Interferon Regulatory Factor 2 Binding Protein 2 Research Articles

IRF2BP2-deficient microglia block the anxiolytic effect of enhanced postnatal care

Enhanced postnatal care (EPC) increases resilience to adversity in adulthood. Since microglia participate in shaping neural circuits, we asked how ablation of an inflammation-suppressing factor IRF2BP2 (Interferon Regulatory Factor 2 Binding Protein 2) in microglia would affect the responses to EPC. Mice lacking IRF2BP2 in microglia (KO) and littermate controls (WT) were subjected to EPC during the first 3 weeks after birth. EPC reduced anxiety in WT but not KO mice. This was associated with reduced inflammatory cytokine expression in the hypothalamus. Whole genome RNAseq profiling of the hypothalamus identified 101 genes whose expression was altered by EPC: 95 in WT, 11 in KO, with 5 in common that changed in opposite directions. Proteoglycan 4 (Prg4), prostaglandin D2 synthase (Ptgds) and extracellular matrix protease inhibitor Itih2 were suppressed by EPC in WT but elevated in KO mice. On the other hand, the glutamate transporter VGLUT1 (Slc17a7) was increased by EPC in WT but not KO mice. Prostaglandin D2 (PGD2) is known to enhance microglial inflammation and promote Gfap expression. ELISA confirmed reduced PGD2 in the hypothalamus of WT mice after EPC, associated with reduced Gfap expression. Our study suggests that the anxiety-reducing effect of EPC operates by suppressing microglial inflammation, likely by reducing neuronal prostaglandin D2 production.

Control of Pathological Cardiac Hypertrophy by Transcriptional Corepressor IRF2BP2 (Interferon Regulatory Factor-2 Binding Protein 2)

The transcription factor NFAT1 (nuclear factor of activated T-cells 1), with the aid of transcriptional coactivators, has been recognized for its necessity and sufficiency to drive pathological cardiac hypertrophy. However, how the transcriptional activity of NFAT1 in terms of cardiac hypertrophy is controlled at the transcriptional level has not been well defined. Herein, we showed that a cardiac-enriched protein IRF2BP2 (interferon regulatory factor-2 binding protein 2) was further upregulated in both human and mouse hypertrophied myocardium and negatively regulated cardiomyocyte hypertrophic response in vitro. By generating cardiomyocyte-specific Irf2bp2 knockout and Irf2bp2-transgenic mouse strains, our in vivo experiments showed that, whereas IRF2BP2 loss-of-function exacerbated both aortic banding- and angiotensin II infusion-induced cardiac hypertrophic response, IRF2BP2 overexpression exerted a strong protective effect against these maladaptive processes. Particularly, IRF2BP2 directly interacted with the C-terminal transactivation domain of NFAT1 by competing with myocyte enhancer factor-2C and disturbing their transcriptional synergism, thereby impeding NFAT1-transactivated hypertrophic transcriptome. As a result, the devastating effect of Irf2bp2 deficiency on cardiac hypertrophy was largely rescued by NFAT1 blockage. Our study, thus, defined IRF2BP2 as a novel negative regulator in controlling pathological cardiac hypertrophy at the transcriptional level.

Abstract 19809: Interferon Regulatory Factor 2 Binding Protein 2 Inhibits Macrophage Inflammation and Reduces Susceptibility to Atherosclerosis in Mice and Humans

