Negative regulators of the RIG-I-like receptor signaling pathway

Toll-interacting protein is activated by the transcription factor GATA1 and Sp1 to negatively regulate NF-κB and MAPK pathways in the Japanese eel (Anguilla japonica)

Toll-interacting protein (Tollip) serves as a crucial inhibitory factor in the modulation of Toll-like receptor (TLR)-mediated innate immunological responses. The structure and function of Tollip have been well documented in mammals, yet the information in teleost remained limited. This work employed in vitro overexpression and RNA interference in vivo and in vitro to comprehensively examine the regulatory effects of AjTollip on NF-κB and MAPK signaling pathways. The levels of p65, c-Fos, c-Jun, IL-1, IL-6, and TNF-α were dramatically reduced following overexpression of AjTollip, whereas knocking down AjTollip in vivo and in vitro enhanced those genes' expression. Protein molecular docking simulations showed AjTollip interacts with AjTLR2, AjIRAK4a, and AjIRAK4b. A better understanding of the transcriptional regulation of AjTollip is crucial to elucidating the role of Tollip in fish antibacterial response. Herein, we cloned and characterized a 2.2 kb AjTollip gene promoter sequence. The transcription factors GATA1 and Sp1 were determined to be associated with the activation of AjTollip expression by using promoter truncation and targeted mutagenesis techniques. Collectively, our results indicate that AjTollip suppresses the NF-κB and MAPK signaling pathways, leading to the decreased expression of the downstream inflammatory factors, and GATA1 and Sp1 play a vital role in regulating AjTollip expression.

Targeted delivery of immune-stimulating bispecific RNA, inducing apoptosis and anti-tumor immunity in cancer cells

Double-stranded RNAs (dsRNA)-based strategies appeared as promising therapies to induce an inflammation in the tumor microenvironment. However, currently described systems generally lack active targeting of tissues, and their clinical translation is thus limited to intratumoral injection. Herein, we developed an antibody-siRNA-5'triphosphate conjugate with multiple modes of action, combining cell surface EphA2-specific internalization, leading to a simultaneous gene silencing and activation of the receptor retinoic acid-inducible gene I (RIG-I). Recognition of cytosolic siRNA-5'triphosphate by RIG-I triggers the expression of interferons and pro-inflammatory cytokines, inducing an inflammation of the tumor environment and activating neighboring immune cells. In addition, these RIG-I-specific effects synergized with siRNA-mediated PLK1 silencing to promote cancer cell death by apoptosis. Altogether, such immune-stimulating antibody-RNA conjugate opens a novel modality to overcome some limitations encountered by dsRNA molecules currently in clinical trials.

Unraveling blunt-end RNA binding and ATPase-driven translocation activities of the RIG-I family helicase LGP2

The RIG-I family helicases, comprising RIG-I, MDA5 and LGP2, are cytoplasmic RNA sensors that trigger an antiviral immune response by specifically recognizing foreign RNAs. While LGP2 lacks the signaling domain necessary for immune activation, it plays a vital role in regulating the RIG-I/MDA5 signaling pathway. In this study, we investigate the mechanisms underlying this regulation by examining the oligomeric state, RNA binding specificity, and translocation activity of human LGP2 and the impact of ATPase activity. We show that LGP2, like RIG-I, prefers binding blunt-ended double-stranded (ds) RNAs over internal dsRNA regions or RNA overhangs and associates with blunt-ends faster than with overhangs. Unlike RIG-I, a 5'-triphosphate (5'ppp), Cap0, or Cap1 RNA-end does not influence LGP2's RNA binding affinity. LGP2 hydrolyzes ATP in the presence of RNA but at a 5-10 fold slower rate than RIG-I. Nevertheless, LGP2 uses its ATPase activity to translocate and displace biotin-streptavidin interactions. This activity is significantly hindered by a methylated RNA patch, particularly on the 3'-strand, suggesting a 3'-strand tracking mechanism like RIG-I. The preference of LGP2 for blunt-end RNA binding, its insensitivity to Cap0/Cap1 modification, and its translocation/protein displacement ability have substantial implications for how LGP2 regulates the RNA sensing process by MDA5/RIG-I.

Molecular and functional characterization of golden pompano (Trachinotus blochii) TBK1 on IFN regulation

The golden pompano (Trachinotus blochii), a pivotal commercial marine species in China, has gained significant popularity worldwide. However, accompanied with rapid growth and high density aquaculture, golden pompano has been seriously threatened by Nervous necrosis virus (NNV), while its molecular biology research regarding the innate immune system remains unexplored, which is crucial for understanding the activation of interferon (IFN) production and antiviral responses. In this study, we aimed to identify the characterization and function of golden pompano TANK-binding kinase 1 (gpTBK1), thereby providing evidence of the conservation of this classical factor in the RLR pathway among marine fish. Initially, we found the expression of gpTBK1 upregulation in diseased golden pompano with NNV infection and we successfully cloned the full-length open reading frame (ORF) of gpTBK1, consisting of 2172 nucleotides encoding 723 amino acids, from the head kidney. Subsequent analysis of the amino acid sequence revealed homology between gpTBK1 and other fish TBK1 proteins, with conserved N-terminal Serine/Threonine protein kinases catalytic domain (S_TKc) and C-terminal coiled coil domain (CCD). Moreover, the expression pattern showed that gpTBK1 exhibited ubiquitous expression across all evaluated tissues. Furthermore, functional identification experiments indicated that gpTBK1 activated interferon promoters' activity in golden pompano and induced the expression of downstream IFN-stimulated genes (ISGs). Notably, gpTBK1 was found to co-localize and interact with gpIRF3 in the cytoplasm. Collectively, these data provide a comprehensive analysis of the characterization and functional role of gpTBK1 in promoting interferon production. This research may facilitate the further study of the innate antiviral response, particularly the anti-NNV mechanisms, in golden pompano.

A novel protein encoded by circVPS13D attenuates antiviral innate immunity by targeting MAVS in teleost fish

IMPORTANCE

The expression of circVPS13D was upregulated with SCRV invasion, which proved that circVPS13D was involved in the regulation of the antiviral immune response. Our study revealed that the existence of circVPS13D promoted the replication of SCRV. Functionally, circVPS13D negatively regulates the antiviral responses of fish. Mechanistically, we confirmed that circVPS13D inhibited RLRs antiviral signaling pathway via the encoded protein VPS13D-170aa by targeting MAVS. Our study provided novel insights into the roles of protein-coding circRNAs and supported VPS13D-170aa as a negative regulator in the antiviral immune responses of teleost fish.

Bioinformatics and in vitro study reveal the roles of microRNA-346 in high glucose-induced human retinal pigment epithelial cell damage

AIM

To study microRNAs (miRNAs) and their potential effects in high glucose-induced human retinal pigment epithelial cell damage.

METHODS

We screened the GSE52233 miRNA expression dataset for differentially expressed miRNAs (DEMs). The target genes of the top 10 DEMs were predicted using miRWalk 2.0 database, followed by function enrichment and protein-protein interaction analysis. miRNA expression was determined in the human retinal pigment epithelial cell line ARPE-19 treated with high glucose (HG) by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Cell proliferation was determined using cell counting kit (CCK)-8 assay. Cell cycle, apoptosis, and reactive oxygen species (ROS) levels were determined by flow cytometry. The direct interaction between miRNA and targets was validated using dual-luciferase reporter assay.

RESULTS

Thirty-nine DEMs were screened, and we predicted 125 miRNA-mRNA pairs for the top 10 DEMs, including 119 target genes of seven DEMs such as miR-346, which was upregulated in diabetic retinopathy (DR). miR-346 target genes were substantially enriched in the regulation of intracellular transport and retinoic acid-inducible gene I (RIG-I)-like receptor signaling pathway. Expression of three upregulated and downregulated miRNAs were verified by qRT-PCR in HG-treated ARPE-19 cells. Expression of miR-346 was elevated in HG treated ARPE-19 cells in a dose-dependent manner. HG inhibited cell proliferation and induced apoptosis, which were partly reversed by transfecting an miR-346 inhibitor, which even decreased the ROS levels elevated due to HG. Argonaute 2 (AGO2) was a target of miR-346.

CONCLUSION

miR-346 is a key miRNA and plays an important role in HG-induced damage in human retinal pigment epithelial cells.

Gain without pain: adaptation and increased virulence of Zika virus in vertebrate host without fitness cost in mosquito vector

IMPORTANCE

Previously, we modeled direct transmission chains of Zika virus (ZIKV) by serially passaging ZIKV in mice and mosquitoes and found that direct mouse transmission chains selected for viruses with increased virulence in mice and the acquisition of non-synonymous amino acid substitutions. Here, we show that these same mouse-passaged viruses also maintain fitness and transmission capacity in mosquitoes. We used infectious clone-derived viruses to demonstrate that the substitution in nonstructural protein 4A contributes to increased virulence in mice.

Analysis of copy number variations and possible candidate genes in spontaneous abortion by copy number variation sequencing

Introduction

Embryonic chromosomal abnormalities represent a major causative factor in early pregnancy loss, highlighting the importance of understanding their role in spontaneous abortion. This study investigates the potential correlation between chromosomal abnormalities and spontaneous abortion using copy number variation sequencing (CNV-seq), a Next-Generation Sequencing (NGS) technology.

