Structural Basis for #Tetherin #Antagonism as a #Barrier to #Zoonotic #Lentiviral Transmission (Cell Host Microbe, abstract)

[Source: Cell, Host & Microbe, full page: (LINK). Abstract, edited.]

Structural Basis for Tetherin Antagonism as a Barrier to Zoonotic Lentiviral Transmission

Cosmo Z. Buffalo, Christina M. Stürzel, Elena Heusinger, Dorota Kmiec, Frank Kirchhoff, James H. Hurley, Xuefeng Ren

Published: August 22, 2019 / DOI:



  • Cryo-EM structure of AP-2, simian tetherin, and SIVsmm Nef complex at a 3.8-Å resolution
  • Nef refolds the β2 subunit of AP-2 for binding of the simian tetherin DIWK sequence
  • Tetherin binding site is distinct from those of Nef substrates MHC class I, CD3, and CD4
  • Tetherin binding site on Nef overlaps with the site for SERINC5 binding



Tetherin is a host defense factor that physically prevents virion release from the plasma membrane. The Nef accessory protein of simian immunodeficiency virus (SIV) engages the clathrin adaptor AP-2 to downregulate tetherin via its DIWK motif. As human tetherin lacks DIWK, antagonism of tetherin by Nef is a barrier to simian-human transmission of non-human primate lentiviruses. To determine the molecular basis for tetherin counteraction, we reconstituted the AP-2 complex with a simian tetherin and SIV Nef and determined its structure by cryoelectron microscopy (cryo-EM). Nef refolds the first α-helix of the β2 subunit of AP-2 to a β hairpin, creating a binding site for the DIWK sequence. The tetherin binding site in Nef is distinct from those of most other Nef substrates, including MHC class I, CD3, and CD4 but overlaps with the site for the restriction factor SERINC5. This structure explains the dependence of SIVs on tetherin DIWK and consequent barrier to human transmission.

Keywords: HIV – SIV – clathrin – adaptor protein – host-factor restriction – trafficking – cryo-EM – tetherin – hydrogen-deuterium exchange

Keywords: Retrovirus; Lentivirus; HIV; Tetherin.



TMPRSS2 is the major activating #protease of #influenza A virus in primary human #airway cells and influenza B virus in human type II #pneumocytes (J Virol., abstract)

[Source: Journal of Virology, full page: (LINK). Abstract, edited.]

TMPRSS2 is the major activating protease of influenza A virus in primary human airway cells and influenza B virus in human type II pneumocytes

Hannah Limburg, Anne Harbig, Dorothea Bestle, David A. Stein, Hong M. Moulton, Julia Jaeger, Harshavardhan Janga, Kornelia Hardes, Janine Koepke, Leon Schulte,Andreas Rembert Koczulla, Bernd Schmeck, Hans-Dieter Klenk, Eva Böttcher-Friebertshäuser

DOI: 10.1128/JVI.00649-19



Cleavage of influenza virus hemagglutinin (HA) by host cell proteases is essential for virus infectivity and spread. We previously demonstrated in vitro that the transmembrane protease TMPRSS2 cleaves influenza A and B virus (IAV/IBV) HA possessing a monobasic cleavage site. Subsequent studies revealed that TMPRSS2 is crucial for activation and pathogenesis of H1N1pdm and H7N9 IAV in mice. In contrast, activation of H3N2 IAV and IBV was found to be independent of TMPRSS2 expression and supported by as-yet undetermined protease(s).

