Human immunodeficiency virus type 1 (HIV-1) Vpr-regulated cell death: insights into mechanism

CRL4-DCAF1 Ubiquitin Ligase Dependent Functions of HIV Viral Protein R and Viral Protein X

The Human Immunodeficiency Virus (HIV) encodes several proteins that contort the host cell environment to promote viral replication and spread. This is often accomplished through the hijacking of cellular ubiquitin ligases. These reprogrammed complexes initiate or enhance the ubiquitination of cellular proteins that may otherwise act to restrain viral replication. Ubiquitination of target proteins may alter protein function or initiate proteasome-dependent destruction. HIV Viral Protein R (Vpr) and the related HIV-2 Viral Protein X (Vpx), engage the CRL4-DCAF1 ubiquitin ligase complex to target numerous cellular proteins. In this review we describe the CRL4-DCAF1 ubiquitin ligase complex and its interactions with HIV Vpr and Vpx. We additionally summarize the cellular proteins targeted by this association as well as the observed or hypothesized impact on HIV.

HIV-1 Vif disrupts phosphatase feedback regulation at the kinetochore, leading to a pronounced pseudo-metaphase arrest

The human immunodeficiency virus type 1 (HIV-1) Virion Infectivity Factor (Vif) targets and degrades cellular APOBEC3 proteins, key regulators of intrinsic and innate antiretroviral immune responses, thereby facilitating HIV-1 infection. While Vif's role in degrading APOBEC3G is well-studied, Vif is also known to cause cell cycle arrest but the detailed nature of Vif's effects on the cell cycle has yet to be delineated. In this study, we employed high-temporal single-cell live imaging and super-resolution microscopy to monitor individual cells during Vif-induced cell cycle arrest. Our findings reveal that Vif does not affect the G2/M boundary as previously thought. Instead, Vif triggers a unique and robust pseudo-metaphase arrest, which is markedly distinct from the mild prometaphase arrest induced by the HIV-1 accessory protein, Vpr, known for modulating the cell cycle. During Vif-mediated arrest, chromosomes align properly to form a metaphase plate but later disassemble, resulting in polar chromosomes. Notably, unlike Vpr, Vif significantly reduces the levels of both Phosphatase 1 (PP1) and 2 (PP2) at kinetochores, which are key regulators of chromosome-microtubule interactions. These results reveal a novel function of Vif in kinetochore regulation that governs the spatial organization of chromosomes during mitosis.

Mechanism of cell cycle regulation and cell proliferation during human viral infection

Over the history of the coevolution of Host viral interaction, viruses have customized the host cellular machinery into their use for viral genome replication, causing effective infection and ultimately aiming for survival. They do so by inducing subversions to the host cellular pathways like cell cycle via dysregulation of important cell cycle checkpoints by viral encoded proteins, arresting the cell cycle machinery, blocking cytokinesis as well as targeting subnuclear bodies, thus ultimately disorienting the cell proliferation. Both DNA and RNA viruses have been active participants in such manipulation resulting in serious outcomes of cancer. They achieve this by employing different mechanisms-Protein-protein interaction, protein-phosphorylation, degradation, redistribution, viral homolog, and viral regulation of APC at different stages of cell cycle events. Several DNA viruses cause the quiescent staged cells to undergo cell cycle which increases nucleotide pools logistically significantly persuading viral replication whereas few other viruses arrest a particular stage of cell cycle. This allows the latter group to sustain the infection which allows them to escape host immune response and support viral multiplication. Mechanical study of signaling such viral mediated pathways could give insight into understanding the etiology of tumorigenesis and progression. Overall this chapter highlights the possible strategies employed by DNA/RNA viral families which impact the normal cell cycle but facilitate viral infected cell replication. Such information could contribute to comprehending viral infection-associated disorders to further depth.

Specific Biological Features of Adipose Tissue, and Their Impact on HIV Persistence

Although white AT can contribute to anti-infectious immune responses, it can also be targeted and perturbed by pathogens. The AT's immune involvement is primarily due to strong pro-inflammatory responses (with both local and paracrine effects), and the large number of fat-resident macrophages. Adipocytes also exert direct antimicrobial responses. In recent years, it has been found that memory T cells accumulate in AT, where they provide efficient secondary responses against viral pathogens. These observations have prompted researchers to re-evaluate the links between obesity and susceptibility to infections. In contrast, AT serves as a reservoir for several persistence pathogens, such as human adenovirus Ad-36, Trypanosoma gondii, Mycobacterium tuberculosis, influenza A virus, and cytomegalovirus (CMV). The presence and persistence of bacterial DNA in AT has led to the concept of a tissue-specific microbiota. The unexpected coexistence of immune cells and pathogens within the specific AT environment is intriguing, and its impact on anti-infectious immune responses requires further evaluation. AT has been recently identified as a site of HIV persistence. In the context of HIV infection, AT is targeted by both the virus and the antiretroviral drugs. AT's intrinsic metabolic features, large overall mass, and wide distribution make it a major tissue reservoir, and one that may contribute to the pathophysiology of chronic HIV infections. Here, we review the immune, metabolic, viral, and pharmacological aspects that contribute to HIV persistence in AT. We also evaluate the respective impacts of both intrinsic and HIV-induced factors on AT's involvement as a viral reservoir. Lastly, we examine the potential consequences of HIV persistence on the metabolic and immune activities of AT.

The construction and analysis of tumor-infiltrating immune cell and ceRNA networks in recurrent soft tissue sarcoma

Soft tissue sarcoma (STS) is one of the most challenging tumors for medical oncologists, with a high rate of recurrence after initial resection. In this study, a recurrent STS-specific competitive endogenous RNA (ceRNA) network including seven recurrence and overall survival (OS)-associated genes (LPP-AS2, MUC1, GAB2, hsa-let-7i-5p, hsa-let-7f-5p, hsa-miR-101-3p and hsa-miR-1226-3p) was established based on the gene expression profiling of 259 primary sarcomas and 3 local recurrence samples from the TCGA database. The algorithm "cell type identification by estimating relative subsets of RNA transcripts (CIBERSORT)" was applied to estimate the fraction of immune cells in sarcomas. Based on 5 recurrence and OS-associated immune cells (NK cells activated, dendritic cells resting, mast cells resting, mast cells activated and macrophages M1), we constructed a recurrent STS-specific immune cells network. Both nomograms were identified to have good reliabilities (Area Under Curve (AUC) of 5-year survival is 0.724 and 0.773, respectively). Then the co-expression analysis was performed to identify the potential regulation network among recurrent STS-specific immune cells and ceRNAs. Hsa-miR-1226-3p and MUC1 were significantly correlated and dendritic cells resting was related to hsa-miR-1226-3p. Additionally, the expression of MUC1 and dendritic cell marker CD11c were also verified by immunohistochemistry (IHC) assay and multidimensional databases. In conclusion, this study illustrated the potential mechanism of hsa-miR-1226-3p regulating MUC1 and dendritic cells resting might play an important role in STS recurrence. These findings might provide potential prognostic biomarkers and therapeutic targets for recurrent STS.

