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United States Department of Agriculture

Agricultural Research Service

Research Project: Combating Viral Hemorrhagic Septicemia and Improving Yellow Perch Aquaculture for the Great Lakes Region

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Title: The Role of Viral Hemorrhagic Septicemia Virus (VHSV) Matrix (M) Protein in Suppressing Host Transcription

Author
item Ke, Qi
item Weaver, Wade
item Pore, Adam
item Gorgoglione, Bartolomeo
item Wildschutte, Julia Halo
item Xiao, Peng
item Shepherd, Brian
item Spear, Allyn
item Malathi, Krishnamurthy
item Stepien, Carol
item Vakharia, Vikram
item Leaman, Douglas

Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: The fish disease called Viral Hemorrhagic Septicemia is caused by a virus. This virus is known as viral hemorrhagic septicemia virus, or VHSV. When a fish is infected with the virus, the immune system has many ways that it can try to fight off the infection. One way is to sense the virus inside an infected cell and make proteins that can block the virus from replicating. In order to fight off these defenses, one of the viral proteins has developed the ability to prevent the cells from making these defensive proteins. This viral protein is called the "Matrix" or M-protein, and it is also involved in building the structure of the virus, in addition to stopping the host cell defenses. Using fish cells grown in dishes, we were able to examine how the M-protein is able to block the infected cell from making the defensive proteins. We were also able to make viruses that had changes to their M-proteins that stopped them from being able to fight off the cell's defenses. One of the changes to the M-protein only affected its ability to fight the cell's defense, but did not affect the ability of the virus to grow. A different change to the M-protein affected both the ability to fight cell defenses and the growth of the virus. That means that the two different functions of the M-protein are a part of two completely different pathways and that they can be studied separately. This will contribute to understanding how this virus causes disease and how we can design live vaccines to prevent infection.

Technical Abstract: Viral Hemorrhagic Septicemia virus (VHSV) is a pathogenic fish rhabdovirus found in discrete locales throughout the northern hemisphere. VHSV infection of fish cells leads to upregulation of the host's virus detection response, but the virus quickly suppresses interferon (IFN) production and antiviral genes expression. By systematically screening each of the six VHSV structural and nonstructural genes, we have identified matrix protein (M) as its most potent anti-host protein. VHSV-IVb M alone suppressed mitochondrial antiviral signaling protein (MAVS) and type I IFN induced gene expression in a dose-dependent manner. M also suppressed the constitutively active SV40 promoter and globally decreased cellular RNA levels. Chromatin immunoprecipitation (ChIP) studies illustrated that M inhibited RNA polymerase II (RNAP II) recruitment to gene promoters, and decreased RNAP II CTD Ser2 phosphorylation during VHSV infection. However, transcription directed by RNAP I-III was suppressed by M. To identify regions of functional importance, M proteins from a variety of VHSV strains were tested in cell-based transcriptional inhibition assays. M protein of a particular VHSV-Ia strain, F1, was significantly less potent than -IVb M at inhibiting SV40/luc expression, yet differed by just four amino acids. Mutation of D62 to alanine alone, or in combination with an E181 to alanine mutation (D62A/E181A), dramatically reduced the ability of -IVb M to suppress host transcription. Introducing either M D62A or D62A/E181A mutations intoVHSV-IVb via reverse genetics resulted in viruses that replicated efficiently but exhibited less cytotoxicity and reduced anti-transcriptional activities, implicating M as a primary regulator of cytopathicity and host transcriptional suppression.

Last Modified: 07/23/2017
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