RESUMO
Zika virus (ZIKV) infection during pregnancy leads to an increased risk of fetal growth restriction and fetal central nervous system malformations, which are outcomes broadly referred to as the Congenital Zika Syndrome (CZS). Here we infect pregnant rhesus macaques and investigate the impact of persistent ZIKV infection on uteroplacental pathology, blood flow, and fetal growth and development. Despite seemingly normal fetal growth and persistent fetal-placenta-maternal infection, advanced non-invasive in vivo imaging studies reveal dramatic effects on placental oxygen reserve accompanied by significantly decreased oxygen permeability of the placental villi. The observation of abnormal oxygen transport within the placenta appears to be a consequence of uterine vasculitis and placental villous damage in ZIKV cases. In addition, we demonstrate a robust maternal-placental-fetal inflammatory response following ZIKV infection. This animal model reveals a potential relationship between ZIKV infection and uteroplacental pathology that appears to affect oxygen delivery to the fetus during development.
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Placenta/metabolismo , Circulação Placentária , Complicações Infecciosas na Gravidez/imunologia , Infecção por Zika virus/imunologia , Imunidade Adaptativa , Animais , Encéfalo/embriologia , Encéfalo/patologia , Citocinas/sangue , Modelos Animais de Doenças , Feminino , Desenvolvimento Fetal , Feto/patologia , Imunidade Inata , Macaca mulatta , Imageamento por Ressonância Magnética , Oxigênio/metabolismo , Permeabilidade , Placenta/imunologia , Placenta/patologia , Placenta/virologia , Gravidez , Complicações Infecciosas na Gravidez/metabolismo , Complicações Infecciosas na Gravidez/patologia , Complicações Infecciosas na Gravidez/fisiopatologia , Carga Viral , Infecção por Zika virus/metabolismo , Infecção por Zika virus/patologia , Infecção por Zika virus/fisiopatologiaRESUMO
The latency-associated nuclear antigen (LANA) of the Kaposi's sarcoma-associated herpesvirus (KSHV) performs a variety of functions to establish and maintain KSHV latency. During latency, LANA localizes to discrete punctate spots in the nucleus, where it tethers viral episomes to cellular chromatin and interacts with nuclear components to regulate cellular and viral gene expression. Using highly sensitive tyramide signal amplification, we determined that LANA localizes to the cytoplasm in different cell types undergoing the lytic cycle of replication after de novo primary infection and after spontaneous, tetradecanoyl phorbol acetate-, or open reading frame 50 (ORF50)/replication transactivator (RTA)-induced activation. We confirmed the presence of cytoplasmic LANA in a subset of cells in lytically active multicentric Castleman disease lesions. The induction of cellular migration by scratch-wounding confluent cell cultures, culturing under subconfluent conditions, or induction of cell differentiation in primary cultures upregulated the number of cells permissive for primary lytic KSHV infection. The induction of lytic replication was characterized by high-level expression of cytoplasmic LANA and nuclear ORF59, a marker of lytic replication. Subcellular fractionation studies revealed the presence of multiple isoforms of LANA in the cytoplasm of ORF50/RTA-activated Vero cells undergoing primary infection. Mass spectrometry analysis demonstrated that cytoplasmic LANA isoforms were full length, containing the N-terminal nuclear localization signal. These results suggest that trafficking of LANA to different subcellular locations is a regulated phenomenon, which allows LANA to interact with cellular components in different compartments during both the latent and the replicative stages of the KSHV life cycle.IMPORTANCE Kaposi's sarcoma-associated herpesvirus (KSHV) causes AIDS-related malignancies, including lymphomas and Kaposi's sarcoma. KSHV establishes lifelong infections using its latency-associated nuclear antigen (LANA). During latency, LANA localizes to the nucleus, where it connects viral and cellular DNA complexes and regulates gene expression, allowing the virus to maintain long-term infections. Our research shows that intact LANA traffics to the cytoplasm of cells undergoing permissive lytic infections and latently infected cells in which the virus is induced to replicate. This suggests that LANA plays important roles in the cytoplasm and nuclear compartments of the cell during different stages of the KSHV life cycle. Determining cytoplasmic function and mechanism for regulation of the nuclear localization of LANA will enhance our understanding of the biology of this virus, leading to therapeutic approaches to eliminate infection and block its pathological effects.