Methods

We analyzed Copy Number Variations (CNVs) in 395 aborted fetal specimens from spontaneous abortion patients by CNV-seq. And collected correlated data, including maternal age, gestational week, and Body Mass Index (BMI), and analyzed their relationship with the CNVs.

Results

Out of the 395 cases, 67.09% of the fetuses had chromosomal abnormalities, including numerical abnormalities, structural abnormalities, and mosaicisms. Maternal age was found to be an important risk factor for fetal chromosomal abnormalities, with the proportion of autosomal trisomy in abnormal karyotypes increasing with maternal age, while polyploidy decreased. The proportion of abnormal karyotypes with mosaic decreased as gestational age increased, while the frequency of polyploidy and sex chromosome monosomy increased. Gene enrichment analysis identified potential miscarriage candidate genes and functions, as well as pathogenic genes and pathways associated with unexplained miscarriage among women aged below or over 35 years old. Based on our study, it can be inferred that there is an association between BMI values and the risk of recurrent miscarriage caused by chromosomal abnormalities.

Discussion

Overall, these findings provide important insights into the understanding of spontaneous abortion and have implications for the development of personalized interventions for patients with abnormal karyotypes.

LGP2 directly interacts with flavivirus NS5 RNA-dependent RNA polymerase and downregulates its pre-elongation activities

LGP2 is a RIG-I-like receptor (RLR) known to bind and recognize the intermediate double-stranded RNA (dsRNA) during virus infection and to induce type-I interferon (IFN)-related antiviral innate immune responses. Here, we find that LGP2 inhibits Zika virus (ZIKV) and tick-borne encephalitis virus (TBEV) replication independent of IFN induction. Co-immunoprecipitation (Co-IP) and confocal immunofluorescence data suggest that LGP2 likely colocalizes with the replication complex (RC) of ZIKV by interacting with viral RNA-dependent RNA polymerase (RdRP) NS5. We further verify that the regulatory domain (RD) of LGP2 directly interacts with RdRP of NS5 by biolayer interferometry assay. Data from in vitro RdRP assays indicate that LGP2 may inhibit polymerase activities of NS5 at pre-elongation but not elongation stages, while an RNA-binding-defective LGP2 mutant can still inhibit RdRP activities and virus replication. Taken together, our work suggests that LGP2 can inhibit flavivirus replication through direct interaction with NS5 protein and downregulates its polymerase pre-elongation activities, demonstrating a distinct role of LGP2 beyond its function in innate immune responses.

Gain without pain: Adaptation and increased virulence of Zika virus in vertebrate host without fitness cost in mosquito vector

Zika virus (ZIKV) is now in a post-pandemic period, for which the potential for re-emergence and future spread is unknown. Adding to this uncertainty is the unique capacity of ZIKV to directly transmit between humans via sexual transmission. Recently, we demonstrated that direct transmission of ZIKV between vertebrate hosts leads to rapid adaptation resulting in enhanced virulence in mice and the emergence of three amino acid substitutions (NS2A-A117V, NS2A-A117T, and NS4A-E19G) shared among all vertebrate-passaged lineages. Here, we further characterized these host-adapted viruses and found that vertebrate-passaged viruses also have enhanced transmission potential in mosquitoes. To understand the contribution of genetic changes to the enhanced virulence and transmission phenotype, we engineered these amino acid substitutions, singly and in combination, into a ZIKV infectious clone. We found that NS4A-E19G contributed to the enhanced virulence and mortality phenotype in mice. Further analyses revealed that NS4A-E19G results in increased neurotropism and distinct innate immune signaling patterns in the brain. None of the substitutions contributed to changes in transmission potential in mosquitoes. Together, these findings suggest that direct transmission chains could enable the emergence of more virulent ZIKV strains without compromising mosquito transmission capacity, although the underlying genetics of these adaptations are complex.

Toll-interacting protein negatively regulated innate immune response via NF-κB signal pathway in blunt snout bream, Megalobrama amblycephala

Toll-interacting protein (Tollip) is an important negative regulator of Toll-like receptor-mediated innate immunity by preventing excessive proinflammatory responses. The structure and function of Tollip have been well identified in mammals, but the piscine Tollip remains poorly understood. In the present study, a homologue of Tollip was identified and characterized from blunt snout bream (named MaTollip), which was composed of an 831 bp open reading frame encoding a protein of 276 amino acids. Phylogenetic analysis indicated that MaTollip is a novel member of Tollip family and possessed the highest similarity to that of grass carp (99.28%). Multiple alignment of amino acid sequence showed that MaTOLLIP shared a high degree of structural conservation, including a TBD domain, a C2 domain and a CUE domain, with its counterparts from other vertebrates. With regard to tissue-specific expression without immune challenge, MaTollip was constitutively expressed in a wide range of normal tissues, with the highest in the head-kidney and the lowest in the intestine. MaTollip expression in the head-kidney was strongly upregulated upon LPS stimulation and A. hydrophila infection. Fluorescence microscopic analysis revealed that the green fluorescent protein-TOLLIP was localized predominantly in the cytoplasm of EPC cells in a dot-like state. When MaTollip was overexpressed in HEK-293T and EPC cells, it could significantly inhibit the activity of nuclear factor-κB (NF-κB) promoter in a dose dependent manner. MaTollip overexpression in MAF cells lowered drastically the transcriptional expression level of lipopolysaccharide-induced proinflammatory cytokines (IL-1β, IL-6 and IL-8), whereas they were dramatically promoted by MaTollip knock down with siRNA. Taken together, this study demonstrated that MaTollip played a pivotal role in mediating host innate immune response to pathogen invasion, and unveiled the involvement of MaTollip in NF-κB-mediated transcription of inflammation genes, which paved the way for further studies of immune negative regulation mechanisms mediated by Tollip in fish.

Transcriptome analysis of largemouth bass (Micropterus salmoides) challenged with LPS and polyI:C

Largemouth bass (Micropterus salmoides) is a worldwide commercially important aquatic species. In recent years, pathogenic diseases cause great economic losses and hinder the industry of largemouth bass. To further understand the immune response against pathogens in largemouth bass, splenic transcriptome libraries of largemouth bass were respectively constructed at 12 h post-challenged with phosphate-buffered saline (PBS), lipopolysaccharide (LPS) and polyinosinic-polycytidylic acid (polyI:C) by using RNA sequencing technology (RNA-seq). RNA libraries were constructed using 9 RNA splenic samples isolated from three biological replicates of the three groups and sequenced on the DNBSEQ platform. A total number of 86,306 unigenes were obtained. Through pairwise comparisons among the three groups, we identified 11,295 different expression genes (DEGs) exhibiting significant differences at the transcript level. There were 7, 7, and 13 signal pathways were significantly enriched in LPS-PBS comparison, polyI:C-PBS comparison, and LPS-polyI:C comparison, respectively, indicating that the immune response to different pathogens was distinct in largemouth bass. To the best of our knowledge, this is the first report on the immune response of largemouth bass against different pathogen-associated molecular patterns (PAMPs) stimuli using transcriptomic analysis. Our results provide a valuable resource and new insights to understanding the immune characteristics of largemouth bass against different pathogens.

IRF1 Is Required for MDA5 (IFIH1) Induction by IFN-α, LPS, and poly(I:C) in Murine Macrophages

Melanoma differentiation-associated protein 5 (MDA5) induces type I interferons (IFNs) after the recognition of viral RNA. In addition, gain-of-function mutations in the interferon induced with helicase C domain 1 (IFIH1) gene, which encodes MDA5, lead to type I interferonopathies. Here, we show that Mda5 is highly expressed in murine macrophages and is regulated by pro-inflammatory stimuli such as the cytokines IFN-α and IFN-γ, the TLR ligand LPS, and a mimic of dsRNA, poly(I:C). Mda5 induction is mediated through the production of reactive oxygen species. The induction by IFN-α or LPS occurs at the transcriptional level since the Mda5 mRNA half-life before and after induction is very stable. Interestingly, STAT1 is required for Mda5 induction by IFN-α, LPS, or poly(I:C). The time course of induction of at least 3 h and the need for protein synthesis indicate that Mda5 requires an intermediate protein for transcription. In transient transfection experiments, we found that a 105-bp fragment of this gene, between -1153 and -1258 bp relative to the transcription start site, is required for transcription. In this specific region, we observed a sequence containing an IRF-binding motif, which, when mutated, abolishes the induction of Mda5. This sequence is strongly conserved in the IFIH1 promoters of eutherian mammals and in other distant species. Kinetic experiments, chromatin immunoprecipitation assays, and gene-silencing experiments revealed that IRF1 is required for induction of Mda5 expression.

