HIV-1 Tat regulates the SOD2 basal promoter by altering Sp1/Sp3 binding activity

The DNA Damage Response and HIV-Associated Pulmonary Arterial Hypertension

The HIV-infected population is at a dramatically increased risk of developing pulmonary arterial hypertension (PAH), a devastating and fatal cardiopulmonary disease that is rare amongst the general population. It is increasingly apparent that PAH is a disease with complex and heterogeneous cellular and molecular pathologies, and options for therapeutic intervention are limited, resulting in poor clinical outcomes for affected patients. A number of soluble HIV factors have been implicated in driving the cellular pathologies associated with PAH through perturbations of various signaling and regulatory networks of uninfected bystander cells in the pulmonary vasculature. While these mechanisms are likely numerous and multifaceted, the overlapping features of PAH cellular pathologies and the effects of viral factors on related cell types provide clues as to the potential mechanisms driving HIV-PAH etiology and progression. In this review, we discuss the link between the DNA damage response (DDR) signaling network, chronic HIV infection, and potential contributions to the development of pulmonary arterial hypertension in chronically HIV-infected individuals.

The HIV-Tat protein interacts with Sp3 transcription factor and inhibits its binding to a distal site of the sod2 promoter in human pulmonary artery endothelial cells

Redox imbalance results in damage to cellular macromolecules and interferes with signaling pathways, leading to an inflammatory cellular and tissue environment. As such, the cellular oxidative environment is tightly regulated by several redox-modulating pathways. Many viruses have evolved intricate mechanisms to manipulate these pathways for their benefit, including HIV-1, which requires a pro-oxidant cellular environment for optimal replication. One such virulence factor responsible for modulating the redox environment is the HIV Transactivator of transcription (Tat). Tat is of particular interest as it is actively secreted by infected cells and internalized by uninfected bystander cells where it can elicit pro-oxidant effects resulting in inflammation and damage. Previously, we demonstrated that Tat regulates basal expression of Superoxide Dismutase 2 (sod2) by altering the binding of the Sp-transcription factors at regions relatively near (approx. -210 nucleotides) upstream of the transcriptional start site. Now, using in silico analysis and a series of sod2 promoter reporter constructs, we have identified putative clusters of Sp-binding sites located further upstream of the proximal sod2 promoter, between nucleotides -3400 to -210, and tested their effect on basal transcription and for their sensitivity to HIV-1 Tat. In this report, we demonstrate that under basal conditions, maximal transcription requires a cluster of Sp-binding sites in the -584 nucleotide region, which is extremely sensitive to Tat. Using chromatin immunoprecipitation (ChIP) we demonstrate that Tat results in altered occupancy of Sp1 and Sp3 at this distal Tat-sensitive regulatory element and strongly stimulated endogenous expression of SOD2 in human pulmonary artery endothelial cells (HPAEC). We also report altered expression of Sp1 and Sp3 in Tat-expressing HPAEC as well as in the lungs of HIV-1 infected humanized mice. Lastly, Tat co-immunoprecipitated with endogenous Sp3 but not Sp1 and did not alter the acetylation state of Sp3. Thus, here, we have defined a novel and important cis-acting factor in HIV-1 Tat-mediated regulation of SOD2, demonstrated that modulation of Sp1 and Sp3 activity by Tat promotes SOD2 expression in primary human pulmonary artery endothelial cells and determined that pulmonary levels of Sp3 as well as SOD2 are increased in the lungs of a mouse model of HIV infection.

The protective effect of beta-casomorphin-7 via promoting Foxo1 activity and nuclear translocation in human lens epithelial cells

PURPOSE

To investigate the protective effect of beta-casomorphin-7 (β-CM-7) in oxidative stressed human lens epithelial cells (HLECs) and to explore the possible mechanism for oxidative stress in HLECs induced by high glucose.

METHODS

We used HLECs to determine the effect of different concentrations of β-CM-7 on cell viability by 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolimol/L bromide (MTT) assay. We used flow cytometry to determine the content of reactive oxygen species (ROS) induced by oxidative stress and a bioassay kit to determine the oxidant malondialdehyde (MDA) and antioxidant enzyme superoxide dismutase (SOD) levels. We used Western blotting and an immunofluorescence assay to determine the expression of Forkhead box o1 (Foxo1), SP1, and the related protein glutathione peroxidase (GSH-px) at the molecular biology level as well as their intracellular localization.