Assuntos
Antígenos Virais/metabolismo , Citoplasma/virologia , Herpesvirus Humano 8/fisiologia , Proteínas Nucleares/metabolismo , Sarcoma de Kaposi/virologia , Replicação Viral , Animais , Antígenos Virais/genética , Linhagem Celular , Chlorocebus aethiops , Herpesvirus Humano 8/genética , Humanos , Proteínas Imediatamente Precoces/metabolismo , Espectrometria de Massas , Proteínas Nucleares/genética , Isoformas de Proteínas , Células Vero , Latência ViralRESUMO
Kaposi sarcoma (KS) is an unusual tumor composed of proliferating spindle cells that is initiated by infection of endothelial cells (EC) with KSHV, and develops most often in the setting of immunosuppression. Despite decades of research, optimal treatment of KS remains poorly defined and clinical outcomes are especially unfavorable in resource-limited settings. KS lesions are driven by pathological angiogenesis, chronic inflammation, and oncogenesis, and various in vitro cell culture models have been developed to study these processes. KS arises from KSHV-infected cells of endothelial origin, so EC-lineage cells provide the most appropriate in vitro surrogates of the spindle cell precursor. However, because EC have a limited in vitro lifespan, and as the oncogenic mechanisms employed by KSHV are less efficient than those of other tumorigenic viruses, it has been difficult to assess the processes of transformation in primary or telomerase-immortalized EC. Therefore, a novel EC-based culture model was developed that readily supports transformation following infection with KSHV. Ectopic expression of the E6 and E7 genes of human papillomavirus type 16 allows for extended culture of age- and passage-matched mock- and KSHV-infected EC and supports the development of a truly transformed (i.e., tumorigenic) phenotype in infected cell cultures. This tractable and highly reproducible model of KS has facilitated the discovery of several essential signaling pathways with high potential for translation into clinical settings.
Assuntos
Transformação Celular Viral/fisiologia , Herpesvirus Humano 8/fisiologia , Sarcoma de Kaposi/patologia , Carcinogênese/patologia , Células Endoteliais/patologia , Humanos , Sarcoma de Kaposi/diagnósticoRESUMO
Kaposi sarcoma herpesvirus (KSHV) is the etiologic agent of Kaposi sarcoma (KS) and certain rare B cell lymphoproliferative disorders. KSHV infection of endothelial cells (EC) in vitro increases expression of the inducible host-encoded enzyme heme oxygenase-1 (HO-1), which is also strongly expressed in KS tumors. HO-1 catalyzes the rate-limiting step in the conversion of heme into iron, biliverdin and the gasotransmitter carbon monoxide (CO), all of which share anti-apoptotic, anti-inflammatory, pro-survival, and tumorigenic activities. Our previous work has shown that HO-1 expression in KSHV-infected EC is characterized by a rapid yet transient induction at early times post-infection, followed by a sustained upregulation co-incident with establishment of viral latency. These two phases of expression are independently regulated, suggesting distinct roles for HO-1 in the virus life cycle. Here, we investigated the role of HO-1 during acute infection, prior to the onset of viral gene expression. The early infection phase involves a series of events that culminate in delivery of the viral genome to the nucleus. Primary infection also leads to activation of host innate immune effectors, including the pattern recognition receptor TLR4, to induce an antiviral response. It has been shown that TLR4-deficient EC are more susceptible to KSHV infection than wild-type controls, suggesting an important inhibitory role for TLR4 in the KSHV life cycle. TLR4 signaling is in turn subject to regulation by several virus-encoded immune evasion factors. In this report we identify HO-1 as a host protein co-opted by KSHV as part of a rapid immune evasion strategy. Specifically, we show that early HO-1 induction by KSHV results in increased levels of endogenous CO, which functions as a TLR4 signaling inhibitor. In addition, we show that CO-mediated inhibition of TLR4 signaling leads to reduced expression of TLR4-induced antiviral genes, thus dampening the host antiviral response and facilitating KSHV infection. Conversely, inhibition of HO-1 activity decreases intracellular CO, enhances the host antiviral response and inhibits KSHV infection. In conclusion, this study identifies HO-1 as a novel innate immune evasion factor in the context of KSHV infection and supports HO-1 inhibition as a viable therapeutic strategy for KS.