The lncRNAs involved in regulating the RIG-I signaling pathway

Understanding the targets and interactions of long non-coding RNAs (lncRNAs) related to the retinoic acid-inducible gene-I (RIG-I) signaling pathway is essential for developing interventions, which would enable directing the host inflammatory response regulation toward protective immunity. In the RIG-I signaling pathway, lncRNAs are involved in the important processes of ubiquitination, phosphorylation, and glycolysis, thus promoting the transport of the interferon regulatory factors 3 and 7 (IRF3 and IRF7) and the nuclear factor kappa B (NF-κB) into the nucleus, and activating recruitment of type I interferons (IFN-I) and inflammatory factors to the antiviral action site. In addition, the RIG-I signaling pathway has recently been reported to contain the targets of coronavirus disease-19 (COVID-19)-related lncRNAs. The molecules in the RIG-I signaling pathway are directly regulated by the lncRNA-microRNAs (miRNAs)-messenger RNA (mRNA) axis. Therefore, targeting this axis has become a novel strategy for the diagnosis and treatment of cancer. In this paper, the studies on the regulation of the RIG-I signaling pathway by lncRNAs during viral infections and cancer are comprehensively analyzed. The aim is to provide a solid foundation of information for conducting further detailed studies on lncRNAs and RIG-I in the future and also contribute to clinical drug development.

High RIG-I and EFTUD2 expression predicts poor survival in endometrial cancer

PURPOSE

Endometrial cancer is the most common gynecological malignancy. The helicase RIG-I, a part of the innate immune system, and EFTUD2, a splicing factor which can upregulate RIG-I expression, are shown to influence tumor growth and disease progression in several malignancies. For endometrial cancer, an immunogenic cancer, data about RIG-I and EFTUD2 are still missing. The aim of this study was to examine the expression of RIG-I and EFTUD2 in endometrial cancer.

METHODS

225 specimen of endometrial cancer were immunohistochemically stained for RIG-I and EFTUD2. The results were correlated to clinicopathological data, overall survival (OS) and progression-free survival (PFS).

RESULTS

High RIG-I expression correlated with advanced tumor stages (FIGO: p = 0.027; pT: p = 0.010) and worse survival rates (OS: p = 0.009; PFS: p = 0.022). High EFTUD2 expression correlated to worse survival rates (OS: p = 0.026; PFS: p < 0.001) and was determined to be an independent marker for progression-free survival.

CONCLUSION

Our data suggest that the expression of RIG-I and EFTUD2 correlates with survival data, which makes both a possible therapeutic target in the future.

Integrated analysis of immune parameters, miRNA-mRNA interaction, and immune genes expression in the liver of rainbow trout following infectious hematopoietic necrosis virus infection

Rainbow trout (Oncorhynchus mykiss) is an important economical cold-water fish worldwide. However, infection with infectious hematopoietic necrosis virus (IHNV) has severely restricted the development of aquaculture and caused huge economic losses. Currently, little is known about the immune defense mechanisms of rainbow trout against IHNV. In this study, we detected the changes of immune parameters over different post-infection periods (6-, 12-, 24-, 48-, 72-, 96-, 120-, and 144 hours post-infection (hpi)), mRNA and miRNA expression profiles under 48 hpi (T48L) compared to control (C48L), and key immune-related genes expression patterns in rainbow trout liver following IHNV challenge through biochemical methods, RNA-seq, and qRT-PCR, and the function of miR-330-y was verified by overexpression and silencing in vitro and in vivo. The results revealed that alkaline phosphatase (AKP), alanine aminotransferase (ALT), catalase (CAT), and total superoxide dismutase (T-SOD) activities, and lysozyme (LZM) content showed significant peaks at 48 hpi, whereas malondialdehyde (MDA) content and aspartate aminotransferase (AST) activity decreased continuously during infection, and acid phosphatase (ACP) activity varied slightly. From RNA-seq, a total of 6844 genes and 86 miRNAs were differentially expressed, and numerous immune-related differentially expressed genes (DEGs) involved in RIG-I-like receptor signaling pathway, Toll-like receptor signaling pathway, NOD-like receptor signaling pathway, cytokine-cytokine receptor interaction, and antigen processing and presentation were significantly upregulated in T48Lm group, including IFIH1, DHX58, MAVS, TRAF3, IRF3, IRF7, MX1, TLR3, TLR8, MYD88, NOD1, NOD2, IL-8, CXCR1, CD209, CD83, and TAP1. Integrated analysis identified seven miRNAs (miR-425-x, miR-185-x, miR-338-x, miR-330-y, miR-361-x, miR-505-y, and miR-191-x) that target at least three key immune-related DEGs. Expression analysis showed that IFIH1, DHX58, IRF3, IRF7, MX1, TLR3, TLR8, and MYD88 showed a marked increase after 24 hpi during infection. Further research confirmed TAP1 as one of the targets of miR-330-y, overexpression of miR-330-y with mimics or agomir significantly reduced the expression levels of TAP1, IRF3, and IFN, and the opposite effects were obtained by inhibitor. These results facilitate in-depth understanding of the immune mechanisms in rainbow trout against IHNV.

BAG6 negatively regulates the RLR signaling pathway by targeting VISA/MAVS

The virus-induced signaling adaptor protein VISA (also known as MAVS, ISP-1, Cardif) is a critical adaptor protein in the innate immune response to RNA virus infection. Upon viral infection, VISA self-aggregates to form a sizeable prion-like complex and recruits downstream signal components for signal transduction. Here, we discover that BAG6 (BCL2-associated athanogene 6, formerly BAT3 or Scythe) is an essential negative regulator in the RIG-I-like receptor signaling pathway. BAG6 inhibits the aggregation of VISA by promoting the K48-linked ubiquitination and specifically attenuates the recruitment of TRAF2 by VISA to inhibit RLR signaling. The aggregation of VISA and the interaction of VISA and TRAF2 are enhanced in BAG6-deficient cell lines after viral infection, resulting in the enhanced transcription level of downstream antiviral genes. Our research shows that BAG6 is a critical regulating factor in RIG-I/VISA-mediated innate immune response by targeting VISA.

Heat shock proteins and viral infection

Heat shock proteins (HSPs) are a kind of proteins which mostly found in bacterial, plant and animal cells, in which they are involved in the monitoring and regulation of cellular life activities. HSPs protect other proteins under environmental and cellular stress by regulating protein folding and supporting the correctly folded structure of proteins as chaperones. During viral infection, some HSPs can have an antiviral effect by inhibiting viral proliferation through interaction and activating immune pathways to protect the host cell. However, although the biological function of HSPs is to maintain the homeostasis of cells, some HSPs will also be hijacked by viruses to help their invasion, replication, and maturation, thereby increasing the chances of viral survival in unfavorable conditions inside the host cell. In this review, we summarize the roles of the heat shock protein family in various stages of viral infection and the potential uses of these proteins in antiviral therapy.

Application and prospect of targeting innate immune sensors in the treatment of autoimmune diseases

Dysregulation of auto-reactive T cells and autoantibody-producing B cells and excessive inflammation are responsible for the occurrence and development of autoimmune diseases. The suppression of autoreactive T cell activation and autoantibody production, as well as inhibition of inflammatory cytokine production have been utilized to ameliorate autoimmune disease symptoms. However, the existing treatment strategies are not sufficient to cure autoimmune diseases since patients can quickly suffer a relapse following the end of treatments. Pattern recognition receptors (PRRs), including Toll-like receptors (TLRs), Nod-like receptors (NLRs), RIG-I like receptors (RLRs), C-type lectin receptors (CLRs) and various nucleic acid sensors, are expressed in both innate and adaptive immune cells and are involved in the development of autoimmune diseases. Here, we have summarized advances of PRRs signaling pathways, association between PRRs and autoimmune diseases, application of inhibitors targeting PRRs and the corresponding signaling molecules relevant to strategies targeting autoimmune diseases. This review emphasizes the roles of different PRRs in activating both innate and adaptive immunity, which can coordinate to trigger autoimmune responses. The review may also prompt the formulation of novel ideas for developing therapeutic strategies against autoimmune diseases by targeting PRRs-related signals.

Microbial Characteristics of Common Tongue Coatings in Patients with Precancerous Lesions of the Upper Gastrointestinal Tract

The tongue coating (TC) microbiota, a crucial component of the tongue coating, illustrates a huge microbial percentage of the body that mostly includes actinobacteria, bacteroides, firmicutes, and fusobacteria. The TC microbiota is closely related to the development of upper gastrointestinal malignancies, such as oral, gastric, and esophageal cancer. Nonetheless, the microbiological characteristics of common TCs in individuals with precancerous lesions of the upper gastrointestinal tract are still unclear. Herein, we designed a case-control study, recruiting 153 PLUGT patients with four different types of TCs, including 47 white-thin, 19 white-thick, 47 yellow-thin, and 40 yellow-thick, as well as 47 volunteers as controls. To analyze microbial characteristics, 16S rRNA microbiome approaches were used. An enzyme-linked immunosorbent assay (ELISA) was employed to assess serum IL-17A and total bile acid (TBA). According to the obtained results, Leptotrichia was found to be a promising biomarker for thin as well as thick yellow coatings. In comparison to the control TC microbiota, 39 different genera developed commensal networks in common TCs. Lachnoanaerobaculum and pseudonocardia were the most striking core bacteria. Lachnoanaerobaculum positively correlated with Leptotrichia in W-thin and Y-thick coatings, with actinomyces and methylobacterium in Y-thin coatings, with Campylobacter in Y-thick coatings, and with Bradyrhizobium in W-thick and Y-thick coatings. Serum IL-17A levels were greater in cases with W-thin coating than in controls, and serum IL-17A was positively linked with Parvimonas in patients with W-thick or Y-thin coating. In Y-thin coating, the oral dominating bacteria Streptococcus was negatively linked with serum TBA. Taken together, the promoted bacteria were found to be synergistically proliferative in the TCs of PLUGT patients. The diverse TCs had distinct bacterial commensal networks, whereas the common TCs were linked by specific bacteria to serum IL-17A and TBA.

