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PubMed1992

Evolution of the primate lentiviruses: evidence from vpx and vpr.

The genomes of the four primate lentiviral groups are complex and contain several regulatory or accessory genes. Two of these genes, vpr and vpx, are found in various combinations within the four groups and encode proteins whose functions have yet to be elucidated. Comparison of the encoded protein sequences suggests that the vpx gene within the HIV-2 group arose by the duplication of an ancestral vpr gene within this group. Evolutionary distance analysis showed that both genes were well conserved when compared with viral regulatory genes, and indicated that the duplication occurred at approximately the same time as the HIV-2 group and the other primate lentivirus groups diverged from a common ancestor. Furthermore, although the SIVagm vpx proteins are homologous to the HIV-2 group vpx proteins, there are insufficient grounds from sequence analysis for classifying them as vpx proteins. Because of their similarity to the vpr proteins of other groups, we suggest reclassifying the SIVagm vpx gene as a vpr gene. This creates a simpler and more uniform picture of the genomic organization of the primate lentiviruses and allows the genomic organization of their common precursor to be defined; it probably contained five accessory genes: tat, rev, vif, nef and vpr.

Amino Acid Sequence↗
PubMed1994

Construction and in vitro properties of SIVmac mutants with deletions in "nonessential" genes.

The so-called "nonessential" genes of primate lentiviruses can be deleted without abrogating the ability of virus to replicate under at least some cell culture conditions. In SIVmac, these genes are vif, vpx, vpr, and nef. Sequences in the upstream region of U3 in the LTR have also been shown to be dispensable for replication in cell culture. We report here the construction and characterization of a panel of 40 single and combination deletion mutants derived from the pathogenic molecular clone SIVmac239. Deletion of the vpr gene caused little or no change in the growth properties of SIVmac239 in CEMx174 cells, in rhesus monkey peripheral blood mononuclear cells (PBMCs), or in rhesus monkey alveolar macrophages. Deletion of the vpx gene resulted in a greatly reduced rate of replication of the virus in the primary PBMC and macrophage cultures, but no significant reduction in replication of the virus in CEMx174 cells. Deletion of the vpx gene appeared to have a greater effect on virus replication in macrophages than in PBMCs. Deletion of the vif gene caused a dramatic reduction in replication in all cell types tested. However, even delta 5, which contains deletions in all five targeted regions (vif, vpx, vpr, nef, and U3), can still replicate in CEMx174 cells albeit with greatly delayed kinetics. Deletion of nef, alone or in combination with deletions in U3 and vpr, had no observable effect on replication of the virus in any of the cells tested. Because the disease induced by the parental SIVmac239 clone in rhesus monkeys has been well characterized and is remarkably similar to AIDS in humans, this collection of mutants will be useful for relating in vitro properties and gene function with in vivo pathogenic potential.

Amino Acid Sequence↗
PubMed2002

[The function of accessory genes of HIV-1].

Human immunodeficiency virus type 1 (HIV-1) has 4 auxiliary genes, vpr, vpu, nef, and vif, which are dispensable for viral replication in vitro. However, many studies with animal model revealed that these genes play important roles on the viral replication and the development of AIDS in vivo through many complicated mechanisms. Although several key factors involved in the function have been identified, further studies are required for the complete understandings of the action mechanisms. The elucidation of the function of the auxiliary genes on molecular bases leads to the discovery of new therapeutic strategies against HIV and the understanding of basic cellular mechanisms. In this review, we summarize new observations mainly about the interactions between auxiliary genes and host cell functions.

Acquired Immunodeficiency Syndrome↗
PubMed2003

Activation of the ATR-mediated DNA damage response by the HIV-1 viral protein R.

DNA damage is a universal inducer of cell cycle arrest at the G2 phase. Infection by the human immunodeficiency virus type 1 (HIV-1) also blocks cellular proliferation at the G2 phase. The HIV-1 accessory gene vpr encodes a conserved 96-amino acid protein (Vpr) that is necessary and sufficient for the HIV-1-induced block of cellular proliferation. In the present study, we examined a recently identified DNA damage-signaling protein, the ATM- and Rad3-related protein, ATR, for its potential role in the induction of G2 arrest by Vpr. We show that inhibition of ATR by pharmacological inhibitors, by expression of the dominant-negative form of ATR, or by RNA interference inhibits Vpr-induced cell cycle arrest. As with DNA damage, activation of ATR by Vpr results in phosphorylation of Chk1. This study provides conclusive evidence of activation of the ATR-initiated DNA damage-signaling pathway by a viral gene product. These observations are important toward understanding how HIV infection promotes cell cycle disruption, cell death, and ultimately, CD4+ lymphocyte depletion.

