Inhibition of proinflarnmatory and innate immune signaling pathways by a cytomegalovirus RIP1-interacting protein

TNF alpha is an important cytokine in antimicrobial immunity and inflammation. The receptor-interacting protein RIM is an essential component of the TNF receptor 1 signaling pathway that mediates the activation of NF-kappa B, MAPKs, and programmed cell death. It also transduces signals derived from Toll-like receptors and intracellular sensors of DNA damage and double-stranded RNA. Here, we show that the murine CMV M45 protein binds to RIM and inhibits TNF alpha-induced activation of NF-alpha B, p38 MAK, and caspase-independent cell death. M45 also inhibited NF-kappa B activation upon stimulation of Toll-like receptor 3 and ubiquitination of RIP1, which is required for NF-kappa B activation. Hence, M45 functions as a viral inhibitor of RIP1-mediated signaling. The results presented here reveal a mechanism of viral immune subversion and demonstrate how a viral protein can simultaneously block proinflammatory and innate immune signaling pathways by interacting with a central mediator molecule.