[Show abstract][Hide abstract] ABSTRACT: Type I interferons (IFN-Is) serve as mediators of antiviral innate immunity and also regulate adaptive immune responses. The molecular mechanism that regulates virus-induced IFN-I production, particularly in tissue-resident immune cells, is incompletely understood.
Here we identified the E3 ubiquitin ligase Peli1 as a negative regulator of IFN-I induction in microglia, innate immune cells of the central nervous system (CNS). Peli1 deficiency profoundly promoted IFN-β expression in microglia in response to in vitro stimulation by toll-like receptor (TLR) ligands or a CNS-tropic virus, the vascular stomatitis virus (VSV). Upon intranasal infection with VSV, the Peli1-deficient mice displayed heightened in vivo IFN-I responses in the CNS, coupled with reduced brain viral titer and increased survival rate.
These results establish Peli1 as an innate immune regulator in the CNS that modulates the threshold of IFN-I responses against viral infections.
Cell and Bioscience 12/2015; 5(1):34. DOI:10.1186/s13578-015-0024-z · 3.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Signal transduction from toll-like receptors (TLRs) is important for innate immunity against infections, but deregulated TLR signalling contributes to inflammatory disorders. Here we show that myeloid cell-specific ablation of TRAF2 greatly promotes TLR-stimulated proinflammatory cytokine expression in macrophages and exacerbates colitis in an animal model of inflammatory bowel disease. TRAF2 deficiency does not enhance upstream signalling events, but it causes accumulation of two transcription factors, c-Rel and IRF5, known to mediate proinflammatory cytokine induction. Interestingly, TRAF2 controls the fate of c-Rel and IRF5 via a proteasome-dependent mechanism that also requires TRAF3 and the E3 ubiquitin ligase cIAP. We further show that TRAF2 also regulates inflammatory cytokine production in tumour-associated macrophages and facilitates tumour growth. These findings demonstrate an unexpected anti-inflammatory function of TRAF2 and suggest a proteasome-dependent mechanism that limits the proinflammatory TLR signalling.
[Show abstract][Hide abstract] ABSTRACT: Development of autoimmune diseases, such as multiple sclerosis and experimental autoimmune encephalomyelitis (EAE), involves the inflammatory action of Th1 and Th17 cells, but the underlying signaling mechanism is incompletely understood. We show that the kinase TPL2 is a crucial mediator of EAE and is required for the pathological action of Th17 cells. TPL2 serves as a master kinase mediating the activation of multiple downstream pathways stimulated by the Th17 signature cytokine IL-17. TPL2 acts by linking the IL-17 receptor signal to the activation of TAK1, which involves a dynamic mechanism of TPL2-TAK1 interaction and TPL2-mediated phosphorylation and catalytic activation of TAK1. These results suggest that TPL2 mediates TAK1 axis of IL-17 signaling, thereby promoting autoimmune neuroinflammation.
Journal of Experimental Medicine 06/2014; 211(8). DOI:10.1084/jem.20132640 · 12.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The noncanonical NF-κB pathway induces processing of the NF-κB2 precursor protein p100, and thereby mediates activation of p52-containing NF-κB complexes. This pathway is crucial for B cell maturation and humoral immunity, but its role in regulating T cell function is less clear. Using mutant mice that express a nonprocessible p100, NF-κB2(lym1), we show that the noncanonical NF-κB pathway has a T cell-intrinsic role in regulating the pathogenesis of a T cell-mediated autoimmunity, experimental autoimmune encephalomyelitis (EAE). Although the lym1 mutation does not interfere with naive T cell activation, it renders the Th17 cells defective in the production of inflammatory effector molecules, particularly the cytokine GM-CSF. We provide evidence that p52 binds to the promoter of the GM-CSF-encoding gene (Csf2) and cooperates with c-Rel in the transactivation of this target gene. Introduction of exogenous p52 or GM-CSF to the NF-κB2(lym1) mutant T cells partially restores their ability to induce EAE. These results suggest that the noncanonical NF-κB pathway mediates induction of EAE by regulating the effector function of inflammatory T cells.
The Journal of Immunology 06/2014; 193(1). DOI:10.4049/jimmunol.1303237 · 4.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Glutamine has been implicated as an immunomodulatory nutrient, but how glutamine uptake is mediated during T cell activation is poorly understood. We have shown that naive T cell activation is coupled with rapid glutamine uptake, which depended on the amino acid transporter ASCT2. ASCT2 deficiency impaired the induction of T helper 1 (Th1) and Th17 cells and attenuated inflammatory T cell responses in mouse models of immunity and autoimmunity. Mechanistically, ASCT2 was required for T cell receptor (TCR)-stimulated activation of the metabolic kinase mTORC1. We have further shown that TCR-stimulated glutamine uptake and mTORC1 activation also required a TCR signaling complex composed of the scaffold protein CARMA1, the adaptor molecule BCL10, and the paracaspase MALT1. This function was independent of IKK kinase, a major downstream target of the CARMA1 complex. These findings highlight a mechanism of T cell activation involving ASCT2-dependent integration of the TCR signal and a metabolic signaling pathway.
