WW Domain Containing E3 Ubiquitin Protein Ligase 1 (WWP1) Negatively Regulates TLR4-Mediated TNF- alpha and IL-6 Production by Proteasomal Degradation of TNF Receptor Associated Factor 6 (TRAF6). e67633

Background Toll-like receptors (TLRs) play a pivotal role in the defense against invading pathogens by detecting pathogen-associated molecular patterns (PAMPs). TLR4 recognizes lipopolysaccharides (LPS) in the cell walls of Gram-negative bacteria, resulting in the induction and secretion of proinflammatory cytokines such as TNF- alpha and IL-6. The WW domain containing E3 ubiquitin protein ligase 1 (WWP1) regulates a variety of cellular biological processes. Here, we investigated whether WWP1 acts as an E3 ubiquitin ligase in TLR-mediated inflammation. Methodology/Results Knocking down WWP1 enhanced the TNF- alpha and IL-6 production induced by LPS, and over-expression of WWP1 inhibited the TNF- alpha and IL-6 production induced by LPS, but not by TNF- alpha . WWP1 also inhibited the I Kappa B- alpha , NF- Kappa B, and MAPK activation stimulated by LPS. Additionally, WWP1 could degrade TRAF6, but not IRAK1, in the proteasome pathway, and knocking down WWP1 reduced the LPS-induced K48-linked, but not K63-linked, polyubiquitination of endogenous TRAF6. Conclusions/Significance We identified WWP1 as an important negative regulator of TLR4-mediated TNF- alpha and IL-6 production. We also showed that WWP1 functions as an E3 ligase when cells are stimulated with LPS by binding to TRAF6 and promoting K48-linked polyubiquitination. This results in the proteasomal degradation of TRAF6.