RESUMO
UNLABELLED: Kaposi sarcoma (KS) herpesvirus (KSHV) infection of endothelial cells (EC) is associated with strong induction of heme oxygenase-1 (HO-1), a stress-inducible host gene that encodes the rate-limiting enzyme responsible for heme catabolism. KS is an angioproliferative tumor characterized by the proliferation of KSHV-infected spindle cells, and HO-1 is highly expressed in such cells. HO-1 converts the pro-oxidant, proinflammatory heme molecule into metabolites with antioxidant, anti-inflammatory, and proliferative activities. Previously published work has shown that KSHV-infected EC in vitro proliferate in response to free heme in a HO-1-dependent manner, thus implicating virus-enhanced HO-1 activity in KS tumorigenesis. The present study investigated the molecular mechanisms underlying KSHV induction of HO-1 in lymphatic EC (LEC), which are the likely spindle cell precursors. In a time course analysis of KSHV-infected cells, HO-1 expression displays biphasic kinetics characterized by an early transient induction that is followed by a more sustained upregulation coincident with the establishment of viral latency. A viral microRNA miR-K12-11 deletion mutant of KSHV was found to be defective for induction of HO-1 during latency. A potential mechanism for this phenotype was provided by BACH1, a cellular HO-1 transcriptional repressor targeted by miR-K12-11. In fact, in KSHV-infected LEC, the BACH1 message level is reduced, BACH1 subcellular localization is altered, and miR-K12-11 mediates the inverse regulation of HO-1 and BACH1 during viral latency. Interestingly, the data indicate that neither miR-K12-11 nor de novo KSHV gene expression is required for the burst of HO-1 expression observed at early times postinfection, which suggests that additional virion components promote this phenotype. IMPORTANCE: While the mechanisms underlying KSHV induction of HO-1 remain unknown, the cellular mechanisms that regulate HO-1 expression have been extensively investigated in the context of basal and pathophysiological states. The detoxifying action of HO-1 is critical for the protection of cells exposed to high heme levels. KS spindle cells are erythrophagocytic and contain erythrocyte ghosts. Erythrocyte degeneration leads to the localized release of heme, creating oxidative stress that may be further exacerbated by environmental or other cofactors. Our previous work showed that KSHV-infected cells proliferate in response to heme and that this occurs in a HO-1-dependent manner. We therefore hypothesize that KSHV induction of HO-1 contributes to KS tumor development via heme metabolism and propose that HO-1 be evaluated as a therapeutic target for KS. Our present work, which aimed to understand the mechanisms whereby KSHV induces HO-1, will be important for the design and implementation of such a strategy.
Assuntos
Células Endoteliais/virologia , Heme Oxigenase-1/biossíntese , Herpesvirus Humano 8/fisiologia , MicroRNAs/metabolismo , RNA Viral/metabolismo , Deleção de Genes , Regulação da Expressão Gênica , Herpesvirus Humano 8/genética , Interações Hospedeiro-Patógeno , Regulação para Cima , Latência ViralRESUMO
BACKGROUND: BST2/tetherin is an innate immune molecule with the unique ability to restrict the egress of human immunodeficiency virus (HIV) and other enveloped viruses, including Ebola virus (EBOV). Coincident with this discovery was the finding that the HIV Vpu protein down-regulates BST2 from the cell surface, thereby promoting viral release. Evidence suggests that the EBOV envelope glycoprotein (GP) also counteracts BST2, although the mechanism is unclear. RESULTS: We find that total levels of BST2 remain unchanged in the presence of GP, whereas surface BST2 is significantly reduced. GP is known to sterically mask surface receptors via its mucin domain. Our evaluation of mutant GP molecules indicate that masking of BST2 by GP is probably responsible for the apparent surface BST2 down-regulation; however, this masking does not explain the observed virus-like particle egress enhancement. We discovered that VP40 coimmunoprecipitates and colocalizes with BST2 in the absence but not in the presence of GP. CONCLUSIONS: These results suggest that GP may overcome the BST2 restriction by blocking an interaction between VP40 and BST2. Furthermore, we have observed that GP may enhance BST2 incorporation into virus-like particles. Understanding this novel EBOV immune evasion strategy will provide valuable insights into the pathogenicity of this deadly pathogen.
