NF-kappaB and p53 are the dominant apoptosis-inducing transcription factors elicited by the HIV-1 envelope

ATF4 Signaling in HIV-1 Infection: Viral Subversion of a Stress Response Transcription Factor

Cellular integrated stress response (ISR), the mitochondrial unfolded protein response (UPRmt), and IFN signaling are associated with viral infections. Activating transcription factor 4 (ATF4) plays a pivotal role in these pathways and controls the expression of many genes involved in redox processes, amino acid metabolism, protein misfolding, autophagy, and apoptosis. The precise role of ATF4 during viral infection is unclear and depends on cell hosts, viral agents, and models. Furthermore, ATF4 signaling can be hijacked by pathogens to favor viral infection and replication. In this review, we summarize the ATF4-mediated signaling pathways in response to viral infections, focusing on human immunodeficiency virus 1 (HIV-1). We examine the consequences of ATF4 activation for HIV-1 replication and reactivation. The role of ATF4 in autophagy and apoptosis is explored as in the context of HIV-1 infection programmed cell deaths contribute to the depletion of CD4 T cells. Furthermore, ATF4 can also participate in the establishment of innate and adaptive immunity that is essential for the host to control viral infections. We finally discuss the putative role of the ATF4 paralogue, named ATF5, in HIV-1 infection. This review underlines the role of ATF4 at the crossroads of multiple processes reflecting host-pathogen interactions.

Methamphetamine Shows Different Joint Toxicity for Different Types of Microplastics on Zebrafish Larvae by Mediating Oxidative Stress

The coexistence of polystyrene (PS) and polypropylene (PVC) microplastics (MPs) and methamphetamine (METH) in aquatic systems is evident. However, the joint toxicity is unclear. Here, zebrafish larvae were exposed to single PS and PVC MPs (20 mg L-1) and combined with METH (250 and 500 μg L-1) for 10 days. The results indicated that acute exposure to PS and PVC MPs induced lethal effects on zebrafish larvae (10-20%). Treatment with MPs markedly suppressed the locomotion of zebrafish, showing as the lengthy immobility (51-74%) and lower velocity (0.09-0.55 cm s-1) compared with the control (1.07 cm s-1). Meanwhile, histopathological analysis revealed pronounced depositions of MPs particles in fish's intestinal tract, triggering inflammatory responses (histological scores: 1.6-2.0). In the coexposure groups, obviously inflammatory responses were found. Furthermore, the up-regulations of the genes involved in the oxidative kinase gene and inflammation related genes implied that oxidative stress triggered by MPs on zebrafish larvae might be responsible for the mortality and locomotion retardant. The antagonistic and stimulatory effects of METH on the expression changes of genes found in PVC and PS groups implied the contrary combined toxicity of PS/PVC MPs and METH. This study for the first time estimated the different toxicity of PS and PVC MPs on fish and the joint effects with METH at high environmental levels. The results suggested PS showed stronger toxicity than PVC for fish larvae. The addition of METH stimulated the effects of PS but antagonized the effects of PVC, promoting control strategy development on MPs and METH in aquatic environments.

APOBEC3G Is a p53-Dependent Restriction Factor in Respiratory Syncytial Virus Infection of Human Cells Included in the p53/Immune Axis

Identifying and understanding genetic factors that influence the propagation of the human respiratory syncytial virus (RSV) can lead to health benefits and possibly augment recent vaccine approaches. We previously identified a p53/immune axis in which the tumor suppressor p53 directly regulates the expression of immune system genes, including the seven members of the APOBEC3 family of DNA cytidine deaminases (A3), which are innate immune sentinels against viral infections. Here, we examined the potential p53 and A3 influence in RSV infection, as well as the overall p53-dependent cellular and p53/immune axis responses to infection. Using a paired p53 model system of p53+ and p53- human lung tumor cells, we found that RSV infection activates p53, leading to the altered p53-dependent expression of A3D, A3F, and A3G, along with p53 site-specific binding. Focusing on A3G because of its 10-fold-greater p53 responsiveness to RSV, the overexpression of A3G can reduce RSV viral replication and syncytial formation. We also observed that RSV-infected cells undergo p53-dependent apoptosis. The study was expanded to globally address at the transcriptional level the p53/immune axis response to RSV. Nearly 100 genes can be directly targeted by the p53/immune axis during RSV infection based on our p53BAER analysis (Binding And Expression Resource). Overall, we identify A3G as a potential p53-responsive restriction factor in RSV infection. These findings have significant implications for RSV clinical and therapeutic studies and other p53-influenced viral infections, including using p53 adjuvants to boost the response of A3 genes.

Host variation in type I interferon signaling genes (MX1), C-C chemokine receptor type 5 gene, and major histocompatibility complex class I alleles in treated HIV+ noncontrollers predict viral reservoir size

OBJECTIVE

Prior genomewide association studies have identified variation in major histocompatibility complex (MHC) class I alleles and C-C chemokine receptor type 5 gene (CCR5Δ32) as genetic predictors of viral control, especially in 'elite' controllers, individuals who remain virally suppressed in the absence of therapy.

DESIGN

Cross-sectional genomewide association study.

METHODS

We analyzed custom whole exome sequencing and direct human leukocyte antigen (HLA) typing from 202 antiretroviral therapy (ART)-suppressed HIV+ noncontrollers in relation to four measures of the peripheral CD4+ T-cell reservoir: HIV intact DNA, total (t)DNA, unspliced (us)RNA, and RNA/DNA. Linear mixed models were adjusted for potential covariates including age, sex, nadir CD4+ T-cell count, pre-ART HIV RNA, timing of ART initiation, and duration of ART suppression.

RESULTS

Previously reported 'protective' host genetic mutations related to viral setpoint (e.g. among elite controllers) were found to predict smaller HIV reservoir size. The HLA 'protective' B∗57:01 was associated with significantly lower HIV usRNA (q = 3.3 × 10-3), and among the largest subgroup, European ancestry individuals, the CCR5Δ32 deletion was associated with smaller HIV tDNA (P = 4.3 × 10-3) and usRNA (P = 8.7 × 10-3). In addition, genomewide analysis identified several single nucleotide polymorphisms in MX1 (an interferon stimulated gene) that were significantly associated with HIV tDNA (q = 0.02), and the direction of these associations paralleled MX1 gene eQTL expression.

CONCLUSIONS

We observed a significant association between previously reported 'protective' MHC class I alleles and CCR5Δ32 with the HIV reservoir size in noncontrollers. We also found a novel association between MX1 and HIV total DNA (in addition to other interferon signaling relevant genes, PPP1CB, DDX3X). These findings warrant further investigation in future validation studies.

Combined effects of polystyrene microplastics and cadmium on oxidative stress, apoptosis, and GH/IGF axis in zebrafish early life stages

The toxicological interactions of microplastics (MPs) and heavy metals have been paid much attention in aquatic organism. The mechanisms are not fully clear, particularly in fish early life stages. To the end, zebrafish embryos were exposed to 500 μg/L MPs, 5 μg/L cadmium (Cd), and their combination for 30 days. Body weight, adsorption characteristics of Cd onto MPs, Cd accumulation, oxidative stress, apoptosis, and growth hormone/insulin-like growth factor-I (GH/IGF) axis were examined. Exposure to MPs and Cd alone reduced body weight, which was aggravated by co-exposure. An increase in reactive oxygen species (ROS) levels was observed in larvae exposed to Cd or MPs + Cd, suggesting an induction of oxidative stress. Lipid peroxidation levels were not affected by exposure to MPs and Cd alone but dramatically enhanced by co-exposure, which may be explained by the reduction of total antioxidant capacity (TAOC) and activity levels of Mn-superoxide dismutase (Mn-SOD) and catalase (CAT) after co-exposure. Increased apoptotic cells were observed in the vertebral body of larvae exposed to Cd, the esophagus of larvae exposed to MPs, and both organs of larvae exposed to MPs + Cd, which was further confirmed by changes in the activities of Caspase-3, Caspase-8 and Caspase-9. PCR array on the transcription of genes related to growth, oxidative stress and apoptosis was examined, showing that the combined exposure resulted in greater magnitude of changes than MPs and Cd alone. The results indicate that MPs can enhance the negative effects of Cd on growth, oxidative damage and apoptosis in early life stages of zebrafish. However, the adsorption of Cd onto MPs was not observed and the combined exposure did not increase the Cd content in larvae compared to the single Cd exposure, implying that vector role of MPs in Cd uptake is negligible.