Introduction: Genetic variants near the gene encoding the transcription cofactor Interferon Regulatory Factor 2 Binding Protein 2 (IRF2BP2) have been tied to ischemic heart disease progression and elevated serum cholesterol. Expression of IRF2BP2 is suppressed in inflammatory macrophages, but the significance of this down-regulation was not known. Hypothesis: This study sought to determine the function of IRF2BP2 in macrophages and its effect on atherosclerosis in mice and humans. Methods and Results: We generated mice that delete IRF2BP2 in macrophages (LysMCre/IRF2BP2flox). IRF2BP2-deficient macrophages increased atherosclerosis in irradiated LDL-receptor null recipient mice and in ApoE null mice. Atherosclerosis was associated with a skewed inflammatory macrophage polarization and increased foam cell formation. Microarray analysis revealed and promoter studies confirmed that the anti-inflammatory transcription factor KLF2 is a target of IRF2BP2, indicating an important role for IRF2BP2 in macrophage polarization. A deletion polymorphism (rs3045215) in the 3’ untranslated sequence of human IRF2BP2 mRNA was examined for its effect on protein expression and on the susceptibility to coronary artery disease (CAD) risk in a cohort of 1,066 angiographic cases and 1,011 controls. Homozygous carriers of this deletion had lower IRF2BP2 (and its target KLF2) protein levels in peripheral blood mononuclear cells and a higher risk of CAD (recessive model, odds ratio (95%CI) = 1.560 (1.179-2.065), p=1.73E-03). The effect of this deletion to suppress protein expression was confirmed with luciferase reporter studies. Haplotype phasing identified two surrogate SNPs in modest LD (rs1887917, r2= 0.755 and rs632180, r2=0.614) that also associated with CAD in a recessive model. These SNPs are being tested for association with CAD in a large international consortium. Conclusion: Ablation of IRF2BP2 in macrophages worsens atherosclerosis in mice and a deletion variant that lowers IRF2BP2 expression predisposes to CAD in humans.

IRF2BP2 Reduces Macrophage Inflammation and Susceptibility to Atherosclerosis.

Inflammation impairs macrophage cholesterol clearance from vascular tissues and promotes atherosclerosis. Inflammatory macrophages suppress expression of the transcription cofactor interferon regulatory factor 2-binding protein 2 (IRF2BP2), and genetic variants near IRF2BP2 associate with ischemic heart disease progression in humans. To test whether IRF2BP2 in macrophages affects atherosclerosis in mice and humans. We generated mice that delete IRF2BP2 in macrophages. IRF2BP2-deficient macrophages worsened atherosclerosis in irradiated low-density lipoprotein receptor null-recipient mice and in apolipoprotein E null mice. IRF2BP2-deficient macrophages were inflammatory and had impaired cholesterol efflux because of their inability to activate the cholesterol transporter ABCA1 in response to cholesterol loading. Their expression of the anti-inflammatory transcription factor Krüppel-like factor 2 was markedly reduced. Promoter studies revealed that IRF2BP2 is required for MEF2-dependent activation of Krüppel-like factor 2. Importantly, restoring Krüppel-like factor 2 in IRF2BP2-deficient macrophages attenuated M1 inflammatory and rescued M2 anti-inflammatory gene activation and improved the cholesterol efflux deficit by restoring ABCA1 activation in response to cholesterol loading. In a cohort of 1066 angiographic cases and 1011 controls, homozygous carriers of a deletion polymorphism (rs3045215) in the 3' untranslated region sequence of human IRF2BP2 mRNA had a higher risk of coronary artery disease (recessive model, odds ratio [95% confidence interval]=1.560 [1.179-2.065], P=1.73E-03) and had lower IRF2BP2 (and Krüppel-like factor 2) protein levels in peripheral blood mononuclear cells. The effect of this deletion polymorphism to suppress protein expression was confirmed in luciferase reporter studies. Ablation of IRF2BP2 in macrophages worsens atherosclerosis in mice, and a deletion variant that lowers IRF2BP2 expression predisposes to coronary artery disease in humans.

