Obesity Drives STAT-1-Dependent NASH and STAT-3-Dependent HCC.

Obesity is a major driver of cancer, especially hepatocellular carcinoma (HCC). The prevailing view is that non-alcoholic steatohepatitis (NASH) and fibrosis or cirrhosis are required for HCC in obesity. Here, we report that NASH and fibrosis and HCC in obesity can be dissociated. We show that the oxidative hepatic environment in obesity inactivates the STAT-1 and STAT-3 phosphatase T cell protein tyrosine phosphatase (TCPTP) and increases STAT-1 and STAT-3 signaling. TCPTP deletion in hepatocytes promoted T cell recruitment and ensuing NASH and fibrosis as well as HCC in obese C57BL/6 mice that normally do not develop NASH and fibrosis or HCC. Attenuating the enhanced STAT-1 signaling prevented T cell recruitment and NASH and fibrosis but did not prevent HCC. By contrast, correcting STAT-3 signaling prevented HCC without affecting NASH and fibrosis. TCPTP-deletion in hepatocytes also markedly accelerated HCC in mice treated with a chemical carcinogen that promotes HCC without NASH and fibrosis. Our studies reveal how obesity-associated hepatic oxidative stress can independently contribute to the pathogenesis of NASH, fibrosis, and HCC.

Methyltransferase SETD2-Mediated Methylation of STAT1 Is Critical for Interferon Antiviral Activity.

Interferon-α (IFNα) signaling is essential for antiviral response via induction of IFN-stimulated genes (ISGs). Through a non-biased high-throughput RNAi screening of 711 known epigenetic modifiers in cellular models of IFNα-mediated inhibition of HBV replication, we identified methyltransferase SETD2 as a critical amplifier of IFNα-mediated antiviral immunity. Conditional knockout mice with hepatocyte-specific deletion of Setd2 exhibit enhanced HBV infection. Mechanistically, SETD2 directly mediates STAT1 methylation on lysine 525 via its methyltransferase activity, which reinforces IFN-activated STAT1 phosphorylation and antiviral cellular response. In addition, SETD2 selectively catalyzes the tri-methylation of H3K36 on promoters of some ISGs such as ISG15, leading to gene activation. Our study identifies STAT1 methylation on K525 catalyzed by the methyltransferase SETD2 as an essential signaling event for IFNα-dependent antiviral immunity and indicates potential of SETD2 in controlling viral infections.

The tissue protective functions of interleukin-22 can be decoupled from pro-inflammatory actions through structure-based design.

Interleukin-22 (IL-22) acts on epithelial cells to promote tissue protection and regeneration, but can also elicit pro-inflammatory effects, contributing to disease pathology. Here, we engineered a high-affinity IL-22 super-agonist that enabled the structure determination of the IL-22-IL-22Rα-IL-10Rß ternary complex to a resolution of 2.6 Å. Using structure-based design, we systematically destabilized the IL-22-IL-10Rß binding interface to create partial agonist analogs that decoupled downstream STAT1 and STAT3 signaling. The extent of STAT bias elicited by a single ligand varied across tissues, ranging from full STAT3-biased agonism to STAT1/3 antagonism, correlating with IL-10Rß expression levels. In vivo, this tissue-selective signaling drove tissue protection in the pancreas and gastrointestinal tract without inducing local or systemic inflammation, thereby uncoupling these opposing effects of IL-22 signaling. Our findings provide insight into the mechanisms underlying the cytokine pleiotropy and illustrate how differential receptor expression levels and STAT response thresholds can be synthetically exploited to endow pleiotropic cytokines with enhanced functional specificity.

Citrulline depletion by ASS1 is required for proinflammatory macrophage activation and immune responses.

