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Document Type

Thesis - University Access Only

Award Date

2014

Degree Name

Doctor of Philosophy (PhD)

Department / School

Biology and Microbiology

First Advisor

Xiuqing Wang

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) is a singlestranded positive-sense RNA virus that belongs to the family of Arteriviridae. PRRSV infection generally results in reproduction failure in sows and respiratory problems in piglets and it has become a significant concern for the swine industry all over the world. PRRSV infection is characterized by delayed and weak host adaptive response possibly due to the ability of PRRSV to suppress the host’s innate immune response, such as the induction of type I interferon (IFN). IFNs are a group of cytokines that serve as a bridge between the innate and adaptive immune response. Previous studies have shown that several viral nonstructural proteins are capable of interfering with the induction of type I IFNs. However, most of the results are obtained through experiments conducted in cells derived from non-natural host species of PRRSV. Here, we first examined the induction of type I IFN in porcine monocyte-derived dendritic cells (Mo-DC). Our results showed that PRRSV infection efficiently activated the transcription of IFN-α and β. However, the protein level of IFN-α in the supernatant and cell lysates of infected cells is either low or below detection limit, suggesting that PRRSV may interfere with the induction of type I IFNs through a post-transcriptional mechanism in Mo-DC. Since previous studies have suggested the essential role of phosphatidylinositol-3 kinase (PI3K) dependent Akt, PI3K/Akt, pathway in the induction of type I IFN in dendritic cells, we next examined the interaction between PRRSV and PI3K/Akt pathway. An early activation and late inhibition of PI3K/Akt were observed in PRRSV infected Mo-DC. Furthermore, inhibition of PI3K/Akt by a PI3K specific inhibitor, LY294002, reduced virus replication. We have also shown that PRRSV induced the transcriptional activation of type I interferon in a PI3K/Akt dependent manner. Protein kinase R (PKR) is activated by dsRNA during virus infection and exhibits its antiviral activities by inhibiting protein synthesis through phosphorylation of its substrate, the α subunit of the translation initiation factor 2 (eIF2α). To determine the role of PKR during PRRSV infection, we first examined the kinetics of PKR activation during PRRSV infection. Results showed that PRRSV transiently activated PKR during early infection. Concurrently, an increased transcription of GADD34, a cofactor of protein phosphatase 1 (PP1) was observed. There is no correlation between PKR activation and eIF2a phosphorylation. However, eIF2a phosphorylation was positively correlated with XBP1 splicing, suggesting the possible role of ER stress in triggering eIf2a phosphorylation. Similarly, PKR silencing did not significantly affect the phosphorylation of eIF2a in PRRSV infected cells, but virus replication was reduced. Future studies are needed to understand the role of PKR in PRRSV replication process in greater detail.

Library of Congress Subject Headings

Swine -- Virus diseases
Porcine reproductive and respiratory syndrome
Host-virus relationship

Description

Includes bibliographic reference (pages 104-170)

Format

application/pdf

Number of Pages

188

Publisher

South Dakota State University

Rights

In Copyright - Non-Commercial Use Permitted
http://rightsstatements.org/vocab/InC-NC/1.0/

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