Virus Replication In Macrophages Research Articles

Inhibition of pathogenic SHIV replication in macaques treated with antisense DNA of interleukin-4

AbstractInterleukin-4 is implicated in the pathogenesis of HIV-induced AIDS and causes enhancement of replication of virus strains that use the CXCR4 (X4) coreceptor. In this study, we explored the effects of interleukin-4 (IL-4) antisense (AS) DNA on replication of X4, simian human immunodeficiency viruses, SHIVKU-2 and SHIV89.6P. AS IL-4 oligomer caused inhibition of virus replication in cultures of CD4+ T cells and macrophages derived from macaques. Plasmid expressing AS IL-4 DNA was also effective in abrogating virus replication in macrophage cultures. Relevance of these cell culture studies was confirmed in vivo by treating SHIV89.6P-infected macaques with AS IL-4 DNA. Six macaques were inoculated with the virus, and 4 were treated with AS IL-4 DNA. This resulted in a significant decrease in viral RNA concentrations in the liver, lungs, and spleen tissues that are all sites of virus replication in macrophages. This is the first demonstration of effective inhibition of an HIV-like virus in tissues by AS DNA of a cytokine. In the present era of increasing resistance of HIV to antiviral compounds, exploration of adjunct therapies directed at host responses in combination with antiretroviral drugs may be of value for the treatment of AIDS.

Simian Human Immunodeficiency Virus-Associated Pneumonia Correlates with Increased Expression of MCP-1, CXCL10, and Viral RNA in the Lungs of Rhesus Macaques

Pulmonary disorders are the most frequent cause of death in HIV-1-infected individuals with AIDS and remain important even in the current era of potent antiretroviral therapy. Macaques infected with Simian/Human Immunodeficiency Virus (SHIV) develop pulmonary disease and concurrent opportunistic infections similar to those observed in HIV-infected individuals, thereby providing an excellent working model to elucidate the pathogenesis of the human lung disease. Since chemokines play a crucial role in the recruitment of inflammatory cells to tissues, we investigated the relationship between respiratory disease and the levels of chemokines, monocyte chemotactic protein-1 (MCP-1) and CXCL10, in the lungs of SHIV-infected rhesus macaques. We found that lung pathology in infected macaques was closely associated with overexpression of MCP-1 and CXCL10. In addition, these chemokines could, in part, be responsible for the recruitment of inflammatory cells infiltrating into the diseased lungs as demonstrated by chemotactic assays. Lung pathology and increased levels of MCP-1 and CXCL10 correlated with high viral loads in the lung parenchyma. Using confocal microscopy, we identified SHIV-infected macrophages as the major producers of MCP-1 and CXCL10 in the diseased lungs. These data suggest that chemokine overexpression plays an important role in the pathogenesis of SHIV-associated pulmonary disease in macaques.

Investigations on four host response factors whose expression is enhanced in X4 SHIV encephalitis

HIV encephalopathy, one of the major complications of HIV infection, involves productive virus replication in macrophages in the brain in association with heightened expression of several host response factors. One or more of these factors are thought to be the cause of the degenerative changes in neurons in the brain. Macaques infected with SIV and SHIV viruses have provided excellent working models for studying mechanisms of the human disease. Although HIV encephalopathy is primarily associated with CCR5-utilizing viruses, our findings have shown that CXCR4-utilizing SHIVs were also capable of causing the syndrome in rhesus macaques. In SHIV-infected macaques, approximately 30% of the animals developed encephalitis. In order to understand the factors leading to end-stage encephalitis, we performed microarray analyses on brains of encephalitic and non-encephalitic-infected macaques, and found pronounced enhancement of expression of interleukin-4, platelet-derived growth factor-B chain, monocyte chemoattractant protein-1 and CXCL10 in the brains of the encephalitic animals. This review discusses the role of each of these factors in mediating SHIV encephalitis.

PU.1 binding to ets motifs within the equine infectious anemia virus long terminal repeat (LTR) enhancer: regulation of LTR activity and virus replication in macrophages.

