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Regulation of translation initiation is essential for maintenance of protein homeostasis and typically involves the phosphorylation of translation initiation factor eIF2α in eukaryotes. In response to stressors, cells employ eIF2α-dependent signaling to control translation initiation, which regulates multiple biological and physiological processes. However, the precise regulatory mechanism remains unclear. In this study, we focus on the role of TRIM21 in the regulation of protein translation mediated by protein kinase R (PKR), one of the classic kinases that phosphorylates eIF2α. TRIM21 deficiency enhances the activation of PKR under different types of stress. TRIM21 interacts with PKR, and the E3 ligase activity of TRIM21 is crucial for stress-triggered PKR inactivation. TRIM21 interacts with the PKR phosphatase PP1α and promotes K6-linked polyubiquitination of PP1α under stresses. Ubiquitination of PP1α augments its interaction with PKR, causing PKR inactivation and subsequent dephosphorylation of eIF2α, initiating protein synthesis. Moreover, TRIM21 constitutively restricts viral infection by reversing PKR-mediated inhibition of the protein synthesis of intrinsic antiviral genes. The TRIM21-PP1α axis acts as a newly discovered program that regulates PKR-associated protein synthesis and broadens our knowledge of antiviral genes. Moreover, TRIM21-mediated regulation of PKR activation provides evidence that TRIM21 may anticipate the interferon-dependent immunotherapy. Our study highlights the essential role of TRIM21 in regulating protein translation and may provide a novel target for the treatment of translation-associated diseases.

The type I interferon (IFN-I) system is important for antiviral and anticancer immunity. Prolonged activation of IFN/JAK/STAT signaling is closely associated with autoimmune diseases. TRIM10 dysfunction may be associated closely with certain autoimmune disorders. Here, we observed that the serum TRIM10 protein level is lower in patients with systemic lupus erythematosus than in healthy control subjects. We speculated the possible involvement of TRIM10-induced modulation of the IFN/JAK/STAT signaling pathway in systemic lupus erythematosus. In line with our hypothesis, TRIM10 inhibited the activation of JAK/STAT signaling pathway triggered by various stimuli. TRIM10 restricted the IFN-I/JAK/STAT signaling pathway, which was independent of its E3 ligase activity. Mechanistically, TRIM10 interacted with the intracellular domain of IFNAR1 and blocked the association of IFNAR1 with TYK2. These data suggest the possible TRIM10 suppresses IFN/JAK/STAT signaling pathway through blocking the interaction between IFNAR1 and TYK2. Targeting TRIM10 is a potential strategy for treating autoimmune diseases.

REC8 meiotic recombination protein (REC8) is a member of structural maintenance of chromosome (SMC) protein partners, which play an important role in meiosis, antitumor activity, and sperm formation. As the adaptor proteins of RIG-I-like receptor (RLR) signaling and cyclic GMP-AMP synthase (cGAS)-DNA signaling, the activity and stability of MAVS (mitochondrial antiviral signaling protein; also known as VISA, Cardif, and IPS-1) and STING (stimulator of interferon genes; also known as MITA) are critical for innate immunity. Here, we report that REC8 interacts with MAVS and STING and inhibits their ubiquitination and subsequent degradation, thereby promoting innate antiviral signaling. REC8 is upregulated through the JAK-STAT signaling pathway during viral infection. Knockdown of REC8 impairs the innate immune responses against vesicular stomatitis virus (VSV), Newcastle disease virus (NDV), and herpes simplex virus (HSV). Mechanistically, during infection with viruses, the SUMOylated REC8 is transferred from the nucleus to the cytoplasm and then interacts with MAVS and STING to inhibit their K48-linked ubiquitination triggered by RNF5. Moreover, REC8 promotes the recruitment of TBK1 to MAVS and STING. Thus, REC8 functions as a positive modulator of innate immunity. Our work highlights a previously undocumented role of meiosis-associated protein REC8 in regulating innate immunity. IMPORTANCE The innate immune response is crucial for the host to resist the invasion of viruses and other pathogens. STING and MAVS play a critical role in the innate immune response to DNA and RNA viral infection, respectively. In this study, REC8 promoted the innate immune response by targeting STING and MAVS. Notably, REC8 interacts with MAVS and STING in the cytoplasm and inhibits K48-linked ubiquitination of MAVS and STING triggered by RNF5, stabilizing MAVS and STING protein to promote innate immunity and gradually inhibiting viral infection. Our study provides a new insight for the study of antiviral innate immunity.

