Interferon Regulatory Factor 5 Activation Research Articles

Diesel exhaust particles activate macrophages and IRF5 expression in atherosclerosis

Abstract Introduction Over 20% of global deaths related to cardiovascular disease have been attributed in part to air pollution, particularly fine particulate matter (PM2.5) (1). In highly trafficked urban areas, smaller ultrafine diesel exhaust particles (DEP) represent a significant proportion of PM2.5. DEP is associated with the progression of atherosclerosis and increased plaque susceptibility to rupture (2). We have previously shown that interferon regulatory factor 5 (IRF5) has a key role in necrotic core formation, a distinguishing feature of vulnerable atherosclerotic plaques, by rendering macrophages defective at efferocytosis (3). Pronounced elevation of IRF5 is also seen in symptomatic carotid plaques, particularly in the rupture-prone shoulder regions (4). Purpose We examined the effect of DEP on macrophage phenotype and IRF5 expression in atherosclerosis. Methods Bone marrow-derived macrophages (BMDMs) from C57BL/6 mice, differentiated with GM-CSF (to mimic inflammatory macrophages) or M-CSF (mimicking homeostatic resident macrophages) were incubated with PBS or DEP (10 µg/mL) in vitro for 18 hours. Expression of inflammatory cytokines (IL-6, IL-12α), macrophage polarisation markers CD11c (itgax, inflammatory) and CD206 (mrc1, resident anti-inflammatory) and IRF5 was quantified by real-time PCR. In addition, high fat-fed ApoE-/- mice were exposed to saline or DEP (35 µL at 1 mg/mL) twice weekly for 5 weeks by pulmonary administration. The pan-macrophage marker CD64, CD206 and IRF5 were quantified in paraffin-embedded sections of brachiocephalic artery lesions by immunohistochemistry. Results In M-CSF-differentiated murine macrophages incubated with DEP, significant fold increases in gene expression (relative to PBS control) were observed: IRF5 (1.4-fold), IL-6 (31.5-fold) and IL-12α (5.8-fold) while CD206 (0.8-fold) decreased (Figure 1a, n = 5, p<0.05, two-tailed paired t-tests). CD11c expression was unchanged. No statistically significant differences were detected in GM-CSF-differentiated macrophages. In the brachiocephalic arteries of DEP-exposed ApoE-/- mice we observed increases in CD64+ macrophages (28.2±7.4 vs 15.5±5.6) and IRF5 (16.6±3.6 vs 10.1±3.4) expression, while CD206 expression decreased (4.1±0.9 vs 11.0±1.2) in comparison to saline-exposed mice (Figure 1b mean±SD, n = 5, p<0.05, two-tailed unpaired t-tests, data expressed as % of intima area). Conclusion DEP promotes CD64+ macrophages and IRF5 expression in murine atherosclerosis, while inflammation and IRF5 is induced in vitro, but only in M-CSF-differentiated murine BMDMs. This suggests that DEP has no impact on inflammatory macrophages but could switch homeostatic resident macrophages to a more inflammatory phenotype via the activation of IRF5. Therefore, IRF5 is a promising candidate for further investigation into the initial macrophage response to inhaled particles that leads to the exacerbation of vascular disease.

The prognostic impact of transforming growth factor beta 2 (TGFB2) mRNA levels, in conjunction with interferon-gamma receptor activation of interferon regulatory factor 5 (IRF5) and expression of CD276/B7-H3 in low-grade gliomas.

