The TRAF protein family comprises seven E3 ligase members, including TRAF6. Distinct receptor signaling pathways have different members, such as the IL-1 receptor family, T-cell receptor (TCR), IL-17 receptor, TNF receptor. TRAF-dependent signaling pathways contribute to the control of diverse cellular processes, including survival, proliferation, differentiation, and cytokine production.  TRAF6 interacts with the heterodimeric E2 enzyme complex Ubc13–Uev1a to attach Lys63-linked ubiquitin chains to its substrate proteins. These Lys63-linked ubiquitin chains are necessary to activate innate and adaptive immune responses mainly through the NF-κB axis. Of note, the TRAF6 ligase activity is strictly determined by its protein-protein interaction with a specific set of E2 enzymes, including Ubc13. Thus, targeting TRAF6 E3 activity requires the identification of protein-protein interaction inhibitors, which disrupt the TRAF6–Ubc13 interaction.  C25-140 is a first-in-class, fairly selective TRAF6-Ubc13 inhibitor. It directly binds to TRAF6 and blocks the interaction of TRAF6 with Ubc13.

C25-140 is a first-in-class, fairly selective TRAF6-Ubc13 inhibitor, which combats autoimmunity.

C25-140 affects cIAP1, an E3 ligase generating Lys63-linked polyubiquitin chains similar to TRAF6. Notably, C25-140 does not influence several other E3 ligases (MDM2, TRIM63, ITCH, E6AP, and RNF4) building other types of poly-ubiquitin chains. Therefore, It shows C25-140 acts on the E3 ligase side. Furthermore, C25-140 efficiently inhibits IL-1β– and TNFα–mediated receptor signaling in the context of cytokine activation. C25-140 also affects TCR-mediated immune response in a human-derived cell line. Besides, C25-140 is effective in cytokine signaling of primary human and murine cells.

C25-140 has appropriate properties in mouse studies for in vivo efficacy testing. C25-140 is able to ameliorate symptoms of autoimmune psoriasis. In addition, C25-140 ameliorates symptoms of rheumatoid arthritis (RA) in a preclinical mouse model.

In summary, the first-in-class TRAF6-Ubc13 inhibitor C25-140 expands the toolbox for studying the impact of the ubiquitin system on immune signaling and underscores the importance of TRAF6 E3 ligase activity in psoriasis and rheumatoid arthritis.


Brenke JK, et al. J Biol Chem. 2018 Aug 24;293(34):13191-13203.