The induction of interferons (IFNs) plays an important role in the elimination of invading pathogens. Heat shock binding protein 21 (HBP21), first known as a molecular chaperone of HSP70, is involved in tumor development. Heat shock binding proteins have been shown to regulate diverse biological processes, such as cell cycle, kinetochore localization, transcription, and cilium formation. Their role in antimicrobial immunity remains unknown. Here, we found that HBP21 drives a positive feedback loop to promote IRF3-mediated IFN production triggered by viral infection. HBP21 deficiency significantly impaired the virus-induced production of IFN and resulted in greater susceptibility to viral infection both in vitro and in vivo. Mechanistically, HBP21 interacted with IRF3 and promoted the formation of a TBK1-IRF3 complex. Moreover, HBP21 abolished the interaction between PP2A and IRF3 to repress the dephosphorylation of IRF3. Analysis of HBP21 protein structure further confirmed that HBP21 promotes the activation of IRF3 by depressing the dephosphorylation of IRF3 by PP2A. Further study demonstrated that virus-induced phosphorylation of Ser85 and Ser153 of HBP21 itself is important for the phosphorylation and dimerization of IRF3. Our study identifies HBP21 as a new positive regulator of innate antiviral response, which adds novel insight into activation of IRF3 controlled by multiple networks that specify behavior of tumors and immunity. IMPORTANCE The innate immune system is the first-line host defense against microbial pathogen invasion. The physiological functions of molecular chaperones, involving cell differentiation, migration, proliferation and inflammation, have been intensively studied. HBP21 as a molecular chaperone is critical for tumor development. Tumor is related to immunity. Whether HBP21 regulates immunity remains unknown. Here, we found that HBP21 promotes innate immunity response by dual regulation of IRF3. HBP21 interacts with IRF3 and promotes the formation of a TBK1-IRF3 complex. Moreover, HBP21 disturbs the interaction between PP2A and IRF3 to depress the dephosphorylation of IRF3. Analysis of HBP21 protein structure confirms that HBP21 promotes the activation of IRF3 by blocking the dephosphorylation of IRF3 by PP2A. Interestingly, virus-induced Ser85 and Ser153 phosphorylation of HBP21 is important for IRF3 activation. Our findings add to the known novel immunological functions of molecular chaperones and provide new insights into the regulation of innate immunity.

The ability to harness innate immunity is a promising solution for improving cancer immunotherapy. Interferon (IFN) induces expression of IFN-stimulated genes (ISGs) by activating the JAK-STAT signaling pathway to promote innate immunity and inhibit malignant tumor growth, but the functions and mechanisms of most ISGs in cancer regulation are unknown. As an innate immune effector, ISG12a promotes the innate immune response to viral infection. In this study, ISG12a was found to be expressed at low levels in gastrointestinal cancer, represented by hepatocellular cancer (HCC) and gastric cancer (GC), and it identified as a tumor suppressor that affects clinical prognosis. ISG12a silencing accelerated the malignant transformation and epithelial–mesenchymal transition of cancer cells. Mechanistically, ISG12a promoted β-catenin proteasomal degradation by inhibiting the degradation of ubiquitinated Axin, thereby suppressing the canonical Wnt/β-catenin signaling pathway. Notably, β-catenin was identified as a transcription factor for PD-L1. Inhibition of Wnt/β-catenin signaling by ISG12a suppressed expression of the immune checkpoint PD-L1, rendering cancer cells sensitive to NK cell-mediated killing. This study reveals a mechanism underlying the anticancer effects of IFN. Some ISGs, as represented by ISG12a, may be useful in cancer therapy and prevention. The identified interrelations among innate immunity, Wnt/β-catenin signaling, and cancer immunity may provide new insight into strategies that will improve the efficiency of immunotherapy.