Sensing of HIV-1 Infection in Tzm-bl Cells with Reconstituted Expression of STING

Production of proinflammatory cytokines indicative of potent recognition by the host innate immune system has long been recognized as a hallmark of the acute phase of HIV-1 infection. The first components of the machinery by which primary HIV target cells sense infection have recently been described; however, the mechanistic dissection of innate immune recognition and viral evasion would be facilitated by an easily accessible cell line model. Here we describe that reconstituted expression of the innate signaling adaptor STING enhanced the ability of the well-established HIV reporter cell line Tzm-bl to sense HIV infection and to convert this information into nuclear translocation of IRF3 as well as expression of cytokine mRNA. STING-dependent immune sensing of HIV-1 required virus entry and reverse transcription but not genome integration. Particularly efficient recognition was observed for an HIV-1 variant lacking expression of the accessory protein Vpr, suggesting a role of the viral protein in circumventing STING-mediated immune signaling. Vpr as well as STING significantly impacted the magnitude and breadth of the cytokine mRNA expression profile induced upon HIV-1 infection. However, cytoplasmic DNA sensing did not result in detectable cytokine secretion in this cell system, and innate immune recognition did not affect infection rates. Despite these deficits in eliciting antiviral effector functions, these results establish Tzm-bl STING and Tzm-bl STING IRF3.GFP cells as useful tools for studies aimed at dissecting mechanisms and regulation of early innate immune recognition of HIV infection.

IMPORTANCE

Cell-autonomous immune recognition of HIV infection was recently established as an important aspect by which the host immune system attempts to fend off HIV-1 infection. Mechanistic studies on host cell recognition and viral evasion are hampered by the resistance of many primary HIV target cells to detailed experimental manipulation. We describe here that expression of the signaling adaptor STING renders the well-established HIV reporter cell line Tzm-bl competent for innate recognition of HIV infection. Key characteristics reflected in this cell model include nuclear translocation of IRF3, expression of a broad range of cytokine mRNAs, and an antagonistic activity of the HIV-1 protein Vpr. These results establish Tzm-bl STING and Tzm-bl STING IRF3.GFP cells as a useful tool for studies of innate recognition of HIV infection.

Influence of glutathione availability on cell damage induced by human immunodeficiency virus type 1 viral protein R

The human immunodeficiency virus type 1 (HIV-1) encodes for accessory viral protein R (Vpr), which arrests the cell cycle of host cells at G2 and causes mitochondrial dysfunction and alterations in glycolysis. High-level expression of Vpr protein correlates with increased viral production and disease progression. Vpr causes structural and functional injury in many types of eukaryotic cells, whether or not they are permissive for viral replication; among them is the budding yeast Saccharomyces cerevisiae. We hypothesized that the dramatic Vpr-induced injuries in yeast could be prevented by strengthening their redox response capacity. We show that exogenous addition of glutathione (GSH) or its prodrug, N-acetylcysteine (NAC), protected budding yeasts from Vpr-induced cytopathic effects. Moreover, addition of adenosine triphosphate (ATP) to growing cultures of Vpr-producing yeast returned cellular growth to control levels, whereas the addition dehydroascorbic acid (DHA) had only a minor protective effect. The diminished protein levels of Cox2p and Cox4p in wild typeVpr-producing yeasts together with the acute sensitivity of petite yeasts to Vpr activity may have been caused by low intracellular ATP levels. As a consequence of this energy deficit, eukaryotic cells would be unable to synthetize adequate supplies of GSH or to signal the mitochondrial retrograde response. Our findings strongly suggest that the cytopathogenic effect of Vpr protein in eukaryotic cells can be prevented by increasing intracellular antioxidant stores or, alternatively, supplying external ATP. Furthermore, these results support a potentially promising future for S. cerevisiae expression as a modality to search for Vpr-targeted inhibitors.

HIV-1 Vpr- and Reverse Transcription-Induced Apoptosis in Resting Peripheral Blood CD4 T Cells and Protection by Common Gamma-Chain Cytokines

HIV-1 infection leads to the progressive depletion of the CD4 T cell compartment by various known and unknown mechanisms. In vivo, HIV-1 infects both activated and resting CD4 T cells, but in vitro, in the absence of any stimuli, resting CD4 T cells from peripheral blood are resistant to infection. This resistance is generally attributed to an intracellular environment that does not efficiently support processes such as reverse transcription (RT), resulting in abortive infection. Here, we show that in vitro HIV-1 infection of resting CD4 T cells induces substantial cell death, leading to abortive infection. In vivo, however, various microenvironmental stimuli in lymphoid and mucosal tissues provide support for HIV-1 replication. For example, common gamma-chain cytokines (CGCC), such as interleukin-7 (IL-7), render resting CD4 T cells permissible to HIV-1 infection without inducing T cell activation. Here, we find that CGCC primarily allow productive infection by preventing HIV-1 triggering of apoptosis, as evidenced by early release of cytochrome c and caspase 3/7 activation. Cell death is triggered both by products of reverse transcription and by virion-borne Vpr protein, and CGCC block both mechanisms. When HIV-1 RT efficiency was enhanced by SIVmac239 Vpx protein, cell death was still observed, indicating that the speed of reverse transcription and the efficiency of its completion contributed little to HIV-1-induced cell death in this system. These results show that a major restriction on HIV-1 infection in resting CD4 T cells resides in the capacity of these cells to survive the early steps of HIV-1 infection.

IMPORTANCE

A major consequence of HIV-1 infection is the destruction of CD4 T cells. Here, we show that delivery of virion-associated Vpr protein and the process of reverse transcription are each sufficient to trigger apoptosis of resting CD4 T cells isolated from peripheral blood. While these 2 mechanisms have been previously described in various cell types, we show for the first time their concerted effect in inducing resting CD4 T cell depletion. Importantly, we found that cytokines such as IL-7 and IL-4, which are particularly active in sites of HIV-1 replication, protect resting CD4 T cells from these cytopathic effects and, primarily through this protection, rather than through enhancement of specific replicative steps, they promote productive infection. This study provides important new insights for the understanding of the early steps of HIV-1 infection and T cell depletion.

