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1.
Mol Cell ; 82(9): 1631-1642.e6, 2022 05 05.
Artigo em Inglês | MEDLINE | ID: mdl-35316659

RESUMO

Innate immune responses induce hundreds of interferon-stimulated genes (ISGs). Viperin, a member of the radical S-adenosyl methionine (SAM) superfamily of enzymes, is the product of one such ISG that restricts the replication of a broad spectrum of viruses. Here, we report a previously unknown antiviral mechanism in which viperin activates a ribosome collision-dependent pathway that inhibits both cellular and viral RNA translation. We found that the radical SAM activity of viperin is required for translation inhibition and that this is mediated by viperin's enzymatic product, 3'-deoxy-3',4'-didehydro-CTP (ddhCTP). Viperin triggers ribosome collisions and activates the MAPKKK ZAK pathway that in turn activates the GCN2 arm of the integrated stress response pathway to inhibit translation. The study illustrates the importance of translational repression in the antiviral response and identifies viperin as a translation regulator in innate immunity.


Assuntos
Oxirredutases atuantes sobre Doadores de Grupo CH-CH , Proteínas , Antivirais/farmacologia , Imunidade Inata , Oxirredutases atuantes sobre Doadores de Grupo CH-CH/genética , Proteínas/metabolismo , Ribossomos/genética , Ribossomos/metabolismo , S-Adenosilmetionina , Replicação Viral
2.
Proc Natl Acad Sci U S A ; 120(1): e2208525120, 2023 01 03.
Artigo em Inglês | MEDLINE | ID: mdl-36574644

RESUMO

Major histocompatibility complex class I (MHC-I) molecules, which are dimers of a glycosylated polymorphic transmembrane heavy chain and the small-protein ß2-microglobulin (ß2m), bind peptides in the endoplasmic reticulum that are generated by the cytosolic turnover of cellular proteins. In virus-infected cells, these peptides may include those derived from viral proteins. Peptide-MHC-I complexes then traffic through the secretory pathway and are displayed at the cell surface where those containing viral peptides can be detected by CD8+ T lymphocytes that kill infected cells. Many viruses enhance their in vivo survival by encoding genes that down-regulate MHC-I expression to avoid CD8+ T cell recognition. Here, we report that two accessory proteins encoded by SARS-CoV-2, the causative agent of the ongoing COVID-19 pandemic, down-regulate MHC-I expression using distinct mechanisms. First, ORF3a, a viroporin, reduces the global trafficking of proteins, including MHC-I, through the secretory pathway. The second, ORF7a, interacts specifically with the MHC-I heavy chain, acting as a molecular mimic of ß2m to inhibit its association. This slows the exit of properly assembled MHC-I molecules from the endoplasmic reticulum. We demonstrate that ORF7a reduces antigen presentation by the human MHC-I allele HLA-A*02:01. Thus, both ORF3a and ORF7a act post-translationally in the secretory pathway to lower surface MHC-I expression, with ORF7a exhibiting a specific mechanism that allows immune evasion by SARS-CoV-2.


Assuntos
COVID-19 , Antígenos de Histocompatibilidade Classe I , SARS-CoV-2 , Proteínas Virais Reguladoras e Acessórias , Humanos , Apresentação de Antígeno , Antígenos de Histocompatibilidade Classe I/genética , Antígenos de Histocompatibilidade Classe I/metabolismo , Antígenos HLA , Peptídeos , SARS-CoV-2/metabolismo , Proteínas Virais Reguladoras e Acessórias/metabolismo
3.
PLoS Pathog ; 19(4): e1011286, 2023 04.
Artigo em Inglês | MEDLINE | ID: mdl-37075076

RESUMO

Flaviviruses continue to emerge as global health threats. There are currently no Food and Drug Administration (FDA) approved antiviral treatments for flaviviral infections. Therefore, there is a pressing need to identify host and viral factors that can be targeted for effective therapeutic intervention. Type I interferon (IFN-I) production in response to microbial products is one of the host's first line of defense against invading pathogens. Cytidine/uridine monophosphate kinase 2 (CMPK2) is a type I interferon-stimulated gene (ISG) that exerts antiviral effects. However, the molecular mechanism by which CMPK2 inhibits viral replication is unclear. Here, we report that CMPK2 expression restricts Zika virus (ZIKV) replication by specifically inhibiting viral translation and that IFN-I- induced CMPK2 contributes significantly to the overall antiviral response against ZIKV. We demonstrate that expression of CMPK2 results in a significant decrease in the replication of other pathogenic flaviviruses including dengue virus (DENV-2), Kunjin virus (KUNV) and yellow fever virus (YFV). Importantly, we determine that the N-terminal domain (NTD) of CMPK2, which lacks kinase activity, is sufficient to restrict viral translation. Thus, its kinase function is not required for CMPK2's antiviral activity. Furthermore, we identify seven conserved cysteine residues within the NTD as critical for CMPK2 antiviral activity. Thus, these residues may form an unknown functional site in the NTD of CMPK2 contributing to its antiviral function. Finally, we show that mitochondrial localization of CMPK2 is required for its antiviral effects. Given its broad antiviral activity against flaviviruses, CMPK2 is a promising potential pan-flavivirus inhibitor.