Pancreatic cancer (PC) is a highly malignant tumor with increased morbidity and mortality, which is difficult to diagnose and cure in the clinic. Through secreting exosomes containing biological molecules, including diverse RNAs and proteins, bone marrow mesenchymal stem cells (BM‐MSCs) influence the immunity, inflammation, tumor environment, and cancer metastasis. In this study, low expression of miRNA‐1231 (miR‐1231) in exosomes derived from the peripheral blood was significantly correlated with the TNM stage of PC, suggesting the potential inhibitory effect of exosomal miR‐1231 on PC occurrence and development. The proliferation, migration, invasion, and adhesion to the matrix of PC cells BxPC‐3 and PANC‐1 were negatively regulated by exosomes derived from the supernatants of BM‐MSCs that transfected with miR‐1231 oligonucleotides. Simultaneously, tumor growth in vivo was seriously restrained in BALB/C nude mice by tail vein injection with exosomes originated from BM‐MSCs that transfected with miR‐1231 mimics. The exosomes extracted from BM‐MSCs with high level of miR‐1231 inhibit the activity of PC, providing the potential application for developing new and efficient medicine for cancer therapy, especially for PC treatment. The exosomal miR‐1231 of peripheral blood may also be a potential indicator for PC diagnosis in the future., The expression change of exosomal miR‐1231 derived from BM‐MSCs may provide important reference value for cancer diagnosis, especially for pancreatic cancer. And the exosomes with a high level of miR‐1231 may develop as promising new and highly efficient medicines for pancreatic cancer therapy.

A CRISPR-Cas–driven positive feedback circuit with exponential dynamic enables ultrasensitive detection of genomic DNA., Artificial nucleic acid circuits with precisely controllable dynamic and function have shown great promise in biosensing, but their utility in molecular diagnostics is still restrained by the inability to process genomic DNA directly and moderate sensitivity. To address this limitation, we present a CRISPR-Cas–powered catalytic nucleic acid circuit, namely, CRISPR-Cas–only amplification network (CONAN), for isothermally amplified detection of genomic DNA. By integrating the stringent target recognition, helicase activity, and trans-cleavage activity of Cas12a, a Cas12a autocatalysis-driven artificial reaction network is programmed to construct a positive feedback circuit with exponential dynamic in CONAN. Consequently, CONAN achieves one-enzyme, one-step, real-time detection of genomic DNA with attomolar sensitivity. Moreover, CONAN increases the intrinsic single-base specificity of Cas12a, and enables the effective detection of hepatitis B virus infection and human bladder cancer–associated single-nucleotide mutation in clinical samples, highlighting its potential as a powerful tool for disease diagnostics.

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

Interferons (IFNs) restrict various kinds of viral infection via induction of hundreds of IFN-stimulated genes (ISGs), while the functions of the majority of ISGs are broadly unclear. Here, we show that a high-IFN-inducible gene, ISG12a (also known as IFI27), exhibits a nonapoptotic antiviral effect on hepatitis C virus (HCV) infection. Viral NS5A protein is targeted specifically by ISG12a, which mediates NS5A degradation via a ubiquitination-dependent proteasomal pathway. K374R mutation in NS5A domain III abrogates ISG12a-induced ubiquitination and degradation of NS5A. S-phase kinase-associated protein 2 (SKP2) is identified as an ubiquitin E3 ligase for NS5A. ISG12a functions as a crucial adaptor that promotes SKP2 to interact with and degrade viral protein. Moreover, the antiviral effect of ISG12a is dependent on the E3 ligase activity of SKP2. These findings uncover an intriguing mechanism by which ISG12a restricts viral infection and provide clues for understanding the actions of innate immunity. IMPORTANCE Upon virus invasion, IFNs induce numerous ISGs to control viral spread, while the functions of the majority of ISGs are broadly unclear. The present study shows a novel antiviral mechanism of ISGs and elucidated that ISG12a recruits an E3 ligase, SKP2, for ubiquitination and degradation of viral protein and restricts viral infection. These findings provide important insights into exploring the working principles of innate immunity.

