title: β-Apo-13-carotenone regulates retinoid X receptor transcriptional activity through tetramerization of the receptor.
abstract: Retinoid X receptor (RXRα) is activated by 9-cis-retinoic acid (9cRA) and regulates transcription as a homodimer or as a heterodimer with other nuclear receptors. We have previously demonstrated that β-apo-13-carotenone, an eccentric cleavage product of β-carotene, antagonizes the activation of RXRα by 9cRA in mammalian cells overexpressing this receptor. However, the molecular mechanism of β-apo-13-carotenone's modulation on the transcriptional activity of RXRα is not understood and is the subject of this report. We performed transactivation assays using full-length RXRα and reporter gene constructs (RXRE-Luc) transfected into COS-7 cells, and luciferase activity was examined. β-Apo-13-carotenone was compared with the RXRα antagonist UVI3003. The results showed that both β-apo-13-carotenone and UVI3003 shifted the dose-dependent RXRα activation by 9cRA. In contrast, the results of assays using a hybrid Gal4-DBD:RXRαLBD receptor reporter cell assay that detects 9cRA-induced coactivator binding to the ligand binding domain demonstrated that UVI3003 significantly inhibited 9cRA-induced coactivator binding to RXRαLBD, but β-apo-13-carotenone did not. However, both β-apo-13-carotenone and UVI3003 inhibited 9-cRA induction of caspase 9 gene expression in the mammary carcinoma cell line MCF-7. To resolve this apparent contradiction, we investigated the effect of β-apo-13-carotenone on the oligomeric state of purified recombinant RXRαLBD. β-Apo-13-carotenone induces tetramerization of the RXRαLBD, although UVI3003 had no effect on the oligomeric state. These observations suggest that β-apo-13-carotenone regulates RXRα transcriptional activity by inducing the formation of the "transcriptionally silent" RXRα tetramer.
authors.affiliation: From the Department of Human Sciences and.
authors.forename: Jian
authors.initials: J
authors.lastname: Sun
authors.affiliation: From the Department of Human Sciences and College of Pharmacy, Ohio State University, Columbus, Ohio 43210.
authors.forename: Sureshbabu
authors.initials: S
authors.lastname: Narayanasamy
authors.affiliation: College of Pharmacy, Ohio State University, Columbus, Ohio 43210.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Curley
authors.affiliation: From the Department of Human Sciences and harrison.304@osu.edu.
authors.forename: Earl H
authors.initials: EH
authors.lastname: Harrison
mesh_terms: D000818:Animals; D019556:COS Cells; D002338:Carotenoids / Q000494:pharmacology*; D053453:Caspase 9 / Q000096:biosynthesis / Q000235:genetics; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D003373:Coumaric Acids / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology; D006801:Humans; D051379:Mice; D055503:Protein Multimerization / Q000187:drug effects* / Q000502:physiology; D047490:Retinoid X Receptor alpha / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D013764:Tetrahydronaphthalenes / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects* / Q000502:physiology
chemical_list: D003373:Coumaric Acids; D047490:Retinoid X Receptor alpha; D013764:Tetrahydronaphthalenes; C525131:UVI 3003; D002338:Carotenoids; C071310:beta-apo-13-carotenone; C506433:CASP9 protein, human; C506434:Casp9 protein, mouse; D053453:Caspase 9
keywords: Apocarotenoid; Carotenoid; Nuclear Receptor; Receptor Regulation; Retinoid; Tetramerization; Vitamin A