Citrulline can be converted into argininosuccinate by argininosuccinate synthetase (ASS1) in the urea cycle and the citrulline-nitric oxide cycle. However, the regulation and biological function of citrulline metabolism remain obscure in the immune system. Unexpectedly, we found that macrophage citrulline declines rapidly after interferon gamma (IFN-γ) and/or lipopolysaccharide (LPS) stimulation, which is required for efficient proinflammatory signaling activation. Mechanistically, IFN-γ and/or LPS stimulation promotes signal transducers and activators of transcription 1 (STAT1)-mediated ASS1 transcription and Janus kinase2 (JAK2)-mediated phosphorylation of ASS1 at tyrosine 87, thereby leading to citrulline depletion. Reciprocally, increased citrulline directly binds to JAK2 and inhibits JAK2-STAT1 signaling. Blockage of ASS1-mediated citrulline depletion suppresses the host defense against bacterial infection in vivo. We therefore define a central role for ASS1 in controlling inflammatory macrophage activation and antibacterial defense through depletion of cellular citrulline and, further, identify citrulline as an innate immune-signaling metabolite that engages a metabolic checkpoint for proinflammatory responses.

Human STAT1 gain of function with chronic mucocutaneous candidiasis: A comprehensive review for strengthening the connection between bedside observations and laboratory research.

Germline human heterozygous STAT1 gain-of-function (GOF) variants were first discovered a common cause of chronic mucocutaneous candidiasis (CMC) in 2011. Since then, numerous STAT1 GOF variants have been identified. A variety of clinical phenotypes, including fungal, viral, and bacterial infections, endocrine disorders, autoimmunity, malignancy, and aneurysms, have recently been revealed for STAT1 GOF variants, which has led to the expansion of the clinical spectrum associated with STAT1 GOF. Among this broad range of complications, it has been determined that invasive infections, aneurysms, and malignancies are poor prognostic factors for STAT1 GOF. The effectiveness of JAK inhibitors as a therapeutic option has been established, although further investigation of their long-term utility and side effects is needed. In contrast to the advancements in treatment options, the precise molecular mechanism underlying STAT1 GOF remains undetermined. Two primary hypotheses for this mechanism involve impaired STAT1 dephosphorylation and increased STAT1 protein levels, both of which are still controversial. A precise understanding of the molecular mechanism is essential for not only advancing diagnostics but also developing therapeutic interventions. Here, we provide a comprehensive review of STAT1 GOF with the aim of establishing a stronger connection between bedside observations and laboratory research.

STAT1 is required to establish but not maintain interferon-γ-induced transcriptional memory.

Exposure of human cells to interferon-γ (IFNγ) results in a mitotically heritable yet reversible state called long-term transcriptional memory. We previously identified the clustered GBP genes as strongly primed by IFNγ. Here, we discovered that in primed cells, both interferon-responsive transcription factors STAT1 and IRF1 target chromatin with accelerated kinetics upon re-exposure to IFNγ, specifically at promotors of primed genes. Priming does not alter the degree of IFNγ-induced STAT1 activation or nuclear import, indicating that memory does not alter upstream JAK-STAT signaling. We found STAT1 to be critical to establish transcriptional memory but in a manner that is independent of mere transcription activation. Interestingly, while Serine 727 phosphorylation of STAT1 was maintained during the primed state, STAT1 is not required for the heritability of GBP gene memory. Our results suggest that the memory of interferon exposure constitutes a STAT1-mediated, heritable state that is established during priming. This renders GBP genes poised for subsequent STAT1 and IRF1 binding and accelerated gene activation upon a secondary interferon exposure.

Epigenetic escape of immunosurveillance by malignant cell precursors.

Newly formed malignant cells must escape immunosurveillance to generate progressing neoplastic lesions of clinical relevance. Recent data indicate that the immunogenicity of nascent cancer cells, at least in some settings, is dictated by inherent epigenetic mechanisms rather than by immunoediting and the consequent Darwinian selection of poorly immunogenic phenotypes.

Fas Promotes T Helper 17 Cell Differentiation and Inhibits T Helper 1 Cell Development by Binding and Sequestering Transcription Factor STAT1.

