Identification and characterization of human cytomegalovirus-encoded proteins interacting with viperin

Abstract

Human cytomegalovirus (HCMV) is a member of beta-herpesvirus family. Infection with HCMV causes acute and chronic diseases in both healthy and immunocompromised hosts. Host employs various defense mechanisms against viral infection. The interferon (IFN) response is the first line of host defense. IFN induces expression of a number of interferon-stimulated genes (ISGs). Viperin is a multifunctional, IFN-inducible protein. During HCMV infection, the function of viperin depends upon when it expresses and where it locates. When viperin is pre-expressed in cells, it localizes to the ER and inhibits viral replication. However, if it is induced directly by HCMV infection, it localizes to the mitochondria through interaction with HCMV viral protein vMIA at the early stage of infection and modulates the cellular metabolism to enhance viral replication. Viperin finally re-localizes to the viral assembly compartment (AC) at the late stage of infection, but its role in this compartment has not been elucidated yet. Here, I hypothesized that viperin’s interaction with HCMV viral proteins at each compartment may play a critical role in determination of viral replication status. In this study, I screened HCMV-encoded proteins interacting with viperin using yeast two hybrid assay. As a result, I identified 10 interacting HCMV protein candidates. An HCMV UL99-encoded tegument protein, pp28, was selected to study its capacity to interact with viperin. The pp28 of HCMV is an essential protein for viral assembly and maturation at the AC. The interaction and co-localization of pp28 and viperin were examined in both infected and transiently expressed cells by performing co-immunoprecipitaion, immunofluorescence, and protein-fragment complementation assays. Viperin was demonstrated to interact as well as co-localize with pp28 to the AC late in HCMV infection. Interestingly, viperin was translocated from the ER to the ERGIC when pp28 was transiently expressed in the absence of viral infection. This study suggests that the pp28 is likely responsible for the translocation of viperin to the AC. Further investigation is required to examine viperin’s function on viral assembly process via interaction with pp28 at the AC during HCMV infection.