Tubular-specific expression of HIV protein Vpr leads to severe tubulointerstitial damage accompanied by progressive fibrosis and cystic development

Chronic kidney disease (CKD) is a common cause of morbidity in human immunodeficiency virus (HIV)-positive individuals. HIV infection leads to a wide spectrum of kidney cell damage, including tubular epithelial cell (TEC) injury. Among the HIV-1 proteins, the pathologic effects of viral protein R (Vpr) are well established and include DNA damage response, cell cycle arrest, and cell death. Several in vitro studies have unraveled the molecular pathways driving the cytopathic effects of Vpr in tubular epithelial cells. However, the in vivo effects of Vpr on tubular injury and CKD pathogenesis have not been thoroughly investigated. Here, we use a novel inducible tubular epithelial cell-specific Vpr transgenic mouse model to show that Vpr expression leads to progressive tubulointerstitial damage, interstitial inflammation and fibrosis, and tubular cyst development. Importantly, Vpr-expressing tubular epithelial cells displayed significant hypertrophy, aberrant cell division, and atrophy; all reminiscent of tubular injuries observed in human HIV-associated nephropathy (HIVAN). Single-cell RNA sequencing analysis revealed the Vpr-mediated transcriptomic responses in specific tubular subsets and highlighted the potential multifaceted role of p53 in the regulation of cell metabolism, proliferation, and death pathways in Vpr-expressing tubular epithelial cells. Thus, our study demonstrates that HIV Vpr expression in tubular cells is sufficient to induce HIVAN-like tubulointerstitial damage and fibrosis, independent of glomerulosclerosis and proteinuria. Additionally, as this new mouse model develops progressive CKD with diffuse fibrosis and kidney failure, it can serve as a useful tool to examine the mechanisms of kidney disease progression and fibrosis in vivo.

Structural insights into Cullin4-RING ubiquitin ligase remodelling by Vpr from simian immunodeficiency viruses

Viruses have evolved means to manipulate the host's ubiquitin-proteasome system, in order to down-regulate antiviral host factors. The Vpx/Vpr family of lentiviral accessory proteins usurp the substrate receptor DCAF1 of host Cullin4-RING ligases (CRL4), a family of modular ubiquitin ligases involved in DNA replication, DNA repair and cell cycle regulation. CRL4DCAF1 specificity modulation by Vpx and Vpr from certain simian immunodeficiency viruses (SIV) leads to recruitment, poly-ubiquitylation and subsequent proteasomal degradation of the host restriction factor SAMHD1, resulting in enhanced virus replication in differentiated cells. To unravel the mechanism of SIV Vpr-induced SAMHD1 ubiquitylation, we conducted integrative biochemical and structural analyses of the Vpr protein from SIVs infecting Cercopithecus cephus (SIVmus). X-ray crystallography reveals commonalities between SIVmus Vpr and other members of the Vpx/Vpr family with regard to DCAF1 interaction, while cryo-electron microscopy and cross-linking mass spectrometry highlight a divergent molecular mechanism of SAMHD1 recruitment. In addition, these studies demonstrate how SIVmus Vpr exploits the dynamic architecture of the multi-subunit CRL4DCAF1 assembly to optimise SAMHD1 ubiquitylation. Together, the present work provides detailed molecular insight into variability and species-specificity of the evolutionary arms race between host SAMHD1 restriction and lentiviral counteraction through Vpx/Vpr proteins.

Distinct MCM10 Proteasomal Degradation Profiles by Primate Lentiviruses Vpr Proteins

Viral protein R (Vpr) is an accessory protein found in various primate lentiviruses, including human immunodeficiency viruses type 1 and 2 (HIV-1 and HIV-2) as well as simian immunodeficiency viruses (SIVs). Vpr modulates many processes during viral lifecycle via interaction with several of cellular targets. Previous studies showed that HIV-1 Vpr strengthened degradation of Mini-chromosome Maintenance Protein10 (MCM10) by manipulating DCAF1-Cul4-E3 ligase in proteasome-dependent pathway. However, whether Vpr from other primate lentiviruses are also associated with MCM10 degradation and the ensuing impact remain unknown. Based on phylogenetic analyses, a panel of primate lentiviruses Vpr/x covering main virus lineages was prepared. Distinct MCM10 degradation profiles were mapped and HIV-1, SIVmus and SIVrcm Vprs induced MCM10 degradation in proteasome-dependent pathway. Colocalization and interaction between MCM10 with these Vprs were also observed. Moreover, MCM10 2-7 interaction region was identified as a determinant region susceptible to degradation. However, MCM10 degradation did not alleviate DNA damage response induced by these Vpr proteins. MCM10 degradation by HIV-1 Vpr proteins was correlated with G₂/M arrest, while induction of apoptosis and oligomerization formation of Vpr failed to alter MCM10 proteolysis. The current study demonstrated a distinct interplay pattern between primate lentiviruses Vpr proteins and MCM10.

Multiple Protein Kinases via Activation of Transcription Factors NF-κB, AP-1 and C/EBP-δ Regulate the IL-6/IL-8 Production by HIV-1 Vpr in Astrocytes

Neurocognitive impairments affect a substantial population of HIV-1 infected individuals despite the success of anti-retroviral therapy in controlling viral replication. Astrocytes are emerging as a crucial cell type that might be playing a very important role in the persistence of neuroinflammation seen in patients suffering from HIV-1 associated neurocognitive disorders. HIV-1 viral proteins including Vpr exert neurotoxicity through direct and indirect mechanisms. Induction of IL-8 in microglial cells has been shown as one of the indirect mechanism through which Vpr reduces neuronal survival. We show that HIV-1 Vpr induces IL-6 and IL-8 in astrocytes in a time-dependent manner. Additional experiments utilizing chemical inhibitors and siRNA revealed that HIV-1 Vpr activates transcription factors NF-κB, AP-1 and C/EBP-δ via upstream protein kinases PI3K/Akt, p38-MAPK and Jnk-MAPK leading to the induction of IL-6 and IL-8 in astrocytes. We demonstrate that one of the mechanism for neuroinflammation seen in HIV-1 infected individuals involves induction of IL-6 and IL-8 by Vpr in astrocytes. Understanding the molecular pathways involved in the HIV-1 neuroinflammation would be helpful in the design of adjunct therapy to ameliorate some of the symptoms associated with HIV-1 neuropathogenesis.

Gene loss and adaptation to hominids underlie the ancient origin of HIV-1

HIV-1 resulted from cross-species transmission of SIVcpz, a simian immunodeficiency virus that naturally infects chimpanzees. SIVcpz, in turn, is a recombinant between two SIV lineages from Old World monkeys. Lentiviral interspecies transmissions are partly driven by the evolution and capacity of viral accessory genes, such as vpx, vpr, and vif, to antagonize host antiviral factors, such as SAMHD1 and the APOBEC3 proteins. We show that vpx, which in other lentiviruses antagonizes SAMHD1, was deleted during the creation of SIVcpz. This genomic deletion resulted in the reconstruction of the overlapping vif gene by "overprinting," creating a unique vif that overlaps in its 3' end with the vpr gene and can antagonize hominid APOBEC3s. Moreover, passage of SIVs through chimpanzees facilitated the subsequent adaptation of HIV-1 to humans. Thus, HIV-1 originated through a series of gene loss and adaptation events that generated its chimpanzee precursor and lowered the species barrier to human infection.

Effect on HIV-1 gene expression, Tat-Vpr interaction and cell apoptosis by natural variants of HIV-1 Tat exon 1 and Vpr from Northern India

BACKGROUND

Since HIV-1 Tat and Vpr genes are involved in promoter transactivation, apoptosis, etc, we carried out studies to find out nature and extent of natural variation in the two genes from seropositive patients from Northern India and determined their functional implications.

METHODS

HIV-1 tat exon 1 and vpr were amplified from the genomic DNA isolated from the blood of HIV-1 infected individuals using specific primers by Polymerase Chain reaction (PCR) and subjected to extensive genetic analysis (CLUSTAL W, Simplot etc). Their expression was monitored by generating myc fusion clones. Tat exon 1 and Vpr variants were co-transfected with the reporter gene construct (LTR-luc) and their transactivation potential was monitored by measuring luciferase activity. Apoptosis and cell cycle analysis was done by Propidium Iodide (PI) staining followed by FACS.

