Down-regulation of T helper 2-associated cytokine expression and selective transcription factors by fisetin

Abstract

Fisetin, a flavonol, has been known as an anti-allergic agent having inhibitory effects on T helper 2 cytokine gene expression in inflammatory immune cells. However, its molecular mechanisms for suppressive effects of fisetin on interleukin (IL)-4 and IL-13 in activated mast cells and basophils have been incompletely understood. In this study we found that fisetin at the concentrations having no effect on cell viability significantly inhibited the phorbol 12-myristate 13-acetate and ionomycin induced production of IL-4 and IL-13 in bone marrow-derived mast cells and RBL-2H3 basophilic cells. The levels of mRNA were dramatically decreased by fisetin, indicating the suppression might be regulated at the transcriptional levels. Transient transfection experiments using luciferase reporter plasmids expressing IL-4 or IL-13 promoter revealed that fisetin inhibited the activation of the promoters in a dose-dependent manner. Western blot analysis of the nuclear expression of various transcription factors involved in the promoter activation indicated that suppressions of c- Fos and CCAAT/enhancer-binding protein alpha were prominent together with significant downregulations of nuclear factor of activated T cell (NF-AT) and NF-κB. Furthermore, nuclear expression of GATA-1 and GATA-2, and the mRNA expression were significantly down regulated by fisetin, whereas cyclosporine A had no significant effects on GATA transcription factors. Taken together, fisetin has suppressive effects on IL-4 and IL-13 gene expressions through the regulation of selective transcription factors.