VAMP8 Contributes to the TRIM6-Mediated Type I Interferon Antiviral Response during West Nile Virus Infection.

Several members of the tripartite motif (TRIM) family of E3 ubiquitin ligases regulate immune pathways, including the antiviral type I interferon (IFN-I) system. Previously, we demonstrated that TRIM6 is involved in IFN-I induction and signaling. In the absence of TRIM6, optimal IFN-I signaling is reduced, allowing increased replication of interferon-sensitive viruses. Despite having evolved numerous mechanisms to restrict the vertebrate host's IFN-I response, West Nile virus (WNV) replication is sensitive to pretreatment with IFN-I. However, the regulators and products of the IFN-I pathway that are important in regulating WNV replication are incompletely defined. Consistent with WNV's sensitivity to IFN-I, we found that in TRIM6 knockout (TRIM6-KO) A549 cells, WNV replication is significantly increased and IFN-I induction and signaling are impaired compared to wild-type (wt) cells. IFN-β pretreatment was more effective in protecting against subsequent WNV infection in wt cells than TRIM6-KO, indicating that TRIM6 contributes to the establishment of an IFN-induced antiviral response against WNV. Using next-generation sequencing, we identified VAMP8 as a potential factor involved in this TRIM6-mediated antiviral response. VAMP8 knockdown resulted in reduced JAK1 and STAT1 phosphorylation and impaired induction of several interferon-stimulated genes (ISGs) following WNV infection or IFN-β treatment. Furthermore, VAMP8-mediated STAT1 phosphorylation required the presence of TRIM6. Therefore, the VAMP8 protein is a novel regulator of IFN-I signaling, and its expression and function are dependent on TRIM6 activity. Overall, these results provide evidence that TRIM6 contributes to the antiviral response against WNV and identify VAMP8 as a novel regulator of the IFN-I system.IMPORTANCE WNV is a mosquito-borne flavivirus that poses a threat to human health across large discontinuous areas throughout the world. Infection with WNV results in febrile illness, which can progress to severe neurological disease. Currently, there are no approved treatment options to control WNV infection. Understanding the cellular immune responses that regulate viral replication is important in diversifying the resources available to control WNV. Here, we show that the elimination of TRIM6 in human cells results in an increase in WNV replication and alters the expression and function of other components of the IFN-I pathway through VAMP8. Dissecting the interactions between WNV and host defenses both informs basic molecular virology and promotes the development of host- and virus-targeted antiviral strategies.