CARP-2 is an endosome-associated ubiquitin ligase for RIP and regulates TNF-induced NF-κB activation

Background: The proinflarnmatory cytokine tumor necrosis factor-alpha (TNF-alpha) elicits cellular responses by signaling through a receptor complex that includes the essential adaptor molecule RIP. One important consequence of signaling is activation of the transcription factor NF-kappa B, and failure to downregulate TNF-induced NF-kappa B transcriptional activity results in chronic inflammation and death. Internalization of the receptor complex plays an important regulatory role in TNF signaling. Results: We report that CARP-2, a RING domain-containing ubiquitin protein ligase (E3), is a negative regulator of TNF-induced NF-kappa B activation. By virtue of its phospholipid-binding FYVE domain, CARP-2 localized to endocytic vesicles, where it interacted with internalized TNF-receptor complex, resulting in RIP ubiquitination and degradation. Knockdown of CARP-2 stabilized TNFR1-associated polyubiquitinated RIP levels after TNF simulation and enhanced activation of NF-kappa B. Conclusions: CARP-2 acts at the level of endocytic vesicles to limit the intensity of TNF-induced NF-kappa B activation by the regulated elimination of a necessary signaling component within the receptor complex.