e14564 Background: Low-grade glioma (LGG) tumors are characterized by a low infiltration of immune cells, requiring therapeutic interventions to boost the immune response. Methods: We analyzed mRNA expression datasets from the UCSC Xena web platform to compare normal brain tissue with LGG tumor samples to screen for upregulated genes. We also used cBioportal to determine the relationship between mRNA expression levels of 513 LGG patients and their overall survival (OS) outcomes. Results: Tumor-associated macrophage (TAM) markers, MSR1/CD204, CD86, and CD68, exhibited a 6-fold (P<0.0001), 8.9-fold (P<0.0001), and 15.6-fold increases in mRNA expression levels, respectively in LGG tumors. Both TGFB1 (4.1-fold increase, P<0.0001) and TGFB2 (2.2-fold increase, P<0.0001) were upregulated in brain tumors, suggesting that TGFB ligands are pivotal in establishing an immunosuppressive TME. In addition, mRNA upregulation of interferon-gamma receptors, IFNGR1 and IFNGR2, and signaling molecules STAT1, IRF1, and IRF5, pointed to an essential role for IFN-γ mediated remodeling of the TME. A tumor-associated antigen, CD276/B7-H3, mRNA expression showed a significant (P<0.0001) 4.03-fold increase in tumor tissue. Multivariate Cox proportional hazards models investigating the interaction of TGFB2 and activation of IFNGR2, STAT1, IRF1, or IRF5 showed that the prognostic impact of high mRNA levels (25 percentile cut-off) of TGFB2high was independent of IFNGR2, STAT1, IRF1, or IRF5 mRNA levels (TGFB2high HR (95% CI) = 4.07 (2.35-7.06), 6 (3.62-10.11), 4.38 (2.67-7.17), and 4.48 (2.82-7.12) for models with IFNGR2, STAT1, IRF1, or IRF5 respectively). Patients with high levels of TGFB2 were overrepresented by LGG patients with IDH wild-type mutation status. The prognostic impact of TGFB2high and IDH wild-type observed by the increases in hazard ratios for TGFB2 (HR (95% CI range) = 2.02 (1.05-3.89)) and IDH wild-type (HR (95% CI range) = 4.44 (1.9-10.4)) were independent predictors of survival requiring risk stratification of patients identify LGG patients with IDH wild-type and TGFB2high in the design of clinical trials. The ratio of TGFB1:TGFB2 expression levels was also a prognostic indicator for OS, whereby patients who exhibited a 2.5-fold greater level of TGFB1 compared to TGFB2 mRNA levels experienced improved survival outcomes. A 1.8-fold higher TGFB2 levels, the mRNA expression corresponded to worse OS. Conclusions: The specific abrogation of TGFB2 and not TGFB1 by OT101, a TGFB2-specific synthetic phosphorothioate antisense oligodeoxynucleotide, is a prerequisite to employing a strategy to target TGFB pathways. IRF5 and CD276/B7-H3 as prognostic markers are potential targets for combination therapies with TGFB2 inhibitors.

Transforming Growth Factor Beta 2 (TGFB2) mRNA Levels, in Conjunction with Interferon-Gamma Receptor Activation of Interferon Regulatory Factor 5 (IRF5) and Expression of CD276/B7-H3, Are Therapeutically Targetable Negative Prognostic Markers in Low-Grade Gliomas.

