IFN Regulatory Factor Research Articles

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

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). We hypothesized that altered and/or prolonged IFN-I signaling contributes to inflammatory complications in these patients. 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. 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. 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.

Marek’s disease virus serine/threonine kinase Us3 facilitates viral replication by targeting IRF7 to block IFN-β production

Marek’s disease virus (MDV) is a highly oncogenic alphaherpesvirus that induces malignant T-cell lymphomas in chickens, leading to great economic loss in poultry industry. The unique-short kinase 3 (Us3), a serine/threonine kinase encoded by three MDV types (MDV-1, MDV-2 and HVT), is important for MDV replication. However, the mechanism of Us3 facilitating MDV replication has not been completely elucidated. In the present study, we report that Us3 significantly facilities MDV replication via inhibition of β interferon (IFN-β) production at the late phase of MDV infection. Overexpression or interference of Us3 significantly promoted or inhibited the replication of MDV, and accordingly inhibited or promoted the expression of IFN-β. Further, Us3 was shown to suppresses interferon stimulatory DNA (ISD)-triggered IFN-β production by targeting IFN regulatory factor 7 (IRF7) rather than NF-κB signaling. Moreover, Us3 but not kinase-dead (KD) Us3 mutant K220A blocked the nuclear translocation of IRF7 by inhibiting dimerization. Importantly, Us3 phosphorylated and interacted with IRF7. Furthermore, Us3-deficient MDV weakened viral replication and increased IFN-β production in infected cells or chickens. These results indicated that Us3 interrupts the cytosolic DNA sensing pathway, thereby leading to inhibition of IFN-β production by targeting IRF7, promoting MDV replication. Our finding expands the knowledge about the role of Us3 in MDV replication.

An alternatively spliced STING isoform localizes in the cytoplasmic membrane and directly senses extracellular cGAMP.

It has been revealed that 2′3′-cyclic-GMP-AMP (cGAMP), a second messenger that activates the antiviral stimulator of IFN genes (STING), elicits an antitumoral immune response. Since cGAMP cannot cross the cell membrane, it is not clear how intracellular STING has been activated by extracellular cGAMP until SLC19A1 was identified as an importer to transport extracellular cGAMP into the cytosol. However, SLC19A1-deficient cells also sense extracellular cGAMP, suggesting the presence of mechanisms other than the facilitating transporters for STING sensing extracellular cGAMP. Here, using immunoprecipitation, immunofluorescence, and flow cytometry, we identified an alternatively spliced STING isoform, plasmatic membrane STING (pmSTING), that localized in the plasma membrane with its C-terminus outside the cell, due to a lack of 1 transmembrane domain in its N-terminus compared with canonical STING. Further studies showed that extracellular cGAMP not only promoted the dimerization of pmSTING and interaction of pmSTING with TANK-binding kinase 1 (TBK1) and IFN regulatory factor 3 (IRF3), but also enhanced the phosphorylation of TBK1 and IRF3 and the production of IFN in pmSTING-transfected cells. Additionally, we also identified similar pmSTING isoforms in other species including human. This study suggests a conserved role for pmSTING in sensing extracellular cGAMP and provides insight into the role of cGAMP as an immunotransmitter.

Two PARP13 isoforms are associated with induction of antiviral factors in oral mucosal cells.

Innate immune systems in the oral cavity have important roles in the host defense against viral invasion of oral mucosa. Poly(ADP‑ribose) polymerase13(PARP13), which has a strong antiviral ability, has been reported to possess two isoforms; a full‑length protein, zinc‑finger antiviral protein long (ZAPL), and a shorter protein (ZAPS). However, the expression and function of these two isoforms in oral mucosa remain unknown. In the present study, the expression levels of ZAPL and ZAPS induced by transfected double‑stranded(ds) RNA, Poly(I:C), and dsDNA, Poly(dA:dT), in immortalized oral keratinocytes and fibroblasts (RT7 and GT1 cell lines, respectively) were investigated. Subsequently, the effects of the knockdown of ZAPL and ZAPS on transfected nucleotide‑induced antiviral factors were examined. The results demonstrated constitutive expression of ZAPL and ZAPS in RT7 and GT1 cells, and their expression in both cell types was notably increased by transfection of Poly(I:C) and Poly(dA:dT) when compared with no transfection. Specific knockdown of ZAPL and ZAPS in RT7 cells decreased IFN‑β and C‑X‑C motif chemokine ligand10(CXCL10) expression induced by transfected Poly(I:C) and Poly(dA:dT). On the other hand, knockdown of ZAPL and ZAPS in GT1 cells decreased the expression of CXCL10 induced by the transfected nucleotides, whereas that had no effect on IFN‑β expression induced by Poly(dA:dT). Their knockdown was also associated with transfected nucleotides‑induced IFN regulatory factor 3 phosphorylation in both cell types. Taken together, these results indicate that ZAPL and ZAPS, isoforms of PARP13, in oral mucosal cells participate in host defense against viral infection of oral mucosa.