Adipose Tissue Is a Neglected Viral Reservoir and an Inflammatory Site during Chronic HIV and SIV Infection

Two of the crucial aspects of human immunodeficiency virus (HIV) infection are (i) viral persistence in reservoirs (precluding viral eradication) and (ii) chronic inflammation (directly associated with all-cause morbidities in antiretroviral therapy (ART)-controlled HIV-infected patients). The objective of the present study was to assess the potential involvement of adipose tissue in these two aspects. Adipose tissue is composed of adipocytes and the stromal vascular fraction (SVF); the latter comprises immune cells such as CD4+ T cells and macrophages (both of which are important target cells for HIV). The inflammatory potential of adipose tissue has been extensively described in the context of obesity. During HIV infection, the inflammatory profile of adipose tissue has been revealed by the occurrence of lipodystrophies (primarily related to ART). Data on the impact of HIV on the SVF (especially in individuals not receiving ART) are scarce. We first analyzed the impact of simian immunodeficiency virus (SIV) infection on abdominal subcutaneous and visceral adipose tissues in SIVmac251 infected macaques and found that both adipocytes and adipose tissue immune cells were affected. The adipocyte density was elevated, and adipose tissue immune cells presented enhanced immune activation and/or inflammatory profiles. We detected cell-associated SIV DNA and RNA in the SVF and in sorted CD4+ T cells and macrophages from adipose tissue. We demonstrated that SVF cells (including CD4+ T cells) are infected in ART-controlled HIV-infected patients. Importantly, the production of HIV RNA was detected by in situ hybridization, and after the in vitro reactivation of sorted CD4+ T cells from adipose tissue. We thus identified adipose tissue as a crucial cofactor in both viral persistence and chronic immune activation/inflammation during HIV infection. These observations open up new therapeutic strategies for limiting the size of the viral reservoir and decreasing low-grade chronic inflammation via the modulation of adipose tissue-related pathways.

Mycobacterium tuberculosis alters the metalloprotease activity of the COP9 signalosome

Inhibition of apoptotic death of macrophages by Mycobacterium tuberculosis represents an important mechanism of virulence that results in pathogen survival both in vitro and in vivo. To identify M. tuberculosis virulence determinants involved in the modulation of apoptosis, we previously screened a transposon bank of mutants in human macrophages, and an M. tuberculosis clone with a nonfunctional Rv3354 gene was identified as incompetent to suppress apoptosis. Here, we show that the Rv3354 gene encodes a protein kinase that is secreted within mononuclear phagocytic cells and is required for M. tuberculosis virulence. The Rv3354 effector targets the metalloprotease (JAMM) domain within subunit 5 of the COP9 signalosome (CSN5), resulting in suppression of apoptosis and in the destabilization of CSN function and regulatory cullin-RING ubiquitin E3 enzymatic activity. Our observation suggests that alteration of the metalloprotease activity of CSN by Rv3354 possibly prevents the ubiquitin-dependent proteolysis of M. tuberculosis-secreted proteins. IMPORTANCE : Macrophage protein degradation is regulated by a protein complex called a signalosome. One of the signalosomes associated with activation of ubiquitin and protein labeling for degradation was found to interact with a secreted protein from M. tuberculosis, which binds to the complex and inactivates it. The interference with the ability to inactivate bacterial proteins secreted in the phagocyte cytosol may have crucial importance for bacterial survival within the phagocyte.

Innate immune responses to HIV infection in the central nervous system

Human immunodeficiency virus (HIV) invades the brain early during infection and generates a chronic inflammatory microenvironment that can eventually result in neurological disease, even in the absence of significant viral replication. Thus, HIV-1 infection of the brain has been characterized both as a neuroimmunological and neurodegenerative disorder. While the brain and central nervous system (CNS) have historically been regarded as immune privileged or immunologically quiescent, newer concepts of CNS immunity suggest an important if not defining role for innate immune responses generated by glial cells. Innate immunity may be the first line of defense against HIV infection of the brain and CNS, with multiple cellular elements providing responses that can be anti-viral and neuroprotective, but also potentially neurotoxic, impairing neurogenesis and promoting neuronal apoptosis. To investigate the effects of HIV exposure on neurogenesis and neuronal survival, we have studied the responses of human neuroepithelial progenitor (NEP) cells, which undergo directed differentiation into astrocytes and neurons in vitro. We identified a group of genes that were differentially expressed in NEP-derived cells during virus exposure. This included genes that are strongly related to interferon-induced responses and antigen presentation. Moreover, we observed that the host factor apolipoprotein E influences the innate immune response expressed by these cells, with a more robust response in the apolipoprotein E3/E3 genotype cultures compared to the apolipoprotein E3/E4 counterparts. Thus, neuroepithelial progenitors and their differentiated progeny recognize HIV and respond to it by mounting an innate immune response with a vigor that is influenced by the host factor apolipoprotein E.

Viral protein R of human immunodeficiency virus type-1 induces retrotransposition of long interspersed element-1

Background

Viral protein R (Vpr), a protein of human immunodeficiency virus type-1 (HIV-1) with various biological functions, was shown to be present in the blood of HIV-1-positive patients. However, it remained unclear whether circulating Vpr in patients’ blood is biologically active. Here, we examined the activity of blood Vpr using an assay system by which retrotransposition of long interspersed element-1 (L1-RTP) was detected. We also investigated the in vivo effects of recombinant Vpr (rVpr) by administrating it to transgenic mice harboring human L1 as a transgene (hL1-Tg mice). Based on our data, we discuss the involvement of blood Vpr in the clinical symptoms of acquired immunodeficiency syndrome (AIDS).

Results

We first discovered that rVpr was active in induction of L1-RTP. Biochemical analyses revealed that rVpr-induced L1-RTP depended on the aryl hydrocarbon receptor, mitogen-activated protein kinases, and CCAAT/enhancer-binding protein β. By using a sensitive L1-RTP assay system, we showed that 6 of the 15 blood samples from HIV-1 patients examined were positive for induction of L1-RTP. Of note, the L1-RTP-inducing activity was blocked by a monoclonal antibody specific for Vpr. Moreover, L1-RTP was reproducibly induced in various organs, including the kidney, when rVpr was administered to hL1-Tg mice.