LGG tumors are characterized by a low infiltration of immune cells, requiring therapeutic interventions to boost the immune response. We conducted a study analyzing mRNA expression datasets from the UCSC Xena web platform. To screen for upregulated genes, we sought to compare normal brain tissue with LGG tumor samples. We also used cBioportal to determine the relationship between mRNA expression levels of 513 LGG patients and their overall survival (OS) outcomes. Three tumor-associated macrophage (TAM) markers, MSR1/CD204, CD86, and CD68, exhibited a 6-fold (p < 0.0001), 8.9-fold (p < 0.0001), and 15.6-fold increase in mRNA expression levels, respectively, in LGG tumors. In addition, both TGFB1 (4.1-fold increase, p < 0.0001) and TGFB2 (2.2-fold increase, p < 0.0001) ligands were also upregulated in these tumors compared to normal brain tissue, suggesting that TGFB ligands are pivotal in establishing an immunosuppressive, angiogenic, and pro-tumorigenic TME in gliomas mediated through TAMs. In addition, mRNA upregulation of interferon-gamma receptors, IFNGR1 and IFNGR2, and the downstream signaling molecules STAT1, IRF1, and IRF5, pointed to an essential role for IFN-γ mediated remodeling of the TME. Interestingly, the mRNA expression of a tumor-associated antigen, CD276/B7-H3, showed a significant (p < 0.0001) 4.03-fold increase in tumor tissue, giving further insights into the roles of macrophages and tumor cells in supporting the immunosuppressive TME. Multivariate Cox proportional hazards models investigating the interaction of TGFB2 and activation of IFNGR2, STAT1, IRF1, or IRF5 showed that the prognostic impact of high mRNA levels (25th percentile cut-off) of TGFB2 was independent of IFNGR2, STAT1, IRF1, or IRF5 mRNA levels (TGFB2high HR (95% CI) = 4.07 (2.35-7.06), 6 (3.62-10.11), 4.38 (2.67-7.17), and 4.48 (2.82-7.12) for models with IFNGR2, STAT1, IRF1, or IRF5, respectively) and age at diagnosis. Patients with high levels of TGFB2 and IFNGR2 were over-represented by LGG patients with isocitrate dehydrogenase wild-type (IDHwt) mutation status. The prognostic impact of high levels of TGFB2 and IDH wild-type observed by the increases in hazard ratios for TGFB2 (HR (95% CI range) = 2.02 (1.05-3.89)) and IDH wild-type (HR (95% CI range) = 4.44 (1.9-10.4)) were independent predictors of survival, suggesting that risk stratification of patients identifies LGG patients with IDH wild-type and high levels of TGFB2 in the design of clinical trials. Furthermore, we have additional IRF5 and CD276/B7-H3 as prognostic markers that can also be targeted for combination therapies with TGFB2 inhibitors. In support of these findings, we demonstrated that low levels of gene methylation in TGFB2, IFNGR2, IRF1, IRF5, STAT1, and CD276 were associated with significantly worse overall survival (OS) outcomes. This suggests that potential mechanisms to increase the expression of these prognostic markers occur via the action of demethylation enzymes.

Early macrophage response to obesity encompasses Interferon Regulatory Factor 5 regulated mitochondrial architecture remodelling

Adipose tissue macrophages (ATM) adapt to changes in their energetic microenvironment. Caloric excess, in a range from transient to diet-induced obesity, could result in the transition of ATMs from highly oxidative and protective to highly inflammatory and metabolically deleterious. Here, we demonstrate that Interferon Regulatory Factor 5 (IRF5) is a key regulator of macrophage oxidative capacity in response to caloric excess. ATMs from mice with genetic-deficiency of Irf5 are characterised by increased oxidative respiration and mitochondrial membrane potential. Transient inhibition of IRF5 activity leads to a similar respiratory phenotype as genomic deletion, and is reversible by reconstitution of IRF5 expression. We find that the highly oxidative nature of Irf5-deficient macrophages results from transcriptional de-repression of the mitochondrial matrix component Growth Hormone Inducible Transmembrane Protein (GHITM) gene. The Irf5-deficiency-associated high oxygen consumption could be alleviated by experimental suppression of Ghitm expression. ATMs and monocytes from patients with obesity or with type-2 diabetes retain the reciprocal regulatory relationship between Irf5 and Ghitm. Thus, our study provides insights into the mechanism of how the inflammatory transcription factor IRF5 controls physiological adaptation to diet-induced obesity via regulating mitochondrial architecture in macrophages.

STK25 functions as an IRF5 kinase to promote TLR7/8-mediated inflammation

Abstract Toll-like receptors (TLRs) represent a subset of pathogen-recognition receptors (PRRs) employed by the innate immune system to detect pathogen-associated molecular patterns (PAMPs) and initiate the response to invading microbes. The transcription factor interferon regulatory factor 5 (IRF5) functions as an important mediator of the inflammatory response downstream of myeloid differentiation factor 88 (MyD88)-dependent TLR activation. While the dysregulation of IRF5 activity has been implicated in the development of several autoimmune diseases including systemic lupus erythematosus and rheumatoid arthritis, the factors that modulate TLR-induced IRF5 post-translational modifications (PTMs) are poorly understood. Therefore, the focus of this study is to identify protein kinases involved in the regulation of TLR7/8 signaling. We performed a kinome-based siRNA screen in human THP-1 monocytic cells and human primary myeloid cells to identify important mediators of TLR7/8-induced TNF-α and IL-6 production. We identified serine/threonine protein kinase 25 (STK25) as a positive regulator of proinflammatory cytokine production in response to TLR7/8 activation in human myeloid cells. We determined that STK25 phosphorylates IRF5 in vitro via multiple biochemical assays. Phosphopeptide mapping by mass spectrometry revealed that STK25 phosphorylates IRF5 at a highly conserved threonine residue. Thus, our data implicate STK25 as a regulator of TLR7/8 signaling through the modulation of IRF5 activity.