Assuntos
Núcleosídeo-Fosfato Quinase , Replicação Viral , Zika virus , Zika virus/fisiologia , Células Vero , Chlorocebus aethiops , Animais , Humanos , Núcleosídeo-Fosfato Quinase/metabolismo , Interferon Tipo I/metabolismo , Flavivirus/fisiologia , Mitocôndrias , Biossíntese de Proteínas
4.
Proc Natl Acad Sci U S A ; 118(24)2021 06 15.
Artigo em Inglês | MEDLINE | ID: mdl-34045361

RESUMO

The ongoing COVID-19 pandemic has caused an unprecedented global health crisis. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of COVID-19. Subversion of host protein synthesis is a common strategy that pathogenic viruses use to replicate and propagate in their host. In this study, we show that SARS-CoV-2 is able to shut down host protein synthesis and that SARS-CoV-2 nonstructural protein NSP14 exerts this activity. We show that the translation inhibition activity of NSP14 is conserved in human coronaviruses. NSP14 is required for virus replication through contribution of its exoribonuclease (ExoN) and N7-methyltransferase (N7-MTase) activities. Mutations in the ExoN or N7-MTase active sites of SARS-CoV-2 NSP14 abolish its translation inhibition activity. In addition, we show that the formation of NSP14-NSP10 complex enhances translation inhibition executed by NSP14. Consequently, the translational shutdown by NSP14 abolishes the type I interferon (IFN-I)-dependent induction of interferon-stimulated genes (ISGs). Together, we find that SARS-CoV-2 shuts down host innate immune responses via a translation inhibitor, providing insights into the pathogenesis of SARS-CoV-2.


Assuntos
COVID-19/imunologia , Exorribonucleases/imunologia , Evasão da Resposta Imune , Imunidade Inata , Biossíntese de Proteínas/imunologia , SARS-CoV-2/imunologia , Proteínas não Estruturais Virais/imunologia , Animais , Chlorocebus aethiops , Humanos , Células Vero
5.
STAR Protoc ; 3(3): 101654, 2022 09 16.
Artigo em Inglês | MEDLINE | ID: mdl-36072758

RESUMO

Translational regulation is a fundamental step in gene expression with critical roles in biological processes within a cell. Here, we describe a protocol to assess translation activity in mammalian cells by incorporation of O-propargyl-puromycin (OP-Puro). OP-Puro is a puromycin analog that is incorporated into newly synthesized proteins and is detected by click chemistry reaction. We use OP-Puro labeling to assess translation activity between different cell types or cells under different growth conditions by confocal microscopy and flow cytometry. For complete details on the use and execution of this protocol, please refer to Hsu et al. (2021) and Hsu et al. (2022).


Assuntos
Química Click , Proteômica , Animais , Linhagem Celular , Química Click/métodos , Mamíferos/metabolismo , Puromicina/análogos & derivados , Puromicina/farmacologia
6.
bioRxiv ; 2022 May 17.
Artigo em Inglês | MEDLINE | ID: mdl-35611331

RESUMO

Major histocompatibility complex class I (MHC-I) molecules, which are dimers of a glycosylated polymorphic transmembrane heavy chain and the small protein ß 2 -microglobulin (ß 2 m), bind peptides in the endoplasmic reticulum that are generated by the cytosolic turnover of cellular proteins. In virus-infected cells these peptides may include those derived from viral proteins. Peptide-MHC-I complexes then traffic through the secretory pathway and are displayed at the cell surface where those containing viral peptides can be detected by CD8 + T lymphocytes that kill infected cells. Many viruses enhance their in vivo survival by encoding genes that downregulate MHC-I expression to avoid CD8 + T cell recognition. Here we report that two accessory proteins encoded by SARS-CoV-2, the causative agent of the ongoing COVID-19 pandemic, downregulate MHC-I expression using distinct mechanisms. One, ORF3a, a viroporin, reduces global trafficking of proteins, including MHC-I, through the secretory pathway. The second, ORF7a, interacts specifically with the MHC-I heavy chain, acting as a molecular mimic of ß 2 m to inhibit its association. This slows the exit of properly assembled MHC-I molecules from the endoplasmic reticulum. We demonstrate that ORF7a reduces antigen presentation by the human MHC-I allele HLA-A*02:01. Thus, both ORF3a and ORF7a act post-translationally in the secretory pathway to lower surface MHC-I expression, with ORF7a exhibiting a novel and specific mechanism that allows immune evasion by SARS-CoV-2. Significance Statement: Viruses may down-regulate MHC class I expression on infected cells to avoid elimination by cytotoxic T cells. We report that the accessory proteins ORF7a and ORF3a of SARS-CoV-2 mediate this function and delineate the two distinct mechanisms involved. While ORF3a inhibits global protein trafficking to the cell surface, ORF7a acts specifically on MHC-I by competing with ß 2 m for binding to the MHC-I heavy chain. This is the first account of molecular mimicry of ß 2 m as a viral mechanism of MHC-I down-regulation to facilitate immune evasion.

7.
Infect Control Hosp Epidemiol ; 42(10): 1286-1288, 2021 10.
Artigo em Inglês | MEDLINE | ID: mdl-33023685

RESUMO

The incubation period of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is rarely >14 days. We report a patient with hypogammaglobulinemia who developed coronavirus disease 2019 (COVID-19) with a confirmed incubation period of at least 21 days. These findings raise concern for a prolonged presymptomatic transmission phase, necessitating a longer quarantine duration in this patient population.


Assuntos
COVID-19 , SARS-CoV-2 , Humanos , Quarentena , Rituximab/uso terapêutico , Fatores de Tempo
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