Date Published: March 24, 2016
Publisher: Public Library of Science
Author(s): Christopher M. Ziegler, Philip Eisenhauer, Emily A. Bruce, Marion E. Weir, Benjamin R. King, Joseph P. Klaus, Dimitry N. Krementsov, David J. Shirley, Bryan A. Ballif, Jason Botten, Benhur Lee.
Arenaviruses cause severe diseases in humans but establish asymptomatic, lifelong infections in rodent reservoirs. Persistently-infected rodents harbor high levels of defective interfering (DI) particles, which are thought to be important for establishing persistence and mitigating virus-induced cytopathic effect. Little is known about what drives the production of DI particles. We show that neither the PPXY late domain encoded within the lymphocytic choriomeningitis virus (LCMV) matrix protein nor a functional endosomal sorting complex transport (ESCRT) pathway is absolutely required for the generation of standard infectious virus particles. In contrast, DI particle release critically requires the PPXY late domain and is ESCRT-dependent. Additionally, the terminal tyrosine in the PPXY motif is reversibly phosphorylated and our findings indicate that this posttranslational modification may regulate DI particle formation. Thus we have uncovered a new role for the PPXY late domain and a possible mechanism for its regulation.
Arenaviruses are a family of rodent-borne viruses with a worldwide distribution. These viruses typically establish persistent, asymptomatic infections in rodent reservoir species . In contrast, arenaviruses cause severe and often fatal diseases in humans. Several arenaviruses, including Lassa virus and Junín virus, cause hemorrhagic fever syndromes whereas infection with the prototypic arenavirus, lymphocytic choriomeningitis virus (LCMV), can lead to aseptic meningitis in immunocompetent individuals, high lethality in immunocompromised individuals, or severe birth defects in the developing fetus [2,3]. U.S. Food and Drug Administration-approved vaccines do not exist for the prevention of arenavirus infection and effective antiviral therapies have been limited to the use of ribavirin for Lassa virus  or immune plasma for Junín virus .
The ability of most arenavirus matrix proteins to drive viral budding is thought to be highly dependent upon one or more encoded late domains [10,11]. The arenavirus LCMV encodes a single late domain, PPPY. The PPXY motif is found in the matrix proteins of several families of enveloped RNA viruses and for many of these viruses is required for the release of infectious virions in an ESCRT-dependent fashion (for review see ). We demonstrate here that the PPXY late domain encoded by LCMV is not absolutely required for infectious virus release. Further, our data suggest that infectious particle release can occur in the absence of a functional ESCRT pathway. Strikingly, we show that the formation of LCMV DI particles critically requires a functional PPXY late domain and that this process is ESCRT-dependent (see Fig 7 for our proposed model). Last, our data demonstrate that the terminal tyrosine in the LCMV PPXY motif is phosphorylated and that this posttranslational modification may exert a regulatory effect on Z’s ability to drive DI particle release. Therefore, we have uncovered an unexpected role for the PPXY late domain and a possible mechanism for its regulation of DI particle production.