Small-molecule disruption of the TRAF6-Ubc13 protein-protein interaction: targeting noncanonical ubiquitin signaling in inflammation and cancer.

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is a central E3 ubiquitin ligase that links immune-receptor activation to nondegradative K63-linked ubiquitin signaling. Through its functional cooperation with the E2 enzyme Ubc13/UBE2N and Uev1A, TRAF6 promotes the formation of polyubiquitin scaffolds that activate TAK1, IKK, NF-κB, MAPK, inflammasome-related pathways, and multiple cancer-associated signaling networks. Because excessive or dysregulated TRAF6 activity contributes to chronic inflammation, autoimmune disease, tumor progression, metabolic reprogramming, immune evasion, and therapy resistance, the TRAF6-Ubc13 interface has emerged as an attractive but challenging target for small-molecule intervention. This review summarizes the structural and mechanistic basis of TRAF6-Ubc13-dependent ubiquitin transfer, highlighting the roles of TRAF6 RING-domain dimerization, zinc-finger support, oligomerization, and Ubc13 engagement in productive K63-linked ubiquitination. Particular emphasis is placed on C25-140, the principal validated small-molecule disruptor of the TRAF6-Ubc13 interaction, and on its ability to suppress TRAF6 E3 ligase activity and attenuate inflammatory signaling in cellular and disease models. The review also evaluates related therapeutic strategies, including Ubc13/UBE2N inhibitors, TRAF6-targeted natural products and synthetic modulators, receptor-side TRAF6 protein-protein interaction inhibitors, and emerging approaches aimed at TRAF6 oligomerization or phase-separated signaling complexes. Although current pharmacological evidence remains limited, available data support TRAF6-Ubc13 disruption as a promising strategy for selectively modulating pathological ubiquitin signaling in inflammation and cancer. Future progress will depend on improved ligand-bound structural validation, selective chemical probes, optimized pharmacological properties, and disease-specific biomarker-guided application.