IFN-γ Induces IL-15 Trans-Presentation by Epithelial Cells via IRF1.

IL-15 exhibits pleiotropic effects on NK and CD8+ T cells and contributes to host protection or immunopathology during infection. Although both type I IFNs and IFN-γ upregulate IL-15 expression, their effects on IL-15 upregulation and underlying mechanisms have not been compared comprehensively. In addition, little is known about trans-presentation of IL-15 by epithelial cells to lymphocytes. In this study, we analyzed the expression of IL-15 and IL-15Rα in the human hepatocyte-derived Huh-7 cell line after stimulation with IFN-α, IFN-β, or IFN-γ using RT-PCR, flow cytometry, and confocal microscopy. We also performed knockdown experiments to investigate the signaling pathway involved in IL-15 upregulation. IFN-γ more potently upregulated IL-15 expression in Huh-7 cells than IFN-α and IFN-β. Knockdown experiments revealed that IFN-γ- and IFN-β-induced IL-15 expression relied on IFN regulatory factor 1 (IRF1), which is upregulated by STAT1 and IFN-stimulated gene factor 3, respectively. Inhibitor of κB kinase α/β was also involved in IFN-γ-induced upregulation of IL-15. Furthermore, human NK cells were activated by coculture with IFN-γ-treated Huh-7 cells, which was abrogated by knocking down IL-15Rα in IFN-γ-treated Huh-7 cells, indicating that IFN-γ-induced IL-15 on Huh-7 cells activates NK cells via trans-presentation. In summary, our data demonstrate that IFN-γ potently elicits IL-15 trans-presentation by epithelial cells via IRF1. These data also suggest that the IFN-γ-IRF1-IL-15 axis may be a regulatory target for the treatment of diseases with IL-15 dysregulation.

DDX56 antagonizes IFN-β production to enhance EMCV replication by inhibiting IRF3 nuclear translocation

DEAD (Asp-Glu-Ala-Asp)-box RNA helicases (DDX) play important roles in viral infection, either as cytosolic viral nucleic acids sensors or as essential host factors for viral replication. In this study, we identified DDX56 as a positive regulator for encephalomyocarditis virus (EMCV) replication. EMCV infection promotes DDX56 expression via its viral proteins, VP3 and 3C. We showed that DDX56 overexpression promotes EMCV replication whereas its loss dampened EMCV replication. Consequently, knockdown of DDX56 increases type I interferon (IFN) expression during EMCV infection. We also showed that DDX56 interrupts IFN regulatory factor 3 (IRF3) phosphorylation and its nucleus translocation by directly targeting KPNA3 and KPNA4 in an EMCV-triggered MDA5 signaling activation cascade leading to the blockade of IFN-β production. Overall, we showed that DDX56 is a novel negative regulator of EMCV-mediated IFN-β responses and that DDX56 plays a critical role in EMCV replication. These findings reveal a novel strategy for EMCV to utilize a host factor to evade the host innate immune response and provide us new insight into the function of DDX56.

Functional analysis and regulation mechanism of interferon gamma in macrophages of large yellow croaker (Larimichthys crocea)

