The methyltransferase PRMT6 attenuates antiviral innate immunity by blocking TBK1-IRF3 signaling

Cyclophilin A promotes porcine deltacoronavirus replication by regulating autophagy via the Ras/AKT/NF-κB pathway

Porcine deltacoronavirus (PDCoV) is an important enteric coronavirus that has caused major worldwide economic losses in the pig industry. Previous studies have shown that cyclophilin A (CypA), a key player in aetiological agent infection, is involved in regulating viral infection. However, the role of CypA during PDCoV replication remains unknown. Therefore, in this study, the role of CypA in PDCoV replication was determined. The results demonstrated that PDCoV infection increased CypA expression in LLC-PK1 cells. CypA overexpression substantially promoted PDCoV replication. Proteomic analysis was subsequently used to assess changes in total protein expression levels after CypA overexpression. Gene Ontology (GO) functional analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were used to further determine the mechanisms by which CypA affects viral replication. Proteomic analysis revealed that CypA protein overexpression significantly upregulated 75 differentially expressed proteins and significantly downregulated 172 differentially expressed proteins. The differentially expressed proteins were involved mainly in autophagy and activation of the host innate immune pathway. Subsequent experimental results revealed that the CypA protein promoted viral replication by reducing the levels of natural immune cytokines and mitigated the inhibitory effect of chloroquine (CQ) on viral replication. Further investigation revealed that CypA could activate the Ras/AKT/NF-κB pathway, mediate autophagy signalling and promote PDCoV replication. In summary, the findings of this study may help elucidate the role of CypA in PDCoV replication.

Chicken PRMT3 facilitates IBDV replication

Protein arginine methyltransferases (PRMTs) in mammals play a role in various signaling pathways, such as virus infection, inflammasome responses, and cancer growth. While some PRMTs have been found to regulate interferon production in mammals, the mechanism in chickens remains to be fully understood. This study focused on investigating the function of chicken PRMTs. Our findings indicate that chicken PRMTs act as inhibitors of interferon production in response to dsRNA or MDA5 stimulation. Each PRMT is involved in different stages of interferon induction through the MDA5-MAVS-TBK1 pathway. Furthermore, we observed the colocalization of multiple PRMTs with the viral protein VP3 of infectious bursal disease virus (IBDV). Among the chicken PRMTs studied, PRMT3 was found to be widely expressed in various organs and its expression was upregulated during IBDV infection. Notably, PRMT3 supported IBDV replication, as demonstrated by ectopic expression and inhibition studies using SGC-707. Silencing of PRMT3 led to enhanced interferon production and inhibition of IBDV replication. This study provides novel insights into the role of chicken PRMTs, particularly PRMT3, in promoting IBDV replication by suppressing interferon signaling.

PRMT6 Epigenetically Drives Metabolic Switch from Fatty Acid Oxidation toward Glycolysis and Promotes Osteoclast Differentiation During Osteoporosis

Epigenetic regulation of metabolism profoundly influences cell fate commitment. During osteoclast differentiation, the activation of RANK signaling is accompanied by metabolic reprogramming, but the epigenetic mechanisms by which RANK signaling induces this reprogramming remain elusive. By transcriptional sequence and ATAC analysis, this study identifies that activation of RANK signaling upregulates PRMT6 by epigenetic modification, triggering a metabolic switching from fatty acids oxidation toward glycolysis. Conversely, Prmt6 deficiency reverses this shift, markedly reducing HIF-1α-mediated glycolysis and enhancing fatty acid oxidation. Consequently, PRMT6 deficiency or inhibitor impedes osteoclast differentiation and alleviates bone loss in ovariectomized (OVX) mice. At the molecular level, Prmt6 deficiency reduces asymmetric dimethylation of H3R2 at the promoters of genes including Ppard, Acox3, and Cpt1a, enhancing genomic accessibility for fatty acid oxidation. PRMT6 thus emerges as a metabolic checkpoint, mediating metabolic switch from fatty acid oxidation to glycolysis, thereby supporting osteoclastogenesis. Unveiling PRMT6's critical role in epigenetically orchestrating metabolic shifts in osteoclastogenesis offers a promising target for anti-resorptive therapy.

Protein arginine methyltransferase 6 mediates antiviral immunity in plants

Viral suppressor RNA silencing (VSR) is essential for successful infection. Nucleotide-binding and leucine-rich repeat (NLR)-based and autophagy-mediated immune responses have been reported to target VSR as counter-defense strategies. Here, we report a protein arginine methyltransferase 6 (PRMT6)-mediated defense mechanism targeting VSR. The knockout and overexpression of PRMT6 in tomato plants lead to enhanced and reduced disease symptoms, respectively, during tomato bush stunt virus (TBSV) infection. PRMT6 interacts with and inhibits the VSR function of TBSV P19 by methylating its key arginine residues R43 and R115, thereby reducing its dimerization and small RNA-binding activities. Analysis of the natural tomato population reveals that two major alleles associated with high and low levels of PRMT6 expression are significantly associated with high and low levels of viral resistance, respectively. Our study establishes PRMT6-mediated arginine methylation of VSR as a mechanism of plant immunity against viruses.

HSV-1 reactivation results in post-herpetic neuralgia by upregulating Prmt6 and inhibiting cGAS-STING

Chronic varicella zoster virus (VZV) infection induced neuroinflammatory condition is the critical pathology of post-herpetic neuralgia (PHN). The immune escape mechanism of VZV remains elusive. As to mice have no VZV infection receptor, herpes simplex virus type 1 (HSV-1) infection is a well established PHN mice model. Transcriptional expression analysis identified that the protein arginine methyltransferases 6 (Prmt6) was upregulated upon HSV-1 infection, which was further confirmed by immunofluorescence staining in spinal dorsal horn. Prmt6 deficiency decreased HSV-1-induced neuroinflammation and PHN by enhancing antiviral innate immunity and decreasing HSV-1 load in vivo and in vitro. Overexpression of Prmt6 in microglia dampened antiviral innate immunity and increased HSV-1 load. Mechanistically, Prmt6 methylated and inactivated STING, resulting in reduced phosphorylation of TANK binding kinase-1 (TBK1) and interferon regulatory factor 3 (IRF3), diminished production of type I interferon (IFN-I) and antiviral innate immunity. Furthermore, intrathecal or intraperitoneal administration of the Prmt6 inhibitor EPZ020411 decreased HSV-1-induced neuroinflammation and PHN by enhancing antiviral innate immunity and decreasing HSV-1 load. Our findings revealed that HSV-1 escapes antiviral innate immunity and results in PHN by upregulating Prmt6 expression and inhibiting the cGAS-STING pathway, providing novel insights and a potential therapeutic target for PHN.

