Isolation and Characterization of a Replication-Competent Molecular Clone of an HIV-1 Circulating Recombinant Form (CRF33_01B)

A growing number of emerging HIV-1 recombinants classified as circulating recombinant forms (CRFs) have been identified in Southeast Asia in recent years, establishing a molecular diversity of increasing complexity in the region. Here, we constructed a replication-competent HIV-1 clone for CRF33_01B (designated p05MYKL045.1), a newly identified recombinant comprised of CRF01_AE and subtype B. p05MYKL045.1 was reconstituted by cloning of the near full-length HIV-1 sequence from a newly-diagnosed individual presumably infected heterosexually in Kuala Lumpur, Malaysia. The chimeric clone, which contains the 5′ LTR (long terminal repeat) region of p93JP-NH1 (a previously isolated CRF01_AE infectious clone), showed robust viral replication in the human peripheral blood mononuclear cells. This clone demonstrated robust viral propagation and profound syncytium formation in CD4⁺, CXCR4-expressing human glioma NP-2 cells, indicating that p05MYKL045.1 is a CXCR4-using virus. Viral propagation, however, was not detected in various human T cell lines including MT-2, M8166, Sup-T1, H9, Jurkat, Molt-4 and PM1. p05MYKL045.1 appears to proliferate only in restricted host range, suggesting that unknown viral and/or cellular host factors may play a role in viral infectivity and replication in human T cell lines. Availability of a CRF33_01B molecular clone will be useful in facilitating the development of vaccine candidates that match the HIV-1 strains circulating in Southeast Asia.     

Cadmium resistance in A549 cells correlates with elevated glutathione content but not antioxidant enzymatic activities

Glutathione has been implicated to function in cytoprotection against cadmium toxicity. The mechanism by which glutathione plays this role has not been well understood. Because glutathione is an important antioxidant and several studies have shown that cadmium induces oxidative stress, this study was undertaken to determine whether development of cadmium resistance is linked to enhanced antioxidant activities. A cadmium-resistant subpopulation of human lung carcinoma A549 cells, which was developed by repeatedly exposing the cells to step-wise increased cadmium concentrations, was compared to a cadmium-sensitive one. The acquired cadmium resistance resulted from neither decreased cadmium uptake nor enhanced cellular metallothionein synthesis. Glutathione content, however, was markedly elevated in the cadmium-resistant cells. In contrast, the activities of the glutathione redox cycle related enzymes, glutathione peroxidase and reductase, were unchanged. Two other antioxidant enzymes, superoxide dismutase and catalase, were also not altered. The results suggest that the development of cadmium resistance in A549 cells unlikely results from enhanced antioxidant enzyme activities, although it is associated with elevated cellular glutathione levels. In addition, measurement of the mRNA and DNA levels for γ-glutamyleysteine synthetase, the rate-limiting enzyme for glutathione biosynthesis, revealed that enhanced expression of the enzyme but not gene amplification is likely responsible for the elevation of cellular glutathione levels.     

<Emphasis Type="Italic">ENPP1</Emphasis> 121Q functional variant enhances susceptibility to coronary artery disease in South Indian patients with type 2 diabetes mellitus

Resveratrol is a dietary polyphenol that displays neuroprotective properties in several in vivo and in vitro experimental models, by modulating oxidative and inflammatory responses. Glutathione (GSH) is a key antioxidant in the central nervous system (CNS) that modulates several cellular processes, and its depletion is associated with oxidative stress and inflammation. Therefore, this study sought to investigate the protective effects of resveratrol against GSH depletion pharmacologically induced by buthionine sulfoximine (BSO) in C6 astroglial cells, as well as its underlying cellular mechanisms. BSO exposure resulted in several detrimental effects, decreasing glutamate-cysteine ligase (GCL) activity, cystine uptake, GSH intracellular content and the activities of the antioxidant enzymes glutathione peroxidase (GPx) and glutathione reductase (GR). Moreover, BSO increased reactive oxygen/nitrogen species (ROS/RNS) levels and pro-inflammatory cytokine release. Resveratrol prevented these effects by protecting astroglial cells against BSO-induced cytotoxicity, by modulating oxidative and inflammatory responses. Additionally, we observed that pharmacological inhibition of heme oxygenase 1 (HO-1), an essential cellular defense against oxidative and inflammatory injuries, abolished all the protective effects of resveratrol. These observations suggest HO-1 pathway as a cellular effector in the mechanism by which resveratrol protects astroglial cells against GSH depletion, a condition that may be associated to neurodegenerative diseases.     