The death receptor Fas removes activated lymphocytes through apoptosis. Previous transcriptional profiling predicted that Fas positively regulates interleukin-17 (IL-17)-producing T helper 17 (Th17) cells. Here, we demonstrate that Fas promoted the generation and stability of Th17 cells and prevented their differentiation into Th1 cells. Mice with T-cell- and Th17-cell-specific deletion of Fas were protected from induced autoimmunity, and Th17 cell differentiation and stability were impaired. Fas-deficient Th17 cells instead developed a Th1-cell-like transcriptional profile, which a new algorithm predicted to depend on STAT1. Experimentally, Fas indeed bound and sequestered STAT1, and Fas deficiency enhanced IL-6-induced STAT1 activation and nuclear translocation, whereas deficiency of STAT1 reversed the transcriptional changes induced by Fas deficiency. Thus, our computational and experimental approach identified Fas as a regulator of the Th17-to-Th1 cell balance by controlling the availability of opposing STAT1 and STAT3 to have a direct impact on autoimmunity.

Transcriptional Responses to IFN-γ Require Mediator Kinase-Dependent Pause Release and Mechanistically Distinct CDK8 and CDK19 Functions.

Transcriptional responses to external stimuli remain poorly understood. Using global nuclear run-on followed by sequencing (GRO-seq) and precision nuclear run-on sequencing (PRO-seq), we show that CDK8 kinase activity promotes RNA polymerase II pause release in response to interferon-γ (IFN-γ), a universal cytokine involved in immunity and tumor surveillance. The Mediator kinase module contains CDK8 or CDK19, which are presumed to be functionally redundant. We implemented cortistatin A, chemical genetics, transcriptomics, and other methods to decouple their function while assessing enzymatic versus structural roles. Unexpectedly, CDK8 and CDK19 regulated different gene sets via distinct mechanisms. CDK8-dependent regulation required its kinase activity, whereas CDK19 governed IFN-γ responses through its scaffolding function (i.e., it was kinase independent). Accordingly, CDK8, not CDK19, phosphorylates the STAT1 transcription factor (TF) during IFN-γ stimulation, and CDK8 kinase inhibition blocked activation of JAK-STAT pathway TFs. Cytokines such as IFN-γ rapidly mobilize TFs to "reprogram" cellular transcription; our results implicate CDK8 and CDK19 as essential for this transcriptional reprogramming.

Threonine phosphorylation of STAT1 restricts interferon signaling and promotes innate inflammatory responses.

Since its discovery over three decades ago, signal transducer and activator of transcription 1 (STAT1) has been extensively studied as a central mediator for interferons (IFNs) signaling and antiviral defense. Here, using genetic and biochemical assays, we unveil Thr748 as a conserved IFN-independent phosphorylation switch in Stat1, which restricts IFN signaling and promotes innate inflammatory responses following the recognition of the bacterial-derived toxin lipopolysaccharide (LPS). Genetically engineered mice expressing phospho-deficient threonine748-to-alanine (T748A) mutant Stat1 are resistant to LPS-induced lethality. Of note, T748A mice exhibited undisturbed IFN signaling, as well as total expression of Stat1. Further, the T748A point mutation of Stat1 recapitulates the safeguard effect of the genetic ablation of Stat1 following LPS-induced lethality, indicating that the Thr748 phosphorylation contributes inflammatory functionalities of Stat1. Mechanistically, LPS-induced Toll-like receptor 4 endocytosis activates a cell-intrinsic IκB kinase-mediated Thr748 phosphorylation of Stat1, which promotes macrophage inflammatory response while restricting the IFN and anti-inflammatory responses. Depletion of macrophages restores the sensitivity of the T748A mice to LPS-induced lethality. Together, our study indicates a phosphorylation-dependent modular functionality of Stat1 in innate immune responses: IFN phospho-tyrosine dependent and inflammatory phospho-threonine dependent. Better understanding of the Thr748 phosphorylation of Stat1 may uncover advanced pharmacologically targetable molecules and offer better treatment modalities for sepsis, a disease that claims millions of lives annually.