Characterizing the role of Tupaia DNA damage inducible transcript 3 (DDIT3) gene in viral infections

DNA damage inducible transcript 3 (DDIT3, also known as CHOP) belongs to the CCAAT/enhancer-binding protein (C/EBP) family and plays an essential role in endoplasmic reticulum stress. Here, we characterized the potential role of the Chinese tree shrew (Tupaia belangeri chinensis) DDIT3 (tDDIT3) in viral infections. The tDDIT3 protein is highly conserved and has a species-specific insertion of the SQSS repeat upstream of the C-terminal basic-leucine zipper (bZIP) domain. Phylogenetic analysis of DDIT3 protein sequences of tree shrew and related mammals indicated a closer genetic affinity between tree shrew and primates than between tree shrew and rodents. Three positively selected sites (PSSs: Glu83, Pro93, and Ser172) were identified in tDDIT3 based on the branch-site model. Expression analysis of tDDIT3 showed a constitutively expressed level in different tissues and a significantly increased level in tree shrew cells upon herpes simplex virus type 1 (HSV-1) and Newcastle disease virus (NDV) infections. Overexpression of tDDIT3 significantly increased the production of HSV-1 and vesicular stomatitis virus (VSV) in tree shrew primary renal cells (TSPRCs), whereas tDDIT3 knockout in tree shrew stable cell line (TSR6 cells) had an inhibitory effect on virus production. The enhanced effect on viral infection by tDDIT3 was not associated with the three PSSs. Mechanistically, tDDIT3 overexpression inhibited type I IFN signaling. tDDIT3 interacted with tMAVS through CARD and PRR domains, but not with other immune-related factors such as tMDA5, tSTING and tTBK1. Collectively, our results revealed tDDIT3 as a negative regulator for virus infection.

Grass Carp Reovirus Nonstructural Proteins Avoid Host Antiviral Immune Response by Targeting the RLR Signaling Pathway

Grass carp reovirus (GCRV) is a highly virulent RNA virus that mainly infects grass carp and causes hemorrhagic disease. The roles of nonstructural proteins NS38 and NS80 of GCRV-873 in the viral replication cycle and viral inclusion bodies have been established. However, the strategies that NS38 and NS80 used to avoid host antiviral immune response are still unknown. In this study, we report the negative regulations of NS38 and NS80 on the RIG-I-like receptors (RLRs) antiviral signaling pathway and the production of IFNs and IFN-stimulated genes. First, both in the case of overexpression and GCRV infection, NS38 and NS80 inhibited the IFN promoter activation induced by RIG-I, MDA5, MAVS, TBK1, IRF3, and IRF7 and mRNA abundance of key antiviral genes involved in the RLR-mediated signaling. Second, both in the case of overexpression and GCRV infection, NS38 interacted with piscine TBK1 and IRF3, but not with piscine RIG-I, MDA5, MAVS, and TNF receptor-associated factor (TRAF) 3. Whereas NS80 interacted with piscine MAVS, TRAF3, and TBK1, but not with piscine RIG-I, MDA5, and IRF3. Finally, both in the case of overexpression and GCRV infection, NS38 inhibited the formation of the TBK1-IRF3 complex, but NS80 inhibited the formation of the TBK1-TRAF3 complex. Most importantly, NS38 and NS80 could hijack piscine TBK1 and IRF3 into the cytoplasmic viral inclusion bodies and inhibit the translocation of IRF3 into the nucleus. Collectively, all of these data demonstrate that GCRV nonstructural proteins can avoid host antiviral immune response by targeting the RLR signaling pathway, which prevents IFN-stimulated gene production and facilitates GCRV replication.

Immune regulator LGP2 targets Ubc13/UBE2N to mediate widespread interference with K63 polyubiquitination and NF-κB activation

Lysine 63-linked polyubiquitin (K63-Ub) chains activate a range of cellular immune and inflammatory signaling pathways, including the mammalian antiviral response. Interferon and antiviral genes are triggered by TRAF family ubiquitin ligases that form K63-Ub chains. LGP2 is a feedback inhibitor of TRAF-mediated K63-Ub that can interfere with diverse immune signaling pathways. Our results demonstrate that LGP2 inhibits K63-Ub by association with and sequestration of the K63-Ub-conjugating enzyme, Ubc13/UBE2N. The LGP2 helicase subdomain, Hel2i, mediates protein interaction that engages and inhibits Ubc13/UBE2N, affecting control over a range of K63-Ub ligase proteins, including TRAF6, TRIM25, and RNF125, all of which are inactivated by LGP2. These findings establish a unifying mechanism for LGP2-mediated negative regulation that can modulate a variety of K63-Ub signaling pathways.

Acute acidification stress weakens the head kidney immune function of juvenile Lates calcarifer

Acidized water environment can impact many physiological processes of aquatic animals. The response of the head kidney to acidification, especially the immune response, is of great significance to health. This study analyzed the histological and transcriptional changes under different acidification levels (C group, pH 8.1; P group, pH 7.4; E group, pH 3.5) in the short term (12 h, 36 h and 60 h) in the head kidney of juvenile L. calcarifer. The results showed that the acidification of the water environment caused tissue damage to the head kidney of L. calcarifer, and the damage appeared earlier and was stronger in the extreme pH group. The transcriptional response of L. calcarifer head kidney increased with the increase of acidification level. The two treatments transcriptional responses showed different trends in terms of time. After KEGG function enrichment, with the increase of stimulation time, the proportion of down-regulated pathways was increasing, and the types of pathway enrichment at different acidification levels were quite different at the initial stage. At 12 h, the first category in the P group with the most significant number of pathways was 'Metabolism', and the first category in the E group with the largest number of pathways was 'Human Diseases'. At 60 h, the enrichment pathways of the two groups were highly overlapping in immune-related pathways, which contained 26 common DEGs. They had a dominant expression pattern. In the P group, the expression level decreased with time. In the E group, the down-regulation degree of expression level at 12 h reached the level of the P group at 60 h, and the expression level remained low until 60 h. Through the correlation network, interferon regulatory factor 7 (IRF7), Tripartite motif containing-21 (TRIM21), Signal transducer and activator of transcription 1 (STAT1) and Signal transducer and activator of transcription 3 (STAT3) were found to have the most correlation with other genes. In this study, juvenile L. calcarifer showed different coping strategies to different levels of acute acidification stress, but all of them resulted in the extensive weakening of head kidney immune function.

Respiratory Microbiota Profiles Associated With the Progression From Airway Inflammation to Remodeling in Mice With OVA-Induced Asthma

Background

The dysbiosis of respiratory microbiota plays an important role in asthma development. However, there is limited information on the changes in the respiratory microbiota and how these affect the host during the progression from acute allergic inflammation to airway remodeling in asthma.

Objective

An ovalbumin (OVA)-induced mouse model of chronic asthma was established to explore the dynamic changes in the respiratory microbiota in the different stages of asthma and their association with chronic asthma progression.

Methods

Hematoxylin and eosin (H&E), periodic acid-schiff (PAS), and Masson staining were performed to observe the pathological changes in the lung tissues of asthmatic mice. The respiratory microbiota was analyzed using 16S rRNA gene sequencing followed by taxonomical analysis. The cytokine levels in bronchoalveolar lavage fluid (BALF) specimens were measured. The matrix metallopeptidase 9 (MMP-9) and vascular endothelial growth factor (VEGF-A) expression levels in lung tissues were measured to detect airway remodeling in OVA-challenged mice.

Results

Acute allergic inflammation was the major manifestation at weeks 1 and 2 after OVA atomization stimulation, whereas at week 6 after the stimulation, airway remodeling was the most prominent observation. In the acute inflammatory stage, Pseudomonas was more abundant, whereas Staphylococcus and Cupriavidus were more abundant at the airway remodeling stage. The microbial compositions of the upper and lower respiratory tracts were similar. However, the dominant respiratory microbiota in the acute inflammatory and airway remodeling phases were different. Metagenomic functional prediction showed that the pathways significantly upregulated in the acute inflammatory phase and airway remodeling phase were different. The cytokine levels in BALF and the expression patterns of proteins associated with airway remodeling in the lung tissue were consistent with the metagenomic function results.

Conclusion

The dynamic changes in respiratory microbiota are closely associated with the progression of chronic asthma. Metagenomic functional prediction indicated the changes associated with acute allergic inflammation and airway remodeling.