RESULTS

Exon 1 of tat was amplified from 21 samples and vpr was amplified from 16 samples. One of the Tat exon 1 variants showed phylogenetic relatedness to subtype B & C and turned out to be a unique recombinant. Two of the Vpr variants were B/C/D recombinants. These natural variations were found to have no impact on the stability of Tat and Vpr. These variants differed in their ability to transactivate B LTR and C LTR promoters. B/C recombinant Tat showed better co-operative interaction with Vpr. B/C/D recombination in Vpr was found to have no effect on its co-operativity with Tat. Recombinant Tat (B/C) induced more apoptosis than wild type B and C Tat. The B/C/D recombination in Vpr did not affect its G2 arrest induction potential but reduced its apoptosis induction ability.

CONCLUSIONS

Extensive sequence and region-specific variations were observed in Tat and Vpr genes from HIV-1 infected individuals from Northern India. These variations have functional implications & therefore important for the pathogenicity of virus.

Viral factors involved in adapter-related protein complex 2 alpha 1 subunit-mediated regulation of human immunodeficiency virus type 1 replication

The presence of siRNA against adapter-related protein complex 2 alpha 1 subunit (AP2alpha) enhances human immunodeficiency virus type 1 (HIV-1) replication by up-regulating nuclear transport of viral genome. In this report, we examined possible viral factors involved in AP2alpha-mediated regulation of HIV-1 replication, namely, Gag matrix protein (MA), integrase (IN) and Vpr. Replication of mutant viruses lacking the nucleophilic property of one of these viral proteins was significantly enhanced by treating cells with AP2alpha siRNA, indicating that Gag MA, IN or Vpr is not specifically involved in AP2alpha-mediated enhancement of viral replication. In contrast, AP2alpha siRNA showed no effect on the level of gene transduction mediated by HIV-1-derived lentiviral vector (LV). Although virus-like LV particle and parental HIV-1 particle are composed of almost equivalent viral structural proteins, LV particles lack three accessory proteins, Vif, Vpr and Vpu, and a large portion of the HIV-1 genome. Vif, Vpr and Vpu were dispensable for AP2alpha siRNA-mediated enhancement of HIV-1 replication, indicating that a particular part of the HIV-1 genomic fragment deleted in the LV genome might be required for the enhancing effect of AP2alpha siRNA on viral replication. Taken together, these results suggest that an as yet undetermined gene fragment of the HIV-1 genome is involved in AP2alpha-mediated regulation of HIV-1 replication.

[Anti-glioma effect of combination of bFGF-siRNA and Vpr in nude mice]

OBJECTIVE

To study the anti-glioma effect of recombinant adenovirus mediated combined gene therapy of bFGF-siRNA and HIV1-Vpr in vivo.

METHODS

Mouse glioma model was established by injecting 5 × 10(6) LN229 cells into BALB/c-nu nude mice. 30 nude mice were randomly divided into 5 groups: the negative control group, mock group, bFGF-siRNA group, Vpr group and combined therapy group, which at regular intervals were injected with PBS, rAd5-null, rAd5-bFGF-siRNA, rAd5-Vpr, rAd5-bFGF-siRNA plus rAd5-Vpr, respectively. The tumor volume was recorded every third day to draw a growth curve. After four weeks treatment, the mice were killed and specimens were taken. HE, immunohistochemical and TUNEL staining were performed to observe the cell morphology, detect the changes of relevant target proteins and cell apoptosis, respectively. Also the ultrastructural changes were observed by electron microscopy.

RESULTS

The tumor growth inhibition rates were 36.9%, 37.2% and 58.6% in the bFGF-siRNA group, Vpr group and combined therapy group, respectively, and the combined therapy group showed the most significant effect (P < 0.05). Also the results of HE, immunohistochemical and TUNEL staining revealed that the combined therapy group had the best effects on proliferation inhibition and apoptosis induced in glioma cells (P < 0.05). The most significant ultrastructural changes were observed in the combined therapy group.

CONCLUSION

The combined gene therapy of bFGF-siRNA with Vpr shows a prominent and synergistic anti-glioma effect compared with that of mono-gene therapy in nude mice.

Characterization of the molecular determinants of primary HIV-1 Vpr proteins: impact of the Q65R and R77Q substitutions on Vpr functions

Although HIV-1 Vpr displays several functions in vitro, limited information exists concerning their relevance during infection. Here, we characterized Vpr variants isolated from a rapid and a long-term non-progressor (LTNP). Interestingly, vpr alleles isolated from longitudinal samples of the LTNP revealed a dominant sequence that subsequently led to diversity similar to that observed in the progressor patient. Most of primary Vpr proteins accumulated at the nuclear envelope and interacted with host-cell partners of Vpr. They displayed cytostatic and proapoptotic activities, although a LTNP allele, harboring the Q65R substitution, failed to bind the DCAF1 subunit of the Cul4a/DDB1 E3 ligase and was inactive. This Q65R substitution correlated with impairment of Vpr docking at the nuclear envelope, raising the possibility of a functional link between this property and the Vpr cytostatic activity. In contradiction with published results, the R77Q substitution, found in LTNP alleles, did not influence Vpr proapoptotic activity.

Accessories to the crime: recent advances in HIV accessory protein biology

Recent advances in understanding the roles of the lentiviral accessory proteins have provided fascinating insight into the molecular biology of the virus and uncovered previously unappreciated innate immune mechanisms by which the host defends itself. HIV-1 and other lentiviruses have developed accessory proteins that counterattack the antiviral defenses in a sort of evolutionary battle. The virus is remarkably adept at co-opting cellular degradative pathways to destroy the protective proteins. This review focuses on recent advances in understanding three of the accessory proteins-virion infectivity factor (Vif), viral protein R (Vpr), and viral protein U (Vpu)-that target different restriction factors to ensure virus replication. These proteins may provide promising targets for the development of novel classes of antiretroviral drugs.

Angiotensin II provokes podocyte injury in murine model of HIV-associated nephropathy

Conditional transgenic mice that express one of the human immunodeficiency virus (HIV)-1 accessory genes, vpr, selectively in podocytes using a podocin promoter and a tetracycline-inducible system develop renal injuries similar to those of patients with HIV-associated nephropathy (HIVAN). We have shown that a heminephrectomy accelerates podocyte injury, which is alleviated by angiotensin II (ANG II) type 1 receptor blocker (ARB). The current study further explores the role of ANG II in the genesis of HIVAN in this murine model. With ANG II infusion, heavy proteinuria was observed at 1 wk after the initiation of doxycycline administration to induce vpr expression in podocytes. Severe morphological and phenotypical changes in the podocytes were observed at 2 wk, together with extensive glomerulosclerosis. Norepinephrine infusion, instead of ANG II, increased the systemic blood pressure to the same level as that achieved using ANG II. However, albuminuria and glomerular injury were modest in norepinephrine-infused mice. Treatment with an ARB, olmesartan, almost completely inhibited glomerular injury. In contrast, lowering the blood pressure with a vasodilator, hydralazine, partially decreased albuminuria but did not produce any histological changes. ANG II infusion alone without doxycycline resulted in a lower level of albuminuria and minimal histological changes. These data demonstrate that excessive ANG II accelerates vpr-induced podocyte injury in a mouse model of HIVAN.

Vpr is required for efficient Nef expression from unintegrated human immunodeficiency virus type 1 DNA

Unintegrated human immunodeficiency virus (HIV) DNA are viral DNA products formed naturally during HIV replication. While the integrated proviral DNA form is transcriptionally active and results in productive infection, unintegrated DNA is also capable of expression of viral RNA and proteins. Previously, we showed that HIV Vpr enhances expression from integrase-defective HIV. Here we show that Vpr activation of expression is partially dependent upon the presence of a transcriptionally active HIV promoter and results in increased transcription of unspliced gag and spliced nef viral RNA. While Tat is detectable during infection with integrase-defective HIV, Tat levels are not affected by the presence of Vpr. Mutation studies reveal that Tat is dispensable for the Vpr-mediated enhancement of expression from unintegrated DNA. We find that virion-associated Vpr is sufficient for Nef expression from unintegrated viral DNA, resulting in the efficient downregulation of CD4 from the surface of infected cells. These results provide a mechanism by which Nef expression from unintegrated HIV type 1 DNA expression occurs.