The metabolic function of hepatocytes differentiated from human mesenchymal stem cells is inversely related to cellular glutathione levels

Differentiation of mesenchymal stem cells (MSCs) to hepatocytes‐like cells is associated with alteration in the level of reactive oxygen species (ROS) and antioxidant defense system. Here, we report the role of glutathione in the functions of hepatocytes derived from MSCs. The stem cells undergoing differentiation were treated with glutathione modifiers [buthionine sulfoxide (BSO) or N‐acetyl cysteine (NAC)], and hepatocytes were collected on day 14 of differentiation and analysed for their biological and metabolic functions. Differentiation process has been performed in presence of glutathione modifiers viz. BSO and NAC. Depending on the level of cellular glutathione, the proliferation rate of MSCs was affected. Glutathione depletion by BSO resulted in increased levels of albumin and ROS in hepatocytes. Whereas, albumin and ROS were inhibited in cells treated with glutathione precursor (NAC). The metabolic function of hepatocytes was elevated in BSO‐treated cells as judged by increased urea, transferrin, albumin, alanine transaminase and aspartate transaminase secretions in the media. However, the metabolic activity of the hepatocytes was inhibited when glutathione was increased by NAC. We conclude that the efficiency of metabolic function of hepatocytes is inversely related to the levels of cellular glutathione. These data may suggest a novel role of glutathione in regulation of metabolic function of hepatocytes. Copyright © 2013 John Wiley & Sons, Ltd.     

HIV-1 Tat potentiates TNF-induced NF-kappa B activation and cytotoxicity by altering the cellular redox state.

This study demonstrates that human immunodeficiency virus type 1 (HIV-1) Tat protein amplifies the activity of tumor necrosis factor (TNF), a cytokine that stimulates HIV-1 replication through activation of NF-kappa B. In HeLa cells stably transfected with the HIV-1 tat gene (HeLa-tat cells), expression of the Tat protein enhanced both TNF-induced activation of NF-kappa B and TNF-mediated cytotoxicity. A similar potentiation of TNF effects was observed in Jurkat T cells and HeLa cells treated with soluble Tat protein. TNF-mediated activation of NF-kappa B and cytotoxicity involves the intracellular formation of reactive oxygen intermediates. Therefore, Tat-mediated effects on the cellular redox state were analyzed. In both T cells and HeLa cells HIV-1 Tat suppressed the expression of Mn-dependent superoxide dismutase (Mn-SOD), a mitochondrial enzyme that is part of the cellular defense system against oxidative stress. Thus, Mn-SOD RNA protein levels and activity were markedly reduced in the presence of Tat. Decreased Mn-SOD expression was associated with decreased levels of glutathione and a lower ratio of reduced:oxidized glutathione. A truncated Tat protein (Tat1-72), known to transactivate the HIV-1 long terminal repeat (LTR), no longer affected Mn-SOD expression, the cellular redox state or TNF-mediated cytotoxicity. Thus, our experiments demonstrate that the C-terminal region of HIV-1 Tat is required to suppress Mn-SOD expression and to induce pro-oxidative conditions reflected by a drop in reduced glutathione (GSH) and the GSH:oxidized GSH (GSSG) ratio.(ABSTRACT TRUNCATED AT 250 WORDS)     

Radiosensitivity of mammalian cell lines engineered to overexpress cytosolic glutathione peroxidase

Reactive oxygen species are believed to be involved in radiation lethality. Glutathione peroxidase is an intracellular enzyme with antioxidant functions. To determine whether increasing the cellular antioxidant capacity can confer radiation resistance, the effect of overexpression of glutathione peroxidase on radiosensitivity was determined in two different cell types. An expression construct including the bovine cytosolic glutathione peroxidase cDNA was used to overexpress this enzyme in cells of the human lymphoblast cell line Sup-T1 as well as the Chinese hamster ovary cell line AA8. Supplementation of the culture media with 30 nM sodium selenite was included to obtain optimal glutathione peroxidase activity. Northern blot analysis confirmed the presence of the construct mRNA, and a standard coupled spectrophotometric assay demonstrated significantly increased glutathione peroxidase activity in the transfected cell lines. An approximately 8-fold increase was found in the Sup-T1 cells, and an approximately 30-fold increase was obtained in the Chinese hamster ovary AA8 cells. Clonogenic survival was assayed in the overexpressing cells and compared to that in control cells transfected with vector alone. Despite significantly increased glutathione peroxidase activity, no observable radioprotection was conferred in either of the two cell lines studied, indicating that increased glutathione peroxidase activity is insufficient to confer radioresistance in the two cell types examined. These data are discussed in the context of using antioxidants as adjuncts to clinical radiotherapy.     

