title: Unique anti-activator protein-1 activity of retinoic acid receptor beta.
abstract: The anticancer effects of retinoids are mainly mediated by two classes of nuclear receptors, the retinoic acid receptors (RARs) and retinoid X receptors (RXRs), which are encoded by three distinct genes (alpha, beta, and gamma). Recent studies have demonstrated that RARbeta plays a critical role in mediating anticancer effects of retinoids. However, how RARbeta exerts its potent anticancer effects remains largely unknown. In this study, we investigated anti-Activator Protein-1 (AP-1) activity of RARbeta. In a transient transfection assay, all three RAR subtypes, RARalpha, RARbeta, and RARgamma, could effectively inhibit phorbol ester 12-O-tetradecanoylphorbol-13-acetate-induced AP-1 activity and the activity of oncogenes c-Jun and c-Fos on AP-1 containing reporter genes in the presence of retinoic acid (RA). However, RARbeta showed a strong RA-independent inhibition of AP-1 activity, whereas inhibition of AP-1 activity by RARalpha and RARgamma was RA dependent. By using several hybrid receptors that contain either the COOH-terminal portion or the NH2-terminal portion of RARbeta, we demonstrated that the NH2-terminal portion of RARbeta, the A/B domain, was mainly responsible for the RA-independent inhibition of AP-1 activity. This activity was not attributable to constitutive AF-1 activity of RARbeta, because it did not activate several RA response element-containing reporter genes. In addition, inhibition of histone deacetylase activity by trichostatin A did not overcome the inhibitory effect of RARbeta. In cancer cells, stable transfection of RARbeta exhibited strong inhibition of AP-1 activity, even in the absence of RA. Moreover, expression of endogenous AP-1-responsive gene collagenase I was strongly repressed in cancer cells stably transfected with RARbeta. In studying the antitransforming activity of RARbeta, we observed that the growth of breast cancer MDA-MB231 cells in soft agar was significantly repressed in a RA-independent manner when cells were stably transfected with RARbeta but not RARalpha. Together, our results demonstrate that RARbeta may exert its potent anticancer effect in part through its unique anti-AP-1 activity.
authors.affiliation: The Burnham Institute Cancer Center, La Jolla, California 92037, USA.
authors.forename: F
authors.initials: F
authors.lastname: Lin
authors.forename: D
authors.initials: D
authors.lastname: Xiao
authors.forename: S K
authors.initials: SK
authors.lastname: Kolluri
authors.forename: X
authors.initials: X
authors.lastname: Zhang
mesh_terms: D001943:Breast Neoplasms / Q000378:metabolism; D002273:Carcinogens; D002455:Cell Division / Q000187:drug effects; D017364:Collagenases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017930:Genes, Reporter; D006367:HeLa Cells; D006655:Histone Deacetylases / Q000378:metabolism; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D016296:Mutagenesis; D010957:Plasmids; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000737:chemistry / Q000378:metabolism*; D000072482:Retinoic Acid Receptor alpha; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013755:Tetradecanoylphorbol Acetate; D018808:Transcription Factor AP-1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014162:Transfection; D014212:Tretinoin / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D002273:Carcinogens; D004791:Enzyme Inhibitors; D006877:Hydroxamic Acids; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; C000607071:RARA protein, human; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; D018808:Transcription Factor AP-1; C082925:retinoic acid receptor beta; C012589:trichostatin A; D014212:Tretinoin; D017364:Collagenases; D006655:Histone Deacetylases; D013755:Tetradecanoylphorbol Acetate