title: Retinoid X receptor-specific ligands synergistically upregulate 1, 25-dihydroxyvitamin D3-dependent transcription in epidermal keratinocytes in vitro and in vivo.
abstract: We have examined the mechanism by which endogenous retinoid X receptor (RXR), vitamin D3 receptor (VDR), and cognate ligands regulate nuclear 1,25-dihydroxyvitamin D3 (D3) signaling in epidermal keratinocytes from skin, a physiologic D3 target. In vitro, RXR and VDR-specific antibodies identified endogenous RXR and VDR bound to a vitamin D3-responsive element (DR3) as heterodimers (VDR-RXR). In cultured keratinocytes, 9-cis retinoic acid (9cRA), a panagonist for RXR and retinoic acid receptor (RAR), and an RXR-selective agonist, SR11237, synergized with D3 to activate DR3 via endogenous as well as overexpressed VDR-RXR, whereas both of these RXR agonists alone were ineffective. In contrast, SR11237 did not synergize with but antagonized an RAR-selective ligand activation of a retinoic acid-responsive element (DR5) via endogenous RAR-RXR. Furthermore, expression of RXR mutated in transactivation domain AF-2 inhibited endogenous VDR-RXR activity over DR3. This mutant efficiently bound to DR3 as VDR-RXR but showed reduced capacity to transactivate DR3 in response to D3 and SR11237. In vivo, D3 and SR11237 synergistically induced the naturally occurring D3-responsive 24-hydroxylase gene in epidermis of mouse skin, whereas SR11237 alone was ineffective. Our data suggest that allosteric changes caused by VDR in DR3-bound VDR-RXR do not block access of ligands to RXR. RXR ligand-induced conformational changes permit VDR-RXR, via both VDR and RXR activation function domains, to mediate maximal D3 signaling in keratinocytes.
authors.affiliation: Department of Dermatology, University of Michigan, Ann Arbor 48109-0609, U.S.A.
authors.forename: X Y
authors.initials: XY
authors.lastname: Li
authors.forename: J H
authors.initials: JH
authors.lastname: Xiao
authors.forename: X
authors.initials: X
authors.lastname: Feng
authors.forename: L
authors.initials: L
authors.lastname: Qin
authors.forename: J J
authors.initials: JJ
authors.lastname: Voorhees
mesh_terms: D000818:Animals; D001565:Benzoates / Q000494:pharmacology; D002117:Calcitriol / Q000235:genetics*; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D004268:DNA-Binding Proteins / Q000502:physiology; D004357:Drug Synergism; D015603:Keratinocytes / Q000737:chemistry* / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018167:Receptors, Calcitriol / Q000502:physiology; D018168:Receptors, Retinoic Acid / Q000502:physiology*; D047488:Retinoid X Receptors; D012176:Retinoids / Q000494:pharmacology; D012867:Skin / Q000166:cytology; D013250:Steroid Hydroxylases / Q000235:genetics; D015534:Trans-Activators / Q000494:pharmacology; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic; D014162:Transfection; D015854:Up-Regulation; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D001565:Benzoates; D004268:DNA-Binding Proteins; D018167:Receptors, Calcitriol; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D012176:Retinoids; D015534:Trans-Activators; D014157:Transcription Factors; C087130:SR 11237; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D002117:Calcitriol