Natural small molecule FMHM inhibits lipopolysaccharide-induced inflammatory response by promoting TRAF6 degradation via K48-linked polyubiquitination

TNF receptor-associated factor 6 (TRAF6) is a key hub protein involved in Toll-like receptor-dependent inflammatory signaling pathway and it recruits additional proteins to form multiprotein complexes capable of activating downstream NF-κB inflammatory signaling pathway. Ubiquitin-proteasome system (UPS) plays a crucial role in various protein degradations, such as TRAF6, leading to inhibitory effects on inflammatory response and immunologic function. However, whether ubiquitination-dependent TRAF6 degradation can be used as a novel anti-inflammatory drug target still remains to be explored. FMHM, a bioactive natural small molecule compound extracted from Chinese herbal medicine Radix Polygalae, suppressed acute inflammatory response by targeting ubiquitin protein and inducing UPS-dependent TRAF6 degradation mechanism. It was found that FMHM targeted ubiquitin protein via Lys48 site directly induced Lys48 residue-linked polyubiquitination. This promoted Lys48 residue-linked polyubiquitin chain formation on TRAF6, resulting in increased TRAF6 degradation via UPS and inactivation of downstream NF-κB inflammatory pathway. Consequently, FMHM down-regulated inflammatory mediator levels in circulation, protected multiple organs against inflammatory injury in vivo and prolong the survival of endotoxemia mouse models. Therefore, FMHM can serve as a novel lead compound for the development of TRAF6 scavenging agent via ubiquitination-dependent mode, which represents a promising strategy for treating inflammatory diseases.