Here, we investigated the role of TMPRSS2 in proteolytic activation of IAV and IBV in three human airway cell culture systems: primary human bronchial epithelial cells (HBEC), primary type II alveolar epithelial cells (AECII) and Calu-3 cells. Knockdown of TMPRSS2 expression was performed using a previously described antisense peptide-conjugated phosphorodiamidate morpholino oligomer, T-ex5, that interferes with splicing of TMPRSS2 pre-mRNA, resulting in the expression of enzymatically inactive TMPRSS2. T-ex5 treatment produced efficient knockdown of active TMPRSS2 in all three airway cell culture models and prevented proteolytic activation and multiplication of H7N9 IAV in Calu-3 cells and H1N1pdm, H7N9 and H3N2 IAV in HBEC and AECII. T-ex5 treatment also inhibited activation and spread of IBV in AECII, but did not affect IBV activation in HBEC and Calu-3 cells.

This study identifies TMPRSS2 as the major HA-activating protease of IAV in human airway cells and IBV in type II pneumocytes and as a potential target for the development of novel drugs to treat influenza infections.



Influenza A and B viruses (IAV/IBV) cause significant morbidity and mortality during seasonal outbreaks. Cleavage of the viral surface glycoprotein hemagglutinin (HA) by host proteases is a prerequisite for membrane fusion and essential for virus infectivity. Inhibition of relevant proteases provides a promising therapeutic approach that may avoid the development of drug resistance. HA of most influenza viruses is cleaved at a monobasic cleavage site and a number of proteases have been shown to cleave HA in vitro. This study demonstrates that the transmembrane protease TMPRSS2 is the major HA-activating protease of IAV in primary human bronchial cells and of both IAV and IBV in primary human type II pneumocytes. It further reveals that human and murine airway cells can differ in their HA-cleaving protease repertoire. Our data will help drive the development of potent and selective protease inhibitors as novel drugs for influenza treatment.

Copyright © 2019 American Society for Microbiology. All Rights Reserved.

Keywords: Influenza A; Influenza B; H1N1pdm09; H3N2; H7N9; Viral pathogenesis.


An #influenza virus-triggered SUMO switch orchestrates co-opted endogenous #retroviruses to stimulate host antiviral #immunity (Proc Natl Acad Sci USA, abstract)

[Source: Proceedings of the National Academy of Sciences of the United States of America, full page: (LINK). Abstract, edited.]

An influenza virus-triggered SUMO switch orchestrates co-opted endogenous retroviruses to stimulate host antiviral immunity

Nora Schmidt, Patricia Domingues, Filip Golebiowski, Corinna Patzina, Michael H. Tatham, Ronald T. Hay, and Benjamin G. Hale

PNAS first published August 7, 2019 / DOI:

Edited by Stephen P. Goff, Columbia University Medical Center, New York, NY, and approved July 15, 2019 (received for review April 24, 2019)



Primary host defenses against viruses involve specific cellular recognition of non-self nucleic acids as pathogen-associated molecular patterns (PAMPs) that trigger induction of cytokine-mediated antiviral responses. Thus, ability to discriminate between “self” and “non-self” nucleic acids, and prevent aberrant immunopathology, is a key tenet of immunity. Here, we identify self-derived endogenous retroviral RNAs as host-encoded PAMPs that are up-regulated during influenza virus infections, and which stimulate antiviral immunity. Normally, endogenous retroviruses are tightly repressed transcriptionally by host TRIM28, but infection triggers changes in the modification status of TRIM28 to alleviate repression. This provides an example of how endogenous retroviruses integrated within the host genome have been functionally co-opted by a regulatory switch to aid defense against newly invading pathogens.



