Cell responses to dysregulated VZV-induced cell-cell fusion

The highly conserved herpesvirus glycoprotein complex, gB/gH-gL, mediates membrane fusion during virion entry and cell-cell fusion. Varicella-zoster virus (VZV) characteristically forms multi-nucleated cells, or syncytia, during the infection of human tissues but little is known about this process. The cytoplasmic domain of VZV gB (gBcyt) has been implicated in cell-cell fusion regulation because a gB[Y881F] substitution causes hyperfusion. The gBcyt regulation is necessary for VZV pathogenesis as the hyperfusogenic mutant gB[Y881F] is severely attenuated in human skin xenografts. In this study, gBcyt regulated fusion was investigated by comparing melanoma cells infected with wild type-like VZV or hyperfusogenic mutants. The gB[Y881F] mutant exhibited dramatically accelerated syncytia formation in melanoma cells caused by fusion of infected cells with many uninfected cells, increased cytoskeleton reorganization and rapid displacement of nuclei to dense central structures when compared to pOka using live cell confocal microscopy. VZV and human transcriptomes were concurrently investigated using RNA-seq to identify viral and cellular responses induced when the gBcyt regulation was disrupted by the gB[Y881F] substitution. The expression of four vital VZV genes, ORF61 and glycoproteins, gC, gE and gI, was significantly reduced at 36 hours post infection for the hyperfusogenic mutants. Importantly, hierarchical clustering demonstrated an association of differential gene expression with dysregulated gBcyt-mediated fusion. A subset of Ras GTPase genes linked to membrane remodeling were upregulated in cells infected with the hyperfusogenic mutants. These data implicate the gBcyt in the regulation gB fusion function that, if unmodulated, triggers cellular processes leading to hyperfusion that attenuates VZV infection. Overall design: Biological duplicates from 3 time points (12, 24 and 36 hours post infection) of uninfected MeWo cells or MeWo cells infected with varicella-zoster virus strain pOka or mutants gB[Y881F], gB[Y920F] or gB[Y881/920F]

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Oliver SL, Yang E, Arvin AM