DDB1 and Cul4A are required for human immunodeficiency virus type 1 Vpr-induced G2 arrest

Vpr-mediated induction of G2 cell cycle arrest has been postulated to be important for human immunodeficiency virus type 1 (HIV-1) replication, but the precise role of Vpr in this cell cycle arrest is unclear. In the present study, we have shown that HIV-1 Vpr interacts with damaged DNA binding protein 1 (DDB1) but not its partner DDB2. The interaction of Vpr with DDB1 was inhibited when DCAF1 (VprBP) expression was reduced by short interfering RNA (siRNA) treatment. The Vpr mutant (Q65R) that was defective for DCAF1 interaction also had a defect in DDB1 binding. However, Vpr binding to DDB1 was not sufficient to induce G2 arrest. A reduction in DDB1 or DDB2 expression in the absence of Vpr also did not induce G2 arrest. On the other hand, Vpr-induced G2 arrest was impaired when the intracellular level of DDB1 or Cullin 4A was reduced by siRNA treatment. Furthermore, Vpr-induced G2 arrest was largely abolished by a proteasome inhibitor. These data suggest that Vpr assembles with DDB1 through interaction with DCAF1 to form an E3 ubiquitin ligase that targets cellular substrates for proteasome-mediated degradation and G2 arrest.

HIV-1 Vpr-induced apoptosis is cell cycle dependent and requires Bax but not ANT

The HIV-1 accessory protein viral protein R (Vpr) causes G₂ arrest and apoptosis in infected cells. We previously identified the DNA damage–signaling protein ATR as the cellular factor that mediates Vpr-induced G₂ arrest and apoptosis. Here, we examine the mechanism of induction of apoptosis by Vpr and how it relates to induction of G₂ arrest. We find that entry into G₂ is a requirement for Vpr to induce apoptosis. We investigated the role of the mitochondrial permeability transition pore by knockdown of its essential component, the adenine nucleotide translocator. We found that Vpr-induced apoptosis was unaffected by knockdown of ANT. Instead, apoptosis is triggered through a different mitochondrial pore protein, Bax. In support of the idea that checkpoint activation and apoptosis induction are functionally linked, we show that Bax activation by Vpr was ablated when ATR or GADD45α was knocked down. Certain mutants of Vpr, such as R77Q and I74A, identified in long-term nonprogressors, have been proposed to inefficiently induce apoptosis while activating the G₂ checkpoint in a normal manner. We tested the in vitro phenotypes of these mutants and found that their abilities to induce apoptosis and G₂ arrest are indistinguishable from those of HIV-1_NL4–3vpr, providing additional support to the idea that G₂ arrest and apoptosis induction are mechanistically linked.

HIV-1 encodes a small gene known as vpr (viral protein regulatory) whose product is a 96–amino acid protein. HIV-1 infects cells of the immune system, such as CD4-positive lymphocytes. When cells become infected with HIV-1, two deleterious effects result from expression of the vpr gene. One effect of vpr is to manipulate the cell cycle by blocking the cells in G₂ (the phase of the cell cycle immediately preceding mitosis). Thus, cells infected with HIV-1 cease to proliferate, due to the action of vpr. A second effect of vpr is the induction of cell death by a process known as apoptosis or programmed cell death. When cells die by apoptosis, they do so following activation of a cellular set of genes and proteins whose primary function is to inactivate various cellular functions that are needed in order to maintain cellular viability. In this study, Andersen et al. demonstrate that the above two effects of vpr are linked. In particular, the authors show that the blockade in cell proliferation in G₂ is a requirement toward the onset of programmed cell death. Programmed cell death can be accomplished by a number of cellular proteins known as “executioners.” Various executioner proteins reside on the mitochondrial membranes and may trigger release of factors from the mitochondria, which in turn will precipitate the onset of apoptosis. In this work Anderson et al. identify the mitochondrial protein, Bax, as the key executioner of apoptosis in the context of HIV-1 vpr. The authors' findings provide important mechanistic understanding of how the vpr gene contributes to HIV-1–induced cell death.

Proline 35 of human immunodeficiency virus type 1 (HIV-1) Vpr regulates the integrity of the N-terminal helix and the incorporation of Vpr into virus particles and supports the replication of R5-tropic HIV-1 in human lymphoid tissue ex vivo

Mutational analysis of the four conserved proline residues in human immunodeficiency virus type 1 (HIV-1) Vpr reveals that only Pro-35 is required for efficient replication of R5-tropic, but not of X4-tropic, viruses in human lymphoid tissue (HLT) cultivated ex vivo. While Vpr-mediated apoptosis and G(2) cell cycle arrest, as well as the expression and subcellular localization of Vpr, were independent, the capacity for encapsidation of Vpr into budding virions was dependent on Pro-35. (1)H nuclear magnetic resonance data suggest that mutation of Pro-35 causes a conformational change in the hydrophobic core of the molecule, whose integrity is required for the encapsidation of Vpr, and thus, Pro-35 supports the replication of R5-tropic HIV-1 in HLT.

Vpr cytopathicity independent of G2/M cell cycle arrest in human immunodeficiency virus type 1-infected CD4+ T cells

The mechanism of CD4(+) T-cell depletion in human immunodeficiency virus type 1 (HIV-1)-infected individuals remains unknown, although mounting evidence suggests that direct viral cytopathicity contributes to this loss. The HIV-1 Vpr accessory protein causes cell death and arrests cells in the G(2)/M phase; however, the molecular mechanism underlying these properties is not clear. Mutation of hydrophobic residues on the surface of its third alpha-helix disrupted Vpr toxicity, G(2)/M arrest induction, nuclear localization, and self-association, implicating this region in multiple Vpr functions. Cytopathicity by virion-delivered mutant Vpr protein correlated with G(2)/M arrest induction but not nuclear localization or self-association. However, infection with whole virus encoding these Vpr mutants did not abrogate HIV-1-induced cell killing. Rather, mutant Vpr proteins that are impaired for G(2)/M block still prevented infected cell proliferation, and this property correlated with the death of infected cells. Chemical agents that inhibit infected cells from entering G(2)/M also did not reduce HIV-1 cytopathicity. Combined, these data implicate Vpr in HIV-1 killing through a mechanism involving inhibiting cell division but not necessarily in G(2)/M. Thus, the hydrophobic region of the third alpha-helix of Vpr is crucial for mediating G(2)/M arrest, nuclear localization, and self-association but dispensable for HIV-1 cytopathicity due to residual cell proliferation blockade mediated by a separate region of the protein.

Human immunodeficiency virus type 1 Vpr interacts with spliceosomal protein SAP145 to mediate cellular pre-mRNA splicing inhibition

Vpr, an accessory gene product of human immunodeficiency virus type 1 (HIV-1), affects both viral and cellular proliferation by mediating long terminal repeat activation, cell cycle arrest at the G2 phase, and apoptosis. We previously found that Vpr plays a novel role as a regulator of pre-mRNA splicing both in vivo and in vitro. However, the cellular target of Vpr, as well as the mechanism of cellular pre-mRNA splicing inhibition by Vpr, is unknown. Here, we show clearly that Vpr inhibits the splicing of cellular pre-mRNA, such as beta-globin pre-mRNA and immunoglobulin (Ig) M pre-mRNA and that the third alpha-helical domain and arginine-rich region are important its ability to inhibit splicing. Additionally, using mutants with specific substitutions in two domains of Vpr, we demonstrated that the interaction between Vpr and SAP145, an essential splicing factor, was indispensable for splicing inhibition. Finally, co-immunoprecipitation and in vitro competitive binding assays indicated that Vpr associates with SAP145 and interferes with SAP145-SAP49 complex formation. Thus, these results suggest that cellular expression of Vpr may block spliceosome assembly by interfering with the function of the SAP145-SAP49 complex in host cells.