Conclusions

Blood Vpr is biologically active, suggesting that its monitoring is worthwhile for clarification of the roles of Vpr in the pathogenesis of AIDS. This is the first report to demonstrate a soluble factor in patients’ blood active for L1-RTP activity, and implies the involvement of L1-RTP in the development of human diseases.

The progestin-only contraceptive medroxyprogesterone acetate, but not norethisterone acetate, enhances HIV-1 Vpr-mediated apoptosis in human CD4+ T cells through the glucocorticoid receptor

The glucocorticoid receptor (GR) regulates several physiological functions, including immune function and apoptosis. The HIV-1 virus accessory protein, viral protein R (Vpr), can modulate the transcriptional response of the GR. Glucocorticoids (GCs) and Vpr have been reported to induce apoptosis in various cells, including T-cells. We have previously shown that the injectable contraceptive, medroxyprogesterone acetate (MPA) is a partial to full agonist for the GR, unlike norethisterone acetate (NET-A). We investigated the functional cross talk between the GR and Vpr in inducing apoptosis in CD4(+) T-cells, in the absence and presence of GCs and these progestins, as well as progesterone. By using flow cytometry, we show that, in contrast to NET-A and progesterone, the synthetic GR ligand dexamethasone (Dex), cortisol and MPA induce apoptosis in primary CD4(+) T-cells. Furthermore, the C-terminal part of the Vpr peptide, or HIV-1 pseudovirus, together with Dex or MPA further increased the apoptotic phenotype, unlike NET-A and progesterone. By a combination of Western blotting, PCR and the use of receptor- selective agonists, we provide evidence that the GR and the estrogen receptor are the only steroid receptors expressed in peripheral blood mononuclear cells. These results, together with the findings that RU486, a GR antagonist, prevents Dex-, MPA- and Vpr-mediated apoptosis, provide evidence for the first time that GR agonists or partial agonists increase apoptosis in primary CD4(+) T-cells via the GR. We show that apoptotic induction involves differential expression of key apoptotic genes by both Vpr and GCs/MPA. This work suggests that contraceptive doses of MPA but not NET-A or physiological doses of progesterone could potentially accelerate depletion of CD4(+) T-cells in a GR-dependent fashion in HIV-1 positive women, thereby contributing to immunodeficiency. The results imply that choice of progestin used in contraception may be critical to susceptibility and progression of diseases such as HIV-1.

Subcellular localization and function of an epitope-tagged p7 viroporin in hepatitis C virus-producing cells

The hepatitis C virus (HCV) viroporin p7 is crucial for production of infectious viral progeny. However, its role in the viral replication cycle remains incompletely understood, in part due to the poor availability of p7-specific antibodies. To circumvent this obstacle, we inserted two consecutive hemagglutinin (HA) epitope tags at its N terminus. HA-tagged p7 reduced peak virus titers ca. 10-fold and decreased kinetics of virus production compared to the wild-type virus. However, HA-tagged p7 rescued virus production of a mutant virus lacking p7, thus providing formal proof that the tag does not disrupt p7 function. In HCV-producing cells, p7 displayed a reticular staining pattern which colocalized with the HCV envelope glycoprotein 2 (E2) but also partially with viral nonstructural proteins 2, 3, and 5A. Using coimmunoprecipitation, we confirmed a specific interaction between p7 and NS2, whereas we did not detect a stable interaction with core, E2, or NS5A. Moreover, we did not observe p7 incorporation into affinity-purified virus particles. Consistently, there was no evidence supporting a role of p7 in viral entry, as an anti-HA antibody was not able to neutralize Jc1 virus produced from an HA-p7-tagged genome. Collectively, these findings highlight a stable interaction between p7 and NS2 which is likely crucial for production of infectious HCV particles. Use of this functional epitope-tagged p7 variant should facilitate the analysis of the final steps of the HCV replication cycle.

Adipogenic/lipid, inflammatory, and mitochondrial parameters in subcutaneous adipose tissue of untreated HIV-1-infected long-term nonprogressors: significant alterations despite low viral burden

BACKGROUND

HIV-1 can induce disturbances in adipose tissue in infected subjects through the effects of some of its proteins or inflammation. It is not known whether this also takes place in HIV-1-infected long-term nonprogressors (LTNPs). Our objectives were to determine whether adipocyte differentiation/lipid, inflammatory, and mitochondrial parameters are perturbed in abdominal wall subcutaneous adipose tissue of untreated HIV-1-infected patients LTNPs.

METHODS

Cross-sectional study involving 10 LTNPs, 10 typical progressors (TPs), and 10 uninfected controls (UCs). The parameters assessed were peroxisome proliferator-activated receptor-gamma (PPARγ), lipoprotein lipase, and fatty acid-binding protein 4 mRNA (adipogenic/lipid); tumor necrosis factor-alpha, interleukin 18 (IL-18), β2-MCG, monocyte chemoattractant protein 1, CD1A, and C3 mRNA (inflammation); and cytochrome c oxidase subunit II (COII), COIV, CYCA, nuclear respiratory factor 1, PPARγ coactivator 1α mRNA, and mtDNA content (mitochondrial).

RESULTS

Regarding adipogenic/lipid parameters, LTNPs had PPARγ, lipoprotein lipase, and fatty acid-binding protein 4 mRNA significantly decreased compared with UCs (P ≤ 0.001 for all comparisons). PPARγ mRNA was significantly greater in LTNP than in TP (P = 0.006). With respect to inflammatory parameters, tumor necrosis factor-alpha, IL-18, and β2-MCG mRNA were significantly higher in LTNPs compared with UCs (P < 0.005 for all comparisons), whereas IL-18 mRNA was greater in TPs compared with LTNPs (P = 0.01). As mitochondrial parameters are concerned, mtDNA was significantly reduced in LTNPs compared with TPs (P = 0.04) and UCs (P = 0.03). COII and COIV were also significantly reduced in LTNPs compared with UCs and TPs.

CONCLUSIONS

Adipose tissue from untreated LTNPs may have limited but significant derangements in some adipogenic/lipid and may have inflammatory processes at a lower degree than that observed in untreated TPs. LTNPs may have mitochondrial-related alterations in adipose tissue which are greater than that observed in TPs.