PRMT6 deficiency or inhibition alleviates neuropathic pain by decreasing glycolysis and inflammation in microglia

Microglia induced chronic inflammation is the critical pathology of Neuropathic pain (NP). Metabolic reprogramming of macrophage has been intensively reported in various chronic inflammation diseases. However, the metabolic reprogramming of microglia in chronic pain remains to be elusive. Here, we reported that immuno-metabolic markers (HIF-1α, PKM2, GLUT1 and lactate) were related with increased expression of PRMT6 in the ipsilateral spinal cord dorsal horn of the chronic construction injury (CCI) mice. PRMT6 deficiency or prophylactic and therapeutic intrathecal administration of PRMT6 inhibitor (EPZ020411) ameliorated CCI-induced NP, inflammation and glycolysis in the ipsilateral spinal cord dorsal horn. PRMT6 knockout or knockdown inhibited LPS-induced inflammation, proliferation and glycolysis in microglia cells. While PRMT6 overexpression exacerbated LPS-induced inflammation, proliferation and glycolysis in BV2 cells. Recent research revealed that PRMT6 could interact with and methylate HIF-1α, which increased HIF-1α protein stability. In sum, increased expression of PRMT6 exacerbates NP progress by increasing glycolysis and neuroinflammation through interacting with and stabilizing HIF-1α in a methyltransferase manner, which outlines novel pathological mechanism and drug target for NP.

Protein arginine methyltransferase 1, a major regulator of biological processes

Protein arginine methyltransferase 1 (PRMT1) is a major type I arginine methyltransferase that catalyzes the formation of monomethyl and asymmetric dimethylarginine in protein substrates. It was first identified to asymmetrically methylate histone H4 at the third arginine residue forming the H4R3me2a active histone mark. However, several protein substrates are now identified as being methylated by PRMT1. As a result of its association with diverse classes of substrates, PRMT1 regulates several biological processes like chromatin dynamics, transcription, RNA processing, and signal transduction. The review provides an overview of PRMT1 structure, biochemical features, specificity, regulation, and role in cellular functions. We discuss the genomic distribution of PRMT1 and its association with tRNA genes. Further, we explore the different substrates of PRMT1 involved in splicing. In the end, we discuss the proteins that interact with PRMT1 and their downstream effects in diseased states.

CRISPR-Cas9-mediated chicken prmt5 gene knockout and its critical role in interferon regulation

Protein arginine methyltransferase 5 (PRMT5), a type II arginine methyltransferase, controls arginine dimethylation of a variety of substrates. While many papers have reported the function of mammalian PRMT5, it remains unclear how PRMT5 functions in chicken cells. In this study, we found that chicken (ch) PRMT5 is widely expressed in a variety of chicken tissues and is distributed in both the cytoplasm and the nucleus. Ectopic expression of chPRMT5 significantly suppresses chIFN-β activation induced by chMDA5. In addition, a prmt5 gene-deficient DF-1 cell line was constructed using CRISPR/Cas9. In comparison with the wild-type cells, the prmt5-/- DF-1 cells displays normal morphology and maintain proliferative capacity. Luciferase reporter assay and overexpression showed that prmt5-/- DF-1 cells had increased IFN-β production. With identified chicken PRMT5 and CRISPR/Cas9 knockout performed in DF-1 cells, we uncovered a functional link of chPRMT5 in suppression of IFN-β production and interferon-stimulated gene expression.

Protein arginine methyltransferases (PRMTs): Orchestrators of cancer pathogenesis, immunotherapy dynamics, and drug resistance

Protein Arginine Methyltransferases (PRMTs) are a family of enzymes regulating protein arginine methylation, which is a post-translational modification crucial for various cellular processes. Recent studies have highlighted the mechanistic role of PRMTs in cancer pathogenesis, immunotherapy, and drug resistance. PRMTs are involved in diverse oncogenic processes, including cell proliferation, apoptosis, and metastasis. They exert their effects by methylation of histones, transcription factors, and other regulatory proteins, resulting in altered gene expression patterns. PRMT-mediated histone methylation can lead to aberrant chromatin remodeling and epigenetic changes that drive oncogenesis. Additionally, PRMTs can directly interact with key signaling pathways involved in cancer progression, such as the PI3K/Akt and MAPK pathways, thereby modulating cell survival and proliferation. In the context of cancer immunotherapy, PRMTs have emerged as critical regulators of immune responses. They modulate immune checkpoint molecules, including programmed cell death protein 1 (PD-1), through arginine methylation. Drug resistance is a significant challenge in cancer treatment, and PRMTs have been implicated in this phenomenon. PRMTs can contribute to drug resistance through multiple mechanisms, including the epigenetic regulation of drug efflux pumps, altered DNA damage repair, and modulation of cell survival pathways. In conclusion, PRMTs play critical roles in cancer pathogenesis, immunotherapy, and drug resistance. In this overview, we have endeavored to illuminate the mechanistic intricacies of PRMT-mediated processes. Shedding light on these aspects will offer valuable insights into the fundamental biology of cancer and establish PRMTs as promising therapeutic targets.

The role of protein arginine N-methyltransferases in inflammation

Protein arginine methyltransferases (PRMTs) promote the methylation of numerous proteins at their arginine residues. An increasing number of publications have suggested that dysregulation of PRMTs participates in various human diseases, such as cardiovascular diseases, cancer, diabetes and neurodegenerative disorders. Inflammation is one normal response to infection or injury by immune system, which can keep body homeostasis. Emerging data reveal that inflammation is associated with the development of numerous diseases. Moreover, accumulated evidence proves that PRMTs have been characterized to regulate inflammation in various diseases. In this review article, we delineate the function and molecular mechanism of PRMTs in regulation of inflammation in current literature. Moreover, we discuss that targeting PRMTs by its inhibitors and compounds could have therapeutic potential.

The Role of Protein Methyltransferases in Immunity

The immune system protects our body from bacteria, viruses, and toxins and removes malignant cells. Activation of immune cells requires the onset of a network of important signaling proteins. Methylation of these proteins affects their structure and biological function. Under stimulation, T cells, B cells, and other immune cells undergo activation, development, proliferation, differentiation, and manufacture of cytokines and antibodies. Methyltransferases alter the above processes and lead to diverse outcomes depending on the degree and type of methylation. In the previous two decades, methyltransferases have been reported to mediate a great variety of immune stages. Elucidating the roles of methylation in immunity not only contributes to understanding the immune mechanism but is helpful in the development of new immunotherapeutic strategies. Hence, we review herein the studies on methylation in immunity, aiming to provide ideas for new approaches.

PRMT6 Promotes the Immune Evasion of Gastric Cancer by Upregulating ANXA1

Gastric cancer is a most malignancy in digestive tract worldwide. This study aimed to investigate the roles of protein arginine methyltransferase 6 (PRMT6) in gastric cancer. Immunohistochemistry was performed to detect PRMT6 expression in gastric tumors. Real-time transcriptase-quantitative polymerase chain reaction (RT-qPCR) was used to detected mRNA levels. Protein expression was determined using western blot. Gastric cancer cells were co-cultured with CD8+ T cells. Colony formation assay was performed to detect cell proliferation. Flow cytometry was performed to determine CD8+ T cell function and tumor cell apoptosis. PRMT6 was overexpressed in gastric tumors. High level of PRMT6 predicted poor outcomes of gastric cancer patients and inhibition of CD8+ T cell infiltration. PRMT6 promoted proliferation of CD8+ T cells and enhanced its tumor killing ability. Moreover, PRMT6 upregulated annexin A1 (ANXA1) and promoted ANXA1 protein stability. ANXA1 overexpression suppressed the proliferation of CD8+ T cells and promoted tumor cell survival. PRMT6 functions as an oncogene in gastric cancer. PRMT6-mediated protein stability inhibits the infiltration of CD8+ T cells, resulting in immune evasion of gastric cancer. The PRMT6-ANXA1 may be a promising strategy for gastric cancer.

