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1.
Front Immunol ; 12: 700926, 2021.
Article in English | MEDLINE | ID: covidwho-1305649

ABSTRACT

RIG-I-like receptors (RLR), RIG-I and MDA5, are cytoplasmic viral RNA sensors that recognize viral double-stranded RNAs and trigger signals to induce antiviral responses, including type I interferon production. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) caused the coronavirus disease 2019 pandemic. However, the RLR role in innate immune response to SARS-CoV-2 has not been fully elucidated. Here, we studied the roles of RLR in cytokine expression responding to SARS-CoV-2 and found that not only MDA5 but also RIG-I are involved in innate immune responses in some types of human cells. Transfection of total RNAs extracted from SARS-CoV-2-infected cells into epithelial cells induced IFN-ß, IP-10, and Ccl5 mRNA expression. The cytokine expression was reduced by knockout of either RIG-I or MDA5, suggesting that both proteins are required for appropriate innate immune response to SARS-CoV-2. Two viral genomic RNA regions strongly induced type I IFN expression, and a 200-base fragment of viral RNA preferentially induced type I IFN in a RIG-I-dependent manner. In contrast, SARS-CoV-2 infectious particles hardly induced cytokine expression, suggesting viral escape from the host response. Viral 9b protein inhibited RIG-I and MAVS interaction, and viral 7a protein destabilized the TBK1 protein, leading to attenuated IRF-3 phosphorylation required for type I IFN expression. Our data elucidated the mechanism underlying RLR-mediated response to SARS-CoV-2 infection and viral escape from the host innate immune response.


Subject(s)
COVID-19/immunology , Interferon-Induced Helicase, IFIH1/metabolism , Receptors, Retinoic Acid/metabolism , SARS-CoV-2/physiology , Severe Acute Respiratory Syndrome/immunology , Gene Knockdown Techniques , HEK293 Cells , Host-Pathogen Interactions , Humans , Immune Evasion , Immunity, Innate , Interferon Regulatory Factor-3/metabolism , Interferon Type I/metabolism , Interferon-Induced Helicase, IFIH1/genetics , Phosphorylation , RNA, Viral/immunology , Receptors, Retinoic Acid/genetics , Signal Transduction , Viral Matrix Proteins/metabolism
2.
Int J Mol Sci ; 22(7)2021 Mar 31.
Article in English | MEDLINE | ID: covidwho-1299438

ABSTRACT

Cancer "stem cells" (CSCs) sustain the hierarchies of dividing cells that characterize cancer. The main causes of cancer-related mortality are metastatic disease and relapse, both of which originate primarily from CSCs, so their eradication may provide a bona fide curative strategy, though there maybe also the need to kill the bulk cancer cells. While classic anti-cancer chemotherapy is effective against the dividing progeny of CSCs, non-dividing or quiescent CSCs are often spared. Improved anti-cancer therapies therefore require approaches that target non-dividing CSCs, which must be underpinned by a better understanding of factors that permit these cells to maintain a stem cell-like state. During hematopoiesis, retinoic acid receptor (RAR) γ is selectively expressed by stem cells and their immediate progeny. It is overexpressed in, and is an oncogene for, many cancers including colorectal, renal and hepatocellular carcinoma, cholangiocarcinomas and some cases of acute myeloid leukemia that harbor RARγ fusion proteins. In vitro studies suggest that RARγ-selective and pan-RAR antagonists provoke the death of CSCs by necroptosis and point to antagonism of RARγ as a potential strategy to treat metastatic disease and relapse, and perhaps provide a cure for some cancers.


Subject(s)
Neoplastic Stem Cells/metabolism , Receptors, Retinoic Acid/genetics , Receptors, Retinoic Acid/metabolism , Cell Division/physiology , Humans , Neoplasms/metabolism , Neoplasms/therapy , Neoplastic Stem Cells/physiology , Oncogenes/genetics , Receptors, Retinoic Acid/antagonists & inhibitors , Receptors, Retinoic Acid/physiology
3.
Cell Rep ; 34(7): 108761, 2021 02 16.
Article in English | MEDLINE | ID: covidwho-1062276

ABSTRACT

Coronavirus disease 2019 (COVID-19) is a current global health threat caused by the novel coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Emerging evidence indicates that SARS-CoV-2 elicits a dysregulated immune response and a delayed interferon (IFN) expression in patients, which contribute largely to the viral pathogenesis and development of COVID-19. However, underlying mechanisms remain to be elucidated. Here, we report the activation and repression of the innate immune response by SARS-CoV-2. We show that SARS-CoV-2 RNA activates the RIG-I-MAVS-dependent IFN signaling pathway. We further uncover that ORF9b immediately accumulates and antagonizes the antiviral type I IFN response during SARS-CoV-2 infection on primary human pulmonary alveolar epithelial cells. ORF9b targets the nuclear factor κB (NF-κB) essential modulator NEMO and interrupts its K63-linked polyubiquitination upon viral stimulation, thereby inhibiting the canonical IκB kinase alpha (IKKα)/ß/γ-NF-κB signaling and subsequent IFN production. Our findings thus unveil the innate immunosuppression by ORF9b and provide insights into the host-virus interplay during the early stage of SARS-CoV-2 infection.


Subject(s)
Coronavirus Nucleocapsid Proteins/genetics , I-kappa B Kinase/metabolism , SARS-CoV-2/metabolism , Adaptor Proteins, Signal Transducing/metabolism , Alveolar Epithelial Cells/metabolism , Alveolar Epithelial Cells/virology , COVID-19/immunology , COVID-19/metabolism , Coronavirus Nucleocapsid Proteins/metabolism , HEK293 Cells , Humans , Immunity, Innate/immunology , Interferon Type I/metabolism , Interferons/metabolism , NF-kappa B/metabolism , Phosphoproteins/genetics , Phosphoproteins/metabolism , Primary Cell Culture , Receptors, Retinoic Acid/metabolism , SARS-CoV-2/genetics , SARS-CoV-2/immunology , Signal Transduction , Ubiquitination
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