The Myc-associated zinc finger protein epigenetically controls expression of interferon-γ-stimulated genes by recruiting STAT1 to chromatin.

The MYC-Associated Zinc Finger Protein (MAZ) plays important roles in chromatin organization and gene transcription regulation. Dysregulated expression of MAZ causes diseases, such as glioblastoma, breast cancer, prostate cancer, and liposarcoma. Previously, it has been reported that MAZ controls the proinflammatory response in colitis and colon cancer via STAT3 signaling, suggesting that MAZ is involved in regulating immunity-related pathways. However, the molecular mechanism underlying this regulation remains elusive. Here, we investigate the regulatory effect of MAZ on interferon-gamma (IFN-γ)-stimulated genes via STAT1, a protein that plays an essential role in immune responses to viral, fungal, and mycobacterial pathogens. We demonstrate that about 80% of occupied STAT1-binding sites colocalize with occupied MAZ-binding sites in HAP1/K562 cells after IFN-γ stimulation. MAZ depletion significantly reduces STAT1 binding in the genome. By analyzing genome-wide gene expression profiles in the RNA-Seq data, we show that MAZ depletion significantly suppresses a subset of the immune response genes, which include the IFN-stimulated genes IRF8 and Absent in Melanoma 2. Furthermore, we find that MAZ controls expression of the immunity-related genes by changing the epigenetic landscape in chromatin. Our study reveals an important role for MAZ in regulating immune-related gene expression.

Genome-wide and targeted CRISPR screens identify RNF213 as a mediator of interferon gamma-dependent pathogen restriction in human cells.

To define cellular immunity to the intracellular pathogen Toxoplasma gondii, we performed a genome-wide CRISPR loss-of-function screen to identify genes important for (interferon gamma) IFN-γ-dependent growth restriction. We revealed a role for the tumor suppressor NF2/Merlin for maximum induction of Interferon Stimulated Genes (ISG), which are positively regulated by the transcription factor IRF-1. We then performed an ISG-targeted CRISPR screen that identified the host E3 ubiquitin ligase RNF213 as necessary for IFN-γ-mediated control of T. gondii in multiple human cell types. RNF213 was also important for control of bacterial (Mycobacterium tuberculosis) and viral (Vesicular Stomatitis Virus) pathogens in human cells. RNF213-mediated ubiquitination of the parasitophorous vacuole membrane (PVM) led to growth restriction of T. gondii in response to IFN-γ. Moreover, overexpression of RNF213 in naive cells also impaired growth of T. gondii. Surprisingly, growth inhibition did not require the autophagy protein ATG5, indicating that RNF213 initiates restriction independent of a previously described noncanonical autophagy pathway. Mutational analysis revealed that the ATPase domain of RNF213 was required for its recruitment to the PVM, while loss of a critical histidine in the RZ finger domain resulted in partial reduction of recruitment to the PVM and complete loss of ubiquitination. Both RNF213 mutants lost the ability to restrict growth of T. gondii, indicating that both recruitment and ubiquitination are required. Collectively, our findings establish RNF213 as a critical component of cell-autonomous immunity that is both necessary and sufficient for control of intracellular pathogens in human cells.

Genome-wide aggregated trans-effects on risk of type 1 diabetes: A test of the "omnigenic" sparse effector hypothesis of complex trait genetics.

The "omnigenic" hypothesis postulates that the polygenic effects of common SNPs on a typical complex trait are mediated through trans-effects on expression of a relatively sparse set of effector ("core") genes. We tested this hypothesis in a study of 4,964 cases of type 1 diabetes (T1D) and 7,497 controls by using summary statistics to calculate aggregated (excluding the HLA region) trans-scores for gene expression in blood. From associations of T1D with aggregated trans-scores, nine putative core genes were identified, of which three-STAT1, CTLA4 and FOXP3-are genes in which variants cause monogenic forms of autoimmune diabetes. Seven of these genes affect the activity of regulatory T cells, and two are involved in immune responses to microbial lipids. Four T1D-associated genomic regions could be identified as master regulators via trans-effects on gene expression. These results support the sparse effector hypothesis and reshape our understanding of the genetic architecture of T1D.