Interferon gamma (IFN-γ) is a widely expressed cytokine that has potent antiviral and immunomodulatory effects. The expression and bioactivity of IFN-γ have been reported in several fish species. However, the molecular mechanism mediated by IFN-γ in fish macrophages has not been completely elucidated. This study used the macrophage cell line to investigate the functional activities and regulation mechanism of large yellow croaker IFN-γ (LcIFN-γ). Herein, the mRNA expression of Lcifn-γ was significantly upregulated in macrophages after LPS and poly(I:C) treatment. Recombinant LcIFN-γ protein (rLcIFN-γ) significantly enhanced the phagocytic ability and respiratory burst activity of macrophages. Meanwhile, rLcIFN-γ induced M1 phenotype polarization of macrophages with the upregulated expressions of pro-inflammatory gene. Moreover, rLcIFN-γ upregulated the IFN-stimulated genes (ISGs) expression and activated JAK (Janus tyrosine kinases)-STAT (signal transducer and activator of transcription) signaling pathway by causing the phosphorylation of JAK1 and STAT1Tyr701. Furthermore, the promoter activity of IFN-regulatory factor 1 (IRF1) was significantly upregulated by the phosphorylated transcription factor STAT1 through binding to its promoter region. In addition to the classical JAK-STAT pathway, rLcIFN-γ also activated multiple distinct signaling cascades such as mitogen-activated protein kinase (MAPK) and protein kinase B (AKT) pathways. Overall, this study indicated the powerful effects of LcIFN-γ on macrophage activation of large yellow croaker and its molecular mechanism.

Role of metapneumoviral glycoproteins in the evasion of the host cell innate immune response.

Human metapneumovirus (HMPV), an unsegmented negative-strand RNA virus, is the second most detected respiratory pathogen and one of the leading causes of respiratory illness in infants and immunodeficient individuals. HMPV infection of permissive cells in culture triggers a transient IFN response, which is efficiently suppressed later in infection. We report that two structural glycoproteins of the virus - namely G (Glycoprotein) and SH (Small Hydrophobic) - suppress the type I interferon (IFN) response in cell culture. This is manifested by inhibition of diverse steps of IFN induction and response, such as phosphorylation and nuclear translocation of IFN regulatory factor-3 and -7 (IRF3, IRF7), major transcription factors of the IFN gene. Furthermore, HMPV suppresses the cellular response to IFN by inhibiting the phosphorylation of STAT1 (Signal Transducer and Activator of Transcription 1), required for the induction of IFN-stimulated genes that act as antivirals. Site-directed mutagenesis revealed an important role of critical cysteine (Cys) residues in the Cys-rich carboxy terminal region of the SH protein in IFN suppression, whereas for G, the ectodomain plays a role. These results shed light on the mechanism of IFN suppression by HMPV, and may also offer avenues for new antiviral approaches in the future.

Retroposition of the Long Transcript from Multiexon IFN-β Homologs in Ancestry Vertebrate Gave Rise to the Proximal Transcription Elements of Intronless IFN-β Promoter in Humans.

IFN-β is a unique member of type I IFN in humans and contains four positive regulatory domains (PRDs), I-II-III-IV, in its promoter, which are docking sites for transcription factors IFN regulatory factor (IRF) 3/7, NF-κB, IRF3/7, and activating transcription factor 2/Jun proto-oncogene, respectively. In chicken IFN-β and zebrafish IFNφ1 promoters, a conserved PRD or PRD-like sequences have been reported. In this study, a type I IFN gene, named as xl-IFN1 in the amphibian model Xenopus laevis, was found to contain similar PRD-like sites, IV-III/I-II, in its promoter, and these PRD-like sites were proved to be functionally responsive to activating transcription factor 2/Jun proto-oncogene, IRF3/IRF7, and p65, respectively. The xl-IFN1, as IFNφ1 in zebrafish, was transcribed into a long and a short transcript, with the long transcript containing all of the transcriptional elements, including PRD-like sites and TATA box in its proximal promoter. A retroposition model was then proposed to explain the transcriptional conservation of IFNφ1, xl-IFN1, and IFN-β in chicken and humans.

Maternal Monocytes Respond to Cell-Free Fetal DNA and Initiate Key Processes of Human Parturition.

Throughout gestation, the maternal immune system is tightly modulated to allow growth of a semiallogeneic fetus. During the third trimester, the maternal immune system shifts to a proinflammatory phenotype in preparation for labor. What induces this shift remains unclear. Cell-free fetal DNA (cffDNA) is shed by the placenta and enters maternal circulation throughout pregnancy. Levels of cffDNA are increased as gestation progresses and peak before labor, coinciding with a shift to proinflammatory maternal immunity. Furthermore, cffDNA is abnormally elevated in plasma from women with complications of pregnancy, including preterm labor. Given the changes in maternal immunity at the end of pregnancy and the role of sterile inflammation in the pathophysiology of spontaneous preterm birth, we hypothesized that cffDNA can act as a damage-associated molecular pattern inducing an inflammatory cytokine response that promotes hallmarks of parturition. To test this hypothesis, we stimulated human maternal leukocytes with cffDNA from primary term cytotrophoblasts or maternal plasma and observed significant IL-1β and CXCL10 secretion, which coincides with phosphorylation of IFN regulatory factor 3 and caspase-1 cleavage. We then show that human maternal monocytes are crucial for the immune response to cffDNA and can activate bystander T cells to secrete proinflammatory IFN-γ and granzyme B. Lastly, we find that the monocyte response to cffDNA leads to vascular endothelium activation, induction of myometrial contractility, and PGE2 release in vitro. Our results suggest that the immune response to cffDNA can promote key features of the parturition cascade, which has physiologic consequences relevant to the timing of labor.

