The Immune Response of OAS1, IRF9, and IFI6 Genes in the Pathogenesis of COVID-19.

COVID-19 is characterized by a wide range of clinical manifestations, where aging, underlying diseases, and genetic background are related to worse outcomes. In the present study, the differential expression of seven genes related to immunity, IRF9, CCL5, IFI6, TGFB1, IL1B, OAS1, and TFRC, was analyzed in individuals with COVID-19 diagnoses of different disease severities. Two-step RT-qPCR was performed to determine the relative gene expression in whole-blood samples from 160 individuals. The expression of OAS1 (p < 0.05) and IFI6 (p < 0.05) was higher in moderate hospitalized cases than in severe ones. Increased gene expression of OAS1 (OR = 0.64, CI = 0.52-0.79; p = 0.001), IRF9 (OR = 0.581, CI = 0.43-0.79; p = 0.001), and IFI6 (OR = 0.544, CI = 0.39-0.69; p < 0.001) was associated with a lower risk of requiring IMV. Moreover, TGFB1 (OR = 0.646, CI = 0.50-0.83; p = 0.001), CCL5 (OR = 0.57, CI = 0.39-0.83; p = 0.003), IRF9 (OR = 0.80, CI = 0.653-0.979; p = 0.03), and IFI6 (OR = 0.827, CI = 0.69-0.991; p = 0.039) expression was associated with patient survival. In conclusion, the relevance of OAS1, IRF9, and IFI6 in controlling the viral infection was confirmed.

Proximal protein landscapes of the type I interferon signaling cascade reveal negative regulation by PJA2.

Deciphering the intricate dynamic events governing type I interferon (IFN) signaling is critical to unravel key regulatory mechanisms in host antiviral defense. Here, we leverage TurboID-based proximity labeling coupled with affinity purification-mass spectrometry to comprehensively map the proximal human proteomes of all seven canonical type I IFN signaling cascade members under basal and IFN-stimulated conditions. This uncovers a network of 103 high-confidence proteins in close proximity to the core members IFNAR1, IFNAR2, JAK1, TYK2, STAT1, STAT2, and IRF9, and validates several known constitutive protein assemblies, while also revealing novel stimulus-dependent and -independent associations between key signaling molecules. Functional screening further identifies PJA2 as a negative regulator of IFN signaling via its E3 ubiquitin ligase activity. Mechanistically, PJA2 interacts with TYK2 and JAK1, promotes their non-degradative ubiquitination, and limits the activating phosphorylation of TYK2 thereby restraining downstream STAT signaling. Our high-resolution proximal protein landscapes provide global insights into the type I IFN signaling network, and serve as a valuable resource for future exploration of its functional complexities.

JAK-STAT signaling maintains homeostasis in T cells and macrophages.

Immune cells need to sustain a state of constant alertness over a lifetime. Yet, little is known about the regulatory processes that control the fluent and fragile balance that is called homeostasis. Here we demonstrate that JAK-STAT signaling, beyond its role in immune responses, is a major regulator of immune cell homeostasis. We investigated JAK-STAT-mediated transcription and chromatin accessibility across 12 mouse models, including knockouts of all STAT transcription factors and of the TYK2 kinase. Baseline JAK-STAT signaling was detected in CD8+ T cells and macrophages of unperturbed mice-but abrogated in the knockouts and in unstimulated immune cells deprived of their normal tissue context. We observed diverse gene-regulatory programs, including effects of STAT2 and IRF9 that were independent of STAT1. In summary, our large-scale dataset and integrative analysis of JAK-STAT mutant and wild-type mice uncovered a crucial role of JAK-STAT signaling in unstimulated immune cells, where it contributes to a poised epigenetic and transcriptional state and helps prepare these cells for rapid response to immune stimuli.

Two IFNa3s mediate the regulation of IRF9 in the process of infection with Streptococcus iniae in yellowfin seabream, Acanthopagrus latus (Hottuyn, 1782).