IRF5 Loss Impairs TLR9/BCR-Induced B Cell Activation, Proliferation and Plasmablast Differentiation through Erk1-Myc Signaling

Upon recognition of antigen, B cells undergo rapid proliferation followed by differentiation to specialized antibody secreting cells (ASCs). During this transition, B cells are reliant upon a multilayer transcription factor network to achieve a dramatic remodeling of the B cell transcriptional landscape. Increased levels of ASCs are seen in autoimmune diseases, such as sytemic lupus erythematosus (SLE), and certain B cell-associated malignancies. Studies suggest that altered expression of regulatory transcription factors play a role in the observed imbalance of B cell subsets in these diseases. The transcription factor interferon regulatory factor 5 (IRF5) is one such candidate as polymorphisms in IRF5 associate with risk of numerous autoimmune diseases and correlate with elevated IRF5 expression. Furthermore, dysregulated IRF5 expression and activation have been implicated in a variety of B cell lymphoproliferative disorders. It remains unclear, however, whether IRF5 has a role in normal B cell function. To date, little is known of IRF5 function in human B cells. We utilized human primary naïve B cells combined with IRF5 knockdown to identify a critical new intrinsic role for IRF5 in B cell activation, proliferation and plasma cell differentiation. IRF5 knockdown resulted in significant IgD retention, reduced proliferation, plasmablast differentiation, and IgG secretion. The observed decreases were due to impaired B cell activation and clonal expansion. Distinct from murine studies, we identify and confirm new IRF5 target genes, IRF4, ERK1, and MYC, and signaling pathways that mediate IRF5 B cell-intrinsic function. Together, these results identify IRF5 as an early regulator of human B cell activation and provide the first dataset in human primary B cells to map IRF5 dysfunction in disease. DisclosuresNo relevant conflicts of interest to declare.

Interferon regulatory factor 5 in Rheumatoid arthritis and systemic lupus erythematosus

Interferon regulatory factor 5 (IRF5) has been described as an important factor in regulating inflammatory response and a key transcription factor in the immune system. In antiviral response, IRF5 promotes the expression of type 1 interferon (IFN) and is also important in the differentiation of macrophages towards pro-inflammatory phenotypes, regulating B-cell maturity and antibody production. Some cancer patients treated with IFNα manifest symptoms resembling systemic lupus erythematosus (SLE). An important mechanism in this response is IRF5 that triggers apoptosis. Herein, we discuss the functional importance of IRF5 in rheumatoid arthritis (RA) and SLE in a setting of polymorphic mutations at the human Irf5 locus. This paper describes murine models, the lessons of IRF functionality learned from these models and the consequences of autoimmune diseases. It is hypothesized that modulation of IRF5 activity may be beneficial in autoimmune diseases therapies.

Immune-phenotyping IRF5 genetic risk and in vivo targeting of Irf5 hyper-activation in mouse models of lupus