Transcription factor MafB-mediated inhibition of type I interferons in plasmacytoid dendritic cells.

Type I IFNs (IFN-α and IFN-β), immunomodulatory cytokines secreted from activated plasmacytoid dendritic cells (pDCs), contribute to the innate defense against pathogenic infections and the pathogenesis of the autoimmune disease psoriasis vulgaris. A previous study has shown that an E26 transformation-specific (Ets) family transcription factor Spi-B can transactivate the type I IFN promoter in synergy with IFN regulatory factor (IRF)-7 and is required for type I IFN production in pDCs. However, the mechanism of negative regulation of type I IFNs by pDCs remains unknown. In this study, we report that a basic leucine zipper (bZip) transcription factor v-maf musculoaponeurotic fibrosarcoma oncogene homolog B (MafB) suppresses the induction of type I IFNs in pDCs. The elevated expression of MafB inhibited the transactivation of type I IFN genes in a dose-dependent manner. At the molecular level, MafB interacted with the Ets domain of Spi-B and interfered with IRF-7-Spi-B complexation. Decreased MafB mRNA expression and degradation of MafB protein in the early phase of immune responses led to the enhancement of type I IFNs in pDCs. In vivo studies indicated that MafB is involved in resistance against imiquimod-induced psoriasis-like skin inflammation. Overall, these findings demonstrate that MafB acts as a negative regulator of type I IFN induction in pDCs and plays an important role in maintaining immune homeostasis.

Selective Induction of Cell Death in Human M1 Macrophages by Smac Mimetics Is Mediated by cIAP-2 and RIPK-1/3 through the Activation of mTORC.

Inflammatory macrophages have been implicated in many diseases, including rheumatoid arthritis and inflammatory bowel disease. Therefore, targeting macrophage function and activation may represent a potential strategy to treat macrophage-associated diseases. We have previously shown that IFN-γ-induced differentiation of human M0 macrophages toward proinflammatory M1 state rendered them highly susceptible to the cytocidal effects of second mitochondria-derived activator of caspases mimetics (SMs), antagonist of the inhibitors of apoptosis proteins (IAPs), whereas M0 and anti-inflammatory M2c macrophages were resistant. In this study, we investigated the mechanism governing SM-induced cell death during differentiation into M1 macrophages and in polarized M1 macrophages. IFN-γ stimulation conferred on M0 macrophages the sensitivity to SM-induced cell death through the Jak/STAT, IFN regulatory factor-1, and mammalian target of rapamycin complex-1 (mTORC-1)/ribosomal protein S6 kinase pathways. Interestingly, mTORC-1 regulated SM-induced cell death independent of M1 differentiation. In contrast, SM-induced cell death in polarized M1 macrophages is regulated by the mTORC-2 pathway. Moreover, SM-induced cell death is regulated by cellular IAP (cIAP)-2, receptor-interacting protein kinase (RIPK)-1, and RIPK-3 degradation through mTORC activation during differentiation into M1 macrophages and in polarized M1 macrophages. In contrast to cancer cell lines, SM-induced cell death in M1 macrophages is independent of endogenously produced TNF-α, as well as the NF-κB pathway. Collectively, selective induction of cell death in human M1 macrophages by SMs may be mediated by cIAP-2, RIPK-1, and RIPK-3 degradation through mTORC activation. Moreover, blocking cIAP-1/2, mTORC, or IFN regulatory factor-1 may represent a promising therapeutic strategy to control M1-associated diseases.