The molecular mechanism of RIG-I activation and signaling

RIG‐I is our first line of defense against RNA viruses, serving as a pattern recognition receptor that identifies molecular features common among dsRNA and ssRNA viral pathogens. RIG‐I is maintained in an inactive conformation as it samples the cellular space for pathogenic RNAs. Upon encounter with the triphosphorylated terminus of blunt‐ended viral RNA duplexes, the receptor changes conformation and releases a pair of signaling domains (CARDs) that are selectively modified and interact with an adapter protein (MAVS), thereby triggering a signaling cascade that stimulates transcription of interferons. Here, we describe the structural determinants for specific RIG‐I activation by viral RNA, and we describe the strategies by which RIG‐I remains inactivated in the presence of host RNAs. From the initial RNA triggering event to the final stages of interferon expression, we describe the experimental evidence underpinning our working knowledge of RIG‐I signaling. We draw parallels with behavior of related proteins MDA5 and LGP2, describing evolutionary implications of their collective surveillance of the cell. We conclude by describing the cell biology and immunological investigations that will be needed to accurately describe the role of RIG‐I in innate immunity and to provide the necessary foundation for pharmacological manipulation of this important receptor.

Pattern recognition receptors in health and diseases

Pattern recognition receptors (PRRs) are a class of receptors that can directly recognize the specific molecular structures on the surface of pathogens, apoptotic host cells, and damaged senescent cells. PRRs bridge nonspecific immunity and specific immunity. Through the recognition and binding of ligands, PRRs can produce nonspecific anti-infection, antitumor, and other immunoprotective effects. Most PRRs in the innate immune system of vertebrates can be classified into the following five types based on protein domain homology: Toll-like receptors (TLRs), nucleotide oligomerization domain (NOD)-like receptors (NLRs), retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), C-type lectin receptors (CLRs), and absent in melanoma-2 (AIM2)-like receptors (ALRs). PRRs are basically composed of ligand recognition domains, intermediate domains, and effector domains. PRRs recognize and bind their respective ligands and recruit adaptor molecules with the same structure through their effector domains, initiating downstream signaling pathways to exert effects. In recent years, the increased researches on the recognition and binding of PRRs and their ligands have greatly promoted the understanding of different PRRs signaling pathways and provided ideas for the treatment of immune-related diseases and even tumors. This review describes in detail the history, the structural characteristics, ligand recognition mechanism, the signaling pathway, the related disease, new drugs in clinical trials and clinical therapy of different types of PRRs, and discusses the significance of the research on pattern recognition mechanism for the treatment of PRR-related diseases.

cGAS Is a Negative Regulator of RIG-I-Mediated IFN Response in Cyprinid Fish

In mammals, cyclic GMP-AMP synthase (cGAS) recognizes cytosolic dsDNA to induce the type I IFN response. However, the functional role of cGAS in the IFN response of fish remains unclear or controversial. In this study, we report that cGAS orthologs from crucian carp Carassius auratus (CacGAS) and grass carp Ctenopharyngodon idellus (CicGAS) target the dsRNA sensor retinoic acid-inducible gene I (RIG-I) for negative regulation of the IFN response. First, poly(deoxyadenylic-deoxythymidylic) acid-, polyinosinic-polycytidylic acid-, and spring viremia of carp virus-induced IFN responses were impaired by overexpression of CacGAS and CicGAS. Then, CacGAS and CicGAS interacted with CiRIG-I and CiMAVS and inhibited CiRIG-I- and CiMAVS-mediated IFN induction. Moreover, the K63-linked ubiquitination of CiRIG-I and the interaction between CiRIG-I and CiMAVS were attenuated by CacGAS and CicGAS. Finally, CacGAS and CicGAS decreased CiRIG-I-mediated the cellular antiviral response and facilitated viral replication. Taken together, data in this study identify CacGAS and CicGAS as negative regulators in RIG-I-like receptor signaling, which extends the current knowledge regarding the role of fish cGAS in the innate antiviral response.

Toll-interacting protein in the freshwater fish Labeo rohita exhibits conserved structural motifs of higher eukaryotes and is distinctly expressed in pathogen-associated molecular pattern stimulations and bacterial infections

Toll-interacting protein (Tollip) is a critical regulator of TOLL- like receptor (TLR)-signaling pathway. It is predominantly associated with TLR2 and TLR4 during acute inflammatory conditions and inhibits the TLR-mediated nuclear factor-kappa activation by suppressing the autophosphorylation of interleukin-1 receptor-associated kinase and its kinase activity. This article describes the Tollip of Labeo rohita (LrTollip), a highly valuable freshwater fish from the Indian subcontinent. The full-length LrTollip complementary DNA (1412 nucleotides) encodes a 276-amino acid (aa) protein, depicting a highly conserved target of the Myb1 (Tom1)-binding domain (TBD; 1-53 aa), conserved core domain 2 (C2; 54-151 aa), and coupling of ubiquitin to endoplasmic reticulum degradation (CUE; 231-273 aa) domains of mouse and human counterparts. The key amino acids exerting the critical functions of Tollip, such as phospholipids recognition and ubiquitination, are present in the C2 and CUE domains of LrTollip, respectively. LrTollip is widely expressed in the kidneys, gills, spleen, liver, and blood, and among these tested tissues, the highest expression is observed in blood. In response to TLR ligands and NOD-like receptor (NLR) ligands stimulations and Aeromonas hydrophila, Edwardsiella tarda, and Bacillus subtilis infections, LrTollip gene expression is induced in various organs/tissues with remarkable difference in their kinetics. These data together suggest the important role of LrTollip in TLR- and NLR-signal transduction pathways and immune-related diseases in fish.

Integrated analysis of the functions and prognostic values of RNA binding proteins in hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC), one of the most common malignant tumors worldwide, ranks as the fifth most common cancer and has been the second most frequent cause of cancer-related death. RNA binding proteins (RBPs) are proteins that interact with different classes of RNA and are commonly detected in cells.

Methods

We used RNA sequencing data from TCGA to display dysfunctional RBPs microenvironments and provide potential useful biomarkers for HCC diagnosis and prognosis.

Results

330 differently expressed RBPs (208 upregulated and 122 downregulated) were identified. KEGG were mainly enriched in RNA degradation, Influenza A, Hepatitis C, RIG-I-like receptor signaling pathway, Herpes simplex virus 1 infection and RNA transport. CBioPortal results demonstrated that these genes were altered in 50 samples out of 357 HCC patients (14%) and the amplification of BRCA1 was the largest frequent copy-number alteration.

Conclusion

Based on the online database, we identified novel RBPs markers for the prognosis of hepatocellular carcinoma.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12876-021-01843-0.

A Multiancestry Sex-Stratified Genome-Wide Association Study of Spontaneous Clearance of Hepatitis C Virus

BACKGROUND

Spontaneous clearance of acute hepatitis C virus (HCV) infection is more common in women than in men, independent of known risk factors.

METHODS

To identify sex-specific genetic loci, we studied 4423 HCV-infected individuals (2903 male, 1520 female) of European, African, and Hispanic ancestry. We performed autosomal, and X chromosome sex-stratified and combined association analyses in each ancestry group.

RESULTS

A male-specific region near the adenosine diphosphate-ribosylation factor-like 5B (ARL5B) gene was identified. Individuals with the C allele of rs76398191 were about 30% more likely to have chronic HCV infection than individuals with the T allele (OR, 0.69; P = 1.98 × 10-07), and this was not seen in females. The ARL5B gene encodes an interferon-stimulated gene that inhibits immune response to double-stranded RNA viruses. We also identified suggestive associations near septin 6 and ribosomal protein L39 genes on the X chromosome. In box sexes, allele G of rs12852885 was associated with a 40% increase in HCV clearance compared with the A allele (OR, 1.4; P = 2.46 × 10-06). Septin 6 facilitates HCV replication via interaction with the HCV NS5b protein, and ribosomal protein L39 acts as an HCV core interactor.

CONCLUSIONS

These novel gene associations support differential mechanisms of HCV clearance between the sexes and provide biological targets for treatment or vaccine development.

The negative regulation of retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) signaling pathway in fish

At each stage of innate immune response, there are stimulatory and inhibitory signals that modulate the strength and character of the response. RIG-I-like receptor (RLR) signaling pathway plays pivotal roles in antiviral innate immune response. Recent studies have revealed the molecular mechanisms that viral infection leads to the activation of RLRs-mediated downstream signaling cascades and the production of type I interferons (IFNs). However, antiviral immune responses must be tightly regulated in order to prevent detrimental type I IFNs production. Previous reviews have highlighted negative regulation of RLR signaling pathway, which mainly target to directly regulate RIG-I, MDA5, MAVS and TBK1 function in mammals. In this review, we summarize recent advances in our understanding of negative regulators of RLR signaling pathway in teleost, with specific focus on piscine and viral regulatory mechanisms that directly or indirectly inhibit the function of RIG-I, MDA5, LGP2, MAVS, TRAF3, TBK1, IRF3 and IRF7 both in the steady state or upon viral infection. We also further discuss important directions for future studies, especially for non-coding RNAs and post-translational modifications via fish specific TRIM proteins. The knowledge of negative regulators of RLR signaling pathway in teleost will shed new light on the critical information for potential therapeutic purposes.