Human immunodeficiency virus (HIV-1) Vpr induced downregulation of NHE1 induces alteration in intracellular pH and loss of ERM complex in target cells

Human immunodeficiency virus type 1 (HIV-1) Vpr is known to dysregulate host cellular functions through its interaction with cellular proteins. Using a protein array we assessed Vpr-mediated differential regulation of host cellular proteins expression. Results demonstrated that Vpr differentially regulated host factors that are involved in functions, such as cell proliferation, differentiation and apoptosis. One of the most highly downregulated proteins attained was the sodium hydrogen exchanger, isoform 1 (NHE1), which showed a significant (60%) decrease in HIV-1 Vpr(+) virus infected cells as compared to HIV-1 Vpr(-) virus infected control. NHE1 downregulation further led to acidification of cells and was directly correlated with loss of ezrin, radixin and moesin (ERM) protein complex and decreased AKT phosphorylation. Vpr-mediated NHE1 dyregulation is in part through GR pathway as GR antagonist, mifepristone reversed Vpr-induced NHE1 downregulation.

Effects of transgenic expression of HIV-1 Vpr on lipid and energy metabolism in mice

HIV infection is associated with abnormal lipid metabolism, body fat redistribution, and altered energy expenditure. The pathogenesis of these complex abnormalities is unclear. Viral protein R (Vpr), an HIV-1 accessory protein, can regulate gene transcription mediated by the glucocorticoid receptor and peroxisome proliferator-activated receptor-gamma and affect mitochondrial function in vitro. To test the hypothesis that expression of Vpr in liver and adipocytes can alter lipid metabolism in vivo, we engineered mice to express Vpr under control of the phosphoenolpyruvate carboxykinase promoter in a tissue-specific and inducible manner and investigated the effects of dietary fat, indinavir, and dexamethasone on energy metabolism and body composition. The transgenic mice expressed Vpr mRNA in white and brown adipose tissues and liver and immunoaffinity capillary electrophoresis revealed that they had free Vpr protein in the plasma. Compared with wild-type (WT) animals, Vpr mice had lower plasma triglyceride levels after 6 wk (P < 0.05) but not after 10 wk of a high-fat diet and lower plasma cholesterol levels after 10 wk of high-fat diet (P < 0.05). Treatment with dexamethasone obviated group differences, whereas indinavir had no significant independent effect on lipids. In the fasted state, Vpr mice had a higher respiratory quotient than WT mice (P < 0.05). These data provide the first in vivo evidence that HIV-1 Vpr expressed at low levels in adipose tissues and liver can 1) circulate in the blood, 2) regulate lipid and fatty acid metabolism, and 3) alter fuel selection for oxidation in the fasted state.

Activation of JNK-dependent pathway is required for HIV viral protein R-induced apoptosis in human monocytic cells: involvement of antiapoptotic BCL2 and c-IAP1 genes

Human immunodeficiency virus (HIV) accessory protein viral protein R (Vpr) plays a key role in virus replication and induces cell cycle arrest and apoptosis in various cell types including T cells and neuronal and tumor cells following infection with Vpr-expressing HIV isolates or exposure to the extracellular Vpr protein. The C-terminal Vpr peptide encompassing amino acids 52-96 (Vpr-(52-96)) is required for exerting the apoptotic effects, whereas the N-terminal Vpr-(1-45) peptide is responsible for virus transcription. We demonstrate that Vpr-(52-96) induced apoptosis in human promonocytic THP-1 cells and primary monocytes through the mitochondrial pathway in a caspase-dependent manner. To understand the regulation of Vpr-induced apoptosis, we investigated the signaling pathways, particularly the MAPKs, and the transcription factors involved. Although both Vpr-(52-96) and Vpr-(1-45) peptides induced phosphorylation of all the three members of the MAPKs, Vpr-(52-96)-activated JNK selectively induced apoptosis in monocytic cells through the mitochondrial pathway as determined by using JNK inhibitors SP60025, dexamethasone, curcumin, and JNK-specific small interfering RNAs. Furthermore Vpr-(52-96)-induced apoptosis was mediated by inhibition of downstream antiapoptotic Bcl2 and c-IAP1 genes whose expression could be restored following pretreatment with JNK-specific inhibitors. Overall the results suggest that Vpr-(52-96)-activated JNK plays a key role in inducing apoptosis through the down-regulation of antiapoptotic Bcl2 and c-IAP1 genes.

Morphological study on biologically distinct vpx/vpr mutants of HIV-2

We have previously shown that human immunodeficiency virus type 2 (HIV-2) without functional vpx and vpr genes is severely defective for viral growth in lymphocytic cells, and suggested that the virions produced in the absence of Vpx and Vpr are critically damaged. To examine the nature of replication-defect for the vpx/vpr double mutant, we quantitatively and morphologically studied the virions produced in cells transfected or infected with wild type clone, single (vpx and vpr mutants) or the double mutant. While no significant difference in virion production was found for various virus clones in transfected cells, a major growth retardation in infected cells was readily observed for the vpx and vpx/vpr mutants. In particular, no viral growth was detected for the double mutant. By contrast to the very distinct growth characteristics of the three mutant clones, no appreciable difference in virion morphology was noted. These results indicated that Vpx and Vpr of HIV-2 may cooperatively contribute to virion infectivity without affecting virion morphogenesis.

Epac- and Rap- independent ERK1/2 phosphorylation induced by Gs-coupled receptor stimulation in HEK293 cells

Serotonin activates Ras and Ras-dependent ERK1/2 phosphorylation in HEK293 cells expressing G(s)-coupled 5-HT(4) or 5-HT(7) serotonin receptors through unknown mechanisms. Both Epac/Rap-dependent and -independent pathways for Ras-dependent ERK1/2 activation have been suggested. Epac overexpression or Epac-specific 8-CPT-2'-O-Me-cAMP did not cause ERK1/2 phosphorylation, despite Rap activation. The data did not support a role for PLCepsilon or DAG-dependent Ras GEFs of the Ras-GRP family in Ras-dependent ERK1/2 phosphorylation. However, serotonin stimulated phosphorylation of endogenous and recombinant Ras-GRF1, increased [Ca(2+)](i) and caused Ca(2+)- and calmodulin-dependent ERK1/2 phosphorylation. Different signalling pathways seem to be utilised by G(s)-coupled receptors in various isolates of HEK293 cells.

[Gene therapy targeting for carcinoma regulated by E2F-1 promoter]

OBJECTIVE

To study the selective effect to tumor cells mediated by a recombinant adenoviral vector carrying E2F-1 promoter.

METHODS

The AdEasy-1 adenoviral vector system was used in this experiment. Several recombinant adenovirus with tumor-targeting E2F-1 promoter were constructed and then the E2F-1 promoter gene was checked by PCR and sequencing. The two adenovirus expressing GFP gene which is regulated by E2F-1 promoter or CMV promoter were used to respectively transfect tumor cells and non-proliferating normal cells, then observed and analyzed the different results caused by different promoters. Vpr gene was cloned into the targeting recombinant adenovirus. The new adenovirus named rvAdE2F-1/vpr was used to transfect tumor cells SMMC-7721, LS174T and non-proliferating normal cells H292, L-02. The surviving rate of each group was registered; the level of E2F-1 protein expressed in normal and tumor cell lines were checked by Western Blot.

RESULT

E2F-1 promoter can regulate the downstream gene GFP selectively expressed in LS174T and its activity in LS174T was similar with CMV promoter's; Vpr gene regulated by E2F-1 promoter can suppress the proliferation of tumor cells and no toxicity to normal cells; In all of the tumor cells, a much higher level of E2F-1 was expressed compared with normal cell lines. E2F-1 promoter's activity correlated well with E2F-1 protein levels.

CONCLUSIONS

E2F-1 promoter can control a selective cell killing to cancer cells, with no effect to normal cells. The system of E2F-1 promoter is a useful method for tumor-targeting gene therapy.

