engleski

The M25 gene is the key to mouse cytomegalovirus- driven cell rounding

Cytomegalovirus (CMV) infection, although mostly harmless for healthy individuals, can lead to severe health problems if the immune system is malfunctioning. During lytic CMV infection cells go through a series of morphological changes resulting in so-called cytopathic effect (CPE). One of the most prominent CPE induced by mouse CMV (MCMV) is cell rounding. Infected cells experience extensive changes in the actin cytoskeleton: loss of stress fibers, disassembly of focal adhesions and formation of cortical actin. Are these morphological changes only a host reaction to virus attack or are they actively triggered by the virus to promote productive infection? In order to address this question, we screened a library of MCMV mutants with deletions of non-essential genes and identified the M25 ORF as a main regulator of cell rounding during MCMV infection. Moreover, when exogenously expressed, the M25 gene alone was able to stimulate cell rounding. Conversely, cells infected with a M25-deficient mutant remained outspread throughout the entire lytic infection cycle, forming protrusions resembling lamellipodia at later stages. Deletion of the M25 ORF also reduced infectious particle production in cell culture and diminished cell- to-cell spread, resulting in a small plaque phenotype. We determined that the observed phenotypes of the mutant virus do not result from delayed viral gene expression or a defect in genome replication. To examine the molecular mechanisms of M25 mediated functions we utilized co-immunoprecipitation linked to SILAC based mass spectrometry to identify host cell proteins interacting with M25. Validation of identified interaction partners implies involvement of M25 in protein de- phosphorylation, cell cycle and cell death pathways. Our results strongly suggest that cell rounding in MCMV infected cells is actively induced by M25 expression leading to increased release of infectious MCMV progeny, most likely through regulation of major cellular kinase cascade signaling.

murine cytomegalovirus, tegument protein, M25, infection, host-virus interaction, cytopathic effect, cytoskeleton

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