Abstract Genetic variations within interferon regulatory factor 5 (IRF5) associate with risk of systemic lupus erythematosus (SLE) and mice lacking Irf5 are protected from lupus onset and severity. Exactly how IRF5 functions in the context of SLE disease progression remains unclear. We sought to determine how IRF5 genetic risk contributes to SLE disease onset and severity, and whether targeting IRF5 with select inhibitors would alleviate disease severity and mortality. Studies were performed in blood from genotyped healthy donors, SLE patients and mouse models of murine lupus. In NZB/W F1 lupus mice, we found that Irf5 is already hyper-activated before clinical onset in a cell type-specific manner. In healthy donors carrying IRF5 genetic risk, we detected IRF5 hyper-activation in the myeloid compartment that drives a pre-symptomatic SLE immune-phenotype. In SLE patients, IRF5 hyper-activation correlates with SLEDAI and dsDNA titers. To test whether IRF5 hyper-activation is a targetable function, we developed novel inhibitors that are cell permeable, non-toxic and selectively bind to the inactive IRF5 monomer. Treatment of NZB/W F1 and MRL/lpr mice with inhibitor attenuated lupus pathology by reducing serum ANA and dsDNA titers. In NZB/W F1 mice, we detected significant reductions in the number of circulating plasma cells and age- or autoimmune-associated B cells (ABCs), which alleviated kidney pathology and improved overall survival. In ex vivo human studies, the inhibitor blocked SLE serum-induced IRF5 activation in healthy immune cells and reversed basal IRF5 hyper-activation in SLE immune cells. This study provides the first in vivo pre-clinical support for treating SLE patients with an IRF5 inhibitor.

Molecular mechanisms by which interferon regulatory factor 5 (IRF5) transduces signaling downstream of BCR and BCR/TLR9 pathways

Abstract The transcription factor IRF5 modulates human B cell activation, proliferation, and plasmablast differentiation via an intrinsic mechanism. Targeted knockdown of IRF5 in human primary naïve B cells revealed a significant reduction in CD19+CD86+ B cells, which demarcate early activated B cells, after BCR/TLR9 stimulation, resulting in reduced clonal expansion and plasmablast differentiation. The mechanism(s) by which IRF5 modulates early B cell activation is not known. We previously found that BCR stimulation alone was insufficient to induce IRF5 nuclear translocation (activation), while BCR/TLR9 stimulation induced robust IRF5 activation. Thus, the focus of this study is to determine the mechanism(s) by which IRF5 functions downstream of BCR and dual BCR/TLR9 signaling at the early time points of activation (5 and 15 min). Experiments were performed in human B cells and B cells from wild-type and Irf5−/− mice. Signaling and protein interactions were examined by Western blot, immunoprecipitation, flow cytometry, and biochemical assay. We identified Bruton’s tyrosine kinase (Btk) as a novel interacting partner of IRF5 in both unstimulated and stimulated human and murine B cells. Of note, active phosphorylated Btk was bound to IRF5 only in stimulated cells. Preliminary data also suggest a defect downstream of Btk activation in Irf5−/− B cells. Together, these data indicate a conserved role for IRF5 in the early stages of B cell activation via BCR/TLR9 signaling.

Native Polyacrylamide Gel Electrophoresis Immunoblot Analysis of Endogenous IRF5 Dimerization.

Interferon regulatory factor 5 (IRF5) is a key transcription factor for regulating the immune response. It is activated downstream of the Toll-like receptor myeloid differentiation primary response gene 88 (TLR-MyD88) signaling pathway. IRF5 activation involves phosphorylation, dimerization, and subsequent translocation from the cytoplasm into the nucleus, which in turn induces the gene expression of various pro-inflammatory cytokines. A detection assay for IRF5 activation is essential to studying IRF5 functions and its relevant pathways. This article describes a robust assay to detect endogenous IRF5 activation in the CAL-1 human plasmacytoid dendritic cell (pDC) line. The protocol consists of a modified nondenaturing electrophoresis assay that can distinguish IRF5 in its monomer and dimer forms, thus providing an affordable and sensitive approach to analyze IRF5 activation.

FcγR-TLR Cross-Talk Enhances TNF Production by Human Monocyte-Derived DCs via IRF5-Dependent Gene Transcription and Glycolytic Reprogramming.

