Human immunodeficiency virus type 1 vpr gene induces phenotypic effects similar to those of the DNA alkylating agent, nitrogen mustard

The product of the human immunodeficiency virus type 1 (HIV-1) vpr gene induces cell cycle arrest in the G₂ phase of the cell cycle and is characterized by an accumulation of the hyperphosphorylated form of cdc2 kinase. This phenotype is similar to the effect of DNA-damaging agents, which can also cause cells to arrest at G₂. We previously reported that Vpr mimicked some of the effects of a DNA alkylating agent known as nitrogen mustard (HN₂). Here we extend these earlier observations by further comparing the activation state of cdc2 kinase, the kinetics of G₂ arrest, and the ability to reverse the arrest with chemical compounds known as methylxanthines. Infection of cells synchronized in the G₁ phase of the cell cycle with a pseudotyped HIV-1 resulted in arrest at G₂ within 12 h postinfection, before the first mitosis. Similar to that induced by HN₂, Vpr-induced arrest led to a decrease in cdc2 kinase activity. Vpr-mediated G₂ arrest was alleviated by methylxanthines at concentrations similar to those needed to reverse the G₂ arrest induced by HN₂, and cells proceeded apparently normally through at least one complete cell cycle. These results are consistent with the hypothesis that Vpr induces G₂ arrest through pathways that are similar to those utilized by DNA-damaging agents.