IRF9 can play an antibacterial role by regulating the type I interferon (IFN) pathway. Streptococcus iniae can cause many deaths of yellowfin seabream, Acanthopagrus latus in pond farming. Nevertheless, the regulatory mechanism of type I IFN signalling by A. latus IRF9 (AlIRF9) against S. iniae remains elucidated. In our study, AlIRF9 has a total cDNA length of 3200 bp and contains a 1311 bp ORF encoding a presumed 436 amino acids (aa). The genomic DNA sequence of AlIRF9 has nine exons and eight introns, and AlIRF9 was expressed in various tissues, containing the stomach, spleen, brain, skin, and liver, among which the highest expression was in the spleen. Moreover, AlIRF9 transcriptions in the spleen, liver, kidney, and brain were increased by S. iniae infection. By overexpression of AlIRF9, AlIRF9 is shown as a whole-cell distribution, mainly concentrated in the nucleus. Moreover, the promoter fragments of -415 to +192 bp and -311 to +196 bp were regarded as core sequences from two AlIFNa3s. The point mutation analyses verified that AlIFNa3 and AlIFNa3-like transcriptions are dependent on both M3 sites with AlIRF9. In addition, AlIRF9 could greatly reduce two AlIFNa3s and interferon signalling factors expressions. These results showed that in A. latus, both AlIFNa3 and AlIFNa3-like can mediate the regulation of AlIRF9 in the process of infection with S. iniae.

Functional characterization of Malabar grouper (Epinephelus malabaricus) interferon regulatory factor 9 involved in antiviral response.

IRF9 is a crucial component in the JAK-STAT pathway. IRF9 interacts with STAT1 and STAT2 to form IFN-I-stimulated gene factor 3 (ISGF3) in response to type I IFN stimulation, which promotes ISG transcription. However, the mechanism by which IFN signaling regulates Malabar grouper (Epinephelus malabaricus) IRF9 is still elusive. Here, we explored the nd tissue-specific mRNA distribution of the MgIRF9 gene, as well as its antiviral function in E. malabaricus. MgIRF9 encodes a protein of 438 amino acids with an open reading frame of 1317 base pairs. MgIRF9 mRNA was detected in all tissues of a healthy M. grouper, with the highest concentrations in the muscle, gills, and brain. It was significantly up-regulated by nervous necrosis virus infection and poly (I:C) stimulation. The gel mobility shift test demonstrated a high-affinity association between MgIRF9 and the promoter of zfIFN in vitro. In GK cells, grouper recombinant IFN-treated samples showed a significant response in ISGs and exhibited antiviral function. Subsequently, overexpression of MgIRF9 resulted in a considerable increase in IFN and ISGs mRNA expression (ADAR1, ADAR1-Like, and ADAR2). Co-immunoprecipitation studies demonstrated that MgIRF9 and STAT2 can interact in vivo. According to the findings, M. grouper IRF9 may play a role in how IFN signaling induces ISG gene expression in grouper species.

Evolution and emergence of primate-specific interferon regulatory factor 9.

The binding of interferon (IFN) to its receptors leads to formation of IFN-stimulated gene factor 3 (ISGF3) complex that activates the transcription of cellular IFN-regulated genes. IFN regulatory factor 9 (IRF9, also called ISGF3γ or p48) is a key component of ISGF3. However, there is limited knowledge regarding the molecular evolution of IRF9 among vertebrates. In this study, we have identified the existence of the IRF9 gene in cartilaginous fish (sharks). Among primates, several isoforms unique to old world moneys and great apes are identified. These IRF9 isoforms are named as primate-specific IRF9 (PS-IRF9) to distinguish from canonical IRF9. PS-IRF9 originates from a unique exon usage and differential splicing in the IRF9 gene. Although the N-terminus are identical for all IRF9s, the C-terminal regions of the PS-IRF9 are completely different from canonical IRF9. In humans, two PS-IRF9s are identified and their RNA transcripts were detected in human primary peripheral blood mononuclear cells. In addition, human PS-IRF9 proteins were detected in human cell lines. Sharing the N-terminal exons with the canonical IRF9 proteins, PS-IRF9 is predicted to bind to the same DNA sequences as the canonical IRF9 proteins. As the C-terminal regions of IRFs are the determinants of IRF functions, PS-IRF9 may offer unique biological functions and represent a novel signaling molecule involved in the regulation of the IFN pathway in a primate-specific manner.