Antineoplastic Agents↗
PubMed2000

HIV-1 Vpr regulates expression of beta chemokines in human primary lymphocytes and macrophages.

The HIV-1 vpr gene encodes a 14-kDa virion-packaged protein that has been implicated in viral pathogenesis. Vpr exhibits profound effects on human primary cells influencing proliferation, differentiation, apoptosis, and cytokine production, in part through NF-kappaB-mediated transcription. NF-kappaB, a potent transcription factor, activates many proinflammatory cytokines/chemokines upon infection. Here, we analyzed the effect of extracellular Vpr as well as the virion-associated Vpr on beta chemokines (MIP-1alpha, MIP-1beta, and RANTES) production in human macrophages and primary lymphocytes (PBLs). Macrophages and PBLs exposed to HIV-1 vpr+ viruses or to recombinant Vpr protein produced significantly less beta chemokines compared with cells infected with HIV-1 vpr-viruses or irrelevant control protein (Gag)-exposed cells. These results suggest that a Vpr-mediated increase in virus replication could be in part through down-regulation of chemokine production.

Chemokines, CC↗
PubMed2005

The role of Vpr in HIV-1 pathogenesis.

The HIV-1 vpr gene is conserved among the human (HIV-1, HIV-2) and simian immunodeficiency viruses (SIV). HIV-1 vpr encodes a 96-amino acid, 14 kDa protein (Vpr). Research from a number of laboratories in the last decade has shown that Vpr performs multiple functions, including the induction of cell cycle arrest in the G(2) phase, transactivation of the viral promoter, nuclear import of preintegration complexes, and induction of apoptosis in the infected cell. More recent studies have attempted to elucidate the cellular targets that Vpr utilizes in order to perform the above functions. This review presents the latest findings about the pathogenic events triggered by Vpr, the cellular pathways involved, and the molecular and cellular consequences of the action of Vpr in the context of HIV-1 infection.

Active Transport, Cell Nucleus↗
PubMed1995

A domain of human immunodeficiency virus type 1 Vpr containing repeated H(S/F)RIG amino acid motifs causes cell growth arrest and structural defects.

Vpr is a virion-associated protein of human immunodeficiency type 1 (HIV-1) whose function in acquired immunodeficiency syndrome (AIDS) has been uncertain. Employing the yeast Saccharomyces cerevisiae as a model to examine the effects of HIV-1 auxiliary proteins on basic cellular functions, we found that the vpr gene caused cell growth arrest and structural defects indicated by osmotic sensitivity and gross cell enlargement. Production of various domains by gene expression showed that this effect arose from within the carboxyl-terminal third of the Vpr protein and implicated the sequence HFRIGCRHSRIG, containing two H(S/F)RIG motifs. Electroporation with a series of peptides containing these motifs caused structural defects in yeast that resulted in osmotic sensitivity. A protein with functions relating to the yeast cytoskeleton, Sac1p [Cleves, A. E., Novick, P.J. & Bankaitis, V.A. (1989) J. Cell Biol. 109, 2939-2950], shows sequence similarity to Vpr, and Vpr's effect in yeast may be to disrupt normal Sac1p functions. The Sac1p equivalent has not yet been described in mammalian cells, but in rhabdomyosarcoma and osteosarcoma cell lines Vpr also caused gross cell enlargement and replication arrest [Levy, D.N., Fernandes, L.S., Williams, W.V. & Weiner, D.B. (1993) Cell 72, 541-550]. We note that there is a correlation between the region containing the H(S/F)RIG motifs and the pathogenicity of primate lentiviruses and we suggest that the function of Vpr may be to bring about cell growth arrest and/or cytoskeletal changes as an early step in HIV-1 infection.

Acquired Immunodeficiency Syndrome↗
PubMed1997

In vitro and in vivo tumor growth suppression by HIV-1 Vpr.