HIV-1 Vpr triggers mitochondrial destruction by impairing Mfn2-mediated ER-mitochondria interaction

Human immunodeficiency virus 1 (HIV-1) viral protein R (Vpr) has been shown to induce host cell death by increasing the permeability of mitochondrial outer membrane (MOM). The mechanism underlying the damage to the mitochondria by Vpr, however, is not clearly illustrated. In this study, Vpr that is introduced, via transient transfection or lentivirus infection, into the human embryonic kidney cell line HEK293, human CD4⁺ T lymphoblast cell line SupT1, or human primary CD4⁺ T cells serves as the model system to study the molecular mechanism of Vpr-mediated HIV-1 pathogenesis. The results show that Vpr injures MOM and causes a loss in membrane potential (MMP) by posttranscriptionally reducing the expression of mitofusin 2 (Mfn2) via VprBP-DDB1-CUL4A ubiquitin ligase complex, gradually weakening MOM, and increasing mitochondrial deformation. Vpr also markedly decreases cytoplasmic levels of dynamin-related protein 1 (DRP1) and increases bulging in mitochondria-associated membranes (MAM), the specific regions of endoplasmic reticulum (ER) which form physical contacts with the mitochondria. Overexpression of Mfn2 and DRP1 significantly decreased the loss of MMP and apoptotic cell death caused by Vpr. Furthermore, by employing time-lapse confocal fluorescence microscopy, we identify the transport of Vpr protein from the ER, via MAM to the mitochondria. Taken together, our results suggest that Vpr-mediated cellular damage may occur on an alternative protein transport pathway from the ER, via MAM to the mitochondria, which are modulated by Mfn2 and DRP1.

Evidence for the innate immune response as a correlate of protection in human immunodeficiency virus (HIV)-1 highly exposed seronegative subjects (HESN)

The description of highly exposed individuals who remain seronegative (HESN) despite repeated exposure to human immunodeficiency virus (HIV)-1 has heightened interest in identifying potential mechanisms of HIV-1 resistance. HIV-specific humoral and T cell-mediated responses have been identified routinely in HESN subjects, although it remains unknown if these responses are a definitive cause of protection or merely a marker for exposure. Approximately half of HESN lack any detectible HIV-specific adaptive immune responses, suggesting that other mechanisms of protection from HIV-1 infection also probably exist. In support of the innate immune response as a mechanism of resistance, increased natural killer (NK) cell activity has been correlated with protection from infection in several high-risk cohorts of HESN subjects, including intravenous drug users, HIV-1 discordant couples and perinatally exposed infants. Inheritance of protective NK KIR3DL1(high) and KIR3DS1 receptor alleles have also been observed to be over-represented in a high-risk cohort of HESN intravenous drug users and HESN partners of HIV-1-infected subjects. Other intrinsic mechanisms of innate immune protection correlated with resistance in HESN subjects include heightened dendritic cell responses and increased secretion of anti-viral factors such as β-chemokines, small anti-viral factors and defensins. This review will highlight the most current evidence in HESN subjects supporting the role of epithelial microenvironment and the innate immune system in sustaining resistance against HIV-1 infection. We will argue that as a front-line defence the innate immune response determines the threshold of infectivity that HIV-1 must overcome to establish a productive infection.

Mesenchymal stem cell derived hematopoietic cells are permissive to HIV-1 infection

BACKGROUND

Tissue resident mesenchymal stem cells (MSCs) are multipotent, self-renewing cells known for their differentiation potential into cells of mesenchymal lineage. The ability of single cell clones isolated from adipose tissue resident MSCs (ASCs) to differentiate into cells of hematopoietic lineage has been previously demonstrated. In the present study, we investigated if the hematopoietic differentiated (HD) cells derived from ASCs could productively be infected with HIV-1.

RESULTS

HD cells were generated by differentiating clonally expanded cultures of adherent subsets of ASCs (CD90+, CD105+, CD45-, and CD34-). Transcriptome analysis revealed that HD cells acquire a number of elements that increase their susceptibility for HIV-1 infection, including HIV-1 receptor/co-receptor and other key cellular cofactors. HIV-1 infected HD cells (HD-HIV) showed elevated p24 protein and gag and tat gene expression, implying a high and productive infection. HD-HIV cells showed decreased CD4, but significant increase in the expression of CCR5, CXCR4, Nef-associated factor HCK, and Vpu-associated factor BTRC. HIV-1 restricting factors like APOBEC3F and TRIM5 also showed up regulation. HIV-1 infection increased apoptosis and cell cycle regulatory genes in HD cells. Although undifferentiated ASCs failed to show productive infection, HIV-1 exposure increased the expression of several hematopoietic lineage associated genes such as c-Kit, MMD2, and IL-10.

CONCLUSIONS

Considering the presence of profuse amounts of ASCs in different tissues, these findings suggest the possible role that could be played by HD cells derived from ASCs in HIV-1 infection. The undifferentiated ASCs were non-permissive to HIV-1 infection; however, HIV-1 exposure increased the expression of some hematopoietic lineage related genes. The findings relate the importance of ASCs in HIV-1 research and facilitate the understanding of the disease process and management strategies.

HIV-1 viral protein r induces ERK and caspase-8-dependent apoptosis in renal tubular epithelial cells

OBJECTIVE

HIV-associated nephropathy (HIVAN) is the most common cause of end-stage renal disease in persons with HIV/AIDS and is characterized by focal glomerulosclerosis and dysregulated renal tubular epithelial cell (RTEC) proliferation and apoptosis. HIV-1 viral protein r (Vpr) has been implicated in HIV-induced RTEC apoptosis but the mechanisms of Vpr-induced RTEC apoptosis are unknown. The aim of this study was therefore to determine the mechanisms of Vpr-induced apoptosis in RTEC.

METHODS

Apoptosis and caspase activation were analyzed in human RTEC (HK2) after transduction with Vpr-expressing and control lentiviral vectors. Bax and BID were inhibited with lentiviral shRNA, and ERK activation was blocked with the MEK1,2 inhibitor, U0126.

RESULTS

Vpr induced apoptosis as indicated by caspase 3/7 activation, PARP-1 cleavage and mitochondrial injury. Vpr activated both caspases-8 and 9. Inhibition of Bax reduced Vpr-induced apoptosis, as reported in other cell types. Additionally, Vpr-induced cleavage of BID to tBID and suppression of BID expression prevented Vpr-induced apoptosis. Since sustained ERK activation can activate caspase-8 in some cell types, we studied the role of ERK in Vpr-induced caspase-8 activation. Vpr induced sustained ERK activation in HK2 cells and incubation with U0126 reduced Vpr-induced caspase-8 activation, BID cleavage and apoptosis. We detected phosphorylated ERK in RTEC in HIVAN biopsy specimens by immunohistochemistry.

