Robust expression of p27Kip1 induced by viral infection is critical for antiviral innate immunity

Functional Involvement of Signal Transducers and Activators of Transcription in the Pathogenesis of Influenza A Virus

Signal transducers and activators of transcription (STATs) function both as signal transducers and transcription regulators. STAT proteins are involved in the signaling pathways of cytokines and growth factors; thus, they participate in various life activities and play especially critical roles in antiviral immunity. Convincing evidence suggests that STATs can establish innate immune status through multiple mechanisms, efficiently eliminating pathogens. STAT1 and STAT2 can activate the antiviral status by regulating the interferon (IFN) signal. In turn, suppressor of cytokine signaling-1 (SOCS1) and SOCS3 can modulate the activation of STATs and suppress the excessive antiviral immune response. STAT3 not only regulates the IFN signal, but also transduces Interleukin-6 (IL-6) to stimulate the host antiviral response. The function of STAT4 and STAT5 is related to CD4+ T helper (Th) cells, and the specific mechanism of STAT5 remains to be studied. STAT6 mainly exerts antiviral effects by mediating IL-4 and IL-13 signaling. Here, we reviewed the recent findings regarding the critical roles of STATs in the interactions between the host and viral infection, especially influenza A virus (IAV) infection. We also discuss the molecular mechanisms underlying their functions in antiviral responses.

African swine fever virus A137R protein inhibits NF-κB activation via suppression of MyD88 signaling in PK15 and 3D4/21 cells in vitro

African swine fever (ASF) is an infectious disease with high mortality caused by African swine fever virus (ASFV), which poses a great threat to the global swine industry. ASFV has evolved multiple strategies to evade host antiviral innate immunity by perturbing inflammatory responses and interferon production. However, the molecular mechanisms underlying manipulation of inflammatory responses by ASFV proteins are not fully understood. Here, we report that A137R protein of ASFV is a key suppressor of host inflammatory responses. Ectopic expression of ASFV A137R in HEK293T cells significantly inhibited the activation of IL-8 and NF-κB promoters triggered by Sendai virus (SeV), influenza A virus (IAV), or vesicular stomatitis virus (VSV). Accordingly, forced A137R expression caused a significant decrease in the production of several inflammatory cytokines such as IL-8, IL-6 and TNF-α in the cells infected with SeV or IAV. Similar results were obtained from experiments using A137R overexpressing PK15 and 3D4/21 cells infected with SeV or VSV. Furthermore, we observed that A137R impaired the activation of MAPK and NF-κB signaling pathways, as enhanced expression of A137R significantly decreased the phosphorylation of JNK, p38 and p65 respectively upon viral infection (SeV or IAV) and IL-1β treatment. Mechanistically, we found that A137R interacted with MyD88, and dampened MyD88-mediated activation of MAPK and NF-κB signaling. Together, these findings uncover a critical role of A137R in restraining host inflammatory responses, and improve our understanding of complicated mechanisms whereby ASFV evades innate immunity.

Coinhibition of topoisomerase 1 and BRD4-mediated pause release selectively kills pancreatic cancer via readthrough transcription

Pancreatic carcinoma lacks effective therapeutic strategies resulting in poor prognosis. Transcriptional dysregulation due to alterations in KRAS and MYC affects initiation, development, and survival of this tumor type. Using patient-derived xenografts of KRAS- and MYC-driven pancreatic carcinoma, we show that coinhibition of topoisomerase 1 (TOP1) and bromodomain-containing protein 4 (BRD4) synergistically induces tumor regression by targeting promoter pause release. Comparing the nascent transcriptome with the recruitment of elongation and termination factors, we found that coinhibition of TOP1 and BRD4 disrupts recruitment of transcription termination factors. Thus, RNA polymerases transcribe downstream of genes for hundreds of kilobases leading to readthrough transcription. This occurs during replication, perturbing replisome progression and inducing DNA damage. The synergistic effect of TOP1 + BRD4 inhibition is specific to cancer cells leaving normal cells unaffected, highlighting the tumor's vulnerability to transcriptional defects. This preclinical study provides a mechanistic understanding of the benefit of combining TOP1 and BRD4 inhibitors to treat pancreatic carcinomas addicted to oncogenic drivers of transcription and replication.