Assuntos
Antígenos CD/metabolismo , Ebolavirus/metabolismo , Ebolavirus/patogenicidade , Glicoproteínas/metabolismo , Liberação de Vírus/fisiologia , Linhagem Celular , Regulação para Baixo/fisiologia , Proteínas Ligadas por GPI/metabolismo , Células HEK293 , Humanos , Mucinas/metabolismo , Mutação/genética , Receptores de Superfície Celular/metabolismo , Proteínas da Matriz Viral , Proteínas Virais/metabolismoRESUMO
The homeostatic function of endothelial cells (EC) is critical for a number of physiological processes including vascular integrity, immunity, and wound healing. Indeed, vascular abnormalities resulting from EC dysfunction contribute to the development and spread of malignancies. The alternative SDF-1/CXCL12 receptor CXCR7 is frequently and specifically highly expressed in tumor-associated vessels. In this study, we investigate whether CXCR7 contributes to vascular dysfunction by specifically examining the effect of CXCR7 expression on EC barrier function and motility. We demonstrate that CXCR7 expression in EC results in redistribution of CD31/PECAM-1 and loss of contact inhibition. Moreover, CXCR7+ EC are deficient in barrier formation. We show that CXCR7-mediated motility has no influence on angiogenesis but contributes to another motile process, the invasion of CXCR7+ EC into ligand-rich niches. These results identify CXCR7 as a novel manipulator of EC barrier function via alteration of PECAM-1 homophilic junctions. As such, aberrant expression of CXCR7 in the vasculature has the potential to disrupt vascular homeostasis and could contribute to vascular dysfunction in cancer systems.
Assuntos
Células Endoteliais/metabolismo , Invasividade Neoplásica/genética , Neoplasias/genética , Receptores CXCR/genética , Células Endoteliais/patologia , Regulação da Expressão Gênica , Regulação Neoplásica da Expressão Gênica , Homeostase , Humanos , Ligantes , Invasividade Neoplásica/patologia , Neoplasias/patologia , Neovascularização Patológica/genética , Neovascularização Patológica/metabolismo , Molécula-1 de Adesão Celular Endotelial a Plaquetas/metabolismo , Receptores CXCR/biossíntese , Transdução de Sinais/genéticaRESUMO
BACKGROUND: Reliable human in vitro blood-brain barrier (BBB) models suitable for high-throughput screening are urgently needed in early drug discovery and development for assessing the ability of promising bioactive compounds to overcome the BBB. To establish an improved human in vitro BBB model, we compared four currently available and well characterized immortalized human brain capillary endothelial cell lines, hCMEC/D3, hBMEC, TY10, and BB19, with respect to barrier tightness and paracellular permeability. Co-culture systems using immortalized human astrocytes (SVG-A cell line) and immortalized human pericytes (HBPCT cell line) were designed with the aim of positively influencing barrier tightness. METHODS: Tight junction (TJ) formation was assessed by transendothelial electrical resistance (TEER) measurements using a conventional epithelial voltohmmeter (EVOM) and an automated CellZscope system which records TEER and cell layer capacitance (CCL) in real-time.Paracellular permeability was assessed using two fluorescent marker compounds with low BBB penetration (sodium fluorescein (Na-F) and lucifer yellow (LY)). Conditions were optimized for each endothelial cell line by screening a series of 24-well tissue culture inserts from different providers. For hBMEC cells, further optimization was carried out by varying coating material, coating procedure, cell seeding density, and growth media composition. Biochemical characterization of cell type-specific transmembrane adherens junction protein VE-cadherin and of TJ proteins ZO-1 and claudin-5 were carried out for each endothelial cell line. In addition, immunostaining for ZO-1 in hBMEC cell line was performed. RESULTS: The four cell lines all expressed the endothelial cell type-specific adherens junction protein VE-cadherin. The TJ protein ZO-1 was expressed in hCMEC/D3 and in hBMEC cells. ZO-1 expression could be confirmed in hBMEC cells by immunocytochemical staining. Claudin-5 expression was detected in hCMEC/D3, TY10, and at a very low level in hBMEC cells. Highest TEER values and lowest paracellular permeability for Na-F and LY were obtained with mono-cultures of hBMEC cell line when cultivated on 24-well tissue culture inserts from Greiner Bio-one® (transparent PET membrane, 3.0 µm pore size). In co-culture models with SVG-A and HBPCT cells, no increase of TEER could be observed, suggesting that none of the investigated endothelial cell lines responded positively to stimuli from immortalized astrocytic or pericytic cells. CONCLUSIONS: Under the conditions examined in our experiments, hBMEC proved to be the most suitable human cell line for an in vitro BBB model concerning barrier tightness in a 24-well mono-culture system intended for higher throughput. This BBB model is being validated with several compounds (known to cross or not to cross the BBB), and will potentially be selected for the assessment of BBB permeation of bioactive natural products.
