Apoptosis subversion: HIV-Nef provides both armor and sword

HIV-1 infection of T cells and macrophages are differentially modulated by virion-associated Hck: a Nef-dependent phenomenon

The proline repeat motif (PxxP) of Nef is required for interaction with the SH3 domains of macrophage-specific Src kinase Hck. However, the implication of this interaction for viral replication and infectivity in macrophages and T lymphocytes remains unclear. Experiments in HIV-1 infected macrophages confirmed the presence of a Nef:Hck complex which was dependent on the Nef proline repeat motif. The proline repeat motif of Nef also enhanced both HIV-1 infection and replication in macrophages, and was required for incorporation of Hck into viral particles. Unexpectedly, wild-type Hck inhibited infection of macrophages, but Hck was shown to enhance infection of primary T lymphocytes. These results indicate that the interaction between Nef and Hck is important for Nef-dependent modulation of viral infectivity. Hck-dependent enhancement of HIV-1 infection of T cells suggests that Nef-Hck interaction may contribute to the spread of HIV-1 infection from macrophages to T cells by modulating events in the producer cell, virion and target cell.

Ingenol Protects Human T Cells From HIV-1 Infection

Objectives

Many natural compounds have been investigated as drug candidates to prevent human immunodeficiency virus (HIV) with low cytotoxicity. We tested whether ingenol from Euphorbia ingens exerts anti-HIV effects in human T cell lines.

Methods and Results

Ingenol effectively maintained high cell viability (CD₅₀, >1 mM) in H9 and MT4 T cells. The efficacy of ingenol to inhibit HIV-1 infection was dose dependent. ED₅₀ for 100 and 200 TCID₅₀ of HIV-1 was 5.06 and 16.87 μM, respectively. Gag p24 antigen production in ingenol-treated MT4 cells was reduced by 24.5% on day 6 post-infection. While p24 antigen was reduced in ingenol-treated cells, levels of cytokines such as TNF-α and IL-6 and chemokines such as RANTES and MCP-1 were increased. dUTP level related to late apoptotic events was increased on day 2 post-infection of HIV by ingenol treatment, whereas expression of annexin V was unchanged. Reduced levels of iNOS and ZAP-70 after HIV infection were recovered by ingenol treatment.

Conclusion

Ingenol helps T cells to survive longer against viremia after HIV-1 infection, without exerting cytotoxic effects. Ingenol can be considered a safe and efficacious candidate for immune-boosting therapy for AIDS patients.

HIV-1 induces DCIR expression in CD4+ T cells

The C-type lectin receptor DCIR, which has been shown very recently to act as an attachment factor for HIV-1 in dendritic cells, is expressed predominantly on antigen-presenting cells. However, this concept was recently challenged by the discovery that DCIR can also be detected in CD4⁺ T cells found in the synovial tissue from rheumatoid arthritis (RA) patients. Given that RA and HIV-1 infections share common features such as a chronic inflammatory condition and polyclonal immune hyperactivation status, we hypothesized that HIV-1 could promote DCIR expression in CD4⁺ T cells. We report here that HIV-1 drives DCIR expression in human primary CD4⁺ T cells isolated from patients (from both aviremic/treated and viremic/treatment naive persons) and cells acutely infected in vitro (seen in both virus-infected and uninfected cells). Soluble factors produced by virus-infected cells are responsible for the noticed DCIR up-regulation on uninfected cells. Infection studies with Vpr- or Nef-deleted viruses revealed that these two viral genes are not contributing to the mechanism of DCIR induction that is seen following acute infection of CD4⁺ T cells with HIV-1. Moreover, we report that DCIR is linked to caspase-dependent (induced by a mitochondria-mediated generation of free radicals) and -independent intrinsic apoptotic pathways (involving the death effector AIF). Finally, we demonstrate that the higher surface expression of DCIR in CD4⁺ T cells is accompanied by an enhancement of virus attachment/entry, replication and transfer. This study shows for the first time that HIV-1 induces DCIR membrane expression in CD4⁺ T cells, a process that might promote virus dissemination throughout the infected organism.

