CELL-CYCLE INHIBITORY EFFECTS OF HIV AND SIV VPR AND VPX IN THE YEASTSCHIZOSACCHAROMYCES-POMBE

The Vpr gene of human immunodeficiency virus type 1 and type 2 (HIV-1, HIV-2) and simian immunodeficiency virus (SIV) encodes a small nuclea r protein which is virion-associated and assists nuclear transport of the preintegration complex. Expression of HIV-1 Vpr has been shown to induce differentiation and prevent proliferation of human cells. HIV-1 Vpr has also been shown to arrest cell growth and cause morphological defects in yeast. In contrast, the Vpx gene of HIV-2 and SIV, which s hares sequence homology with Vpr, does not seem to inhibit proliferati on of human cells. It has been suggested that the cell cycle arrest ef fect of Vpr and Vpx is species and cell-type dependent In this study, we have taken advantage of a conditional expression system to characte rize the growth inhibitory effects of Vpr and Vpx of HIV-1, HIV-2, and SIV in the fission yeast Schizosaccharomyces pombe. Our results show that both Vpr and/or Vpx of HIV-1, HIV-2, and SIV arrest cell growth i n S. pombe, and HIV-1 Vpr is more cytotoxic than HIV-2 or SIV Vpr or V px. Flow cytometry analysis indicated that yeast cells cease prolifera ting with DNA contents indicative of arrest in G(1) and G(2), with som e cells showing signs of overreplication of DNA. While the observed ce ll cycle arrest phenotype was not identical to that observed in mammal ian cells, there were similarities of growth arrest phenotype caused b y Vpr and Vpx in yeast and mammalian cells. Specifically, the observat ion that yeast and mammalians cell both arrest in G(2) with reduced p3 4/cdc2 kinase activity indicates that Vpr and Vpx interact with conser ved target(s) in yeast and mammalian cells. The ability to use genetic analysis to elucidate the mechanisms involved makes S. pombe an excel lent model system in which to study the effects of Vpr and Vpx on cell ular function. (C) 1997 Academic Press.