Particles rather than released Zn2+ from ZnO nanoparticles aggravate microplastics toxicity in early stages of exposed zebrafish and their unexposed offspring

Knowledge on the interaction between microplastics (MPs) and zinc oxide nanoparticles (ZnO NPs) is limited. Here, we investigated effects of embryo-larvae exposure to 500 μg/L polystyrene MPs (5 µm), 1200 μg/L ZnO NPs (< 100 nm), 500 μg/L dissolved Zn²⁺ from ZnSO4^, and the mixtures of MPs and ZnO NPs or ZnSO4 on exposed F0 larvae and unexposed F1 larvae. Consequently, ZnO particles adhered to MPs surfaces rather than Zn²⁺, and increased Zn transport into larvae. Growth inhibition, oxidative stress, apoptosis, and disturbance of growth hormone and insulin-like growth factor (GH/IGF) axis were induced by MPs and ZnO NPs alone, which were further aggravated by their co-exposure in F0 larvae. MPs + ZnO increased apoptotic cells in the gill and esophagus compared with MPs and ZnO NPs alone. Reduced growth and antioxidant capacity and down-regulated GH/IGF axis were merely observed in F1 larvae from F0 parents exposed to MPs + ZnO. Contrary to ZnO NPs, dissolved Zn²⁺ reversed MPs toxicity, suggesting the protective role of Zn²⁺ may be not enough to ameliorate thfie negative effects of ZnO particles. To summarize, we found that particles rather than released Zn²⁺ from ZnO nanoparticles amplified MPs toxicity in early stages of exposed zebrafish and their unexposed offspring.

Cadmium induced oxidative stress, endoplasmic reticulum (ER) stress and apoptosis with compensative responses towards the up-regulation of ribosome, protein processing in the ER, and protein export pathways in the liver of zebrafish

The present study identified that exposure to 5, 10, and 20 µg/L Cd for 48 days reduced growth, increased Cd accumulation and levels of reactive oxygen species (ROS) and lipid peroxidation, and induced ER stress and cellular apoptosis in the liver in a dose-dependent manner. However, the survival rate was not affected by Cd. The increased production of ROS might result from reduced catalase (CAT) and copper/zinc-superoxide dismutase (Cu/Zn-SOD) activities, which might trigger ER stress pathways and subsequently induce apoptotic responses, ultimately leading to growth inhibition. Transcriptomic analyses indicated that the differentially expressed genes (DEGs) involved in metabolic pathways were significantly enriched and dysregulated by Cd, suggesting that metabolic disturbances may contribute to Cd toxicity. However, there were increases in glutathione peroxidase (GPX) activity, protein levels of metallothioneins (MTs) and heat shock protein 70 (HSP70), and mRNA levels of sod1, cat, gpx, mt2, and hsp70. Furthermore, DEGs related to ribosome, protein processing in the ER, and protein export pathways were significantly enriched and up-regulated by Cd. These increases may be compensatory responses following oxidative stress, ER stress, and apoptosis to resist negative effects. Taken together, we demonstrated that environmentally relevant levels of Cd induced adaptive responses with compensatory mechanisms in fish, which may help to maintain fish survival at the cost of growth.

The Underrated Salivary Virome of Men Who Have Sex With Men Infected With HIV

Salivary virome is important for oral ecosystem, but there are few reports on people living with HIV. We performed metagenomic sequencing to compare composition and functional genes of salivary virobiota between one HIV-negative and four HIV-positive groups in which participants were all men who have sex with men (MSM) with different immunosuppression statuses (five samples per group) to find the evidence that salivary virobiota plays a role in the pathogenesis of oral disease. Acute-stage subjects achieved a positive result of HIV RNA, but HIV antibody negative or indeterminate, whereas individuals with mild, moderate, and severe immunosuppression exhibited CD4⁺ T-lymphocyte counts of at least 500, 200–499, and less than 200 cells/μL or opportunistic infection, respectively. The results showed the composition of salivary virus genera in subjects with mild immunosuppression was the most similar to that in healthy people, followed by that in the acute stage; under severe immunosuppression, virus genera were suppressed and more similar to that under moderate immunosuppression. Furthermore, abnormally high abundance of Lymphocryptovirus was particularly obvious in MSM with HIV infection. Analysis of KEGG Pathway revealed that Caulobacter cell cycle, which affects cell duplication, became shorter in HIV-positive subjects. It is worth noting that in acute-stage participants, protein digestion and absorption related to the anti-HIV-1 activity of secretory leukocyte protease inhibitor was increased. Moreover, in the severely immunosuppressed subjects, glutathione metabolism, which is associated with the activation of lymphocytes, was enhanced. Nevertheless, the ecological dysbiosis in HIV-positive salivary virobiota possibly depended on the changes in blood viral load, and salivary dysfunction of MSM infected with HIV may be related to CD4 counts. Ribonucleoside diphosphate reductase subunit M1 in purine metabolism was negatively correlated, though weakly, to CD4 counts, which may be related to the promotion of HIV-1 DNA synthesis in peripheral blood lymphocytes. 7-Cyano-7-deazaguanine synthase in folate biosynthesis was weakly positively correlated with HIV viral load, suggesting that this compound was produced excessively to correct oral dysfunction for maintaining normal cell development. Despite the limited number of samples, the present study provided insight into the potential role of salivary virome in the oral function of HIV infected MSM.

Implications of viral infection in cancer development

Since the identification of the first human oncogenic virus in 1964, viruses have been studied for their potential role in aiding the development of cancer. Through the modulation of cellular pathways associated with proliferation, immortalization, and inflammation, viral proteins can mimic the effect of driver mutations and contribute to transformation. Aside from the modulation of signaling pathways, the insertion of viral DNA into the host genome and the deregulation of cellular miRNAs represent two additional mechanisms implicated in viral oncogenesis. In this review, we will discuss the role of twelve different viruses on cancer development and how these viruses utilize the abovementioned mechanisms to influence oncogenesis. The identification of specific mechanisms behind viral transformation of human cells could further elucidate the process behind cancer development.

Selective BCL-XL Antagonists Eliminate Infected Cells from a Primary-Cell Model of HIV Latency but Not from Ex Vivo Reservoirs