Oncogenic Potential of the Dual-Function Protein MEX3A

MEX3A belongs to the MEX3 (Muscle EXcess) protein family consisting of four members (MEX3A-D) in humans. Characteristic for MEX3 proteins is their domain structure with 2 HNRNPK homology (KH) domains mediating RNA binding and a C-terminal really interesting new gene (RING) domain that harbors E3 ligase function. In agreement with their domain composition, MEX3 proteins were reported to modulate both RNA fate and protein ubiquitination. MEX3 paralogs exhibit an oncofetal expression pattern, they are severely downregulated postnatally, and re-expression is observed in various malignancies. Enforced expression of MEX3 proteins in various cancers correlates with poor prognosis, emphasizing their oncogenic potential. The latter is supported by MEX3A's impact on proliferation, self-renewal as well as migration of tumor cells in vitro and tumor growth in xenograft studies.

DDAH2 suppresses RLR-MAVS-mediated innate antiviral immunity by stimulating nitric oxide-activated, Drp1-induced mitochondrial fission

The RIG-I-like receptor (RLR) signaling pathway is pivotal for innate immunity against invading viruses, and dysregulation of this molecular cascade has been linked to various diseases. Here, we identified dimethylarginine dimethylaminohydrolase 2 (DDAH2) as a potent regulator of the RLR-mediated antiviral response in human and mouse. Overexpression of DDAH2 attenuated RLR signaling, whereas loss of DDAH2 function enhanced RLR signaling and suppressed viral replication ex vivo and in mice. Upon viral infection, DDAH2 relocated to mitochondria, where it induced the production of nitric oxide (NO) and the activation of dynamin-related protein 1 (Drp1), which promoted mitochondrial fission and blocked the activation of innate immune responses mediated by mitochondrial antiviral signaling (MAVS). TANK-binding kinase 1 (TBK1), a kinase downstream of MAVS, inhibited DDAH2 by phosphorylating DDAH2 at multiple sites. Our study thus identifies a reciprocal inhibitory loop between the DDAH2-NO cascade and the RLR signaling pathway that fine-tunes the antiviral immune response.

Tissue comparison of transcriptional response to acute acidification stress of barramundi Lates calcarifer in coastal and estuarine areas

In order to explore the common and unique physiological changes in tissues of juvenile barramundi Lates calcarifer in acidified water environment, RNA sequence analysis was used to analyze the molecular responses of liver, head kidney, and gill of juvenile barramundi in pH 7.4 and pH 8.1 seawater environment. The number of differential expression genes identified in liver, head kidney and gill were 860, 388 and 1792, respectively. Through functional enrichment analysis, the differential expression genes common to the three tissues were all related to immunity. Among the unique differential genes in the liver, pathways related to digestion, endocrine, and metabolism were enriched. Among the unique differential expression genes in gill, pathways related to genetic information processing, immunity and metabolism were enriched. The findings of the present study uncover the transcriptional changes in fish correspond to environmental pH change, and provide a better understanding on the biological process at molecular level to environmental pH adapting. This work highlights that assessments for the potential of estuarine fishes to cope with environmental pH change to develop the future conservation strategies.

Encephalomyocarditis Virus Abrogates the Interferon Beta Signaling Pathway via Its Structural Protein VP2

Type I interferon (IFN)-mediated antiviral responses are critical for modulating host-virus responses, and indeed, viruses have evolved strategies to antagonize this pathway. Encephalomyocarditis virus (EMCV) is an important zoonotic pathogen, which causes myocarditis, encephalitis, neurological disease, reproductive disorders, and diabetes in pigs. This study aims to understand how EMCV interacts with the IFN pathway. EMCV circumvents the type I IFN response by expressing proteins that antagonize cellular innate immunity. Here, we show that EMCV VP2 is a negative regulator of the IFN-β pathway. This occurs via the degradation of the MDA5-mediated cytoplasmic double-stranded RNA (dsRNA) antiviral sensing RIG-I-like receptor (RLR) pathway. We show that structural protein VP2 of EMCV interacts with MDA5, MAVS, and TBK1 through its C terminus. In addition, we found that EMCV VP2 could significantly degrade RLRs by the proteasomal and lysosomal pathways. For the first time, EMCV VP2 was shown to play an important role in EMCV evasion of the type I IFN signaling pathway. This study expands our understanding that EMCV utilizes its capsid protein VP2 to evade the host antiviral response.IMPORTANCE Encephalomyocarditis virus is an important pathogen that can cause encephalitis, myocarditis, neurological diseases, and reproductive disorders. It also causes huge economic losses for the swine industry worldwide. Innate immunity plays an important role in defending the host from pathogen infection. Understanding pathogen microorganisms evading the host immune system is of great importance. Currently, whether EMCV evades cytosolic RNA sensing and signaling is still poorly understood. In the present study, we found that viral protein VP2 antagonized the RLR signaling pathway by degrading MDA5, MAVS, and TBK1 protein expression to facilitate viral replication in HEK293 cells. The findings in this study identify a new mechanism for EMCV evading the host's innate immune response, which provide new insights into the virus-host interaction and help develop new antiviral approaches against EMCV.

A novel role of Zebrafish TMEM33 in negative regulation of interferon production by two distinct mechanisms

The transmembrane protein 33 (TMEM33) was originally identified as an endoplasmic reticulum (ER) protein that influences the tubular structure of the ER and modulates intracellular calcium homeostasis. However, the role of TMEM33 in antiviral immunity in vertebrates has not been elucidated. In this article, we demonstrate that zebrafish TMEM33 is a negative regulator of virus-triggered interferon (IFN) induction via two mechanisms: mitochondrial antiviral signaling protein (MAVS) ubiquitination and a decrease in the kinase activity of TANK binding kinase 1 (TBK1). Upon stimulation with viral components, tmem33 was remarkably upregulated in the zebrafish liver cell line. The IFNφ1 promoter (IFNφ1pro) activity and mRNA level induced by retinoic acid-inducible gene (RIG)-I-like receptors (RLRs) were significantly inhibited by TMEM33. Knockdown of TMEM33 increased host ifn transcription. Subsequently, we found that TMEM33 was colocalized in the ER and interacted with the RLR cascades, whereas MAVS was degraded by TMEM33 during the K48-linked ubiquitination. On the other hand, TMEM33 reduced the phosphorylation of mediator of IFN regulatory factor 3 (IRF3) activation (MITA)/IRF3 by acting as a decoy substrate of TBK1, which was also phosphorylated. A functional domain assay revealed that the N-terminal transmembrane domain 1 (TM1) and TM2 regions of TMEM33 were necessary for IFN suppression. Finally, TMEM33 significantly attenuated the host cellular antiviral capacity by blocking the IFN response. Taken together, our findings provide insight into the different mechanisms employed by TMEM33 in cellular IFN-mediated antiviral process.

LncRNAs and Immunity: Coding the Immune System with Noncoding Oligonucleotides

Long noncoding RNAs (lncRNAs) represent key regulators of gene transcription during the inflammatory response. Recent findings showed lncRNAs to be dysregulated in human diseases, such as inflammatory bowel disease, diabetes, allergies, asthma, and cancer. These noncoding RNAs are crucial for immune mechanism, as they are involved in differentiation, cell migration and in the production of inflammatory mediators through regulating protein–protein interactions or their ability to assemble with RNA and DNA. The last interaction can occur in cis or trans and is responsible for all the possible lncRNAs biological effects. Our proposal is to provide an overview on lncRNAs roles and functions related to immunity and immune mediated diseases, since these elucidations could be beneficial to untangle the complex bond between them.

Dual Effects of Let-7b in the Early Stage of Hepatitis C Virus Infection

MicroRNA let-7b expression is induced by infection of hepatitis C virus (HCV) and is involved in the regulation of HCV replication by directly targeting the HCV genome. The current study demonstrated that let-7b directly targets negative regulators of type I interferon (IFN) signaling thereby limiting HCV replication in the early stage of HCV infection. Let-7b-regulated genes which are involved in host cellular responses to HCV infection were unveiled by microarray profiling and bioinformatic analyses, followed by various molecular and cellular assays using Huh7 cells expressing wild-type (WT) or the seed region-mutated let-7b. Let-7b targeted the cytokine signaling 1 (SOCS1) protein, a negative regulator of JAK/STAT signaling, which then enhanced STAT1-Y701 phosphorylation leading to increased expression of the downstream interferon-stimulated genes (ISGs). Let-7b augmented retinoic acid-inducible gene I (RIG-I) signaling, but not MDA5, to phosphorylate and nuclear translocate IRF3 leading to increased expression of IFN-β. Let-7b directly targeted the ATG12 and IκB kinase alpha (IKKα) transcripts and reduced the interaction of the ATG5-ATG12 conjugate and RIG-I leading to increased expression of IFN, which may further stimulate JAK/STAT signaling. Let-7b induced by HCV infection elicits dual effects on IFN expression and signaling, along with targeting the coding sequences of NS5B and 5' UTR of the HCV genome, and limits HCV RNA accumulation in the early stage of HCV infection. Controlling let-7b expression is thereby crucial in the intervention of HCV infection.IMPORTANCE HCV is a leading cause of liver disease, with an estimated 71 million people infected worldwide. During HCV infection, type I interferon (IFN) signaling displays potent antiviral and immunomodulatory effects. Host factors, including microRNAs (miRNAs), play a role in upregulating IFN signaling to limit HCV replication. Let-7b is a liver-abundant miRNA that is induced by HCV infection and targets the HCV genome to suppress HCV RNA accumulation. In this study, we demonstrated that let-7b, as a positive regulator of type I IFN signaling, plays dual roles against HCV replication by increasing the expression of IFN and interferon-sensitive response element (ISRE)-driven interferon-stimulated genes (ISGs) in the early stage of HCV infection. This study sheds new insight into understanding the role of let-7b in combatting HCV infection. Clarifying IFN signaling regulated by miRNA during the early phase of HCV infection may help researchers understand the initial defense mechanisms to other RNA viruses.