Proteome, Lysine Acetylome, and Succinylome Identify Posttranslational Modification of STAT1 as a Novel Drug Target in Silicosis.

Inhalation of crystalline silica dust induces incurable lung damage, silicosis, and pulmonary fibrosis. However, the mechanisms of the lung injury remain poorly understood, with limited therapeutic options aside from lung transplantation. Posttranslational modifications can regulate the function of proteins and play an important role in studying disease mechanisms. To investigate changes in posttranslational modifications of proteins in silicosis, combined quantitative proteome, acetylome, and succinylome analyses were performed with lung tissues from silica-injured and healthy mice using liquid chromatography-mass spectrometry. Combined analysis was applied to the three omics datasets to construct a protein landscape. The acetylation and succinylation of the key transcription factor STAT1 were found to play important roles in the silica-induced pathophysiological changes. Modulating the acetylation level of STAT1 with geranylgeranylacetone effectively inhibited the progression of silicosis. This report revealed a comprehensive landscape of posttranslational modifications in silica-injured mouse and presented a novel therapeutic strategy targeting the posttranslational level for silica-induced lung diseases.

The balance between gasdermin D and STING signaling shapes the severity of schistosome immunopathology.

There is significant disease heterogeneity among mouse strains infected with the helminth Schistosoma mansoni. Here, we uncover a unique balance in two critical innate pathways governing the severity of disease. In the low-pathology setting, parasite egg-stimulated dendritic cells (DCs) induce robust interferon (IFN)ß production, which is dependent on the cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) cytosolic DNA sensing pathway and results in a Th2 response with suppression of proinflammatory cytokine production and Th17 cell activation. IFNß induces signal transducer and activator of transcription (STAT)1, which suppresses CD209a, a C-type lectin receptor associated with severe disease. In contrast, in the high-pathology setting, enhanced DC expression of the pore-forming protein gasdermin D (Gsdmd) results in reduced expression of cGAS/STING, impaired IFNß, and enhanced pyroptosis. Our findings demonstrate that cGAS/STING signaling represents a unique mechanism inducing protective type I IFN, which is counteracted by Gsdmd.

Unique aspects of IFN-γ/STAT1 signaling in neurons.

The IFN-γ/STAT1 immune signaling pathway impacts many homeostatic and pathological aspects of neurons, beyond its canonical role in controlling intracellular pathogens. Well known for its potent pro-inflammatory and anti-viral functions in the periphery, the IFN-γ/STAT1 pathway is rapidly activated then deactivated to prevent excessive inflammation; however, neurons utilize unique IFN-γ/STAT1 activation patterns, which may contribute to the non-canonical neuron-specific downstream effects. Though it is now well-established that the immune system interacts and supports the CNS in health and disease, many aspects regarding IFN-γ production in the CNS and how neurons respond to IFN-γ are unclear. Additionally, it is not well understood how the diversity of the IFN-γ/STAT1 pathway is regulated in neurons to control homeostatic functions, support immune surveillance, and prevent pathologies. In this review, we discuss the neuron-specific mechanisms and kinetics of IFN-γ/STAT1 activation, the potential sources and entry sites of IFN-γ in the CNS, and the diverse set of homeostatic and pathological effects IFN-γ/STAT1 signaling in neurons has on CNS health and disease. We will also highlight the different contexts and conditions under which IFN-γ-induced STAT1 activation has been studied in neurons, and how various factors might contribute to the vast array of downstream effects observed.

Regulation of macrophage IFNγ-stimulated gene expression by the transcriptional coregulator CITED1.