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Angiogenesis is a critical factor in the growth and dissemination of solid tumors. Indeed, tumor vasculature is abnormal and contributes to the development and spread of malignancies by creating a hostile microenvironment. The alternative SDF-1/CXCL12 receptor, CXCR7, is frequently and specifically expressed in tumor-associated vessels. In this study, we examine the role of endothelium-expressed CXCR7 in tumor vascular dysfunction by specifically examining the contribution of CXCR7 to endothelial cell (EC) proliferation. We demonstrate that CXCR7 expression is sufficient to drive post-confluent growth in EC cultures. Further, we provide a novel mechanism for CXCR7-mediated proliferation via proteasomal degradation of the tumor suppressor protein Rb. These findings identify a heretofore unappreciated role for CXCR7 in vascular dysfunction and confirm this receptor as a plausible target for anti-tumor therapy.
Assuntos
Células Endoteliais/citologia , Receptores CXCR/metabolismo , Proteína do Retinoblastoma/metabolismo , Proliferação de Células , Células Cultivadas , Células Endoteliais/metabolismo , Endotélio Linfático/citologia , Endotélio Linfático/metabolismo , Endotélio Vascular/citologia , Endotélio Vascular/metabolismo , Humanos , Ligantes , Mutação , Neovascularização Patológica/metabolismo , Neovascularização Patológica/patologia , Complexo de Endopeptidases do Proteassoma/metabolismo , Análise Serial de Proteínas , Receptores CXCR/antagonistas & inibidores , Receptores CXCR/genéticaRESUMO
We have undertaken a genetic strategy to map Vpu regions necessary for BST-2 antagonism and viral egress. This approach is based on our identification of an egress-defective Vpu variant encoded by an HIV-1 subtype C strain. We constructed a series of chimeric Vpu molecules made from the Vpu C variant and Vpu B from a standard laboratory strain. The TM domain from the inactive Vpu C, which contains multiple non-conserved residues, was responsible for a significant decrease in egress activity and BST-2 downregulation, confirming the functional importance of the Vpu TM domain. However, for complete inactivation, both the N-terminus and TM domain from the inactive Vpu C molecule were required, suggesting a new role for the Vpu N-terminus. In addition, determinants in the C-terminus of Vpu B that may be involved in efficient TGN accumulation were also necessary for enhanced viral egress but are missing or non-functional in Vpu C.
Assuntos
HIV-1/fisiologia , Proteínas do Vírus da Imunodeficiência Humana/genética , Proteínas do Vírus da Imunodeficiência Humana/metabolismo , Proteínas Virais Reguladoras e Acessórias/genética , Proteínas Virais Reguladoras e Acessórias/metabolismo , Liberação de Vírus , Sequência de Aminoácidos , Antígenos CD , Linhagem Celular , Análise Mutacional de DNA , Proteínas Ligadas por GPI/antagonistas & inibidores , HIV-1/genética , Humanos , Dados de Sequência MolecularRESUMO
Although the transcription factors IRF-3 and IRF-7 are considered master regulators of type I interferon (IFN) induction and IFN stimulated gene (ISG) expression, Irf3(-/-)×Irf7(-/-) double knockout (DKO) myeloid dendritic cells (mDC) produce relatively normal levels of IFN-ß after viral infection. We generated Irf3(-/-)×Irf5(-/-)×Irf7(-/-) triple knockout (TKO) mice to test whether IRF-5 was the source of the residual induction of IFN-ß and ISGs in mDCs. In pathogenesis studies with two unrelated positive-sense RNA viruses (West Nile virus (WNV) and murine norovirus), TKO mice succumbed at rates greater than DKO mice and equal to or approaching those of mice lacking the type I IFN receptor (Ifnar(-/-)). In ex vivo studies, after WNV infection or exposure to Toll-like receptor agonists, TKO mDCs failed to produce IFN-ß or express ISGs. In contrast, this response was sustained in TKO macrophages following WNV infection. To define IRF-regulated gene signatures, we performed microarray analysis on WNV-infected mDC from wild type (WT), DKO, TKO, or Ifnar(-/-) mice, as well as from mice lacking the RIG-I like receptor adaptor protein MAVS. Whereas the gene induction pattern in DKO mDC was similar to WT cells, remarkably, almost no ISG induction was detected in TKO or Mavs(-/-) mDC. The relative equivalence of TKO and Mavs(-/-) responses suggested that MAVS dominantly regulates ISG induction in mDC. Moreover, we showed that MAVS-dependent induction of ISGs can occur through an IRF-5-dependent yet IRF-3 and IRF-7-independent pathway. Our results establish IRF-3, -5, and -7 as the key transcription factors responsible for mediating the type I IFN and ISG response in mDC during WNV infection and suggest a novel signaling link between MAVS and IRF-5.