Influenza A Virus-Induced circRNA circMerTK Negatively Regulates Innate Antiviral Responses

Circular RNAs (circRNAs) are an important subclass of noncoding RNAs implicated in the regulation of multiple biological processes. However, the functional involvement of circRNAs in the pathogenesis of influenza A viruses (IAVs) remains largely unknown. Here, we employed RNA sequencing (RNA-Seq) to examine the differentially expressed circRNAs in mouse lung tissues challenged or not challenged with IAV to evaluate the impact of viral infection on circRNAs in vivo. We observed that 413 circRNAs exhibited significantly altered levels following IAV infection. Among these, circMerTK, the derivative of myeloid-epithelial-reproductive tyrosine kinase (MerTK) pre-mRNA, was highly induced by IAV. Interestingly, circMerTK expression was also increased upon infection with multiple DNA and RNA viruses in human and animal cell lines, and thus it was selected for further studies. Poly(I:C) and interferon β (IFN-β) stimulated circMerTK expression, while RIG-I knockout and IFNAR1 knockout cell lines failed to elevate circMerTK levels after IAV infection, demonstrating that circMerTK is regulated by IFN signaling. Furthermore, circMerTK overexpression or silencing accelerated or impeded IAV and Sendai virus replication, respectively. Silencing circMerTK enhanced the production of type I IFNs and interferon-stimulating genes (ISGs), whereas circMerTK overexpression suppressed their expression at both the mRNA and protein levels. Notably, altering circMerTK expression had no effect on the MerTK mRNA level in cells infected or not infected with IAV, and vice versa. In addition, human circMerTK and mouse homologs functioned similarly in antiviral responses. Together, these results identify circMerTK as an enhancer of IAV replication through suppression of antiviral immunity. IMPORTANCE CircRNAs are an important class of noncoding RNAs characterized by a covalently closed circular structure. CircRNAs have been proven to impact numerous cellular processes, where they conduct specialized biological activities. In addition, circRNAs are believed to play a crucial role in regulating immune responses. Nevertheless, the functions of circRNAs in the innate immunity against IAV infection remain obscure. In this study, we employed transcriptomic analysis to investigate the alterations in circRNAs expression following IAV infection in vivo. It was found that expression of 413 circRNAs was significantly altered, of which 171 were upregulated, and 242 were downregulated following the IAV infection. Interestingly, circMerTK was identified as a positive regulator of IAV replication in both human and mouse hosts. CircMerTK was shown to influence IFN-β production and its downstream signaling, enhancing IAV replication. This finding provides new insights into the critical roles of circRNAs in regulating antiviral immunity.

miR-146a, miR-221, and miR-155 are Involved in Inflammatory Immune Response in Severe COVID-19 Patients

COVID-19 infection triggered a global public health crisis during the 2020-2022 period, and it is still evolving. This highly transmissible respiratory disease can cause mild symptoms up to severe pneumonia with potentially fatal respiratory failure. In this cross-sectional study, 41 PCR-positive patients for SARS-CoV-2 and 42 healthy controls were recruited during the first wave of the pandemic in Mexico. The plasmatic expression of five circulating miRNAs involved in inflammatory and pathological host immune responses was assessed using RT-qPCR (Reverse Transcription quantitative Polymerase Chain Reaction). Compared with controls, a significant upregulation of miR-146a, miR-155, and miR-221 was observed; miR-146a had a positive correlation with absolute neutrophil count and levels of brain natriuretic propeptide (proBNP), and miR-221 had a positive correlation with ferritin and a negative correlation with total cholesterol. We found here that CDKN1B gen is a shared target of miR-146a, miR-221-3p, and miR-155-5p, paving the way for therapeutic interventions in severe COVID-19 patients. The ROC curve built with adjusted variables (miR-146a, miR-221-3p, miR-155-5p, age, and male sex) to differentiate individuals with severe COVID-19 showed an AUC of 0.95. The dysregulation of circulating miRNAs provides new insights into the underlying immunological mechanisms, and their possible use as biomarkers to discriminate against patients with severe COVID-19. Functional analysis showed that most enriched pathways were significantly associated with processes related to cell proliferation and immune responses (innate and adaptive). Twelve of the predicted gene targets have been validated in plasma/serum, reflecting their potential use as predictive prognosis biomarkers.

