title: Down-regulation of the tumor suppressor gene retinoic acid receptor beta2 through the phosphoinositide 3-kinase/Akt signaling pathway.
abstract: The retinoic acid receptor beta2 (RARbeta2) is a potent, retinoid-inducible tumor suppressor gene, which is a critical molecular relay for retinoid actions in cells. Its down-regulation, or loss of expression, leads to resistance of cancer cells to retinoid treatment. Up to now, no primary mechanism underlying the repression of the RARbeta2 gene expression, hence affecting cellular retinoid sensitivity, has been identified. Here, we demonstrate that the phosphoinositide 3-kinase/Akt signaling pathway affects cellular retinoid sensitivity, by regulating corepressor recruitment to the RARbeta2 promoter. Through direct phosphorylation of the corepressor silencing mediator for retinoic and thyroid hormone receptors (SMRT), Akt stabilized RAR/SMRT interaction, leading to an increased tethering of SMRT to the RARbeta2 promoter, decreased histone acetylation, down-regulation of the RARbeta2 expression, and impaired cellular differentiation in response to retinoid. The phosphoinositide 3-kinase/Akt signaling pathway, an important modulator of cellular survival, has thus a direct impact on cellular retinoid sensitivity, and its deregulation may be the triggering event in retinoid resistance of cancer cells.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale, Unité 545, Faculté de Médecine Henri Warembourg, 1 Place de Verdun, 59045 Lille cedex, France. bruno.lefebvre@lille.inserm.fr
authors.forename: Bruno
authors.initials: B
authors.lastname: Lefebvre
authors.forename: Céline
authors.initials: C
authors.lastname: Brand
authors.forename: Sébastien
authors.initials: S
authors.lastname: Flajollet
authors.forename: Philippe
authors.initials: P
authors.lastname: Lefebvre
mesh_terms: D000107:Acetylation; D000818:Animals; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism; D019281:Dimerization; D015536:Down-Regulation; D004789:Enzyme Activation; D006657:Histones / Q000378:metabolism; D006801:Humans; D051379:Mice; D009154:Mutation / Q000235:genetics; D056985:Nuclear Receptor Co-Repressor 2; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D012319:RNA Polymerase II / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism; D047488:Retinoid X Receptors / Q000378:metabolism; D012176:Retinoids / Q000378:metabolism; D015398:Signal Transduction; D013379:Substrate Specificity; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D006657:Histones; C539130:NCOR2 protein, human; C539131:Ncor2 protein, mouse; D056985:Nuclear Receptor Co-Repressor 2; D018168:Receptors, Retinoic Acid; D012097:Repressor Proteins; D047488:Retinoid X Receptors; D012176:Retinoids; D025521:Tumor Suppressor Proteins; C082925:retinoic acid receptor beta; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D012319:RNA Polymerase II