JQ1, a bromodomain inhibitor, suppresses Th17 effectors by blocking p300-mediated acetylation of RORγt

Background and Purpose Th17 cells play critical roles in chronic inflammation, including fibrosis. Histone acetyltransferase p300, a bromodomain-containing protein, acetylates ROR gamma t and promotes Th17 cell development. The bromodomain inhibitor JQ1 was shown to alleviate Th17-mediated pathologies, but the underlying mechanism remains unclear. We hypothesized that JQ1 suppresses the response of Th17 cells by impairing p300-mediated acetylation of ROR gamma t. Experimental Approach The effect of JQ1 on p300-mediated acetylation of ROR gamma t was investigated in HEK293T (overexpressing Flag-p300 and Myc-ROR gamma t) and human Th17 cells through immunoprecipitation and western blotting. To determine the regions of p300 responsible for JQ1-mediated suppression of HAT activity, we performed HAT assays on recombinant p300 fragments with/without the bromodomain, after exposure to JQ1. Additionally, the effect of JQ1 on p300-mediated acetylation of ROR gamma t and Th17 cell function was verified in vivo, using murine Schistosoma-induced fibrosis models. Liver injury was assessed by histopathological examination and measurement of serum enzyme levels. Expression of Th17 effectors was detected by qRT-PCR, whereas IL-17- and ROR gamma t-positive granuloma cells were detected by FACS. Key Results JQ1 impaired p300-mediated ROR gamma t acetylation in human Th17 and HEK293T cells. JQ1 failed to suppress the acetyltransferase activity of p300 fragments lacking the bromodomain. JQ1 treatment attenuated Schistosoma-induced fibrosis in mice, by inhibiting ROR gamma t acetylation and IL-17 expression. Conclusions and Implications JQ1 impairs p300-mediated ROR gamma t acetylation, thus reducing the expression of ROR gamma t target genes, including Th17-specific cytokines. JQ1-mediated inhibition of p300 acetylase activity requires the p300 bromodomain. Strategies targeting p300 may provide new therapeutic approaches for controlling Th17-related diseases.