The type II transmembrane protein DCIR belongs to the C-type lectin domain family receptor and is predominantly expressed in cells of the myeloid lineage. However recent evidence suggests that it can also be induced in CD4⁺ T cells placed under an inflammatory condition. We assessed the capacity of HIV-1 to promote DCIR expression in CD4⁺ T cells because the establishment of an inflammatory state is a hallmark of this retroviral infection in humans. We report here that a higher DCIR expression is detected not only in CD4⁺ T cells acutely infected with HIV-1 in vitro but also in clinical cell samples. Additional studies suggest a possible link between DCIR induction and apoptosis through both caspase-dependent and -independent intrinsic pathways. The greater expression of DCIR on the surface of CD4⁺ T cells results in more efficient virus attachment/entry, replication and transfer processes.

Human immunodeficiency virus (HIV-1) infection selectively downregulates PD-1 expression in infected cells and protects the cells from early apoptosis in vitro and in vivo

Programmed Death-1 (PD-1), a member of T cell costimulatory molecules is expressed in high levels on antigen specific T cells during chronic viral infection, whereas PD-1 expression in the context of HIV-1 infected CD4+ T cells is not known. Here we report that productively infected CD4+ T cells lose PD-1, whereas bystander cells were unaffected. Additionally, p24+/PD-1 negative cells are less susceptible to apoptosis compared to bystander cells in the same infected milieu. Similar results were observed in vivo, as infected T cells isolated from HIV-1+ individuals have significantly low level of PD-1 and the observed loss of PD-1 in vivo is independent of viral load, CD4 count, and/or antiviral treatment. Together these results indicate that productively infected cells are resistant to early apoptosis by downregulating PD-1, whereas PD-1 enhances the susceptibility of effector T cells to apoptosis suggesting a dual role for PD-1 during HIV-1 infection.

Molecular interactions of human immunodeficiency virus type 1 with primary human oral keratinocytes

Infection of the oral mucosa of human immunodeficiency virus type 1 (HIV-1)-infected individuals remains an under-evaluated and somewhat enigmatic process. Nonetheless, it is of profound importance in the ongoing AIDS pandemic, based on its potential as a site of person-to-person transmission of the virus as well as a location of HIV-1 pathogenesis and potential reservoir of disease in the setting of virally suppressive highly active antiretroviral therapy. We utilized molecular and virological techniques to analyze HIV-1 infection of primary human mucosal cells and also evaluated the proapoptotic potential of selected HIV-1 proteins in primary isolated human oral keratinocytes. Primary isolated human oral keratinocytes were plated on 0.4 microM polyethylenetetraphthalate cell culture inserts to form an in vitro oral mucosal layer. The strength of this layer in forming a barrier was determined by measuring trans-epithelial electrical current passage across the monolayer. The oral keratinocyte monolayers had trans-epithelial electrical resistance of approximately 176 to 208 omega. For viral infectivity assays, the macrophage-tropic (R5) HIV-1 strains, YU-2 and ADA, and T-cell-line-tropic (X4), NL4-3 virions, incubated with or without deoxynucleoside triphosphates (dNTPs) and/or the polyamines spermine and spermidine, were used to infect oral keratinocytes. Of importance, polyamines and dNTPs have been shown to enhance natural endogenous reverse transcription (NERT), a step essential for early lentiviral infection, and are abundantly present in human semen. The infectivities of HIV-1 strains YU-2, ADA, and NL4-3 for these primary keratinocytes were dramatically increased by the addition of physiological concentrations of dNTPs, spermine, and spermidine. Binding and viral internalization assay studies showed no differences in these oral mucosal cells, with or without NERT-altering agents. It was also observed that the recombinant, cell-free HIV-1 proteins Nef, Tat, and gp120 (R5) induced apoptosis in primary oral keratinocytes compared with the results seen with nontreated cells or cells treated with glutathione S-transferase protein as a control under similar conditions. Microarray analyses suggested that HIV-1 gp120 and Tat induce apoptosis in primary human oral keratinocytes via the Fas/FasL apoptotic pathway, whereas induction of apoptosis by Nef occurs through both Fas/FasL and mitochondrial apoptotic pathways. Thus, these findings suggest molecular mechanisms by which semen in particular, as well as other bodily fluids such as cervicovaginal secretions, could increase oral transmission of HIV-1 via increasing infectivity in confluent and low-replicating oral keratinocytes. As well, the induction of apoptosis in human oral keratinocytes with relevant HIV-1-specific proteins suggests another potential complementary mechanism by which the oral mucosa barrier may be disrupted during HIV-1 infection in vivo.

