Isoflavones enhance interleukin-17 gene expression via retinoic acid receptor-related orphan receptors α and γ

The retinoic acid receptor-related orphan receptors a and gamma (ROR alpha and ROR gamma), are key regulators of helper T (Th)17 cell differentiation, which is involved in the innate immune system and autoimmune disorders. In this study, we investigated the effects of isoflavones on ROR alpha/gamma, activity and the gene expression of interleukin (IL)-17, which mediates the function of Th17 cells. In doxycycline-inducible CHO stable cell lines, we found that four isoflavones, biochanin A (BA), genistein, formononetin, and daidzein, enhanced ROR alpha- or ROR gamma-mediated transcriptional activity in a dose-dependent manner. In an activation assay of the Il17a promoter using Jurkat cells, these compounds enhanced the ROR alpha- or ROR gamma-mediated activation of the Il17a promoter at concentrations of 1 x 10(-6) M to 1 x 10(-5) M. In mammalian two-hybrid assays, the four isoflavones enhanced the interaction between the RORa- or ROR gamma-ligand binding domain and the co-activator LXXLL peptide in a dose-dependent manner. In addition, these isoflavones potently enhanced Il17a mRNA expression in mouse T lymphoma EL4 cells treated with phorbol myristate acetate and ionomycin, but showed slight enhancement of Il17a gene expression in ROR alpha/gamma-knockdown EL4 cells. Immunoprecipitation and immunoblotting assays also revealed that BA enhanced the interaction between ROR-gamma t and SRC-1, which is a co-activator for nuclear receptors. Taken together, these results suggest that the isoflavones have the ability to enhance IL-17 gene expression by stabilizing the interactions between ROR alpha/gamma, and co-activators. This also provides the first evidence that dietary chemicals can enhance IL-17 gene expression in immune cells. (C) 2015 Elsevier Ireland Ltd. All rights reserved.