RORα and ROR γ are expressed in human skin and serve as receptors for endogenously produced noncalcemic 20-hydroxy- and 20,23-dihydroxyvitamin D

ROR alpha and ROR gamma are expressed in human skin cells that produce the noncalcemic 20-hydroxyvitamin D-3 [20(OH)D-3] and 20,23-dihydroxyvitamin D-3 [20,23(OH)(2)D-3]. Chinese hamster ovary (CHO) cells stably expressing a Tet-on ROR alpha or ROR gamma expression vector and a ROR-responsive element (RORE)-LUC reporter, and a mammalian 2-hybrid model examining the interaction between the ligand binding domain (LBD) of ROR alpha or ROR gamma with an LBD-interacting LXXLL-peptide, were used to study ROR-antagonist activities. These assays revealed that 20(OH)D-3 and 20,23(OH)(2)D-3 function as antagonists of ROR alpha and ROR gamma. Moreover, 20(OH)D-3 inhibited the activation of the promoter of the Bmal1 and G6pase genes, targets of ROR alpha, and 20(OH)D-3 and 20,23(OH)(2)D-3 inhibited Il17 promoter activity in Jurkat cells overexpressing ROR alpha or ROR gamma. Molecular modeling using crystal structures of the LBDs of ROR alpha and ROR gamma revealed docking scores for 20(OH)D-3, 20, 23(OH)(2)D-3 and 1,25(OH)(2)D-3 similar to those of the natural ligands, predicting good binding to the receptor. Notably, 20(OH)D-3, 20,23(OH)(2)D-3, and 1,25(OH)(2)D-3 inhibited RORE-mediated activation of a reporter in keratinocytes and melanoma cells and inhibited IL-17 production by immune cells. Our study identifies a novel signaling pathway, in which 20(OH)D-3 and 20,23(OH)(2)D-3 act as antagonists or inverse agonists of ROR alpha and ROR gamma, that opens new possibilities for local (skin) or systemic regulation.