Interactions of Viral Proteins from Pathogenic and Low or Non-Pathogenic Orthohantaviruses with Human Type I Interferon Signaling

Rodent-borne orthohantaviruses are asymptomatic in their natural reservoir, but they can cause severe diseases in humans. Although an exacerbated immune response relates to hantaviral pathologies, orthohantaviruses have to antagonize the antiviral interferon (IFN) response to successfully propagate in infected cells. We studied interactions of structural and nonstructural (NSs) proteins of pathogenic Puumala (PUUV), low-pathogenic Tula (TULV), and non-pathogenic Prospect Hill (PHV) viruses, with human type I and III IFN (IFN-I and IFN-III) pathways. The NSs proteins of all three viruses inhibited the RIG-I-activated IFNβ promoter, while only the glycoprotein precursor (GPC) of PUUV, or its cleavage product Gn/Gc, and the nucleocapsid (N) of TULV inhibited it. Moreover, the GPC of both PUUV and TULV antagonized the promoter of IFN-stimulated responsive elements (ISRE). Different viral proteins could thus contribute to inhibition of IFNβ response in a viral context. While PUUV and TULV strains replicated similarly, whether expressing entire or truncated NSs proteins, only PUUV encoding a wild type NSs protein led to late IFN expression and activation of IFN-stimulated genes (ISG). This, together with the identification of particular domains of NSs proteins and different biological processes that are associated with cellular proteins in complex with NSs proteins, suggested that the activation of IFN-I is probably not the only antiviral pathway to be counteracted by orthohantaviruses and that NSs proteins could have multiple inhibitory functions.

Control of IFN-I responses by the aminopeptidase IRAP in neonatal C57BL/6 alveolar macrophages during RSV infection

Respiratory Syncytial Virus (RSV) is the major cause of lower respiratory tract infection in infants, in whom, the sensing of RSV by innate immune receptors and its regulation are still poorly described. However, the severe bronchiolitis following RSV infection in neonates has been associated with a defect in type I interferons (IFN-I) production, a cytokine produced mainly by alveolar macrophages (AMs) upon RSV infection in adults. In the present study, neonatal C57BL/6 AMs mobilized very weakly the IFN-I pathway upon RSV infection in vitro and failed to restrain virus replication. However, IFN-I productions by neonatal AMs were substantially increased by the deletion of Insulin-Responsive AminoPeptidase (IRAP), a protein previously involved in the regulation of IFN-I production by dendritic cells. Moreover, neonatal IRAP^KO AMs showed a higher expression of IFN-stimulated genes than their wild-type C57BL/6 counterpart. Interestingly, depletion of IRAP did not affect adult AM responses. Finally, we demonstrated that newborn IRAP^KO mice infected with RSV had more IFN-I in their lungs and eliminated the virus more efficiently than WT neonates. Taken together, early-life susceptibility to RSV infection may be related to an original age-dependent suppressive function of IRAP on the IFN-I driven-antiviral responses in neonatal AMs.

Genomic variations and signatures of selection in Wuhua yellow chicken

Wuhua yellow chicken (WHYC) is an important traditional yellow-feathered chicken from China, which is characterized by its white tail feathers, white flight feathers, and strong disease resistance. However, the genomic basis of these unique traits associated with WHYC is poorly understood. In this study, whole-genome resequencing was performed with an average coverage of 20.77-fold to investigate heritable variation and identify selection signals in WHYC. Reads were mapped onto the chicken reference genome (Galgal5) with a coverage of 85.95%. After quality control, 11,953,471 single nucleotide polymorphisms and 1,069,574 insertion/deletions were obtained. In addition, 41,408 structural variants and 33,278 copy number variants were found. Comparative genomic analysis of WHYC and other yellow-feathered chicken breeds showed that selected regions were enriched in genes involved in transport and catabolism, immune system, infectious diseases, signal transduction, and signaling molecules and interactions. Several genes associated with disease resistance were also identified, including IFNA, IFNB, CD86, IL18, IL11RA, VEGFC, and ATG10. Furthermore, our results suggest that PMEL and TYRP1 may contribute to the white feather coloring in WHYC. These findings can improve our understanding of the genetic characteristics of WHYC and may contribute to future breed improvement.

The innate immune response in Zika virus infection

Zika virus (ZIKV; Flaviviridae, Flavivirus) was discovered in 1947 in Uganda, Africa, from the serum of a sentinel Rhesus monkey (Macaca mulatta). It is an enveloped, positive-sense, single-stranded RNA virus, which encodes a single polyprotein that is cleaved into 10 individual proteins. In 2015, the Zika-epidemic in Brazil was marked mainly by the exponential growth of microcephaly cases and other congenital defects. With regard to host-pathogen relationships, understanding the role of the immune response in the pathogenesis ZIKV infection is challenging. The innate immune response is the first-line immunological defence, in which pathogen-associated molecular patterns are recognized by pattern-recognition receptors that trigger macrophages, dendritic cells, natural killer cells and endothelial cells to produce several mediators, which modulate viral replication and immune evasion. In this review, we have summarized current knowledge on the innate immune response against ZIKV.

A dissection of SARS‑CoV2 with clinical implications (Review)

We are being confronted with the most consequential pandemic since the Spanish flu of 1918‑1920 to the extent that never before have 4 billion people quarantined simultaneously; to address this global challenge we bring to the forefront the options for medical treatment and summarize SARS‑CoV2 structure and functions, immune responses and known treatments. Based on literature and our own experience we propose new interventions, including the use of amiodarone, simvastatin, pioglitazone and curcumin. In mild infections (sore throat, cough) we advocate prompt local treatment for the naso‑pharynx (inhalations; aerosols; nebulizers); for moderate to severe infections we propose a tried‑and‑true treatment: the combination of arginine and ascorbate, administered orally or intravenously. The material is organized in three sections: i) Clinical aspects of COVID‑19; acute respiratory distress syndrome (ARDS); known treatments; ii) Structure and functions of SARS‑CoV2 and proposed antiviral drugs; iii) The combination of arginine‑ascorbate.

Exploration of Long Non-coding RNAs and Circular RNAs in Porcine Milk Exosomes

RNA in milk exosomes can be absorbed in the mammalian intestinal tract and function in gene expression regulations. Our previous work demonstrated that porcine milk exosomes (PME) contain large amounts of miRNAs and mRNAs. Increasing evidence suggests that long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) are of particular interest, given their key role in diverse biological processes of animals. However, the expression profiles and the potential functions of lncRNAs and circRNAs in PME are still unknown. In the present study, we isolated PME by ultracentrifugation and performed a comprehensive analysis of lncRNA and circRNA in PME by using RNA sequencing. As a result, 2,466 novel lncRNAs, 809 annotated lncRNAs, and 61 circRNAs were identified in PME. The lncRNAs shared similar characteristics with other mammals in terms of length, exon number, and open reading frames. However, lncRNAs showed a higher level compared with mRNAs. Eight lncRNAs and five circRNAs in PME were selected for PCR identification. A functional enrichment analysis on the target genes of lncRNAs indicated that these genes were involved in cellular macromolecule metabolic, RNA metabolic, and immune processes. The circRNAs host genes were enriched in nucleic acid binding and adherence junction. We also evaluated the potential interaction targets between miRNAs and PME lncRNAs or circRNAs, and the results showed that the PME lncRNAs and the circRNAs have a high density of miRNA target sites. The top 20 highly expressed lncRNAs were found to interact with the proliferation-related miRNAs, and the circRNAs potentially targeted many miRNAs that are associated with the intestinal barrier. This study is the first to provide a resource for lncRNA and circRNA research of porcine milk. Moreover, the potential interaction between lncRNA/circRNA and miRNA is revealed. The present study expands our knowledge of non-coding RNAs in milk, and additional research is necessary to confirm their exactly physiological functions.