Phosphorylation of interferon regulatory factor 9 (IRF9).

BACKGROUND: IRF9 is a transcription factor that mediates the expression of interferon-stimulated genes (ISGs) through the Janus kinase-Signal transducer and activator of transcription (JAK-STAT) pathway. The JAK-STAT pathway is regulated through phosphorylation reactions, in which all components of the pathway are known to be phosphorylated except IRF9. The enigma surrounding IRF9 regulation by a phosphorylation event is intriguing. As IRF9 plays a major role in establishing an antiviral state in host cells, the topic of IRF9 regulation warrants deeper investigation. METHODS: Initially, total lysates of 2fTGH and U2A cells (transfected with recombinant IRF9) were filter-selected and concentrated using phosphoprotein enrichment assay. The phosphoprotein state of IRF9 was further confirmed using Phos-tag™ assay. All protein expression was determined using Western blotting. Tandem mass spectrometry was conducted on immunoprecipitated IRF9 to identify the phosphorylated amino acids. Finally, site-directed mutagenesis was performed and the effects of mutated IRF9 on relevant ISGs (i.e., USP18 and Mx1) was evaluated using qPCR. RESULTS: IRF9 is phosphorylated at S252 and S253 under IFNß-induced condition and R242 under non-induced condition. Site-directed mutagenesis of S252 and S253 to either alanine or aspartic acid has a modest effect on the upregulation of USP18 gene-a negative regulator of type I interferon (IFN) response-but not Mx1 gene. CONCLUSION: Our preliminary study shows that IRF9 is phosphorylated and possibly regulates USP18 gene expression. However, further in vivo studies are needed to determine the significance of IRF9 phosphorylation.

How cancer cells make and respond to interferon-I.

Acute exposure of cancer cells to high concentrations of type I interferon (IFN-I) drives growth arrest and apoptosis, whereas chronic exposure to low concentrations provides important prosurvival advantages. Tyrosine-phosphorylated IFN-stimulated gene (ISG) factor 3 (ISGF3) drives acute deleterious responses to IFN-I, whereas unphosphorylated (U-)ISGF3, lacking tyrosine phosphorylation, drives essential constitutive prosurvival mechanisms. Surprisingly, programmed cell death-ligand 1 (PD-L1), often expressed on the surfaces of tumor cells and well recognized for its importance in inactivating cytotoxic T cells, also has important cell-intrinsic protumor activities, including dampening acute responses to cytotoxic high levels of IFN-I and sustaining the expression of the low levels that benefit tumors. More thorough understanding of the newly recognized complex roles of IFN-I in cancer may lead to the identification of novel therapeutic strategies.

Positive selection-driven fixation of a hominin-specific amino acid mutation related to dephosphorylation in IRF9.

The arms race between humans and pathogens drives the evolution of the human genome. It is thus expected that genes from the interferon-regulatory factors family (IRFs), a critical family for anti-viral immune response, should be undergoing episodes of positive selection. Herein, we tested this hypothesis and found multiple lines of evidence for positive selection on the amino acid site Val129 (NP_006075.3:p.Ser129Val) of human IRF9. Interestingly, the ancestral reconstruction and population distribution analyses revealed that the ancestral state (Ser129) is conserved among mammals, while the derived positively selected state (Val129) was fixed before the "out-of-Africa" event ~ 500,000 years ago. The motif analysis revealed that this young amino acid (Val129) may serve as a dephosphorylation site of IRF9. Structural parallelism between homologous genes further suggested the functional effects underlying the dephosphorylation that may affect the immune activity of IRF9. This study provides a model in which a strong positive Darwinian selection drives a recent fixation of a hominin-specific amino acid leading to molecular adaptation involving dephosphorylation in an immune-responsive gene.

IRF9 and XAF1 as Diagnostic Markers of Primary Sjogren Syndrome.