The emerging roles of protein arginine methyltransferases in antiviral innate immune signaling pathways

The Protein Arginine Methyltransferases (PRMTs) family is involved in various biological processes, including gene transcription, pre-mRNA splicing, mRNA translation, and protein stability. Recently, mounting evidence has shown that PRMTs also play critical roles in regulating the host antiviral immune response, either in an enzymatic activity dependent or independent manner. This review aims to provide an overview of the recent findings regarding the function and regulatory mechanisms of PRMTs in the antiviral response. These findings have the potential to aid in the discovery and design of novel therapeutic strategies for viral infections.

Protein arginine methylation in viral infection and antiviral immunity

Protein arginine methyltransferase (PRMT)-mediated arginine methylation is an important post-transcriptional modification that regulates various cellular processes including epigenetic gene regulation, genome stability maintenance, RNA metabolism, and stress-responsive signal transduction. The varying substrates and biological functions of arginine methylation in cancer and neurological diseases have been extensively discussed, providing a rationale for targeting PRMTs in clinical applications. An increasing number of studies have demonstrated an interplay between arginine methylation and viral infections. PRMTs have been found to methylate and regulate several host cell proteins and different functional types of viral proteins, such as viral capsids, mRNA exporters, transcription factors, and latency regulators. This modulation affects their activity, subcellular localization, protein-nucleic acid and protein-protein interactions, ultimately impacting their roles in various virus-associated processes. In this review, we discuss the classification, structure, and regulation of PRMTs and their pleiotropic biological functions through the methylation of histones and non-histones. Additionally, we summarize the broad spectrum of PRMT substrates and explore their intricate effects on various viral infection processes and antiviral innate immunity. Thus, comprehending the regulation of arginine methylation provides a critical foundation for understanding the pathogenesis of viral diseases and uncovering opportunities for antiviral therapy.

Asymmetric arginine dimethylation of cytosolic RNA and DNA sensors by PRMT3 attenuates antiviral innate immunity

The cytosolic RNA and DNA sensors initiate type I interferon signaling when binding to RNA or DNA. To effectively protect the host against virus infection and concomitantly avoid excessive interferonopathy at resting states, these sensors must be tightly regulated. However, the key molecular mechanisms regulating these sensors' activation remain elusive. Here, we identify PRMT3, a type I protein arginine methyltransferase, as a negative regulator of cytosolic RNA and DNA sensors. PRMT3 interacts with RIG-I, MDA5, and cGAS and catalyzes asymmetric dimethylation of R730 on RIG-I, R822 on MDA5, and R111 on cGAS. These modifications reduce RNA-binding ability of RIG-I and MDA5 as well as DNA-binding ability and oligomerization of cGAS, leading to the inhibition of downstream type I interferon production. Furthermore, mice with loss of one copy of Prmt3 or in vivo treatment of the PRMT3 inhibitor, SGC707, are more resistant to RNA and DNA virus infection. Our findings reveal an essential role of PRMT3 in the regulation of antiviral innate immunity and give insights into the molecular regulation of cytosolic RNA and DNA sensors' activation.

PRMT1 mediated methylation of cGAS suppresses anti-tumor immunity

Activation of the cGAS/STING innate immunity pathway is essential and effective for anti-tumor immunotherapy. However, it remains largely elusive how tumor-intrinsic cGAS signaling is suppressed to facilitate tumorigenesis by escaping immune surveillance. Here, we report that the protein arginine methyltransferase, PRMT1, methylates cGAS at the conserved Arg133 residue, which prevents cGAS dimerization and suppresses the cGAS/STING signaling in cancer cells. Notably, genetic or pharmaceutical ablation of PRMT1 leads to activation of cGAS/STING-dependent DNA sensing signaling, and robustly elevates the transcription of type I and II interferon response genes. As such, PRMT1 inhibition elevates tumor-infiltrating lymphocytes in a cGAS-dependent manner, and promotes tumoral PD-L1 expression. Thus, combination therapy of PRMT1 inhibitor with anti-PD-1 antibody augments the anti-tumor therapeutic efficacy in vivo. Our study therefore defines the PRMT1/cGAS/PD-L1 regulatory axis as a critical factor in determining immune surveillance efficacy, which serves as a promising therapeutic target for boosting tumor immunity.

ER-localized JmjC domain-containing protein JMJD8 targets STING to promote immune evasion and tumor growth in breast cancer

The STING-mediated type I interferon (IFN) signaling pathway has been shown to play critical roles in antitumor immunity. Here, we demonstrate that an endoplasmic reticulum (ER)-localized JmjC domain-containing protein, JMJD8, inhibits STING-induced type I IFN responses to promote immune evasion and breast tumorigenesis. Mechanistically, JMJD8 competes with TBK1 for binding with STING, blocking STING-TBK1 complex formation and restricting type I IFN and IFN-stimulated gene (ISG) expression as well as immune cell infiltration. JMJD8 knockdown improves the efficacy of chemotherapy and immune checkpoint therapy in treating both human and mouse breast cancer cell-derived implanted tumors. The clinical relevance is highlighted in that JMJD8 is highly expressed in human breast tumor samples, and its expression is inversely correlated with that of type I IFN and ISGs as well as immune cell infiltration. Overall, our study found that JMJD8 regulates type I IFN responses, and targeting JMJD8 triggers antitumor immunity.

Chicken PRMT1 promotes infectious bursal disease virus replication via suppressing IFN-β production

The protein arginine methyltransferase (PRMT) family, such as PRMT1, regulates the arginine methylation of various substrates. Many studies have examined the role of PRMT1 in mammals, however, it is still unknown how PRMT1 works in chickens. To investigate the effect of chicken PRMT1 (chPRMT1) on regulating IFN-β production and IBDV replication, chPRMT1 knock out DF-1 cells were constructed in this study. First, we found that chPRMT1 was widely expressed in a variety of chicken tissues and that it was distributed in the cytoplasm and nucleus of DF-1 cells. Additionally, IFN-β activation was inhibited by chPRMT1 at the step of chMAVS. In addition, chPRMT1 knock out DF-1 cells were constructed using CRISPR-Cas9 technique. The morphology and viability of chPRMT1 knock out DF-1 cells were similar with the wild-type cells. In addition, the IFN-β as well as interferon stimulate genes activation induced by chMAVS in PRMT1 knock out DF-1 cells were significantly higher than that in WT cells. Furthermore, ectopic expression of chPRMT1 significantly supports IBDV replication. We also found that the ability of IBDV replication in PRMT1 knock out DF-1 cells was remarkably lower than that of in WT cells, suggesting that PRMT1 negatively regulate IBDV replication via suppressing IFN-β production. In conclusion, the PRMT1 knock out DF-1 cells were constructed, which was further used to demonstrate an inhibitory role of chPRMT1 in IFN-β production, and a contributor of chPRMT1 in IBDV replication.

p120-catenin promotes innate antiviral immunity through stabilizing TBK1-IRF3 complex

TBK1-IRF3 complex plays vital roles in antiviral immune responses, its regulatory mechanisms are currently incompletely understood. p120-catenin (p120), an armadillo-repeat protein, mainly regulates the stability of classical cadherins and the development of epithelial-to-mesenchymal transitions (EMTs). Here we report that p120 is a positive regulator of type I IFN production. Ectopic expression of p120 enhanced Vesicular stomatitis virus and Sendai-virus-induced type I IFN production, whereas knockdown of p120 expression suppressed type I IFN production. Mechanistically, p120 promoted phosphorylation of IRF3 via stabilizing the TBK1-IRF3 complex. Consistently, p120 knock down mice are more susceptible to VSV infection as indicated by higher tissue viral titers, less IFN-I production and greater infiltration of immune cells. This study reveals p120 as an important positive regulator in innate immunity and identifies that p120 facilitates host antiviral response through stabilizing TBK1-IRF3 complex.

