The RXRα-mediated Anti-inflammatory Effect Of Sulindac Analog K-80003 And The Underlying Molecular Mechanism

Retinoid X receptor-a(RXRa),a unique member of the nuclear receptor superfamily,plays an integral role in a wide range of cellular pathways,including proliferation,differentiation,survival,and apoptosis.Ligands of RXRa could activate RXRa homodimer and heterodimer to regulate the expression of target genes.Cytoplasmic location of RXRa also mediates the crosstalk between RXRa pathway and other signaling pathways.Thus,abnormal activation of RXRa signaling is implicated in the development of cancer and diseases,including inflammatory diseases,cancer,metabolic syndrome and neurodegenerative diseases.Chronic inflammation is cloased related to human health because of its signifiacant role during development from steatosis,liver fibrosis,cirrhosis to hepatocellular carcinoma.However,whether and how RXRa signaling and its ligands are involved in the regulation of chronic inflammation remain largely undetermined.Our previous results showing that RXRa served as an intracellular target of Sulindac action provided an opportunity to design RXRa-selective Sulindac derivatives for the anti-inflammatory therapy.Because of its much-improved affinity to RXRa and lack of COX inhibitory effect,Sulindac analog K-80003 was chosen for evaluation in this study.Here,we showed that K-80003 could inhibit the activation of the NF-κB pathway,including IκBa degradation,and p65 nuclear translocation induced by various of pro-inflammatory cytokines in a RXRa-dependent manner.Moreover,K-80003 could inhibit the ubiquitination of TRAF6 induced by IL-1β in dose-dependent manner.In the Methionine-Choline-Deficient(MCD)-induecd Non-alcoholic fatty liver disease(NAFLD or NASH)animal model,K-80003 alleviated excess accumulation of fat in hepatocytes accompanied with inhibition of inflammation.Interestingly,we found that a modified-RXRa protein could interact with TRAF6 under IL-1β treatment.Furthermore,K-80003 could inhibt the interaction between RXRa and TRAF6,resulting in inhibition of NF-κB signaling pathway.We also demonsatrated that the ligand-bnding domain(LBD)of RXRa and the TRAF domain of TRAF6 are essential for their cytoplasmic co-localization.Together,our study show that Sulindac analog K-80003 could inhibit inflammation by inducing RXRa interaciton with TRAF6 complex and identify K-80003 as a promising lead for the treatment of inflammatory and metabolic disorders,such as NASH.