Dynamic small ubiquitin-like modifier (SUMO) linkages to diverse cellular protein groups are critical to orchestrate resolution of stresses such as genome damage, hypoxia, or proteotoxicity. Defense against pathogen insult (often reliant upon host recognition of “non-self” nucleic acids) is also modulated by SUMO, but the underlying mechanisms are incompletely understood. Here, we used quantitative SILAC-based proteomics to survey pan-viral host SUMOylation responses, creating a resource of almost 600 common and unique SUMO remodeling events that are mounted during influenza A and B virus infections, as well as during viral innate immune stimulation. Subsequent mechanistic profiling focused on a common infection-induced loss of the SUMO-modified form of TRIM28/KAP1, a host transcriptional repressor. By integrating knockout and reconstitution models with system-wide transcriptomics, we provide evidence that influenza virus-triggered loss of SUMO-modified TRIM28 leads to derepression of endogenous retroviral (ERV) elements, unmasking this cellular source of “self” double-stranded (ds)RNA. Consequently, loss of SUMO-modified TRIM28 potentiates canonical cytosolic dsRNA-activated IFN-mediated defenses that rely on RIG-I, MAVS, TBK1, and JAK1. Intriguingly, although wild-type influenza A virus robustly triggers this SUMO switch in TRIM28, the induction of IFN-stimulated genes is limited unless expression of the viral dsRNA-binding protein NS1 is abrogated. This may imply a viral strategy to antagonize such a host response by sequestration of induced immunostimulatory ERV dsRNAs. Overall, our data reveal that a key nuclear mechanism that normally prevents aberrant expression of ERV elements (ERVs) has been functionally co-opted via a stress-induced SUMO switch to augment antiviral immunity.

influenza – SUMO – endogenous retroviruses – dsRNA – interferon

Keywords: Influenza A; Retrovirus; Immunopathology; Viral pathogenesis.


Expression #Profile and #Function Analysis of Long Non-coding #RNAs in the #Infection of #Coxsackievirus B3 (Virol Sin., abstract)

[Source: Virologica Sinica, full page: (LINK). Abstract, edited.]

Expression Profile and Function Analysis of Long Non-coding RNAs in the Infection of Coxsackievirus B3

Authors: Lei Tong, Ye Qiu, Hui Wang, Yunyue Qu, Yuanbo Zhao, Lexun Lin, Yan Wang, Weizhen Xu, Wenran Zhao, Hongyan He, Guangze Zhao, Mary H. Zhang, Decheng Yang, Xingyi Ge, Zhaohua Zhong

Research article / First Online: 06 August 2019



The roles of lncRNAs in the infection of enteroviruses have been barely demonstrated. In this study, we used coxsackievirus B3 (CVB3), a typical enterovirus, as a model to investigate the expression profiles and functional roles of lncRNAs in enterovirus infection. We profiled lncRNAs and mRNA expression in CVB3-infected HeLa cells by lncRNA-mRNA integrated microarrays. As a result, 700 differentially expressed lncRNAs (431 up-regulated and 269 down-regulated) and 665 differentially expressed mRNAs (299 up-regulated and 366 down-regulated) were identified in CVB3 infection. Then we performed lncRNA-mRNA integrated pathway analysis to identify potential functional impacts of the differentially expressed mRNAs, in which lncRNA-mRNA correlation network was built. According to lncRNA-mRNA correlation, we found that XLOC-001188, an lncRNA down-regulated in CVB3 infection, was negatively correlated with NFAT5 mRNA, an anti-CVB3 gene reported previously. This interaction was supported by qPCR detection following siRNA-mediated knockdown of XLOC-001188, which showed an increase of NFAT5 mRNA and a reduction of CVB3 genomic RNA. In addition, we observed that four most significantly altered lncRNAs, SNHG11, RP11-145F16.2, RP11-1023L17.1 and RP11-1021N1.2 share several common correlated genes critical for CVB3 infection, such as BRE and IRF2BP1. In all, our studies reveal the alteration of lncRNA expression in CVB3 infection and its potential influence on CVB3 replication, providing useful information for future studies of enterovirus infection.