Binding of the transcription factor PU.1 to its DNA binding motif regulates the expression of a number of B-cell- and myeloid-specific genes. The long terminal repeat (LTR) of macrophage-tropic strains of equine infectious anemia virus (EIAV) contains three PU.1 binding sites, namely an invariant promoter-proximal site as well as two upstream sites. We have previously shown that these sites are important for EIAV LTR activity in primary macrophages (W. Maury, J. Virol. 68:6270-6279, 1994). Since the sequences present in these three binding motifs are not identical, we sought to determine the role of these three sites in EIAV LTR activity. While DNase I footprinting studies indicated that all three sites within the enhancer were bound by recombinant PU.1, reporter gene assays demonstrated that the middle motif was most important for basal levels of LTR activity in macrophages and that the 5' motif had little impact. The impact of the 3' site became evident in Tat transactivation studies, in which the loss of the site reduced Tat-transactivated expression 40-fold. In contrast, elimination of the 5' site had no effect on Tat-mediated activity. Binding studies were performed to determine whether differences in PU.1 binding affinity for the three sites correlated with the relative impact of each site on LTR transcription. While small differences were observed in the binding affinities of the three sites, with the promoter-proximal site having the strongest binding affinity, these differences could not account for the dramatic differences observed in the transcriptional effects. Instead, the promoter-proximal position of the 3' motif appeared to be critical for its transcriptional impact and suggested that the PU.1 sites may serve different roles depending upon the location of the sites within the enhancer. Infectivity studies demonstrated that an LTR containing an enhancer composed of the three PU.1 sites was not sufficient to drive viral replication in macrophages. These findings indicate that while the promoter-proximal PU.1 site is the most critical site for EIAV LTR activity in the presence of Tat, other elements within the enhancer are needed for EIAV replication in macrophages.

Fcgamma receptor-mediated suppression of human immunodeficiency virus type 1 replication in primary human macrophages.

Permissiveness of monocytes and macrophages to human immunodeficiency virus (HIV) infection is modulated by various stimuli. In this study we demonstrate that stimulation of primary monocytes and monocyte-derived macrophages (MDM) through the receptors for the Fc portion of immunoglobulin G (IgG) (FcgammaR) inhibits HIV type 1 (HIV-1) replication. Viral p24 production was decreased by 1.5 to 3 log units in MDM infected with both R5 and X4 HIV-1 strains upon stimulation by immobilized IgG but not upon stimulation by soluble IgG or by F(ab')(2) IgG fragments. Although MDM activation by immobilized IgG induced high levels of macrophage-derived chemokine secretion as well as a sustained down-regulation of CD4 and a transient decrease in CCR5 expression, these factors did not appear to play a major role in the suppression of HIV-1 replication. Single-cycle infection of FcgammaR-stimulated MDM with HIV-1 virions pseudotyped with either HIV-1 R5 or vesicular stomatitis virus G envelopes was inhibited, suggesting a postentry restriction of viral replication. PCR analyses of HIV-1 DNA intermediate replication forms suggested that reverse transcription is not affected by stimulation with immobilized human IgG, at least during the first replication cycle. The accumulation of PCR products corresponding to nuclear unintegrated two-long-terminal-repeat circles and the relative decrease of integrated HIV-1 DNA signals suggest an inhibition of proviral integration. Our data, showing that FcgammaR-mediated activation of MDM is a potent mechanism of HIV-1 suppression, raise the possibility that FcgammaR cross-linking by immune complexes may contribute to the control of viral replication in macrophages.

Glucocorticoid regulation of lactate dehydrogenase-elevating virus replication in macrophages

Lactate dehydrogenase-elevating virus (LDV) is a macrophage-tropic arterivirus which generally causes a persistent viremic infection in mice. LDV replication in vivo seems to be primarily regulated by the extent and dynamics of a virus-permissive macrophage population. Previous studies have shown that glucocorticoid treatment of chronically LDV-infected mice transiently increases viremia 10–100-fold, apparently by increasing the productive infection of macrophages. We have further investigated this phenomenon by comparing the effect of dexamethasone on the in vivo and in vitro replication of two LDV quasispecies that differ in sensitivity to immune control by the host. The single neutralizing epitope of LDV-P is flanked by two N-glycans that impair its immunogenicity and render LDV-P resistant to antibody neutralization. In contrast, replication of the neuropathogenic mutant LDV-C is suppressed by antibody neutralization because its epitope lacks the two protective N-glycans. Dexamethasone treatment of mice 16 h prior to LDV-P infection, or of chronically LDV-P infected mice, stimulated viremia 10–100-fold, which correlated with an increase of LDV permissive macrophages in the peritoneum and increased LDV infected cells in the spleen, respectively. The increase in viremia occurred in the absence of changes in total anti-LDV and neutralizing antibodies. The results indicate that increased viremia was due to increased availability of LDV permissive macrophages, and that during a chronic LDV-P infection virus replication is strictly limited by the rate of regeneration of permissive macrophages. In contrast, dexamethasone treatment had no significant effect on the level of viremia in chronically LDV-C infected mice, consistent with the view that LDV-C replication is primarily restricted by antibody neutralization and not by a lack of permissive macrophages. β-Glucan, the receptor of which is induced on macrophages by dexamethasone treatment, had no effect on the LDV permissiveness of macrophages.