HIV persists, despite immune responses and antiretroviral therapy, in viral reservoirs that seed rebound viremia if therapy is interrupted. Previously, we showed that the BCL-2 protein contributes to HIV persistence by conferring a survival advantage to reservoir-harboring cells. Here, we demonstrate that many of the BCL-2 family members are overexpressed in HIV-infected CD4⁺ T cells, indicating increased tension between proapoptotic and prosurvival family members-and suggesting that inhibition of prosurvival members may disproportionately affect the survival of HIV-infected cells. Based on these results, we chose to study BCL-X_L due to its consistent overexpression and the availability of selective antagonists. Infection of primary CD4⁺ T cells with HIV resulted in increased BCL-X_L protein expression, and treatment with two selective BCL-X_L antagonists, A-1155463 and A-1551852, led to selective death of productively infected CD4⁺ T cells. In a primary cell model of latency, both BCL-X_L antagonists drove reductions in HIV DNA and in infectious cell frequencies both alone and in combination with the latency reversing agent bryostatin-1, with little off-target cytotoxicity. However, these antagonists, with or without bryostatin-1 or in combination with the highly potent latency reversing agent combination phorbol myristate acetate (PMA) + ionomycin, failed to reduce total HIV DNA and infectious reservoirs in ex vivo CD4⁺ T cells from antiretroviral therapy (ART)-suppressed donors. Our results add to growing evidence that bona fide reservoir-harboring cells are resistant to multiple "kick and kill" modalities-relative to latency models. We also interpret our results as encouraging further exploration of BCL-X_L antagonists for cure, where combination approaches, including with immune effectors, may unlock the ability to eliminate ex vivo reservoirs. IMPORTANCE Although antiretroviral therapy (ART) has transformed HIV infection into a manageable chronic condition, there is no safe or scalable cure. HIV persists in "reservoirs" of infected cells that reinitiate disease progression if ART is interrupted. Whereas most efforts to eliminate this reservoir have focused on exposing these cells to immune-mediated clearance by reversing viral latency, recent work shows that these cells also resist being killed. Here, we identify a "prosurvival" factor, BCL-X_L, that is overexpressed in HIV-infected cells, and demonstrate selective toxicity to these cells by BCL-X_L antagonists. These antagonists also reduced reservoirs in a primary-cell latency model but were insufficient to reduce "natural" reservoirs in ex vivo CD4⁺ T cells-adding to growing evidence that the latter are resilient in a way that is not reflected in models. We nonetheless suggest that the selective toxicity of BCL-X_L antagonists to HIV-infected cells supports their prioritization for testing in combinations aimed at reducing ex vivo reservoirs.

Regulation of innate immune responses by cell death-associated caspases during virus infection

Viruses are obligate intracellular pathogens that rely on cellular machinery for successful replication and dissemination. The host cells encode a number of different strategies to sense and restrict the invading viral pathogens. Caspase-mediated programmed cell death pathways that are triggered by virus infection, such as apoptosis and pyroptosis, provide a means for the infected cells to limit viral proliferation, leading to suicidal cell death (apoptosis) or lytic cell death and alerting uninfected cells to mount anti-viral responses (pyroptosis). However, some viruses can employ activated caspases to dampen the anti-viral responses and facilitate viral replication through cleavage of critical molecules of the innate immune pathways. The regulation of innate immune responses by caspase activation during virus infection has recently become an important topic. In this review, we briefly introduce the characteristics of different classes of caspases and the cell death pathways regulated by these caspases. We then describe how viruses trigger or dampen caspase activation during infection and how these activated caspases regulate three major innate immune response pathways of viral infections: the retinoic acid-inducible gene I-like receptor, toll-like receptor and cyclic GMP-AMP synthase-stimulator of interferon genes pathways.

HIV-1 Envelope Overcomes NLRP3-Mediated Inhibition of F-Actin Polymerization for Viral Entry

Purinergic receptors and nucleotide-binding domain leucine-rich repeat containing (NLR) proteins have been shown to control viral infection. Here, we show that the NLR family member NLRP3 and the purinergic receptor P2Y2 constitutively interact and regulate susceptibility to HIV-1 infection. We found that NLRP3 acts as an inhibitory factor of viral entry that represses F-actin remodeling. The binding of the HIV-1 envelope to its host cell receptors (CD4, CXCR4, and/or CCR5) overcomes this restriction by stimulating P2Y2. Once activated, P2Y2 enhances its interaction with NLRP3 and stimulates the recruitment of the E3 ubiquitin ligase CBL to NLRP3, ultimately leading to NLRP3 degradation. NLRP3 degradation is permissive for PYK2 phosphorylation (PYK2Y402^∗) and subsequent F-actin polymerization, which is required for the entry of HIV-1 into host cells. Taken together, our results uncover a mechanism by which HIV-1 overcomes NLRP3 restriction that appears essential for the accomplishment of the early steps of HIV-1 entry.

Walnut Polyphenol Extract Protects against Malathion- and Chlorpyrifos-Induced Immunotoxicity by Modulating TLRx-NOX-ROS

Malathion (MT) and chlorpyrifos (CPF) are immunotoxic organophosphate pesticides that are used extensively in agriculture worldwide. Dietary polyphenols protect against a variety of toxins. In this study, walnut polyphenol extract (WPE) prevents MT- or CPF-induced toxicity to splenic lymphocytes in vitro. WPE promotes the proliferation of MT-exposed splenocytes, as indicated by increases in the proportions of splenic T-lymphocyte subpopulations (CD3+, CD4+, and CD8+ T cells) and levels of T-cell-related cytokines interleukin (IL)-2, interferon-γ, IL-4, and granzyme B, and decreases the apoptosis-associated proteins Bax and p53. WPE also significantly enhances the proliferation of CPF-exposed splenic B lymphocytes (CD19+ B cells) and levels of the B-cell-related cytokine IL-6, leading to decreases of the apoptosis-associated proteins Bax and p53. These effects are related to reduced production of reactive oxygen species (ROS), as evidenced by normalized hydroxyl radical (•OH), malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT), and glutathione (GSH) levels, which are associated with decreased expression of NADPH oxidase 2 (NOX2) and dual oxidase 1 (DUOX1). WPE inhibits the production of ROS and expression of NOX by regulating toll-like receptors 4 and 7 in MT- and CPF-exposed splenic lymphocytes. In conclusion, WPE protects against MT- or CPF-mediated immunotoxicity and inhibits oxidative damage by modulating toll-like receptor (TLR)x-NOX-ROS.

Mechanisms of Human Immunodeficiency Virus-Associated Lymphocyte Regulated Cell Death

Human immunodeficiency virus-1 (HIV-1) causes CD4 T cell depletion through a number of mechanisms, including programmed cell death pathways (both apoptotic and nonapoptotic). In the setting of HIV-1 infection, the enhanced lymphocyte cell death occurs as a consequence of complex interactions between the host immune system and viral factors, which are reviewed herein. On the other hand, the main challenge to HIV-1 eradication is the development of latent infection in a subset of long lived cells, including CD4+ T cells and macrophages, which resist HIV-induced cell death. Understanding the potential mechanisms of how HIV-1 induces lymphocyte cell death is critical to the "kick and kill" cure strategy, which relies on the effective killing of reactivated, HIV-1-infected cells.

The Role of the BCL-2 Family of Proteins in HIV-1 Pathogenesis and Persistence

Advances in HIV-1 therapy have transformed the once fatal infection into a manageable, chronic condition, yet the search for a widely applicable approach to cure remains elusive. The ineffectiveness of antiretroviral therapy (ART) in reducing the size of the HIV-1 latent reservoir has prompted investigation into the mechanisms of HIV-1 latency and immune escape. One of the major regulators of apoptosis, the BCL-2 protein, alongside its homologous family members, is a major target of HIV-1-induced change. Recent studies have now demonstrated the association of this protein with cells that support proviral forms in the setting of latency and have helped identify BCL-2 as a novel and promising therapeutic target for HIV-1 therapy directed at possible cure. This review aims to systematically review the interactions of HIV-1 with BCL-2 and its homologs and to examine the possibility of using BCL-2 inhibitors in the study and elimination of the latent reservoir.

Microcystin-LR exposure induced nephrotoxicity by triggering apoptosis in female zebrafish

Recently, several studies showed that microcystin-LR (MCLR) can accumulate and induce toxicity in kidney. However, the exact mechanism is unknown. The aim of this study was to explore the mechanism of MCLR-induced nephrotoxicity. To this end, adult zebrafish were exposed to MCLR (0, 1, 5 and 25 μg/L) for 60 days. Exposure to MCLR caused histopathological lesions, which were characterized by renal tubules filled with eosinophilic casts, abnormal renal tubules, intertubular space decrease, and blood infiltration in renal cells. RNA-Seq analysis indicated that exposure to MCLR significantly interfered with renal gene expressions, and these genes were enriched in various pathways, such as oxidative phosphorylation, cell cycle, and protein processing in endoplasmic reticulum, which were related to apoptosis. Furthermore, terminal deoxynucleotide transferase-mediated deoxy-UTP nick end labelling (TUNEL) assay showed that MCLR exposure induced renal cell apoptosis. In addition, negative changes of the reactive oxygen species (ROS) level as well as apoptotic-related gene, protein expressions and enzyme activities suggested that MCLR could induce production of ROS, subsequently triggering apoptosis via p53-bcl-2 and caspase-dependent pathway in the kidney of zebrafish. Therefore, it can be concluded that apoptosis is a primary case of MCLR-induced nephrotoxicity.