RESULTS

The expression of Foxo1 and SP1 was weakly expressed when the glucose concentration was 40 mM/L, but was highly expressed when cells were pre-treated with an appropriate concentration of β-CM-7. After pre-treatment with β-CM-7, the cells treated with 40 mM/L glucose for 48 h showed Foxo1 was transferred to the nucleus, and the expression of SP1 was increased. The content of ROS and MDA in the HLECs that were pre-treated with β-CM-7 was lower than in those that was not pre-treated (p <0.05). Accordingly, SOD was elevated in the cells pre-treated with β-CM-7. The relative expression of GSH-px increased with increases of Foxo1 and SP1.

CONCLUSION

β-CM-7 protects HLECs from oxidative damage by upregulating the relative expression of Foxo1 and promoting Foxo1 nuclear translocation.

Redox Regulation of the Superoxide Dismutases SOD3 and SOD2 in the Pulmonary Circulation

When evaluating the role of redox-regulating signaling in pulmonary vascular diseases, it is intriguing to consider the modulation of key antioxidant enzymes like superoxide dismutase (SOD) because SOD isoforms are regulated by redox reactions, and, in turn, modulate downstream redox sensitive processes. The emerging field of redox biology is built upon understanding the regulation and consequences of tightly controlled and specific reduction-oxidation reactions that are critical for diverse cellular processes including cell signaling. Of relevance, both the site of production of specific reactive oxygen and nitrogen species and the site of the antioxidant defenses are highly compartmentalized within the cell. For example, superoxide is generated during oxidative phosphorylation in the mitochondria as well as by a number of enzymatic sources within the cytosol and at the cell membrane. In the pulmonary circulation, these sources include the mitochondrial electron transport chain, NADPH oxidases (NOX1-4, Duox1,2), nitric oxide synthases, and xanthine oxidase; this important topic has been thoroughly reviewed recently [1]. In parallel with these different cellular sites of superoxide production, the three SOD isoforms are also specifically localized to the cytosol (SOD1), mitochondria (SOD2) or extracellular compartment (SOD3). This chapter focuses on the role of redox mechanisms regulating SOD2 and SOD3, with an emphasis on these processes in the setting of pulmonary hypertension.

Oxidative Stress during HIV Infection: Mechanisms and Consequences

It is generally acknowledged that reactive oxygen species (ROS) play crucial roles in a variety of natural processes in cells. If increased to levels which cannot be neutralized by the defense mechanisms, they damage biological molecules, alter their functions, and also act as signaling molecules thus generating a spectrum of pathologies. In this review, we summarize current data on oxidative stress markers associated with human immunodeficiency virus type-1 (HIV-1) infection, analyze mechanisms by which this virus triggers massive ROS production, and describe the status of various defense mechanisms of the infected host cell. In addition, we have scrutinized scarce data on the effect of ROS on HIV-1 replication. Finally, we present current state of knowledge on the redox alterations as crucial factors of HIV-1 pathogenicity, such as neurotoxicity and dementia, exhaustion of CD4+/CD8+ T-cells, predisposition to lung infections, and certain side effects of the antiretroviral therapy, and compare them to the pathologies associated with the nitrosative stress.

Label-free proteomic analysis of PBMCs reveals gender differences in response to long-term antiretroviral therapy of HIV

The association of gender with the treatment outcome during long-term antiretroviral therapy (ART) in human immunodeficiency virus (HIV)-infected patients has been controversial. Here, we performed a comparative proteomic analysis of peripheral blood mononuclear cells (PBMC) by using a label-free shotgun method with nano-LC-MS/MS to investigate the gender differences in responses to long-term ART. This analysis enrolled 30 HIV-infected patients (16 males and 14 females), as well as 20 healthy adults (10 males and 10 females) as control. Quantitative real-time RT-PCR and immunoblotting were used to validate the results of proteomic approach. A total of 53 proteins showing differential expression (± 1.5 fold, p < 0.05) were identified in HIV-infected patients versus healthy adults. Of these proteins, 22 proteins showed identical regulation patterns in both men and women, while 31 proteins were gender-specific (21 men-specific and 10 women-specific proteins). Bioinformatics analysis indicated that long-term ART causes up-regulation of apoptosis, oxidative phosphorylation and mitochondrial dysfunction while down-regulation of oxidative stress and immune system process in men compared to women. These findings point to a concept that gender has a significant influence on the outcomes of ART at protein level and women present a potential favorable immunological pattern and recovery during long-term ART.