Avian Metapneumovirus Subgroup C Phosphoprotein Suppresses Type I Interferon Production by Blocking Interferon Regulatory Factor 3 Nuclear Translocation

Avian metapneumovirus subgroup C (aMPV/C) is an important pathogen that causes upper respiratory symptoms and egg production decline in turkeys and chickens. aMPV/C infection leads to inhibition of the host antiviral immune response. However, our understanding of the molecular mechanisms underlying host immune response antagonized by aMPV/C infection is limited. In this study, we demonstrated that the aMPV/C phosphoprotein (P) inhibits the IFN antiviral signaling pathway triggered by melanoma differentiation gene 5 (MDA5) and reduces interferon β (IFN-β) production and IFN-stimulated genes (ISGs) by targeting IFN regulatory factor 7 (IRF7) but not nuclear factor κB (NF-κB) in DF-1 cells. Moreover, we found that aMPV/C P protein only blocks the nuclear translocation of IRF3 by interacting with IRF3 in HEK-293T cells, instead of affecting IRF3 phosphorylation and inducing IRF3 degradation, which suppresses IRF3 signaling activation and results in a decrease in IFN-β production. Collectively, these results reveal a novel mechanism by which aMPV/C infection disrupts IFN-β production in the host. IMPORTANCE The innate immune response is the first defense line of host cells and organisms against viral infections. When RNA viruses infect cells, viral RNA induces activation of retinoic acid-induced gene I and melanoma differentiation gene 5, which initiates downstream molecules and finally produces type I interferon (IFN-I) to regulate antiviral immune responses. The mechanism for avian metapneumovirus (aMPV) modulating IFN-I production to benefit its replication remains unknown. Here, we demonstrate that phosphoprotein of aMPV subgroup C (aMPV/C) selectively inhibits the nuclear translocation of interferon regulatory 3 (IRF3), instead of affecting the expression and phosphorylation of IRF3, which finally downregulates IFN-I production. This study showed a novel mechanism for aMPV/C infection antagonizing the host IFN response.

TBK1 and IRF3 are potential therapeutic targets in Enterovirus A71-associated diseases

BACKGROUND

Enterovirus A71 (EV-A71) is an important causative agent of hand-foot-and-mouth disease (HFMD) associated with enormous healthcare and socioeconomic burden. Although a range of studies about EV-A71 pathogenesis have been well described, the underlying molecular mechanism in terms of innate immune response is still not fully understood, especially the roles of TANK-binding kinase 1 (TBK1) and interferon-regulatory factor 3 (IRF3).

METHODOLOGY/PRINCIPAL FINDINGS

Here, we applied TBK1 inhibitor and IRF3 agonist, for the first time, to evaluate the antiviral activities of TBK1 and IRF3 in vivo. We found that, through regulating EV-A71-induced type I interferon (IFN) response, IRF3 agonist effectively alleviated EV-A71-induced illness, while TBK1 inhibitor aggravated disease progression. In addition, EV-A71 replication was suppressed in EVA-71-infected mice administrated with IRF3 agonist. On the other hand, more severe pathological alterations of neuronal degeneration, muscle fiber breaks, fractured or fused alveolar walls, and diffuse congestion occurred in EVA-71-infected mice treated with TBK1 inhibitor administration. Furthermore, we determined the concentrations of interleukin (IL)-6, tumor necrosis factor-alpha (TNF-α), IL-1β, monocyte chemotactic protein-1 (MCP-1), and IL-10 in both lungs and brains of mice and found that TBK1 inhibitor promoted EV-A71-induced inflammatory response, while IRF3 agonist alleviated it, which was consistent with clinical manifestations and pathological alterations.

CONCLUSIONS

Collectively, our findings suggest that TBK1 and IRF3 are potential therapeutic targets in EV-A71-induced illness.

eIF4A3 Promotes RNA Viruses’ Replication by Inhibiting Innate Immune Responses

Production of type I IFN is pivotal for the cellular antiviral immunity. Virus infection leads to the activation of transcription factor IRF3 and subsequent production of type I IFN to eliminate viral infection.

Long noncoding RNA IRF1-AS is associated with peste des petits ruminants infection

Peste des petits ruminants (PPR) is an acute and highly contagious disease and has long been a significant threat to small ruminant productivity worldwide. However, the molecular mechanism underlying host-PPRV interactions remains unclear and the long noncoding RNAs (lncRNAs) regulation of PPR virus (PPRV) infection has rarely been reported so far. Here, we first demonstrated that PPRV infection can induce an obvious innate immune response in caprine endometrial epithelial cells (EECs) at 48 h post-infection (hpi) with an MOI of 3. Subsequently, we determined that PPRV infection is associated with 191 significantly differentially expressed (SDE) lncRNAs, namely, 137 upregulated and 54 downregulated lncRNAs, in caprine EECs compared with mock control cells at 48 hpi by using deep sequencing technology. Importantly, bioinformatics preliminarily analyses revealed that these DE lncRNAs were closely related to the immune response. Furthermore, we identified a system of lncRNAs related to the immune response and focused on the role of lncRNA 10636385 (IRF1-AS) in regulating the innate immune response. Interestingly, we found that IRF1-AS was a potent positive regulator of IFN-β and ISG production, which can significantly inhibit PPRV replication in host cells. In addition, our data revealed that IRF1-AS was positively correlated with its potential target gene, IRF1, which enhanced the activation of IRF3 and the expression of ISGs and interacted with IRF3. This study suggests that IRF1-AS could be a new host factor target for developing antiviral therapies against PPRV infection.

The protein arginine methyltransferase PRMT9 attenuates MAVS activation through arginine methylation

The signaling adaptor MAVS forms prion-like aggregates to activate the innate antiviral immune response after viral infection. However, spontaneous aggregation of MAVS can lead to autoimmune diseases. The molecular mechanism that prevents MAVS from spontaneous aggregation in resting cells has been enigmatic. Here we report that protein arginine methyltransferase 9 targets MAVS directly and catalyzes the arginine methylation of MAVS at the Arg41 and Arg43. In the resting state, this modification inhibits MAVS aggregation and autoactivation of MAVS. Upon virus infection, PRMT9 dissociates from the mitochondria, leading to the aggregation and activation of MAVS. Our study implicates a form of post-translational modification on MAVS, which can keep MAVS inactive in physiological conditions to maintain innate immune homeostasis.

