The methyltransferase Ezh2 controls cell adhesion and migration through direct methylation of the extranuclear regulatory protein talin.

A cytosolic role for the histone methyltransferase Ezh2 in regulating lymphocyte activation has been suggested, but the molecular mechanisms underpinning this extranuclear function have remained unclear. Here we found that Ezh2 regulated the integrin signaling and adhesion dynamics of neutrophils and dendritic cells (DCs). Ezh2 deficiency impaired the integrin-dependent transendothelial migration of innate leukocytes and restricted disease progression in an animal model of multiple sclerosis. Direct methylation of talin, a key regulatory molecule in cell migration, by Ezh2 disrupted the binding of talin to F-actin and thereby promoted the turnover of adhesion structures. This regulatory effect was abolished by targeted disruption of the interactions of Ezh2 with the cytoskeletal-reorganization effector Vav1. Our studies reveal an unforeseen extranuclear function for Ezh2 in regulating adhesion dynamics, with implications for leukocyte migration, immune responses and potentially pathogenic processes.

Mesenchymal stromal cell exosome-enhanced regulatory T-cell production through an antigen-presenting cell-mediated pathway.

BACKGROUND AIMS: The immunomodulatory property of mesenchymal stromal cell (MSC) exosomes is well documented. On the basis of our previous report that MSC exosomes increased regulatory T-cell (Treg) production in mice with allogenic skin graft but not in ungrafted mice, we hypothesize that an activated immune system is key to exosome-mediated Treg production. METHODS: To test our hypothesis, MSC exosomes were incubated with mouse spleen CD4+ T cells that were activated with either anti-CD3/CD28 mAbs or allogenic antigen-presenting cell (APC)-enriched spleen CD11c+ cells to determine whether production of mouse CD4+CD25+ T cells or CD4+CD25+Foxp3+ Tregs could be induced. MSC exosomes were also administered to the lethal chimeric human-SCID mouse model of graft-versus-host disease (GVHD) in which human peripheral blood mononuclear cells were infused into irradiated NSG mice to induce GVHD. RESULTS: We report here that MSC exosome-induced production of CD4+CD25+ T cells or CD4+CD25+Foxp3+ Tregs from CD4+ T cells activated by allogeneic APC-enriched CD11C+ cells but not those activated by anti-CD3/CD28 mAbs. This induction was exosome- and APC dose-dependent. In the mouse GVHD model in which GVHD was induced by transplanted human APC-stimulated human anti-mouse CD4+ T cell effectors, MSC exosome alleviated GVHD symptoms and increased survival. Surviving exosome-treated mice had a significantly higher level of human CD4+CD25+CD127low/- Tregs than surviving mice treated with Etanercept, a tumor necrosis factor inhibitor. CONCLUSIONS: MSC exosome enhanced Treg production in vitro and in vivo through an APC-mediated pathway.

Bromodomain-containing protein 4 (BRD4) regulates RNA polymerase II serine 2 phosphorylation in human CD4+ T cells.

Transcriptional elongation by RNA polymerase II (Pol II) is regulated by positive transcription elongation factor b (P-TEFb) in association with bromodomain-containing protein 4 (BRD4). We used genome-wide chromatin immunoprecipitation sequencing in primary human CD4+ T cells to reveal that BRD4 co-localizes with Ser-2-phosphorylated Pol II (Pol II Ser-2) at both enhancers and promoters of active genes. Disruption of bromodomain-histone acetylation interactions by JQ1, a small-molecule bromodomain inhibitor, resulted in decreased BRD4 binding, reduced Pol II Ser-2, and reduced expression of lineage-specific genes in primary human CD4+ T cells. A large number of JQ1-disrupted BRD4 binding regions exhibited diacetylated H4 (lysine 5 and -8) and H3K27 acetylation (H3K27ac), which correlated with the presence of histone acetyltransferases and deacetylases. Genes associated with BRD4/H3K27ac co-occupancy exhibited significantly higher activity than those associated with H3K27ac or BRD4 binding alone. Comparison of BRD4 binding in T cells and in human embryonic stem cells revealed that enhancer BRD4 binding sites were predominantly lineage-specific. Our findings suggest that BRD4-driven Pol II phosphorylation at serine 2 plays an important role in regulating lineage-specific gene transcription in human CD4+ T cells.

IRF8 and IRF3 cooperatively regulate rapid interferon-ß induction in human blood monocytes.