Insights into the biology of HIV-1 viral protein R.

HIV-1 viral protein R (Vpr) is a small, highly conserved accessory protein encoded by the HIV genome that serves many functions in the viral life cycle. Vpr induces G2 cell cycle arrest, which is thought to indirectly enhance viral replication by increasing transcription from the LTR. Vpr has also been implicated in facilitating infection of nondividing cells, most notably macrophages. Because Vpr is a nucleo-cytoplasmic shuttling protein, its role in enhancing viral replication in macrophages may be mediated through enhanced entry of the HIV preintegration complex through the limiting nuclear pore. Free Vpr is detectable in the serum of patients, and in vitro studies implicate extracellular forms of Vpr as an effector of cellular responses mediated through its ability to transduce through intact cytoplasmic membranes. We review the biologic properties of Vpr, focusing on its mechanism of action, role in HIV replication, and significance for host pathogenesis.

Temporal relationship between V1V2 variation, macrophage replication, and coreceptor adaptation during HIV-1 disease progression.

Specific mutations in VPR and V2 potentially restrict HIV-1 replication in macrophages. Such restriction could potentially limit HIV replication in long-term non-progressors (LTNP), thus accounting for low viral load and delayed progression to AIDS. To examine whether a specific VPR phenotype (truncated versus non-truncated) correlates with disease progression and whether elongated V2 restricts viral replication in macrophages or alters viral tropism. Sequence analysis was carried for VPR and V1-V3 env from four rapid progressors (RPs), six late progressors (LPs), and three LTNPs in cohort of HIV-1-infected homosexual men. The replication kinetics of sequential isolates was examined in primary CD4 cells and macrophages and coreceptor usage was determined by GHOST infection assays. No differences were found in the VPR protein from RP and LTNP isolates. Analysis of the V2 region revealed that all RPs maintained similar V2 lengths (40 aa), whereas LPs and LTNPs acquired additional amino acids (2-13 aa) in the V2 region. Coreceptor specificity revealed that RP switch from CCR5 to multiple coreceptor usage, whereas LTNPs maintained R5 viruses. Sequential isolates from each group revealed comparable replication efficiencies in both T-cells and macrophages, regardless of the V2 length or coreceptor utilization. In addition, cross-section analysis of six LTNPs from Australia revealed extended V2 with consistent usage of CCR5 coreceptor. The present results suggest that acquisition of a V2 extension over time in HIV-1-infected LPs/LTNPs appears to correlate with maintenance of CCR5 usage among LTNPs. These findings may be important for a better understanding of the host interactions and disease progression.

Granulocyte macrophage colony stimulating factor is elevated in alveolar macrophages from sheep naturally infected with maedi-visna virus and stimulates maedi-visna virus replication in macrophages in vitro.

Infection by maedi-visna virus, a lentivirus of sheep, leads to chronic inflammatory reactions of various tissues. In this report we have analysed the role of specific cytokines in the disease process. A significant increase in expression of interleukin-6, interleukin-10, granulocyte macrophage-colony stimulating factor (GM-CSF) and transforming growth factor-beta1 mRNA was observed in alveolar macrophages isolated from the lungs of naturally infected animals when compared with lungs of seronegative controls. Levels of GM-CSF mRNA expression in alveolar macrophages correlated with the presence of lung lesions, but there was no correlation of interleukin-10, interleukin-6, tumour necrosis factor-alpha and transforming growth factor-beta1 mRNA levels in alveolar macrophages from animals with pulmonary lesions. In vitro investigation showed that GM-CSF in the range 0.1-10 ng/ml induced a significant increase in viral p25 production after 7 days in acutely infected blood monocyte-derived macrophages. The production of p25 peaked between 7 and 14 days exposure to 10 ng/ml of GM-CSF. Quantitative polymerase chain reaction showed that the level of viral DNA in monocyte-derived macrophages was dose-dependent following GM-CSF treatment in the range 0.1-100 ng/ml after 7 days. Viral mRNA expression was also enhanced. These findings indicate a role for GM-CSF in the pathogenesis of lymphoid interstitial pneumonia in infected animals.