Objective: Primary Sjogren syndrome (pSS) is characterized by lymphocytic infiltration of the salivary and lacrimal glands. It is a chronic systemic autoimmune disease. Genetic contributions and disturbed biological systems are the two major causes of pSS, but its etiology is unclear. This study is aimed at identifying potential pSS diagnostic markers and mechanisms at the transcriptome level. Methods: Whole blood datasets of patients with pSS were downloaded from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) were identified using the online tool, GEO2R. R software was used to perform enrichment analyses to understand the functions and enriched pathways of the DEGs. A protein-protein interaction network was constructed to identify hub genes and significant gene clusters. The least absolute shrinkage and selection operator logistic regression was used to screen pSS diagnostic markers. The expression level and diagnostic performance of the identified genes were tested using another GEO dataset. Results: A total of 221 DEGs were screened from the whole blood samples of 161 patients with pSS and 59 healthy controls. Functional enrichment analysis demonstrated that DEGs were mostly enriched in defense response to virus, response to virus, and type I interferon signaling pathway. Cytoscape identified 10 hub genes and two gene clusters. IRF9 (AUC = 0.799) and XAF1 (AUC = 0.792) were identified as pSS diagnostic markers. The expression levels of the two identified genes were validated by GSE51092. Conclusion: IRF9 and XAF1 were identified as diagnostic markers. The potential underlying molecular mechanism of pSS was explored.

Deciphering SARS CoV-2-associated pathways from RNA sequencing data of COVID-19-infected A549 cells and potential therapeutics using in silico methods.

BACKGROUND: Coronavirus (CoV) disease (COVID-19) identified in Wuhan, China, in 2019, is mainly characterized by atypical pneumonia and severe acute respiratory syndrome (SARS) and is caused by SARS CoV-2, which belongs to the Coronaviridae family. Determining the underlying disease mechanisms is central to the identification and development of COVID-19-specific drugs for effective treatment and prevention of human-to-human transmission, disease complications, and deaths. METHODS: Here, next-generation RNA sequencing (RNA Seq) data were obtained using Illumina Next Seq 500 from SARS CoV-infected A549 cells and mock-treated A549 cells from the Gene Expression Omnibus (GEO) (GSE147507), and quality control (QC) was assessed before RNA Seq analysis using CLC Genomics Workbench 20.0. Differentially expressed genes (DEGs) were imported into BioJupies to decipher COVID-19 induced signaling pathways and small molecules derived from chemical synthesis or natural sources to mimic or reverse COVID -19 specific gene signatures. In addition, iPathwayGuide was used to identify COVID-19-specific signaling pathways, as well as drugs and natural products with anti-COVID-19 potential. RESULTS: Here, we identified the potential activation of upstream regulators such as signal transducer and activator of transcription 2 (STAT2), interferon regulatory factor 9 (IRF9), and interferon beta (IFNß), interleukin-1 beta (IL-1ß), and interferon regulatory factor 3 (IRF3). COVID-19 infection activated key infectious disease-specific immune-related signaling pathways such as influenza A, viral protein interaction with cytokine and cytokine receptors, measles, Epstein-Barr virus infection, and IL-17 signaling pathway. Besides, we identified drugs such as prednisolone, methylprednisolone, diclofenac, compound JQ1, and natural products such as Withaferin-A and JinFuKang as candidates for further experimental validation of COVID-19 therapy. CONCLUSIONS: In conclusion, we have used the in silico next-generation knowledge discovery (NGKD) methods to discover COVID-19-associated pathways and specific therapeutics that have the potential to ameliorate the disease pathologies associated with COVID-19.

[Effects of interferon regulatory factor 9 on the biological phenotypes in PML-RARα-induced promyelocytic leukemia].