Keywords Coxsackievirus B3 (CVB3) lncRNA-mRNA correlation network Long non-coding RNA (lncRNA) XLOC-001188 NFAT5

Abbreviations: ARRDC3 – Arrestin domain containing 3; BRE – Brain and reproductive organ-expressed; CCRN4L – Carbon catabolite repression 4-like; CDCA3 – Cell division cycle associated 3;  CVB3 – Coxsackievirus B3; FIBP – FGF1 intracellular binding protein; HLA-DQA1 – Major histocompatibility complex, class II, DQ alpha 1; hnRNPH3 – Heterogeneous nuclear ribonucleoprotein H3; IRF2BP1 – Insulin-like growth factor 2 mRNA-binding protein 1; KEGG – Kyoto Encyclopedia of Genes and Genomes; LncRNA – Long non-coding RNA; MDA5 – Melanoma differentiation associated gene 5; MTX1 – Metaxin 1; NEMF – Nuclear export mediator factor; NFAT5 – Nuclear factor of activated T cells 5; SNHG11 – Small nucleolar RNA host gene 11; TIMP1 – TIMP metallopeptidase inhibitor 1; TMED9 – Transmembrane p24 trafficking protein 9; ZNF295 – Zinc finger protein 295

Lei Tong and Ye Qiu these authors contributed equally to this work.

Electronic supplementary material: The online version of this article ( contains supplementary material, which is available to authorized users.

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This work was supported by the National Natural Science Foundation of China (81101234 to Lei Tong; 81571999, 81871652 to Zhaohua Zhong; 31470260 to Xingyi Ge; 81672007 to Wenran Zhao; 81772188 to Yan Wang), the Foundation of Heilongjiang Provincial Postdoctor of China (LBH-Z11076 to Lei Tong), the China Postdoctoral Science Foundation (2015M580269 to Lexun Lin), the Research Foundation of Education Bureau of Heilongjiang Province (12511176 to Lei Tong), the Hu-Xiang Youth Talents Scholar Program of Hunan Province (2017RS3017 to Xingyi Ge), Health and Family Planning Commission of Heilongjiang Province (2016-165 to Lexun Lin), the Provincial Natural Science Foundation of Hunan Province (Grant Number 2019JJ50035 to Ye Qiu) and the Fundamental Research Funds for the Central Universities of China (Grant Number 531107051162 to Ye Qiu). We are grateful to the technical support from Heilongjiang Provincial Key Laboratory of Pathogens and Immunity and Heilongjiang Provincial Science and Technology Innovation Team in Higher Education Institutes for Infection and Immunity of Harbin Medical University. We thank Jing Li (Cnkingbio Company Ltd, Beijing, China) for technical support.

Author Contributions

LT, YQ, XG and ZZ designed the experiments. HW, YQ, LL, YW, WX, WZ and HH carried out the experiments. LT, YQ, YZ, GZ, MHZ and DY analyzed the data. YQ wrote the paper. LT, YQ, DY, XG and ZZ checked and finalized the manuscript. All authors read and approved the final manuscript.


Compliance with Ethical Standards

Conflict of interest

The authors declare that they have no conflict of interest.

Animal and Human Rights Statement

This article does not contain any studies with human or animal subjects performed by any of the authors.

Keywords: Enterovirus; Coxsackievirus B3; Viral pathogenesis.


#Zika virus #infection induces #DNA #damage response in #human #neural progenitors that enhances viral replication (J Virol., abstract)

[Source: Journal of Virology, full page: (LINK). Abstract, edited.]

Zika virus infection induces DNA damage response in human neural progenitors that enhances viral replication

Christy Hammack, Sarah C. Ogden, Joseph C. Madden, Jr., Angelica Medina, Chongchong Xu, Ernest Phillips, Yuna Son, Allaura Cone, Serena Giovinazzi, Ruth A. Didier, David M. Gilbert,Hongjun Song, Guoli Ming, Zhexing Wen, Margo A. Brinton, Akash Gunjan, Hengli Tang

