Effect of human immunodeficiency virus type 1 protein R (vpr) gene expression on basic cellular function of fission yeast Schizosaccharomyces pombe

The human immunodeficiency virus type 1 (HIV-1) Vpr protein affects cell morphology and prevents proliferation of human cells by induction of cell cycle G₂ arrest. In this study, we used the fission yeast Schizosaccharomyces pombe as a model system to investigate the cellular effects of HIV-1 vpr gene expression. The vpr gene was cloned into an inducible fission yeast gene expression vector and expressed in wild-type S. pombe cells, and using these cells, we were able to demonstrate the specific Vpr-induced effects by induction and suppression of vpr gene expression. Induction of HIV-1 vpr gene expression affected S. pombe at the colonial, cellular, and molecular levels. Specifically, Vpr induced small-colony formation, polymorphic cells, growth delay, and cell cycle G₂ arrest. Additionally, Vpr-induced G₂ arrest appeared to be independent of cell size and morphological changes. The cell cycle G₂ arrest correlated with increased phosphorylation of p34(cdc2), suggesting negative regulation of mitosis by HIV-1 Vpr. Treatment of Vpr-induced cells with a protein phosphatase inhibitor, okadaic acid, transiently suppressed cell cycle arrest and morphological changes. This observation implicates possible involvement of protein phosphatase(s) in the effects of Vpr. Together, these data showed that the HIV-1 Vpr-induced cellular changes in S. pombe are similar to those observed in human cells. Therefore, the S. pombe system is suited for further investigation of the HIV-1 vpr gene functions.