Macrophages serve as a first line of defense against microbial pathogens. Exposure to interferon-γ (IFNγ) increases interferon-stimulated gene (ISG) expression in these cells, resulting in enhanced antimicrobial and proinflammatory activity. Although this response must be sufficiently vigorous to ensure the successful clearance of pathogens, it must also be carefully regulated to prevent tissue damage. This is controlled in part by CBP/p300-interacting transactivator with glutamic acid/aspartic acid-rich carboxyl-terminal domain 2 (CITED2), a transcriptional coregulator that limits ISG expression by inhibiting STAT1 and IRF1. Here, we show that the closely related Cited1 is an ISG, which is expressed in a STAT1-dependent manner, and that IFNγ stimulates the nuclear accumulation of CITED1 protein. In contrast to CITED2, ectopic CITED1 enhanced the expression of a subset of ISGs, including Ccl2, Ifit3b, Isg15 and Oas2. This effect was reversed in a Cited1-null cell line produced by CRISPR-based genomic editing. Collectively, these data show that CITED1 maintains proinflammatory gene expression during periods of prolonged IFNγ exposure and suggest that there is an antagonistic relationship between CITED proteins in the regulation of macrophage inflammatory function. This article has an associated First Person interview with the first author of the paper.

Deacetylase Sirtuin 1 mitigates type I IFN- and type II IFN-induced signaling and antiviral immunity.

Type I and type II IFNs are important immune modulators in both innate and adaptive immunity. They transmit signaling by activating JAK-STAT pathways. Sirtuin 1 (SIRT1), a class III NAD+-dependent deacetylase, has multiple functions in a variety of physiological processes. Here, we characterized the novel functions of SIRT1 in the regulation of type I and type II IFN-induced signaling. Overexpression of SIRT1 inhibited type I and type II IFN-induced interferon-stimulated response element activation. In contrast, knockout of SIRT1 promoted type I and type II IFN-induced expression of ISGs and inhibited viral replication. Treatment with SIRT1 inhibitor EX527 had similar positive effects. SIRT1 physically associated with STAT1 or STAT3, and this interaction was enhanced by IFN stimulation or viral infection. By deacetylating STAT1 at K673 and STAT3 at K679/K685/K707/K709, SIRT1 downregulated the phosphorylation of STAT1 (Y701) and STAT3 (Y705). Sirt1+/- primary peritoneal macrophages and Sirt1+/- mice exhibited enhanced IFN-induced signaling and antiviral activity. Thus, SIRT1 is a novel negative regulator of type I and type II IFN-induced signaling through its deacetylase activity.IMPORTANCESIRT1 has been reported in the precise regulation of antiviral (RNA and DNA) immunity. However, its functions in type I and type II IFN-induced signaling are still unclear. In this study, we deciphered the important functions of SIRT1 in both type I and type II IFN-induced JAK-STAT signaling and explored the potential acting mechanisms. It is helpful for understanding the regulatory roles of SIRT1 at different levels of IFN signaling. It also consolidates the notion that SIRT1 is an important target for intervention in viral infection, inflammatory diseases, or even interferon-related therapies.

Enterovirus D68 3C protease antagonizes type I interferon signaling by cleaving signal transducer and activator of transcription 1.