[Show abstract][Hide abstract] ABSTRACT: Deubiquitinases (DUBs) are a new class of drug targets, although the physiological function of only few DUBs has been characterized. Here we identified the DUB USP15 as a crucial negative regulator of T cell activation. USP15 stabilized the E3 ubiquitin ligase MDM2, which in turn negatively regulated T cell activation by targeting the degradation of the transcription factor NFATc2. USP15 deficiency promoted T cell activation in vitro and enhanced T cell responses to bacterial infection and tumor challenge in vivo. USP15 also stabilized MDM2 in cancer cells and regulated p53 function and cancer-cell survival. Our results suggest that inhibition of USP15 may both induce tumor cell apoptosis and boost antitumor T cell responses.
[Show abstract][Hide abstract] ABSTRACT: Production of type I interferons (IFN-I) is a crucial innate immune mechanism against viral infections. IFN-I induction is subject to negative regulation by both viral and cellular factors, but the underlying mechanism remains unclear. We report that the noncanonical NF-κB pathway was stimulated along with innate immune cell differentiation and viral infections and had a vital role in negatively regulating IFN-I induction. Genetic deficiencies in major components of the noncanonical NF-κB pathway caused IFN-I hyperinduction and rendered cells and mice substantially more resistant to viral infection. Noncanonical NF-κB suppressed signal-induced histone modifications at the Ifnb promoter, an action that involved attenuated recruitment of the transcription factor RelA and a histone demethylase, JMJD2A. These findings reveal an unexpected function of the noncanonical NF-κB pathway and highlight an important mechanism regulating antiviral innate immunity.
[Show abstract][Hide abstract] ABSTRACT: Microglia are crucial for the pathogenesis of multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). Here we show that the E3 ubiquitin ligase Peli1 is abundantly expressed in microglia and promotes microglial activation during the course of EAE induction. Peli1 mediates the induction of chemokines and proinflammatory cytokines in microglia and thereby promotes recruitment of T cells into the central nervous system. The severity of EAE is reduced in Peli1-deficient mice despite their competent induction of inflammatory T cells in the peripheral lymphoid organs. Notably, Peli1 regulates Toll-like receptor (TLR) pathway signaling by promoting degradation of TNF receptor-associated factor 3 (Traf3), a potent inhibitor of mitogen-activated protein kinase (MAPK) activation and gene induction. Ablation of Traf3 restores microglial activation and CNS inflammation after the induction of EAE in Peli1-deficient mice. These findings establish Peli1 as a microglia-specific mediator of autoimmune neuroinflammation and suggest a previously unknown signaling mechanism of Peli1 function.
Nature medicine 04/2013; 19(5). DOI:10.1038/nm.3111 · 27.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The non-canonical NF-κB pathway forms a major arm of NF-κB signalling that mediates important biological functions, including lymphoid organogenesis, B-lymphocyte function, and cell growth and survival. Activation of the non-canonical NF-κB pathway involves degradation of an inhibitory protein, TNF receptor-associated factor 3 (TRAF3), but how this signalling event is controlled is still unknown. Here we have identified the deubiquitinase OTUD7B as a pivotal regulator of the non-canonical NF-κB pathway. OTUD7B deficiency in mice has no appreciable effect on canonical NF-κB activation but causes hyperactivation of non-canonical NF-κB. In response to non-canonical NF-κB stimuli, OTUD7B binds and deubiquitinates TRAF3, thereby inhibiting TRAF3 proteolysis and preventing aberrant non-canonical NF-κB activation. Consequently, the OTUD7B deficiency results in B-cell hyper-responsiveness to antigens, lymphoid follicular hyperplasia in the intestinal mucosa, and elevated host-defence ability against an intestinal bacterial pathogen, Citrobacter rodentium. These findings establish OTUD7B as a crucial regulator of signal-induced non-canonical NF-κB activation and indicate a mechanism of immune regulation that involves OTUD7B-mediated deubiquitination and stabilization of TRAF3.
[Show abstract][Hide abstract] ABSTRACT: Immunoglobulin class switching is crucial for the generation of antibody diversity in humoral immunity and, when deregulated, also has severe pathological consequences. How the magnitude of immunoglobulin isotype switching is controlled is still poorly understood. Here we identify the kinase TBK1 as a pivotal negative regulator of class switching to the immunoglobulin A (IgA) isotype. B cell-specific ablation of TBK1 in mice resulted in uncontrolled production of IgA and the development of nephropathy-like disease signs. TBK1 negatively regulated IgA class switching by attenuating noncanonical signaling via the transcription factor NF-κB, an action that involved TBK1-mediated phosphorylation and subsequent degradation of the NF-κB-inducing kinase NIK. Our findings establish TBK1 as a pivotal negative regulator of the noncanonical NF-κB pathway and identify a unique mechanism that controls IgA production.