ATG12 is involved in the antiviral immune response in large yellow croaker (Larimichthys crocea)

ATG12, a core autophagy protein, forms a conjugate with ATG5 to promote the formation of autophagosome membrane, and plays an important role in antiviral immunity. However, little is known about the function of ATG12 in fish. Here, we cloned the open reading frame (ORF) of large yellow croaker (Larimichthys crocea) ATG12 (LcATG12), which is 354 nucleotides long and encodes a protein of 117 amino acids. The deduced LcATG12 possesses a conserved APG12 domain (residues 31 to 117), and shares 91.45% identities with ATG12 in orange-spotted grouper (Epinephelus coioides). LcATG12 was constitutively expressed in all examined tissues, with the highest level in intestine. Its transcript was also detected in primary head kidney granulocytes (PKG), primary head kidney macrophages (PKM), primary head kidney lymphocytes (PKL), and large yellow croaker head kidney (LYCK) cell line, and was significantly up-regulated by poly(I:C). LcATG12 was regularly distributed in both cytoplasm and nucleus of LYCK and epithelioma papulosum cyprinid (EPC) cells. Overexpression of LcATG12 in EPC cells significantly inhibited the replication of spring viremia of carp virus (SVCV). Further studies reveled that LcATG12 could induce the occurrence of autophagy in LYCK cells. Furthermore, overexpression of LcATG12 in LYCK cells increased the expression levels of large yellow croaker type I interferons (IFNs, IFNc, IFNd, and IFNh), IFN regulatory factors (IRF3 and IRF7), and IFN-stimulated genes (PKR, Mx, and Viperin). All these data indicated that LcATG12 plays a role in the antiviral immunity possibly by inducing both autophagy and type I IFN response in large yellow croaker.

The identification of a shorter cyclic GMP-AMP synthase gene from chickens and bioinformatics analysis of its potential signaling in IFN regulation

Chicken has an impaired innate immune system compared with mammals. Some key innate immune genes, such as Retinoic acid–inducible gene I (RIG-I), Toll like receptor 8 (TLR8), Absent in melanoma 2 (AIM2) and IFN regulatory factor 3 (IRF3), are inactivated or missing due to DNA Insertion, gene partial deletion, or gene total deletion. A predicted N-terminal deleted chicken Cyclic GMP-AMP synthase (chcGAS) gene, which is proven as the most essential cytosolic DNA sensor in other species, be obtained from the GenBank database. The large fragment deletion makes the sequence accuracy and functional integrity of the predicted chcGAS open to dispute. Here, the exact chcGAS gene was first experimentally determined by 5′ and 3′ rapid amplification of cDNA ends (RACE) PCR, which specifically lacked 83 amino acids in the DNA binding domain. In addition, the conservation and feasibility of cGAS-STING signaling among different species were conducted by bioinformatics to explore the possibility of the existence of the conserved pathway in chickens. The basic characteristics of the chcGAS, such as macroscopic and microscopic distribution patterns of chcGAS have been studied. In order to better research the function of chGAS, a chcGAS knockout chicken cell line has been generated by CRISPR/CAS9. Together, chicken owns an N-terminal deleted cGAS gene, and more experimental evidences are urgently needed to verify the functional integrity of chcGAS.

Degradation of WTAP blocks antiviral responses by reducing the m6 A levels of IRF3 and IFNAR1 mRNA.

N 6‐methyladenosine (m6A) is a chemical modification present in multiple RNA species and is most abundant in mRNAs. Studies on m6A reveal its comprehensive roles in almost every aspect of mRNA metabolism, as well as in a variety of physiological processes. Although some recent discoveries indicate that m6A can affect the life cycles of numerous viruses as well as the cellular antiviral immune response, the roles of m6A modification in type I interferon (IFN‐I) signaling are still largely unknown. Here, we reveal that WT1‐associated protein (WTAP), one of the m6A “writers”, is degraded via the ubiquitination‐proteasome pathway upon activation of IFN‐I signaling. With the degradation of WTAP, the m6A levels of IFN‐regulatory factor 3 (IRF3) and interferon alpha/beta receptor subunit 1 (IFNAR1) mRNAs are reduced, leading to translational suppression of IRF3 and instability of IFNAR1 mRNA. Thus, the WTAP‐IRF3/IFNAR1 axis may serve as negative feedback pathway to fine‐tune the activation of IFN‐I signaling, which highlights the roles of m6A in the antiviral response by dictating the fate of mRNAs associated with IFN‐I signaling.

Continuous Culture of Mouse Primary B Lymphocytes by Forced Expression of Bach2.