The role of Vpr in the regulation of HIV-1 gene expression

Expression of the viral protein R, Vpr, of HIV-1 affects many biological events in host cells including cell cycle progression, and modulates HIV-1 gene transcription. Earlier studies implicating the cellular protein p21(WAF1) (p21) in regulation of HIV-1 transcription, led us to investigate the functional and physical interaction of Vpr and p21. Our results show that Vpr modestly activated HIV-LTR in cells lacking p21 gene. Here, we describe the mechanisms by which p21 and Vpr leading to stimulation of HIV-1 transcription. Data from the protein-protein interaction experiments revealed the ability of Vpr, p21 and p300 to form a complex. Further, we show that, Vpr interacts with the N- and the C-terminal domains of p21. Furthermore, in cells expressing Vpr, p21 localizes to both the cytoplasm and the nucleus. Interestingly, expression of Vpr alleviates p21-mediated inhibition of cell departure from G1 phase. Expression of a mutant Vpr, with arginine 73 altered to serine, did not affect the ability of p21 to cause cells arrest or its sub-cellular localization. These observations reveal a new cellular partner for Vpr, and provide a new therapeutic avenue for controlling HIV-1 expression.

SIV Vpr evolution is inversely related to disease progression in a morphine-dependent rhesus macaque model of AIDS

Three of six morphine-dependent monkeys progressed rapidly to AIDS and died by 20 weeks in our SIV/SHIV non-human primate model of drug addiction and AIDS. We studied the evolution of the SIV vpr gene in both cerebrospinal fluid (CSF) and plasma in these rapid progressors, in their normal progressor counterparts and in infected, drug-free controls at 12 and 20 weeks post infection. Viral RNA was amplified, cloned, and sequenced to permit phylogenetic analyses of diversity and divergence of the vpr locus. As we found for SIV tat and env, the vpr gene evolves inversely to the rate of disease progression. Further, we found evidence that compartmentalization of the virus in plasma and CSF is significantly greater in the normal progressors than in the morphine-dependent, rapid progressors. Interestingly, although our previous work with the accessory gene nef indicated no association between disease progression and evolution, the accessory factor, vpr, behaves similarly to the essential lentiviral genes tat and env.

The Vif accessory protein alters the cell cycle of human immunodeficiency virus type 1 infected cells

The viral infectivity factor gene (vif) of HIV-1 increases the infectivity of viral particles by inactivation of cellular anti-viral factors, and supports productive viral replication in primary human CD4 T cells and in certain non-permissive T cell lines. Here, we demonstrate that Vif also contributes to the arrest of HIV-1 infected cells in the G(2) phase of the cell cycle. Viruses deleted in Vif or Vpr induce less cell cycle arrest than wild-type virus, while cells infected with HIV-1 deleted in both Vif and Vpr have a cell cycle profile equivalent to that of uninfected cells. Furthermore, expression of Vif alone induces accumulation of cells in the G(2) phase of the cell cycle. These data demonstrate a novel role for Vif in cell cycle regulation and suggest that Vif and Vpr independently drive G(2) arrest in HIV-1 infected cells. Our results may have implications for the actions and interactions of key HIV-1 accessory proteins in AIDS pathogenesis.

The Role of Vpr in HIV-1 Disease Progression is Independent of Its G2 Arrest Induction Function

Vpr (viral protein R) is a vital HIV-1 accessory protein with multiple functions in the viral life cycle, including nuclear import of preintegration complex, induction of apoptosis and G(2) cell cycle arrest. The cell cycle perturbation activity of Vpr requires activation of the ATR (Ataxia-Telangiectasia and Rad3-related) pathway and the integrity of Vpr C-terminal motif that is crucial for chromatin binding. Recent studies also demonstrated Vpr as one of the viral factors that influence HIV disease progression, as mutations in Vpr were overrepresented in some cohorts of long-term nonprogressors (LTNP). The LTNP-associated mutations of Vpr are frequently observed in the C-terminal domain. This raises the question whether the LTNP phenotype of Vpr is the result of the loss its ability to induce G(2) arrest. Here we report that the LTNP-associated mutants of Vpr function normally in the induction of G(2) arrest. No defects in ATR activation and direct binding to chromatin are observed. These mutants also show similar levels of apoptosis induction as wild-type Vpr. These data differentiate the LTNP-associated mutations of Vpr with those defective in inducing G(2) arrest. We propose that the G(2) arrest function of Vpr is separated from the LTNP phenotype, and the role of Vpr in HIV disease progression may involve other functions of Vpr.

The dose-dependent H2O2 stress response promotes increased survival forSchizosaccharomyces pombe cells expressing HIV-1 Vpr

Human immunodeficiency virus type 1 (HIV-1) viral protein R (Vpr) exerts multiple effects on viral and host cellular activities during infection, including induction of the cell cycle G2 arrest, and cell death in both human cells and the fission yeast Schizosaccharomyces pombe. We show that treament of exponential-phase wild-type Vpr-expressing S. pombe cells with a low, subinhibitory concentration (0.15 mmol/L) of hydrogen peroxide and 0.1 mmol/L thiamine significantly increased both cell proliferation and survival rates and decreased the number of elongated G2-arrested cells. Short-term, H2O2-induced adaptive stress increased the survival of the cells while acute stress conditions interrupted the Vpr-mediated death of the cells; however, no changes in cell length or cell phase were detected. The results suggest the importance of the oxidative status of the cells in Vpr-mediated processes. Our findings contribute to the development of a new approach via which to investigate the contribution of Vpr to HIV pathogenesis and to reduce the Vpr-mediated effects in HIV-infected patients.

Complete regression of established subcutaneous B16 murine melanoma tumors after delivery of an HIV-1 Vpr-expressing plasmid by in vivo electroporation

Novel therapies and delivery methods directed against malignancies such as melanoma, and particularly metastatic melanoma, are needed. The HIV-1 accessory protein Vpr (viral protein R) has previously been demonstrated to induce G2 cell cycle arrest as well as in vitro growth inhibition/killing of a number of tumor cells by apoptosis. In vivo electroporation has been utilized as an effective delivery method for pharmacologic agents and DNA plasmids that express "therapeutic" proteins and has been targeted to various tissues, including malignant tumors. For the study reported here, we hypothesized that intratumoral delivery of a Vpr expression plasmid through in vivo electroporation would induce apoptosis and growth attenuation or regression of melanoma tumors. Established subcutaneous B16.F10 melanoma tumors were injected intratumorally with a Vpr-expressing (either 25 or 100 microg) plasmid, followed by electroporation, on day 0 (i.e., when tumors had attained an appropriate size) and day 4. Treatment with 25 or 100 microg of the Vpr-expressing plasmid resulted in complete tumor regression with long-term survival in 14.3 and 7.1% of the mice, respectively. In addition, electroporative delivery of the Vpr-expressing plasmid was shown to induce apoptosis in tumors after intratumoral injection. This is the first report demonstrating the ability of Vpr, when delivered as a DNA expression plasmid with in vivo electroporation, to attenuate melanoma lesion growth and induce complete tumor regression coupled with long-term survival of mice in a highly aggressive and metastatic solid tumor model.

HIV-1 Vpr induces G2 cell cycle arrest in fission yeast associated with Rad24/14-3-3-dependent, Chk1/Cds1-independent Wee1 upregulation

Viral protein R (Vpr), an accessory protein of human immunodeficiency virus type 1 (HIV-1), induces the G2 cell cycle arrest in fission yeast for which host factors, such as Wee1 and Rad24, are required. Catalyzing the inhibitory phosphorylation of Cdc2, Wee1 is known to serve as a major regulator of G2/M transition in the eukaryotic cell cycle. It has been reported that the G2 checkpoint induced by DNA damage or incomplete DNA replication is associated with phosphorylation and upregulation of Wee1 for which Chk1 and Cds1 kinase is required. In this study, we demonstrate that the G2 arrest induced by HIV-1 Vpr in fission yeast is also associated with increase in the phosphorylation and amount of Wee1, but in a Chk1/Cds1-independent manner. Rad24 and human 14-3-3 appear to contribute to Vpr-induced G2 arrest by elevating the level of Wee1 expression. It appears that Vpr could cause the G2 arrest through a mechanism similar to, but distinct from, the physiological G2 checkpoint controls. The results may provide useful insights into the mechanism by which HIV-1 Vpr causes the G2 arrest in eukaryotic cells. Vpr may also serve as a useful molecular tool for exploring novel cell cycle control mechanisms.

