title: The N-terminal of the estrogen receptor (ERalpha) mediates transcriptional cross-talk with the retinoic acid receptor in human breast cancer cells.
abstract: Transcriptional cross-talk exists between the estrogen receptor (ERalpha) and retinoic acid receptor (RAR) pathways in human breast cancer cells. We have previously shown that re-expression of ERalpha in ER-negative cells stimulates the transcriptional and growth inhibitory effects of all-trans-retinoic acid (tRA) by a mechanism that is independent of the ER ligands estradiol and tamoxifen. In this study, we generated cell lines stably expressing ERalpha-deletion mutants to elucidate the mechanism whereby ERalpha modulates RAR transcriptional activity. Using RT-PCR and RNAse protection assays, we observed that expression of ERalpha suppresses basal expression of the RA-responsive gene RARbeta2, while allowing it to be strongly induced by tRA. Repression of basal RARbeta2 transcription was confirmed by transient expression of the reporter plasmid betaRE-tk-CAT, containing the RARbeta2 promoter. In the ERalpha-negative cells, on the other hand, transcription was only weakly induced by RA. We further determined that this effect of ERalpha on RARbeta induction required the N-terminal AF-1-containing region, including the DNA-binding domain, but was independent of the C-terminal ligand-binding domain. Consistent with these results, the ER agonist estradiol and the AF-2 antagonist 4-hydroxytamoxifen had no significant effect on betaRARE activity. Conversely, the full ER antagonist ICI 182,780, which blocks ERalpha AF-1 activity, was able to completely relieve repression of basal betaRARE activity. The effect of ERalpha is specific for RAR-mediated transcription and does not occur on promoters containing typical response elements for the Vitamin D or thyroid hormone receptors. Moreover, the cross-talk between ERalpha and RAR does not seem to be mediated by sequestration of a number of common co-regulators, suggesting a novel mechanism whereby the N-terminal region of ERalpha modulates the transcriptional activity of RAR.
authors.affiliation: Departments of Oncology and Medicine, Lady Davis Institute for Medical Research, SMBD-Jewish General Hospital (McGill University), 3755 Cote Ste Catherine Road, Que., H3T 1E2, Montreal, Canada.
authors.forename: Caroline
authors.initials: C
authors.lastname: Rousseau
authors.forename: Filippa
authors.initials: F
authors.lastname: Pettersson
authors.forename: Marie Claude
authors.initials: MC
authors.lastname: Couture
authors.forename: Andre
authors.initials: A
authors.lastname: Paquin
authors.forename: Jacques
authors.initials: J
authors.lastname: Galipeau
authors.forename: Sylvie
authors.initials: S
authors.lastname: Mader
authors.forename: Wilson H
authors.initials: WH
authors.lastname: Miller
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000378:metabolism*; D004958:Estradiol / Q000494:pharmacology; D047628:Estrogen Receptor alpha; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology; D017930:Genes, Reporter / Q000235:genetics; D006801:Humans; D051379:Mice; D010957:Plasmids / Q000235:genetics; D017434:Protein Structure, Tertiary; D020239:Receptor Cross-Talk; D011960:Receptors, Estrogen / Q000819:agonists / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018168:Receptors, Retinoic Acid / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D013629:Tamoxifen / Q000494:pharmacology; D015534:Trans-Activators / Q000096:biosynthesis; D014158:Transcription, Genetic / Q000502:physiology; D014212:Tretinoin / Q000737:chemistry / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D047628:Estrogen Receptor alpha; D011960:Receptors, Estrogen; D018168:Receptors, Retinoic Acid; D011994:Recombinant Proteins; D015534:Trans-Activators; D013629:Tamoxifen; D004958:Estradiol; D014212:Tretinoin