Restriction of DNA viruses by TRIM5a and ZAP / TRIM25 / KHNYN: mechanisms of restriction and viral evasion

The host restriction factors TRIM5a, ZAP, TRIM25 and KHNYN provide defense against RNA viruses. For instance, TRIM5a provides protection against different retroviruses, including HIV. Proteins ZAP, TRIM25 and KHNYN, which show some functional interdependence, are also active against RNA viruses with CpG rich genomes and recently, ZAP and TRIM25 were shown to also restrict human cytomegalovirus (HCMV). We discovered that vaccinia virus (VACV) infection induce degradation of all 4 cellular proteins, and so hypothesised that they may have anti-VACV activity. This hypothesis was proved correct, for cells lacking TRIM5a, ZAP, TRIM25 or KHNYN individually, supported enhanced VACV replication, showing these proteins do provide defense against this large DNA virus. Like HIV, VACV virions also package cyclophilin A and VACV replication is inhibited by cyclosporine A in a TRIM5-dependent way. Loss of TRIM5a also enhanced herpes simplex virus (HSV) 1 replication. The project will investigate how these host proteins restrict VACV replication and how VACV evades such restriction. What viral proteins do they bind to? At what stage is virus replication restricted? Is this a direct effect following recognition of specific virus components, or indirect, by activation of the innate immunity by these restriction factors? We will also test if these host proteins can restrict the replication of other dsDNA viruses, such as HSV-1 and HCMV, and, for TRIM5a, monkeypox virus and variola virus. In parallel, the VACV protein(s) that induce the degradation of these cellular proteins will be identified, where not known already, and then their mechanism(s) of action will be studied. Can they act independently? Since the degradation of these cellular proteins is proteasome-dependent, it suggests these proteins may be ubiquitylated by E3 ubiquitin ligases and thereby marked for destruction. Which E3 ligases or other factors are involved?