Classical Swine Fever Virus Infection and Its NS4A Protein Expression Induce IL-8 Production through MAVS Signaling Pathway in Swine Umbilical Vein Endothelial Cells.

Wang Dong,Mingxing Jin,Yueling Ouyang,Tao Wang,Kangkang Guo,Huifang Lv,Yanming Zhang

doi:10.3389/fmicb.2017.02687

Abstract

Classical swine fever virus (CSFV) infection causes a severe disease of pigs, which is characterized by hemorrhage, disseminated intravascular coagulation, and leucopenia. IL-8, a main chemokine and activator of neutrophils, regulates the permeability of endothelium, which may be related to the hemorrhage upon CSFV infection. Until now, the molecular mechanisms of IL-8 regulation during CSFV infection are poorly defined. Here, we showed that CSFV infection induced IL-8 production and the upregulation of IL-8 required virus replication in swine umbilical vein endothelial cells (SUVECs). Additionally, MAVS expression was increased and was required for IL-8 production upon CSFV infection. Moreover, ROS was involved in CSFV-induced IL-8 production. Subsequent studies demonstrated that ROS was involved in MAVS-induced IL-8 production and CSFV induced ROS production through MAVS pathway. These results indicate that CSFV induces IL-8 production through MAVS pathway and production of ROS. The role of NS4A in the pathogenesis of CSFV is not well-understood. In this study, we further demonstrated that CSFV NS4A induced IL-8 production through enhancing MAVS pathway and promoted CSFV replication. In addition, we discovered that CSFV NS4A was localized in the cell nucleus and cytoplasm, including endoplasmic reticulum (ER) and mitochondria. Taken together, these results provide insights into the mechanisms of IL-8 regulation and NS4A functions during CSFV infection.

Highlights

Classical swine fever (CSF) is a highly contagious and fatal viral disease against pigs worldwide, which has led to huge economic losses in the swine industry (Dreier et al, 2007; Luo et al, 2014)
We found increased secretion of IL-8 at 24, 36, and 48 hpi compared to the mock-infected controls (Figure 1D), implying the increase of IL-8 expression might be correlated with Classical swine fever virus (CSFV) growth
To detect whether the upregulation of IL-8 was dependent on viral replication, swine umbilical vein endothelial cells (SUVECs) were infected with UV-inactivated CSFV or transfected with poly(I:C), a synthetic analog of double-stranded RNA

Summary

Introduction

Classical swine fever (CSF) is a highly contagious and fatal viral disease against pigs worldwide, which has led to huge economic losses in the swine industry (Dreier et al, 2007; Luo et al, 2014). Classical swine fever virus (CSFV), the causative agent of CSF, is an enveloped RNA virus with a single-stranded positive-sense RNA genome of ∼12.3 kb with one large open reading frame (ORF) flanked by 5′ and 3′ untranslated regions (UTRs). CSFV is a member of the Pestivirus genus within the Flaviviridae family. CSFV NS4A is an 8 kDa protein, consisting of 64 amino acids, and serves as an essential cofactor for the NS3 protease (Tautz et al, 1997, 2000). Cleaved NS4A is essential for the infectious CSFV particles formation together with NS2-3. CSFV NS4A interacts with NS3 protein and the downstream nonstructural proteins of the replication complex at the endoplasmic reticulum (ER) membrane where negative-sense RNA templates and progeny viral genomes are produced (Moulin et al, 2007). CSFV NS4A is a poorly characterized protein and its roles in the pathogenesis of CSFV are not well-understood

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Results

Conclusion