Assuntos
Fator Regulador 3 de Interferon/imunologia , Fator Regulador 7 de Interferon/imunologia , Fatores Reguladores de Interferon/imunologia , Interferon beta/imunologia , Vírus do Nilo Ocidental/imunologia , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Animais , Células Dendríticas/imunologia , Células Dendríticas/metabolismo , Fator Regulador 3 de Interferon/genética , Fator Regulador 3 de Interferon/metabolismo , Macrófagos/imunologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Células Mieloides/imunologia , Células Mieloides/metabolismo , Receptor de Interferon alfa e beta/genética , Transdução de Sinais , Receptores Toll-Like/imunologia , Carga Viral , Febre do Nilo Ocidental/genética , Febre do Nilo Ocidental/imunologia , Febre do Nilo Ocidental/virologia , Vírus do Nilo Ocidental/genéticaRESUMO
The cellular protein BST-2/CD317/Tetherin has been shown to inhibit the release of HIV-1 and other enveloped viruses from infected cells. The HIV-1 accessory protein Vpu binds to both BST-2 and ßTrCP, a substrate-recognition subunit for the SCF (Skip1-Cullin1-F-box protein) E3 ubiquitin ligase complex. This interaction leads to both the degradation of BST-2 and the enhancement of viral egress. Recently BST-2 was shown to be ubiquitinated in this process. Here we have confirmed the Vpu- and ßTrCP-dependent multi/polyubiquitination of BST-2. Ubiquitinated BST-2 accumulated in cells treated with a lysosomal inhibitor but not a proteasomal inhibitor. Additionally, we observed that a BST-2 mutant deleted for its cytosolically exposed lysine residues is also ubiquitinated. Subsequent experiments suggested that Vpu promotes BST-2 ubiquitination upon amino acid residues bearing hydroxyl- but not thiol-bearing side chains. However, a BST-2 mutant bearing substitutions for its cytoplasmically exposed Ser, Thr, and Lys residues was still down-regulated, ubiquitinated, and degraded in a Vpu-dependent manner. Our results suggest that Vpu may target either the BST-2 cytoplasmic Tyr residues or the NH(2) terminus itself for ubiquitination.
Assuntos
Antígenos CD/metabolismo , HIV-1/metabolismo , Proteínas do Vírus da Imunodeficiência Humana/metabolismo , Ubiquitinação , Proteínas Virais Reguladoras e Acessórias/metabolismo , Liberação de Vírus , Substituição de Aminoácidos , Antígenos CD/genética , Linhagem Celular , Proteínas Ligadas por GPI/genética , Proteínas Ligadas por GPI/metabolismo , HIV-1/genética , Proteínas do Vírus da Imunodeficiência Humana/genética , Humanos , Mutação de Sentido Incorreto , Ligação Proteica , Ubiquitina-Proteína Ligases/genética , Ubiquitina-Proteína Ligases/metabolismo , Proteínas Virais Reguladoras e Acessórias/genética , Proteínas Contendo Repetições de beta-Transducina/genética , Proteínas Contendo Repetições de beta-Transducina/metabolismoRESUMO
Like the other more well-characterized post-translational modifications (phosphorylation, methylation, acetylation, acylation, etc.), the attachment of the 76 amino acid ubiquitin (Ub) protein to substrates has been shown to govern countless cellular processes. As obligate intracellular parasites, viruses have evolved the capability to commandeer many host processes in order to maximize their own survival, whether it be to increase viral production or to ensure the long-term survival of latently infected host cells. The first evidence that viruses could usurp the Ub system came from the DNA tumor viruses and Adenoviruses, each of which use Ub to dysregulate the host cell cycle (Scheffner et al., 1990; Querido et al., 2001). Today, the list of viruses that utilize Ub includes members from almost every viral class, encompassing both RNA and DNA viruses. Among these, there are examples of Ub usage at every stage of the viral life cycle, involving both ubiquitination and de-ubiquitination. In addition to viruses that merely modify the host Ub system, many of the large DNA viruses encode their own Ub modifying machinery. In this review, we highlight the latest discoveries regarding the myriad ways that viruses utilize Ub to their advantage.