Human immunodeficiency virus type 1 Vpr induces G2 checkpoint activation by interacting with the splicing factor SAP145

Vpr, the viral protein R of human immunodeficiency virus type 1, induces G(2) cell cycle arrest and apoptosis in mammalian cells via ATR (for "ataxia-telangiectasia-mediated and Rad3-related") checkpoint activation. The expression of Vpr induces the formation of the gamma-histone 2A variant X (H2AX) and breast cancer susceptibility protein 1 (BRCA1) nuclear foci, and a C-terminal domain is required for Vpr-induced ATR activation and its nuclear localization. However, the cellular target of Vpr, as well as the mechanism of G(2) checkpoint activation, was unknown. Here we report that Vpr induces checkpoint activation and G(2) arrest by binding to the CUS1 domain of SAP145 and interfering with the functions of the SAP145 and SAP49 proteins, two subunits of the multimeric splicing factor 3b (SF3b). Vpr interacts with and colocalizes with SAP145 through its C-terminal domain in a speckled distribution. The depletion of either SAP145 or SAP49 leads to checkpoint-mediated G(2) cell cycle arrest through the induction of nuclear foci containing gamma-H2AX and BRCA1. In addition, the expression of Vpr excludes SAP49 from the nuclear speckles and inhibits the formation of the SAP145-SAP49 complex. To conclude, these results point out the unexpected roles of the SAP145-SAP49 splicing factors in cell cycle progression and suggest that cellular expression of Vpr induces checkpoint activation and G(2) arrest by interfering with the function of SAP145-SAP49 complex in host cells.

HIV-1 Vpr: enhancing sensitivity of tumors to apoptosis

Cancers can adapt several evasive functions including apoptosis evasion, self-sufficiency in growth signals, insensitivity to anti-growth signals, sustained angiogenesis, limitless replication potential, tissue invasion and metastasis. The invariable hurdle for development of therapies against such aberrant conditions requires both selective and potent cytotoxicity. Analysis of HIV-1 Vpr's apoptotic and anti-proliferative activity have revealed potentially important implications for cancer therapy. Accordingly, we have reviewed the properties of Vpr that will likely contribute to its efficacious function as an anti-tumor agent. Among these are its ability to induce cell cycle arrest, inhibit inflammation, provoke p53 independent apoptosis, and selective killing of rapidly dividing cells.

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.

Activation of the ATR pathway by human immunodeficiency virus type 1 Vpr involves its direct binding to chromatin in vivo

The human immunodeficiency virus type 1 (HIV-1) protein Vpr (viral protein R) arrests cells in the G2 phase of the cell cycle, a process that requires activation of the ATR (ataxia-telangiectasia and Rad3-related) pathway. In this study we demonstrate that the expression of Vpr does not cause DNA double-strand breaks but rather induces ATR activation, as indicated by induction of Chk1 phosphorylation and the formation of gamma-H2AX and 53BP1 nuclear foci. We define a C-terminal domain containing repeated H(F/S)RIG sequences required for Vpr-induced activation of ATR. Further investigation of the mechanism by which Vpr activates the ATR pathway reveals an increase in chromatin binding of replication protein A (RPA) upon Vpr expression. Immunostaining shows that RPA localizes to nuclear foci in Vpr-expressing cells. Furthermore, we demonstrate direct binding of Vpr to chromatin in vivo, whereas Vpr C-terminal domain mutants lose this chromatin-binding activity. These data support a mechanism whereby HIV-1 Vpr induces ATR activation by targeting the host cell DNA and probably interfering with normal DNA replication.

Human immunodeficiency virus type 1 Vpr induces cell cycle arrest at the G(1) phase and apoptosis via disruption of mitochondrial function in rodent cells

Vpr of human immunodeficiency virus type 1 causes cell cycle arrest at the G(2)/M phase and induces apoptosis after G(2)/M arrest in primate cells. We have reported previously that Vpr also induces apoptosis independently of G(2)/M arrest in human HeLa cells. By contrast, Vpr does not induce G(2)/M arrest in rodent cells, but it retards cell growth. To clarify the relationship between cell cycle arrest and apoptosis, we expressed Vpr endogenously in rodent cells and investigated cell cycle profiles and apoptosis. We show here that Vpr induces cell cycle arrest at the G(1) phase and apoptosis in rodent cells. Vpr increased the activity of caspase-3 and caspase-9, but not of caspase-8. Moreover, Vpr-induced apoptosis could be inhibited by inhibitors of caspase-3 and caspase-9, but not by inhibitor of caspase-8. We also showed that Vpr induces the release of cytochrome c from mitochondria into the cytosol and disrupts the mitochondrial transmembrane potential. Finally, we showed that apoptosis occurred in HeLa cells through an identical pathway. These results suggest that disruption of mitochondrial functions by Vpr induces apoptosis via cell cycle arrest at G(1), but that apoptosis is independent of G(2)/M arrest. Furthermore, it appears that Vpr acts species-specifically with respect to induction of cell cycle arrest but not of apoptosis.

Codon-optimized reading frames facilitate high-level expression of the HIV-1 minor proteins

We have constructed reading frames for the HIV-1 YU-2 minor proteins Vpr, Vpu, Vif and Nef that are codon-optimized for high-level expression in mammalian cells. We show that, in the absence of the Rev/Rev-response element system, these codon-optimized reading frames result in greatly increased levels of expression of the corresponding proteins in cell culture systems when compared with the native reading frame. Northern blot analysis shows that the increase in expression found with the codon-optimized reading frames is largely owing to increased steady-state mRNA levels.

A novel small reporter gene and HIV-1 fitness assay

Most currently available HIV-1 reporter gene constructs are large and disrupt the nef reading frame. This report describes a novel reporter gene based on the small murine heat stable antigen (HSA) protein, which is expressed on the surface of infected cells. This HSA reporter can be inserted in the vpr reading frame, leaving nef intact. Nine amino acids from the extracellular domain of HSA are replaced with an influenza hemagglutinin (HA) antibody epitope (HSA-HA). Like the parental reporter protein, this novel reporter is expressed on the surface of infected cells. Antibodies for HSA and HA specifically detect reporter viruses with each construct, indicating disruption of the original HSA antibody epitope. Finally, a strategy is developed to detect each reporter virus by real-time PCR quantitation. The growth of viruses tagged with each reporter allows precise assessment of the relative growth of viruses differing in mutations of interest. Moreover, the availability of these reporters in either of two half-genome plasmids allows convenient production of reporter and non-reporter HIV-1 by co-transfection of appropriately paired plasmids. These paired reporter viruses offer a potentially useful standardized method for measurement of HIV-1 fitness in competition assays.

The cell cycle independence of HIV infections is not determined by known karyophilic viral elements

Human immunodeficiency virus and other lentiviruses infect cells independent of cell cycle progression, but gammaretroviruses, such as the murine leukemia virus (MLV) require passage of cells through mitosis. This property is thought to be important for the ability of HIV to infect resting CD4+ T cells and terminally differentiated macrophages. Multiple and independent redundant nuclear localization signals encoded by HIV have been hypothesized to facilitate migration of viral genomes into the nucleus. The integrase (IN) protein of HIV is one of the HIV elements that targets to the nucleus; however, its role in nuclear entry of virus genomes has been difficult to describe because mutations in IN are pleiotropic. To investigate the importance of the HIV IN protein for infection of non-dividing cells, and to investigate whether or not IN was redundant with other viral signals for cell cycle-independent nuclear entry, we constructed an HIV-based chimeric virus in which the entire IN protein of HIV was replaced by that of MLV. This chimeric virus with a heterologous IN was infectious at a low level, and was able to integrate in an IN-dependent manner. Furthermore, this virus infected non-dividing cells as well as it infected dividing cells. Moreover, we used the chimeric HIV with MLV IN to further eliminate all of the other described nuclear localization signals from an HIV genome—matrix, IN, Viral Protein R, and the central polypurine tract—and show that no combination of the virally encoded NLS is essential for the ability of HIV to infect non-dividing cells.