The IRF2BP2-RARα Fusion Generated By a Cryptic Rearrangement Transforms Hematopoietic Stem/Progenitor Cells and Induces Retinoid Sensitive Acute Promyelocytic Leukemia (APL)

APL is characterised by chromosomal rearrangements involving the gene encoding the myeloid transcription factor Retinoic Acid Receptor Alpha (RARα). While RARA is fused to PML in the majority of cases consequent upon the t(15;17)(q22;q21), significant insights can be gained into pathogenesis through analysis of APL involving alternative fusion partners. It is now apparent that the fusion partner has a critical bearing on disease biology, particularly with respect to sensitivity to molecularly targeted therapies i.e. all transretinoic acid (ATRA) and arsenic trioxide (ATO). While ATO sensitivity is restricted to PML-RARA+ APL, the fusion partner influences sensitivity to ATRA, with involvement of STAT5b or PLZF (ZBTB16) being associated with resistance and poorer clinical outcome. In the European Working Party study (Blood 2000;96:1297-1308) we previously established that ~10% of morphological APL cases lack the classic t(15;17). While PML is involved in the majority due to insertion events or more complex rearrangements, the molecular basis of disease in some patients has been unexplained. Analysis was undertaken in a normal karyotype APL (WBC 3.8 x 109/l, plt 7 x 109/l) presenting in a 37 year old man, PML-RARA negative by RT-PCR, with intact PML nuclear bodies on immunofluorescence. Due to the suggestive morphology, the patient was commenced on ATRA as a single agent (45mg/m2) pending further molecular investigation. ATRA induced maturation of the leukemic blasts, apparent in bone marrows taken at day 7 and day 16, associated with normalization of the platelet count (100 x 109/l by day 25). Diagnostic material was subject to gene expression profiling (TaqMan® Array Card, Life Technologies) and on unsupervised analysis clustered with PML-RARA+ cases, with a common signature associated with upregulation of HGF and FGF13 and downregulation of HOXA7, HOXA9 and MEIS1. 5’ RACE-PCR confirmed involvement of RARA and identified the fusion partner as IRF2BP2 (Interferon Regulatory Factor 2 Binding Protein 2), which is located at 1q42. The cDNA breakpoint involved fusion of exon 1 of IRF2BP2 to exon 3 of RARA leading to retention of the regions mediating binding to DNA, retinoic acid (ligand binding domain, LBD) and RXR. Chromosome 1 painting was undertaken, which appeared normal and a reciprocal RARA-IRF2BP2 fusion transcript was not detected, consistent with formation of IRF2BP2-RARA by cryptic insertion. Whole exome sequencing identified 17 non-synonymous exonic single nucleotide variants, three (with predicted functional impact) were in genes known to be recurrently mutated in AML (LRP1B, GATA2 and EZH2). The patient’s treatment response was tracked by real-time quantitative PCR (sensitivity 1 in 10e4), which showed persistent high level IRF2BP2-RARA fusion transcripts following single agent ATRA. The patient was commenced on the PETHEMA treatment schedule, achieved molecular remission (CRm) following the first course of chemotherapy and remains in ongoing CRm in the marrow 32 months from diagnosis.IRF2BP2 is a downstream target of p53 and repressor of the cell cycle regulator NFAT1; it is fused to CDX1 as a result of the t(1;5)(q42;q32) in mesenchymal chondrosarcoma, has been reported to be mutated in CLL and primary CNS lymphoma, but has not previously been implicated in myeloid malignancy. To investigate the biology of IRF2BP2-RARα, co-immunoprecipitation assays were performed in 293T cells using tagged constructs, which revealed that the fusion protein has the capacity to self-associate. In reporter assays, IRF2BP2-RARα behaved similarly to PML-RARα, inducing repression at retinoid response elements, which was overcome by 1μM ATRA. Full length IRF2BP2-RARA was cloned into the MSCV vector, expressed in lin- murine stem/progenitor cells and replating assays performed in three conditions (SCF, IL3 + IL6/ SCF, IL3, IL6 + G-CSF/ SCF, IL3, IL6, G-CSF + GM-CSF). Expression of IRF2BP2-RARA consistently induced large numbers of third round colonies under all 3 conditions; whereas, colony formation was completely abrogated in the presence of 1μM ATRA in accordance with the sensitivity to retinoid observed in vivo.In conclusion, these data extend the range of malignancies involving IRF2BP2, identifying a novel retinoid sensitive subtype of APL and provide further evidence that forced dimerization of RARα mediated by the fusion partner plays a critical role in leukemogenesis. DisclosuresNo relevant conflicts of interest to declare.

