Extracellular UDP and P2Y6 Function as a Danger Signal To Protect Mice from Vesicular Stomatitis Virus Infection through an Increase in IFN-β Production

Extracellular nucleotides that constitute a danger signal play an important role in the regulation of immune responses. However, the function and mechanism of extracellular UDP and P2Y(6) in antiviral immunity remain unknown. In this study, we demonstrated the in vitro and in vivo protection of UDP/P2Y(6) signaling in vesicular stomatitis virus (VSV) infection. First, we demonstrated that VSV-infected cells secrete UDP from the cytoplasm as a danger signal to arouse surrounding cells. Meanwhile, expression of the UDP-specific receptor P2Y(6) also was enhanced by VSV. Consequently, UDP protects RAW 264.7 cells, murine embryonic fibroblasts, bone marrow-derived macrophages, and L929 cells from VSV and GFP lentivirus infection. This protection can be blocked by the P2Y(6) selective antagonist MRS2578 or IFN-alpha/beta receptor-blocking Ab. VSV-induced cell death and virus replication were both enhanced significantly by knocking down and knocking out P2Y(6) in different cells. Mechanistically, UDP facilitates IFN-beta secretion through the p38/JNK- and ATF-2/c-Jun-signaling pathways, which are crucial in promoting antiviral immunity. Interestingly, UDP was released through a caspase-cleaved pannexin-1 channel in VSV-induced apoptotic cells and protected cells from infection through P2Y(6) receptor in an autocrine or paracrine manner. Furthermore, UDP also protected mice from VSV infection through P2Y(6) receptors in an acute neurotropic infection mouse model. Taken together, these results demonstrate the important role of extracellular UDP and P2Y(6) as a danger signal in antiviral immune responses and suggest a potential therapeutic role for UDP/P2Y(6) in preventing and controlling viral diseases.