We have previously reported that the human immunodeficiency virus type 1 (HIV-1) regulatory gene vpr induces differentiation of rhabdomyosarcoma (embryonal muscle tumor cell line) cells, an effect that is accompanied by reduced proliferative capacity of the transfected cells. In this report, we examine the effect of Vpr expression on several different tumor cell lines derived from unique lineages. These tumor cells display different patterns of modulated oncogenes including both ras and p53 mutations. Here we demonstrate that the growth of tumor cells in vitro and in vivo is arrested by the expression of HIV-1 Vpr. Expression of Vpr in several human tumor cell lines upon transfection resulted in an accumulation of cells in the G2/M phase of cell cycle with altered cellular morphology, including an increase in adherence, and growth arrest, consistent with a differentiated phenotype. Vpr expression in B78/H1 cells results in a marked reduction in colony formation in vitro and an associated reduction in melanin synthesis by the cells. Vpr-transfected melanoma cells inoculated into syngenic C57BL/6 mice showed a markedly reduced ability to form tumors in vivo. These results suggest that this retroviral regulatory gene has broad tumor suppressor effects, likely mediated by transcriptional regulation of the state of the host cell.

Animals↗
PubMed1997

HIV-1 Vpr: G2 cell cycle arrest, macrophages and nuclear transport.

HIV-1 possesses six open reading frames in addition to the gag, pol, and env shared by all retroviruses. One of these accessory genes, vpr, is required for maximal viral replication in macrophages. The molecular mechanism underlying this effect may be related to one of the unusual properties of the encoded protein: some believe Vpr promotes nuclear translocation of preintegration complexes in non-dividing cells; also, Vpr arrests the cell cycle in G2 by inhibiting an upstream activator of p34cdc2-cyclin B. Elucidation of Vpr-cell cycle interactions may provide insight into both HIV-1 and basic cell biology.

Acquired Immunodeficiency Syndrome↗
PubMed2005

ATR and GADD45alpha mediate HIV-1 Vpr-induced apoptosis.

The human immunodeficiency virus type-1 (HIV-1) accessory gene vpr encodes a conserved 96-amino-acid protein that is necessary and sufficient for the HIV-1-induced block of cellular proliferation. Expression of vpr in CD4+ lymphocytes results in G2 arrest, followed by apoptosis. In a previous study, we identified the ataxia telangiectasia-mutated (ATM) and Rad3-related protein (ATR) as a cellular factor that mediates Vpr-induced cell cycle arrest. In the present study, we report that the breast cancer-associated protein-1 (BRCA1), a known target of ATR, is activated in the presence of Vpr. In addition, the gene encoding the growth arrest and DNA damage-45 protein alpha (GADD45alpha), a known transcriptional target of BRCA1, is upregulated by Vpr in an ATR-dependent manner. We demonstrate that RNAi-mediated silencing of either ATR or GADD45alpha leads to nearly complete suppression of the proapoptotic effect of Vpr. Our results support a model in which Vpr-induced apoptosis is mediated via ATR phosphorylation of BRCA1, and consequent upregulation of GADD45alpha.

Apoptosis↗
PubMed1995

The p6gag domain of human immunodeficiency virus type 1 is sufficient for the incorporation of Vpr into heterologous viral particles.

The vpr gene of human immunodeficiency virus type 1 (HIV-1) encodes a virion-associated regulatory protein. Mutagenesis has shown that the virion association of Vpr requires sequences near the C terminus of the HIV-1 Gag polyprotein Pr55gag. To investigate whether Vpr incorporation is mediated by a specific domain of Pr55gag, we examined the ability of chimeric HIV-1/Moloney murine leukemia virus (MLV) Gag polyproteins to direct the incorporation of Vpr. Vpr expressed in trans did not associate with particles formed by the authentic MLV Gag polyprotein or with particles formed by chimeric Gag polyproteins that had the matrix (MA) or capsid (CA) domain of MLV precisely replaced by the corresponding domain of HIV-1HXB2. By contrast, Vpr was efficiently incorporated upon replacement of the C-terminal nucleocapsid (NC) domain of the MLV Gag polyprotein with HIV-1 p15 sequences. Vpr was also efficiently incorporated into particles formed by a MLV Gag polyprotein that had the HIV-1 p6 domain fused to its C terminus. Furthermore, a deletion analysis revealed that a conserved region near the C terminus of the p6 domain is essential for Vpr incorporation, whereas sequences downstream of the conserved region are dispensable. These results show that a virion association motif for Vpr is located within residues 1 to 46 of p6.

Amino Acid Sequence↗
PubMed2006

Suppressive effect of elongation factor 2 on apoptosis induced by HIV-1 viral protein R.