CONCLUSIONS

These studies delineate a novel pathway of Vpr-induced apoptosis in RTEC, which is mediated by sustained ERK activation, resulting in caspase 8-mediated cleavage of BID to tBID, thereby facilitating Bax-mediated mitochondrial injury and apoptosis.

Modulation of HIV-1 virulence via the host glucocorticoid receptor: towards further understanding the molecular mechanisms of HIV-1 pathogenesis

The glucocorticoid receptor (GR) is a steroid receptor that regulates diverse functions, which include the immune response. In humans, the GR acts via binding to cortisol, resulting in the transcriptional modulation of key host genes. Several lines of evidence suggest that the host GR could be a key protein exploited by HIV at multiple levels to ensure its pathogenic success. Endogenous and therapeutic glucocorticoids play important roles in patients with HIV due to their well-established effects on immune function. AIDS patients develop glucocorticoid hypersensitivity, consistent with a mechanism involving an HIV-1-induced increase in expression or activity of the GR. Both the HIV-1 accessory protein Vpr and the host GR affect transcription of viral proteins from the long terminal repeat (LTR) region of the HIV-1 promoter. In addition, Vpr modulates host GR function to affect transcription of host genes, most likely via direct interaction with the GR. Vpr appears to regulate GR function by acting as a co-activator for the GR. Since both the GR and Vpr are involved in apoptosis in T cells and dendritic cells, crosstalk between these proteins may also regulate apoptosis in these and other cells. Given that cortisol is not the only ligand that activates the GR, other endogenous as well as synthetic GR ligands such as progestins may also modulate HIV pathogenesis, in particular in the cervicovaginal environment. Investigating the molecular determinants, ligand-selectivity and role in HIV pathogenesis of the GR-Vpr interaction may lead to new strategies for development of anti-HIV drugs.

The functions of the HIV1 protein Vpr and its action through the DCAF1.DDB1.Cullin4 ubiquitin ligase

Among the proteins encoded by human and simian immunodeficiency viruses (HIV and SIV) at least three, Vif, Vpu and Vpr, subvert cellular ubiquitin ligases to block the action of anti-viral defenses. This review focuses on Vpr and its HIV2/SIV counterparts, Vpx and Vpr, which all engage the DDB1.Cullin4 ubiquitin ligase complex through the DCAF1 adaptor protein. Here, we discuss the multiple functions that have been linked to Vpr expression and summarize the current knowledge on the role of the ubiquitin ligase complex in carrying out a subset of these activities.

Novel HIV-1 knockdown targets identified by an enriched kinases/phosphatases shRNA library using a long-term iterative screen in Jurkat T-cells

HIV-1 is a complex retrovirus that uses host machinery to promote its replication. Understanding cellular proteins involved in the multistep process of HIV-1 infection may result in the discovery of more adapted and effective therapeutic targets. Kinases and phosphatases are a druggable class of proteins critically involved in regulation of signal pathways of eukaryotic cells. Here, we focused on the discovery of kinases and phosphatases that are essential for HIV-1 replication but dispensable for cell viability. We performed an iterative screen in Jurkat T-cells with a short-hairpin-RNA (shRNA) library highly enriched for human kinases and phosphatases. We identified 14 new proteins essential for HIV-1 replication that do not affect cell viability. These proteins are described to be involved in MAPK, JNK and ERK pathways, vesicular traffic and DNA repair. Moreover, we show that the proteins under study are important in an early step of HIV-1 infection before viral integration, whereas some of them affect viral transcription/translation. This study brings new insights for the complex interplay of HIV-1/host cell and opens new possibilities for antiviral strategies.

FAT10: a novel mediator of Vpr-induced apoptosis in human immunodeficiency virus-associated nephropathy

Human immunodeficiency virus (HIV)-associated nephropathy is a significant cause of morbidity and mortality in HIV-infected persons. Vpr-induced cell cycle dysregulation and apoptosis of renal tubular epithelial cells are important components of the pathogenesis of HIV-associated nephropathy (HIVAN). FAT10 is a ubiquitin-like protein that is upregulated in renal tubular epithelial cells in HIVAN. In these studies, we report that Vpr induces increased expression of FAT10 in tubular cells and that inhibition of FAT10 expression prevents Vpr-induced apoptosis in human and murine tubular cells. Moreover, we found that Vpr interacts with FAT10 and that these proteins colocalize at mitochondria. These studies establish FAT10 as a novel mediator of Vpr-induced cell death.

HIV-1 accessory proteins--ensuring viral survival in a hostile environment

One of the features of primate immunodeficiency viruses (HIVs and SIVs) that distinguishes them from other retroviruses is the array of "accessory" proteins they encode. Here, we discuss recent advances in understanding the interactions of the HIV-1 Nef, Vif, Vpu, and Vpr proteins with factors and pathways expressed in cells of the immune system. In at least three instances, the principal activity of the accessory proteins appears to be evasion from various forms of cell-mediated (or intrinsic), antiviral resistance. Broadly speaking, the HIV-1 accessory proteins modify the local environment within infected cells to ensure viral persistence, replication, dissemination, and transmission.

Lipodystrophy in HIV 1-infected patients: lessons for obesity research

Lipodystrophy is a common alteration in HIV 1-infected patients under anti-retroviral treatment. This syndrome is usually associated with peripheral lipoatrophy, central adiposity and, in some cases, lipomatosis, as well as systemic insulin resistance and hyperlipidemia. Research on the ethiopathogenesis of the disease revealed novel aspects of adipose tissue biology highly relevant to obesity research: the pivotal role of mitochondria in white adipose tissue function, the role that interference with master transcription factors of adipogenesis may have in human adipose tissue, the capacity of human white adipose tissue to acquire brown fat-like features, as well as the importance of apoptosis and the potential impact of viral infections in adipose tissue. The dramatic difference between subcutaneous adipose depots, prone to lipoatrophy, and the visceral adipose depots, prone to enlargement, has been further evidenced in the study of the lipodystrophy syndrome. The recognition of a local pro-inflammatory environment in lipoatrophic adipose tissue from affected patients, including macrophage infiltration and enhanced expression of chemokines and cytokines, points to events paradoxically similar to those in the hypertrophied adipose tissue in obesity. However, this also potentially provides an explanation for the existence of systemic alterations common to lipodystrophy and obese patients and reminiscent of the metabolic syndrome.

