HIV-1 VPR modulates cell cycle G2/M transition through an alternative cellular mechanism other than the classic mitotic checkpoints

HIV-1 Vpr induces cell cycle G2/M arrest in both human and fission yeast cells, suggesting a highly conserved activity of this viral protein. In this review, we summarize the current understanding of Vpr-induced G2 arrest based on studies from both mammalian cells and the fission yeast (Schizosaccharomyces pombe) model system. Fission yeast has proven to be an excellent model system to investigate cell cycle G2/M control of eukaryotic cells. Similarly, fission yeast has also been instrumental in defining the molecular mechanism underlying the G2 arrest induced by Vpr. We have compared the classic DNA-damage and DNA- replication checkpoint controls of the cell cycle G2/M transition to the G2 arrest conferred by Vpr. Based on the current findings, we hypothesize that Vpr induces cell cycle G2 arrest through an alternative novel cellular pathway(s) rather than through the classic mitotic checkpoint controls. A number of cellular proteins which may be involved in this new cellular pathway( s) have been identified and are discussed.