Schmallenberg virus induces apoptosis in Vero cell line via extrinsic and intrinsic pathways in a time and dose dependent manner

Schmallenberg virus (SBV), discovered in 2011 in Germany, is associated with clinical manifestations of fever, diarrhea, reduced milk yield, abortions and congenital malformations in ruminants. Despite many studies performed for SBV, there is no detailed research on in vitro apoptotic effect of SBV. This study is aimed to determine apoptosis pathways and role of pro-apoptotic and anti-apoptotic molecules in Vero cells infected with SBV. The study results showed that SBV induced apoptosis via both extrinsic and intrinsic pathways by activating both caspase-8 and caspase-9, respectively. Expression analyses of pro-apoptotic (Bax, Bak and Puma) and anti-apoptotic (Bcl-2 and Bcl-XL) genes revealed that SBV-induced apoptosis causes upregulation of pro-apoptotic genes, dominantly via Puma gene, whereas Bcl-2 and Bcl-XL genes were downregulated. In conclusion, this is the first detailed report about SBV induced apoptosis in the Vero cells via both extrinsic and intrinsic cascades and apoptosis induction is seem to be regulated by Puma.

Reassessment of the capacity of the HIV-1 Env cytoplasmic domain to trigger NF-κB activation

The cytoplasmic domain of lentiviral Envelopes (EnvCD) ensures Env incorporation into nascent virions and regulates Env trafficking to and from the plasma membrane. It has also been reported to promote transcription from the viral LTR both directly and indirectly. Noticeably, the HIV-1 and SIV_mac239 EnvCDs were described to trigger nuclear translocation of NF-κB (Postler, Cell Host Microbes 2012). Given the paramount importance of identifying viral and host factors regulating HIV transcription, cellular signaling pathways and latency, and given that viral replication capacity is dependent on Env, we asked whether HIV EnvCDs from different HIV-1 subtypes differently modulated NF-κB. To that aim, we evaluated the ability of primary HIV-1 Envs from subtypes B and C to activate the NF-κB pathway. Primary subtype B and C Envs all failed to activate the NF-κB pathway. In contrast, when the EnvCD of HIV-1 Envs was fused to the the CD8-α chain, it induced ~ 10-fold increase in NF-κB induction, and this increase was much stronger with a truncated form of the HIV EnvCD lacking the 76 C-terminal residues and containing the proposed TAK-1 binding domain. Our results indicate that the HIV-1 EnvCD is unlikely to trigger the NF-κB pathway in its native trimeric form.

The interaction between HIV-1 Nef and adaptor protein-2 reduces Nef-mediated CD4+ T cell apoptosis

Acquired Immune Deficiency Syndrome is characterized by a decline in CD4⁺ T cells. Here, we elucidated the mechanism underlying apoptosis in Human Immunodeficiency Virus-1 (HIV-1) infection by examining host apoptotic pathways hijacked by the HIV-1 Nef protein in the CD4⁺ T-cell line Sup-T1. Using a panel of Nef mutants unable to bind specific host proteins we uncovered that Nef generates pro- and anti-apoptotic signals. Apoptosis increased upon mutating the motifs involved in the interaction of Nef:AP-1 (Nef_M20A or Nef_{EEEE62-65AAAA}) or Nef:AP-2 (Nef_LL164/165AA), implying these interactions limit Nef-mediated apoptosis. In contrast, disrupting the Nef:PAK2 interaction motifs (Nef_H89A or Nef_F191A) reduced apoptosis. To validate further, apoptosis was measured after short-hairpin RNA knock-down of AP-1, AP-2 and PAK2. AP-2α depletion enhanced apoptosis, demonstrating that disrupting the Nef:AP-2α interaction limits Nef-mediated apoptosis. Collectively, we describe a mechanism by which HIV-1 regulates cell survival and demonstrate the consequence of interfering with Nef:host protein interactions.

Entosis: The emerging face of non-cell-autonomous type IV programmed death

The present review summarizes recent experimental evidences about the existence of the non-cell-autonomous death entosis in physiological and pathophysiological contexts, discusses some aspects of this form of cell death, including morphological, biochemical and signaling pathways that distinguish non-cell-autonomous demises from other death modalities and propose to define this new modality of death as type IV programmed cell death.

Cytotoxic effects of Avermectin on human HepG2 cells in vitro bioassays

Avermectin (AVM) has been widely used in agriculture and animal husbandry based on its broad spectrum of effective anthelmintic activity and specificity targets. However, AVM induction of cytotoxicity in human liver is largely unknown. In this study, we investigate the cytotoxic effects of AVM on HepG2 cells in vitro. The results revealed that AVM inhibited the viability of HepG2 cells and enhanced apoptosis. Established assays of cytotoxicity were performed to characterize the mechanism of AVM toxicity on HepG2 cells. Typical apoptosis morphological changes were shown in AVM-treatment cells including chromatin condensation and DNA fragmentation. We demonstrated that AVM-induced apoptosis of HepG2 cells were mediated by generated ROS. Moreover, a decrease in mitochondrial membrane potential (MMP) and up-regulating the Bax/Bcl-2 ratio, resulted in a release of cytochrome-c as well as activation of caspase-9/-3. In conclusion, our experimental results show that AVM has a potential threat to human health which may be induce apoptosis of human hepatocyte cells via caspase-dependent mitochondrial pathways.

Transcriptomic Analysis Implicates the p53 Signaling Pathway in the Establishment of HIV-1 Latency in Central Memory CD4 T Cells in an In Vitro Model

The search for an HIV-1 cure has been greatly hindered by the presence of a viral reservoir that persists despite antiretroviral therapy (ART). Studies of HIV-1 latency in vivo are also complicated by the low proportion of latently infected cells in HIV-1 infected individuals. A number of models of HIV-1 latency have been developed to examine the signaling pathways and viral determinants of latency and reactivation. A primary cell model of HIV-1 latency, which incorporates the generation of primary central memory CD4 T cells (TCM), full-length virus infection (HIVNL4-3) and ART to suppress virus replication, was used to investigate the establishment of HIV latency using RNA-Seq. Initially, an investigation of host and viral gene expression in the resting and activated states of this model indicated that the resting condition was reflective of a latent state. Then, a comparison of the host transcriptome between the uninfected and latently infected conditions of this model identified 826 differentially expressed genes, many of which were related to p53 signaling. Inhibition of the transcriptional activity of p53 by pifithrin-α during HIV-1 infection reduced the ability of HIV-1 to be reactivated from its latent state by an unknown mechanism. In conclusion, this model may be used to screen latency reversing agents utilized in shock and kill approaches to cure HIV, to search for cellular markers of latency, and to understand the mechanisms by which HIV-1 establishes latency.

Modulation of apoptosis and viral latency - an axis to be well understood for successful cure of human immunodeficiency virus

Human immunodeficiency virus (HIV) is the causative agent of the deadly disease AIDS, which is characterized by the progressive decline of CD4(+)T-cells. HIV-1-encoded proteins such as envelope gp120 (glycoprotein gp120), Tat (trans-activator of transcription), Nef (negative regulatory factor), Vpr (viral protein R), Vpu (viral protein unique) and protease are known to be effective in modulating host cell signalling pathways that lead to an alteration in apoptosis of both HIV-infected and uninfected bystander cells. Depending on the stage of the virus life cycle and host cell type, these viral proteins act as mediators of pro- or anti-apoptotic signals. HIV latency in viral reservoirs is a persistent phenomenon that has remained beyond the control of the human immune system. To cure HIV infections completely, it is crucial to reactivate latent HIV from cellular pools and to drive these apoptosis-resistant cells towards death. Several previous studies have reported the role of HIV-encoded proteins in apoptosis modulation, but the molecular basis for apoptosis evasion of some chronically HIV-infected cells and reactivated latently HIV-infected cells still needs to be elucidated. The current review summarizes our present understanding of apoptosis modulation in HIV-infected cells, uninfected bystander cells and latently infected cells, with a focus on highlighting strategies to activate the apoptotic pathway to kill latently infected cells.