Antigen-presenting cells (APCs) such as dendritic cells (DCs) are crucial for initiation of adequate inflammatory responses, which critically depends on the cooperated engagement of different receptors. In addition to pattern recognition receptors (PRRs), Fc gamma receptors (FcγRs) have recently been identified to be important in induction of inflammation by DCs. FcγRs that recognize IgG immune complexes, which are formed upon opsonization of pathogens, induce pro-inflammatory cytokine production through cross-talk with PRRs such as Toll-like receptors (TLRs). While the physiological function of FcγR-TLR cross-talk is to provide protective immunity against invading pathogens, undesired activation of FcγR-TLR cross-talk, e.g., by autoantibodies, also plays a major role in the development of chronic inflammatory disorders such as rheumatoid arthritis (RA). Yet, the molecular mechanisms of FcγR-TLR cross-talk are still largely unknown. Here, we identified that FcγR-TLR cross-talk-induced cytokine production critically depends on activation of the transcription factor interferon regulatory factor 5 (IRF5), which results from induction of two different pathways that converge on IRF5 activation. First, TLR stimulation induced phosphorylation of TBK1/IKKε, which is required for IRF5 phosphorylation and subsequent activation. Second, FcγR stimulation induced nuclear translocation of IRF5, which is essential for gene transcription by IRF5. We identified that IRF5 activation by FcγR-TLR cross-talk amplifies pro-inflammatory cytokine production by increasing cytokine gene transcription, but also by synergistically inducing glycolytic reprogramming, which is another essential process for induction of inflammatory responses by DCs. Combined, here we identified IRF5 as a pivotal component of FcγR-TLR cross-talk in human APCs. These data may provide new potential targets to suppress chronic inflammation in autoantibody-associated diseases that are characterized by undesired or excessive FcγR-TLR cross-talk, such as RA, systemic sclerosis, and systemic lupus erythematous.

Microbial recognition by GEF-H1 controls IKK\u03b5 mediated activation of IRF5

During infection, transcription factor interferon regulatory factor 5 (IRF5) is essential for the control of host defense. Here we show that the microtubule-associated guanine nucleotide exchange factor (GEF)-H1, is required for the phosphorylation of IRF5 by microbial muramyl-dipeptides (MDP), the minimal structural motif of peptidoglycan of both Gram-positive and Gram-negative bacteria. Specifically, GEF-H1 functions in a microtubule based recognition system for microbial peptidoglycans that mediates the activation of IKKε which we identify as a new upstream IKKα/β and IRF5 kinase. The deletion of GEF-H1 or dominant-negative variants of GEF-H1 prevent activation of IKKε and phosphorylation of IRF5. The GEF-H1-IKKε-IRF5 signaling axis functions independent of NOD-like receptors and is critically required for the recognition of intracellular peptidoglycans and host defenses against Listeria monocytogenes.

Advances and challenges in targeting IRF5, a key regulator of inflammation.

Interferon regulatory factor 5 (IRF5) belongs to a family of transcription factors, originally implicated in antiviral responses and interferon production. However, studies conducted in different laboratories over the last decade have placed IRF5 as a central regulator of the inflammatory response. It has become clear that IRF5 contributes to the pathogenesis of many inflammatory and autoimmune diseases, such as rheumatoid arthritis, inflammatory bowel disease and systemic lupus erythematosus. Given the role of IRF5 in physiology and disease, IRF5 represents a potential therapeutic target. However, despite a significant interest from the pharmaceutical industry, inhibitors that interfere with the IRF5 pathway remain elusive. Here, we review the advances made by various studies in targeting multiple steps of signalling leading to IRF5 activation with their therapeutic potential, and the possible complications of such strategies are discussed.

IRF-5 Promotes Cell Death in CD4 T Cells during Chronic Infection

The transcription factor interferon regulatory factor 5 (IRF-5) plays an important function in innate immunity and in initiating pro-inflammatory responses against pathogens. IRF-5 is constitutively expressed in several cell types, including plasmacytoid dendritic cells, monocytes, and B cells. We have previously reported that IRF-5 is also expressed in Tcells during infection. The role of IRF-5 in Tcells is yet unknown. Here, we demonstrate that IRF-5 is increasingly expressed in interferon (IFN)-γ+ CD4 Tcells over the course of L.donovani infection. This transcription factor is induced by apoptotic material via Toll-like receptor 7 (TLR7) and promotes the expression of death receptor 5 (DR5). IRF-5 activation sensitizes CD4 Tcells to cell death. Because tissue disruption and chronic inflammation are common characteristics of persistent infections, activation of IRF-5 in CD4 Tcells may represent a common pathway that leads to suppression of protective CD4 Tcell responses, favoring the establishment of chronic infection.