Assuntos
Quimiocina CCL21/metabolismo , Células Endoteliais/metabolismo , Infecções por Herpesviridae/metabolismo , Receptores CCR7/metabolismo , Sarcoma de Kaposi/metabolismo , Neoplasias Cutâneas/metabolismo , Quimiocina CCL21/genética , Humanos , RNA Mensageiro/metabolismo , Sarcoma de Kaposi/virologia , Neoplasias Cutâneas/virologia , Células Tumorais Cultivadas , Regulação para CimaRESUMO
The interferon-induced BST-2 protein has the unique ability to restrict the egress of HIV-1, Kaposi's sarcoma-associated herpesvirus (KSHV), Ebola virus, and other enveloped viruses. The observation that virions remain attached to the surface of BST-2-expressing cells led to the renaming of BST-2 as "tetherin". However, viral proteins such as HIV-1 Vpu, simian immunodeficiency virus Nef, and KSHV K5 counteract BST-2, thereby allowing mature virions to readily escape from infected cells. Since the anti-viral function of BST-2 was discovered, there has been an explosion of research into several aspects of this intriguing interplay between host and virus. This review focuses on recent work addressing the molecular mechanisms involved in BST-2 restriction of viral egress and the species-specific countermeasures employed by various viruses.
Assuntos
Antígenos CD/metabolismo , Infecções por HIV/metabolismo , Infecções por HIV/virologia , HIV-1/crescimento & desenvolvimento , Glicoproteínas de Membrana/metabolismo , Antígenos CD/genética , Proteínas Ligadas por GPI , Humanos , Glicoproteínas de Membrana/genética , Vírion/metabolismo , Viroses/metabolismo , Viroses/virologiaRESUMO
Kaposi sarcoma (KS) is a complex cancer that arises from the initial infection of an appropriate endothelial or progenitor cell by Kaposi Sarcoma Herpesvirus/Human Herpesvirus-8 (KSHV/HHV8). However, the majority of KS cases occur when infected patients also suffer from some coincident form of immune deregulation, providing a favorable microenvironment for tumor development. Cellular hallmarks of KS progression include both the hyper-proliferation of KSHV-infected cells and the infiltration of immune modulatory cells into KS lesions, which together result in chronic inflammation, the induction of angiogenesis and tumor growth. This review describes the current understanding of the interactions between KSHV and host responses that result in this unusual cancer, along with existing treatments and prospects for future therapeutic approaches.
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K3/MIR1 and K5/MIR2 of Kaposi's sarcoma-associated herpesvirus (KSHV) are viral members of the membrane-associated RING-CH (MARCH) ubiquitin ligase family and contribute to viral immune evasion by directing the conjugation of ubiquitin to immunostimulatory transmembrane proteins. In a quantitative proteomic screen for novel host cell proteins downregulated by viral immunomodulators, we previously observed that K5, as well as the human immunodeficiency virus type 1 (HIV-1) immunomodulator VPU, reduced steady-state levels of bone marrow stromal cell antigen 2 (BST2; also called CD317 or tetherin), suggesting that BST2 might be a novel substrate of K5 and VPU. Recent work revealed that in the absence of VPU, HIV-1 virions are tethered to the plasma membrane in BST2-expressing HeLa cells. By targeting BST2, K5 might thus similarly overcome an innate antiviral host defense mechanism. Here we establish that despite its type II transmembrane topology and carboxy-terminal glycosylphosphatidylinositol (GPI) anchor, BST2 represents a bona fide target of K5 that is downregulated during primary infection by and reactivation of KSHV. Upon exit of the protein from the endoplasmic reticulum, lysines in the short amino-terminal domain of BST2 are ubiquitinated by K5, resulting in rapid degradation of BST2. Ubiquitination of BST2 is required for degradation, since BST2 lacking cytosolic lysines was K5 resistant and ubiquitin depletion by proteasome inhibitors restored BST2 surface expression. Thus, BST2 represents the first type II transmembrane protein targeted by K5 and the first example of a protein that is both ubiquitinated and GPI linked. We further demonstrate that KSHV release is decreased in the absence of K5 in a BST2-dependent manner, suggesting that K5 contributes to the evasion of intracellular antiviral defense programs.