Objective: To investigate the prognostic significance of interferon regulatory factor 9 (IRF9) expression and identify its role as a potential therapeutic target in acute promyelocytic leukemia (APL) . Methods: The gene expression profile and survival data applied in the bioinformatic analysis were obtained from The Cancer Genome Atlas and Beat acute myeloid leukemia (AML) cohorts. A dox-induced lentiviral system was used to induce the expression of PML-RARα (PR) in U937 cells, and the expression level of IRF9 in U937 cells treated with or without ATRA was examined. We then induced the expression of IRF9 in NB4, a promyelocytic leukemia cell line. In vitro studies focused on leukemic phenotypes triggered by IRF9 expression. Results: ①Bioinformatic analysis of the public database demonstrated the lowest expression of IRF9 in APL among all subtypes of AML, with lower expression associated with worse prognosis. ②We successfully established a PR-expression-inducible U937 cell line and found that IRF9 was downregulated by the PR fusion gene in APL, with undetectable expression in NB4 promyelocytic cells. ③An IRF9-inducible NB4 cell line was successfully established. The inducible expression of IRF9 promoted the differentiation of NB4 cells and had a synergistic effect with lower doses of ATRA. In addition, the inducible expression of IRF9 significantly reduced the colony formation capacity of NB4 cells. Conclusion: In this study, we found that the inducible expression of PR downregulates IRF9 and can be reversed by ATRA, suggesting a specific regulatory relationship between IRF9 and the PR fusion gene. The induction of IRF9 expression in NB4 cells can promote cell differentiation as well as reduce the colony forming ability of leukemia cells, implying an anti-leukemia effect for IRF9, which lays a biological foundation for IRF9 as a potential target for the treatment of APL.

Aberrant inflammatory responses to type I interferon in STAT2 or IRF9 deficiency.

BACKGROUND: Inflammatory phenomena such as hyperinflammation or hemophagocytic lymphohistiocytosis are a frequent yet paradoxical accompaniment to virus susceptibility in patients with impairment of type I interferon (IFN-I) signaling caused by deficiency of signal transducer and activator of transcription 2 (STAT2) or IFN regulatory factor 9 (IRF9). OBJECTIVE: We hypothesized that altered and/or prolonged IFN-I signaling contributes to inflammatory complications in these patients. METHODS: We explored the signaling kinetics and residual transcriptional responses of IFN-stimulated primary cells from individuals with complete loss of one of STAT1, STAT2, or IRF9 as well as gene-edited induced pluripotent stem cell-derived macrophages. RESULTS: Deficiency of any IFN-stimulated gene factor 3 component suppressed but did not abrogate IFN-I receptor signaling, which was abnormally prolonged, in keeping with insufficient induction of negative regulators such as ubiquitin-specific peptidase 18 (USP18). In cells lacking either STAT2 or IRF9, this late transcriptional response to IFN-α2b mimicked the effect of IFN-γ. CONCLUSION: Our data suggest a model wherein the failure of negative feedback of IFN-I signaling in STAT2 and IRF9 deficiency leads to immune dysregulation. Aberrant IFN-α receptor signaling in STAT2- and IRF9-deficient cells switches the transcriptional output to a prolonged, IFN-γ-like response and likely contributes to clinically overt inflammation in these individuals.

Systematic identification of NF90 target RNAs by iCLIP analysis.

RNA-binding proteins (RBPs) interact with and determine the fate of many cellular RNAs directing numerous essential roles in cellular physiology. Nuclear Factor 90 (NF90) is an RBP encoded by the interleukin enhancer-binding factor 3 (ILF3) gene that has been found to influence RNA metabolism at several levels, including pre-RNA splicing, mRNA turnover, and translation. To systematically identify the RNAs that interact with NF90, we carried out iCLIP (individual-nucleotide resolution UV crosslinking and immunoprecipitation) analysis in the human embryonic fibroblast cell line HEK-293. Interestingly, many of the identified RNAs encoded proteins involved in the response to viral infection and RNA metabolism. We validated a subset of targets and investigated the impact of NF90 on their expression levels. Two of the top targets, IRF3 and IRF9 mRNAs, encode the proteins IRF3 and IRF9, crucial regulators of the interferon pathway involved in the SARS-CoV-2 immune response. Our results support a role for NF90 in modulating key genes implicated in the immune response and offer insight into the immunological response to the SARS-CoV-2 infection.

Monoclonal antibody-mediated neutralization of SARS-CoV-2 in an IRF9-deficient child.