[Show abstract][Hide abstract] ABSTRACT: The maintenance of immune homeostasis requires regulatory T cells (Treg cells). Here we found that Treg cell–specific ablation of Ubc13, a Lys63 (K63)-specific ubiquitin-conjugating enzyme, caused aberrant T cell activation and autoimmunity. Although Ubc13 deficiency did not affect the survival of Treg cells or expression of the transcription factor Foxp3, it impaired the in vivo suppressive function of Treg cells and rendered them sensitive to the acquisition of T helper type 1 (TH1) cell– and interleukin 17 (IL-17)-producing helper T (TH17) cell–like effector phenotypes. This function of Ubc13 involved its downstream target, the kinase IKK. The Ubc13-IKK signaling axis controlled the expression of specific Treg cell effector molecules, including IL-10 and SOCS1. Collectively, our findings suggest that the Ubc13-IKK signaling axis regulates the molecular program that maintains Treg cell function and prevents Treg cells from acquiring inflammatory phenotypes.
[Show abstract][Hide abstract] ABSTRACT: T cell activation is subject to tight regulation to avoid inappropriate responses to self antigens. Here we show that genetic deficiency in the ubiquitin ligase Peli1 caused hyperactivation of T cells and rendered T cells refractory to suppression by regulatory T cells and transforming growth factor-β (TGF-β). As a result, Peli1-deficient mice spontaneously developed autoimmunity characterized by multiorgan inflammation and autoantibody production. Peli1 deficiency resulted in the nuclear accumulation of c-Rel, a member of the NF-κB family of transcription factors with pivotal roles in T cell activation. Peli1 negatively regulated c-Rel by mediating its Lys48 (K48) ubiquitination. Our results identify Peli1 as a critical factor in the maintenance of peripheral T cell tolerance and demonstrate a previously unknown mechanism of c-Rel regulation.
[Show abstract][Hide abstract] ABSTRACT: Follicular helper T (Tfh) cells have a central role in mediating humoral immune responses. Generation of Tfh cells depends on both T-cell intrinsic factors and the supporting function of B cells, but the underlying molecular mechanisms are incompletely understood. Here we show that NF-κB-inducing kinase (NIK), a central component of the noncanonical NF-κB signaling pathway, is required for Tfh cell development. Unlike other known Tfh regulators, NIK acts by controlling the supporting function of B cells. NIK and its upstream BAFF receptor regulate B-cell expression of inducible costimulator ligand (ICOSL), a molecule required for Tfh cell generation. Consistently, injection of a recombinant ICOSL protein into NIK-deficient mice largely rescues their defect in Tfh cell development. We provide biochemical and genetic evidence indicating that the ICOSL gene is a specific target of the noncanonical NF-κB. Our findings suggest that the noncanonical NF-κB pathway regulates the development of Tfh cells by mediating ICOSL gene expression in B cells.
Proceedings of the National Academy of Sciences 08/2011; 108(31):12827-32. DOI:10.1073/pnas.1105774108 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: T cell receptor-stimulated NF-kappaB activation requires CARMA1 and is negatively regulated by the deubiquitinase CYLD. Recent studies suggest that CARMA1 regulates regulatory T cell (Treg) development, although the role of NF-kappaB in this event is incompletely understood. We show that CYLD deficiency causes constitutive NF-kappaB activation in thymocytes, which is associated with enhanced frequency of Treg cells. The NF-kappaB activation in CYLD-deficient thymocytes is independent of CARMA1, because the NF-kappaB activation was also detected in CYLD/CARMA1 double knock-out thymocytes. Interestingly, although loss of CYLD causes NF-kappaB activation in the CARMA1-deficient thymocytes, the CYLD deficiency fails to rescue the defect of CARMA1 knock-out mice in Treg development. Furthermore, inhibition of canonical NF-kappaB by an IkappaBalpha transgene only partially inhibits Treg development. We demonstrate that CARMA1 regulates IL-2 receptor signaling and controls the IL-2-stimulated maturation of Treg precursors to mature Tregs. These results suggest that the role of CARMA1 in Treg regulation involves both NF-kappaB activation and IL-2 receptor signaling.
[Show abstract][Hide abstract] ABSTRACT: Th17 cells play an important role in mediating autoimmune diseases, but the molecular mechanism underlying Th17 differentiation is incompletely understood. We show here that NF-kappaB-inducing kinase (NIK), which is known to regulate B-cell maturation and lymphoid organogenesis, is important for the induction of Th17 cells. NIK-deficient naive CD4 T cells are attenuated in the differentiation to Th17 cells, although they are competent in committing to the other effector lineages. Consistently, NIK knockout mice are resistant to experimental autoimmune encephalomyelitis, a disease model that involves the function of Th17 cells. This phenotype was also detected in Rag2 knockout mice reconstituted with NIK-deficient T cells, confirming a T-cell intrinsic defect. We further show that NIK mediates synergistic activation of STAT3 by T-cell receptor and IL-6 receptor signals. NIK deficiency attenuates activation of STAT3 and induction of STAT3 target genes involved in Th17-commitment program. These findings establish NIK as an important signaling factor that regulates Th17 differentiation and experimental autoimmune encephalitis induction.