TRAF6 initiates inflammatory signaling via organizing membraneless cytoplasmic condensates

Abstract

The tumor necrosis factor receptor-associated factor 6 (TRAF6) is a central molecule in multiple signaling pathways, i.e. the TNF receptor, the Toll-like receptors (TLRs), and interleukin-1 receptor (IL-1R) pathways. Upon pathogen associated molecular patterns (PAMPs) or damage associated molecular patterns (DAMPs) stimulations, TRAF6 activates downstream of NF-{kappa}B signaling. However, the precise mechanism of how TRAF6 activates downstream molecules remains unclear. Here, we demonstrate that TRAF6 acts as a sensor for upstream signals to initiate liquid-liquid phase separation (LLPS) of itself and downstream proteins, forming membraneless condensates. Subsequent recruitment, enrichment and activation of downstream effectors in the condensates lead to robust inflammatory signal transduction. The multivalent interactions mediated by its RING domain, zinc finger domain 1, and coiled-coil domain mediates the LLPS process. Forced phase separation of TRAF6 induced NF-{kappa}B activation. Disruption of TRAF6 phase separation abrogates activation of NF-{kappa}B signaling. Overall, we uncover the spatial organization of molecules by TRAF6 through phase separation as a subcellular platform to activate inflammatory signaling. Targeting TRAF6 phase separation hold promises for therapeutics aiming autoimmune diseases, inflammation and cancers.