Role of HIV-1 Vpr-induced apoptosis on the release of mitochondrial lysyl-tRNA synthetase

Mitochondrial lysyl-tRNA synthetase (LysRS) is thought to be involved in the specific packaging of tRNA(3)(Lys) into HIV-1 viral particles. The HIV-1 auxiliary viral protein Vpr is an apoptogenic protein that affects the integrity of the mitochondrial membrane and has also been reported to interact with LysRS. In the present study, we show that HIV-1 Vpr expressed in E. coli and purified to homogeneity does not interact specifically with LysRS and does not impact its aminoacylation activity. However, we also show that the mitochondrial localization of LysRS in HeLa cells is altered after addition of Vpr in the culture medium. These results suggest that HIV-1 Vpr fulfills an essential role in the process of packaging of mitochondrial LysRS.

Centrosome and retroviruses: the dangerous liaisons

Centrosomes are the major microtubule organizing structures in vertebrate cells. They localize in close proximity to the nucleus for the duration of interphase and play major roles in numerous cell functions. Consequently, any deficiency in centrosome function or number may lead to genetic instability. Several viruses including retroviruses such as, Foamy Virus, HIV-1, JSRV, M-PMV and HTLV-1 have been shown to hamper centrosome functions for their own profit, but the outcomes are very different. Foamy viruses, HIV-1, JSRV, M-PMV and HTLV-1 use the cellular machinery to traffic towards the centrosome during early and/or late stages of the infection. In addition HIV-1 Vpr protein alters the cell-cycle regulation by hijacking centrosome functions. Enthrallingly, HTLV-1 Tax expression also targets the functions of the centrosome, and this event is correlated with centrosome amplification, aneuploidy and transformation.

Infection of human immunodeficiency virus and intracellular viral Tat protein exert a pro-survival effect in a human microglial cell line

The interaction of human immunodeficiency virus type 1 (HIV-1) with CD4+ T lymphocytes is well studied and typically results in virally induced cytolysis. In contrast, relatively little is known concerning the interplay between HIV-1 and microglia. Recent findings suggest that, counter-intuitively, HIV-1 infection may extend the lifespan of microglia. We developed a novel cell line model system to confirm and mechanistically study this phenomenon. We found that transduction of a human microglial cell line with an HIV-1 vector results in a powerful cytoprotective effect following apoptotic challenge. This effect was reproduced by ectopic expression of a single virus-encoded protein, Tat. Subsequent studies showed that the pro-survival effects of intracellular Tat could be attributed to activation of the PI-3-kinase (PI3K)/Akt pathway in the microglial cell line. Furthermore, we found that expression of Tat led to decreased expression of PTEN, a negative regulator of the PI-3-K pathway. Consistent with this, decreased p53 activity and increased E2F activity were observed. Based on these findings, a model of possible regulatory circuits that intracellular Tat and HIV-1 infection engage during the cytoprotective event in microglia has been suggested. We propose that the expression of Tat may enable HIV-1 infected microglia to survive throughout the course of infection, leading to persistent HIV-1 production and infection in the central nervous system.

Cytobiological consequences of calcium-signaling alterations induced by human viral proteins

Since calcium-signaling regulates specific and fundamental cellular processes, it represents the ideal target of viral proteins, in order for the virus to control cellular functions and favour its persistence, multiplication and spread. A detailed analysis of reports focused on the impact of viral proteins on calcium-signaling has shown that virus-related elevations of cytosolic calcium levels allow increased viral protein expression (HIV-1, HSV-1/2), viral replication (HBx, enterovirus 2B, HTLV-1 p12(I), HHV-8, EBV), viral maturation (rotavirus), viral release (enterovirus 2B) and cell immortalization (EBV). Interestingly, virus-induced decreased cytosolic calcium levels have been found to be associated with inhibition of immune cells functions (HIV-1 Tat, HHV-8 K15, EBV LMP2A). Finally, several viral proteins are able to modulate intracellular calcium-signaling to control cell viability (HIV-1 Tat, HTLV-1 p13(II), HCV core, HBx, enterovirus 2B, HHV-8 K7). These data point out calcium-signaling as a key cellular target for viral infection and should stimulate further studies exploring new calcium-related therapeutic strategies.

Targeted Vpr-derived peptides reach mitochondria to induce apoptosis of alphaVbeta3-expressing endothelial cells

The HIV-1 encoded apoptogenic protein Vpr induces mitochondrial membrane permeabilization (MMP) via interactions with the voltage-dependent anion channel (VDAC) and the adenine nucleotide translocator (ANT). We have designed a peptide, TEAM-VP, composed of two functional domains, one a tumor blood vessel RGD-like 'homing' motif and the other an MMP-inducing sequence derived from Vpr. When added to isolated mitochondria, TEAM-VP interacts with ANT and VDAC, reduces oxygen consumption and overcomes Bcl-2 protection to cause inner and outer MMP. TEAM-VP specifically recognizes cell-surface expressed alpha(V)beta(3) integrins, internalizes, temporarily localizes to lysosomes and progressively co-distributes with the mitochondrial compartment with no sign of lysosomal membrane permeabilization. Finally TEAM-VP reaches mitochondria of angiogenic endothelial cells to induce mitochondrial fission, dissipation of the mitochondrial transmembrane potential (DeltaPsi(m)), cytochrome c release and apoptosis hallmarks. Hence, this chimeric peptide constitutes the first example of a virus-derived mitochondriotoxic compound as a candidate to kill selectively tumor neo-endothelia.

Development and characterization of ten monoclonal anti-Vpr antibodies

HIV-1 Vpr is a 96-amino acid auxiliary protein that performs numerous activities during viral infection. In the present study, 10 antibodies were generated after mice immunization with either the N- or the C-terminus domain of Vpr, respectively, Vpr(1-51) and Vpr(52-96). ELISA and immunoblot experiments using pure synthetic overlapping Vpr peptides suggested that these anti-Vpr antibodies could be classified into five groups and that they recognized conformational or linear Vpr epitopes. Further analysis revealed the effect of C-terminal arginine mutations on the antibody binding. Two of the antibodies precipitated Vpr expressed after transfection of a Vpr-encoding vector in human cells. More importantly, one of them was able to detect Vpr in HIV-1-infected U1 cells and in HIV-1-infected human PBMC. Surface plasmon resonance experiments demonstrated that some of these antibodies prevented the interaction between Vpr and one of its cellular partners, the adenine nucleotide translocator. Thus, these anti-Vpr monoclonal antibodies may be useful to any laboratory working on the molecular mechanism of HIV-1 infection.

