Novel intracellular actions of sphingosine-1-phosphate to regulate NF-kB activation.

ALVAREZ SE; HARIKUMAR KB; MILSTIEN S; SPIEGEL S

Puerto Madryn

Congreso; 46th Reunion Anual SAIB; 2010

Sphingosine 1-phosphate (S1P), a pro-survival lipid mediator, is produced inside the cell by the action of sphingosine kinases (SphK1 and SphK2). SphK1 binds TNF receptor-associated factor 2 (TRAF2), a key component in NF-kB signaling. Genetic data indicate that TRAF2 is necessary for polyubiquitination (Ub) of receptor interacting protein 1 (RIP1) that then serves as a platform for IKK complex recruitment and NF-kB activation. However, direct evidence that TRAF2 catalyzes the Ub of RIP1 is still missing. Here we show that S1P is required for TNF-induced Ub of RIP1 and phosphorylation of IKK and IkBa, leading to NF-kB activation. These responses were mediated by intracellular S1P independently of its cell surface G protein-coupled receptors. Importantly, S1P specifically binds to TRAF2 at the N-terminal RING domain and stimulates its E3 ligase activity. S1P, but not related lipids, dramatically increased recombinant TRAF2-catalyzed Lys 63- but not Lys 48- linked Ub of RIP1 in vitro. Our data reveal that TRAF2 is a novel intracellular target of S1P, and that S1P is a missing co-factor for TRAF2 E3 ubiquitin ligase activity, suggesting a new paradigm for regulation of Lys 63-linked Ub. These results also highlight the key role of SphK1 and its product S1P in TNFa signaling and the canonical NF-kB activation pathway important in inflammatory, anti-apoptotic, and immune processes.