Regulation of viral recognition signaling by ubiquitin modification.

As a defense mechanism against infection, host cells have evolved sensor molecules which detect pathogen components directly and induce protective responses against the infection. TLRs, well known receptors, recognize a pathogen on the surface of cells or endosome/lysosome. Many pathogens penetrate into cytoplasm, in where non-TLR sensors recognize pathogen components including double-stranded RNA (dsRNA). On the downstream of each sensor, a variety of functional signaling molecules are activated to produce various cytokines upon the microbial invasion to induce host defense responses. Because that cytokines produced to regulate the host defense responses are known to affect cell proliferation also, the level of these molecules are needed to be controlled tightly, which means requisites of negative regulation of the signaling activated by pathogen after the completion of proper immune responses. Recent studies suggest important roles of some ubiquitin systems in this regulation. Here we focus, in particular, ubiquitin conjugation to signaling molecules by virus activation and like to show how ubiquitin signaling plays roles in this regulation by introducing some recent works.