HIV-1, reactive oxygen species, and vascular complications

Over 1 million people in the United States and 33 million individuals worldwide suffer from HIV/AIDS. Since its discovery, HIV/AIDS has been associated with an increased susceptibility to opportunistic infection due to immune dysfunction. Highly active antiretroviral therapies restore immune function and, as a result, people infected with HIV-1 are living longer. This improved survival of HIV-1 patients has revealed a previously unrecognized risk of developing vascular complications, such as atherosclerosis and pulmonary hypertension. The mechanisms underlying these HIV-associated vascular disorders are poorly understood. However, HIV-induced elevations in reactive oxygen species (ROS), including superoxide and hydrogen peroxide, may contribute to vascular disease development and progression by altering cell function and redox-sensitive signaling pathways. In this review, we summarize the clinical and experimental evidence demonstrating HIV- and HIV antiretroviral therapy-induced alterations in reactive oxygen species and how these effects are likely to contribute to vascular dysfunction and disease.

Intestinal cell targeting of a stable recombinant Cu-Zn SOD from Cucumis melo fused to a gliadin peptide

The mRNA encoding full length chloroplastic Cu-Zn SOD (superoxide dismutase) of Cucumis melo (Cantaloupe melon) was cloned. This sequence was then used to generate a mature recombinant SOD by deleting the first 64 codons expected to encode a chloroplastic peptide signal. A second hybrid SOD was created by inserting ten codons to encode a gliadin peptide at the N-terminal end of the mature SOD. Taking account of codon bias, both recombinant proteins were successfully expressed and produced in Escherichia coli. Both recombinant SODs display an enzymatic activity of ~5000U mg(-1) and were shown to be stable for at least 4h at 37°C in biological fluids mimicking the conditions of intestinal transit. These recombinant proteins were capable in vitro, albeit at different levels, of reducing ROS-induced-apoptosis of human epithelial cells. They also stimulated production and release in a time-dependent manner of an autologous SOD activity from cells located into jejunum biopsies. Nevertheless, the fused gliadin peptide enable the recombinant Cu-Zn SOD to maintain a sufficiently sustained interaction with the intestinal cells membrane in vivo rather than being eliminated with the flow. According to these observations, the new hybrid Cu-Zn SOD should show promise in applications for managing inflammatory bowel diseases.

EGCG inhibits Tat-induced LTR transactivation: role of Nrf2, AKT, AMPK signaling pathway

AIMS

Transcription is a crucial step for human immunodeficiency virus 1 (HIV-1) gene expression in infected host cells. The HIV-1 Tat activates the nuclear factor-kappa B (NF-κB) signaling transduction pathway, which is necessary for viral replication. Epigallocatechin-3-gallate (EGCG) has antioxidant, anti-inflammatory, and anti-viral properties. In this study, we investigated the effects of EGCG on Tat-induced HIV-1 transactivation and potential mechanisms by which EGCG inhibited activation of NF-κB pathway.

MAIN METHODS

HeLa-CD4-long terminal repeat (LTR)-β-gal (MAGI) cells were transfected with Tat plasmid. Tat-induced HIV-1 LTR transactivation was determined by MAGI cell assay. The reactive oxygen species (ROS) levels and glutathione (GSH) levels were measured. In addition, the protein expressions were assayed by western blotting.

KEY FINDINGS

Tat caused a significant decrease in the intracellular glutathione (GSH) levels, a mild increase in the expression of nuclear levels of NF-E2-related factor-2 (Nrf2), a significant increase in the levels of NF-κB (phosphorylation of p65 and IKK) and a significant increase in ROS production. EGCG supplementation significantly improved the changes associated with Tat-induced oxidative stress by increasing nuclear levels of Nrf2, decreasing levels of NF-κB and ROS production. EGCG reversed Tat-mediated AKT activation and AMPK inhibition in MAGI cells. EGCG inhibited Tat-induced LTR transactivation in a dose-dependent manner.

SIGNIFICANCE

The results suggest that Nrf2 signaling pathway may be the primary target for prevention of Tat-induced HIV-1 transactivation by EGCG, and EGCG also reduce NF-κB activation by inhibiting AKT signaling pathway and activating AMPK signaling pathway.

