Conservation and host specificity of Vpr-mediated cell cycle arrest suggest a fundamental role in primate lentivirus evolution and biology.

The human immunodeficiency virus type 1 (HIV-1) Vpr protein prevents infected cells from passing through mitosis by arresting them in the G2 phase of the cell cycle. Vpr is conserved among all primate lentiviruses, suggesting an important role in the virus life cycle. Moreover, in this study we show that the ability to cause cell cycle arrest is also conserved in Vpr proteins from a wide variety of both tissue culture-passaged and uncultured human (HIV-1 and HIV-2), sooty mangabey (simian immunodeficiency virus SIV(SM)), African green monkey (SIV(AGM)), and Sykes' monkey (SIV(SYK)) isolates. However, this property is cell type specific and appears to depend on the particular primate species from which the cells are derived. SIV(AGM) and SIV(SYK) Vpr proteins are capable of arresting African green monkey cells but are completely inactive in human cells. By contrast, HIV-1, HIV-2, and SIV(SM) Vpr proteins function in both simian and human cell types, although SIV(SM) Vpr functions more efficiently in simian cells than it does in human cells. Neither differential protein stability nor subcellular localization explains the species-specific activities of these proteins. These results thus suggest that Vpr exerts its G2 arrest function by interacting with cellular factors that have evolved differently among the various primate species.