Phosphorylation of Vpr regulates HIV type 1 nuclear import and macrophage infection.

Viral protein R (Vpr) of human immunodeficiency virus type 1 (HIV-1) is a small accessory protein that regulates nuclear import of the viral preintegration complex and facilitates infection of nondividing cells, such as macrophages. Studies demonstrated that a fraction of Vpr molecules is phosphorylated in the virions and in HIV-1-infected cells, but the role of phosphorylation in nuclear import activity of Vpr has not been established. We found that Vpr is phosphorylated predominantly on the serine residue in position 79, and mutations affecting Vpr phosphorylation significantly attenuated viral replication in macrophages, but not in activated T lymphocytes or cell lines. The replication defect was mapped by polymerase chain reaction analysis to the step of nuclear import. These results suggest that phosphorylation of Vpr regulates its activity in the nuclear import of the HIV-1 preintegration complex.

Antibodies that neutralize SIV(mac)251 in T lymphocytes cause interruption of the viral life cycle in macrophages by preventing nuclear import of viral DNA.

Previous reports from our lab had shown that sera obtained from SIV(mac)-infected animals neutralized SIV(mac) infectivity in CD4(+) T cells but failed to protect monkey primary macrophages from infection with the virus. However, the antibodies could inhibit completion of the viral life cycle in the macrophages at the postentry stage(s). In this report we examined the mechanisms of the late effect of the antibodies. Using monoclonal antibodies (MAbs), we demonstrated that only antibodies to the SIV envelope protein (KK17 and KK42) but not antibody to the viral core protein (FA2) had the same inhibitory effect as that of the anti-SIV sera. To identify the stage of the viral replication cycle that was inhibited by anti-SIV antibodies in macrophages, we used various PCR techniques to study viral entry/reverse transcription (by amplifying the viral gag gene), viral genome nuclear transport (by amplifying 2-LTR circular forms), viral integration (by Alu-PCR assay), and viral protein expression (by RIPA). We found that in macrophage cultures inoculated with SIV(mac)251 that were preincubated with antienvelope MAbs, viral DNA was detected at 8 h postinoculation but the 2-LTR circular forms and integrated viral DNAs were undetectable, and viral proteins were not expressed in these infected macrophages. These results strongly suggested that anti-SIV antibodies inhibited SIV(mac) replication in macrophages by blocking nuclear transport of viral genomes since viral DNA could not be detected in the nuclei of treated cultures. Furthermore, we showed that although viral replication in macrophages was interrupted by the antibodies, when cocultured with permissive T cells, the viral genomes presented in the cytoplasm of the macrophages could readily transfer to T cells during cell-cell contact. Importantly, this transfer could not be prevented by the antibodies. These results might explain the failure of passive antibody immunization against SIV(mac)251--a critical obstacle in AIDS vaccine development.

Role of nitric oxide synthase type 2 in acute infection with murine cytomegalovirus.

Whether or not NO plays a critical role in murine CMV (MCMV) infection has yet to be elucidated. In this study, we examined the role of NO in acute infection with MCMV using NO synthase type 2 (NOS2)-deficient mice. NOS2(-/-) mice were more susceptible to lethal infection with MCMV than NOS2(+/+) mice and generated a much higher peak virus titer in the salivary gland after acute infection. A moderate increase in the MCMV titer was also observed in other organs of NOS2(-/-) mice such as the spleen, lung, and liver. The immune responses to MCMV infection including NK cell cytotoxicity and CTL response in NOS2(-/-) mice were comparable with those of NOS2(+/+) mice. Moreover, the ability to produce IFN-gamma is not impaired in NOS2(-/-) mice after MCMV infection. The peritoneal macrophages from NOS2(-/-) mice, however, exhibited a lower antiviral activity than those from NOS2(+/+) mice, resulting in an enhanced viral replication in macrophages themselves. Treatment of these cells from NOS2(+/+) mice with a selective NOS2 inhibitor decreased the antiviral activity to a level below that obtained with NOS2(-/-) mice. In addition, the absence of NOS2 and NOS2-mediated antiviral activity of macrophages resulted in not only an enhanced MCMV replication and a high mortality but also a consequent risk of the latency. It was thus concluded that the NOS2-mediated antiviral activity of macrophages via NO plays a protective role against MCMV infection at an early and late stage of the infection.

