title: Characterization of the chimeric retinoic acid receptor RARalpha/VDR.
abstract: The chimeric receptor, RARalpha/VDR, contains the DNA-binding domain of the retinoic acid receptor (RARalpha) and the ligand-binding domain of the vitamin D receptor (VDR). The ligand-binding properties of RARalpha/VDR are equivalent to that of VDR, with an observed Kd for 1alpha,25 dihydroxy-vitamin D3 (D3) of 0.5 nM. In CV-1 cells, both RARalpha and RARalpha/VDR induce comparable levels of ligand-mediated transcriptional activity from the retinoic acid responsive reporter gene, beta(RARE)3-TK-luciferase, in the presence of the ligand predicted from the receptor ligand-binding domain. Two chimeric RAR receptors were constructed which contained the ligand-binding domain of the estrogen receptor (ER): RARalpha/ER and ER/RARalpha/ER. Both RARalpha/ER and ER/RARalpha/ER bind beta-estradiol with high affinity, and are transcriptionally active only from palindromic RAREs (TREpal and/or (TRE3)3). Only RARalpha/VDR matched in kind and degree the functional characteristics of RARalpha: (1) maximally active from the beta(RARE); (2) moderately active from the TREs; (3) inactive from the retinoic X receptor response elements (RXREs) ApoA1 and CRBP II; (4) forms heterodimers with RXRalpha; and (5) binds to the betaRARE. F9 embryonal carcinoma cell lines were generated which express RARalpha/VDR mRNA (F9RARalpha/VDR cells) and compared with F9 wild-type (F9-Wt) cells, which do not express VDR mRNA. Treatment with all-trans retinoic acid (tRA) inhibits cell growth and induces the differentiation morphology in both F9-Wt and F9-RARalpha/VDR cells; whereas, treatment with D3 is similarly effective only for F9-RARalpha/VDR cells. It is concluded RARalpha/VDR is an useful 'tool' to pinpoint, or to augment transcription from RAREs in gene pathways controlled by RAR without inhibiting the retinoid responsiveness of endogenous RARs.
authors.affiliation: Department of Metabolic Diseases, Hoffmann-La Roche, Inc., Nutley, NJ, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Pemrick
authors.forename: P
authors.initials: P
authors.lastname: Abarzúa
authors.forename: C
authors.initials: C
authors.lastname: Kratzeisen
authors.forename: M S
authors.initials: MS
authors.lastname: Marks
authors.forename: J A
authors.initials: JA
authors.lastname: Medin
authors.forename: K
authors.initials: K
authors.lastname: Ozato
authors.forename: J F
authors.initials: JF
authors.lastname: Grippo
mesh_terms: D000818:Animals; D019556:COS Cells; D002454:Cell Differentiation / Q000502:physiology; D002762:Cholecalciferol / Q000378:metabolism; D019281:Dimerization; D004958:Estradiol / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D018167:Receptors, Calcitriol / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011960:Receptors, Estrogen / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D018168:Receptors, Retinoic Acid / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000072482:Retinoic Acid Receptor alpha; D047488:Retinoid X Receptors; D013379:Substrate Specificity; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation / Q000502:physiology; D014162:Transfection
chemical_list: C000607072:Rara protein, mouse; D018167:Receptors, Calcitriol; D011960:Receptors, Estrogen; D018168:Receptors, Retinoic Acid; D011993:Recombinant Fusion Proteins; D000072482:Retinoic Acid Receptor alpha; D047488:Retinoid X Receptors; D014157:Transcription Factors; D002762:Cholecalciferol; D004958:Estradiol