The Influence of Arginine Methylation in Immunity and Inflammation

Exploration in the field of epigenetics has revealed that protein arginine methyltransferases (PRMTs) contribute to disease, and this has given way to the development of specific small molecule compounds that inhibit arginine methylation. Protein arginine methylation is known to regulate fundamental cellular processes, such as transcription; pre-mRNA splicing and other RNA processing mechanisms; signal transduction, including the anti-viral response; and cellular metabolism. PRMTs are also implicated in the regulation of physiological processes, including embryonic development, myogenesis, and the immune system. Finally, the dysregulation of PRMTs is apparent in cancer, neurodegeneration, muscular disorders, and during inflammation. Herein, we review the functions of PRMTs in immunity and inflammation. We also discuss recent progress with PRMTs regarding the modulation of gene expression related to T and B lymphocyte differentiation, germinal center dynamics, and anti-viral signaling responses, as well as the clinical relevance of using PRMT inhibitors alone or in combination with other drugs to treat cancer, immune, and inflammatory-related diseases.

Protein Arginine Methylation: An Emerging Modification in Cancer Immunity and Immunotherapy

In recent years, protein arginine methyltransferases (PRMTs) have emerged as new members of a gene expression regulator family in eukaryotes, and are associated with cancer pathogenesis and progression. Cancer immunotherapy has significantly improved cancer treatment in terms of overall survival and quality of life. Protein arginine methylation is an epigenetic modification function not only in transcription, RNA processing, and signal transduction cascades, but also in many cancer-immunity cycle processes. Arginine methylation is involved in the activation of anti-cancer immunity and the regulation of immunotherapy efficacy. In this review, we summarize the most up-to-date information on regulatory molecular mechanisms and different underlying arginine methylation signaling pathways in innate and adaptive immune responses during cancer. We also outline the potential of PRMT-inhibitors as effective combinatorial treatments with immunotherapy.

Grass carp PRMT6 negatively regulates innate immunity by inhibiting the TBK1/IRF3 binding and cutting down IRF3 phosphorylation level

Subcellular localization analysis implicated that CiPRMT6 was mainly located in the nucleus, with a small part of them located in the cytoplasm. PRMT6, namely protein arginine methyltransferase 6, was first identified and demonstrated to catalyze the methylation of arginine residue on the chromatin histones in mammals. Mammalian PRMT6 usually acts as an arginine methyltransferase in the nucleus, but induces antiviral innate immune response in the cytoplasm. Nowadays, there have been few reports about PRMT6 in teleost. In this study, we investigated the potential molecular mechanisms underlying the interaction of PRMT6 expression and IFN1 response in grass carp. We first cloned and identified a grass carp PRMT6 (named CiPRMT6, MN781672.1), which is 1068bp in length encoding a deduced polypeptide of 355 amino acids. In CIK cell, CiPRMT6 expression was up-regulated upon stimulation with poly (I:C); while overexpression of PRMT6 suppressed the promoter activity of grass carp IFN1 and reduced the phosphorylation of IRF3; however, the amount of PRMT6 mutant (lack of methyltransferase domain) was increased in the cytoplasm. Our results also showed that grass carp PRMT6 and IRF3 (but not TBK1) were co-located and bound to each other in the cytoplasm. The binding of CiPRMT6 to IRF3 impairs the interaction between TBK1 and IRF3, indicating that CiPRMT6 is a negative regulator for IFN1 expression through TBK1-IRF3 signaling pathway in grass carp. In conclusion, we identified that CiPRMT6 negatively regulated IFN1 expression by inhibiting the TBK1-IRF3 interaction as well as IRF3 phosphorylation.

Inhibiting Type I Arginine Methyltransferase Activity Promotes T Cell-Mediated Antitumor Immune Responses

Protein arginine methyltransferases (PRMT) are a widely expressed class of enzymes responsible for catalyzing arginine methylation on numerous protein substrates. Among them, type I PRMTs are responsible for generating asymmetric dimethylarginine. By controlling multiple basic cellular processes, such as DNA damage responses, transcriptional regulation, and mRNA splicing, type I PRMTs contribute to cancer initiation and progression. A type I PRMT inhibitor, GSK3368715, has been developed and has entered clinical trials for solid and hematologic malignancies. Although type I PRMTs have been reported to play roles in modulating immune cell function, the immunologic role of tumor-intrinsic pathways controlled by type I PRMTs remains uncharacterized. Here, our The Cancer Genome Atlas dataset analysis revealed that expression of type I PRMTs associated with poor clinical response and decreased immune infiltration in patients with melanoma. In cancer cell lines, inhibition of type I PRMTs induced an IFN gene signature, amplified responses to IFN and innate immune signaling, and decreased expression of the immunosuppressive cytokine VEGF. In immunocompetent mouse tumor models, including a model of T-cell exclusion that represents a common mechanism of anti-programmed cell death protein 1 (PD-1) resistance in humans, type I PRMT inhibition increased T-cell infiltration, produced durable responses dependent on CD8+ T cells, and enhanced efficacy of anti-PD-1 therapy. These data indicate that type I PRMT inhibition exhibits immunomodulatory properties and synergizes with immune checkpoint blockade (ICB) to induce durable antitumor responses in a T cell-dependent manner, suggesting that type I PRMT inhibition can potentiate an antitumor immunity in refractory settings.

PRMT7 ablation stimulates anti-tumor immunity and sensitizes melanoma to immune checkpoint blockade

Despite the success of immune checkpoint inhibitor (ICI) therapy for cancer, resistance and relapse are frequent. Combination therapies are expected to enhance response rates and overcome this resistance. Herein, we report that combining PRMT7 inhibition with ICI therapy induces a strong anti-tumor T cell immunity and restrains tumor growth in vivo by increasing immune cell infiltration. PRMT7-deficient B16.F10 melanoma exhibits increased expression of genes in the interferon pathway, antigen presentation, and chemokine signaling. PRMT7 deficiency or inhibition with SGC3027 in B16.F10 melanoma results in reduced DNMT expression, loss of DNA methylation in the regulatory regions of endogenous retroviral elements (ERVs) causing their increased expression. PRMT7-deficient cells increase RIG-I and MDA5 expression with a reduction in the H4R3me2s repressive histone mark at their gene promoters. Our findings identify PRMT7 as a regulatory checkpoint for RIG-I, MDA5, and their ERV-double-stranded RNA (dsRNA) ligands, facilitating immune escape and anti-tumor T cell immunity to restrain tumor growth.

Heat Shock-Binding Protein 21 Regulates the Innate Immune Response to Viral Infection

The innate immune system is the first-line host defense against microbial pathogen invasion. The physiological functions of molecular chaperones, involving cell differentiation, migration, proliferation and inflammation, have been intensively studied.

The Emerging Role of PRMT6 in Cancer

Protein arginine methyltransferase 6 (PRMT6) is a type I PRMT that is involved in epigenetic regulation of gene expression through methylating histone or non-histone proteins, and other processes such as alternative splicing, DNA repair, cell proliferation and senescence, and cell signaling. In addition, PRMT6 also plays different roles in various cancers via influencing cell growth, migration, invasion, apoptosis, and drug resistant, which make PRMT6 an anti-tumor therapeutic target for a variety of cancers. As a result, many PRMT6 inhibitors are being utilized to explore their efficacy as potential drugs for various cancers. In this review, we summarize the current knowledge on the function and structure of PRMT6. At the same time, we highlight the role of PRMT6 in different cancers, including the differentiation of its promotive or inhibitory effects and the underlying mechanisms. Apart from the above, current research progress and the potential mechanisms of PRMT6 behind them were also summarized.

