Herpes simplex virus type 1 immediate-early protein Vmw110 inhibits progression of cells through mitosis and from G(1) into S phase of the cell cycle

Herpes simplex virus type 1 (HSV-1) immediate-early protein Vmw110 stimulat es the onset of virus infection in a multiplicity-dependent manner and is r equired for efficient reactivation from latency. Recent work has shown that Vmw110 is able to interact with or modify the stability of several cellula r proteins. In this report we analyze the ability of Vmw110 to inhibit the progression of cells through the cell cycle. We show by fluorescence-activa ted cell sorter and/or confocal microscopy analysis that an enhanced green fluorescent protein-tagged Vmw110 possesses the abilities both to prevent t ransfected cells moving from G(1) into S phase and to block infected cells at an unusual stage of mitosis defined as pseudo-prometaphase. The latter p roperty correlates with the Vmw110-induced proteasome-dependent degradation of CENP-C, a centromeric protein component of the inner plate of human kin etochores. We also show that whereas Vmw110 is not the only viral product i mplicated in the block of infected cells at the G(1)/S border, the mitotic block is a specific property of Vmw110 and more particularly of its RING fi nger domain. These data explain the toxicity of Vmw110 when expressed alone in transfected cells and provide an explanation for the remaining toxicity of replication-defective mutants of HSV-1 expressing Vmw110. In addition t o contributing to our understanding of the effects of Vmw110 on the cell, o ur results demonstrate that Vmw110 expression is incompatible with the prol iferation of a dividing cell population. This factor is of obvious importan ce to the design of gene therapy vectors based on HSV-1.