Stable, long-term culture of primary B lymphocytes has many potential scientific and medical applications, but remains an elusive feat. A major obstacle to long-term culture is that in vitro mitogens quickly drive B cells to differentiate into short-lived plasma cells (PCs). PC differentiation is governed by opposing teams of transcription factors: Pax5, Bach2, and Bcl6 suppress PC commitment, whereas IFN regulatory factor 4 and Blimp1 promote it. To determine whether transcriptional programming could prolong B cell culture by blocking PC commitment, we generated mouse primary B cells harboring gain- or loss-of-function in the key transcription factors, continuously stimulated these cells with CD154 and IL-21, and determined growth potential and phenotypes in vitro. We found that transgenic expression of Bach2 prohibits PC commitment and endows B cells with extraordinary growth potential in response to external proliferation and survival cues. Long-term Bach2-transgenic B cell lines have genetically stable BCRs [i.e., do not acquire V(D)J mutations], express high levels of MHC class II and molecules for costimulation of T cells, and transduce intracellular signals when incubated with BCR ligands. Silencing the Bach2 transgene in an established transgenic cell line causes the cells to secrete large quantities of Ig. This system has potential applications in mAb production, BCR signaling studies, Ag presentation to T cells, and ex vivo clonal expansion for adoptive cell transfer. Additionally, our results provide insight into molecular control over activated B cell fate and suggest that forced Bach2 expression in vivo may augment germinal center B cell or memory B cell differentiation at the expense of PC commitment.

Multimodal Intralesional Therapy for Reshaping the Myeloid Compartment of Tumors Resistant to Anti-PD-L1 Therapy via IRF8 Expression.

Intralesional therapy is a promising approach for remodeling the immunosuppressive tumor microenvironment while minimizing systemic toxicities. A combinatorial in situ immunomodulation (ISIM) regimen with intratumoral administration of Fms-like tyrosine kinase 3 ligand (Flt3L), local irradiation, and TLR3/CD40 stimulation induces and activates conventional type 1 dendritic cells in the tumor microenvironment and elicits de novo adaptive T cell immunity in poorly T cell-inflamed tumors. However, the impact of ISIM on myeloid-derived suppressor cells (MDSCs), which may promote treatment resistance, remains unknown. In this study, we examined changes in the frequencies and heterogeneity of CD11b+Ly-6CloLy-6G+ polymorphonuclear (PMN)-MDSCs and CD11b+Ly-6ChiLy-6G- monocytic (M)-MDSCs in ISIM-treated tumors using mouse models of triple-negative breast cancer. We found that ISIM treatment decreased intratumoral PMN-MDSCs, but not M-MDSCs. Although the frequency of M-MDSCs remained unchanged, ISIM caused a substantial reduction of CX3CR1+ M-MDSCs that express F4/80. Importantly, these ISIM-induced changes in tumor-residing MDSCs were not observed in Batf3-/- mice. ISIM upregulated PD-L1 expression in both M-MDSCs and PMN-MDSCs and synergized with anti-PD-L1 therapy. Furthermore, ISIM increased the expression of IFN regulatory factor 8 (IRF8) in myeloid cells, a known negative regulator of MDSCs, indicating a potential mechanism by which ISIM decreases PMN-MDSC levels. Accordingly, ISIM-mediated reduction of PMN-MDSCs was not observed in mice with conditional deletion of IRF8 in myeloid cells. Altogether, these findings suggest that ISIM holds promise as a multimodal intralesional therapy to alter both lymphoid and myeloid compartments of highly aggressive poorly T cell-inflamed, myeloid-enriched tumors resistant to anti-PD-L1 therapy.

The Smac mimetic BV6 cooperates with STING to induce necroptosis in apoptosis-resistant pancreatic carcinoma cells