Syncytial apoptosis signaling network induced by the HIV-1 envelope glycoprotein complex: an overview

Infection by human immunodeficiency virus-1 (HIV-1) is associated with a progressive decrease in CD4 T-cell numbers and the consequent collapse of host immune defenses. The major pathogenic mechanism of AIDS is the massive apoptotic destruction of the immunocompetent cells, including uninfected cells. The latter process, also known as by-stander killing, operates by various mechanisms one of which involves the formation of syncytia which undergo cell death by following a complex pathway. We present here a detailed and curated map of the syncytial apoptosis signaling network, aimed at simplifying the whole mechanism that we have characterized at the molecular level in the last 15 years. The map was created using Systems Biology Graphical Notation language with the help of CellDesigner software and encompasses 36 components (proteins/genes) and 54 interactions. The simplification of this complex network paves the way for the development of novel therapeutic strategies to eradicate HIV-1 infection. Agents that induce the selective death of HIV-1-elicited syncytia might lead to the elimination of viral reservoirs and hence constitute an important complement to current antiretroviral therapies.

Human immunodeficiency virus-1 (HIV-1)-mediated apoptosis: new therapeutic targets

HIV has posed a significant challenge due to the ability of the virus to both impair and evade the host’s immune system. One of the most important mechanisms it has employed to do so is the modulation of the host’s native apoptotic pathways and mechanisms. Viral proteins alter normal apoptotic signaling resulting in increased viral load and the formation of viral reservoirs which ultimately increase infectivity. Both the host’s pro- and anti-apoptotic responses are regulated by the interactions of viral proteins with cell surface receptors or apoptotic pathway components. This dynamic has led to the development of therapies aimed at altering the ability of the virus to modulate apoptotic pathways. These therapies are aimed at preventing or inhibiting viral infection, or treating viral associated pathologies. These drugs target both the viral proteins and the apoptotic pathways of the host. This review will examine the cell types targeted by HIV, the surface receptors exploited by the virus and the mechanisms whereby HIV encoded proteins influence the apoptotic pathways. The viral manipulation of the hosts’ cell type to evade the immune system, establish viral reservoirs and enhance viral proliferation will be reviewed. The pathologies associated with the ability of HIV to alter apoptotic signaling and the drugs and therapies currently under development that target the ability of apoptotic signaling within HIV infection will also be discussed.

Autophagy plays an important role in the containment of HIV-1 in nonprogressor-infected patients

Recent in vitro studies have suggested that autophagy may play a role in both HIV-1 replication and disease progression. In this study we investigated whether autophagy protects the small proportion of HIV-1 infected individuals who remain clinically stable for years in the absence of antiretroviral therapy, these named long-term nonprogressors (LTNP) and elite controllers (EC). We found that peripheral blood mononuclear cells (PBMC) of the HIV-1 controllers present a significantly higher amount of autophagic vesicles associated with an increased expression of autophagic markers with respect to normal progressors. Of note, ex vivo treatment of PBMC from the HIV-1 controllers with the MTOR inhibitor rapamycin results in a more efficient autophagic response, leading to a reduced viral production. These data lead us to propose that autophagy contributes to limiting viral pathogenesis in HIV-1 controllers by targeting viral components for degradation.

The role of apoptosis in MCLR-induced developmental toxicity in zebrafish embryos

We previously demonstrated that cyanobacteria-derived microcystin-leucine-arginine (MCLR) is able to induce developing toxicity, such as malformation, growth delay and also decreased heart rates in zebrafish embryos. However, the molecular mechanisms by which MCLR induces its toxicity during the development of zebrafish remain largely unknown. Here, we evaluate the role of apoptosis in MCLR-induced developmental toxicity. Zebrafish embryos were exposed to various concentrations of MCLR (0, 0.2, 0.5, 2, and 5.0 mg L(-1)) for 96 h, at which time reactive oxygen species (ROS) was significantly induced in the 2 and 5.0 mg L(-1) MCLR exposure groups. Acridine orange (AO) staining and terminal deoxynucleotide transferase-mediated deoxy-UTP nick end labelling (TUNEL) assay showed that MCLR exposure resulted in cell apoptosis. To test the apoptotic pathway, the expression pattern of several apoptotic-related genes was examined for the level of enzyme activity, gene and protein expression, respectively. The overall results demonstrate that MCLR induced ROS which consequently triggered apoptosis in the heart of developing zebrafish embryos. Our results also indicate that the p53-Bax-Bcl-2 pathway and the caspase-dependent apoptotic pathway play major roles in MCLR-induced apoptosis in the developing embryos.

NF-κB-dependent and -independent pathways in the protective effects of activated protein C in hippocampal and cortical neurons at excitotoxicity

The transcription factor NF-κB regulates the expression of multiple genes involved in inflammation, apoptotic cell death and cell survival. We previously demonstrated that activated protein C (APC), a serine protease of hemostasis with anticoagulant activity, protected cultured rat cortical and hippocampal neurons against glutamate-induced excitotoxicity, a model of ischemic stroke. We reported that APC suppressed the translocation of NF-κBp65/RelA into the nucleus of neurons. However, it is not known whether APC-induced protection of neurons against cell death occurs via regulation of NF-κB activation or NF-κB-independent p53 expression. It is also unclear whether cleaved caspase-3 and caspase-independent AIF and Bax/Bcl-2 expression are involved at excitotoxicity. To elucidate the NF-κB dependent and -independent mechanisms in the APC-mediated cell survival, we analyzed in cortical and hippocampal neurons the effects of helenalin, a specific inhibitor of NF-κB activity, and APC on neuronal cell death and on the level of nuclear AIF, p53, caspase-3 and the apoptotic index (Bax/Bcl-2 ratio). We could demonstrate that helenalin (5 μM), like APC (1 nM), protects cultured neurons from glutamate-induced excitotoxicity. Both APC and helenalin inhibit AIF release from mitochondria and its translocation into the nucleus. They decrease the apoptotic index in neurons at excitotoxicity. However, APC, but not helenalin, reduced the glutamate-induced activation of caspase-3. Incubation of neurons with APC blocked the glutamate-induced increase in the nuclear level of p53 via NF-κB-independent pathway. Our findings demonstrate that, in the protective effect of APC in neurons at excitotoxicity, the NF-κB pathway is an important, but not the only pathway, and is significantly connected with neuronal survival at excitotoxicity.

HIV-1 induced bystander apoptosis

Apoptosis of uninfected bystander cells is a key element of HIV pathogenesis and believed to be the driving force behind the selective depletion of CD4+ T cells leading to immunodeficiency. While several viral proteins have been implicated in this process the complex interaction between Env glycoprotein expressed on the surface of infected cells and the receptor and co-receptor expressing bystander cells has been proposed as a major mechanism. HIV-1 utilizes CD4 as the primary receptor for entry into cells; however, it is the viral co-receptor usage that greatly influences CD4 decline and progression to AIDS. This phenomenon is relatively simple for X4 viruses, which arise later during the course of the disease, are considered to be highly fusogenic, and cause a rapid CD4+ T cell decline. However, in contrast, R5 viruses in general have a greater transmissibility, are encountered early during the disease and have a lesser pathogenic potential than the former. The above generalization gets complicated in numerous situations where R5 viruses persist throughout the disease and are capable of causing a rigorous CD4+ T cell decline. This review will discuss the multiple factors that are reported to influence HIV induced bystander apoptosis and pathogenesis including Env glycoprotein phenotype, virus tropism, disease stage, co-receptor expression on CD4+ T cells, immune activation and therapies targeting the viral envelope.

