title: Glucocorticoid signaling is perturbed by the atypical orphan receptor and corepressor SHP.
abstract: SHP (NROB2) is an atypical orphan nuclear receptor that lacks a DNA-binding domain but contains a putative ligand-binding domain. Previous studies have revealed that SHP interacts with a variety of nuclear receptors and inhibits their transcriptional activity, thereby acting as a corepressor. In this report we identify the glucocorticoid receptor (GR) as a novel downstream target receptor for SHP inhibition. SHP potently inhibits dexamethasone-induced transcriptional GR activity in mammalian cells, and the inhibition involves a functional second NR-box within SHP. Interestingly, this motif shows a high homology with the NR-box in the glucocorticoid and cAMP-inducible GR coactivator PGC-1, indicating similar binding specificity and shared target receptors. We show that SHP antagonizes PGC-1 coactivation and, in addition, we identify the PGC- 1-regulated phospho(enol)pyruvate carboxykinase (PEPCK) promoter as a novel target promoter for SHP inhibition. This implies a physiologically relevant role for SHP in modulating hepatic glucocorticoid action. Furthermore, when coexpressing green fluorescent protein-tagged GR together with SHP, an intranuclear redistribution of GR was observed. As inhibition-deficient SHP mutants were unable to induce this redistribution, intranuclear tethering of target receptors may represent yet another, previously uncovered, aspect of SHP inhibition.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D005938:Glucocorticoids / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D049452:Green Fluorescent Proteins; D006801:Humans; D008099:Liver / Q000378:metabolism; D008164:Luminescent Proteins / Q000378:metabolism; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D010179:Pancreas / Q000378:metabolism; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000235:genetics; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D005938:Glucocorticoids; D008164:Luminescent Proteins; D018160:Receptors, Cytoplasmic and Nuclear; C099713:nuclear receptor subfamily 0, group B, member 2; D049452:Green Fluorescent Proteins; D000242:Cyclic AMP; D010729:Phosphoenolpyruvate Carboxykinase (GTP); D005947:Glucose