Human immunodeficiency virus can infect many cells irrespective of whether or not they are dividing, whereas some other retroviruses, such as the murine leukemia virus can only infect cells that are proliferating. This property is important for the ability of HIV to establish infections in critical cell types in infected people. Multiple and redundant signals encoded by HIV have been hypothesized to facilitate migration of viral genomes into the nucleus. However, here the authors eliminated all four described nuclear localizing signals from an HIV genome and show that no combination of these virally encoded signals is essential for the ability of HIV to infect non-dividing cells. They suggest that another step of the virus lifecycle, other than nuclear import, is the rate-limiting step that determines the cell cycle dependence/independence of retroviral infections.

Mutational analysis of growth arrest and cellular localization of human immunodeficiency virus type 1 Vpr in the budding yeast, Saccharomyces cerevisiae

Viral protein R (Vpr), one of the accessory gene products of human immunodeficiency virus type 1 (HIV-1), is responsible for the incorporation of a viral genome into the nucleus upon infection. Vpr also arrests the cell cycle and induces apoptosis in infected cells. Similarly, in yeast, Vpr localizes in the nucleus and shows growth inhibitory activity; however, the molecular mechanism of growth inhibition remains unknown. To elucidate this mechanism, several point mutations of Vpr, which are known to perturb several phenotypes of Vpr in mammalian cells, were introduced in the budding yeast, Saccharomyces cerevisiae. For the first time, we found that growth inhibition by Vpr occurred independently of intracellular localization in yeast, as has previously been reported in mammals. We also identified several amino acid residues, the mutation of which cancels growth inhibitory activity, and/or alters localization, both in yeast and mammalian cells, suggesting the importance of these residues for the phenotypes.

Comparative study on the structure and cytopathogenic activity of HIV Vpr/Vpx proteins

The three-dimensional (3-D) structure of human immunodeficiency virus type 2 (HIV-2) Vpr/Vpx was predicted by homology modeling based on the NMR structure of human immunodeficiency virus type 1 (HIV-1) Vpr. The three proteins similarly have three major amphipathic alpha-helices. In contrast to HIV-1 Vpr, Vpr/Vpx of HIV-2 have a long N-terminal loop and clustered prolines in the second half of the C-terminal loop. HIV-2 Vpx uniquely contains a long region between the second and third major helices, and bears several glycines in the first half of the C-terminal loop. Instead of the glycines, there is a group of hydrophilic amino acids and arginines in the corresponding regions of the two Vprs. To compare the cytopathogenic potentials of HIV-1 Vpr and HIV-2 Vpr/Vpx, we examined the production of luciferase as a marker of cell damage. We further analyzed the characteristics of cells transduced with vpr/vpx genes driven by an inducible promoter. The results obtained clearly show that structurally similar, but distinct, HIV Vpr/Vpx proteins are detrimental to target cells.

Retroviral recombination in vivo: viral replication patterns and genetic structure of simian immunodeficiency virus (SIV) populations in rhesus macaques after simultaneous or sequential intravaginal inoculation with SIVmac239Deltavpx/Deltavpr and SIVmac239Deltanef

To characterize the occurrence, frequency, and kinetics of retroviral recombination in vivo, we intravaginally inoculated rhesus macaques, either simultaneously or sequentially, with attenuated simian immunodeficiency virus (SIV) strains having complementary deletions in their accessory genes and various degrees of replication impairment. In monkeys inoculated simultaneously with SIVmac239Deltavpx/Deltavpr and SIVmac239Deltanef, recombinant wild-type (wt) virus and wild-type levels of plasma viral RNA (vRNA) were detected in blood by 2 weeks postinoculation. In monkeys inoculated first with SIVmac239Deltavpx/Deltavpr and then with SIVmac239Deltanef, recombination occurred but was associated with lower plasma vRNA levels than plasma vRNA levels seen for monkeys inoculated intravaginally with wt SIVmac239. In one monkey, recombination occurred 6 weeks after the challenge with SIVmac239Deltanef when plasma SIVmac239Deltavpx/Deltavpr RNA levels were undetectable. In monkeys inoculated first with the more highly replicating strain, SIVmac239Deltanef, and then with SIVmac239Deltavpx/Deltavpr, wild-type recombinant virus was not detected in blood or tissues. Instead, a virus that had repaired the deletion in the nef gene by a compensatory mutation was found in one animal. Overall, recombinant SIV was eventually found in four of six animals intravaginally inoculated with the two SIVmac239 deletion mutants. These findings show that recombination can occur readily in vivo after mucosal SIV exposure and thus contributes to the generation of viral genetic diversity and enhancement of viral fitness.

Human immunodeficiency virus type 1-induced macrophage gene expression includes the p21 gene, a target for viral regulation

In contrast to CD4+ T cells, human immunodeficiency virus type 1 (HIV-1)-infected macrophages typically resist cell death, support viral replication, and consequently, may facilitate HIV-1 transmission. To elucidate how the virus commandeers the macrophage's intracellular machinery for its benefit, we analyzed HIV-1-infected human macrophages for virus-induced gene transcription by using multiple parameters, including cDNA expression arrays. HIV-1 infection induced the transcriptional regulation of genes associated with host defense, signal transduction, apoptosis, and the cell cycle, among which the cyclin-dependent kinase inhibitor 1A (CDKN1A/p21) gene was the most prominent. p21 mRNA and protein expression followed a bimodal pattern which was initially evident during the early stages of infection, and maximum levels occurred concomitant with active HIV-1 replication. Mechanistically, viral protein R (Vpr) independently regulates p21 expression, consistent with the reduced viral replication and lack of p21 upregulation by a Vpr-negative virus. Moreover, the treatment of macrophages with p21 antisense oligonucleotides or small interfering RNAs reduced HIV-1 infection. In addition, the synthetic triterpenoid and peroxisome proliferator-activated receptor gamma ligand, 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO), which is known to influence p21 expression, suppressed viral replication. These data implicate p21 as a pivotal macrophage facilitator of the viral life cycle. Moreover, regulators of p21, such as CDDO, may provide an interventional approach to modulate HIV-1 replication.

Vpr protein of human immunodeficiency virus type 1 binds to 14-3-3 proteins and facilitates complex formation with Cdc25C: implications for cell cycle arrest

Vpr and selected mutants were used in a Saccharomyces cerevisiae two-hybrid screen to identify cellular interactors. We found Vpr interacted with 14-3-3 proteins, a family regulating a multitude of proteins in the cell. Vpr mutant R80A, which is inactive in cell cycle arrest, did not interact with 14-3-3. 14-3-3 proteins regulate the G(2)/M transition by inactivating Cdc25C phosphatase via binding to the phosphorylated serine residue at position 216 of Cdc25C. 14-3-3 overexpression in human cells synergized with Vpr in the arrest of cell cycle. Vpr did not arrest efficiently cells not expressing 14-3-3sigma. This indicated that a full complement of 14-3-3 proteins is necessary for optimal Vpr function on the cell cycle. Mutational analysis showed that the C-terminal portion of Vpr, known to harbor its cell cycle-arresting activity, bound directly to the C-terminal part of 14-3-3, outside of its phosphopeptide-binding pocket. Vpr expression shifted localization of the mutant Cdc25C S216A to the cytoplasm, indicating that Vpr promotes the association of 14-3-3 and Cdc25C, independently of the presence of serine 216. Immunoprecipitations of cell extracts indicated the presence of triple complexes (Vpr/14-3-3/Cdc25C). These results indicate that Vpr promotes cell cycle arrest at the G(2)/M phase by facilitating association of 14-3-3 and Cdc25C independently of the latter's phosphorylation status.