Robust and rapid induction of interferon-ß (IFN-ß) in monocytes after pathogenic stimulation is a hallmark of innate immune responses. Here, we reveal the molecular mechanism underlying this key property that is exclusive to human blood monocytes. We found that IFN-ß was produced rapidly in primary human monocytes as a result of cooperation between the myeloid-specific transcription factor IRF8 and the ubiquitous transcription factor IRF3. Knockdown of IRF8 in monocytes abrogated IFN-ß transcription, whereas reintroduction of IRF8 into the IRF8(-/-) 32Dcl3 murine myeloid cell line reinstated IFN-ß transcription. Moreover, we provide evidence that IRF8 constitutively binds to the ETS/IRF composite element of the IFN-ß promoter region together with PU.1 in vivo. Furthermore we uncovered a requirement for IRF3, a master regulator of IFN-ß production, as a previously un-indentified interaction partner of IRF8. We mapped the protein-protein interacting regions of IRF3 and IRF8, and found that their interaction was independent of the DNA-binding domain and the IRF association domain of IRF8 and IRF3, respectively. Therefore, we propose a model for the rapid induction of IFN-ß in monocytes, whereby IRF8 and PU.1 form a scaffold complex on the IFN-ß promoter to facilitate the recruitment of IRF3, thus enabling rapid IFN-ß transcription.

Gut microbiota accelerate tumor growth via c-jun and STAT3 phosphorylation in APCMin/+ mice.

Chronic inflammation is increasingly recognized as a major contributor of human colorectal cancer (CRC). While gut microbiota can trigger inflammation in the intestinal tract, the precise signaling pathways through which host cells respond to inflammatory bacterial stimulation are unclear. Here, we show that gut microbiota enhances intestinal tumor load in the APC(Min/+) mouse model of CRC. Furthermore, systemic anemia occurs coincident with rapid tumor growth, suggesting a role for intestinal barrier damage and erythropoiesis-stimulating mitogens. Short-term stimulation assays of murine colonic tumor cells reveal that lipopolysaccharide, a microbial cell wall component, can accelerate cell growth via a c-Jun/JNK activation pathway. Colonic tumors are also infiltrated by CD11b+ myeloid cells expressing high levels of phospho-STAT3 (p-Tyr705). Our results implicate the role of gut microbiota, through triggering the c-Jun/JNK and STAT3 signaling pathways in combination with anemia, in the acceleration of tumor growth in APC(Min/+) mice.

In vivo and in vitro studies on the antiviral activities of viperin against influenza H1N1 virus infection.

Influenza A virus has caused a number of pandemics in past decades, including the recent H1N1-2009 pandemic. Viperin is an interferon (IFN)-inducible protein of innate immunity, and acts as a broad-spectrum antiviral protein. We explored the antiviral activities and mechanisms of viperin during influenza virus (IFV) infection in vitro and in vivo. Wild-type (WT) HeLa and viperin-expressing HeLa cells were infected with influenza A/WSN/33/H1N1 (WSN33) virus, and subjected to virological, light and electron microscopic analyses. Viperin expression reduced virus replication and titres, and restricted viral budding. Young and old viperin-knockout (KO) mice and WT control animals were challenged with influenza WSN33 at lethal doses of 10(3) and 10(4) p.f.u. via the intratracheal route. Lungs were subjected to histopathological, virological and molecular studies. Upon lethal IFV challenge, both WT and KO mice revealed similar trends of infection and recovery with similar mortality rates. Viral quantification assay and histopathological evaluation of lungs from different time points showed no significant difference in viral loads and lung damage scores between the two groups of mice. Although the in vitro studies demonstrated the ability of viperin to restrict influenza H1N1 virus replication, the viperin-deficient mouse model indicated that absence of viperin enhanced neither the viral load nor pulmonary damage in the lungs of infected mice. This may be due to the compensation of IFN-stimulated genes in the lungs and/or the influenza non-structural protein 1-mediated IFN antagonism dampening the IFN response, thereby rendering the loss of viperin insignificant. Nevertheless, further investigations that exploit the antiviral mechanisms of viperin as prophylaxis are still warranted.

Viperin is required for optimal Th2 responses and T-cell receptor-mediated activation of NF-kappaB and AP-1.

Viperin (virus inhibitory protein, endoplasmic reticulum [ER]-associated, interferon-inducible) has been identified as a highly inducible ER protein that has antiviral activity. Here, we characterized the phenotype of mice deficient in viperin and examined the biological function of viperin in peripheral T-cell activation and differentiation. Splenic CD4(+) T cells deficient in viperin exhibited normal anti-T-cell receptor (TCR)-induced proliferation and IL-2 production, but produced significantly less T helper 2 (Th2) cytokines, including IL-4, IL-5, and IL-13, in association with impaired GATA3 activation, after stimulation with anti-CD3 antibody, which was not restored upon costimulation with anti-CD28. Th2 differentiation of viperin-deficient naive T cells was also impaired in the presence of strong TCR signaling and minimum IL-4, but not under optimal Th2-skewed conditions. In parallel, viperin-deficient T cells showed decreases in NF-kappaB1/p50 and AP-1/JunB DNA binding activities after TCR engagement. Thus, viperin facilitates TCR-mediated GATA-3 activation and optimal Th2 cytokine production by modulating NF-kappaB and AP-1 activities.

IRF-7 Mediates Type I IFN Responses in Endotoxin-Challenged Mice.

IRF-7 mediates robust production of type I IFN via MyD88 of the TLR9 pathway in plasmacytoid dendritic cells (pDCs). Previous in vitro studies using bone marrow-derived dendritic cells lacking either Irf7 or Irf3 have demonstrated that only IRF-3 is required for IFN-ß production in the TLR4 pathway. Here, we show that IRF-7 is essential for both type I IFN induction and IL-1ß responses via TLR4 in mice. Mice lacking Irf7 were defective in production of both IFN-ß and IL-1ß, an IFN-ß-induced pro-inflammatory cytokine, after LPS challenge. IFN-ß production in response to LPS was impaired in IRF-7-deficient macrophages, but not dendritic cells. Unlike pDCs, IRF-7 is activated by the TRIF-, but not MyD88-, dependent pathway via TBK-1 in macrophages after LPS stimulation. Like pDCs, resting macrophages constitutively expressed IRF-7 protein. This basal IRF-7 protein was completely abolished in either Ifnar1-/- or Stat1-/- macrophages, which corresponded with the loss of LPS-stimulated IFN-ß induction in these macrophages. These findings demonstrate that macrophage IRF-7 is critical for LPS-induced type I IFN responses, which in turn facilitate IL-1ß production in mice.

Dominant-negative NFKBIA mutation promotes IL-1ß production causing hepatic disease with severe immunodeficiency.

Although IKK-ß has previously been shown as a negative regulator of IL-1ß secretion in mice, this role has not been proven in humans. Genetic studies of NF-κB signaling in humans with inherited diseases of the immune system have not demonstrated the relevance of the NF-κB pathway in suppressing IL-1ß expression. Here, we report an infant with a clinical pathology comprising neutrophil-mediated autoinflammation and recurrent bacterial infections. Whole-exome sequencing revealed a de novo heterozygous missense mutation of NFKBIA, resulting in a L34P IκBα variant that severely repressed NF-κB activation and downstream cytokine production. Paradoxically, IL-1ß secretion was elevated in the patient's stimulated leukocytes, in her induced pluripotent stem cell-derived macrophages, and in murine bone marrow-derived macrophages containing the L34P mutation. The patient's hypersecretion of IL-1ß correlated with activated neutrophilia and liver fibrosis with neutrophil accumulation. Hematopoietic stem cell transplantation reversed neutrophilia, restored a resting state in neutrophils, and normalized IL-1ß release from stimulated leukocytes. Additional therapeutic blockade of IL-1 ameliorated liver damage, while decreasing neutrophil activation and associated IL-1ß secretion. Our studies reveal a previously unrecognized role of human IκBα as an essential regulator of canonical NF-κB signaling in the prevention of neutrophil-dependent autoinflammatory diseases. These findings also highlight the therapeutic potential of IL-1 inhibitors in treating complications arising from systemic NF-κB inhibition.

Erratum: E3 Ubiquitin ligase ZNRF4 negatively regulates NOD2 signalling and induces tolerance to MDP.

This corrects the article DOI: 10.1038/ncomms15865.

E3 Ubiquitin ligase ZNRF4 negatively regulates NOD2 signalling and induces tolerance to MDP.

Optimal regulation of the innate immune receptor nucleotide-binding oligomerization domain-containing protein 2 (NOD2) is essential for controlling bacterial infections and inflammatory disorders. Chronic NOD2 stimulation induces non-responsiveness to restimulation, termed NOD2-induced tolerance. Although the levels of the NOD2 adaptor, RIP2, are reported to regulate both acute and chronic NOD2 signalling, how RIP2 levels are modulated is unclear. Here we show that ZNRF4 induces K48-linked ubiquitination of RIP2 and promotes RIP2 degradation. A fraction of RIP2 localizes to the endoplasmic reticulum (ER), where it interacts with ZNRF4 under either 55 unstimulated and muramyl dipeptide-stimulated conditions. Znrf4 knockdown monocytes have sustained nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation, and Znrf4 knockdown mice have reduced NOD2-induced tolerance and more effective control of Listeria monocytogenes infection. Our results thus demonstrate E3-ubiquitin ligase ZNRF4-mediated RIP2 degradation as a negative regulatory mechanism of NOD2-induced NF-κB, cytokine and anti-bacterial responses in vitro and in vivo, and identify a ZNRF4-RIP2 axis of fine-tuning NOD2 signalling to promote protective host immunity.

