Histone H2A Nuclear/Cytoplasmic Trafficking Is Essential for Negative Regulation of Antiviral Immune Response and Lysosomal Degradation of TBK1 and IRF3

Xiao Man Wu,Yong Hong Bi,Hong Fang,Jie Zhang,Ming Xian Chang

doi:10.3389/fimmu.2021.771277

Abstract

Histone H2A is a nuclear molecule tightly associated in the form of the nucleosome. Our previous studies have demonstrated the antibacterial property of piscine H2A variants against gram-negative bacteria Edwardsiella piscicida and Gram-positive bacteria Streptococcus agalactiae. In this study, we show the function and mechanism of piscine H2A in the negative regulation of RLR signaling pathway and host innate immune response against spring viremia of carp virus (SVCV) infection. SVCV infection significantly inhibits the expression of histone H2A during an early stage of infection, but induces the expression of histone H2A during the late stage of infection such as at 48 and 72 hpi. Under normal physiological conditions, histone H2A is nuclear-localized. However, SVCV infection promotes the migration of histone H2A from the nucleus to the cytoplasm. The in vivo studies revealed that histone H2A overexpression led to the increased expression of SVCV gene and decreased survival rate. The overexpression of histone H2A also significantly impaired the expression levels of those genes involved in RLR antiviral signaling pathway. Furthermore, histone H2A targeted TBK1 and IRF3 to promote their protein degradation via the lysosomal pathway and impair the formation of TBK1-IRF3 functional complex. Importantly, histone H2A completely abolished TBK1-mediated antiviral activity and enormously impaired the protein expression of IRF3, especially nuclear IRF3. Further analysis demonstrated that the inhibition of histone H2A nuclear/cytoplasmic trafficking could relieve the protein degradation of TBK1 and IRF3, and blocked the negative regulation of histone H2A on the SVCV infection. Collectively, our results suggest that histone H2A nuclear/cytoplasmic trafficking is essential for negative regulation of RLR signaling pathway and antiviral immune response in response to SVCV infection.

Highlights

Pathogen-associated molecular patterns (PAMPs) are recognized by evolutionarily conserved host sensors known as pattern recognition receptors (PRRs), which include peptidoglycan recognition proteins (PGRPs), Toll-like receptors (TLRs), RIGI-like receptors (RLRs), NOD-like receptors (NLRs), C-type lectin receptors (CLRs) and DNA receptors [1,2,3]
The expressions of Spring viremia of carp virus (SVCV) genes including SVCV-N, SVCV-P and SVCV-G were significantly decreased by the histone H2A and LMB treatment compared with the control group transfected with empty plasmids and the group transfected with histone H2A but without LMB treatment (Figures 7F–H). These results suggest that the cytoplasmic localization of histone H2A is required for the protein degradations of TBK1 and IRF3 and the negative regulation of histone H2A on the SVCV infection
Double-stranded DNA stimulation induced the aggregation of histone H2B and the interaction between histone H2B and MAVS in the cytoplasm, which triggered antiviral innate immune responses against DNA viruses [29]

Summary

Introduction

Pathogen-associated molecular patterns (PAMPs) are recognized by evolutionarily conserved host sensors known as pattern recognition receptors (PRRs), which include peptidoglycan recognition proteins (PGRPs), Toll-like receptors (TLRs), RIGI-like receptors (RLRs), NOD-like receptors (NLRs), C-type lectin receptors (CLRs) and DNA receptors [1,2,3]. It is well known that the activated RLR signaling by interacting with the adapter protein MAVS leads to initiation of a signaling cascade that includes activation of TBK1 and IKKε protein kinases, which phosphorylate and activate IRF3 and NF-kB transcription factors Following this activation, IRF3 and NF-kB translocate from the cytoplasm to the nucleus and induce transcription of IFNs and ISGs [5]. Histones are located mainly in the nucleus, and have been suggested as important DAMPs by binding to PRRs once they are released to the extracellular space or translocate to the cytoplasm following infection, sterile inflammation and various types of cell death [9,10,11,12]. Extracellular histones could bind to TLRs receptors and induce NALP3 inflammation activation [13]

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Results

Conclusion