PUMA, a critical mediator of cell death--one decade on from its discovery

PUMA (p53 upregulated modulator of apoptosis) is a pro-apoptotic member of the BH3-only subgroup of the Bcl-2 family. It is a key mediator of p53-dependent and p53-independent apoptosis and was identified 10 years ago. The PUMA gene is mapped to the long arm of chromosome 19, a region that is frequently deleted in a large number of human cancers. PUMA mediates apoptosis thanks to its ability to directly bind known anti-apoptotic members of the Bcl-2 family. It mainly localizes to the mitochondria. The binding of PUMA to the inhibitory members of the Bcl-2 family (Bcl-2-like proteins) via its BH3 domain seems to be a critical regulatory step in the induction of apoptosis. It results in the displacement of the proteins Bax and/or Bak. This is followed by their activation and the formation of pore-like structures on the mitochondrial membrane, which permeabilizes the outer mitochondrial membrane, leading to mitochondrial dysfunction and caspase activation. PUMA is involved in a large number of physiological and pathological processes, including the immune response, cancer, neurodegenerative diseases and bacterial and viral infections.

Exon level transcriptomic profiling of HIV-1-infected CD4(+) T cells reveals virus-induced genes and host environment favorable for viral replication

HIV-1 is extremely specialized since, even amongst CD4⁺ T lymphocytes (its major natural reservoir in peripheral blood), the virus productively infects only a small proportion of cells under an activated state. As the percentage of HIV-1-infected cells is very low, most studies have so far failed to capture the precise transcriptomic profile at the whole-genome scale of cells highly susceptible to virus infection. Using Affymetrix Exon array technology and a reporter virus allowing the magnetic isolation of HIV-1-infected cells, we describe the host cell factors most favorable for virus establishment and replication along with an overview of virus-induced changes in host gene expression occurring exclusively in target cells productively infected with HIV-1. We also establish that within a population of activated CD4⁺ T cells, HIV-1 has no detectable effect on the transcriptome of uninfected bystander cells at early time points following infection. The data gathered in this study provides unique insights into the biology of HIV-1-infected CD4⁺ T cells and identifies genes thought to play a determinant role in the interplay between the virus and its host. Furthermore, it provides the first catalogue of alternative splicing events found in primary human CD4⁺ T cells productively infected with HIV-1.

Some previous studies have monitored HIV-1-induced gene expression in various host cell targets and tissues but the discrimination between productively infected cells and uninfected bystander cells represents a technical challenge yet to be solved. Consequently, data interpretation has always been biased towards the transcriptional response of a majority of uninfected bystander cells that were exposed to soluble factors released by virus-infected cells. Following the design of a unique and innovative molecular tool to identify cells productively infected with HIV-1 and the description of an efficient magnetic beads-based technique to separate them from uninfected bystander cells, we undertake this challenge and perform the first comparative whole-genome transcriptomic and large-scale proteomic profiling of both HIV-1-infected and uninfected bystander CD4⁺ T cells. We demonstrate herein that HIV-1- infected and uninfected bystander cells display distinctive transcriptomic signatures which might permit to identify new susceptibility and resistance factors.

Retinoblastoma protein induction by HIV viremia or CCR5 in monocytes exposed to HIV-1 mediates protection from activation-induced apoptosis: ex vivo and in vitro study

We have previously described an antiapoptotic steady-state gene expression profile in circulating human monocytes from asymptomatic viremic HIV(+) donors, but the mechanism associated with this apoptosis resistance remains to be fully elucidated. Here, we show that Rb1 activation is a dominant feature of apoptosis resistance in monocytes exposed to HIV-1 in vivo (as measured ex vivo) and in vitro. Monocytes from asymptomatic viremic HIV(+) individuals show a positive correlation between levels of hypophosphorylated (active) Rb1 and VL in conjunction with increases in other p53-inducible proteins associated with antiapoptosis regulation, such as p21 and PAI-1 (SERPINE1), when compared with circulating monocytes from uninfected donors. Monocytes exposed in vitro to HIV-1 R5 isolates but not X4 isolates showed lower caspase-3 activation after apoptosis induction, indicating a role for the CCR5 signaling pathway. Moreover, monocytes exposed to R5 HIV-1 or MIP-1 β induced Rb1 and p21 expression and an accumulation of autophagy markers, LC3 and Beclin. The inhibition of Rb1 activity in HIV-1 R5 viral-exposed monocytes using siRNA led to increased apoptosis sensitivity, thereby confirming a central role for Rb1 in the antiapoptotic phenotype. Our data identify Rb1 induction in chronic asymptomatic HIV-1 infection as a mediator of apoptosis resistance in monocytes in association with protective autophagy and contributing to monocyte survival during immune activation and/or HIV-1 viremia.

Multifaceted roles of purinergic receptors in viral infection

Extracellular nucleotides and purinergic receptors participate in numerous cellular processes during viral infection. Despite their positive role in the immune response, purinergic signals can also favor the infection of cells by viruses and the pathogeny of viral diseases. Here, we highlight the multiple ambiguous roles of purinergic receptors in viral infections.

Targeting HIV-1 gp41-induced fusion and pathogenesis for anti-viral therapy

HIV gp41 is a metastable protein whose native conformation is maintained in the form of a heterodimer with gp120. The non-covalently associated gp41/gp120 complex forms a trimer on the virus surface. As gp120 engages with HIV's receptor, CD4, and coreceptor, CXCR4 or CCR5, gp41 undergoes several conformational changes resulting in fusion between the viral and cellular membranes. Several lipophilic and amphiphilic domains have been shown to be critical in that process. While the obvious function of gp41 in viral entry is well-established its role in cellular membrane fusion and the link with pathogenesis are only now beginning to appear. Recent targeting of gp41 via fusion inhibitors has revealed an important role of this protein not only in viral entry but also in bystander apoptosis and HIV pathogenesis. Studies by our group and others have shown that the phenomenon of gp41-mediated hemifusion initiates apoptosis in bystander cells and correlates with virus pathogenesis. More interestingly, recent clinical evidence suggests that gp41 mutants arising after Enfuvirtide therapy are associated with CD4 cell increase and immunological benefits. This has in turn been correlated to a decrease in bystander apoptosis in our in vitro as well as in vivo assays. Although a great deal of work has been done to unravel HIV-1 gp41-mediated fusion mechanisms, the factors that regulate gp41-mediated fusion versus hemifusion and the mechanism by which hemifusion initiates bystander apoptosis are not fully understood. Further insight into these issues will open new avenues for drug development making gp41 a critical anti-HIV target both for neutralization and virus attenuation.

Extracellular ATP acts on P2Y2 purinergic receptors to facilitate HIV-1 infection

Extracellular adenosine triphosphate (ATP) can activate purinergic receptors of the plasma membrane and modulate multiple cellular functions. We report that ATP is released from HIV-1 target cells through pannexin-1 channels upon interaction between the HIV-1 envelope protein and specific target cell receptors. Extracellular ATP then acts on purinergic receptors, including P2Y2, to activate proline-rich tyrosine kinase 2 (Pyk2) kinase and transient plasma membrane depolarization, which in turn stimulate fusion between Env-expressing membranes and membranes containing CD4 plus appropriate chemokine co-receptors. Inhibition of any of the constituents of this cascade (pannexin-1, ATP, P2Y2, and Pyk2) impairs the replication of HIV-1 mutant viruses that are resistant to conventional antiretroviral agents. Altogether, our results reveal a novel signaling pathway involved in the early steps of HIV-1 infection that may be targeted with new therapeutic approaches.