Enterovirus 71 Antagonizes Antiviral Effects of Type III Interferon and Evades the Clearance of Intestinal Intraepithelial Lymphocytes

Enterovirus 71 (EV71) is the major pathogen causing severe neurological complications and hand, foot, and mouth disease. The intestinal mucosal immune system has a complete immune response and immune regulation mechanism, consisting of densely arranged monolayer intestinal epithelial cells (IECs) and intestinal intraepithelial lymphocytes (iIELs) distributed among the IECs, which constitute the first line of intestinal mucosa against infection of foreign pathogens. As an enterovirus, EV71 is transmitted by the intestinal tract; however, the mechanisms it uses to evade the immunosurveillance of the intestinal mucosal immune system are still incompletely clarified. The present study investigated how EV71 evades from recognizing and eliminating IECs, iIELs, and iNK cells. We found that EV71 infection induced a higher level of type III interferons (IFN-λ) than type I interferons (IFN-β) in IECs, and the addition of IFN-λ markedly restricted EV71 replication in IECs. These results indicate that IFN-λ plays a more important role in anti-EV71 intestinal infection. However, EV71 infection could markedly attenuate the antiviral responses of IFN-λ. Mechanistically, 2A protease (2Apro) and 3C protease (3Cpro) of EV71 inhibited the IFN-λ production and IFN-λ receptor expression and further decreased the response of IECs to IFN-λ. In addition, we found that EV71-infected IECs were less susceptible to the lysis of intestinal NK (iNK) cells and CD3⁺iIELs. We revealed that the viral 2Apro and 3Cpro could significantly reduce the expression of the ligands of natural killer group 2D (NKG2D) and promote the expression of PD-L1 on IECs, rendering them to evade the recognition and killing of iNK and CD3⁺iIELs. These results provide novel evasion mechanisms of EV71 from intestinal mucosal innate immunity and may give new insights into antiviral therapy.

ID2 inhibits innate antiviral immunity by blocking TBK1- and IKKε-induced activation of IRF3

[Figure: see text].

Zebrafish prmt2 Attenuates Antiviral Innate Immunity by Targeting traf6

TNFR-associated factor 6 (TRAF6) not only recruits TBK1/IKKε to MAVS upon virus infection but also catalyzes K63-linked polyubiquitination on substrate or itself, which is critical for NEMO-dependent and -independent TBK1/IKKε activation, leading to the production of type I IFNs. The regulation at the TRAF6 level could affect the activation of antiviral innate immunity. In this study, we demonstrate that zebrafish prmt2, a type I arginine methyltransferase, attenuates traf6-mediated antiviral response. Prmt2 binds to the C terminus of traf6 to catalyze arginine asymmetric dimethylation of traf6 at arginine 100, preventing its K63-linked autoubiquitination, which results in the suppression of traf6 activation. In addition, it seems that the N terminus of prmt2 competes with mavs for traf6 binding and prevents the recruitment of tbk1/ikkε to mavs. By zebrafish model, we show that loss of prmt2 promotes the survival ratio of zebrafish larvae after challenge with spring viremia of carp virus. Therefore, we reveal, to our knowledge, a novel function of prmt2 in the negative regulation of antiviral innate immunity by targeting traf6.

Cellular pathways influenced by protein arginine methylation: Implications for cancer

Arginine methylation is an influential post-translational modification occurring on histones, RNA binding proteins, and many other cellular proteins, affecting their function by altering their protein-protein and protein-nucleic acid interactions. Recently, a wealth of information has been gathered, implicating protein arginine methyltransferases (PRMTs), enzymes that deposit arginine methylation, in transcription, pre-mRNA splicing, DNA damage signaling, and immune signaling with major implications for cancer therapy, especially immunotherapy. This review summarizes this recent progress and the current state of PRMT inhibitors, some in clinical trials, as promising drug targets for cancer.

The protein arginine methyltransferase PRMT1 promotes TBK1 activation through asymmetric arginine methylation

TBK1 is an essential kinase for the innate immune response against viral infection. However, the key molecular mechanisms regulating the TBK1 activation remain elusive. Here, we identify PRMT1, a type I protein arginine methyltransferase, as an essential regulator of TBK1 activation. PRMT1 directly interacts with TBK1 and catalyzes asymmetric methylation of R54, R134, and R228 on TBK1. This modification enhances TBK1 oligomerization after viral infection, which subsequently promotes TBK1 phosphorylation and downstream type I interferon production. More important, myeloid-specific Prmt1 knockout mice are more susceptible to infection with DNA and RNA viruses than Prmt1^fl/fl mice. Our findings reveal insights into the molecular regulation of TBK1 activation and demonstrate the essential function of protein arginine methylation in innate antiviral immunity.

Structure, Activity and Function of the Protein Arginine Methyltransferase 6

Members of the protein arginine methyltransferase (PRMT) family methylate the arginine residue(s) of several proteins and regulate a broad spectrum of cellular functions. Protein arginine methyltransferase 6 (PRMT6) is a type I PRMT that asymmetrically dimethylates the arginine residues of numerous substrate proteins. PRMT6 introduces asymmetric dimethylation modification in the histone 3 at arginine 2 (H3R2me2a) and facilitates epigenetic regulation of global gene expression. In addition to histones, PRMT6 methylates a wide range of cellular proteins and regulates their functions. Here, we discuss (i) the biochemical aspects of enzyme kinetics, (ii) the structural features of PRMT6 and (iii) the diverse functional outcomes of PRMT6 mediated arginine methylation. Finally, we highlight how dysregulation of PRMT6 is implicated in various types of cancers and response to viral infections.

Arginine monomethylation by PRMT7 controls MAVS-mediated antiviral innate immunity

Accurate control of innate immune responses is required to eliminate invading pathogens and simultaneously avoid autoinflammation and autoimmune diseases. Here, we demonstrate that arginine monomethylation precisely regulates the mitochondrial antiviral-signaling protein (MAVS)-mediated antiviral response. Protein arginine methyltransferase 7 (PRMT7) forms aggregates to catalyze MAVS monomethylation at arginine residue 52 (R52), attenuating its binding to TRIM31 and RIG-I, which leads to the suppression of MAVS aggregation and subsequent activation. Upon virus infection, aggregated PRMT7 is disabled in a timely manner due to automethylation at arginine residue 32 (R32), and SMURF1 is recruited to PRMT7 by MAVS to induce proteasomal degradation of PRMT7, resulting in the relief of PRMT7 suppression of MAVS activation. Therefore, we not only reveal that arginine monomethylation by PRMT7 negatively regulates MAVS-mediated antiviral signaling in vitro and in vivo but also uncover a mechanism by which PRMT7 is tightly controlled to ensure the timely activation of antiviral defense.

Human TBK1 deficiency leads to autoinflammation driven by TNF-induced cell death

TANK binding kinase 1 (TBK1) regulates IFN-I, NF-κB, and TNF-induced RIPK1-dependent cell death (RCD). In mice, biallelic loss of TBK1 is embryonically lethal. We discovered four humans, ages 32, 26, 7, and 8 from three unrelated consanguineous families with homozygous loss-of-function mutations in TBK1. All four patients suffer from chronic and systemic autoinflammation, but not severe viral infections. We demonstrate that TBK1 loss results in hypomorphic but sufficient IFN-I induction via RIG-I/MDA5, while the system retains near intact IL-6 induction through NF-κB. Autoinflammation is driven by TNF-induced RCD as patient-derived fibroblasts experienced higher rates of necroptosis in vitro, and CC3 was elevated in peripheral blood ex vivo. Treatment with anti-TNF dampened the baseline circulating inflammatory profile and ameliorated the clinical condition in vivo. These findings highlight the plasticity of the IFN-I response and underscore a cardinal role for TBK1 in the regulation of RCD.