Pancreatic cancer (PC) still remains a major cause of cancer-related death worldwide and alternative treatments are urgently required. A common problem of PC is the development of resistance against apoptosis that limits therapeutic success. Here we demonstrate that the prototypical Smac mimetic BV6 cooperates with the stimulator of interferon (IFN) genes (STING) ligand 2′,3′-cyclic guanosine monophosphate–adenosine monophosphate (2′3′-cGAMP) to trigger necroptosis in apoptosis-deficient PC cells. Pharmacological inhibition of key components of necroptosis signaling, such as receptor-interacting protein 1 (RIPK1), RIPK3, and mixed lineage kinase domain-like protein (MLKL), significantly rescues PC cells from 2′3′-cGAMP/BV6/zVAD.fmk-mediated cell death, suggesting the induction of necroptosis. Consistently, 2′3′-cGAMP/BV6 co-treatment promotes phosphorylation of MLKL. Furthermore, we show that 2′3′-cGAMP stimulates the production of type I IFNs, which cooperate with BV6 to trigger necroptosis in apoptosis-deficient settings. STING silencing via siRNA or CRISPR/Cas9-mediated gene knockout protects PC cells from 2′3′-cGAMP/BV6/zVAD.fmk-mediated cell death. Interestingly, we demonstrate that nuclear factor-κB (NF-κB), tumor necrosis factor-α (TNFα), and IFN-regulatory factor 1 (IRF1) signaling are involved in triggering 2′3′-cGAMP/BV6/zVAD.fmk-induced necroptosis. In conclusion, we show that activated STING and BV6 act together to exert antitumor effects on PC cells with important implications for the design of new PC treatment concepts.

Brucella spp. Omp25 Promotes Proteasome-Mediated cGAS Degradation to Attenuate IFN-β Production.

Type I interferons (IFN), a family of cytokines widely expressed in various tissues, play important roles in anti-infection immunity. Nevertheless, it is not known whether Brucella spp. could interfere with IFN-I production induced by other pathogens. This study investigated the regulatory roles of Brucella outer membrane protein (Omp)25 on the IFN-I signaling pathway and found that Omp25 inhibited the production of IFN-β and its downstream IFN-stimulated genes induced by various DNA viruses or IFN-stimulatory DNA in human, murine, porcine, bovine, and ovine monocyte/macrophages or peripheral blood mononuclear cells. Brucella Omp25 suppressed the phosphorylation of stimulator of IFN genes (STINGs) and IFN regulatory factor 3 and nuclear translocation of phosphorylated IFN regulatory factor 3 in pseudorabies virus- or herpes simplex virus-1-infected murine, human, or porcine macrophages. Furthermore, we found that Brucella Omp25 promoted cyclic guanosine monophosphate–adenosine monophosphate synthase (cGAS) degradation via the proteasome-dependent pathway, resulting in a decreased cyclic guanosine monophosphate–adenosine monophosphate production and downstream signaling activation upon DNA virus infection or IFN-stimulatory DNA stimulation. Mapping the predominant function domain of Omp25 showed that the amino acids 161 to 184 of Omp25 were required for Omp25-induced cGAS degradation, among which five amino acid residues (R176, Y179, R180, Y181, and Y184) were required for the inhibitory effect of Omp25 on IFN-β induction. Altogether, our results demonstrated that Brucella Omp25 inhibits cGAS STING signaling pathway-induced IFN-β via facilitating the ubiquitin–proteasome-dependent degradation of cGAS in various mammalian monocyte/macrophages.

Extracellular CIRP activates STING to exacerbate hemorrhagic shock.

Stimulator of IFN genes (STING) activates TANK-binding kinase 1 (TBK1) and IFN regulatory factor 3 (IRF3) to produce type I IFNs. Extracellular cold-inducible RNA-binding protein (eCIRP) is released from cells during hemorrhagic shock (HS). We hypothesized that eCIRP activates STING to induce inflammation and acute lung injury (ALI) after HS. WT and STING–/– mice underwent controlled hemorrhage by bleeding, followed by fluid resuscitation. Blood and lungs were collected at 4 hours after resuscitation. Serum ALT, AST, LDH, IL-6, and IFN-β were significantly decreased in STING–/– mice compared with WT mice after HS. In STING–/– mice, the levels of pTBK1 and pIRF3, and expression of TNF-α, IL-6, and IL-1β mRNAs and proteins in the lungs, were significantly decreased compared with WT HS mice. The 10-day mortality rate in STING–/– mice was significantly reduced. I.v. injection of recombinant mouse CIRP (rmCIRP) in STING–/– mice showed a significant decrease in pTBK1 and pIRF3 and in IFN-α and IFN-β mRNAs and proteins in the lungs compared with rmCIRP-treated WT mice. Treatment of TLR4–/–, MyD88–/–, and TRIF–/– macrophages with rmCIRP significantly decreased pTBK1 and pIRF3 levels and IFN-α and IFN-β mRNAs and proteins compared with WT macrophages. HS increases eCIRP levels, which activate STING through TLR4/MyD88/TRIF pathways to exacerbate inflammation.