DOI: 10.1128/JVI.00638-19



Zika virus (ZIKV) infection attenuates the growth of human neural progenitor cells (hNPCs). As these hNPCs generate the cortical neurons during early brain development, the ZIKV-mediated growth retardation potentially contributes to the neurodevelopmental defects of the congenital Zika syndrome. Here, we investigate the mechanism by which ZIKV manipulates the cell cycle in hNPCs and the functional consequence of cell cycle perturbation on the replication of ZIKV and related flaviviruses. We demonstrate that ZIKV, but not dengue virus (DENV), induces DNA double-strand breaks (DSBs), triggering the DNA damage response through the ATM/Chk2 signaling pathway while suppressing the ATR/Chk1 signaling pathway. Furthermore, ZIKV infection impedes the progression of cells through S phase, thereby preventing the completion of host DNA replication. Recapitulating the S-phase arrest state with inhibitors led to an increase in ZIKV replication, but not of West Nile virus or DENV. Our data identify ZIKV’s ability to induce DSBs and suppress host DNA replication, which results in a cellular environment favorable for its replication.



Clinically, Zika virus (ZIKV) infection can lead to developmental defects in the cortex of the fetal brain. How ZIKV triggers this event in developing neural cells is not well understood at a molecular level, and likely requires many contributing factors. ZIKV efficiently infects human neural progenitor cells (hNPCs) and leads to growth arrest of these cells which are critical for brain development. Here, we demonstrate that infection with ZIKV, but not dengue virus, disrupts the cell cycle of hNPCs by halting DNA replication during S phase and inducing DNA damage. We further show that ZIKV infection activates the ATM/Chk2 checkpoint but prevents the activation of another checkpoint, the ATR/Chk1 pathway. These results unravel an intriguing mechanism by which a RNA virus interrupts host DNA replication. Lastly, by mimicking virus-induced S-phase arrest, we show that ZIKV manipulates the cell cycle to benefit viral replication.

Copyright © 2019 American Society for Microbiology. All Rights Reserved.

Keywords: Zika Virus; Neuroinvasion; Viral pathogenesis.


#Influenza A virus protein #NS1 exhibits strain-independent #conformational #plasticity (J Virol., abstract)

[Source: Journal of Virology, full page: (LINK). Abstract, edited.]

Influenza A virus protein NS1 exhibits strain-independent conformational plasticity

Sayantan Mitra, Dilip Kumar, Liya Hu, Banumathi Sankaran, Mahdi Muhammad Moosa, Andrew P. Rice, Josephine C. Ferreon, Allan Chris M. Ferreon, B.V.Venkataram Prasad

DOI: 10.1128/JVI.00917-19



Influenza A virus (IAV) non-structural protein 1 (NS1), a potent antagonist of host immune response, is capable of interacting with RNA and a wide range of cellular proteins. NS1 consists of an RNA-binding domain (RBD) and an effector domain (ED) separated by a flexible linker region (LR). H5N1-NS1 has a characteristic 5-residue deletion in the LR with either G (minor group) or E (major group) at the 71st position, and non-H5N1-NS1 contains E71 with an intact linker. Based on the orientation of ED with respect to RBD, previous crystallographic studies have shown that minor group H5N1-NS1(G71), a non-H5N1-NS1 (H6N6-NS1(E71)), and the LR-deletion mutant H6N6-NS1(Δ80-84/E71) mimicking the major group H5N1-NS1, exhibit ‘open’, ‘semi-open’, and ‘closed’ conformations, respectively, suggesting that NS1 exhibits strain-dependent conformational preference. Here we report the first crystal structure of a naturally occurring H5N1-NS1(E71) and show that it adopts an ‘open’ conformation similar to the minor group of H5N1-NS1 (H5N1-NS1(G71)). We also show that H6N6-NS1(Δ80-84/E71) under a different crystallization condition and H6N6-NS1(Δ80-84/G71) also exhibit ‘open’ conformations, suggesting NS1 can adopt an ‘open’ conformation irrespective of E or G at the 71st position. Our single-molecule FRET analysis to investigate the conformational preference of NS1 in solution showed that all NS1 constructs predominantly exist in ‘open’ conformation. Further, our co-immunoprecipitation and binding studies showed that they all bind to cellular factors with similar affinity. Taken together, our studies suggest that NS1 exhibits strain-independent structural plasticity that allows it to interact with a wide variety of cellular ligands during viral infection.