Activation and regulation of interferon-ß in immune responses.

Interferons (IFNs) were discovered more than half a century ago, and extensive research has since identified multifarious roles for type I IFN in human immune responses. Here, we review the functions of IFN-ß in innate and adaptive immunity. We also discuss the activation and influence of IFN-ß on myeloid cell types, including monocytes and dendritic cells, as well as address the effects of IFN-ß on T cells and B cells. Findings from our own laboratory, which explores the molecular mechanisms of IFN-ß activation by LPS and viruses, as well as from other groups investigating the regulation of IFN-ß by viral proteins and endogenous factors are described. The effects of post-translational modifications of the interferon regulatory factor (IRF)-3 on IFN-ß induction are also highlighted. Many unanswered questions remain concerning the regulation of the type I IFN response in inflammation, especially the role of transcription factors in the modulation of inflammatory gene expression, and these questions will form the basis for exciting avenues of future research.

Viperin restricts chikungunya virus replication and pathology.

Chikungunya virus (CHIKV) is a mosquito-borne arthralgia arbovirus that is reemergent in sub-Saharan Africa and Southeast Asia. CHIKV infection has been shown to be self-limiting, but the molecular mechanisms of the innate immune response that control CHIKV replication remain undefined. Here, longitudinal transcriptional analyses of PBMCs from a cohort of CHIKV-infected patients revealed that type I IFNs controlled CHIKV infection via RSAD2 (which encodes viperin), an enigmatic multifunctional IFN-stimulated gene (ISG). Viperin was highly induced in monocytes, the major target cell of CHIKV in blood. Anti-CHIKV functions of viperin were dependent on its localization in the ER, and the N-terminal amphipathic α-helical domain was crucial for its antiviral activity in controlling CHIKV replication. Furthermore, mice lacking Rsad2 had higher viremia and severe joint inflammation compared with wild-type mice. Our data demonstrate that viperin is a critical antiviral host protein that controls CHIKV infection and provide a preclinical basis for the design of effective control strategies against CHIKV and other reemerging arthrogenic alphaviruses.

BLIMP1 regulates cell growth through repression of p53 transcription.

Tight regulation of p53 is essential for maintaining normal cell growth. Here we report that BLIMP1 acts in an autoregulatory feedback loop that controls p53 activity through repression of p53 transcription. p53 binds to and positively regulates BLIMP1, which encodes for a known B cell transcriptional repressor. Knockdown of BLIMP1 by siRNA results in both apoptosis and growth arrest in human colon cancer cells and cell-cycle arrest in primary human fibroblasts. Interestingly, the levels of both p53 mRNA and protein are substantially increased after BLIMP1 depletion, which is accompanied by the induction of p53 target genes. Importantly, the apoptosis induced by BLIMP1 depletion in HCT116 cells is largely abrogated in cells lacking p53 or in cells depleted in p53 by siRNA. We further demonstrate that BLIMP1 binds to the p53 promoter and represses p53 transcription, and this provides a mechanistic explanation for the induction of p53 response in cells depleted of BLIMP1. Hence, suppression of p53 transcription is a crucial function of endogenous BLIMP1 and is essential for normal cell growth.

Host gene expression profiling of dengue virus infection in cell lines and patients.

BACKGROUND: Despite the seriousness of dengue-related disease, with an estimated 50-100 million cases of dengue fever and 250,000-500,000 cases of dengue hemorrhagic fever/dengue shock syndrome each year, a clear understanding of dengue pathogenesis remains elusive. Because of the lack of a disease model in animals and the complex immune interaction in dengue infection, the study of host response and immunopathogenesis is difficult. The development of genomics technology, microarray and high throughput quantitative PCR have allowed researchers to study gene expression changes on a much broader scale. We therefore used this approach to investigate the host response in dengue virus-infected cell lines and in patients developing dengue fever. METHODOLOGY/PRINCIPAL FINDINGS: Using microarray and high throughput quantitative PCR method to monitor the host response to dengue viral replication in cell line infection models and in dengue patient blood samples, we identified differentially expressed genes along three major pathways; NF-kappaB initiated immune responses, type I interferon (IFN) and the ubiquitin proteasome pathway. Among the most highly upregulated genes were the chemokines IP-10 and I-TAC, both ligands of the CXCR3 receptor. Increased expression of IP-10 and I-TAC in the peripheral blood of ten patients at the early onset of fever was confirmed by ELISA. A highly upregulated gene in the IFN pathway, viperin, was overexpressed in A549 cells resulting in a significant reduction in viral replication. The upregulation of genes in the ubiquitin-proteasome pathway prompted the testing of proteasome inhibitors MG-132 and ALLN, both of which reduced viral replication. CONCLUSION/SIGNIFICANCE: Unbiased gene expression analysis has identified new host genes associated with dengue infection, which we have validated in functional studies. We showed that some parts of the host response can be used as potential biomarkers for the disease while others can be used to control dengue viral replication, thus representing viable targets for drug therapy.

