title: Involvement of all-trans-retinoic acid in the breakdown of retinoic acid receptors alpha and gamma through proteasomes in MCF-7 human breast cancer cells.
abstract: Most studies have reported an up-regulation of retinoic acid receptor (RAR) mRNA expression by all-trans retinoic acid (RA). We aimed to study the effect of RA on RAR protein levels in MCF-7 human breast cancer cells. Incubation of these cells with 10(-6) M RA induced a rapid breakdown of both RARalpha and RARgamma in spite of the accumulation of their mRNAs. Proteasome specific inhibitors blocked the RA-induced breakdown of RARs. Furthermore, RA enhanced the formation of the complex between RARalpha and ubiquitin in a concentration- and time-dependent manner, suggesting the involvement of ubiquitin and proteasome in this reaction. Retinoid X receptor alpha (RXRalpha) was also decreased, albeit to a lesser extent, in RA-treated cells. Use of synthetic receptor agonists and antagonists clearly showed that the effect of the retinoid on the breakdown of the retinoid receptors is receptor-ligand agonist-dependent and blunted by the antagonist. An electrophoretic mobility shift assay, using nuclear extracts from RA-treated cells, showed that a reduction in complex formation with hormone response elements correlated with the reduction of RAR and RXR protein. These data suggest that RA induces the breakdown of RARs through a process involving ubiquitination and that this phenomenon causes a reduction in the formation of DNA-receptor complexes.
authors.affiliation: National Cancer Institute, National Institutes of Health, Building 37, Room 3A-17, 37 Convent Drive, Bethesda, MD 20892-4255, USA.
authors.forename: T
authors.initials: T
authors.lastname: Tanaka
authors.forename: M L
authors.initials: ML
authors.lastname: Rodríguez de la Concepción
authors.forename: L M
authors.initials: LM
authors.lastname: De Luca
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004247:DNA / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D020218:Response Elements / Q000187:drug effects; D000072482:Retinoic Acid Receptor alpha; D014212:Tretinoin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D014452:Ubiquitins / Q000378:metabolism; D000097768:Retinoic Acid Receptor gamma
chemical_list: D000970:Antineoplastic Agents; D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors; D004247:DNA; D007976:Leupeptins; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; D046988:Proteasome Endopeptidase Complex; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; D014212:Tretinoin; D014452:Ubiquitins; D000097768:Retinoic Acid Receptor gamma; C000607071:RARA protein, human; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde