Role of Brg1 and HDAC2 in GR trans-repression of the pituitary POMC gene and misexpression in Cushing disease
Bilodeau, Steve; Vallette-Kasic, Sophie; Gauthier, Yves; Figarella-Branger, Dominique; Brue, Thierry; Berthelet, France; Lacroix, Andre; Batista, Dalia; Stratakis, Constantine; Hanson, Jeanette; Meij, Bjorn; Drouin, Jacques
Negative feedback regulation of the proopiomelanocortin ( POMC) gene by the glucocorticoid (Gc) receptor (GR) is a critical feature of the hypothalamo-pituitary-adrenal axis, and it is in part exerted by trans-repression between GR and the orphan nuclear receptors related to NGFI-B. We now show that Brg1, the ATPase subunit of the Swi/Snf complex, is essential for this trans-repression and that Brg1 is required in vivo to stabilize interactions between GR and NGFI-B as well as between GR and HDAC2. Whereas Brg1 is constitutively present at the POMC promoter, recruitment of GR and HDAC2 is ligand-dependent and results in histone H4 deacetylation of the POMC locus. In addition, GR-dependent repression inhibits promoter clearance by RNA polymerase II. Thus, corecruitment of repressor and activator at the promoter and chromatin modification jointly contribute to trans-repression initiated by direct interactions between GR and NGFI-B. Loss of Brg1 or HDAC2 should therefore produce Gc resistance, and we show that similar to 50% of Gc-resistant human and dog corticotroph adenomas, which are the hallmark of Cushing disease, are deficient in nuclear expression of either protein. In addition to providing a molecular basis for Gc resistance, these deficiencies may also contribute to the tumorigenic process.
repression; nuclear receptor; Swi/Snf; pituitary tumors; POMC; Cushing
Genes and Development
2006, Volym: 20, nummer: 20, sidor: 2871-2886
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