HIV-1 Nef-induced FasL induction and bystander killing requires p38 MAPK activation

The human immunodeficiency virus (HIV) has been reported to target noninfected CD4 and CD8 cells for destruction. This effect is manifested in part through up-regulation of the death receptor Fas ligand (FasL) by HIV-1 negative factor (Nef), leading to bystander damage. However, the signal transduction and transcriptional regulation of this process remains elusive. Here, we provide evidence that p38 mitogen-activated protein kinase (MAPK) is required for this process. Loss-of-function experiments through dominant-negative p38 isoform, p38 siRNA, and chemical inhibitors of p38 activation suggest that p38 is necessary for Nef-induced activator protein-1 (AP-1) activation, as inhibition leads to an attenuation of AP-1-dependent transcription. Furthermore, mutagenesis of the FasL promoter reveals that its AP-1 enhancer element is required for Nef-mediated transcriptional activation. Therefore, a linear pathway for Nef-induced FasL expression that encompasses p38 and AP-1 has been elucidated. Furthermore, chemical inhibition of the p38 pathway attenuates HIV-1-mediated bystander killing of CD8 cells in vitro.

Impact of Nef-mediated downregulation of major histocompatibility complex class I on immune response to simian immunodeficiency virus

Functional activities that have been ascribed to the nef gene product of simian immunodeficiency virus (SIV) and human immunodeficiency virus (HIV) include CD4 downregulation, major histocompatibility complex (MHC) class I downregulation, downregulation of other plasma membrane proteins, and lymphocyte activation. Monkeys were infected experimentally with SIV containing difficult-to-revert mutations in nef that selectively eliminated MHC downregulation but not these other activities. Monkeys infected with these mutant forms of SIV exhibited higher levels of CD8(+) T-cell responses 4 to 16 weeks postinfection than seen in monkeys infected with the parental wild-type virus. Furthermore, unusual compensatory mutations appeared by 16 to 32 weeks postinfection which restored some or all of the MHC-downregulating activity. These results indicate that nef does serve to limit the virus-specific CD8 cellular response of the host and that the ability to downregulate MHC class I contributes importantly to the totality of nef function.

A novel mechanism for HIV1-mediated bystander CD4+ T-cell death: neighboring dying cells drive the capacity of HIV1 to kill noncycling primary CD4+ T cells

CD4+ T-cell death is a crucial feature of AIDS pathogenesis, but the mechanisms involved remain unclear. Here, we present in vitro findings that identify a novel process of HIV1 mediated killing of bystander CD4+ T cells, which does not require productive infection of these cells but depends on the presence of neighboring dying cells. X4-tropic HIV1 strains, which use CD4 and CXCR4 as receptors for cell entry, caused death of unstimulated noncycling primary CD4+ T cells only if the viruses were produced by dying, productively infected T cells, but not by living, chronically infected T cells or by living HIV1-transfected HeLa cells. Inducing cell death in HIV1-transfected HeLa cells was sufficient to obtain viruses that caused CD4+ T-cell death. The addition of supernatants from dying control cells, including primary T cells, allowed viruses produced by living HIV1-transfected cells to cause CD4+ T-cell death. CD4+ T-cell killing required HIV1 fusion and/or entry into these cells, but neither HIV1 envelope-mediated CD4 or CXCR4 signaling nor the presence of the HIV1 Nef protein in the viral particles. Supernatants from dying control cells contained CD95 ligand (CD95L), and antibody-mediated neutralization of CD95L prevented these supernatants from complementing HIV1 in inducing CD4+ T-cell death. Our in vitro findings suggest that the very extent of cell death induced in vivo during HIV1 infection by either virus cytopathic effects or immune activation may by itself provide an amplification loop in AIDS pathogenesis. More generally, they provide a paradigm for pathogen-mediated killing processes in which the extent of cell death occurring in the microenvironment might drive the capacity of the pathogen to induce further cell death.