Demalonylation of DDX3 by Sirtuin 5 promotes antiviral innate immune responses

Rationale: Hosts defend against viral infection by sensing viral pathogen-associated molecular patterns and activating antiviral innate immunity through TBK1-IRF3 signaling. However, the underlying molecular mechanism remains unclear.

Methods: SiRNAs targeting Sirt1-7 were transfected into macrophages to screen the antiviral function. Sirt5 deficient mice or macrophages were subjected to viral infection to assess in vivo and in vitro function of Sirt5 by detecting cytokines, viral replicates and survival rate. Immunoprecipitation, WesternBlot and luciferase reporter assay were used to reveal molecular mechanism.

Results: In this study, we functionally screened seven Sirtuin family members, and found that Sirtuin5 (Sirt5) promotes antiviral signaling and responses. Sirt5 deficiency leads to attenuated antiviral innate immunity in vivo and in vitro upon viral infection by decreasing TBK1-IRF3 activation and type I IFN production. Sirt5 overexpression increased antiviral innate immunity. Mechanism investigation revealed that Sirt5 interacts with DDX3 and demalonylates DDX3, which is critical for TBK1-IRF3 activation. Mutation of the demalonylation lysine sites (K66, K130, and K162) of DDX3 increased ifnβ transcription. Furthermore, the acetylation on lysine 118 of DDX3 positively regulated ifnβ transcription, whereas Sirt5 could not deacetylate this site.

Conclusion: Sirt5 promotes anti- RNA and DNA virus innate immune responses by increasing TBK1 signaling through demalonylating DDX3, which identifies a novel regulatory pathway of antiviral innate immune response.

F-Box Protein FBXW17-Mediated Proteasomal Degradation of Protein Methyltransferase PRMT6 Exaggerates CSE-Induced Lung Epithelial Inflammation and Apoptosis

Chronic obstructive pulmonary disease (COPD) is a chronic debilitating lung disease, characterized by progressive airway inflammation and lung structural cell death. Cigarette smoke is considered the most common risk factor of COPD pathogenesis. Understanding the molecular mechanisms of persistent inflammation and epithelial apoptosis induced by cigarette smoke would be extremely beneficial for improving the treatment and prevention of COPD. A histone methyl modifier, protein arginine N-methyltransferase 6 (PRMT6), is reported to alleviate cigarette smoke extract (CSE)-induced emphysema through inhibiting inflammation and cell apoptosis. However, few studies have focused on the modulation of PRMT6 in regulating inflammation and cell apoptosis. In this study, we showed that protein expression of PRMT6 was aberrantly decreased in the lung tissue of COPD patients and CSE-treated epithelial cells. FBXW17, a member of the Skp1-Cullin-F-box (SCF) family of E3 ubiquitin ligases, selectively bound to PRMT6 in nuclei to modulate its elimination in the proteasome system. Proteasome inhibitor or silencing of FBXW17 abrogated CSE-induced PRMT6 protein degradation. Furthermore, negative alteration of FBXW17/PRMT6 signaling lessened the proapoptotic and proinflammatory effects of CSE in lung epithelial cells. Our study, therefore, provides a potential therapeutic target against the airway inflammation and cell death in CS-induced COPD.

Systematic investigation of PRMT6 substrate recognition reveals broad specificity with a preference for an RG motif or basic and bulky residues

Protein arginine methyltransferase 6 (PRMT6) catalyses the asymmetric dimethylation of arginines on numerous substrate proteins within the human cell. In particular, PRMT6 methylates histone H3 arginine 2 (H3R2) which affects both gene repression and activation. However, the substrate specificity of PRMT6 has not been comprehensively analysed. Here, we systematically characterise the substrate recognition motif of PRMT6, finding that it has broad specificity and recognises the RG motif. Working with a H3 tail peptide as a template, on which we made 204 amino acid substitutions, we use targeted mass spectrometry to measure their effect on PRMT6 in vitro activity. We first show that PRMT6 methylates R2 and R8 in the H3 peptide, although H3R8 is methylated with lower efficiency and is not an in vivo PRMT6 substrate. We then quantify the effect of 194 of these amino acid substitutions on methylation at both H3R2 and H3R8. In both cases, we find that PRMT6 tolerates essentially any amino acid substitution in the H3 peptide, but that positively charged and bulky residues are preferred near the target arginine. We show that PRMT6 also has preference for glycine, but only in the position immediately following the target arginine. This indicates that PRMT6 recognises the RG motif rather than the RGG motif. We further confirm this preference for the RG motif on another PRMT6 substrate, histone H4R3. This broad specificity and recognition of RG rather than RGG are distinctive among the PRMT family and has implications for the development of drugs to selectively target PRMT6. DATABASES: Panorama Public (https://panoramaweb.org/PRMT6motif.url); ProteomeXchange (PXD016711).

Arginine methyltransferase PRMT5 negatively regulates cGAS-mediated antiviral immune response

Cyclic GMP-AMP synthase (cGAS) functions as an essential DNA sensor, which senses the cytoplasmic double-stranded DNA and activates the antiviral response. However, the posttranslational modification of cGAS remains to be fully understood and whether it has arginine methylation modification remains unknown. Here, we identified protein arginine methyltransferase 5 (PRMT5) as a direct binding partner of cGAS, and it catalyzed the arginine symmetrical dimethylation of cGAS at the Arg¹²⁴ residue. Further investigation demonstrated that methylation of cGAS by PRMT5 attenuated cGAS-mediated antiviral immune response by blocking the DNA binding ability of cGAS. Oral administration of PRMT5 inhibitors significantly protected mice from HSV-1 infection and prolonged the survival time of these infected mice. Therefore, our findings revealed an essential regulatory effect of PRMT5 on cGAS-mediated antiviral immune response and provided a promising potential antiviral strategy by modulating PRMT5.

Cigarette smoke extract induces airway epithelial cell death via repressing PRMT6/AKT signaling

Chronic obstructive pulmonary disease (COPD) is a severe public health threat world-wide. Cigarette smoke (CS)-induced airway epithelial cell death is a major pathway of pathogenesis in emphysema, a subtype of COPD. Protein arginine methyltransferase 6 (PRMT6) is a type I PRMT that catalyzes mono- and di-methylation on arginine residues within histone and non-histone proteins to modulate a variety of life processes, such as apoptosis. However, its role in CS-induced lung epithelial death has not been fully elucidated. Here we report that PRMT6 was decreased in mouse lung tissues from a cigarette smoke extract (CSE)-mediated experimental emphysematous model and in CSE treated or cigarette smoke exposed lung epithelial cells. Depletion of PRMT6 increased the protein levels of phosphatase PTEN and PI3K regulatory subunit p85 but decreased a downstream kinase PDK1, resulting in AKT dephosphorylation and thereafter, lung epithelial cell death. Knockout of PRMT6 inhibited epithelial survival and promoted CSE-mediated epithelial cell death, while ectopic expression of PRMT6 protein partially reversed epithelial cell death via PI3K/AKT-mediated cell survival signaling in CSE cellular models. These findings demonstrate that PRMT6 plays a crucial role in CS-induced bronchial epithelial cell death that may be a potential therapeutic target against the airway cell death in CS-induced COPD.