Influenza PB1-F2 Inhibits Avian MAVS Signaling

RIG-I plays an essential role in the duck innate immune response to influenza infection. RIG-I engages the critical adaptor protein mitochondrial antiviral signaling (MAVS) to activate the downstream signaling pathway. The influenza A virus non-structural protein PB1-F2 interacts with MAVS in human cells to inhibit interferon production. As duck and human MAVS share only 28% amino acid similarity, it is not known whether the influenza virus can similarly inhibit MAVS signaling in avian cells. Using confocal microscopy we show that MAVS and the constitutively active N-terminal end of duck RIG-I (2CARD) co-localize in DF-1 cells, and duck MAVS is pulled down with GST-2CARD. We establish that either GST-2CARD, or duck MAVS can initiate innate signaling in chicken cells and their co-transfection augments interferon-beta promoter activity. Demonstrating the limits of cross-species interactions, duck RIG-I 2CARD initiates MAVS signaling in chicken cells, but works poorly in human cells. The D122A mutation of human 2CARD abrogates signaling by affecting MAVS engagement, and the reciprocal A120D mutation in duck 2CARD improves signaling in human cells. We show mitochondrial localization of PB1-F2 from influenza A virus strain A/Puerto Rico/8/1934 (H1N1; PR8), and its co-localization and co-immunoprecipitation with duck MAVS. PB1-F2 inhibits interferon-beta promoter activity induced by overexpression of either duck RIG-I 2CARD, full-length duck RIG-I, or duck MAVS. Finally, we show that the effect of PB1-F2 on mitochondria abrogates TRIM25-mediated ubiquitination of RIG-I CARD in both human and avian cells, while an NS1 variant from the PR8 influenza virus strain does not.

Germline Genetic Risk Variants for Progressive Multifocal Leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a rare demyelinating disorder of the brain caused by reactivation of the JC virus (JCV), a polyomavirus that infects at least 60% of the population but is asymptomatic or results in benign symptoms in most people. PML occurs as a secondary disease in a variety of disorders or as a serious adverse event from immunosuppressant agents, but is mainly found in three groups: HIV-infected patients, patients with hematological malignancies, or multiple sclerosis (MS) patients on the immunosuppressant therapy natalizumab. It is severely debilitating and is deadly in ~50% HIV cases, ~90% of hematological malignancy cases, and ~24% of MS-natalizumab cases. A PML risk prediction test would have clinical utility in all at risk patient groups but would be particularly beneficial in patients considering therapy with immunosuppressant agents known to cause PML, such as natalizumab, rituximab, and others. While a JC antibody test is currently used in the clinical decision process for natalizumab, it is suboptimal because of its low specificity and requirement to periodically retest patients for seroconversion or to assess if a patient's JCV index has increased. Whereas a high specificity genetic risk prediction test comprising host genetic risk variants (i.e., germline variants occurring at higher frequency in PML patients compared to the general population) could be administered one time to provide clinicians with additional risk prediction information that is independent of JCV serostatus. Prior PML case reports support the hypothesis that PML risk is greater in patients with a genetically caused immunodeficiency disorder. To identify germline PML risk variants, we performed exome sequencing on 185 PML cases (70 in a discovery cohort and 115 in a replication cohort) and used the gnomAD variant database for interpretation. Our study yielded 19 rare variants (maximum allele frequency of 0.02 in gnomAD ethnically matched populations) that impact 17 immune function genes (10 are known to cause inborn errors of immunity). Modeling of these variants in a PML genetic risk test for MS patients considering natalizumab treatment indicates that at least a quarter of PML cases may be preventable.

Barrier-to-Autointegration Factor 1 Protects against a Basal cGAS-STING Response

Although the pathogen recognition receptor pathways that activate cell-intrinsic antiviral responses are well delineated, less is known about how the host regulates this response to prevent sustained signaling and possible immune-mediated damage. Using a genome-wide CRISPR-Cas9 screening approach to identify host factors that modulate interferon-stimulated gene (ISG) expression, we identified the DNA binding protein Barrier-to-autointegration factor 1 (Banf1), a previously described inhibitor of retrovirus integration, as a modulator of basal cell-intrinsic immunity. Ablation of Banf1 by gene editing resulted in chromatin activation near host defense genes with associated increased expression of ISGs, including Oas2, Rsad2 (viperin), Ifit1, and ISG15 The phenotype in Banf1-deficient cells occurred through a cGAS-, STING-, and IRF3-dependent signaling axis, was associated with reduced infection of RNA and DNA viruses, and was reversed in Banf1 complemented cells. Confocal microscopy and biochemical studies revealed that a loss of Banf1 expression resulted in higher level of cytosolic double-stranded DNA at baseline. Our study identifies an undescribed role for Banf1 in regulating the levels of cytoplasmic DNA and cGAS-dependent ISG homeostasis and suggests possible therapeutic directions for promoting or inhibiting cell-intrinsic innate immune responses.IMPORTANCE Although the interferon (IFN) signaling pathway is a key host mechanism to restrict infection of a diverse range of viral pathogens, its unrestrained activity either at baseline or in the context of an immune response can result in host cell damage and injury. Here, we used a genome-wide CRISPR-Cas9 screen and identified the DNA binding protein Barrier-to-autointegration factor 1 (Banf1) as a modulator of basal cell-intrinsic immunity. A loss of Banf1 expression resulted in higher level of cytosolic double-stranded DNA at baseline, which triggered IFN-stimulated gene expression via a cGAS-STING-IRF3 axis that did not require type I IFN or STAT1 signaling. Our experiments define a regulatory network in which Banf1 limits basal inflammation by preventing self DNA accumulation in the cytosol.

The Japanese Encephalitis Virus NS1' Protein Inhibits Type I IFN Production by Targeting MAVS

Japanese encephalitis virus (JEV) is a mosquito-borne Flavivirus that causes severe neurologic disease in humans. NS1' is a NS1-related protein only reported in the Japanese encephalitis serogroup members of Flavivirus It is produced through programmed -1 ribosomal frameshift in NS2A. Our previous study demonstrated that JEV NS1' could antagonize type I IFN (IFN-I) production, but the mechanism is still unclear. In the current study, we found that JEV NS1' inhibits the expression of MAVS, and knockdown of MAVS hampers inhibition of IFN-β induction by NS1', suggesting that JEV NS1' inhibits IFN-I production by targeting MAVS. This finding is further supported by the result of the in vivo assay that showed the similar mortality caused by NS1'-deficient virus and its wild type virus in MAVS-deficient mice. Based on our previous sequencing results of noncoding RNA in JEV-infected cells, microRNA-22 (miR-22) was identified to be a key regulator for MAVS expression during JEV infection. Furthermore, we demonstrated that JEV NS1' could induce the expression of miR-22 by increasing the binding of transcriptional factors, CREB and c-Rel, to the promoter elements of miR-22. Taken together, our results reveal a novel mechanism by which JEV NS1' antagonizes host MAVS by regulating miR-22, thereby inhibiting the IFN-I production and facilitating viral replication.

Interactome networks between the human respiratory syncytial virus (HRSV), the human metapneumovirus (ΗMPV), and their host: In silico investigation and comparative functional enrichment analysis

BACKGROUND AND OBJECTIVES

Human respiratory syncytial virus (HRSV) and human metapneumovirus (HMPV) are leading causes of upper and lower respiratory tract infections in non-immunocompetent subjects, yet the mechanisms by which they induce their pathogenicity differ significantly and remain elusive. In this study we aimed at identifying the gene interaction networks between the HRSV, HMPV respiratory pathogens and their host along with the different cell-signaling pathways associated with the above interactomes.

MATERIALS AND METHODS

The Viruses STRING database (http://viruses.string-db.org/) was used for the identification of the host-viruses interaction networks. The two lists of the predicted functional partners were entered in the FunRich tool (http://www.funrich.org) for the construction of the Venn diagram and the comparative Funcional Enrichment Analysis (FEA) with respect to biological pathways. The sets of the common and unique human genes identified in the two networks were also analyzed. The computational predictions regarding the shared human genes in the host-HRSV and the host-HMPV interactomes were further evaluated via the analysis of the GSE111732 dataset. miRNA transcriptomics data were mapped to gene targets using the miRNomics pipeline of the GeneTrail2 database (https://genetrail2.bioinf.uni-sb.de/).

RESULTS

Eleven out of twenty predicted human genes were common in the two interactomes (TLR4, SOCS3, SFXN1, AKT1, SFXN3, LY96, SFXN2, SOCS7, CISH, SOCS6, SOCS1). FEA of these common genes identified the kit receptor and the GH receptor signaling pathways as the most significantly enriched annotations. The remaining nine genes of the host-HRSV and the host-HMPV interaction networks were the IFIH1, DDX58, NCL, IRF3, STAT2, HSPA4, CD209, KLF6, CHKA and the MYD88, SOCS4, SOCS2, SOCS5 AKT2, AKT3, SFXN4, SFXN5 and TLR3 respectively. Distinct cell-signaling pathways were enriched per interactome. The comparative FEA highlighted the association of the host-HRSV functional partners with the negative regulation of RIG-I/MDA5 signaling. The analysis with respect to miRNAs mapping to gene targets of the GSE111732 dataset indicated that nine out of the eleven common host genes are either enriched or depleted in the sample sets (HRSV or HMPV infected) as compared with the reference set (non-infected), although with no significant scores.

CONCLUSIONS

We have identified both shared and unique host genes as members of the HRSV and HMPV interaction networks. The disparate human genes likely contribute to distinct responses in airway epithelial cells.