title: Phosphorylation of activation function-1 regulates proteasome-dependent nuclear mobility and E6-associated protein ubiquitin ligase recruitment to the estrogen receptor beta.
abstract: The ubiquitin-proteasome pathway has been recognized as an important regulator in the hormonal response by estrogen receptor (ER) alpha, but its impact on ERbeta function is poorly characterized. In the current study, we investigated the role of the ubiquitin-proteasome pathway in regulating ERbeta activity and identified regulatory sites within the activation function (AF)-1 domain that modulate ERbeta ubiquitination and nuclear dynamics in a hormone-independent manner. Although both ERalpha and ERbeta were dependent on proteasome function for their maximal response to estrogen, they were regulated differently by proteasome inhibition in the absence of hormone, an effect shown to be dependent on their respective AF-1 domain. Given the role of AF-1 phosphorylation to regulate ER activity, we found that sequential substitutions of specific serine residues contained in MAPK consensus sites conferred transcriptional activation of ERbeta in a proteasome-dependent manner through reduced ubiquitination and enhanced accumulation of mutant receptors. Specifically, serines 94 and 106 within ERbeta AF-1 domain were found to modulate subnuclear mobility of the receptor to transit between inactive clusters and a more mobile state in a proteasome-dependent manner. In addition, cellular levels of ERbeta were regulated through these sites by facilitating the recruitment of the ubiquitin ligase E6-associated protein in a phosphorylation-dependent manner. These findings suggest a role for ERbeta AF-1 in contributing to the activation-degradation cycling of the receptor through a functional clustering of phosphorylated serine residues that cooperate in generating signals to the ubiquitin-proteasome pathway.
authors.affiliation: Research Center, Ste-Justine Hospital, 3175 Côte Ste-Catherine, Montréal, Québec, Canada.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Picard
authors.forename: Catherine
authors.initials: C
authors.lastname: Charbonneau
authors.forename: Mélanie
authors.initials: M
authors.lastname: Sanchez
authors.forename: Anne
authors.initials: A
authors.lastname: Licznar
authors.forename: Muriel
authors.initials: M
authors.lastname: Busson
authors.forename: Gwendal
authors.initials: G
authors.lastname: Lazennec
authors.forename: André
authors.initials: A
authors.lastname: Tremblay
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D016384:Consensus Sequence; D047628:Estrogen Receptor alpha / Q000235:genetics / Q000378:metabolism; D047629:Estrogen Receptor beta / Q000235:genetics / Q000378:metabolism*; D036681:Fluorescence Recovery After Photobleaching; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D008954:Models, Biological; D009154:Mutation; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism*; D061988:Proteasome Inhibitors; D012694:Serine / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D007976:Leupeptins; D061988:Proteasome Inhibitors; D012694:Serine; C471639:UBE3A protein, human; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde