Evidence of a role for nonmuscle myosin II in herpes simplex virus type 1 egress.

After cell entry, herpes simplex virus (HSV) particles are transported through the host cell cytoplasm to nuclear pores. Following replication, newly synthesized virus particles are transported back to the cell periphery via a complex pathway including a cytoplasmic phase involving some form of unenveloped particle. These various transport processes are likely to make use of one or more components of the cellular cytoskeletal systems and associated motor proteins. Here we report that the HSV type 1 (HSV-1) major tegument protein, VP22, interacts with the actin-associated motor protein nonmuscle myosin IIA (NMIIA). HSV-1 infection resulted in reorganization of NMIIA, inducing retraction of NMIIA from the cell periphery and condensation into a spoke-like distribution around the nucleus along with a second effect of accumulation in a perinuclear cluster. VP22 did not appear to colocalize with the reorganized cagelike distribution of NMIIA. However, VP22 has been previously reported to localize in a perinuclear vesicular pattern, and significant overlap was observed between this pattern and the perinuclear clusters of NMIIA. Inhibition of the ATPase activity of NMIIA with the myosin-specific inhibitor butanedione monoxime impaired the formation of the perinuclear vesicular VP22 accumulations and also the release of virus into the extracellular medium while having much less effect on the yield of cell-associated virus. Virus infection frequently results in the induction of highly extended processes emanating from the infected cell, and we observed that VP22-containing particles line up along NMIIA-containing filaments which run through these protrusions.