Emerging evidence indicates that long noncoding RNAs (lncRNAs) regulate various biological processes, especially innate and adaptive immunity. However, the relationship between lncRNAs and the interferon (IFN) pathway remains largely unknown. Here, we report that lncRNA ITPRIP-1 (lncITPRIP-1) is involved in viral infection and plays a crucial role in the virus-triggered IFN signaling pathway through the targeting of melanoma differentiation-associated gene 5 (MDA5). LncITPRIP-1 can be induced by viral infection, which is not entirely dependent on the IFN signal. Besides, there is no coding potential found in the lncITPRIP-1 transcript. LncITPRIP-1 binds to the C terminus of MDA5, and it possesses the ability to boost the oligomerization of both the full length and the 2 caspase activation and recruitment domains of MDA5 in a K63-linked polyubiquitination-independent manner. Amazingly, we also found that MDA5 can suppress hepatitis C virus (HCV) replication independently of IFN signaling through its C-terminal-deficient domain bound to viral RNA, in which lncITPRIP-1 plays a role as an assistant. In addition, the expression of lncITPRIP-1 is highly consistent with MDA5 expression, indicating that lncITPRIP-1 may function as a cofactor of MDA5. All the data suggest that lncITPRIP-1 enhances the innate immune response to viral infection through the promotion of oligomerization and activation of MDA5. Our study discovers the first lncRNA ITPRIP-1 involved in MDA5 activation.IMPORTANCE Hepatitis C virus infection is a global health issue, and there is still no available vaccine, which makes it urgent to reveal the underlying mechanisms of HCV and host factors. Although RIG-I has been recognized as the leading cytoplasmic sensor against HCV for a long time, recent findings that MDA5 regulates the IFN response to HCV have emerged. Our work validates the significant role of MDA5 in IFN signaling and HCV infection and proposes the first lncRNA inhibiting HCV replication by promoting the activation of MDA5 and mediating the association between MDA5 and HCV RNA, the study of which may shed light on the MDA5 function and treatment for hepatitis C patients. Our suggested model of how lncITPRIP-1 orchestrates signal transduction for IFN production illustrates the essential role of lncRNAs in virus elimination.

Activation of innate immunity is essential for host cells to restrict the spread of invading viruses and other pathogens. However, attenuation or termination of signaling is also necessary for preventing immune-mediated tissue damage and spontaneous autoimmunity. Here, we identify nucleotide binding oligomerization domain (NOD)-like receptor X1 (NLRX1) as a negative regulator of the mitochondrial antiviral signaling protein (MAVS)-mediated signaling pathway during hepatitis C virus (HCV) infection. The depletion of NLRX1 enhances the HCV-triggered activation of interferon (IFN) signaling and causes the suppression of HCV propagation in hepatocytes. NLRX1, a HCV-inducible protein, interacts with MAVS and mediates the K48-linked polyubiquitination and subsequent degradation of MAVS via the proteasomal pathway. Moreover, poly(rC) binding protein 2 (PCBP2) interacts with NLRX1 to participate in the NLRX1-induced degradation of MAVS and the inhibition of antiviral responses during HCV infection. Mutagenic analyses further revealed that the NOD of NLRX1 is essential for NLRX1 to interact with PCBP2 and subsequently induce MAVS degradation. Our study unlocks a key mechanism of the fine-tuning of innate immunity by which NLRX1 restrains the retinoic acid-inducible gene I-like receptor (RLR)-MAVS signaling cascade by recruiting PCBP2 to MAVS for inducing MAVS degradation through the proteasomal pathway. NLRX1, a negative regulator of innate immunity, is a pivotal host factor for HCV to establish persistent infection. IMPORTANCE Innate immunity needs to be tightly regulated to maximize the antiviral response and minimize immune-mediated pathology, but the underlying mechanisms are poorly understood. In this study, we report that NLRX1 is a proviral host factor for HCV infection and functions as a negative regulator of the HCV-triggered innate immune response. NLRX1 recruits PCBP2 to MAVS and induces the K48-linked polyubiquitination and degradation of MAVS, leading to the negative regulation of the IFN signaling pathway and promoting HCV infection. Overall, this study provides intriguing insights into how innate immunity is regulated during viral infection.