Nrf2 is involved in inhibiting Tat-induced HIV-1 long terminal repeat transactivation

HIV-1 Tat is one of six regulatory proteins that are required for viral replication and is an attractive target for the development of new anti-HIV agents. The induction of oxidative stress, as shown with Tat, may have a bearing on the transactivation mechanism of transcription. The transcription factor Nrf2 is a key player in the regulation of genes encoding many antioxidative response enzymes. Thus, the effect of Nrf2 on Tat-induced HIV-1 transcription was studied in MAGI cells. We found, for the first time, that Tat enhanced cellular expression of Nrf2 at the transcriptional and protein levels in these cells, and Tat activated antioxidant response element-driven gene expression. Tat simultaneously decreased the intracellular glutathione (GSH) levels and increased reactive oxygen species (ROS) production. The coordinated induction of ROS production, GSH depletion, and nuclear Nrf2 accumulation induced by Tat suggests that Nrf2 activation induced by Tat is not sufficient for protection against Tat-induced oxidative stress. Furthermore, when cells were pretreated with scavengers of hydrogen peroxide such as N-acetylcysteine, or overexpression of Nrf2, or Keap1 knockdown by siRNA, Tat-induced HIV-1 LTR transactivation was suppressed, whereas buthionine sulfoximine or Nrf2 knockdown by siRNA potentiated Tat-induced HIV-1 LTR transactivation. Similar results were found in HIV-IIIB virus infection. Taken together, these data clearly show that Nrf2 inhibits Tat-induced HIV-1 LTR transactivation. This negative regulation of Tat-induced HIV-1 LTR transactivation by Nrf2 might be an important mechanism leading to its anti-HIV-1 replicative activity.

Impact of extracellular HIV-TAT on the regulation of EDF-1 levels in human endothelial cells

EDF-1 has been isolated by RNA fingerprinting from human endothelial cells exposed to human immunodeficiency virus type 1 (HIV-) Tat, a viral protein known to function as a cytokine in the activation of endothelial cells. Here we provide the molecular evidence that the inhibition of EDF-1 mRNA is transcriptionally regulated in human endothelial cells. Indeed, HIV-Tat inhibits the luciferase activity of endothelial cells transiently transfected with a construct containing 2300 bp of EDF-1 promoter cloned upstream of a luciferase reporter system. The decrease of EDF-1 RNA, however, does not translate into any alteration at the protein level, even when the cells are exposed to MG132, a proteasome inhibitor. Analogously, no modulation of the total amounts of EDF-1 by HIV-Tat has been observed in the presence of pro-inflammatory cytokine interleukin 1beta, which induces endothelial responsiveness to the in vitro effects of HIV-Tat. We have previously shown that EDF-1 is cytosolic and can be translocated to the nucleus upon activation of protein kinases A and C. In response to HIV-Tat, EDF-1 is mainly in the cytosol. Since cytosolic EDF-1 binds and sequesters calmodulin, an important regulator of endothelial nitric oxide synthase, these results might explain why we do not observe any induction of nitric oxide in endothelial cells exposed to HIV-Tat.

Design and characterization of an HIV-1 Tat mutant: Inactivation of viral and cellular functions but not antigenicity

Among HIV-1 proteins, Tat is a promising antigen for consideration as a component of anti-HIV-1 vaccine formulations. Nevertheless, this viral protein is able to affect the expression of several cellular genes that are implicated in immune response. In this study, we designed and characterized a mutant form of Tat ("STLA Tat"), which is unable to transactivate viral transcription, and which has lost the deleterious effects on the expression of MHC I, IL-2, and CD25 genes compared with wild-type Tat, as observed in lymphoid Jurkat cells that stably express the tat genes. In vivo experiments in mice revealed that STLA Tat induces anti-Tat antibodies at the same titers as wild-type Tat, which recognize both autologous and heterologous Tat antigens. Finally, STLA Tat did not induce the immunosuppression observed after injection of wild-type Tat. Therefore, this STLA Tat mutant appears to be a safe and promising antigen for further evaluation in anti-HIV-1 vaccine strategies.

Morphine-mediated deterioration of oxidative stress leads to rapid disease progression in SIV/SHIV-infected macaques

Oxidative stress is well documented in HIV infection, but the effect of concomitant substance abuse is largely unknown. We studied oxidative stress in our macaque model of morphine abuse and AIDS. In plasma, we found an approximately 50% decrease in catalase activity with morphine dependence that was exacerbated by infection in rapid progressors. Superoxide dismutase was decreased by a similar degree, but only in the presence of both morphine and viral infection. The loss of these antioxidant systems was coincident with significantly increased plasma malondialdehyde upon viral infection that displayed a synergistic increase in conjunction with morphine and rapid disease.