Structure and function of HIV-1 auxiliary regulatory protein Vpr: novel clues to drug design

Vpr is a 96-amino acid auxiliary regulatory protein that is packaged in the HIV-1 virion. It enhances the nuclear transport of the pre-integration complex, and regulates cell cycle, transcription and apoptosis. These biological activities suggest strongly that Vpr interacts with cellular biochemical pathways to regulate HIV-1 replication and pathogenesis. The karyophilic property of Vpr appears to be due to direct interaction of Vpr with nuclear transport factors and residents of the nuclear pore complex, whereas transcriptional effects of Vpr may be exerted through direct and indirect mechanisms. Cell cycle arrest at the G2/M checkpoint by Vpr is correlated with the hyperphosphorylation of Cdc2. The pro-apoptotic activity of Vpr is dependent on the subtype of the HIV-1 isolate, and may be dramatically enhanced by a single L64P mutation. Mitochondria- and caspase-dependent mechanisms appear to mediate Vpr-induced apoptosis. Recent evidence suggests that Vpr interacts with a cellular ubiquitination machinery and promotes degradation of Vpr mutants carrying the L64P mutation. Vpr interaction with the ubiquitination machinery may contribute to the regulation of the HIV-1 life cycle at various stages. NMR studies of Vpr have shown a Vpr monomer with three helical domains arranged in a twisted-U shape. However, Vpr most likely exists as a trimer in vivo. Structural/functional domains have been tentatively mapped for Vpr induction of apoptosis and for Vpr interaction with the ubiquitination machinery. Structural refinement of Vpr, specially by crystallography of the potential Vpr trimer, should help design therapeutic approaches to specifically target Vpr.

The Vpr protein from HIV-1: distinct roles along the viral life cycle

The genomes of human and simian immunodeficiency viruses (HIV and SIV) encode the gag, pol and env genes and contain at least six supplementary open reading frames termed tat, rev, nef, vif, vpr, vpx and vpu. While the tat and rev genes encode regulatory proteins absolutely required for virus replication, nef, vif, vpr, vpx and vpu encode for small proteins referred to "auxiliary" (or "accessory"), since their expression is usually dispensable for virus growth in many in vitro systems. However, these auxiliary proteins are essential for viral replication and pathogenesis in vivo. The two vpr- and vpx-related genes are found only in members of the HIV-2/SIVsm/SIVmac group, whereas primate lentiviruses from other lineages (HIV-1, SIVcpz, SIVagm, SIVmnd and SIVsyk) contain a single vpr gene. In this review, we will mainly focus on vpr from HIV-1 and discuss the most recent developments in our understanding of Vpr functions and its role during the virus replication cycle.

The ataxia telangiectasia-mutated and Rad3-related protein is dispensable for retroviral integration

Integration into the host cell DNA is an essential part of the retroviral life cycle and is required for the productive replication of a retrovirus. Retroviral integration involves cleavage of the host DNA and insertion of the viral DNA, forming an integration intermediate that contains two gaps, each with a viral 5' flap. The flaps are then removed, and the gap is filled by as yet unidentified nuclease and polymerase activities. It is thought that repair of these gaps flanking the site of retroviral integration is achieved by host DNA repair machinery. The ATM and Rad3-related protein (ATR) is a member of the phosphatidylinositol 3 kinase-related family of protein kinases that play a major role in sensing and triggering repair of DNA lesions in mammalian cells. In an effort to examine the role of ATR in retroviral integration, we used RNA interference to selectively downregulate ATR and measured integration efficiency. In addition, we examined the possible role that Vpr may play in enhancing integration and, in particular, whether activation of ATR by Vpr (Roshal et al., J. Biol. Chem. 278:25879-25886, 2003) will favor human immunodeficiency virus type 1 integration. We conclude that cells in which ATR has been depleted are competent for retroviral integration. We also conclude that the presence of Vpr as a virion-bound protein does not enhance integration of a lentivirus vector in dividing cells.

HIV viral protein R causes atrial cardiomyocyte mitosis, mesenchymal tumor, dysrhythmia, and heart failure

HIV viral protein R (Vpr) affects the immunocyte cell cycle and circulates as free polypeptide in plasma of AIDS patients. Effects of Vpr on cardiomyocytes were explored using transgenic mice (TG) with Vpr targeted to cardiomyocytes by the alpha-myosin heavy-chain promoter. TG and WT littermate hearts were evaluated histopathologically, ultrastructurally, molecularly via RNA microarray analysis and quantitative RT-PCR, and functionally by cardiac magnetic resonance imaging (MRI) and electrocardiograms (ECG). Six hemizygous lines were created (Vpr(a,b,c,d,e,h)). Vpr RNA was expressed exclusively in myocardium and Vpr mRNA expression correlated with phenotypic changes. Vpr(b) exhibited the highest expression and mortality. TGs developed congestive heart failure ( approximately 8 weeks), abnormal cardiomyocyte nuclei and mitoses ( approximately 12 weeks), and became moribund ( approximately 20 weeks) with atrial mesenchymal tumors. MRI revealed four-chamber dilation, defective contraction, and atrial masses. Pathologically, cardiomegaly and atrial mesenchymal tumors occurred ( approximately 16-20 weeks). ECGs showed prolonged R-R, Q-T, and P-R intervals ( approximately 12 weeks). RNA encoding collagen and bone morphogenic protein 4, 6, and 7 were increased. Vpr targeted to cardiomyocytes caused defective contractility and atrial tumors. Since some Vpr cardiomyocytic effects resemble those found in terminally differentiated immunocytes, some pathogenetic mechanisms may be shared at the subcellular level.

The functionally conserved nucleoporins Nup124p from fission yeast and the human Nup153 mediate nuclear import and activity of the Tf1 retrotransposon and HIV-1 Vpr

We report that the fission yeast nucleoporin Nup124p is required for the nuclear import of both, retrotransposon Tf1-Gag as well as the retroviral HIV-1 Vpr. Failure to import Tf1-Gag into the nucleus in a nup124 null mutant resulted in complete loss of Tf1 transposition. Similarly, nuclear import of HIV-1 Vpr was impaired in nup124 null mutant strains and cells became resistant to Vpr's cell-killing activity. On the basis of protein domain similarity, the human nucleoporin Nup153 was identified as a putative homolog of Nup124p. We demonstrate that in vitro-translated Nup124p and Nup153 coimmunoprecipitate Tf1-Gag or HIV-1 Vpr. Though full-length Nup153 was unable to complement the Tf1 transposition defect in a nup124 null mutant, we provide evidence that both nucleoporins share a unique N-terminal domain, Nup124p(AA264-454) and Nup153(AA448-634) that is absolutely essential for Tf1 transposition. Epigenetic overexpression of this domain in a wild-type (nup124(+)) background blocked Tf1 activity implying that sequences from Nup124p and the human Nup153 challenged the same pathway affecting Tf1 transposition. Our results establish a unique relationship between two analogous nucleoporins Nup124p and Nup153 wherein the function of a common domain in retrotransposition is conserved.

HIV-1 Vpr inhibits the maturation and activation of macrophages and dendritic cells in vitro

Human immunodeficiency virus-1 (HIV-1) Vpr encodes a 14 kDa protein that has been implicated in viral pathogenesis through in vitro modulation of several host cell functions. Vpr modulates cellular proliferation, cell differentiation, apoptosis and host cell transcription in a manner that involves the glucocorticoid pathway. To better understand the role of HIV-1 Vpr in host gene expression, approximately 9600 cellular RNA transcripts were assessed for their modulation in primary APC after treatment with a bioactive recombinant Vpr (rVpr) by DNA micro-array. As an extracellular delivered protein, Vpr down-modulated the expression of several immunologically important molecules including CD40, CD80, CD83 and CD86 costimulatory molecules on MDM (monocyte-derived macrophage) and MDDC (monocyte-derived dendritic cells). Maturation of dendritic cells (DC) is known to result in a decreased capacity to produce HIV due to a post-entry block of the HIV-1 replicative cycle. Based on the changes observed in the gene array, we analyzed maturation of DC generated from monocytes in tissue culture as influenced by Vpr. We observed that Vpr-treated immature MDM and MDDC were unable to acquire high levels of costimulatory molecules and failed to develop into mature DC, even in the presence of maturation signals. These studies have importance for understanding the interaction of HIV with the host immune system.