Alpha interferon inhibits early stages of the human immunodeficiency virus type 1 replication cycle.

In this study, we have analyzed the effect of human alpha interferon (IFN-alpha) on a single replication cycle of human immunodeficiency virus type 1 (HIV-1) infection in the lymphocytic cell line CEM-174, which is highly sensitive to the antiviral effects of IFN. Pretreatment of cells with 50 to 500 U of recombinant human IFN-alpha per ml resulted in a marked reduction in viral RNA and protein synthesis. The effect of IFN-alpha was dose dependent and was amplified in multiple infection cycles. IFN-induced inhibition of viral protein synthesis could be detected only when cells were treated with IFN-alpha prior to infection or when IFN-alpha was added up to 10 h postinfection, but not if IFN-alpha was added at the later stages of HIV-1 replication cycle or after the HIV-1 infection was already established. Analysis of the integrated HIV-1 provirus showed a marked decrease in the levels of proviral DNA in IFN-treated cells. Thus, in contrast to the previous studies on established HIV-1 infection in T cells, in which the IFN block appeared to be at the posttranslational level, during de novo infection, IFN-alpha interferes with an early step of HIV-1 replication cycle that occurs prior to the integration of the proviral DNA. These results indicate that the early IFN block of HIV-1 replication, which has been previously observed only in primary marcophages, can also be detected in the IFN-sensitive T cells, indicating that the early IFN block is not limited to macrophages.     

Cyclin K inhibits HIV-1 gene expression and replication by interfering with cyclin-dependent kinase 9 (CDK9)-cyclin T1 interaction in Nef-dependent manner

Human immunodeficiency virus-1 (HIV-1) exploits a number of host cellular factors for successful survival and propagation. The viral protein Nef plays an important role in HIV-1 pathogenesis by interacting with various cellular proteins. In the present work, we identified Cyclin K (CycK) as a novel Nef-interacting protein, and for the first time, we showed that CycK inhibits HIV-1 gene expression and replication in a Nef-dependent manner. The positive elongation factor b complex comprising cyclin-dependent kinase 9 (CDK9) and Cyclin T1 is a critical cellular complex required for viral gene expression and replication. Enhanced expression of CycK in the presence of Nef induced CycK-CDK9 binding, which prevented CDK9-Cyclin T1 complex formation and nuclear translocation of CDK9, resulting in inhibition of HIV-1 long terminal repeat-driven gene expression. Furthermore, this effect of CycK was not observed with Nef-deleted virus, indicating the importance of Nef in this phenomenon. Finally, silencing of CycK in HIV-1-infected cells resulted in increased translocation of CDK9 into the nucleus, leading to increased viral gene expression and replication. These data also suggest that endogenous CycK might act as an inhibitory factor for HIV-1 gene expression and replication in T-cells. Thus, our results clearly demonstrate that CycK utilizes HIV-1 Nef protein to displace CycT1 from the positive elongation factor b complex, resulting in inhibition of HIV-1 gene expression and replication.     

HIV-1-specific interleukin-21+ CD4+ T cell responses contribute to durable viral control through the modulation of HIV-specific CD8+ T cell function

Functional defects in cytotoxic CD8(+) T cell responses arise in chronic human viral infections, but the mechanisms involved are not well understood. In mice, CD4 cell-mediated interleukin-21 (IL-21) production is necessary for the maintenance of CD8(+) T cell function and control of persistent viral infections. To investigate the potential role of IL-21 in a chronic human viral infection, we studied the rare subset of HIV-1 controllers, who are able to spontaneously control HIV-1 replication without treatment. HIV-specific triggering of IL-21 by CD4(+) T cells was significantly enriched in these persons (P = 0.0007), while isolated loss of IL-21-secreting CD4(+) T cells was characteristic for subjects with persistent viremia and progressive disease. IL-21 responses were mediated by recognition of discrete epitopes largely in the Gag protein, and expansion of IL-21(+) CD4(+) T cells in acute infection resulted in lower viral set points (P = 0.002). Moreover, IL-21 production by CD4(+) T cells of HIV controllers enhanced perforin production by HIV-1-specific CD8(+) T cells from chronic progressors even in late stages of disease, and HIV-1-specific effector CD8(+) T cells showed an enhanced ability to efficiently inhibit viral replication in vitro after IL-21 binding. These data suggest that HIV-1-specific IL-21(+) CD4(+) T cell responses might contribute to the control of viral replication in humans and are likely to be of great importance for vaccine design.     

