Erwann Le Rouzic; Serge Benichou

“ In agreement, the Vpr-induced G2 arrest correlates with high level of viral replication in primary human T cells.
The determinants of the G2 arrest activity are mainly located in the C-terminal unstructured basic region of HIV-1 Vpr and phosphorylation of the protein is required [99] , [100] . Regulators of the cell cycle, such as cyclin-dependant kinases (CDKs) , control progression through the cell cycle by reversible phosphorylation [101] . The p34/cdc2 CDK associates with cyclin B1 in the G2 phase (for review, see [102] ) to regulate the G2 to M transition. ”

“ In contrast to oncoretroviruses which require nuclear envelope disintegration during mitosis to integrate their viral genome into host chromosomes, lentiviruses, such HIV and SIV, have evolved a strategy to import their own genome through the envelope of the interphasic nucleus via an active mechanism 4–6 h after infection (for review, see [60] ) . Vpr has been reported to enhance the transport of the viral DNA into the nucleus of nondividing cells [61] - [62] , by promoting direct or indirect interactions with the cellular machinery regulating the nucleo-cytoplasmic shuttling [63] - [64] . ”

“ However, it has also been reported that Vpr induces cell cycle arrest via a DNA damage-sensitive pathway [111] . The G2 DNA damage checkpoint is under the control of the phosphatidylinositol 3-kinase-like proteins, ATR and ATM [112] , which lead to the inactivation of the cdc2-cyclinB complex. The ATR protein has been recently linked to the G2-arrest induced by Vpr [113] . Inhibition of ATR either by drugs, a dominant-negative form of ATR or by siRNA reverts the Vpr-induced cell cycle arrest while activation of ATR by Vpr results in Chk1 phosphorylation, the kinase regulating cdc25c activity. ”

“ Furthermore, recent analysis in non-dividing cells shows that this phenotype is exacerbated in primary monocyte-derived macrophages (MDM) leading to a 18-fold increase of the HIV-1 mutation frequency [50] . This activity strikingly correlates with the interaction of Vpr with the nuclear form of uracil DNA glycosylase (UNG2) [51] , an enzyme involved in the base excision repair pathway that specifically removes the RNA base uracil from DNA. Uracil can occur in DNA either by misincorporation of dUTP or by cytosine deamination. ”

“ Initially identified from a yeast two-hybrid screening using Vpr as a bait, the interaction with UNG was confirmed both in vitro and ex vivo in Vpr-expressing cells. While the Trp residue in position 54 located in the exposed loop connecting the second and the third α-helix of HIV-1 Vpr has been shown critical to maintain the interaction with UNG, the Vpr-binding site was mapped within the C-terminal part of UNG2 and occurs through a TrpXXPhe motif. ”

“ Nuclear role (s) of Vpr
The first reported function of Vpr was a modest transcriptional activity on the viral LTR promotor as well as on heterologous cellular promotors [148] , [149] . While the connection between cell cycle arrest and LTR-transactivation by Vpr is not well understood, it was concluded that activation of the Vpr-induced viral transcription is secondary to its G2/M arrest function [98] , [150] . An increase transcriptional activity is indeed observed from the viral LTR in arrested cells expressing Vpr [151] - [152] . ”

“ Neurons killed by extracellular Vpr display typical features of apoptosis evidenced by direct activation of the initiator caspase-8 that will lead to subsequent activation of effector caspases. These effects have been linked to the property of the first amphipathic α-helix of Vpr to form cation-selective ion channels in planar lipid bilayers, causing a depolarization of the plasma membrane [6] , [145] , [146] , [147] . These observations indicate that Vpr can trigger apoptotic processes by different alternative pathways depending of the target cells. ”

“ Srinivasan, A; et al. (2004) , “Differential regulation of host cellular genes by HIV-1 viral protein R (Vpr) : cDNA microarray analysis using isogenic virus”, Biochem Biophys Res Commun 314: 1126–1132, 1475125010.1016/j.bbrc.2004.01.008, pmid:14751250, DOI 10.1016/j.bbrc.2004.01.008
This work is released under the Creative Commons Attribution 2.0 license, which allows free use, distribution, and creation of derivatives, so long as the license is unchanged and clearly noted, and the original author is attributed. ”

“ Vpr, a nucleocytoplasmic protein
In addition to its nonconventional NLS for targeting into the nucleus, Vpr is a dynamic mobile protein able to shuttle between the nucleus and cytoplasmic compartments [23] , [89] , [90] . Photobleaching experiments on living cells expressing a Vpr-GFP fusion confirmed that Vpr displays nucleocytoplasmic shuttling properties [63] . This shuttling activity has been related to the distal leucine-rich helix which could form a classical CRM1-dependant nuclear export signal (NES) [89] . ”

“ Chrousos, GP & Pavlakis, GN (2002) , “Human immunodeficiency virus type 1 (HIV-1) accessory protein Vpr induces transcription of the HIV-1 and glucocorticoid-responsive promoters by binding directly to p300/CBP coactivators”, J Virol 76: 9724–9734, 1220895110.1128/JVI.76.19.9724-9734.2002, pmid:12208951, DOI 10.1128/JVI.76.19.9724-9734.2002 ↑ Sherman, MP ”

“ Belardelli, F; et al. (1998) , “The HIV-1 vpr protein acts as a negative regulator of apoptosis in a human lymphoblastoid T cell line: possible implications for the pathogenesis of AIDS”, J Exp Med 187: 403–413, 944972010.1084/jem.187.3.403, pmid:9449720, DOI 10.1084/jem.187.3.403 ↑ Stewart, SA; Poon, B; Jowett, JB & Chen, IS (1997) , “Human immunodeficiency virus type 1 Vpr induces apoptosis following cell cycle arrest”, J Virol 71: 5579–5592, 9188632, pmid:9188632 1 2 Muthumani, K ”

“ Greenway, AL & McPhee, DA (2003) , “Studies with GFP-Vpr fusion proteins: induction of apoptosis but ablation of cell-cycle arrest despite nuclear membrane or nuclear localization”, Virology 313: 91–104, 1295102410.1016/S0042-6822 (03) 00258-7, pmid:12951024, DOI 10.1016/S0042-6822 (03) 00258-7 1 2 3 Depienne, C ”

“ Rougeau, N & Cohen, EA (1999) , “Human immunodeficiency virus type 1 (HIV-1) Vpr functions as an immediate-early protein during HIV-1 infection”, J Virol 73: 4101–4109, 10196306, pmid:10196306 ↑ Hogan, TH ”

“ Emerman, M & Hope, TJ (2002) , “Visualization of the intracellular behavior of HIV in living cells”, J Cell Biol 159: 441–452, 1241757610.1083/jcb.200203150, pmid:12417576, DOI 10.1083/jcb.200203150 1 2 McDonald, D ”