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Antígenos CD/biossíntese , Regulação Viral da Expressão Gênica , Herpesvirus Humano 8/metabolismo , Proteínas Imediatamente Precoces/biossíntese , Glicoproteínas de Membrana/biossíntese , Proteínas Virais/biossíntese , Biotinilação , Células Cultivadas , Células Endoteliais/virologia , Proteínas Ligadas por GPI , Células HeLa , Humanos , Microcirculação , Modelos Biológicos , Reação em Cadeia da Polimerase , Complexo de Endopeptidases do Proteassoma/metabolismoRESUMO
Kaposi sarcoma (KS) is intimately linked to several aspects of the host immune system. KS development is linked to immunodeficiency in several clinical-epidemiological settings. The development of KS at local inflammatory sites has also been documented. Inflammatory cells are almost always present within KS lesions. Depending upon the inflammatory milieu, KS lesions may progress or regress. Not surprisingly, iatrogenic manipulation of host immunity with drugs may provoke KS growth and/or flare. Given the close association between KS and the immune system, the etiologic agent Kaposi Sarcoma Herpesvirus has developed a variety of mechanisms to evade the host immune system, all of which have cleverly evolved to promote oncogenesis and viral persistence.
Assuntos
Herpesvirus Humano 8/imunologia , Sarcoma de Kaposi/imunologia , Sarcoma de Kaposi/patologia , Sarcoma de Kaposi/virologia , Granuloma/imunologia , Granuloma/patologia , Granuloma/virologia , HumanosRESUMO
The primary roles attributed to the human immunodeficiency virus type 1 (HIV-1) Vpu protein are the degradation of the viral receptor CD4 and the enhancement of virion release. With regard to CD4 downregulation, Vpu has been shown to act as an adapter linking CD4 with the ubiquitin-proteasome machinery via interaction with the F-box protein betaTrCP. To identify additional cellular betaTrCP-dependent Vpu targets, we performed quantitative proteomics analyses using the plasma membrane fraction of HeLa cells expressing either wild-type Vpu or a Vpu mutant (S52N/S56N) that does not bind betaTrCP. One cellular protein, BST-2 (CD317), was consistently underrepresented in the membrane proteome of cells expressing wild-type Vpu compared to the proteome of cells expressing the Vpu mutant. To verify the biological relevance of this phenotype for HIV pathogenesis, we showed that in T cells infected with HIV-1, BST-2 downregulation occurred in a Vpu-dependent manner. Recently, BST-2 has been identified as the interferon-inducible cellular factor Tetherin, which restricts HIV virion release in the absence of Vpu. We address here the unresolved mechanism of Vpu-mediated BST-2 downregulation. Our data show that the presence of wild-type Vpu reduced cell surface and total steady-state BST-2 levels, whereas that of the mutant Vpu had no effect. In addition, treatment of cells with the lysosome acidification inhibitor concanamycin A, but not treatment with the proteasome inhibitor MG132, reduced BST-2 downregulation by wild-type Vpu, thereby suggesting that the presence of Vpu leads to the degradation of BST-2 via an endosome-lysosome degradation pathway. The importance of betaTrCP in this process was confirmed by demonstrating that in the absence of betaTrCP, BST-2 levels were restored despite the presence of Vpu. Taken together, these data support the hypothesis that, in similarity to its role in CD4 degradation, Vpu acts as an adapter molecule linking BST-2 to the cellular ubiquitination machinery via betaTrCP. However, in contrast to the proteasome-dependent degradation of CD4, which occurs in the endoplasmic reticulum, Vpu appears to interact with BST-2 in the trans-Golgi network or in early endosomes, leading to lysosomal degradation of BST-2. Via this action, Vpu could counter the tethering function of BST-2, resulting in enhanced HIV-1 virion release. Interestingly, although HIV-2 does not express Vpu, an isolate known to exhibit enhanced viral egress can downregulate surface BST-2 by an as-yet-unknown mechanism that does not appear to involve degradation. Understanding the molecular mechanisms of both Vpu-dependent and -independent mediated antagonism of BST-2 will be critical for therapeutic strategies that exploit this novel viral function.