IAV is responsible for several pandemics over the last century and continues to infect millions annually. The frequent rise in drug-resistant strains necessitates exploring novel targets for developing antiviral drugs that can reduce the global burden of influenza infection. Because of its critical role in the replication and pathogenesis of IAV, non-structural protein 1 (NS1) is a potential target for developing antivirals. Previous studies suggested that NS1 adopts strain-dependent ‘open’, ‘semi-open’, and ‘closed’ conformations. Here we show, based on three crystal structures, that NS1 irrespective of strain differences can adopt ‘open’ conformation. We further show that NS1 from different strains primarily exists in ‘open’ conformation in solution and binds to cellular proteins with similar affinity. Together, our findings suggest that conformational polymorphism facilitated by a flexible linker is intrinsic to NS1, and this may be the underlying factor allowing NS1 to bind several cellular factors during IAV replication.

Copyright © 2019 American Society for Microbiology. All Rights Reserved.

Keywords: Influenza A; Avian Influenza; H5N1; H6N6; Viral pathogenesis.


#Spike proteins of novel #MERS #coronavirus isolates from North- and West- #African dromedary #camels mediate robust viral entry into #human target cells (Virology, abstract)

[Source: US National Library of Medicine, full page: (LINK). Abstract, edited.]

Virology. 2019 Jul 19;535:261-265. doi: 10.1016/j.virol.2019.07.016. [Epub ahead of print]

Spike proteins of novel MERS-coronavirus isolates from North- and West-African dromedary camels mediate robust viral entry into human target cells.

Kleine-Weber H1, Pöhlmann S2, Hoffmann M3.

Author information: 1 Infection Biology Unit, Deutsches Primatenzentrum – Leibniz Institute for Primate Research, Kellnerweg 4, 37077 Göttingen, Germany; Faculty of Biology and Psychology, University Göttingen, Wilhelm-Weber-Str. 2, 37073 Göttingen, Germany. 2 Infection Biology Unit, Deutsches Primatenzentrum – Leibniz Institute for Primate Research, Kellnerweg 4, 37077 Göttingen, Germany; Faculty of Biology and Psychology, University Göttingen, Wilhelm-Weber-Str. 2, 37073 Göttingen, Germany. Electronic address: 3 Infection Biology Unit, Deutsches Primatenzentrum – Leibniz Institute for Primate Research, Kellnerweg 4, 37077 Göttingen, Germany.



The highly pathogenic Middle East respiratory syndrome (MERS)-related coronavirus (CoV) is transmitted from dromedary camels, the natural reservoir, to humans. For at present unclear reasons, MERS cases have so far only been observed in the Arabian Peninsula, although MERS-CoV also circulates in African dromedary camels. A recent study showed that MERS-CoV found in North/West- (Morocco) and West-African (Burkina Faso and Nigeria) dromedary camels are genetically distinct from Arabian viruses and have reduced replicative capacity in human cells, potentially due to amino acid changes in one or more viral proteins. Here, we show that the spike (S) proteins of the prototypic Arabian MERS-CoV strain, human betacoronavirus 2c EMC/2012, and the above stated African MERS-CoV variants do not appreciably differ in expression, DPP4 binding and ability to drive entry into target cells. Thus, virus-host-interactions at the entry stage may not limit spread of North- and West-African MERS-CoV in human cells.

Copyright © 2019. Published by Elsevier Inc.

KEYWORDS: Dromedary camel; Entry; MERS-coronavirus; Spike; Zoonosis

PMID: 31357164 DOI: 10.1016/j.virol.2019.07.016

Keywords: MERS-CoV; Camels; Viral pathogenesis.