Abstract 19581: Embryonic Lethality of Mice Deficient for IRF2BP2: An Essential Ischemia-Inducible Transcriptional Coactivator of VEGFA

Background - VEGF (vascular endothelial growth factor) is a master regulator of angiogenesis is a major player in ischemic heart disease. In 2010, we found that IRF2BP2 (interferon regulatory factor-2 binding protein-2) coactivates VEGFA expression in muscle. IRF2BP2 protein levels show a 7-fold increase is ischemic muscle whereas its mRNA expression is not increased, indicating that IRF2BP2 is translational repressed in normoxic tissues and becomes translationally derepressed during ischemia. Methods - To characterize the mechanisms repressing translation of IRF2BP2 mRNA in normoxic conditions and enabling derepression during ischemia, luciferase reporter plasmids were transiently transfected in cultured cells. In addition, we generated transgenic mice with targeted deletion of the IRF2BP2 gene and others with a floxed IRF2BP2 allele enabling tissue specific ablation by Cre-transgene expression. Results - In the 3’UTR of IRF2BP2 mRNA, microRNAs miR-17 and -20a were found to differentially regulate translation. A common 9 nucleotide deletion polymorphism (rs3045215) disrupted the miRNA target sequence in IRF2BP2 mRNA and associated with coronary artery disease risk in the Ottawa Heart Genomics study (p<0.0045). The RNA binding protein Staufen-1 (Stau1) binds to the 3’UTR of IRF2BP2 mRNA and inhibits its translation. Stau1 levels increased during C2C12 skeletal muscle differentiation, coincident with the downregulation of IRF2BP2 protein levels. Of interest, IRF2BP2 knockout mice died during embryonic development. Out of 11 litters from hemizygous matings, 42 offspring were born: 15 wild type (35.7%), 25 hemizygous (59.5%), and 2 homozygous null (4.8%) mice, deviating from the expected Mendelian ratio of 25% wild type:50% hemizygous: 25% null. The 2 surviving IRF2BP2 null mice displayed severe growth retardation. We are currently characterizing the phenotype of embryonic lethality in these mice. Conclusion - Translational derepression enables expression of IRF2BP2 protein in ischemic tissues, an emerging mechanism of gene regulation. Our data show the IRF2BP2 gene is critical for mouse development. These transgenic models will enable the elucidation of IRF2BP2 function in angiogenesis and the response to ischemia.

Identification of a Phosphorylation-Dependent Nuclear Localization Motif in Interferon Regulatory Factor 2 Binding Protein 2

BackgroundInterferon regulatory factor 2 binding protein 2 (IRF2BP2) is a muscle-enriched transcription factor required to activate vascular endothelial growth factor-A (VEGFA) expression in muscle. IRF2BP2 is found in the nucleus of cardiac and skeletal muscle cells. During the process of skeletal muscle differentiation, some IRF2BP2 becomes relocated to the cytoplasm, although the functional significance of this relocation and the mechanisms that control nucleocytoplasmic localization of IRF2BP2 are not yet known.Methodology/Principal FindingsHere, by fusing IRF2BP2 to green fluorescent protein and testing a series of deletion and site-directed mutagenesis constructs, we mapped the nuclear localization signal (NLS) to an evolutionarily conserved sequence 354ARKRKPSP361 in IRF2BP2. This sequence corresponds to a classical nuclear localization motif bearing positively charged arginine and lysine residues. Substitution of arginine and lysine with negatively charged aspartic acid residues blocked nuclear localization. However, these residues were not sufficient because nuclear targeting of IRF2BP2 also required phosphorylation of serine 360 (S360). Many large-scale phosphopeptide proteomic studies had reported previously that serine 360 of IRF2BP2 is phosphorylated in numerous human cell types. Alanine substitution at this site abolished IRF2BP2 nuclear localization in C2C12 myoblasts and CV1 cells. In contrast, substituting serine 360 with aspartic acid forced nuclear retention and prevented cytoplasmic redistribution in differentiated C2C12 muscle cells. As for the effects of these mutations on VEGFA promoter activity, the S360A mutation interfered with VEGFA activation, as expected. Surprisingly, the S360D mutation also interfered with VEGFA activation, suggesting that this mutation, while enforcing nuclear entry, may disrupt an essential activation function of IRF2BP2.Conclusions/SignificanceNuclear localization of IRF2BP2 depends on phosphorylation near a conserved NLS. Changes in phosphorylation status likely control nucleocytoplasmic localization of IRF2BP2 during muscle differentiation.