IRF1 Promotes the Innate Immune Response to Viral Infection by Enhancing the Activation of IRF3

Innate immunity is an essential way for host cells to resist viral infection through the production of interferons (IFNs) and proinflammatory cytokines. Interferon regulatory factor 3 (IRF3) plays a critical role in the innate immune response to viral infection. However, the role of IRF1 in innate immunity remains largely unknown. In this study, we found that IRF1 is upregulated through the IFN/JAK/STAT signaling pathway upon viral infection. The silencing of IRF1 attenuates the innate immune response to viral infection. IRF1 interacts with IRF3 and augments the activation of IRF3 by blocking the interaction between IRF3 and protein phosphatase 2A (PP2A). The DNA binding domain (DBD) of IRF1 is the key functional domain for its interaction with IRF3. Overall, our study reveals a novel mechanism by which IRF1 promotes the innate immune response to viral infection by enhancing the activation of IRF3, thereby inhibiting viral infection.IMPORTANCE The activation of innate immunity is essential for host cells to restrict the spread of invading viruses and other pathogens. IRF3 plays a critical role in the innate immune response to RNA viral infection. However, whether IRF1 plays a role in innate immunity is unclear. In this study, we demonstrated that IRF1 promotes the innate immune response to viral infection. IRF1 is induced by viral infection. Notably, IRF1 targets and augments the phosphorylation of IRF3 by blocking the interaction between IRF3 and PP2A, leading to the upregulation of innate immunity. Collectively, the results of our study provide new insight into the regulatory mechanism of IFN signaling and uncover the role of IRF1 in the positive regulation of the innate immune response to viral infection.

Beta-catenin inhibits bovine parainfluenza virus type 3 replication via innate immunity pathway

Background

Bovine parainfluenza virus type 3 (BPIV3) is one of the important viral respiratory agents associated with the bovine respiratory disease complex (BRDC) in cattle. Previous study has demonstrated that infection of BPIV3 causes innate immune response within the host cell. β-catenin is a key component of the Wnt/β-catenin signal pathway which is involved in the regulation of interferon-beta (IFN-β) transcription. Some viruses can activate while others can inhibit the Wnt/β-catenin signaling pathway. However, the role of β-catenin in BPIV3 infection remains unclear.

Results

Here we found that the expression of β-catenin mRNA was up-regulated and β-catenin protein was down-regulated after BPIV3 infection in MDBK cells. Moreover, it was confirmed that overexpression of β-catenin suppressed BPIV3 replication and knockdown of β-catenin promoted viral replication, suggesting that β-catenin inhibits BPIV3 replication. Furthermore, IFN-β signal pathway and virus titer analysis using the GSK3β inhibitor (LiCl) revealed that Wnt/β-catenin can serve as a mechanism to suppress virus replication in infected cells. The results indicated that LiCl promoted the expression and accumulation in the nucleus of β-catenin, which further promoted the expression of IFN-β and OSA1 and suppressed BPIV3 replication. Most importantly, BPIV3 down-regulating β-catenin protein expression was due to degradation of GSK3β mediated proteasome pathway.

Conclusions

In summary, we discovered the relationship between β-catenin and BPIV3 replication. These results provided further insight into the study of BPIV3 pathogenesis.

Zebrafish prmt7 negatively regulates antiviral responses by suppressing the retinoic acid-inducible gene-I-like receptor signaling

Arginine methylation is a post-translational modification in histone and nonhistone proteins that can affect numerous cellular activities. Protein arginine methyltransferase 7 (Prmt7), a type III arginine methyltransferase, catalyzes the formation of stable monomethylarginines of histones. The role of PRMT7 in virus-induced innate immunity signaling, however, remains largely unknown. We demonstrate that zebrafish prmt7 could be inhibited by spring viremia of carp virus (SVCV) and grass carp reovirus (GCRV) infection. The overexpression of prmt7 suppresses cellular antiviral responses that are partially dependent on the arginine methyltransferase activity of prmt7. Consistently, prmt7-null zebrafish were more resistant to SVCV or GCRV infection, exhibiting enhanced expression of key antiviral genes and fewer necrotic cells in the liver and kidney upon viral infection. Furthermore, we established a zebrafish model to investigate grass carp hemorrhagic disease. Our findings suggest that by suppressing the RIG-I-like receptors signaling, zebrafish prmt7 negatively regulates antiviral responses, indicating the vital role of prmt7 and its arginine methyltransferase activity in innate immunity.

Black carp PRMT6 inhibits TBK1-IRF3/7 signaling during the antiviral innate immune activation

Protein arginine methylation is a prevalent posttranslational modification and protein arginine methyltransferases 6 (PRMT6) has been identified as a suppressor of TBK1/IRF3 in human and mammals. To explore the role of PRMT6 in teleost fish, PRMT6 homologue of black carp (Mylopharyngodon piceus) has been cloned and characterized in this study. Black carp PRMT6 (bcPRMT6) transcription in host cells varies in response to different stimuli and bcPRMT6 migrates around 43 kDa in the immunoblot assay. Like its mammalian counterpart, bcPRMT6 has been identified to distribute majorly in the nucleus through the immunofluorescent staining assay. bcPRMT6 shows little interferon (IFN) promoter-inducing activity in the reporter assay and bcPRMT6 shows no antiviral activity against either grass carp reovirus (GCRV) or spring viremia of carp virus (SVCV) in plaque assay. When co-expressed with bcPRMT6, the IFN promoter-inducing abilities of black carp TBK1 (bcTBK1) and IRF3/7 (bcIRF3/7) are fiercely attenuated. Accordingly, bcTBK1-mediated antiviral activity in EPC cells is obviously dampened by bcPRMT6. The interaction between bcPRMT6 and bcIRF3/7 has been identified by co-immunoprecipitation assay; however, no direct association between bcPRMT6 and bcTBK1 has been detected. Taken together, our data elucidates for the first time in teleost fish that PRMT6 suppresses TBK1-IRF3/7 signaling during host antiviral innate immune activation.

Noncanonical Role of FBXO6 in Regulating Antiviral Immunity

The evolutionarily conserved F-box family of proteins are well known for their role as the key component of SKP1-Cullin1-F-box (SCF) E3 ligase in controlling cell cycle, cell proliferation and cell death, carcinogenesis, and cancer metastasis. However, thus far, there is only limited investigation on their involvement in antiviral immunity. In contrast to the canonical function of FBXO6 associated with SCF E3 ligase complex, we report, in this study, that FBXO6 can also potently regulate the activation of IFN-I signaling during host response to viral infection by targeting the key transcription factor IFN-regulatory factor 3 (IRF3) for accelerated degradation independent of SCF in human embryonic kidney cells (HEK293T) and human lung cancer epithelial cells (A549). Structure and function delineation has further revealed that FBXO6 interacts with IAD domain of IRF3 through its FBA region to induce ubiquitination and degradation of IRF3 without the involvement of SCF. Thus, our studies have identified a general but, to our knowledge, previously unrecognized role and a novel noncanonical mechanism of FBXO6 in modulating IFN-I-mediated antiviral immune responses, which may protect the host from immunopathology of overreactive and harmful IFN-I production.