Function: Inhibits NF-kappa-B activation triggered by overexpression of RIPK1 and TRAF6 but not of RELA. Inhibits also tumor necrosis (TNF), IL-1 and TLR4-induced NF-kappa-B activation in a dose-dependent manner. Overexpression sensitizes cells to TNF-induced apoptosis. Could be involved in regulating NF-kappa-B activation and apoptosis. Is a potent inhibitory factor for osteoclast differentiation. Involved in protein degradation via the ubiquitin-proteasome system and plays a critical role in muscle atrophy. May act by anchoring ubiquitinylated proteins to the proteasome, playing a critical role in protein degradation.