Involvement of Noxa in mediating cellular ER stress responses to lytic virus infection

Noxa is a Bcl-2 homology domain-containing pro-apoptotic mitochondrial protein. Noxa mRNA and protein expression are upregulated by dsRNA or virus, and ectopic Noxa expression enhances cellular sensitivity to virus or dsRNA-induced apoptosis. Here we demonstrate that Noxa null baby mouse kidney (BMK) cells are deficient in normal cytopathic response to lytic viruses, and that reconstitution of the knockout cells with wild-type Noxa restored normal cytopathic responses. Noxa regulation by virus mirrored its regulation by proteasome inhibitors or ER stress inducers and the ER stress response inhibitor salubrinal protected cells against viral cytopathic effects. Noxa mRNA and protein were synergistically upregulated by IFN or dsRNA when combined with ER stress inducers, leading to Noxa/Mcl-1 interaction, activation of Bax and pro-apoptotic caspases, degradation of Mcl-1, loss of mitochondrial membrane potential and initiation of apoptosis. These data highlight the importance of ER stress in augmenting the expression of Noxa following viral infection.

Inhibition of β-TrcP-dependent ubiquitination of p53 by HIV-1 Vpu promotes p53-mediated apoptosis in human T cells

HIV-1 viral protein U (Vpu) is involved in ubiquitination and degradation of BM stromal cell Ag 2 and surface receptor CD4 through their recruitment to SCF(β-TrcP) (Skp1/Cul1/F-box) ubiquitin ligase (SCF) complex. Here, we show that specific interaction of wild-type Vpu protein with SCF complex leads to inhibition of ubiquitination and proteasomal degradation of p53 protein in a β-TrcP-dependent manner. Successful interaction of SCF(β-TrcP) complex with β-TrcP binding motif (DS(52)GNES(56)) present in Vpu is essential because mutant Vpu possessing specific alanine substitutions (DA(52)GNEA(56)) in the β-TrcP binding motif not only failed to stabilize p53 protein but was also unable to inhibit ubiquitination of p53 protein. Furthermore, Vpu competes efficiently with the interaction of p53 protein with the β-TrcP subunit of the SCF complex and inhibits subsequent ubiquitination of p53 proteins in a dose-dependent manner. We also observed potent apoptotic activity in a p53 null cell line (H-1299) that was cotransfected with p53 and Vpu-expressing plasmids. Furthermore, MOLT-3 (human T-lymphoblast) cells when infected with vesicular stomatitis virus glycoprotein-pseudotypic HIV-1 possessing wild-type vpu gene exhibited maximum activation of p53/Bax proteins and p53-mediated cell death. These findings establish a novel function of Vpu in modulating the stability of p53 protein that correlates positively with apoptosis during late stages of HIV-1 infection.

Mechanisms of HIV-associated lymphocyte apoptosis: 2010

The inevitable decline of CD4T cells in untreated infection with the Human immunodeficiency virus (HIV) is due in large part to apoptosis, one type of programmed cell death. There is accumulating evidence that the accelerated apoptosis of CD4T cells in HIV infection is multifactorial, with direct viral cytotoxicity, signaling events triggered by viral proteins and aberrant immune activation adding to normal immune defense mechanisms to contribute to this phenomenon. Current antiviral treatment strategies generally lead to reduced apoptosis, but this approach may come at the cost of preserving latent viral reservoirs. It is the purpose of this review to provide an update on the current understanding of the role and mechanisms of accelerated apoptosis of T cells in the immunopathogenesis of HIV infection, and to highlight potential ways in which this seemingly deleterious process could be harnessed to not just control, but treat HIV infection.

Mitochondria and viruses

Mitochondria are involved in a variety of cellular metabolic processes, and their functions are regulated by extrinsic and intrinsic stimuli including viruses. Recent studies have shown that mitochondria play a central role in the primary host defense mechanisms against viral infections, and a number of novel viral and mitochondrial proteins are involved in these processes. Some viral proteins localize in mitochondria and interact with mitochondrial proteins to regulate cellular responses. This review summarizes recent findings on the functions and roles of these molecules as well as mitochondrial responses to viral infections.

Apoptosis: a clinically useful measure of antiretroviral drug toxicity?

Antiretroviral therapy (ART) has improved life expectancy with HIV infection, but long-term toxicities associated with these medications are now a major global disease burden. There is a clear need to develop useful methods for monitoring patients on antiretroviral drugs for early signs of toxicity. Assays with predictive utility -- allowing therapy to be changed before serious end organ damage occurs -- would be ideal. Attempts to develop biochemical methods of monitoring ART toxicity have concentrated on the mitochondrial toxicity of nucleoside analogue reverse transcriptase inhibitors and have not generally lead to assays with widespread clinical applications. For example, plasma lactate and peripheral blood measurements of mitochondrial DNA associate with exposure to potentially toxic nucleoside analogue reverse transcriptase inhibitors but have not reliably predicted clinical toxicity. Better assays are needed, including markers of toxicity from additional drug classes. Apoptosis may be a potential marker of ART toxicity. Increased apoptosis has been demonstrated both in vitro and in vivo in association with various antiretroviral drug classes and a range of clinical toxicities. However, quantifying apoptosis on biopsy specimens of tissue (such as adipose tissue) is impractical for patient monitoring. Novel assays have been described that can quantify apoptosis using minute tissue samples and initial results from clinical samples suggest peripheral blood may have utility in predicting ART toxicities. The limitations and potential of such techniques for monitoring patients for drug side effects will be discussed.

Gut mucosal FOXP3+ regulatory CD4+ T cells and Nonregulatory CD4+ T cells are differentially affected by simian immunodeficiency virus infection in rhesus macaques

The gastrointestinal tract represents a major site for human and simian immunodeficiency virus (HIV and SIV) replication and CD4(+) T-cell depletion. Despite severe depletion of mucosal CD4(+) T cells, FOXP3(+) regulatory CD4(+) T cells (T(reg)) are highly increased in the gut mucosa of chronically HIV-infected individuals and may contribute to HIV pathogenesis, either by their immunosuppressive function or as a significant target cell population for virus production. Little is known about the susceptibility of mucosal T(reg) to viral infection and the longitudinal effect of HIV/SIV infection on T(reg) dynamics. In this study, we determined the level of SIV infection in T(reg) and nonregulatory CD4(+) T cells (non-T(reg)) isolated from the colon of SIV-infected rhesus macaques. The dynamics of mucosal T(reg) and alterations in the mucosal CD4(+) T-cell pool were examined longitudinally. Our findings indicate that mucosal T(reg) were less susceptible to productive SIV infection than non-T(reg) and thus were selectively spared from SIV-mediated cell death. In addition to improved survival, local expansion of T(reg) by SIV-induced proliferation of the mucosal CD4(+) T-cell pool facilitated the accumulation of mucosal T(reg) during the course of infection. High frequency of mucosal T(reg) in chronic SIV infection was strongly related to a reduction of perforin-expressing cells. In conclusion, this study suggests that mucosal T(reg) are less affected by productive SIV infection than non-T(reg) and therefore spared from depletion. Although SIV production is limited in mucosal T(reg), T(reg) accumulation may indirectly contribute to viral persistence by suppressing antiviral immune responses.

53BP1 represses mitotic catastrophe in syncytia elicited by the HIV-1 envelope

p53 binding protein-1 (53BP1) participates in checkpoint signaling during the DNA damage response (DDR) and during mitosis. In this study we report that 53BP1 aggregates in nuclear foci within syncytia elicited by the human immunodeficiency virus (HIV)-1 envelope. 53BP1 aggregation occurs as a consequence of nuclear fusion (karyogamy (KG)). It colocalizes partially with the promyelomonocytic leukemia protein (PML), and the ataxia telangiectasia mutated kinase (ATM), the two components of the DDR that mediate apoptosis induced by the HIV-1 envelope. ATM-dependent phosphorylation of 53BP1 on serines 25 and 1778 (53BP1S25P and 53BP1S1778P) occurs at these DNA damage foci. 53BP1S25P was also detected in syncytia present in the lymph nodes or frontal brain sections from HIV-1-infected carriers, as well as in peripheral blood mononucleated cells from HIV-1-infected individuals, correlating with viral load. Knockdown of 53BP1 caused HIV-1 envelope-induced syncytia to enter abnormal mitoses, leading to their selective destruction through mitochondrion-dependent and caspase-dependent pathways. In conclusion, depletion of 53BP1 triggers the demise of HIV-1-elicited syncytia through mitotic catastrophe.