Leishmania major-mediated prevention of programmed cell death induction in infected macrophages is associated with the repression of mitochondrial release of cytochrome c

Leishmania are obligate, intracellular parasites of macrophages in their vertebrate hosts, including humans, in which they cause disease. Here, we report that in vitro infection with Leishmania major protects murine bone marrow-derived macrophages against programmed cell death (PCD) induced by deprival of macrophage-colony stimulating factor and delays PCD caused by treatment with staurosporine, a broad inducer of PCD. This preventive effect was observed in macrophages from L. major-susceptible BALB/c and L. major-resistant C57BL/6 mice, indicating that repression of PCD did not depend on genetic background-specific regulation of T helper cell type 1 (Th1)/Th2 cytokine secretion. Prevention of effector caspase activation and PCD was associated with a repression of mitochondrial release of cytochrome c and did not involve the nuclear factor-kappaB pathway. The capacity of L. major to delay PCD induction in the infected macrophages may have implications for Leishmania pathogenesis by favoring the invasion of its host and the persistence of the parasite in the infected cells.

Interactions of processed Nef (58-206) with virion proteins of HIV type 1

The Nef protein plays a major role in vivo in promoting HIV and SIV replication and pathogenesis. In vitro, Nef has been shown to down-regulate cell surface molecules, such as CD4 and MHC-I, alter T cell signaling, and enhance virion infectivity. These effects are attributed to interactions of Nef with cellular proteins. In addition, HIV Nef is incorporated into viral particles, mainly localizing in the virion cores. However, no report has been published to date regarding Nef interactions with virion proteins. By immunoprecipitation, Nef was found to bind to viral enzymes. Using yeast two-hybrid and GST pulldown procedures to find out direct potential partners of Nef, Nef was consistently found to interact with viral integrase (IN). The interaction between Nef and IN was stronger when Nef was present as the viral protease-cleaved isoform. We hypothesize that the interaction of Nef with viral integrase or other virion proteins may explain the presence of Nef in viral cores. In addition, this interaction suggests that Nef may accompany the reverse transcription and the preintegration complexes during the early steps of the infection cycle and potentially affect infectivity during these steps.

Differential gene expression during HIV-1 infection analyzed by suppression subtractive hybridization

OBJECTIVE

Characterization of the effects of HIV-1 infection and apoptosis on cellular and viral gene expression.

METHODS

Flow cytometry was used to analyze infection and apoptosis concurrently in HIV-1IIIB-infected CEM-SS T cells. Suppression subtractive hybridization (SSH) was applied to cells from different time points of infection to construct subtracted complementary DNA (cDNA) libraries. Differential screening and Northern blots confirmed differential gene expression and these genes were sequenced and compared with database.

RESULTS

T cells undergo apoptosis at early stages of HIV-1IIIB infection (days 5-7 post-infection). Surprisingly, cells begin to recover after day 9 and by day 18 almost all infected cells are viable, even though they maintain the same level of infection. By SSH, differential gene expression profiles between day 7 and day 18 after HIV-1IIIB infection were characterized. SSH yielded two subtracted cDNA libraries; differential screening of the subtracted cDNA libraries suggested that 200 out of 864 colonies were highly expressed at their respective time points. DNA sequence analysis identified specific apoptosis-related genes, HIV-1 viral genes, and other candidate genes of interest. Northern blot analysis confirmed that some of these genes were expressed predominantly at the 'apoptotic' or 'non-apoptotic' time points.