Following the successful control of poliovirus, the re-emergence of respiratory enterovirus D68 (EV-D68), a prominent non-polio enterovirus, has become a serious public health concern worldwide. Host innate immune responses are the primary defense against EV-D68 invasion; however, the mechanism underlying viral evasion of the antiviral activity of interferons (IFN) remains unclear. In this study, we found that EV-D68 inhibited type I IFN signaling by cleaving signal transducer and activator of transcription 1 (STAT1), a crucial factor in cellular responses to interferons and other cytokines. We observed that the prototype and circulating EV-D68 strains conserved their ability to induce STAT1 cleavage and attenuate IFN signal transduction. Further investigation revealed that EV-D68 3C protease cleaves STAT1 at the 131Q residue. Interestingly, not all enterovirus-encoded 3C proteases exhibited this ability. EV-D68 and poliovirus 3C proteases efficiently induced STAT1 cleavage; whereas, 3C proteases from EV-A71, coxsackievirus A16, and echoviruses did not. STAT1 cleavage also abolished the nuclear translocation capacity of STAT1 in response to IFN stimulation to activate downstream signaling elements. Overall, these results suggest that STAT1, targeted by viral protease 3C, is utilized by EV-D68 to subvert the host's innate immune response.IMPORTANCEEnterovirus D68 (EV-D68) has significantly transformed over the past decade, evolving from a rare pathogen to a potential pandemic pathogen. The interferon (IFN) signaling pathway is an important defense mechanism and therapeutic target for the host to resist viral invasion. Previous studies have reported that the EV-D68 virus blocks or weakens immune recognition and IFN production in host cells through diverse strategies; however, the mechanisms of EV-D68 resistance to IFN signaling have not been fully elucidated. Our study revealed that EV-D68 relies on its own encoded protease, 3C, to directly cleave signal transducer and activator of transcription 1 (STAT1), a pivotal transduction component in the IFN signaling pathway, disrupting the IFN-mediated antiviral response. Previous studies on human enteroviruses have not documented direct cleavage of the STAT1 protein to evade cellular immune defenses. However, not all enteroviral 3C proteins can cleave STAT1. These findings highlight the diverse evolutionary strategies different human enteroviruses employ to evade host immunity.

Porcine deltacoronavirus nucleocapsid protein antagonizes JAK-STAT signaling pathway by targeting STAT1 through KPNA2 degradation.

Porcine deltacoronavirus (PDCoV) is an enteric pathogenic coronavirus that causes acute and severe watery diarrhea in piglets and has the ability of cross-species transmission, posing a great threat to swine production and public health. The interferon (IFN)-mediated signal transduction represents an important component of virus-host interactions and plays an essential role in regulating viral infection. Previous studies have suggested that multifunctional viral proteins encoded by coronaviruses antagonize the production of IFN via various means. However, the function of these viral proteins in regulating IFN-mediated signaling pathways is largely unknown. In this study, we demonstrated that PDCoV and its encoded nucleocapsid (N) protein antagonize type I IFN-mediated JAK-STAT signaling pathway. We identified that PDCoV infection stimulated but delayed the production of IFN-stimulated genes (ISGs). In addition, PDCoV inhibited JAK-STAT signal transduction by targeting the nuclear translocation of STAT1 and ISGF3 formation. Further evidence showed that PDCoV N is the essential protein involved in the inhibition of type I IFN signaling by targeting STAT1 nuclear translocation via its C-terminal domain. Mechanistically, PDCoV N targets STAT1 by interacting with it and subsequently inhibiting its nuclear translocation. Furthermore, PDCoV N inhibits STAT1 nuclear translocation by specifically targeting KPNA2 degradation through the lysosomal pathway, thereby inhibiting the activation of downstream sensors in the JAK-STAT signaling pathway. Taken together, our results reveal a novel mechanism by which PDCoV N interferes with the host antiviral response.IMPORTANCEPorcine deltacoronavirus (PDCoV) is a novel enteropathogenic coronavirus that receives increased attention and seriously threatens the pig industry and public health. Understanding the underlying mechanism of PDCoV evading the host defense during infection is essential for developing targeted drugs and effective vaccines against PDCoV. This study demonstrated that PDCoV and its encoded nucleocapsid (N) protein antagonize type I interferon signaling by targeting STAT1, which is a crucial signal sensor in the JAK-STAT signaling pathway. Further experiments suggested that PDCoV N-mediated inhibition of the STAT1 nuclear translocation involves the degradation of KPNA2, and the lysosome plays a role in KPNA2 degradation. This study provides new insights into the regulation of PDCoV N in the JAK-STAT signaling pathway and reveals a novel mechanism by which PDCoV evades the host antiviral response. The novel findings may guide us to discover new therapeutic targets and develop live attenuated vaccines for PDCoV infection.