Preventing HIV-1 tat-induced neuronal apoptosis using antioxidant enzymes: Mechanistic and therapeutic implications

HIV-1 proteins, especially gp120 and Tat, elicit reactive oxygen species (ROS) and cause neuron apoptosis. We used antioxidant enzymes, Cu/Zn superoxide dismutase (SOD1) and glutathione peroxidase (GPx1) to study signaling and neuroprotection from Tat-induced apoptosis. SOD1 converts superoxide to peroxide; GPx1 converts peroxide to water. Primary human neurons were transduced with SV40-derived vectors carrying SOD1 and GPx1, then HIV-1 Tat protein was added. Both SV(SOD1) and SV(GPx1) delivered substantial transgene expression. Tat decreased endogenous cellular, but not transduced, SOD1 and GPx1. Tat rapidly increased neuron [Ca(2+)](i), which effect was not altered by SV(SOD1) or SV(GPx1). However, both vectors together blocked Tat-induced [Ca(2+)](i) fluxes. Similarly, neither SV(SOD1) nor SV(GPx1) protected neurons from Tat-induced apoptosis, but both vectors together did. Tat therefore activates multiple signaling pathways, in one of which superoxide acts as an intermediate while the other utilizes peroxide. Gene delivery to protect neurons from Tat must therefore target both.

Suppression of survival in human SKBR3 breast carcinoma in response to metal–chelator complexes is preferential for copper–dithiocarbamate

Since diethyl dithiocarbamate (DEDTC) forms complexes with either zinc or copper, and 8-hydroxyquinoline (8-OHQ) also complexes with copper, we now compared the cytotoxic activity of Cu[DEDTC]2, Zn[DEDTC]2 and Cu[8-OHQ]2. This report shows that at nanomolar levels, only copper-[DEDTC]2, suppresses proliferation and clonogenicity of SKBR3 human breast carcinoma, concurrently with induction of apoptosis-associated PARP fragmentation. Susceptibility to these agents was paralleled by reactive oxygen generation (ROS) and greater expression of anti-oxidant enzymes like MnSOD and catalase, with no comparable effect on Cu/Zn superoxide dismutase. The lethal effects of Cu[DEDTC]2 manifested when adding the two separate aqueous components or the preformed synthetic complexes in DMSO, was prevented by N-acetyl cysteine or glutathione, with no comparable protection afforded by non-thiol anti-oxidants like mannitol or DMSO. Exogenously added catalase also protected cells from Cu[DEDTC]2, suggesting that this complex may kill after the levels of superoxide anion [O2*-] dismutated by MnSOD increase hydrogen peroxide-related stress. Cu[DEDTC]2 also induced p21WAF1, a cdk inhibitor usually not inducible in mutant p53 tumors like SKBR3 carcinoma, correlating with dephosphorylation of the Sp1 transcription factor. Concentrations of Cu[DEDTC]2 cytotoxic for SKBR3 carcinoma did not induce comparable damage versus normal diploid human WI-38 fibroblasts. In contrast to the cytotoxic effect of nM levels of Cu[DEDTC]2 against SKBRR3 cells, no response was seen in the same cells exposed to 20 microM cis-platin. Since neither DEDTC bound to zinc, nor copper bound to 8-OHQ showed comparable cytotoxicity, our results suggest that the greater activity of copper-DEDTC reflects a specific structure-activity relationship for the active complex. Since Cu[DEDTC]2 shows more effectiveness than other metal-chelator complexes, it may be worth further investigation as an alternative to cancer therapies.

Different roles of Sp family members in HIV-1 Tat-mediated manganese superoxide dismutase suppression in hepatocellular carcinoma cells

The expression of manganese superoxide dismutase (MnSOD) is regulated by agents associated with cancer development. It has been shown that infection with the human immunodeficiency virus type 1 (HIV-1) is associated with the development of liver cancer and that the transactivating transcriptional factor (Tat) of human HIV-1 reduces the expression of MnSOD in several cell types. However, the role of Tat in the expression of MnSOD in hepatocellular carcinoma is unknown. Furthermore, the precise mechanisms whereby Tat suppresses MnSOD expression in hepatocellular carcinoma cells remain unclear. In this report, we build on our original observations that Tat changes the distribution of Sp family members on the MnSOD promoter, which accounts for Tat-dependent changes in basal expression. In hepatic cells, Tat expression upregulates Sp1/Sp3, which play different roles in regulating MnSOD transcription. While overexpression of Sp1 stimulates, overexpression of Sp3 represses transcriptional activity. The transcription repression effect of Sp3 is not due to Sp3 competing for the binding site with Sp1 because only the full-length Sp3 but not the truncated Sp3 suppresses MnSOD promoter activity. These findings suggest a novel mechanism by which Tat modulates the repression of the MnSOD gene and establish a link between HIV infection and liver cancer.