CONCLUSIONS

Known and novel cellular gene products have been identified that are directly (or inversely) correlated with apoptosis and may regulate cell death in HIV-1 infection. These results provide a framework for functional studies on the differentially expressed genes and may suggest novel therapeutic approaches for treatment of HIV-1-infected individuals.

Avances en la inmunopatología de la infección por el VIH

The progressive and irreversible destruction of the immune system represents the hallmark of HIV infection. Even though this process is directly related to the infection of CD4 lymphocytes, the destruction of this lymphocyte population observed along infection is not solely due to a direct cytopathic effect elicited by HIV replication. AIDS immune pathogenesis is an extremely complex phenomenon involving different mechanisms which are not fully understood yet. In this article the mechanisms involved in HIV infection and destruction of target cells and the immune response elicited by HIV are analysed. Finally, viral escape mechanisms to host immune response are considered.

Frequent loss of Fas expression and function in human lung tumours with overexpression of FasL in small cell lung carcinoma

Fas (CD95) and its ligand FasL signal apoptosis and are involved in tissue homeostasis and the elimination of target cells by cytotoxic T cells. Corruption of this signalling pathway in tumour cells, for example by reduced Fas expression or increased FasL expression, can participate in tumour development and immune escape. The present study has analysed Fas/FasL expression and Fas death signalling function in vivo in lung tumour tissues [57 non-small cell lung carcinomas and 64 neuroendocrine lung tumours including small cell lung carcinoma (SCLC)] in comparison with normal lung tissue, and in vitro in neuroendocrine tumour cell lines in comparison with normal human bronchial epithelial cells. The Fas expression score was markedly decreased compared with normal lung tissue in 90% of the 121 lung tumours and was completely lost in 24%. The Fas staining pattern suggested cytoplasmic Fas expression in tumours, whereas membrane expression was observed in normal lung tissue. Loss of Fas at the cell surface was also shown in vitro by FACS analysis of neuroendocrine tumour cell lines and was concomitant with the resistance of tumour cells to FasL-mediated apoptosis according to in vitro cell viability. The lack of cell surface Fas expression in tumour cell lines resulted from the lack of intracellular Fas protein due to impaired Fas gene transcription. The FasL expression score was also decreased in most non-small cell lung carcinomas compared with normal bronchial cells, whereas 91% of SCLCs had higher expression than normal cells. FasL overexpression was related to advanced tumour stage as well as to a Fas/FasL ratio less than 1. It is concluded that a marked decrease in Fas expression may be part of lung tumourigenesis allowing tumour cells to escape from apoptosis. FasL overexpression in the context of Fas down-regulation in SCLC predicts the ability of SCLC cells to induce paracrine killing of Fas-expressing cytotoxic T cells. In lung tumours, Fas restoration may represent a key, although not unique, step in therapeutic strategies to reconstitute the ability of tumour cells to undergo apoptosis.

[HIV1-associated CD4 T lymphocyte apoptosis]

PURPOSE

Apoptosis during HIV infection has been evoked for ten years. The role of apoptosis during HIV infection have be confirmed by several authors but the exact relationships between viral replication, apoptosis and lymphocyte depletion remain to be clarified.

CURRENT KNOWLEDGE AND KEY POINTS

HIV may induce apoptosis of infected but also of uninfected bystander CD4+ lymphocytes. Those two types of HIV induced apoptosis lie on different pathways. While Fas and FasL are involved in apoptosis of bystander cells, mitochondrial pathway is required for apoptosis of infected cells. Cytokines but also anti HIV drugs may modulate HIV-induced lymphocyte apoptosis. Morever while protease inhibitor influence HIV replication and then secondary apotosis of infected cells, they can also interfere with spontaneous apoptosis of lymphocyte beside the context of HIV infection.