PUMA, a potent killer with or without p53

PUMA (p53 upregulated modulator of apoptosis) is a Bcl-2 homology 3 (BH3)-only Bcl-2 family member and a critical mediator of p53-dependent and -independent apoptosis induced by a wide variety of stimuli, including genotoxic stress, deregulated oncogene expression, toxins, altered redox status, growth factor/cytokine withdrawal and infection. It serves as a proximal signaling molecule whose expression is regulated by transcription factors in response to these stimuli. PUMA transduces death signals primarily to the mitochondria, where it acts indirectly on the Bcl-2 family members Bax and/or Bak by relieving the inhibition imposed by antiapoptotic members. It directly binds and antagonizes all known antiapoptotic Bcl-2 family members to induce mitochondrial dysfunction and caspase activation. PUMA ablation or inhibition leads to apoptosis deficiency underlying increased risks for cancer development and therapeutic resistance. Although elevated PUMA expression elicits profound chemo- and radiosensitization in cancer cells, inhibition of PUMA expression may be useful for curbing excessive cell death associated with tissue injury and degenerative diseases. Therefore, PUMA is a general sensor of cell death stimuli and a promising drug target for cancer therapy and tissue damage.

9-Aminoacridine inhibition of HIV-1 Tat dependent transcription

As part of a continued search for more efficient anti-HIV-1 drugs, we are focusing on the possibility that small molecules could efficiently inhibit HIV-1 replication through the restoration of p53 and p21WAF1 functions, which are inactivated by HIV-1 infection. Here we describe the molecular mechanism of 9-aminoacridine (9AA) mediated HIV-1 inhibition. 9AA treatment resulted in inhibition of HIV LTR transcription in a specific manner that was highly dependent on the presence and location of the amino moiety. Importantly, virus replication was found to be inhibited in HIV-1 infected cell lines by 9AA in a dose-dependent manner without inhibiting cellular proliferation or inducing cell death. 9AA inhibited viral replication in both p53 wildtype and p53 mutant cells, indicating that there is another p53 independent factor that was critical for HIV inhibition. p21WAF1 is an ideal candidate as p21WAF1 levels were increased in both p53 wildtype and p53 mutant cells, and p21WAF1 was found to be phosphorylated at S146, an event previously shown to increase its stability. Furthermore, we observed p21WAF1 in complex with cyclin T1 and cdk9 in vitro, suggesting a direct role of p21WAF1 in HIV transcription inhibition. Finally, 9AA treatment resulted in loss of cdk9 from the viral promoter, providing one possible mechanism of transcriptional inhibition. Thus, 9AA treatment was highly efficient at reactivating the p53 – p21WAF1 pathway and consequently inhibiting HIV replication and transcription.

Simian varicella virus induces apoptosis in monkey kidney cells by the intrinsic pathway and involves downregulation of bcl-2 expression

Simian varicella virus (SVV) causes varicella in primates, becomes latent in ganglionic neurons, and reactivates to produce zoster. SVV produces a cytopathic effect in monkey kidney cells in tissue culture. To study the mechanism by which SVV-infected cells die, we examined markers of apoptosis 24 to 64 h postinfection (hpi). Western blot analysis of virus-infected cell lysates revealed a significant increase in the levels of the cleaved active form of caspase-3, accompanied by a parallel increase in caspase-3 activity at 40 to 64 hpi. Caspase-9, a marker for the intrinsic pathway, was activated significantly in SVV-infected cells at all time points, whereas trace levels of the active form of caspase-8, an extrinsic pathway marker, was detected only at 64 hpi. Bcl-2 expression at the mRNA and protein levels was decreased by 50 to 70% throughout the course of virus infection. Release of cytochrome c, an activator of caspase-9, from mitochondria into the cytoplasm was increased by 200% at 64 hpi. Analysis of Vero cells infected with SVV expressing green fluorescent protein (SVV-GFP) at 64 hpi revealed colocalization of the active forms of caspase-3 and caspase-9 and terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) staining with GFP. A significant decrease in the bcl-2 mRNA levels along with an abundance of mRNA specific for SVV genes 63, 40, and 21 was seen in the fraction of Vero cells that were infected with SVV-GFP. Together, these findings indicate that SVV induces apoptosis in cultured Vero cells through the intrinsic pathway in which Bcl-2 is downregulated.

The role of mitochondria in cellular defense against microbial infection

Mitochondria have been long recognized for their key role in the modulation of cell death pathways. Thus, it is therefore not surprising that this organelle represents a recurrent target for pathogenic microbes, aiming to manipulate the fate of the infected host cell. More recently, mitochondria have been shown to serve as a crucial platform for innate immune signaling, as illustrated by the identification of MAVS (also known as IPS-1, VISA and Cardif), NLRX1 and STING as mitochondrial proteins. This review discusses the tight interplay between microbial infection, innate immune signaling and mitochondria.

New insights on the role of apoptosis and autophagy in HIV pathogenesis

Viruses manipulate host cells to ensure their own survival and, at late stages of the viral life cycle, they kill the infected target cell to ensure their propagation. In addition, some viruses induce a bystander killing, a viral strategy to escape from the host's innate and cognate defense systems. In HIV-infection, the disabling of the immune system is initially due to the preferential depletion by apoptosis of virus-specific CD4(+) T cells in lymphoid tissues, followed by the destruction of non-infected bystander cells. Both the extrinsic and the intrinsic pathways are activated, and this is the consequence of systemic immune activation. This review presents recent developments showing that the gastrointestinal tract is the major reservoir of infected cells and the site of rapid and profound loss of CD4 T cells, and that microbial translocation from the gastrointestinal tract is the cause of immune activation. Furthermore, apoptosis mechanisms involved in HIV-induced neuropathological disorders are discussed, including the role of syncytia that involve the sequential activation of ATM, p38MAPK and p53. Finally, HIV-associated dementia (HAD) was recently found in monkey models to be linked to inhibition of autophagy in neurons, suggesting that homeostasis of autophagy is a reliable security factor for neurons, and challenging the development of new therapeutics aimed at boosting neuronal autophagy to prevent HAD.

c-FLIPL regulates PKC via AP-2 to inhibit Bax-mediated apoptosis induced by HIV-1 gp120 in Jurkat cells

c-FLIPL, an inhibitor of caspase 8, is known to inhibit the Fas/caspase 8 apoptotic pathway; however, its involvement of Bax/mitochondrial apoptosis is not well understood. Using human cells, Jurkat cell line, induced with HIV-1 gp120, we studied the effects of c-FLIPL on Bax/mitochondrial apoptosis. We found that the induction of apoptosis by HIV-1 envelope protein, gp120, involved the activation of both Bax-dependent and death receptor-mediated pathways, and HIV-1 infection deceased c-FLIPL expression. Interestingly, c-FLIPL expression downregulated protein kinase C (PKC) expression at the transcript level involving activated protein-2 (AP-2). c-FLIPL expression reduced AP-2 protein levels required to promote PKC protein expression and PKC-associated inactive form of Bax, and inhibited Bax activation, suggesting that c-FLIPL inhibits Bax activation via modulating PKC expression at the transcriptional level involving AP-2 during gp120 treatment. Collectively, these findings further corroborate the concept that gp120 plays an important role, via involvement of molecules such as c-FLIPL, in apoptotic cell death due to HIV-1 infection.