Fumagillin suppresses HIV-1 infection of macrophages through the inhibition of Vpr activity

HIV-1 viral protein R (Vpr) is one of the human immunodeficiency virus type 1 encoded proteins that have important roles in viral pathogenesis. However, no clinical drug for AIDS therapy that targets Vpr has been developed. Here, we have established a screening system to isolate Vpr inhibitors using budding yeast cells. We purified a Vpr inhibitory compound from fungal metabolites and identified it as fumagillin, a chemical already known to be a potent inhibitor of angiogenesis. Fumagillin not only reversed the growth inhibitory activity of Vpr in yeast and human cells, but also inhibited Vpr-dependent viral gene expression upon the infection of human macrophages.

Neuroimmunity and the blood-brain barrier: molecular regulation of leukocyte transmigration and viral entry into the nervous system with a focus on neuroAIDS

HIV infection of the central nervous system (CNS) can result in neurologic dysfunction with devastating consequences in a significant number of individuals with AIDS. Two main CNS complications in individuals with HIV are encephalitis and dementia, which are characterized by leukocyte infiltration into the CNS, microglia activation, aberrant chemokine expression, blood-brain barrier (BBB) disruption, and eventual damage and/or loss of neurons. One of the major mediators of NeuroAIDS is the transmigration of HIV-infected leukocytes across the BBB into the CNS. This review summarizes new key findings that support a critical role of the BBB in regulating leukocyte transmigration. In addition, we discuss studies on communication among cells of the immune system, BBB, and the CNS parenchyma, and suggest how these interactions contribute to the pathogenesis of NeuroAIDS. We also describe some of the animal models that have been used to study and characterize important mechanisms that have been proposed to be involved in HIV-induced CNS dysfunction. Finally, we review the pharmacologic interventions that address neuroinflammation, and the effect of substance abuse on HIV-1 related neuroimmunity.

Effect of R77Q, R77A and R80A changes in Vpr on HIV-1 replication and CD4 T cell depletion in human lymphoid tissue ex vivo

BACKGROUND

It has been suggested that mutations of R77A and R80A in the HIV-1 viral protein R (Vpr) impair its proapoptotic activity and that a naturally occurring R77Q variation is associated with non-progressive HIV-1 infection.

RATIONALE

To assess the effect of Vpr R77Q, R77A and R80A mutations on the efficiency of CCR5(R5)- and CXCR4(X4)-tropic HIV-1 replication and cytopathicity in human lymphoid tissue (HLT).

METHODS

Vpr mutants of the X4-tropic HIV-1 NL4-3 clone and an R5-tropic derivative were generated by PCR mutagenesis. Virus stocks established by transfection of 293T cells were used to infect macrophages and ex vivo HLT. HIV-1 replication was assessed by measuring p24 core antigen in the culture supernatants and CD4 T-cell depletion and apoptosis were measured by flow cytometric analysis.

RESULTS

The R5-tropic HIV-1 Vpr mutants replicated with slightly (R77A, R77Q) to moderately (R80A) reduced efficiency in ex vivo-infected HLT and macrophages. In comparison, the changes in Vpr had negligible effects on replication of the X4-tropic forms in lymphatic tissues. Mutation of R77Q and R80A reduced apoptosis of HIV-1-infected cells in ex vivo-infected HLT independently of the viral coreceptor tropism. However, only the R5-tropic HIV-1 Vpr mutants caused markedly less CD4 T-cell depletion than wild-type HIV-1 at the end of ex vivo HLT culture.

CONCLUSIONS

The observation that Vpr R77Q reduces the cytopathicity of R5-tropic HIV-1 in lymphoid tissues supports a role in non-progressive HIV-1 infection but the attenuating effects might be dependent on the viral subtype and coreceptor tropism.

The HIV-1 Vpr and glucocorticoid receptor complex is a gain-of-function interaction that prevents the nuclear localization of PARP-1

The Vpr protein of HIV-1 functions as a vital accessory gene by regulating various cellular functions, including cell differentiation, apoptosis, nuclear factor of kappaB (NF-kappaB) suppression and cell-cycle arrest of the host cell. Several reports have indicated that Vpr complexes with the glucocorticoid receptor (GR), but it remains unclear whether the GR pathway is required for Vpr to function. Here, we report that Vpr uses the GR pathway as a recruitment vehicle for the NF-kappaB co-activating protein, poly(ADP-ribose) polymerase-1 (PARP-1). The GR interaction with Vpr is both necessary and sufficient to facilitate this interaction by potentiating the formation of a Vpr-GR-PARP-1 complex. The recruitment of PARP-1 by the Vpr-GR complex prevents its nuclear localization, which is necessary for Vpr to suppress NF-kappaB. The association of GR with PARP-1 is not observed with steroid (glucocorticoid) treatment, indicating that the GR association with PARP-1 is a gain of function that is solely attributed to HIV-1 Vpr. These data provide important insights into Vpr biology and its role in HIV pathogenesis.

Molecular and functional characterization of a novel splice variant of ANKHD1 that lacks the KH domain and its role in cell survival and apoptosis

Multiple ankyrin repeat motif-containing proteins play an important role in protein-protein interactions. ANKHD1 proteins are known to possess multiple ankyrin repeat domains and a single KH domain with no known function. Using yeast two-hybrid system analysis, we identified a novel splice variant of ANKHD1. This splice variant of ANKHD1, which we designated as HIV-1 Vpr-binding ankyrin repeat protein (VBARP), does not contain the signature KH domain, and codes for only a single ankyrin repeat motif. We characterized VBARP by molecular and functional analysis, revealing that VBARP is ubiquitously expressed in different tissues as well as cell lines of different lineage. In addition, blast searches indicated that orthologs and homologs to VBARP exist in different phyla, suggesting that VBARP might be evolutionarily conserved, and thus may be involved in basic cellular function(s). Furthermore, biochemical analysis revealed the presence of two VBARP isoforms coding for 69 and 49 kDa polypeptides, respectively, that are primarily localized in the cytoplasm. Functional analysis using short interfering RNA approaches indicate that this gene product is essential for cell survival through its regulation of caspases. Taken together, these results indicate that VBARP is a novel splice variant of ANKHD1 and may play a role in cellular apoptosis (antiapoptotic) and cell survival pathway(s).