Small molecule inhibitor of HIV-1 nuclear import suppresses HIV-1 replication in human lymphoid tissue ex vivo: a potential addition to current anti-HIV drug repertoire

Despite recent progress in anti-HIV therapy, which has to do mainly with introduction of protease inhibitors into clinical practice, drug toxicity and emergence of drug-resistant isolates during the long-term treatment of the patients necessitates search for new drugs that can be added to currently used components of a multi-drug cocktail in highly active anti-retroviral therapy (HAART). Recently, we described a class of arylene bis(methylketone) compounds that inhibit nuclear import of HIV-1 pre-integration complexes and suppress viral replication in macrophages and PBMC in vitro. In this report, we demonstrate that one of these compounds, CNI-H1194, inhibited HIV-1 replication in primary lymphoid tissue ex vivo. The compound did not antagonize the activity of currently used anti-HIV drugs that inhibit viral reverse transcriptase or protease. These results suggest that arylene bis(methylketone) compounds might be a valuable addition to HAART.

Macrophage colony-stimulating factor antagonists inhibit replication of HIV-1 in human macrophages.

Macrophages infected with HIV-1 produce high levels of M-CSF and macrophage-inflammatory protein-1alpha (MIP-1alpha). M-CSF facilitates the growth and differentiation of macrophages, while the chemotactic properties of MIP-1alpha attract both T lymphocytes and macrophages to the site of HIV infection. Studies described in this work indicate M-CSF may function in an autocrine/paracrine manner to sustain HIV replication, and data suggest possible therapeutic strategies for decreasing viral load following HIV infection. We show that macrophage infection with measles virus or respiratory syncytial virus, in contrast to HIV-1, results in production of MIP-1alpha, but not M-CSF. Thus, M-CSF appears to be specifically produced upon infection of macrophages with HIV-1. Furthermore, addition of M-CSF antagonists to HIV-1-infected macrophages, including anti-M-CSF monoclonal or polyclonal Abs or soluble M-CSF receptors, dramatically inhibited HIV-1 replication and reduced production of MIP-1alpha. Our results suggest that biologic antagonists for M-CSF may represent novel strategies for inhibiting the spread of HIV-1 by 1) blocking virus replication in macrophages, 2) reducing recruitment of HIV-susceptible T cells and macrophages by MIP-1alpha, and 3) preventing the establishment and maintenance of infected macrophages as a reservoir for HIV.

Effects of MS-8209, an amphotericin B derivative, on tumor necrosis factor alpha synthesis and human immunodeficiency virus replication in macrophages.

Amphotericin B derivatives, such as MS-8209, have been evaluated as a therapeutic approach to human immunodeficiency virus (HIV) infection. We show that MS-8209, like amphotericin B, increases tumor necrosis factor alpha (TNF-alpha) mRNA expression and TNF-alpha production and consequently HIV replication in human macrophages. These effects confirm the pharmacological risk associated with the administration of amphotericin B or its derivatives to HIV-infected patients.

IFN gamma inhibits porcine reproductive and respiratory syndrome virus replication in macrophages.

This study reports the effect of IFN gamma on the replication of porcine reproductive and respiratory syndrome virus (PRRSV) in macrophages. Pretreatment with IFN gamma profoundly affected PRRSV replication in porcine macrophages evaluated by reduction in titer and percentage of positive cells. The effect of IFN gamma on PRRSV replication was both dose-dependent and related to the time of exposure. The mechanism of action was not due to blocking virus attachment. The inhibitory effect on PRRSV replication in macrophages suggests that IFN gamma may play an important role in protection.

Macrophage cytoplasmic vesicle pH gradients and vacuolar H+-ATPase activities relative to virus infection.