Generation of cytotoxic T cells against virus-infected human brain macrophages in a murine model of HIV-1 encephalitis

HIV-1 encephalitis (HIVE) and its associated dementia can occur in up to 20% of infected individuals, usually when productive viral replication in brain mononuclear phagocytes (macrophages and microglia) and depletion of CD4(+) T lymphocytes are most significant. T cells control viral replication through much of HIV-1 disease, but how this occurs remains incompletely understood. With this in mind, we studied HIV-1-specific CTL responses in a nonobese diabetic (NOD)-SCID mouse model of HIVE. HIV-1-infected monocyte-derived macrophages (MDM) were injected into the basal ganglia after syngeneic immune reconstitution by HLA-A*0201-positive human PBL to generate a human PBL-NOD-SCID HIVE mouse. Engrafted T lymphocytes produced HIV-1gag- and HIV-1pol-specific CTL against virus-infected brain MDM within 7 days. This was demonstrated by tetramer staining of human PBL in mouse spleens and by IFN-gamma ELISPOT. CD8, granzyme B, HLA-DR, and CD45R0 Ag-reactive T cells and CD79alpha-positive B cells migrated to and were in contact with human MDM in brain areas where infected macrophages were abundant. The numbers of productively infected MDM were markedly reduced (>85%) during 2 wk of observation. The human PBL-NOD-SCID HIVE mouse provides a new tool for studies of cellular immune responses against HIV-1-infected brain mononuclear phagocytes during natural disease and after vaccination.     

GCN2 Has Inhibitory Effect on Human Immunodeficiency Virus-1 Protein Synthesis and Is Cleaved upon Viral Infection

The reversible phosphorylation of the alpha-subunit of eukaryotic translation initiation factor 2 (eIF2alpha) is a well-characterized mechanism of translational control in response to a wide variety of cellular stresses, including viral infection. Beside PKR, the eIF2alpha kinase GCN2 participates in the cellular response against viral infection by RNA viruses with central nervous system tropism. PKR has also been involved in the antiviral response against HIV-1, although this antiviral effect is very limited due to the distinct mechanisms evolved by the virus to counteract PKR action. Here we report that infection of human cells with HIV-1 conveys the proteolytic cleavage of GCN2 and that purified HIV-1 and HIV-2 proteases produce direct proteolysis of GCN2 in vitro, abrogating the activation of GCN2 by HIV-1 RNA. Transfection of distinct cell lines with a plasmid encoding an HIV-1 cDNA clone competent for a single round of replication resulted in the activation of GCN2 and the subsequent eIF2alpha phosphorylation. Moreover, transfection of GCN2 knockout cells or cells with low levels of phosphorylated eIF2alpha with the same HIV-1 cDNA clone resulted in a marked increase of HIV-1 protein synthesis. Also, the over-expression of GCN2 in cells led to a diminished viral protein synthesis. These findings suggest that viral RNA produced during HIV-1 infection activates GCN2 leading to inhibition of viral RNA translation, and that HIV-1 protease cleaves GCN2 to overcome its antiviral effect.     

Persistent human immunodeficiency virus type 1 infection in human fetal glial cells reactivated by T-cell factor(s) or by the cytokines tumor necrosis factor alpha and interleukin-1 beta.

Human immunodeficiency virus type 1 (HIV-1) infection of the brain has been associated with a severe dementing illness in children and adults. However, HIV-1 antigens are most frequently found in macrophages and microglial cells. To determine the extent of susceptibility of neuroglial cells to infection, the HIV-1 genome was introduced into cells cultured from human fetal brain tissue. Astroglial cells rapidly transcribed the viral genome producing high levels of p24 protein and infectious virions which peaked two to three days posttransfection. Thereafter HIV-1 genome expression progressively diminished and a persistent phase of infection developed during which neither virus nor viral proteins could be demonstrated by immunodetection methods. Cocultivation with CD4+ T cells at any time during the persistent infection resulted in resumption of p24 synthesis and virus multiplication. The release of persistence did not require direct cell-cell contact between the glial and T cells, since separation of the two cell types across a permeable membrane resulted in a delayed but similar resumption of p24 synthesis and virus multiplication. The persistently infected glial cells could also be stimulated to produce viral p24 protein if either tumor necrosis factor alpha or interleukin-1 beta was added to the medium without T cells present. These results suggest that astrocytes may serve as an undetected reservoir for HIV-1 and disseminate the virus to other susceptible cells in the brain upon triggering by some cellular or biochemical signal.