Rapid CD4+ lymphocyte depletion due to cell death caused by HIV infection is one of the hallmarks of acquired immunodeficiency syndrome. HIV-1 viral protein R (Vpr) induces apoptosis and is believed to contribute to CD4+ lymphocyte depletion. Thus, identification of cellular factors that potentially counteract this detrimental viral effect will not only help us to understand the molecular action of Vpr but also to design future antiviral therapies. In this report, we describe identification of elongation factor 2 (EF2) as such a cellular factor. Specifically, EF2 protein level is responsive to vpr gene expression; it is able to suppress Vpr-induced apoptosis when it is overproduced beyond its physiological level. EF2 was initially identified through a genome-wide multicopy suppressor search for Vpr-induced apoptosis in a fission yeast model system. Overproduction of fission yeast Ef2 completely abolishes Vpr-induced cell killing in fission yeast. Similarly, overexpression of the human homologue of yeast Ef2 in a neuroblastoma SKN-SH cell line and two CD4+ H9 and CEM-SS T-cell lines also blocked Vpr-induced apoptosis. The anti-apoptotic property of EF2 is demonstrated by its ability to suppress caspase 9 and caspase 3-mediated apoptosis induced by Vpr. In addition, it also reduces cytochrome c release induced by Vpr, staurosporine and TNFalpha. The fact that overproduction of EF2 blocks Vpr-induced cell death both in fission yeast and human cells, suggested that EF2 posses a highly conserved anti-apoptotic activity. Moreover, the responsive elevation of EF2 to Vpr suggests a possible host innate antiviral response.

Apoptosis↗
PubMed1995

Mutagenic analysis of human immunodeficiency virus type 1 Vpr: role of a predicted N-terminal alpha-helical structure in Vpr nuclear localization and virion incorporation.

The Vpr gene product of human immunodeficiency virus type 1 is a virion-associated protein that is important for efficient viral replication in nondividing cells such as macrophages. At the cellular level, Vpr is primarily localized in the nucleus when expressed in the absence of other viral proteins. Incorporation of Vpr into viral particles requires a determinant within the p6 domain of the Gag precursor polyprotein Pr55gag. In the present study, we have used site-directed mutagenesis to identify a domain(s) of Vpr involved in virion incorporation and nuclear localization. Truncations of the carboxyl (C)-terminal domain, rich in basic residues, resulted in a less stable Vpr protein and in the impairment of both virion incorporation and nuclear localization. However, introduction of individual substitution mutations in this region did not impair Vpr nuclear localization and virion incorporation, suggesting that this region is necessary for the stability and/or optimal protein conformation relevant to these Vpr functions. In contrast, the substitution mutations within the amino (N)-terminal region of Vpr that is predicted to adopt an alpha-helical structure (extending from amino acids 16 to 34) impaired both virion incorporation and nuclear localization, suggesting that this structure may play a pivotal role in modulating both of these biological properties. These results are in agreement with a recent study showing that the introduction of proline residues in this predicted alpha-helical region abolished Vpr virion incorporation, presumably by disrupting this secondary structure (S. Mahalingam, S. A. Khan, R. Murali, M. A. Jabbar, C. E. Monken, R. G. Collman, and A. Srinivasan, Proc. Natl. Acad. Sci. USA 92:3794-3798, 1995). Interestingly, our results show that two Vpr mutants harboring single amino acid substitutions (L to F at position 23 [L23F] and A30F) on the hydrophobic face of the predicted helix coded for relatively stable proteins that retained their ability to translocate to the nucleus but exhibited dramatic reduction in Vpr incorporation, suggesting that this hydrophobic face might mediate protein-protein interactions required for Vpr virion incorporation but not nuclear localization. Furthermore, a single mutation (E25K) located on the hydrophilic face of this predicted alpha-helical structure affected not only virion incorporation but also nuclear localization of Vpr. The differential impairment of Vpr nuclear localization and virion incorporation by mutations in the predicted N-terminal alpha-helical region suggests that this region of Vpr plays a role in both of these biological functions of Vpr.

Amino Acid Sequence↗
PubMed1999

Human immunodeficiency virus type 1 Vpr modifies cell proliferation via multiple pathways.

