title: Human immunodeficiency virus type 1 viral protein R (Vpr) arrests cells in the G2 phase of the cell cycle by inhibiting p34cdc2 activity.
abstract: The Vpr accessory gene product of human immunodeficiency virus types 1 and 2 and simian immunodeficiency virus is believed to play a role in permitting entry of the viral core into the nucleus of nondividing cells. A second role for Vpr was recently suggested by Rogel et al. (M. E. Rogel, L. I. Wu, and M. Emerman, J. Virol. 69:882-888, 1995), who showed that Vpr prevents the establishment in vitro of chronically infected HIV producer cell lines, apparently by causing infected cells to arrest in the G2/M phase of the cell cycle. In cycling cells, progression from G2 to M phase is driven by activation of the p34cdc2/cyclin B complex, an event caused, in part, by dephosphorylation of two regulatory amino acids of p34cdc2 (Thr-14 and Tyr-15). We show here that Vpr arrests the cell cycle in G2 by preventing the activation of the p34cdc2/cyclin B complex. Vpr expression in cells caused p34cdc2 to remain in the phosphorylated, inactive state, p34cdc2/cyclin B complexes immunoprecipitated from cells expressing Vpr were almost completely inactive in a histone H1 kinase assay. Coexpression of a constitutively active mutant p34cdc2 molecule with Vpr relieved the G2 arrest. These findings strongly suggest that Vpr arrests cells in G2 by preventing the activation of the p34cdc2/cyclin B complex that is required for entry into M phase. In vivo, Vpr might, by preventing p34cdc2 activation, delay or prevent apoptosis of infected cells. This would increase the amount of virus each infected cell produced.
mesh_terms: D016203:CDC2 Protein Kinase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002453:Cell Cycle; D002460:Cell Line; D004789:Enzyme Activation; D016195:G2 Phase; D015870:Gene Expression; D016336:Gene Products, vpr / Q000096:biosynthesis* / Q000378:metabolism; D015497:HIV-1 / Q000235:genetics / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008938:Mitosis; D015302:Simian Immunodeficiency Virus / Q000502:physiology; D013997:Time Factors; D014162:Transfection; D054325:vpr Gene Products, Human Immunodeficiency Virus
chemical_list: D016336:Gene Products, vpr; D054325:vpr Gene Products, Human Immunodeficiency Virus; D016203:CDC2 Protein Kinase