FUTURES AND PROJECTS

Apoptosis is thought to be one of the mechanism involved in CD4 T lymphocyte cell death during HIV infection. However relationships between apoptosis and HIV replication may be more complex. In fact it has been recently reported that while HIV replication induced lymphocyte apoptosis, apoptosis may in turn induced HIV replication in a loop amplification pathway

Extensive apoptosis in lymphoid organs during primary SIV infection predicts rapid progression towards AIDS

OBJECTIVE

The acute phase of HIV and SIV infections leads to a host/virus equilibrium, and accumulating evidence suggests that this early phase dictates further progression towards AIDS. To gain insight into the early events that determine rapid disease progression, we performed a longitudinal study in the SIV rhesus macaque model, allowing an in-depth analysis of the primary stage of infection.

METHODS

We assessed viral replication (quantification of replicating and infected cells in lymph nodes, plasma viral load), immune response (cytotoxic T lymphocyte, antibody, proliferative responses), apoptosis and cycling cells (Ki-67 labelling) on lymph nodes and blood in nine rhesus macaques infected with the pathogenic SIVmac251 isolate.

RESULTS

Six primates remained asymptomatic during the one year follow-up period of the study, whereas three developed AIDS within 5-6 months. During the first 2 weeks of infection, peak numbers of apoptotic cells in the lymph node T-cell areas were significantly higher in the three future rapid progressors than in the six future slow progressors, and were correlated with subsequent viraemia levels measured 6 months after infection. The numbers of infected or cycling cells in the same lymph node T-cell areas, however, only became significantly different in future rapid and slow progressors 8 weeks after infection, at the end of the primary phase.

CONCLUSION

Our findings identified extensive apoptosis induction in peripheral lymphoid organs as an early and predictive event that may play a crucial role in impairing the capacity of the immune system to control viral replication and progression towards disease.

Cardiomyocytes undergo apoptosis in human immunodeficiency virus cardiomyopathy through mitochondrion- and death receptor-controlled pathways

We investigated 18 AIDS hearts (5 with and 13 without cardiomyopathy) by using immunocytochemistry and computerized image analysis regarding the roles of HIV-1 proteins and tumor necrosis factor ligands in HIV cardiomyopathy (HIVCM). HIVCM and cardiomyocyte apoptosis were significantly related to each other and to the expression by inflammatory cells of gp120 and tumor necrosis factor-alpha. In HIVCM heart, active caspase 9, a component of the mitochondrion-controlled apoptotic pathway, and the elements of the death receptor-mediated pathway, tumor necrosis factor-alpha and Fas ligand, were expressed strongly on macrophages and weakly on cardiomyocytes. HIVCM showed significantly greater macrophage infiltration and cardiomyocyte apoptosis rate compared with non-HIVCM. HIV-1 entered cultured neonatal rat ventricular myocytes by macropinocytosis but did not replicate. HIV-1- or gp120-induced apoptosis of rat myocytes through a mitochondrion-controlled pathway, which was inhibited by heparin, AOP-RANTES, or pertussis toxin, suggesting that cardiomyocyte apoptosis is induced by signaling through chemokine receptors. In conclusion, in patients with HIVCM, cardiomyocytes die through both mitochondrion- and death receptor-controlled apoptotic pathways.

On the origin, evolution, and nature of programmed cell death: a timeline of four billion years

Programmed cell death is a genetically regulated process of cell suicide that is central to the development, homeostasis and integrity of multicellular organisms. Conversely, the dysregulation of mechanisms controlling cell suicide plays a role in the pathogenesis of a wide range of diseases. While great progress has been achieved in the unveiling of the molecular mechanisms of programmed cell death, a new level of complexity, with important therapeutic implications, has begun to emerge, suggesting (i) that several different self-destruction pathways may exist and operate in parallel in our cells, and (ii) that molecular effectors of cell suicide may also perform other functions unrelated to cell death induction and crucial to cell survival. In this review, I will argue that this new level of complexity, implying that there may be no such thing as a 'bona fide' genetic death program in our cells, might be better understood when considered in an evolutionary context. And a new view of the regulated cell suicide pathways emerges when one attempts to ask the question of when and how they may have become selected during evolution, at the level of ancestral single-celled organisms.