MIR155HG Plays a Bivalent Role in Regulating Innate Antiviral Immunity by Encoding Long Noncoding RNA-155 and microRNA-155-5p

MIR155HG encodes a precursor RNA of microRNA-155 (miRNA-155). We previously identified this RNA also as a long noncoding RNA (lncRNA) that we call lncRNA-155. To define the functions of miRNA-155 and lncRNA-155, we generated miRNA-155 knockout (KO) mice lacking only 19 bp of the miRNA-155 core sequence without affecting the expression of lncRNA-155. Surprisingly, compared with the miRNA-155KO mice, previously generated lncRNA-155KO mice were more susceptible to both influenza virus (RNA virus) and pseudorabies virus (DNA virus) infection, as characterized by lower survival rate, higher body weight loss, and higher viral load. We found that miRNA-155-5p enhanced antiviral responses by positively regulating activation of signal transducer and activator of transcription 1 (STAT1), but the STAT1 activity differed greatly in the animals (lncRNA-155KO < miRNA-155KO < wild type). In line with this, expression levels of several critical interferon-stimulated genes (ISGs) were also significantly different (lncRNA-155KO < miRNA-155KO < wild type). We found that lncRNA-155 augmented interferon beta (IFN-β) production during the viral infection, but miRNA-155 had no significant effect on the virus-induced IFN-β expression. Furthermore, we observed that lncRNA-155 loss in mice resulted in dramatic inhibition of virus-induced activation of interferon regulatory factor 3 compared to both miRNA-155KO and wild-type (WT) animals. Moreover, lncRNA-155 still significantly suppressed the viral infection even though the miRNA-155 derived from lncRNA-155 was deleted or blocked. These results reveal that lncRNA-155 and miRNA-155 regulate antiviral responses through distinct mechanisms, indicating a bivalent role for MIR155HG in innate immunity. IMPORTANCE Here, we found that lncRNA-155KO mice lacking most of the lncRNA-155 sequences along with pre-miRNA-155, were more susceptible to influenza virus or pseudorabies virus infection than miRNA-155KO mice lacking only 19 bp of the miRNA-155 core sequence without affecting the expression of lncRNA-155, as evidenced by faster body weight loss, poorer survival, and higher viral load, suggesting an additional role of lncRNA-155 in regulating viral pathogenesis besides via processing miRNA-155. Congruously, miRNA-155-deleted lncRNA-155 significantly attenuated the viral infection. Mechanistically, we demonstrated miRNA-155-5p potentiated antiviral responses by promoting STAT1 activation but could not directly regulate the IFN-β expression. In contrast, lncRNA-155 enhanced virus-induced IFN-β production by regulating the activation of interferon regulatory factor 3. This finding reveals a bivalent role of MIR155HG in regulating antiviral responses through encoding lncRNA-155 and miRNA-155-5p and provides new insights into complicated mechanisms underlying interaction between virus and host innate immunity.

I226R Protein of African Swine Fever Virus Is a Suppressor of Innate Antiviral Responses

African swine fever is one of the most devastating swine diseases caused by African swine fever virus (ASFV). Although ASFV encodes more than 160 viral proteins, the implication of a majority of ASFV proteins in regulating host immunity is yet to be explored, and the mechanisms of immune evasion by ASFV proteins are largely unknown. Here, we report that the I226R protein of ASFV significantly suppressed innate immune responses. The ectopic expression of ASFV I226R in 293T cells significantly inhibited the activation of interferon-stimulated response element promoters triggered by Sendai virus (SeV), poly(I:C), or cyclic GMP-AMP synthase (cGAS)/STING. The I226R protein caused a significant decrease in the expression of interferons and interferon-stimulating genes in cells infected with SeV. Similar results were obtained from experiments using I226R-overexpressed PK15 and 3D4/21 cells stimulated with vesicular stomatitis virus. We observed that I226R inhibited the activation of both nuclear factor-kappa B (NF-κB) and interferon regulatory factor 3 (IRF3). Furthermore, it was shown that overexpression of I226R suppressed IRF3 activation and caused the degradation of NF-κB essential modulator (NEMO) protein. The I226R-induced NEMO degradation could be prevented by treatment with MG132, a proteasome inhibitor. Together, these results reveal that the ASFV I226R protein impairs antiviral responses, likely through multiple mechanisms including the suppression of NF-κB and IRF3 activation, to counteract innate immune responses during the viral infection.

A novel imatinib-upregulated long noncoding RNA plays a critical role in inhibition of tumor growth induced by Abl oncogenes

BACKGROUND

Dysregulation of long noncoding RNAs (lncRNAs) has been linked to various human cancers. Bcr-Abl oncogene that results from a reciprocal translocation between human chromosome 9 and 22, is associated with several hematological malignancies. However, the role of lncRNAs in Bcr-Abl-induced leukemia remains largely unexplored.

