Tumor Necrosis Factor-α Induces RelA Degradation via Ubiquitination at Lysine 195 to Prevent Excessive Nuclear Factor-κB Activation

Ubiquitination-mediated degradation of the RelA subunit of nuclear factor-kappa B (NF-kappa B) is critical for the termination of NF-kappa B activation. However, the precise mechanism for the ubiquitination of RelA is still not fully understood. Here we report that tumor necrosis factor-alpha (TNF alpha) induces RelA polyubiquitination at the lysine 195 residue, and this ubiquitination event is critical for the degradation of RelA and termination of TNF alpha-mediated NF-kappa B activation. Overexpression of a RelA mutant with an arginine substitution for the lysine 195 residue dramatically inhibits RelA polyubiquitination and induces a stronger NF-kappa B activation compared with the wild type. Reconstitution of RelA-deficient mouse embryo fibroblast cells with wild-type RelA or RelA containing a K195R mutation revealed the importance of this site in TNF alpha-mediated RelA polyubiquitination, degradation, and attenuation of NF-kappa B activation. Our finding is the first report that substitution of a key RelA lysine residue with arginine inhibits TNF alpha-induced RelA ubiquitination and enhances TNF alpha-induced NF-kappa B activation.