Regulation and role of the transcription factor IRF5 in innate immune responses and systemic lupus erythematosus.

The transcription factor interferon regulatory factor-5 (IRF5) plays an important role in innate immune responses via the TLR-MyD88 (Toll-like receptor - myeloid differentiation primary response 88) pathway. IRF5 is also involved in the pathogenesis of the autoimmune disease systemic lupus erythematosus (SLE). Recent studies have identified new regulators, both positive and negative, which act on IRF5 activation events in the TLR-MyD88 pathway such as post-translational modifications, dimerization and nuclear translocation. A model of the causal relationship between IRF5 activation and SLE pathogenesis proposes that a loss of the negative regulation of IRF5 causes its hyperactivation, resulting in hyperproduction of type I interferons and other cytokines, and ultimately in the development of SLE. Importantly, to our knowledge, all murine models of SLE studied thus far have shown that IRF5 is required for the pathogenesis of SLE-like diseases. During the development of SLE-like diseases, IRF5 plays key roles in various cell types, including dendritic cells and B cells. It is noteworthy that the onset of SLE-like diseases can be inhibited by reducing the activity or amount of IRF5 by half. Therefore, IRF5 is an important therapeutic target of SLE, and selective suppression of its activity and expression may potentially lead to the development of new therapies.

Lineage-Specific Functionality of an Interferon Regulatory Factor 5 Lupus Risk Haplotype: Lack of B Cell Intrinsic Effects.

Interferon regulatory factor 5 (IRF5) is widely recognized as a risk locus for systemic lupus erythematosus (SLE). Risk gene and IRF5 activation is triggered through toll-like receptor signaling. In myeloid cells, this leads to production of type I interferon and inflammatory cytokines, with enhanced production in cells of individuals harboring IRF5 risk alleles. Mouse models have also demonstrated the importance of IRF5 in B cell function, particularly plasma cell differentiation and isotype switching. Here, we evaluated the major SLE risk haplotype of IRF5 on the functional attributes of freshly isolated B cells from human subjects who do not have evidence of SLE or other forms of autoimmunity. We took this approach to avoid the complications of studying genotype-phenotype relationships in B cells that have been chronically exposed to an inflammatory disease environment before isolation. We focused on B cell endophenotypes that included gene expression, antibody secretion, class switching, and apoptotic susceptibility. We performed IRF5 overexpression studies, genetic reporter assays and electro-mobility shift assays on B and myeloid cell lines. Somewhat surprisingly, the results of our analyses indicate that IRF5 risk genotypes do not have a B cell intrinsic effect on these B cell functions. By contrast, we confirmed that the IRF5 risk and non-risk haplotypes exert differential effects in myeloid cells, including an increased susceptibility to apoptosis conferred by the risk haplotype. We also demonstrated an increased binding of the transcription factor specificity protein 1 to an insertion/deletion present in the risk haplotype. Our findings raise the specter that genetic risk alleles can have complex and unexpected lineage-specific effects, and these must be carefully considered when guiding or developing therapies based on understanding disease risk haplotypes.

IRF5 hyper-activation is a driver of systemic lupus erythematosus (SLE) onset and severity

Abstract The transcription factor interferon regulatory factor 5 (IRF5) is a central mediator of innate and adaptive immunity. Genetic variations within IRF5 associate with risk for systemic lupus erythematosus (SLE) and mice lacking Irf5 are protected from lupus onset and severity. Here we show that IRF5 genetic variants confer risk by increasing basal IRF5 activation in plasmacytoid dendritic cells resulting in elevated IFNα production. IRF5 hyperactivation in SLE immune cells correlates with SLEDAI and dsDNA titers. Upon characterization of immune cells from NZB/W F1 lupus-prone mice, we found that Irf5 was hyperactivated at 19 weeks-old, which precedes clinical onset. To test whether IRF5 hyperactivation is a driver of SLE, we developed novel therapeutics targeting IRF5 activation. Inhibitors are cell permeable, non-toxic and selectively bind to full-length inactive IRF5 monomer. In vivo analysis revealed functional mimicry with Irf5 knockout mice and treatment of NZB/W F1 mice for a two-week period prior to clinical onset gave significantly reduced dsDNA titers, anti-nuclear antibody (ANA) staining, and improved survival. The IRF5 inhibitor also blocked ex vivo SLE serum-induced IRF5 activation and reversed IRF5 hyperactivation detected in SLE immune cells. Results implicate IRF5 hyperactivation as a risk factor that drives SLE and provide the first pre-clinical support for treating SLE patients or those at risk of SLE with IRF5 inhibitors.

