinge domain. Indeed, mutating these lysines or adding the SUMO isopeptidase SENP1 dramatically increased both native and Gal4-chimera receptor activities. The mechanism by which SUMO conjugation attenuates SF-1 activity was found to be largely histone deacetylase independent and was unaffected by the AF2 corepressor Dax1. Instead, our data suggest that SUMO-mediated repression involves direct interaction of the DEAD-box protein DP103 with sumoylated SF-1. Of potential E3-SUMO ligase candidates, PIASy and PIASxalpha strongly promoted SF-1 sumoylation, and addition of DP103 enhanced both PIAS-dependent receptor sumoylation and SF-1 relocalization to discrete nuclear bodies. Taken together, we propose that DEAD-box RNA helicases are directly coupled to transcriptional repression by protein sumoylation.