A number of viruses replicate in macrophages, some having an obligate requirement for a macrophage host. This raised the question concerning the role of the macrophage endosomal/lysosomal compartment during such infections. Both lysosomotropic weak bases, amantadine and chloroquine, which interfere with endosomal/lysosomal pH gradients, and the macrolide antibiotic bafilomycin A1, which interferes with vacuolar H+-ATPase, inhibited African swine fever (ASF) virus replication in porcine macrophages. This inhibition was reversible: replenishment of bafilomycin, but not amantadine or chloroquine, maintained the inhibition. The characteristics of the inhibition, and the capacity of virus to escape and re-commence replication, related to the capacity of each drug to interfere with the endosomal/lysosomal proton pump. These results demonstrate that the virus actually requires macrophage endosomal/lysosomal activity for its replication. Therein, vacuolar H+-ATPase activity is particularly critical for successful virus replication, which is interesting considering the importance of this for endosomal/lysosomal activity and macrophage function.

Role of the beta-chemokine receptors CCR3 and CCR5 in human immunodeficiency virus type 1 infection of monocytes and microglia.

Human immunodeficiency virus type 1 (HIV-1) infection in mononuclear phagocyte lineage cells (monocytes, macrophages, and microglia) is a critical component in the pathogenesis of viral infection. Viral replication in macrophages serves as a reservoir, a site of dissemination, and an instigator for neurological sequelae during HIV-1 disease. Recent studies demonstrated that chemokine receptors are necessary coreceptors for HIV-1 entry which determine viral tropism for different cell types. To investigate the relative contribution of the beta-chemokine receptors CCR3 and CCR5 to viral infection of mononuclear phagocytes we utilized a panel of macrophage-tropic HIV-1 strains (from blood and brain tissue) to infect highly purified populations of monocytes and microglia. Antibodies to CD4 (OKT4A) abrogated HIV-1 infection. The beta chemokines and antibodies to CCR3 failed to affect viral infection of both macrophage cell types. Antibodies to CCR5 (3A9) prevented monocyte infection but only slowed HIV replication in microglia. Thus, CCR5, not CCR3, is an essential receptor for HIV-1 infection of monocytes. Microglia express both CCR5 and CCR3, but antibodies to them fail to inhibit viral entry, suggesting the presence of other chemokine receptors for infection of these cells. These studies demonstrate the importance of mononuclear phagocyte heterogeneity in establishing HIV-1 infection and persistence.

Role of nitric oxide in the regulation of lymphocyte apoptosis and HIV-1 replication

Nitric oxide (NO) has been implicated in certain immunopathogenetic mechanisms during the course of infection with human immunodeficiency virus (HIV). We have evaluated the levels of NO release and lymphocyte apoptosis in peripheral blood mononuclear cell (PBMC) cultures from HIV-1 infected subjects and healthy controls. We have also examined these 2 parameters in parallel cultures maintained under conditions where either NO synthesis was inhibited or high level of NO was present. Nitrite contents in culture supernatants were measured as the stable end products of the released NO. Levels of spontaneous apoptosis and activation-induced cell death (AICD) by anti-CD3 or by phytohemagglutinin were evaluated using flow cytometry. Additional experiments were also aimed at addressing a potential link between NO synthesis and HIV-1 replication in human monocyte-derived macrophages (MDMs). Acutely infected MDMs with HIV-1Bal were maintained in culture, without any additional activation signal, for a period of 14 days. Nitrites in the supernatants and mRNA accumulation of the inducible NO synthase (iNOS) in infected cells were assessed over the whole culture period. In addition, the effect of blocking NO synthesis during and after infection of MDMs, using an inhibitor of NO, was evaluated on the level of viral replication as measured by the presence of P24 antigen in the supernatants. Similarly, the effect on HIV replication of high NO levels in MDM cultures, supplied by a donor of NO during the 24 h period of infection, was also studied. We conclude that no elevation in NO release could be detected in PBMC cultures from HIV-1 infected subjects and that modulation of NO content may slightly regulate the level of spontaneous lymphocyte apoptosis but not that of AICD. Infection of MDMs with HIV-1 does not seem to induce detectable NO release or iNOS mRNA accumulation. Similarly, neither inhibition of NO synthesis nor the presence of high NO levels during the infection period could modify the outcome of virus replication in macrophages.

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.