title: Dexamethasone induces a putative repressor complex and chromatin modifications in the CRH promoter.
abstract: Glucocorticoids down-regulate expression of hypothalamic CRH; however, mechanisms by which they do so are not fully understood. The proximal promoter cAMP response element, negative glucocorticoid response element (nGRE), and methylated CpG islands all play a role in crh down-regulation. Dexamethasone (Dex)-repressed crh expression is associated with glucocorticoid receptor (GR) and histone deacetylase 1 (HDAC1) recruitment to the region of the crh promoter. Given that HDAC1 may be present in methylated CpG binding protein 2 (MeCP2) complexes, and that MeCP2 is known to play a role in regulating crh expression, we sought to determine whether or not HDAC1 and/or MeCP2 could interact with the GR. Dex enhanced GR interactions with both proteins. Glucocorticoid regulation of crh has also been associated with CpG methylation; thus we assessed whether GR could interact with a DNA methyltransferase (DnMT). Indeed, the GR interacted with DnMT3b, but not DnMT3a. In addition, Dex-induced occupancy of the crh promoter by HDAC1, MeCP2, and DnMT3b was associated with an increased level of promoter methylation, which appeared to be CpG site specific. Lastly, to extend previous assessment of chromatin modifications in this promoter region, the degree of histone methylation was measured. Dex increased trimethylation of histone 3-lysine 9, a marker of gene suppression; however, levels of di- and trimethylated histone 3-lysine 4, markers of gene activation, were not significantly changed. Taken together, the data suggest that Dex-mediated crh suppression involves formation of a repressor complex consisting of GR, MeCP2, and HDAC1, recruitment of DnMT3b, and associated changes in proximal promoter CpG methylation.
authors.affiliation: Institute for Aging and Alzheimer's Disease, Department of Pharmacology & Neuroscience, University of North Texas Health Science Center, CBH 469, 3500 Camp Bowie Boulevard, Fort Worth, Texas 76107, USA.
authors.forename: Dharmendra
authors.initials: D
authors.lastname: Sharma
authors.forename: Shreyas
authors.initials: S
authors.lastname: Bhave
authors.forename: Elaine
authors.initials: E
authors.lastname: Gregg
authors.forename: Rosalie
authors.initials: R
authors.lastname: Uht
mesh_terms: D000818:Animals; D001483:Base Sequence; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism*; D003346:Corticotropin-Releasing Hormone / Q000235:genetics* / Q000378:metabolism; D018899:CpG Islands / Q000235:genetics; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000378:metabolism; D019175:DNA Methylation / Q000187:drug effects / Q000235:genetics; D003907:Dexamethasone / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D056284:Histone Deacetylase 1 / Q000378:metabolism; D006657:Histones / Q000378:metabolism; D051783:Methyl-CpG-Binding Protein 2 / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011485:Protein Binding / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D000097584:DNA Methyltransferase 3B
chemical_list: D002843:Chromatin; D003346:Corticotropin-Releasing Hormone; D004248:DNA (Cytosine-5-)-Methyltransferases; D003907:Dexamethasone; D056284:Histone Deacetylase 1; D006657:Histones; D051783:Methyl-CpG-Binding Protein 2; D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; D012097:Repressor Proteins; D000097584:DNA Methyltransferase 3B