We describe an unvaccinated child at risk for life-threatening COVID-19 due to an inherited deficiency of IRF9, which governs ISGF-3-dependent responses to type I and III interferons (IFN). She was admitted, with a high nasal SARS-CoV-2 load on day 1 of upper respiratory tract infection. She was viremic on day 2 and received casirivimab and imdevimab. Her clinical manifestations and viremia disappeared on days 3 and 4, respectively. Circulating SARS-CoV-2 virus induced the expression of IFN-stimulated genes in leukocytes on day 1, whereas the secretion of blood type I IFNs, which peaked on day 4, did not. Antibody-mediated SARS-CoV-2 neutralization is, therefore, sufficient to overcome a deficiency of antiviral IFNs.

Expression characteristics of interferon-stimulated genes and possible regulatory mechanisms in lupus patients using transcriptomics analyses.

BACKGROUND: Type I interferon signature is one of the most important features of systemic lupus erythematosus (SLE), which indicates an active immune response to antigen invasion. Characteristics of type I interferon-stimulated genes (ISGs) in SLE patients have not been well described thus far. METHODS: We analyzed 35,842 cells of PBMC single-cell RNA sequencing data of five SLE patients and three healthy controls. Thereafter, 178 type I ISGs among DEGs of all cell clusters were screened based on the Interferome Database and AUCell package was used for ISGs activity calculation. To determine whether common ISG features exist in PBMCs and kidneys of patients with SLE, we analyzed kidney transcriptomic data from patients with lupus nephritis (LN) from the GEO database. MRL/lpr mice model were used to verify our findings. FINDINGS: We found that monocytes, B cells, dendritic cells, and granulocytes were significantly increased in SLE patients, while subsets of T cells were significantly decreased. Neutrophils and low-density granulocytes (LDGs) exhibited the highest ISG activity. GO and pathway enrichment analyses showed that DEGs focused on leukocyte activation, cell secretion, and pathogen infection. Thirty-one common ISGs were found expressed in both PBMCs and kidneys; these ISGs were also most active in neutrophils and LDGs. Transcription factors including PLSCR1, TCF4, IRF9 and STAT1 were found to be associated to ISGs expression. Consistently, we found granulocyte infiltration in the kidneys of MRL/lpr mice. Granulocyte inhibitor Avacopan reduced granulocyte infiltration and reversed renal conditions in MRL/lpr mice. INTERPRETATION: This study shows for the first time, the use of the AUCell method to describe ISG activity of granulocytes in SLE patients. Moreover, Avacopan may serve as a granulocyte inhibitor for treatment of lupus patients in the future. FUNDING: None.

PRL-3 induces a positive signaling circuit between glycolysis and activation of STAT1/2.

Multiple myeloma (MM) is an incurable hematologic malignancy resulting from the clonal expansion of plasma cells. MM cells are interacting with components of the bone marrow microenvironment such as cytokines to survive and proliferate. Phosphatase of regenerating liver (PRL)-3, a cytokine-induced oncogenic phosphatase, is highly expressed in myeloma patients and is a mediator of metabolic reprogramming of cancer cells. To find novel pathways and genes regulated by PRL-3, we characterized the global transcriptional response to PRL-3 overexpression in two MM cell lines. We used pathway enrichment analysis to identify pathways regulated by PRL-3. We further confirmed the hits from the enrichment analysis with in vitro experiments and investigated their function. We found that PRL-3 induced expression of genes belonging to the type 1 interferon (IFN-I) signaling pathway due to activation of signal transducer and activator of transcription (STAT) 1 and STAT2. This activation was independent of autocrine IFN-I secretion. The increase in STAT1 and STAT2 did not result in any of the common consequences of increased IFN-I or STAT1 signaling in cancer. Knockdown of STAT1/2 did not affect the viability of the cells, but decreased PRL-3-induced glycolysis. Interestingly, glucose metabolism contributed to the activation of STAT1 and STAT2 and expression of IFN-I-stimulated genes in PRL-3-overexpressing cells. In summary, we describe a novel signaling circuit where the key IFN-I-activated transcription factors STAT1 and STAT2 are important drivers of the increase in glycolysis induced by PRL-3. Subsequently, increased glycolysis regulates the IFN-I-stimulated genes by augmenting the activation of STAT1/2.

Cx43 phosphorylation sites regulate pancreatic cancer metastasis.

