title: Ubiquitination of RIP1 regulates an NF-kappaB-independent cell-death switch in TNF signaling.
abstract: TNF receptor 1 (TNFR1) can trigger opposing responses within the same cell: a prosurvival response or a cell-death pathway [1, 2]. Cell survival requires NF-kappaB-mediated transcription of prosurvival genes [3-9]; apoptosis occurs if NF-kappaB signaling is blocked [5, 7-9]. Hence, activation of NF-kappaB acts as a cell-death switch during TNF signaling. This study demonstrates that the pathway includes another cell-death switch that is independent of NF-kappaB. We show that lysine 63-linked ubiquitination of RIP1 on lysine 377 inhibits TNF-induced apoptosis first through an NF-kappaB-independent mechanism and, subsequently, through an NF-kappaB-dependent mechanism. In contrast, in the absence of ubiquitination, RIP1 serves as a proapoptotic signaling molecule by engaging CASPASE-8. Therefore, RIP1 is a dual-function molecule that can be either prosurvival or prodeath depending on its ubiquitination state, and this serves as an NF-kappaB-independent cell-death switch early in TNF signaling. These results provide an explanation for the conflicting reports on the role of RIP1 in cell death; this role was previously suggested to be both prosurvival and prodeath [10-12]. Because TRAF2 is the E3 ligase for RIP1 [13], these observations provide an explanation for the NF-kappaB-independent antiapoptotic function previously described for TRAF2 [14-16].
authors.affiliation: Immunobiology Center, Mount Sinai School of Medicine, Box 1630, One Gustave L. Levy Place, New York, NY 10029, USA.
authors.forename: Marie Anne
authors.initials: MA
authors.lastname: O'Donnell
authors.forename: Diana
authors.initials: D
authors.lastname: Legarda-Addison
authors.forename: Penelopi
authors.initials: P
authors.lastname: Skountzos
authors.forename: Wen Chen
authors.initials: WC
authors.lastname: Yeh
authors.forename: Adrian T
authors.initials: AT
authors.lastname: Ting
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D005786:Gene Expression Regulation; D006801:Humans; D019169:Jurkat Cells; D008239:Lysine / Q000737:chemistry; D016328:NF-kappa B / Q000378:metabolism; D053422:Receptor-Interacting Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction; D047992:TNF Receptor-Associated Factor 2 / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D014452:Ubiquitins / Q000378:metabolism*
chemical_list: D016328:NF-kappa B; D047992:TNF Receptor-Associated Factor 2; D014409:Tumor Necrosis Factor-alpha; D014452:Ubiquitins; C506249:RIPK1 protein, human; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; D008239:Lysine