Highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) induces IL-6 production through TAK-1/JNK/AP-1 and TAK-1/NF-κB signaling pathways

doi:10.1016/j.vetmic.2021.109061

Veterinary Microbiology

Volume 256, May 2021, 109061

https://doi.org/10.1016/j.vetmic.2021.109061 Get rights and content

Highlights

•
HP-PRRSV can up-regulate the IL-6 expression in vivo and in vitro.
•
HP-PRRSV activates TAK-1/JNK/AP-1 and TAK-1/ NF-κB signaling pathways to promote the IL-6 production.
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AP-1 and NF-κB play a crucial role in the activation of porcine IL-6 promoter by HP-PRRSV.

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) mainly infects monocyte/macrophage lineage and regulates the production of cytokines to influence host immune responses. Interleukin-6 (IL-6) is originally identified as a B-cell stimulatory factor and has important functions in regulating immune response, hemopoiesis, and inflammation. In this study, we verified that highly pathogenic PRRSV (HP-PRRSV) infection up-regulated IL-6 production in vivo and in vitro. Subsequently, we demonstrated that HP-PRRSV infection activated JNK and NF-κB signaling pathways to enhance IL-6 expression. We further showed that TAK-1 was important in the activation of JNK and NF-κB pathways following HP-PRRSV infection. Moreover, AP-1 and NF-κB binding motifs were found in the cloned porcine IL-6 (pIL-6) promoter, and deletion of these motifs abrogated the activation of pIL-6 promoter by HP-PRRSV, suggesting that IL-6 expression is dependent on AP-1 and NF-κB activation. These findings imply that IL-6 induced by HP-PRRSV infection is dependent on the activation of TAK-1/JNK/AP-1 and TAK-1/NF-κB signaling pathways.

Introduction

Porcine reproductive and respiratory syndrome virus (PRRSV) is the etiological agent of a global epidemic called porcine reproductive and respiratory syndrome (PRRS) (Lunney et al., 2016). PRRSV is highly restricted to porcine cells of the monocyte/macrophage lineage, and preferentially infects porcine alveolar macrophages (PAMs) (Shi et al., 2015). PRRSV is an enveloped, single-stranded RNA virus belonging to the genus Arterivirus, family Arteriviridae, order Nidovirales. The genome of PRRSV is about 15.4 kb and contains at least 11 open reading frames (ORFs; ORF1a, ORF1b, ORF2a, ORF2b, ORFs 3–7, ORF5a, and ORF2 (TF)), encoding 8 structural proteins and at least 16 non-structural proteins (nsps). The majority of the genome (∼70 %) encodes nsps involved in virus replication (ORF1a and ORF1ab), whereas ORFs 2–7 encode structural proteins (GP2-GP5, E, GP5a, M, and N) (Lunney et al., 2016). In 2006, a highly pathogenic PRRSV (HP-PRRSV) strain was isolated in China, which can cause prolonged high fever and high mortality (Li et al., 2007). Since then, HP-PRRSV has been recognized as one of the dominating PRRSV strain in Asia (An et al., 2011). In recent years, NADC30-like strains have widely spread in China and become locally dominant strains in some provinces, although they are less pathogenic than HP-RRRSV (Yu et al., 2020).

In 1986, the complementary DNA encoding B-cell stimulator-2, now called IL-6, was successfully cloned (Kishimoto, 2010). Human IL-6 consists of 184 amino acids and is produced by various types of cells, including most stromal cells and immune cells. IL-6 remains relatively low in healthy individuals, but is rapidly synthesized when homeostasis is disrupted by external infections or tissue damages. While IL-6 expression is activated primarily by IL-1β and tumor-necrosis factor (TNF), other pathways such as Toll-like receptors, stress responses, adipokines, prostaglandins, and viral infections can also promote IL-6 synthesis (Zhang et al., 2020). The soluble mediator exerts its biological activity through two molecules: IL-6R (IL-6 receptor) and gp130, as well as MAPK and JAK-STAT signaling pathways (Garbers and Rose-John, 2018). Studies have shown that IL-6, a multi-functional cytokine, plays important roles in immune responses and host defense. For instance, it is important for antibody production by B cells, the differentiation of Th17 cells, acute-phase protein synthesis on hepatocytes, and the development of cancers (Heink et al., 2017; Johnson et al., 2018; Kim et al., 2019; Tanaka et al., 2014). In addition, IL-6 also plays an essential role in inflammation responses. Excessive expression of IL-6 contributes to inflammation and injuries through the stimulation of activating acute-phase responses, such as cytokine release syndrome, fever, and chronic immune disorders. Therefore, IL-6 is a critical cytokine mediating immunomodulatory.