Interferon regulatory factor 2 binding protein 2 is a new NFAT1 partner and represses its transcriptional activity.

The nuclear factor of activated T cells (NFAT) family of transcription factors is expressed in a wide range of cell types and regulates genes involved in cell cycle, differentiation, and apoptosis. NFAT proteins share two well-conserved regions, the regulatory domain and the DNA binding domain. The N- and C-terminal ends are transactivation sites and show less sequence similarity, whereas their molecular functions remain poorly understood. Here, we identified a transcriptional repressor, interferon regulatory factor 2 binding protein 2 (IRF-2BP2), which specifically interacts with the C-terminal domain of NFAT1 among the NFAT family members. IRF-2BP2 was described as a corepressor by inhibiting both enhancer-activated and basal transcription. Gene reporter assays demonstrated that IRF-2BP2 represses the NFAT1-dependent transactivation of NFAT-responsive promoters. The ectopic expression of IRF-2BP2 in CD4 T cells resulted in decreased interleukin-2 (IL-2) and IL-4 production, supporting a repressive function of IRF-2BP2 for NFAT target genes. Furthermore, NFAT1 and IRF-2BP2 colocalized in the nucleus in activated cells, and the mutation of a newly identified nuclear localization signal in the IRF-2BP2 rendered it cytoplasmic, abolishing its repressive effect on NFAT1 activity. Collectively, our data demonstrate that IRF-2BP2 is a negative regulator of the NFAT1 transcription factor and suggest that NFAT1 repression occurs at the transcriptional level.

Uncovering Haematopoietic System Dynamics and Single Multipotent Progenitors Activity In Vivo In Humans by Retroviral Tagging.

