Severe Acute Respiratory Syndrome Coronavirus ORF7a Inhibits Bone Marrow Stromal Antigen 2 Virion Tethering through a Novel Mechanism of Glycosylation Interference.

Abstract

UNLABELLED:

Severe acute respiratory syndrome (SARS) emerged in November 2002 as a case of atypical pneumonia in China, and the causative agent of SARS was identified to be a novel coronavirus, severe acute respiratory syndrome coronavirus (SARS-CoV). Bone marrow stromal antigen 2 (BST-2; also known as CD317 or tetherin) was initially identified to be a pre-B-cell growth promoter, but it also inhibits the release of virions of the retrovirus human immunodeficiency virus type 1 (HIV-1) by tethering budding virions to the host cell membrane. Further work has shown that BST-2 restricts the release of many other viruses, including the human coronavirus 229E (hCoV-229E), and the genomes of many of these viruses encode BST-2 antagonists to overcome BST-2 restriction. Given the previous studies on BST-2, we aimed to determine if BST-2 has the ability to restrict SARS-CoV and if the SARS-CoV genome encodes any proteins that modulate BST-2's antiviral function. Through an in vitro screen, we identified four potential BST-2 modulators encoded by the SARS-CoV genome: the papain-like protease (PLPro), nonstructural protein 1 (nsp1), ORF6, and ORF7a. As the function of ORF7a in SARS-CoV replication was previously unknown, we focused our study on ORF7a. We found that BST-2 does restrict SARS-CoV, but the loss of ORF7a leads to a much greater restriction, confirming the role of ORF7a as an inhibitor of BST-2. We further characterized the mechanism of BST-2 inhibition by ORF7a and found that ORF7a localization changes when BST-2 is overexpressed and ORF7a binds directly to BST-2. Finally, we also show that SARS-CoV ORF7a blocks the restriction activity of BST-2 by blocking the glycosylation of BST-2.

IMPORTANCE:

The severe acute respiratory syndrome coronavirus (SARS-CoV) emerged from zoonotic sources in 2002 and caused over 8,000 infections and 800 deaths in 37 countries around the world. Identifying host factors that regulate SARS-CoV pathogenesis is critical to understanding how this lethal virus causes disease. We have found that BST-2 is capable of restricting SARS-CoV release from cells; however, we also identified a SARS-CoV protein that inhibits BST-2 function. We show that the SARS-CoV protein ORF7a inhibits BST-2 glycosylation, leading to a loss of BST-2's antiviral function.

• Authors: Justin K Taylor, Christopher M Coleman, Sandra Postel, Jeanne M Sisk, John G Bernbaum, Thiagarajan Venkataraman, Eric J Sundberg, Matthew B Frieman
• Journal: Journal of virology (J Virol) Vol. 89 Issue 23 Pg. 11820-33 (Dec 2015) ISSN: 1098-5514 [Electronic] United States
• PMID: 26378163 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, N.I.H., Intramural)
• Copyright: Copyright © 2015, American Society for Microbiology. All Rights Reserved.

Chemical References

• Antigens, CD
• BST2 protein, human
• DNA Primers
• GPI-Linked Proteins
• Viral Nonstructural Proteins
• Viral Proteins
• Nsp1 protein, SARS coronavirus
• RNA-Dependent RNA Polymerase
• Cysteine Endopeptidases
• Coronavirus 3C Proteases

Topics

• Animals
• Antigens, CD (physiology)
• Chlorocebus aethiops
• Chromatography, Affinity
• Cloning, Molecular
• Coronavirus 3C Proteases
• Cysteine Endopeptidases (genetics)
• DNA Primers (genetics)
• Flow Cytometry
• GPI-Linked Proteins (physiology)
• Glycosylation
• HEK293 Cells
• Humans
• Immunoprecipitation
• Microscopy, Confocal
• Microscopy, Electron
• Open Reading Frames (genetics, physiology)
• RNA-Dependent RNA Polymerase (genetics)
• Reverse Transcriptase Polymerase Chain Reaction
• Severe acute respiratory syndrome-related coronavirus (physiology)
• Severe Acute Respiratory Syndrome (virology)
• Vero Cells
• Viral Nonstructural Proteins (genetics)
• Viral Proteins (genetics)
• Virion (physiology)
• Virus Attachment