engleski

The mouse cytomegalovirus M25 protein interferes with the host signaling platform STRIPAK

Cytomegalovirus (CMV) is highly prevalent in the human population. Although infection is mostly asymptomatic in healthy individuals it can lead to serious complications in immunocompromised patients. CMV establishes life-long latency with sporadic periods of reactivation. Spread of CMV in vivo is highly cell-associated, underlining the importance of direct cell-to-cell spread for the CMV life cycle. The molecular mechanisms of CMV cell-to- cell spread are still poorly understood but extensive cytoskeleton remodelling induced upon CMV infection, results in cell rounding and suggests a mechanistic link between the host cytoskeleton and virus transmission to neighbouring cells. We identified the mouse CMV protein M25, as a crucial regulator of virus- induced cell rounding. A mutant ∆M25 virus could not promote cell rounding of infected cells. Moreover, spread of the ∆M25 mutant was significantly reduced both in vitro and in vivo. We hypothesize that M25 facilitates MCMV spread by interfering with host cellular pathways involved in cytoskeleton rearrangements. In order to investigate the molecular mechanisms of the M25-mediated phenotypes we performed SILAC-based co- immunoprecipitation followed by mass spectrometry identification of potential cellular interaction partners of the M25 protein in infected cells. Components of STRIPAK (Striatin interacting phosphatases and kinases) were identified as both early (12 h.p.i.) and late (36 h.p.i.) M25 interaction partners. Striatins are STRIPAK scaffold proteins that in addition to other adaptor proteins bind germinal centre like kinases III (GCKIII). Within the complex the activity of GCKIIIs is inhibited by the phosphatase action of the protein phosphatase 2A, another core component of STRIPAK. Further validation experiments showed that M25 indeed binds all core STRIPAK components early during infection, but interestingly at later stages binding to GCKIII is reduced. Intriguingly, STRIPAK is involved in regulation of cell shape, polarity and migration as well as Golgi morphogenesis. We discovered that actin cytoskeleton changes in MCMV-infected cells were accompanied with reduction of focal adhesions and de- phosphorylation of paxillin and focal adhesion kinase. On the contrary, these alterations were not observed in ∆M25-infected cells. Our data suggest that M25 induces cytoskeletal rearrangements in host cells and facilitates MCMV spread through interaction with the STRIPAK complex.

murine cytomegalovirus, tegument protein, M25, host-virus interaction, phosphatase, STRIPAK

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