Genome-wide mapping of RELA(p65) binding identifies E2F1 as a transcriptional activator recruited by NF-kappaB upon TLR4 activation.

NF-kappaB is a key mediator of inflammation. Here, we mapped the genome-wide loci bound by the RELA subunit of NF-kappaB in lipopolysaccharide (LPS)-stimulated human monocytic cells, and together with global gene expression profiling, found an overrepresentation of the E2F1-binding motif among RELA-bound loci associated with NF-kappaB target genes. Knockdown of endogenous E2F1 impaired the LPS inducibility of the proinflammatory cytokines CCL3(MIP-1alpha), IL23A(p19), TNF-alpha, and IL1-beta. Upon LPS stimulation, E2F1 is rapidly recruited to the promoters of these genes along with p50/RELA heterodimer via a mechanism that is dependent on NF-kappaB activation. Together with the observation that E2F1 physically interacts with p50/RELA in LPS-stimulated cells, our findings suggest that NF-kappaB recruits E2F1 to fully activate the transcription of NF-kappaB target genes. Global gene expression profiling subsequently revealed a spectrum of NF-kappaB target genes that are positively regulated by E2F1, further demonstrating the critical role of E2F1 in the Toll-like receptor 4 pathway.

HERC5 is an IFN-induced HECT-type E3 protein ligase that mediates type I IFN-induced ISGylation of protein targets.

Type I IFNs induce the expression of IFN-stimulated gene 15 (ISG15) and its conjugation to cellular targets. ISGylation is a multistep process involving IFN-inducible Ube1L, UbcH8, and a yet-to-be identified E3 ligase. Here we report the identification of an IFN-induced HECT-type E3 protein ligase, HERC5/Ceb1, which mediates ISGylation. We also defined a number of proteins modified by ISG15 after IFN triggering or HERC5 overexpression. A reduction in endogenous HERC5 by small interfering RNA inhibition blocks the IFN-induced ISG15 conjugation. Conversely, HERC5 coexpression with Ube1L and UbcH8 induces the ISG15 conjugation in vivo independent of IFN stimulation. A targeted substitution of Cys-994 to Ala in the HECT domain of HERC5 completely abrogates its E3 protein ligase activity. Therefore, this study demonstrates that HERC5/Ceb1 is involved in the conjugation of ISG15 to cellular proteins.

TLR3 ligation activates an antiviral response in human fetal astrocytes: a role for viperin/cig5.

TLR3 functions as a viral nucleic acid sentinel activated by dsRNA viruses and virus replication intermediates within intracellular vesicles. To explore the spectrum of genes induced in human astrocytes by TLR3, we used a microarray approach and the analog polyriboinosinic polyribocytidylic acid (pIC) as ligand. As expected for TLR activation, pIC induced a wide array of cytokines and chemokines known for their role in inflammatory responses, as well as up-regulation of the receptor itself. The data also showed activation of a broad spectrum of antiviral response genes. To determine whether pIC induced an antiviral state in astrocytes, a pseudotyped HIV viral particle, vesicular stomatitis virus g-env-HIV-1, was used. pIC significantly abrogated HIV-1 replication, whereas IL-1, which also potently activates astrocytes, did not. One of the most highly up-regulated genes on microarray was the protein viperin/cig5. We found that viperin/cig5 expression was dependent on IFN regulatory factor 3 and NF-kappaB signaling, and that repetitive stimulation with pIC, but not IL-1, further increased expression. Viperin induction could also be substantially inhibited by neutralizing Abs to IFN-beta, as could HIV-1 replication. To explore a role for viperin in IFN-beta-mediated inhibition of HIV-1, we used an RNA interference (RNAi) approach. RNAi directed against viperin, but not a scrambled RNAi, significantly inhibited viperin expression, and also significantly reversed pIC-induced inhibition of HIV-1 replication. We conclude that viperin contributes to the antiviral state induced by TLR3 ligation in astrocytes, supporting a role for astrocytes as part of the innate immune response against infection in the CNS.