title: Proteasomal inhibition enhances glucocorticoid receptor transactivation and alters its subnuclear trafficking.
abstract: The ubiquitin-proteasome pathway regulates the turnover of many transcription factors, including steroid hormone receptors such as the estrogen receptor and progesterone receptor. For these receptors, proteasome inhibition interferes with steroid-mediated transcription. We show here that proteasome inhibition with MG132 results in increased accumulation of the glucocorticoid receptor (GR), confirming that it is likewise a substrate for the ubiquitin-proteasome degradative pathway. Using the mouse mammary tumor virus (MMTV) promoter integrated into tissue culture cells, we found that proteasome inhibition synergistically increases GR-mediated transactivation. This increased activation was observed in a number of cell lines and on various MMTV templates, either as transiently transfected reporters or stably integrated into chromatin. These observations suggest that the increase in GR-mediated transcription due to proteasome inhibition may occur downstream of the initial chromatin remodeling step. In support of this concept, the increase in transcription did not correlate with an increase in chromatin remodeling, as measured by restriction enzyme hypersensitivity, or transcription factor loading, as exemplified by nuclear factor 1. To investigate the relationship between GR turnover, transcription, and subnuclear trafficking, we examined the effect of proteasome inhibition on the mobility of the GR within the nucleus and association of the GR with the nuclear matrix. Blocking GR turnover reduced the mobility of the GR within the nucleus, and this correlated with increased association of the receptor with the nuclear matrix. As a result of proteasome inhibition, GR mobility within the nucleus was reduced while its association with the nuclear matrix was increased. Thus, while altered nuclear mobility of steroid receptors may be a common feature of proteasome inhibition, GR is unique in its enhanced transactivation activity that results when proteasome function is compromised. Proteasomes may therefore impact steroid receptor action at multiple levels and exert distinct effects on individual receptor types.
authors.affiliation: Chromatin and Gene Expression Section, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Bonnie J
authors.initials: BJ
authors.lastname: Deroo
authors.forename: Claudia
authors.initials: C
authors.lastname: Rentsch
authors.forename: Sowmini
authors.initials: S
authors.lastname: Sampath
authors.forename: Janel
authors.initials: J
authors.lastname: Young
authors.forename: Donald B
authors.initials: DB
authors.lastname: DeFranco
authors.forename: Trevor K
authors.initials: TK
authors.lastname: Archer
mesh_terms: D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000821:virology; D002467:Cell Nucleus / Q000378:metabolism*; D002843:Chromatin / Q000235:genetics; D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D004265:DNA Helicases; D004268:DNA-Binding Proteins; D005260:Female; D051548:Histone Acetyltransferases; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D008324:Mammary Tumor Virus, Mouse / Q000235:genetics; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors*; D009687:Nuclear Proteins / Q000378:metabolism; D056920:Nuclear Receptor Coactivator 1; D011401:Promoter Regions, Genetic; D046988:Proteasome Endopeptidase Complex; D021381:Protein Transport; D011965:Receptors, Glucocorticoid / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism; D056264:Sin3 Histone Deacetylase and Corepressor Complex; D013698:Templates, Genetic; D014157:Transcription Factors / Q000187:drug effects / Q000378:metabolism; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
chemical_list: D002843:Chromatin; D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; D007976:Leupeptins; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; D011965:Receptors, Glucocorticoid; D012097:Repressor Proteins; C099683:SIN3A transcription factor; C101682:SMARCC2 protein, human; D014157:Transcription Factors; D051548:Histone Acetyltransferases; C538859:NCOA1 protein, human; C538861:Ncoa1 protein, mouse; D056920:Nuclear Receptor Coactivator 1; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D056264:Sin3 Histone Deacetylase and Corepressor Complex; C084108:SMARCA4 protein, human; C513194:Smarca4 protein, mouse; D004265:DNA Helicases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde