Master Regulator Of Type Research Articles

IRF8-driven reprogramming of the immune microenvironment enhances anti-tumor adaptive immunity and reduces immunosuppression in murine glioblastoma.

Glioblastoma (GBM) has a highly immunosuppressive tumor immune microenvironment (TIME), largely mediated by myeloid-derived suppressor cells (MDSCs). Here, we utilized a retroviral replicating vector (RRV) to deliver Interferon Regulatory Factor 8 (IRF8), a master regulator of type 1 conventional dendritic cell (cDC1) development, in a syngeneic murine GBM model. We hypothesized that RRV-mediated delivery of IRF8 could "reprogram" intratumoral MDSCs into antigen-presenting cells (APCs) and thereby restore T-cell responses. Effects of RRV-IRF8 on survival and tumor growth kinetics were examined in the SB28 murine GBM model. Immunophenotype was analyzed by flow cytometry and gene expression assays. We assayed functional immunosuppression and antigen presentation by ex vivo T-cell-myeloid co-culture. Intratumoral injection of RRV-IRF8 in mice bearing intracerebral SB28 glioma significantly suppressed the tumor growth and prolonged survival. RRV-IRF8 treated tumors exhibited significant enrichment of cDC1s and CD8+ T-cells. Additionally, myeloid cells derived from RRV-IRF8 tumors showed decreased expression of the immunosuppressive markers Arg1 and IDO1 and demonstrated reduced suppression of naïve T-cell proliferation in ex vivo co-culture, compared to controls. Furthermore, DCs from RRV-IRF8 tumors showed increased antigen presentation compared to those from control tumors. In vivo treatment with azidothymidine (AZT), a viral replication inhibitor, showed that IRF8 transduction in both tumor and non-tumor cells is necessary for survival benefit, associated with a reprogrammed, cDC1- and CD8 T-cell-enriched TIME. Our results indicate that reprogramming of glioma-infiltrating myeloid cells by in vivo expression of IRF8 may reduce immunosuppression and enhance antigen presentation, achieving improved tumor control.

Abstract 1417: IRF8 driven reprogramming of the immune microenvironment enhances anti-tumor adaptive immunity and reduces immunosuppression in murine glioblastoma

Abstract Glioblastoma (GBM) has an extremely immunosuppressive microenvironment, primarily mediated by the recruitment of immature myeloid cells (IMCs) to the tumor. IMCs suppress T cell function and dampen the anti-tumor response. In this study, we sought to “reprogram” IMCs into antigen-presenting cells (APCs) to enhance anti-tumor T cell responses. To induce IMC differentiation into APCs, we utilized a retroviral replicating vector (RRV) expressing IRF8, a master regulator of type 1 conventional dendritic cell (cDC1) development. We evaluated the impact of IRF8 RRV on in vivo tumor growth kinetics, survival, immunosuppression, and immune microenvironment. Because RRV transduction requires the proliferation of target cells, we assessed the proliferative capacity of myeloid cells in murine and human GBM samples. We utilized the SB28 cell line, a poorly immunogenic murine GBM model. We pre-transduced SB28 cells with IRF8 RRV and implanted them intracranially into syngeneic C57BL/6 mice; controls expressed an empty vector. Intratumoral myeloid cells were proliferative in both murine and human samples. In vivo, tumor and myeloid cells are infected proportionately to their respective levels of proliferation. Mice with IRF8 RRV pre-transduced intracranial tumors had significantly longer survival (median 28 days) compared to controls (median 19 days) (p <0.0001). Additionally, tumor growth was delayed in IRF8 RRV mice. IRF8 RRV mice had significant enrichment of dendritic cells (p = 0.0145), cDC1s (p < 0.0001), T cells (p = 0.0025) and CD8+ T cells (p < 0.0001). Both monocytic and granulocytic IMCs had decreased expression of the immunosuppressive markers Arginase 1 and IDO1. Further, ex vivo co-culture of intra-tumoral myeloid cells with naïve T cells showed a functional decrease in immunosuppression in IRF8 RRV tumors compared to controls (p < 0.0001). To study the mechanism of action, we assessed whether IRF8 transduction of tumor cells alone or both tumor and immune cells, was necessary for the observed survival benefit. To inhibit RRV spread from infected cells to other cells, we treated mice with azidothymidine, a reverse transcription inhibitor. A robust survival benefit and tumor growth inhibition were seen only in mice where the RRV could spread freely (p = 0.0005). This finding shows that both tumor and immune cells must be infected to cause the phenotype and suggests that reprogramming immune cells is required for therapeutic efficacy. Our novel approach used RRV to deliver a myeloid transcriptional regulator in intracerebral GBM. This therapy achieved significant survival benefits and increased intratumoral cytotoxic T cells and APCs, while decreasing myeloid immunosuppression. Further studies will expand upon the mechanism of action and test combination therapies. Citation Format: Megan Montoya, Sara A. Collins, Pavlina Chuntova, Noriyuki Kasahara, Hideho Okada. IRF8 driven reprogramming of the immune microenvironment enhances anti-tumor adaptive immunity and reduces immunosuppression in murine glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1417.

Development of a novel humanized anti-TSLP monoclonal antibody HZ-1127 with anti-allergic diseases and cancer potential.

Thymic stromal lymphopoietin (TSLP) is a member of the IL-2 cytokine family and has been widely recognized as a master regulator of type 2 inflammatory responses at barrier surfaces. Recent studies found dysregulation of the TSLP-TSLP receptor (TSLPR) pathway is associated with the pathogenesis of not only allergic diseases but also a wide variety of cancers including both solid tumors and hematological tumors. Thus, the blockade of TSLP represents an attractive therapeutic strategy for allergic diseases and cancer. In this study, we report the development of a novel humanized anti-TSLP monoclonal antibody (mAb) HZ-1127. Binding affinity, specificity, and ability of HZ-1127 in inhibiting TSLP were tested. HZ-1127 selectively binds to the TSLP cytokine with high affinity and specificity. Furthermore, HZ-1127 dramatically inhibits TSLP-dependent STAT5 activation and is more potent than Tezepelumab, which is an FDA-approved humanized mAb against TSLP for severe asthma treatment in inhibiting TSLP-induced CCL17 and CCL22 chemokines secretion in human peripheral blood mononuclear cells. Our pre-clinical study demonstrates that HZ-1127 may serve as a potential therapeutic agent for allergic diseases and cancer.

The significance of T-BET-positive CD8 T-cells with diminished CD5 expression in Kikuchi-Fujimoto disease.

Kikuchi-Fujimoto disease (KFD), also known as histiocytic necrotizing lymphadenitis, is a rare condition characterized by benign localized lymphadenopathy and clinical symptoms such as fever, sore throat, odynophagia, and leukopenia. Though the etiology of KFD is unknown, this condition is similar to viral infection, including increased infiltration of activated plasmacytoid dendritic cells. KFD exhibits three histological phases that reflect its progression status: proliferative, necrotic, and xanthomatous lesions. The expression loss of pan T-cell markers, such as CD2, CD5, and CD7, of infiltrating T-cells is observed in KFD cases, complicating the distinction from T-cell lymphoma. However, reports on the loss of their expression in KFD have been limited. Furthermore, the precise population of the T-cell subset in KFD is still unclear. Here, we focused on surface markers and transcription factors for T-cell differentiation and analyzed them immunohistochemically in 46 KFD cases. We observed diminished CD5 expression of CD8-positive (CD5dim CD8+) T-cells in the proliferative lesion of KFD cases. Furthermore, these CD5dim CD8+ T-cells expressed T-BET, a master regulator of type 1 helper T-cells. The upregulation of T-BET and downregulation of CD5 in CD8+ T-cells causes dysregulated activation and proliferation of CD8+ T-cells, potentially contributing to the unique histopathological features of KFD. Recognizing the frequent infiltration of T-BET-positive CD5dim CD8+ T-cells in KFD is important for distinguishing it from mature T-cell lymphoma. Our findings suggest that the immune response in KFD shares similarities with viral infections and highlight the importance of characterizing T-BET-positive CD5dim CD8+ T-cell populations for understanding KFD pathogenesis.

Value of thymic stromal lymphopoietin as a biomarker in children with asthma

BackgroundThymic stromal lymphopoietin (TSLP), an epithelium-derived pro-inflammatory cytokine, activates distinct immune and non-immune cells. It has been shown to be a master regulator of type 2 immune responses. Limited information is available on TSLP in childhood asthma. The aim of the present study was to find out whether there is association between TSLP concentrations and asthma phenotypes or disease activity. MethodsA total of 207 children with asthma and 100 healthy children aged 1–13 years were enrolled. This study examined serum TSLP concentrations using ELISA Kit in asthma patients and controls, analyzed its correlation with asthma phenotypes and pulmonary function. We also examined TSLP concentrations in 23 patients during stable asthma and in acute asthma exacerbation. ResultsThe serum concentrations of TSLP were significantly elevated in asthma patients compared with healthy controls (p < 0.05), but there was no significant difference (p > 0.05) in TSLP concentrations between three different asthma phenotypes (allergic asthma, virus induced asthma and nonallergic asthma). There was no significant correlation between TSLP concentrations and FEV1pred% (r = 0.01, p > 0.05).In the acute asthma exacerbation TSLP concentrations were not significantly different than in stable phase of disease (p > 0.05). ConclusionChildren with asthma have higher serum TSLP concentrations when compared to healthy controls. TSLP does not seem to be a biomarker of disease exacerbation in children. Different asthma phenotypes have similar TSLP concentration profile in peripheral blood and TSLP does not seem to be useful biomarker in asthma phenotyping in children.

IRGM1, a guardian of mitochondrial DAMP-mediated autoinflammation.

IRGM1 is recognized as a master regulator of type I interferon responses against pathogens, while also protecting against autoimmune diseases. It has now been shown that IRGM1 controls autoinflammatory responses by modulating mitophagy flux.

Abstract LB-A20: True small molecule STING agonist generates systemic and potent anti-tumor immunity required for effective cancer immunotherapy

Abstract STING (Stimulator of Interferon Genes) is a master regulator of type I interferons and a key mediator of innate immunity. Activation of STING provides two critical anti-tumor responses – (1) The “spark” for initiating a robust innate immune response and (2) Priming and activation of a potent T cell mediated anti-tumor adaptive response. By serving as a bridge between the two arms of the immune system, activation of STING has the potential to transform the tumor microenvironment from immunologically “cold” to “hot” (inflamed), making otherwise resistant tumors respond to checkpoint blockade as well as other T cell targeting immunotherapies. Many preclinical and clinical drug discovery programs targeting STING activation are based on modifications of the naturally occurring cyclic dinucleotide (CDN) agonists. However, the CDN molecules suffer from poor drug-like properties and consequently cannot be delivered systemically. Thus, the benefits of STING activation by these first generation CDNs will be limited to only a subset of tumors that are accessible to intratumoral injection. The large, polar and charged binding site as well as the mechanism of activation of STING present unique drug discovery challenges to designing a small molecule that can induce the optimal, active conformation of the STING dimer while maintaining the physical-chemical properties required for systemic exposure. Using our proprietary physics-driven discovery engine with our integrative chemistry/biophysics/biology approach we have developed novel small molecule agonists of STING that exhibit selective and potent activity across all known isoforms of the human protein. Our small molecule agonist rapidly activates the STING/TBK1/IRF3 pathway (phosphorylation and translocation) and induces the expression of type I IFN in cells in a STING-dependent manner. Treatment of primary immune cells from healthy human donors results in the activation of dendritic cells and upregulation of costimulatory markers. Drug characteristics and STING pharmacology allow for unique dosing paradigm in vivo with robust induction of type I IFN after intravenous (i.v.) administration. A single i.v. dose produces potent and durable anti-tumor immunity and complete tumor regression in mice bearing syngeneic tumors. Activation of tumor directed T cell response provides long term protection against tumor re-challenge and effective systemic immunity. Our work highlights the tremendous potential of a small molecule STING agonist as a well-tolerated, systemically delivered cancer immunotherapeutic. Citation Format: Meghana M Kulkarni, Timothy Dwight, Kristen Marino, Bryce K Allen, Mohammed Taimi, Cecilia Bastos, Sujen Lai, Cheryl Koh, Ramya Samant, Bethany Tesar, Huang Huang, Brian Chamberlain, James M Rice, Dazhi Tan, Zhixiong Lin, Sharon Shechter, Stella Li, Sam Sparks, Holly Soutter, Steven Swann, Woody Sherman, Christopher Winter. True small molecule STING agonist generates systemic and potent anti-tumor immunity required for effective cancer immunotherapy [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr LB-A20. doi:10.1158/1535-7163.TARG-19-LB-A20

Interferon regulatory factor 7 (IRF7) represents a link between inflammation and fibrosis in the pathogenesis of systemic sclerosis

ObjectivesThere is considerable evidence that implicates dysregulation of type I interferon signalling (or type I IFN signature) in the pathogenesis of systemic sclerosis (SSc). Interferon regulatory factor 7 (IRF7) has...

Kallikrein–Kinin System Suppresses Type I Interferon Responses: A Novel Pathway of Interferon Regulation

The Kallikrein–Kinin System (KKS), comprised of kallikreins (klks), bradykinins (BKs) angiotensin-converting enzyme (ACE), and many other molecules, regulates a number of physiological processes, including inflammation, coagulation, angiogenesis, and control of blood pressure. In this report, we show that KKS regulates Type I IFN responses, thought to be important in lupus pathogenesis. We used CpG (TLR9 ligand), R848 (TLR7 ligand), or recombinant IFN-α to induce interferon-stimulated genes (ISGs) and proteins, and observed that this response was markedly diminished by BKs, klk1 (tissue kallikrein), or captopril (an ACE inhibitor). BKs significantly decreased the ISGs induced by TLRs in vitro and in vivo (in normal and lupus-prone mice), and in human PBMCs, especially the induction of Irf7 gene (p < 0.05), the master regulator of Type I IFNs. ISGs induced by IFN-α were also suppressed by the KKS. MHC Class I upregulation, a classic response to Type I IFNs, was reduced by BKs in murine dendritic cells (DCs). BKs decreased phosphorylation of STAT2 molecules that mediate IFN signaling. Among the secreted pro-inflammatory cytokines/chemokines analyzed (IL-6, IL12p70, and CXCL10), the strongest suppressive effect was on CXCL10, a highly Type I IFN-dependent cytokine, upon CpG stimulation, both in normal and lupus-prone DCs. klks that break down into BKs, also suppressed CpG-induced ISGs in murine DCs. Captopril, a drug that inhibits ACE and increases BK, suppressed ISGs, both in mouse DCs and human PBMCs. The effects of BK were reversed with indomethacin (compound that inhibits production of PGE2), suggesting that BK suppression of IFN responses may be mediated via prostaglandins. These results highlight a novel regulatory mechanism in which members of the KKS control the Type I IFN response and suggest a role for modulators of IFNs in the pathogenesis of lupus and interferonopathies.

Functions of the two zebrafish MAVS variants are opposite in the induction of IFN1 by targeting IRF7.

IFNs create the first line of host cells to defense viral infection, however, unrestricted expression of IFN can be hazardous to the host. IRF7 is the master regulator of type I IFN expression. To our knowledge, non research about the inhibition of IFN expression by targeting IRF7 has been reported in fish. In this study, we reported that the splicing variant of wildtype MAVS (MAVS_tv1), MAVS_tv2, negatively regulated IRF7-mediated IFN production. Firstly, in vivo, the transcriptional levels of MAVS_tv2 in trunk kidney and spleen from the zebrafish infected with SVCV were monitored. Then, in vitro, the protein expression pattern of MAVS_tv2 in zebrafish cell lines was detected using anti-MAVS_tv2 antibody. Furthermore, overexpression of MAVS_tv2 decreased the activation of IFN1 promoter that induced by IRF7 in a dose-dependent manner, whereas it had little effect on IRF3, a close relative of IRF7. In addition, such inhibition was also observed in IRF7-mediated epcIFN promoter and ISRE activities, but not in the activation of the promoters of type II IFNs and NF-ĸB, due to IRF7 not regulating their expression. Lastly, overexpression of MAVS_tv2 decreased the transcriptional levels of several IFN-stimulated genes activated by IRF7. These findings suggest that MAVS_tv2 is a negative regulator of IFN1 by targeting IRF7.

TRIM35 negatively regulates TLR7- and TLR9-mediated type I interferon production by targeting IRF7

Toll-like receptor 7 (TLR7) and TLR9 sense viral nucleic acids and induce type I IFN production, which must be properly controlled to avoid autoimmune diseases. Here, we report the negative regulation of TLR7/9-mediated type I IFN production by TRIM35. TRIM35 expression is induced by TLR7/9 stimulation and then interacts with IRF7, which is the master regulator of type I IFN response. Furthermore, TRIM35 promotes the K48-linked ubiquitination of IRF7 and induces its degradation via a proteasome-dependent pathway. Therefore, TRIM35 is a negative feedback regulator of TLR7/9-mediated type I IFN production due to its ability to suppress the stability of IRF7.

Spatiotemporal requirements for IRF7 in mediating type I IFN-dependent susceptibility to blood-stage Plasmodium infection.

Type I IFN signaling suppresses splenic T helper 1 (Th1) responses during blood-stage Plasmodium berghei ANKA (PbA) infection in mice, and is crucial for mediating tissue accumulation of parasites and fatal cerebral symptoms via mechanisms that remain to be fully characterized. Interferon regulatory factor 7 (IRF7) is considered to be a master regulator of type I IFN responses. Here, we assessed IRF7 for its roles during lethal PbA infection and nonlethal Plasmodium chabaudi chabaudi AS (PcAS) infection as two distinct models of blood-stage malaria. We found that IRF7 was not essential for tissue accumulation of parasites, cerebral symptoms, or brain pathology. Using timed administration of anti-IFNAR1 mAb, we show that late IFNAR1 signaling promotes fatal disease via IRF7-independent mechanisms. Despite this, IRF7 significantly impaired early splenic Th1 responses and limited control of parasitemia during PbA infection. Finally, IRF7 also suppressed antiparasitic immunity and Th1 responses during nonlethal PcAS infection. Together, our data support a model in which IRF7 suppresses antiparasitic immunity in the spleen, while IFNAR1-mediated, but IRF7-independent, signaling contributes to pathology in the brain during experimental blood-stage malaria.

Human endogenous retrovirus expression is inversely related with the up-regulation of interferon-inducible genes in the skin of patients with lichen planus.

Lichen planus (LP) is a common inflammatory skin disease of unknown etiology. Reports of a common transactivation of quiescent human endogenous retroviruses (HERVs) support the connection of viruses to the disease. HERVs are ancient retroviral sequences in the human genome and their transcription is often deregulated in cancer and autoimmune diseases. We explored the transcriptional activity of HERV sequences as well as the antiviral restriction factor and interferon-inducible genes in the skin from LP patients and healthy control (HC) donors. The study included 13 skin biopsies from patients with LP and 12 controls. Real-time PCR assay identified significant decrease in the HERV-K gag and env mRNA expression levels in LP subjects, when compared to control group. The expressions of HERV-K18 and HERV-W env were also inhibited in the skin of LP patients. We observed a strong correlation between HERV-K gag with other HERV sequences, regardless the down-modulation of transcripts levels in LP group. In contrast, a significant up-regulation of the cytidine deaminase APOBEC 3G (apolipoprotein B mRNA-editing), and the GTPase MxA (Myxovirus resistance A) mRNA expression level was identified in the LP skin specimens. Other transcript expressions, such as the master regulator of type I interferon-dependent immune responses, STING (stimulator of interferon genes) and IRF-7 (interferon regulatory factor 7), IFN-β and the inflammassome NALP3, had increased levels in LP, when compared to HC group. Our study suggests that interferon-inducible factors, in addition to their role in innate immunity against exogenous pathogens, contribute to the immune control of HERVs. Evaluation of the balance between HERV and interferon-inducible factor expression could possibly contribute to surveillance of inflammatory/malignant status of skin diseases.

Regulatory function of interferon regulatory factor 3 in obesity, inflammation and insulin resistance (HUM7P.287)

Abstract Obesity is a major risk factor for diseases ranging from insulin resistance, type 2 diabetes mellitus to nonalcoholic fatty liver disease. Obesity is associated with a state of chronic, low-grade inflammation. In this study, we found the important regulatory role of interferon regulatory factor 3 (IRF3), a master regulator of type I interferon-dependent immune responses, in obesity. We found that the expression of IRF3 was increased in white adipose tissue (WAT) from mice fed with high fat diet compared with that from mice fed with normal chow. IRF3 knockout (KO) mice developed obesity spontaneously with increased adiposity compared with wild-type (WT) controls. Deficiency of IRF3 in mice resulted in impaired insulin sensitivity and lipid homeostasis. The development of obesity in IRF3 KO mice was associated with increased infiltration of macrophages which was more inflammatory in the WAT compared with macrophages in WT mice. IRF3 deficient macrophages exhibited increased M1 polarization than WT cells. Additionally, IRF3 KO mice developed hepatic steatosis with increased expression of lipogenesis genes in the liver. Our study therefore demonstrated that IRF3 played an important role in the regulation of insulin sensitivity, inflammation and lipid homeostasis, which may provide a new strategy for treatment of obesity, type 2 diabetes mellitus and hepatic steatosis.

Evidence for a Functional Thymic Stromal Lymphopoietin Signaling Axis in Fibrotic Lung Disease

Thymic stromal lymphopoietin (TSLP) recently has emerged as a key cytokine in the development of type 2 immune responses. Although traditionally associated with allergic inflammation, type 2 responses are also recognized to contribute to the pathogenesis of tissue fibrosis. However, the role of TSLP in the development of non-allergen-driven diseases, characterized by profibrotic type 2 immune phenotypes and excessive fibroblast activation, remains underexplored. Fibroblasts represent the key effector cells responsible for extracellular matrix production but additionally play important immunoregulatory roles, including choreographing immune cell recruitment through chemokine regulation. The aim of this study was to examine whether TSLP may be involved in the pathogenesis of a proto-typical fibrotic disease, idiopathic pulmonary fibrosis (IPF). We combined the immunohistochemical analysis of human IPF biopsy material with signaling studies by using cultured primary human lung fibroblasts and report for the first time, to our knowledge, that TSLP and its receptor (TSLPR) are highly upregulated in IPF. We further show that lung fibroblasts represent both a novel cellular source and target of TSLP and that TSLP induces fibroblast CCL2 release (via STAT3) and subsequent monocyte chemotaxis. These studies extend our understanding of TSLP as a master regulator of type 2 immune responses beyond that of allergic inflammatory conditions and suggest a novel role for TSLP in the context of chronic fibrotic lung disease.

Anti-allergic effect of strawberry extract

We examined the anti-allergic effect of strawberry extract on human peripheral blood mononuclear cells (PBMCs) and atopic dermatitis model mice NC/NgaTndCrlj. The addition of strawberry extract suppressed total IgE production in the cedar pollen antigen Cry j 1-stimulated PBMCs. Flow cytometric analysis showed that strawberry extract decreased the rate of CD3+CD4+ helper T cells by 17.3% and increased the rate of CD3+CD8+ cytotoxic T cells by 19.7% in PBMCs. Moreover, the extract inhibited the expression level of GATA3 that is the master regulator of type 2 helper T cells (Th2) in human primary pan T cells isolated from PBMCs. Oral administration of strawberry extract lowered dermatitis scores and serum IgE levels in mice. In addition, it also decreased the GATA3 expression level in mouse blood cells. These results revealed that strawberry extract suppressed the severity of atopic dermatitis through the down-regulation of serum IgE by inhibition of Th2 differentiation.

Negative Regulation of Nmi on Virus-Triggered Type I IFN Production by Targeting IRF7

Viral infection causes host cells to produce type I IFNs, which play a critical role in viral clearance. IFN regulatory factor (IRF) 7 is the master regulator of type I IFN-dependent immune responses. In this article, we report that N-Myc and STATs interactor (Nmi), a Sendai virus-inducible protein, interacted with IRF7 and inhibited virus-triggered type I IFN production. The overexpression of Nmi inhibited the Sendai virus-triggered induction of type I IFNs, whereas the knockdown of Nmi promoted IFN production. Furthermore, the enhanced production of IFNs resulting from Nmi knockdown was sufficient to protect cells from infection by vesicular stomatitis virus. In addition, Nmi was found to promote the K48-linked ubiquitination of IRF7 and the proteasome-dependent degradation of this protein. Finally, an impairment of antiviral responses is also detectable in Nmi-transgenic mice. These findings suggest that Nmi is a negative regulator of the virus-triggered induction of type I IFNs that targets IRF7.

Interferon regulatory factor 7 deficiency prevents diet-induced obesity and insulin resistance

Obesity-related inflammation has been implicated in the pathogenesis of insulin resistance and type 2 diabetes. In this study, we addressed the potential role of interferon regulatory factor 7 (IRF7), a master regulator of type I interferon-dependent immune responses, in the regulation of energy metabolism. The expression levels of IRF7 were increased in white adipose tissue, liver tissue, and gastrocnemius muscle of both diet-induced obese mice and ob/ob mice compared with their lean counterparts. After feeding a high-fat diet (HFD) for 24 wk, IRF7 knockout (KO) mice showed less weight gain and adiposity than wild-type controls. KO of IRF7 improved glucose and lipid homeostasis and insulin sensitivity. Additionally, KO of IRF7 ameliorated diet-induced hepatic steatosis. Next, we assessed the inflammatory state of the IRF7 KO mice on the HFD. These mice showed less macrophage infiltration into multiple organs and were protected from local and systemic inflammation. This study demonstrates a role for IRF7 in diet-induced alterations in energy metabolism and insulin sensitivity. Our results also suggest that IRF7 is involved in the etiology of metabolic abnormalities, which suggests a new strategy for treating obesity and type 2 diabetes.

Tripartite Motif-Containing Protein 28 Is a Small Ubiquitin-Related Modifier E3 Ligase and Negative Regulator of IFN Regulatory Factor 7

IFN regulatory factor 7 (IRF7) is a potent transcription factor of type I IFNs and IFN-stimulated genes and is known as the master regulator of type I IFN-dependent immune responses. Because excessive responses could harm the host, IRF7 itself is delicately regulated at the transcriptional, translational, and posttranslational levels. Modification of IRF7 by small ubiquitin-related modifiers (SUMOs) has been shown to regulate IFN expression and antiviral responses negatively, but the specific E3 ligase needed for IRF7 SUMOylation has remained unknown. As reported in this article, we have identified the tripartite motif-containing protein 28 (TRIM28) as a binding partner of IRF7. We have demonstrated that TRIM28 also interacts with the SUMO E2 enzyme and increases SUMOylation of IRF7 both in vivo and in vitro, suggesting it acts as a SUMO E3 ligase of IRF7. Unlike the common SUMO E3 ligase, protein inhibitor of activated STAT1, the E3 activity of TRIM28 is specific to IRF7, because it has little effect on IRF7's close relative IRF3. TRIM28 is therefore, so far as we know, the first IRF7-specific SUMO E3 reported. TRIM28-mediated SUMOylation of IRF7 is increased during viral infection, and SUMOylation of transcription factors usually results in transcriptional repression. Overexpression of TRIM28 therefore inhibits IRF7 transactivation activity, whereas knockdown of TRIM28 has the opposite effect and potentiates IFN production and antiviral responses. Collectively, our results suggest that TRIM28 is a specific SUMO E3 ligase and negative regulator of IRF7.

Negative Regulation of IRF7 Activation by Activating Transcription Factor 4 Suggests a Cross-Regulation between the IFN Responses and the Cellular Integrated Stress Responses

Cells react to viral infection by exhibiting IFN-based innate immune responses and integrated stress responses, but little is known about the interrelationships between the two. In this study, we report a linkage between these two host-protective cellular mechanisms. We found that IFN regulatory factor (IRF)7, the master regulator of type I IFN gene expression, interacts with activating transcription factor (ATF)4, a key component of the integrated stress responses whose translation is induced by viral infection and various stresses. We have demonstrated that IRF7 upregulates ATF4 activity and expression, whereas ATF4 in return inhibits IRF7 activation, suggesting a cross-regulation between the IFN response and the cellular integrated stress response that controls host innate immune defense against viral infection.