Corrected and Republished from: The COP9 Signalosome Interacts with and Regulates Interferon Regulatory Factor 5 Protein Stability.

The transcription factor interferon regulatory factor 5 (IRF5) exerts crucial functions in the regulation of host immunity against extracellular pathogens, DNA damage-induced apoptosis, death receptor signaling, and macrophage polarization. Tight regulation of IRF5 is thus warranted for an efficient response to extracellular stressors and for limiting autoimmune and inflammatory responses. Here we report that the COP9 signalosome (CSN), a general modulator of diverse cellular and developmental processes, associates constitutively with IRF5 and promotes its protein stability. The constitutive CSN/IRF5 interaction was identified using proteomics and confirmed by endogenous immunoprecipitations. The CSN/IRF5 interaction occurred on the carboxyl and amino termini of IRF5; a single internal deletion (Δ455-466) was found to significantly reduce IRF5 protein stability. CSN3 was identified as a direct interacting partner of IRF5, and knockdown of this subunit with small interfering RNAs (siRNAs) resulted in enhanced degradation. Degradation was further augmented by knockdown of CSN1 and CSN3 together. The ubiquitin E1 inhibitor UBEI-41 or the proteasome inhibitor MG132 prevented IRF5 degradation, supporting that its stability is regulated by the ubiquitin-proteasome system. Importantly, activation of IRF5 by the death receptor ligand tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) resulted in enhanced degradation via loss of the CSN/IRF5 interaction. This study defines the CSN as a new interacting partner of IRF5 that controls its stability.

Functional characterization of IRF5 exon 6 variants in SLE risk

Abstract The goal of the proposed research is to determine how the interferon regulatory factor 5(IRF5) lupus risk variant translates into biological risk of systemic lupus erythematosus (SLE). Genome wide association studies (GWAS) have identified IRF5 as one of the most strongly associated genes with susceptibility to SLE. Although the genetic association of IRF5 with lupus is clear, the exact mechanism by which IRF5 risk variant promotes susceptibility for lupus is still unknown. We are investigating negative regulatory factors of IRF5 activity under normal conditions, which are unable to regulate IRF5 exon 6 risk variants thereby activating type I IFNs leading to aberrant immune activation. We have characterized IRF5 exon 6 variants in pDCs using molecular and biochemical approaches, and investigated the effect of negative regulators on IRF5 exon 6 variants. This will be a significant step to gain the mechanistic understanding of aberrant production type I IFNs and immune activation in lupus.

A critical role for IRF5 in regulating allergic airway inflammation.

Interferon regulatory factor 5 (IRF5) is a key transcription factor involved in the control of the expression of pro-inflammatory cytokine and responses to infection, however its role in regulating pulmonary immune responses to allergen is unknown. We used genetic ablation, adenoviral vector-driven overexpression and adoptive transfer approaches to interrogate the role of IRF5 in pulmonary immunity and during challenge with the aero-allergen, house dust mite. Global IRF5 deficiency resulted in impaired lung function and extracellular matrix (ECM) deposition. IRF5 was also essential for effective responses to inhaled allergen, controlling airway hyper-responsiveness, mucus secretion and eosinophilic inflammation. Adoptive transfer of IRF5-deficient alveolar macrophages into the WT pulmonary milieu was sufficient to drive airway hyper-reactivity, at baseline or following antigen challenge. These data identify IRF5-expressing macrophages as a key component of the immune defence of the airways. Manipulation of IRF5 activity in the lung could therefore be a viable strategy for the redirection of pulmonary immune responses and thus, the treatment of lung disorders.