AbstractAbstract 2611The long-standing model of human haematopoiesis postulates that myeloid and lymphoid lineages branch separately at very early stages, producing myeloid or erythroid cells and T or B cells, respectively. Conversely, a revised scheme of haematopoietic hierarchy was recently proposed, in which myeloid cells represent a prototype of blood cells, while erythroid, T and B cells are specialized cell types. The validity of these models has been mainly tested in vivo in the mouse, and in vitro through clonal assays on human haemopoietic stem cells (HSC). However, a clear definitive elucidation of the real nature of human haemopoiesis should ideally involve the ability to track the dynamics, survival and differentiation potential of haemopoietic progenitor clones for a long period of time directly in vivo in humans. Upon retroviral gene transfer, transduced cells are univocally tagged by vector insertions allowing them to be distinguished and tracked in vivo by integration profiling. We previously showed that gene therapy (GT) for adenosine deaminase (ADA) deficient SCID based on infusion of transduced CD34+ cells and reduced intensity conditioning, resulted in full multilineage engraftment, in the absence of aberrant expansions. Therefore, long-term studies in these patients provide a unique human model to study in depth haemopoietic clonal dynamics by retroviral tagging. For this reason, we performed a comprehensive multilineage longitudinal insertion profile of bone marrow (BM) (CD34+, CD15+, CD19+, Glycophorin+) and peripheral blood (PB) (CD15+, CD19+, CD4+, CD8+ cells, naïve and memory T cell subpopulations) cells in 4 patients 3–6 years after GT, retrieving to date 1055 and 1999 insertions from BM and PB cell lineages respectively. We could shape the insertional landscape of each lineage through a tri-factorial analysis based on the number of integrations retrieved, the percentage of vector positive cells and the number of insertion shared with other lineages. We were able to uncover the effects of selective advantages of gene-corrected cells in periphery and the frequency of identical integrants in different haematopoietic compartments. BM cells displayed the highest proportion of shared integrants (up to 58.1%), reflecting the real-time repopulating activity of gene-corrected progenitors. On the other hand, PB samples carried in general a higher frequency of vector positive cells, with the exception of PB CD15+ cells showing insertional landscapes very similar to the one of BM lineages. Interestingly, the detection of exclusively shared myeloid-T\\B or myeloid-erythroid integrants may be supportive of a myeloid-based haemopoiesis model. We also uncovered “core integrants”, shared between CD34+ cells and both lymphoid and myeloid lineages, stably tagging active long-term multipotent progenitors overtime. Strikingly, one of these progenitor clones carried an insertion inside one of the two fragile sites of MLLT3 gene, involved by translocation events in mixed lineage leukemia. We were able to track this and another integrant (downstream the LRRC30 gene) by specific PCRs, confirming the multilineage contribution to haematopoiesis of the relative progenitor clones and their fluctuating lineage outputs over 4 years, without showing aberrant expansions. We also retrieved 170 and 174 integrations from 4 T cell subtypes (Naive, TEMRA, Central and Effector memory) in two patients under PBL-GT and HSC-GT respectively. We found evidences that single naive T cell clones may survive in patients for up to 10 years after last infusion while maintaining their differentiation capacity into different T cell subpopulations. Interestingly, a cluster of 4 insertions (one of them shared among all T cell subtypes) was found in proximity of the interferon regulatory factor 2 binding protein 2 (IRF2BP2) gene in naive T cells from PBL-GT patient, thus suggesting an influence of transcriptional activity of this region on selective advantage of gene-corrected lymphocytes. In conclusion, through retroviral tagging, we can uniquely track single transduced haemopoietic cells directly in vivo in humans. The application of mathematical models to our insertion datasets is allowing to uncover new information on the fate and activity of haematopoietic progenitors and their differentiated progeny years after transplantation in GT patients. Disclosures:No relevant conflicts of interest to declare.

The novel p53 target gene IRF2BP2 participates in cell survival during the p53 stress response

The tumor suppressor p53 contributes to the cellular fate after genotoxic insults, mainly through the regulation of target genes, thereby allowing e.g. repair mechanisms resulting in cell survival or inducing apoptosis. Unresolved so far is the issue, which exact mechanisms lead to one or the other cellular outcome. Here, we describe the interferon regulatory factor-2-binding protein-2 (IRF2BP2) as a new direct target gene of p53, influencing the p53-mediated cellular decision. We show that upregulation of IRF2BP2 after treatment with actinomycin D (Act.D) is dependent on functional p53 in different cell lines. This occurs in parallel with the down-regulation of the interacting partner of IRF2BP2, the interferon regulatory factor-2 (IRF2), which is known to positively influence cell growth. Analyzing the molecular functions of IRF2BP2, it appears to be able to impede on the p53-mediated transactivation of the p21- and the Bax-gene. We show here that overexpressed IRF2BP2 has an impact on the cellular stress response after Act.D treatment and that it diminishes the induction of apoptosis after doxorubicin treatment. Furthermore, the knockdown of IRF2BP2 leads to an upregulation of p21 and faster induction of apoptosis after doxorubicin as well as Act.D treatment.