Pancreatic ductal adenocarcinoma (PDA) is aggressive, highly metastatic and characterized by a robust desmoplasia. Connexin proteins that form gap junctions have been implicated in tumor suppression for over 30 years. Cx43, the most widely expressed connexin, regulates cell behaviors, including migration and proliferation. Thus, we hypothesized that Cx43 could regulate PDA progression. Phosphorylation of Cx43 by Casein Kinase 1 (CK1) regulates gap junction assembly. We interbred the well-established KrasLSL-G12D/+;p48Cre/+ (KC) mouse model of PDA with homozygous "knock-in" mutant Cx43 mice bearing amino acid substitution at CK1 sites (Cx43CK1A) and found profound and surprising effects on cancer progression. Crossing the Cx43CK1A mouse onto the KC background (termed KC;CxCK1A) led to significant extension of lifespan, from a median of 370 to 486 days (p = 0.03) and a decreased incidence of metastasis (p = 0.045). However, when we examined early stages of disease, we found more rapid onset of tissue remodeling in the KC;CxCK1A mouse followed by divergence to a cystic phenotype. During tumorigenesis, gap junctions are increasingly present in stromal cells of the KC mice but are absent from the KC;Cx43CK1A mice. Tail vein metastasis assays with cells derived from KC or KC;CxCK1A tumors showed that KC;CxCK1A cells could efficiently colonize the lung and downregulate Cx43 expression, arguing that inhibition of metastasis was not occurring at the distal site. Instead, stromal gap junctions, their associated signaling events or other unknown Cx43-dependent events facilitate metastatic capacity in the primary tumor.

SARS-CoV-2-Encoded MiRNAs Inhibit Host Type I Interferon Pathway and Mediate Allelic Differential Expression of Susceptible Gene.

Infection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), causing the rapid spread of coronavirus disease 2019 (COVID-19), has generated a public health crisis worldwide. The molecular mechanisms of SARS-CoV-2 infection and virus-host interactions are still unclear. In this study, we identified four unique microRNA-like small RNAs encoded by SARS-CoV-2. SCV2-miR-ORF1ab-1-3p and SCV2-miR-ORF1ab-2-5p play an important role in evasion of type I interferon response through targeting several genes in type I interferon signaling pathway. Particularly worth mentioning is that highly expressed SCV2-miR-ORF1ab-2-5p inhibits some key genes in the host innate immune response, such as IRF7, IRF9, STAT2, OAS1, and OAS2. SCV2-miR-ORF1ab-2-5p has also been found to mediate allelic differential expression of COVID-19-susceptible gene OAS1. In conclusion, these results suggest that SARS-CoV-2 uses its miRNAs to evade the type I interferon response and links the functional viral sequence to the susceptible genetic background of the host.

ADAR1 Suppresses Interferon Signaling in Gastric Cancer Cells by MicroRNA-302a-Mediated IRF9/STAT1 Regulation.

ADAR (adenosine deaminase acting on RNA) catalyzes the deamination of adenosine to generate inosine, through its binding to double-stranded RNA (dsRNA), a phenomenon known as RNA editing. One of the functions of ADAR1 is suppressing the type I interferon (IFN) response, but its mechanism in gastric cancer is not clearly understood. We analyzed changes in RNA editing and IFN signaling in ADAR1-depleted gastric cancer cells, to clarify how ADAR1 regulates IFN signaling. Interestingly, we observed a dramatic increase in the protein level of signal transducer and activator of transcription 1 (STAT1) and interferon regulatory factor 9 (IRF9) upon ADAR1 knockdown, in the absence of type I or type II IFN treatment. However, there were no changes in protein expression or localization of the mitochondrial antiviral signaling protein (MAVS) and interferon alpha and beta-receptor subunit 2 (IFNAR2), the two known mediators of IFN production. Instead, we found that miR-302a-3p binds to the untranslated region (UTR) of IRF9 and regulate its expression. The treatment of ADAR1-depleted AGS cells with an miR-302a mimic successfully restored IRF9 as well as STAT1 protein level. Hence, our results suggest that ADAR1 regulates IFN signaling in gastric cancer through the suppression of STAT1 and IRF9 via miR-302a, which is independent from the RNA editing of known IFN production pathway.