Vpr, one of the accessory molecules of HIV-1, has been demonstrated to arrest the cell cycle at the G2 phase. This Vpr-mediated cell cycle arrest is implicated to have an important role in the viral life cycle. In the present study, we quantitate the extent of Vpr-mediated cell cycle arrest with the use of a bicistronic vector consisting of a vpr gene and a green fluorescence protein sequence. Using this system, we examined the effect of several Vprs on cell cycle progression and growth of cells from different species quantitatively. We found that Vpr from the T-cell line-adapted HIV-1SF2 strain (Vpr2) could not significantly induce G2 arrest in HeLa cells but was able to induce it in 293T cells. However, strong inhibition of cell proliferation in HeLa cells as well as in 293T cells was observed by Vpr2. This ability of Vpr2 to inhibit cell proliferation without G2 arrest was also observed when expressed in monkey cell line. Analyses of chimeric Vprs revealed that this species-non-specific growth inhibitory activity of Vpr was not mediated solely by the C-terminal region of Vpr. These results indicated that the growth inhibitory activity of Vpr is independent of its G2 arresting activity. In addition, the species-non-specific nature of this activity suggests that Vpr has a novel mechanism to retard cell proliferation by influencing basic cellular functions.

Adaptation, Biological↗
PubMed1999

Micronuclei formation and aneuploidy induced by Vpr, an accessory gene of human immunodeficiency virus type 1.

Vpr, an accessory gene of HIV-1, induces cell cycle abnormality with accumulation at G2/M phase and increased ploidy. Since abnormality of mitotic checkpoint control provides a molecular basis of genomic instability, we studied the effects of Vpr on genetic integrity using a stable clone, named MIT-23, in which Vpr expression is controlled by the tetracycline-responsive promoter. Treatment of MIT-23 cells with doxycycline (DOX) induced Vpr expression with a giant multinuclear cell formation. Increased micronuclei (MIN) formation was also detected in these cells. Abolishment of Vpr expression by DOX removal induced numerous asynchronous cytokinesis in the multinuclear cells with leaving MIN in cytoplasm, suggesting that the transient Vpr expression could cause genetic unbalance. Consistent with this expectation, MIT-23 cells, originally pseudodiploid cells, became aneuploid after repeated expression of Vpr. Experiments using deletion mutants of Vpr revealed that the domain inducing MIN formation as well as multinucleation was located in the carboxy-terminal region of Vpr protein. These results suggest that Vpr induces genomic instability, implicating the possible role in the development of AIDS-related malignancies.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Induction of cell differentiation by human immunodeficiency virus 1 vpr.

Cell lines from rhabdomyosarcomas, which are tumors of muscle origin, have been used as models of CD4-independent HIV infection. These cell lines can be induced to differentiate in vitro. We report here that the vpr gene of HIV1 is sufficient for the differentiation of the human rhabdomyosarcoma cell line TE671. Differentiated cells are characterized by great enlargement, altered morphology, lack of replication, and high level expression of the muscle-specific protein myosin. We have also observed the morphological differentiation and inhibition of proliferation of two other transformed cell lines. vpr-transfected cells remain fully viable in culture for extended periods. These observations elucidate a potential role for vpr in the virus life cycle and raise the possibility that some aspects of HIV-induced pathologies may be caused by a disturbance of cells by vpr.

Cell Differentiation↗
PubMed1998

Vpr stimulates viral expression and induces cell killing in human immunodeficiency virus type 1-infected dividing Jurkat T cells.

In this study we investigated the effects of Vpr during human immunodeficiency virus (HIV) infection of proliferating Jurkat T cells by using a vesicular stomatitis virus envelope G glycoprotein pseudotyped HIV superinfection system. We observe that the expression of Vpr results in a severe reduction in the life span of HIV type 1 (HIV-1)-infected dividing T cells in culture. In agreement with a recent report (S. A. Stewart, B. Poon, J. B. M. Jowett, and I. S. Chen, J. Virol. 71:5579-5592, 1997), we show that events characteristic of apoptotic cell death are involved in the Vpr-mediated cytopathic effects. Our results also show that infection with viruses expressing the wild-type vpr gene results in an increase in viral gene expression and production. Interestingly, the effects of Vpr on cell viability and on viral gene expression both correlate with the ability of the protein to induce a cell cycle arrest in the G2/M phase. Mutagenesis analyses show that the C terminus of Vpr is essential for these biological activities. Although the role of Vpr is currently associated with the infection of nondividing cells, our results suggest that Vpr can also directly increase viral replication in vivo in infected dividing T cells. Furthermore, these in vitro observations suggest that Vpr-mediated cytotoxic effects could contribute to the CD4+ depletion associated with AIDS progression.

Cell Cycle↗