Virus infection is sensed by pattern recognition receptors (PRRs) detecting virus nucleic acids and initiating an innate immune response. DNA-dependent protein kinase (DNA-PK) is a PRR that binds cytosolic DNA and is antagonized by vaccinia virus (VACV) protein C16. Here, VACV protein C4 is also shown to antagonize DNA-PK by binding to Ku and blocking Ku binding to DNA, leading to a reduced production of cytokines and chemokines in vivo and a diminished recruitment of inflammatory cells. C4 and C16 share redundancy in that a double deletion virus has reduced virulence not seen with single deletion viruses following intradermal infection. However, non-redundant functions exist because both single deletion viruses display attenuated virulence compared to wild-type VACV after intranasal infection. It is notable that VACV expresses two proteins to antagonize DNA-PK, but it is not known to target other DNA sensors, emphasizing the importance of this PRR in the response to infection in vivo. DNA-PK is a pattern recognition receptor (PRR) that binds cytosolic DNA and stimulates IRF3 signaling. Scutts et al. show that vaccinia virus antagonizes this DNA sensor with two proteins, C4 and C16, which both block DNA binding.
Scutts, S. R., Ember, S. W., Ren, H., Ye, C., Lovejoy, C. A., Mazzon, M., … Smith, G. L. (2018). DNA-PK Is Targeted by Multiple Vaccinia Virus Proteins to Inhibit DNA Sensing. Cell Reports, 25(7), 1953-1965.e4. https://doi.org/10.1016/j.celrep.2018.10.034