Previous studies have shown that HP-PRRSV causes more severe lung injuries and damages in lymphoid organs such as thymus, spleen, lymph nodes, and tonsils (Han et al., 2017). PRRSV infection leads to the increased expressions of large amounts of proinflammatory cytokines and chemokines, including IL-1β, IL-12, IL-8, and TNF-α (Chen et al., 2014; Liu et al., 2017). However, it is not clear how HP-PRRSV infection affects the expression of IL-6.

In this study, we demonstrated that HP-PRRSV infection induced IL-6 expression. Subsequently, we showed that activation of TAK-1/JNK/AP-1 and TAK-1/NF-κB signaling pathways was required for HP-PRRSV to activate IL-6 production. These data might help us further understand the pathogenesis of HP-PRRSV in pigs.

Section snippets

Ethics statement

All animal trials in the study were performed in accordance with the guidelines of the Beijing Laboratory Animal Welfare and Ethics of the Beijing Administration Committee of Laboratory Animals and were approved by the Beijing Association for Science and Technology (approval ID SYXK [Beijing] 2007−0023). The project also complied with the China Agricultural University Institutional Animal Care and Use Committee guidelines (ID: SKLAB-B-2010−003) and was approved by the Animal Welfare Committee

HP-PRRSV infection up-regulates IL-6 expression

To verify whether HP-PRRSV could induce IL-6 expression, we infected porcine alveolar macrophages (PAMs) with HP-PRRSV isolate HV, and then analyzed the expression of IL-6 mRNA by real-time PCR at different time points post infection. The results showed that HP-PRRSV infection up-regulated IL-6 expression, but heat-inactivated HP-PRRSV did not (Fig. 1A). Consistently, IL-1β and TNF-α expression were also significantly up-regulated by HP-PRRSV infection (Fig. 1B). Next, we infected PAMs with

Discussion

In this study, we investigated the mechanism of HP-PRRSV regulating IL-6 expression. We found that HP-PRRSV could up-regulate IL-6 expression in PAMs. Subsequently, we showed that TAK-1, JNK, AP-1, and NF-κB signaling pathways were crucial for IL-6 induction by HP-PRRSV.

IL-6 is a multifunctional cytokine that regulates the immune response, inflammation, and a variety of physiological activity (Unver and McAllister, 2018). For example, IL-6 promotes the differentiation of naïve CD4⁺ T cells, CD8⁺

Declaration of Competing Interest

The authors declare no conflict of interest.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (Grant No. 31572516) and the National Key Research and Development Program of China (Grant No. 2017YFD0500601-1).

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¹: These authors contributed equally to the manuscript.

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Highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) induces IL-6 production through TAK-1/JNK/AP-1 and TAK-1/NF-κB signaling pathways

Highlights

Abstract

Introduction

Section snippets

Ethics statement

HP-PRRSV infection up-regulates IL-6 expression

Discussion

Declaration of Competing Interest

Acknowledgments

Vet. Microbiol.

Vet. Microbiol.

Vet. J.

Virology

J. Biol. Chem.

Cell Metab.

Heliyon

FEBS Lett.

Cytokine Growth F R

iScience

Virology

Blood

Biomed. Pharmacother.

Int. J. Antimicrob. Agents

Highly pathogenic porcine reproductive and respiratory syndrome virus, Asia

Emerg Infect Dis

HIV glycoprotein Gp120 impairs fast axonal transport by activating Tak1 signaling pathways

ASN Neuro

Natural and semisynthetic diterpenoids with antiviral and immunomodulatory activities block the ERK signaling pathway

Med. Microbiol. Immunol.