METHODS

LncRNA cDNA microarray was employed to identify key lncRNAs involved in Bcr-Abl-mediated cellular transformation. Abl-transformed cell survival and xenografted tumor growth in mice were evaluated to dissect the role of imatinib-upregulated lncRNA 1 (IUR1) in Abl-induced tumorigenesis. Primary bone marrow transformation and in vivo leukemia transplant using lncRNA-IUR1 knockout (KO) mice were further conducted to address the functional relevance of lncRNA-IUR1 in Abl-mediated leukemia. Transcriptome RNA-seq and Western blotting were performed to determine the mechanisms by which lncRNA-IUR1 regulates Bcr-Abl-induced tumorigenesis.

RESULTS

We identified lncRNA-IUR1 as a critical negative regulator of Bcr-Abl-induced tumorigenesis. LncRNA-IUR1 expressed in a very low level in Bcr-Abl-positive cells from chronic myeloid leukemia patients. Interestingly, it was significantly induced in Abl-positive leukemic cells treated by imatinib. Depletion of lncRNA-IUR1 promoted survival of Abl-transformed human leukemic cells in experiments in vitro and xenografted tumor growth in mice, whereas ectopic expression of lncRNA-IUR1 sensitized the cells to apoptosis and suppressed tumor growth. In concert, silencing murine lncRNA-IUR1 in Abl-transformed cells accelerated cell survival and the development of leukemia in mice. Furthermore, lncRNA-IUR1 deficient mice were generated, and we observed that knockout of murine lncRNA-IUR1 facilitated Bcr-Abl-mediated primary bone marrow transformation. Moreover, animal leukemia model revealed that lncRNA-IUR1 deficiency promoted Abl-transformed cell survival and development of leukemia in mice. Mechanistically, we demonstrated that lncRNA-IUR1 suppressed Bcr-Abl-induced tumorigenesis through negatively regulating STAT5-mediated GATA3 expression.

CONCLUSIONS

These findings unveil an inhibitory role of lncRNA-IUR1 in Abl-mediated cellular transformation, and provide new insights into molecular mechanisms underlying Abl-induced leukemogenesis.

Acute Infection of Viral Pathogens and Their Innate Immune Escape

Viral infections can cause rampant disease in human beings, ranging from mild to acute, that can often be fatal unless resolved. An acute viral infection is characterized by sudden or rapid onset of disease, which can be resolved quickly by robust innate immune responses exerted by the host or, instead, may kill the host. Immediately after viral infection, elements of innate immunity, such as physical barriers, various phagocytic cells, group of cytokines, interferons (IFNs), and IFN-stimulated genes, provide the first line of defense for viral clearance. Innate immunity not only plays a critical role in rapid viral clearance but can also lead to disease progression through immune-mediated host tissue injury. Although elements of antiviral innate immunity are armed to counter the viral invasion, viruses have evolved various strategies to escape host immune surveillance to establish successful infections. Understanding complex mechanisms underlying the interaction between viruses and host’s innate immune system would help develop rational treatment strategies for acute viral infectious diseases. In this review, we discuss the pathogenesis of acute infections caused by viral pathogens and highlight broad immune escape strategies exhibited by viruses.

Induction of the Antiviral Immune Response and Its Circumvention by Coronaviruses

Some coronaviruses are zoonotic viruses of human and veterinary medical importance. The novel coronavirus, severe acute respiratory symptoms coronavirus 2 (SARS-CoV-2), associated with the current global pandemic, is characterized by pneumonia, lymphopenia, and a cytokine storm in humans that has caused catastrophic impacts on public health worldwide. Coronaviruses are known for their ability to evade innate immune surveillance exerted by the host during the early phase of infection. It is important to comprehensively investigate the interaction between highly pathogenic coronaviruses and their hosts. In this review, we summarize the existing knowledge about coronaviruses with a focus on antiviral immune responses in the respiratory and intestinal tracts to infection with severe coronaviruses that have caused epidemic diseases in humans and domestic animals. We emphasize, in particular, the strategies used by these coronaviruses to circumvent host immune surveillance, mainly including the hijack of antigen-presenting cells, shielding RNA intermediates in replication organelles, 2′-O-methylation modification for the evasion of RNA sensors, and blocking of interferon signaling cascades. We also provide information about the potential development of coronavirus vaccines and antiviral drugs.