Author Correction: Contrasting roles of histone 3 lysine 27 demethylases in acute lymphoblastic leukaemia.
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Published Erratum↗
Biomedical subjects
Shizuo Akira
Publications and source records attributed to Shizuo Akira.
Contrasting roles of histone 3 lysine 27 demethylases in acute lymphoblastic leukaemia.
T-cell acute lymphoblastic leukaemia (T-ALL) is a haematological malignancy with a dismal overall prognosis, including a relapse rate of up to 25%, mainly because of the lack of non-cytotoxic targeted therapy options. Drugs that target the function of key epigenetic factors have been approved in the context of haematopoietic disorders, and mutations that affect chromatin modulators in a variety of leukaemias have recently been identified; however, 'epigenetic' drugs are not currently used for T-ALL treatment. Recently, we described that the polycomb repressive complex 2 (PRC2) has a tumour-suppressor role in T-ALL. Here we delineated the role of the histone 3 lysine 27 (H3K27) demethylases JMJD3 and UTX in T-ALL. We show that JMJD3 is essential for the initiation and maintenance of T-ALL, as it controls important oncogenic gene targets by modulating H3K27 methylation. By contrast, we found that UTX functions as a tumour suppressor and is frequently genetically inactivated in T-ALL. Moreover, we demonstrated that the small molecule inhibitor GSKJ4 (ref. 5) affects T-ALL growth, by targeting JMJD3 activity. These findings show that two proteins with a similar enzymatic function can have opposing roles in the context of the same disease, paving the way for treating haematopoietic malignancies with a new category of epigenetic inhibitors.
Animals↗
Viral infections activate types I and III interferon genes through a common mechanism.
Viral infections trigger innate immune responses, including the production of type I interferons (IFN-alpha and -beta) and other proinflammatory cytokines. Novel antiviral cytokines IFN-lambda1, IFN-lambda2, and IFN-lambda3 are classified as type III IFNs and have evolved independently of type I IFNs. Type III IFN genes are regulated at the level of transcription and induced by viral infection. Although the regulatory mechanism of type I IFNs is well elucidated, the expression mechanism of IFN-lambdas is not well understood. Here, we analyzed the mechanism by which IFN-lambda gene expression is induced by viral infections. Loss- and gain-of-function experiments revealed the involvement of RIG-I (retinoic acid-inducible gene I), IPS-1, TBK1, and interferon regulatory factor-3, key regulators of the virus-induced activation of type I IFN genes. Consistent with this, a search for the cis-regulatory element of the human ifnlambda1 revealed a cluster of interferon regulatory factor-binding sites and a NF-kappaB-binding site. Functional analysis demonstrated that all of these sites are essential for gene activation by the virus. These results strongly suggest that types I and III IFN genes are regulated by a common mechanism.
Adaptor Proteins, Signal Transducing↗
Interleukin-1 (IL-1)-induced TAK1-dependent Versus MEKK3-dependent NFkappaB activation pathways bifurcate at IL-1 receptor-associated kinase modification.
Interleukin-1 (IL-1) receptor-associated kinase (IRAK) is phosphorylated after it is recruited to the receptor, subsequently ubiquitinated, and eventually degraded upon IL-1 stimulation. Although a point mutation changing lysine 134 to arginine (K134R) in IRAK abolished IL-1-induced IRAK ubiquitination and degradation, mutations of serines and threonines adjacent to lysine 134 to alanines ((S/T)A (131-144)) reduced IL-1-induced IRAK phosphorylation and abolished IRAK ubiquitination. Through the study of these IRAK modification mutants, we uncovered two parallel IL-1-mediated signaling pathways for NFkappaB activation, TAK1-dependent and MEKK3-dependent, respectively. These two pathways bifurcate at the level of IRAK modification. The TAK1-dependent pathway leads to IKKalpha/beta phosphorylation and IKKbeta activation, resulting in classical NFkappaB activation through IkappaBalpha phosphorylation and degradation. The TAK1-independent MEKK3-dependent pathway involves IKKgamma phosphorylation and IKKalpha activation, resulting in NFkappaB activation through IkappaBalpha phosphorylation and subsequent dissociation from NFkappaB but without IkappaBalpha degradation. These results provide significant insight to our further understanding of NFkappaB activation pathways.
Animals↗
Regulation of innate antiviral defenses through a shared repressor domain in RIG-I and LGP2.
RIG-I is an RNA helicase containing caspase activation and recruitment domains (CARDs). RNA binding and signaling by RIG-I are implicated in pathogen recognition and triggering of IFN-alpha/beta immune defenses that impact cell permissiveness for hepatitis C virus (HCV). Here we evaluated the processes that control RIG-I signaling. RNA binding studies and analysis of cells lacking RIG-I, or the related MDA5 protein, demonstrated that RIG-I, but not MDA5, efficiently binds to secondary structured HCV RNA to confer induction of IFN-beta expression. We also found that LGP2, a helicase related to RIG-I and MDA5 but lacking CARDs and functioning as a negative regulator of host defense, binds HCV RNA. In resting cells, RIG-I is maintained as a monomer in an autoinhibited state, but during virus infection and RNA binding it undergoes a conformation shift that promotes self-association and CARD interactions with the IPS-1 adaptor protein to signal IFN regulatory factor 3- and NF-kappaB-responsive genes. This reaction is governed by an internal repressor domain (RD) that controls RIG-I multimerization and IPS-1 interaction. Deletion of the RIG-I RD resulted in constitutive signaling to the IFN-beta promoter, whereas RD expression alone prevented signaling and increased cellular permissiveness to HCV. We identified an analogous RD within LGP2 that interacts in trans with RIG-I to ablate self-association and signaling. Thus, RIG-I is a cytoplasmic sensor of HCV and is governed by RD interactions that are shared with LGP2 as an on/off switch controlling innate defenses. Modulation of RIG-I/LGP2 interaction dynamics may have therapeutic implications for immune regulation.
Antiviral Agents↗
Antiviral signaling through pattern recognition receptors.
Viral infection is detected by the host innate immune system. Innate immune cells such as dendritic cells and macrophages detect nucleic acids derived from viruses through pattern recognition receptors (PRRs). Viral recognition by PRRs initiates the activation of signaling pathways that lead to production of type I interferon and inflammatory cytokines, which are important for the elimination of viruses. Two types of PRRs that recognize viral nucleic acids, Toll-like receptors (TLR) and RIG-I-like RNA helicases (RLH), have been identified. Of the TLRs, TLR3 recognizes viral double-stranded (ds) RNA, TLR7 and human TLR8 identify viral single-stranded (ss) RNA and TLR9 detects viral DNA. TLRs are located in endosomal compartments, whereas RLH are present in the cytoplasm where they detect viral dsRNA or ssRNA. Here we review the role of TLRs and RLHs in the antiviral innate immune response.
Animals↗
IL-21-induced Bepsilon cell apoptosis mediated by natural killer T cells suppresses IgE responses.
Epidemiological studies have suggested that the recent increase in the incidence and severity of immunoglobulin (Ig)E-mediated allergic disorders is inversely correlated with Mycobacterium bovis bacillus Calmette Guerin (BCG) vaccination; however, the underlying mechanisms remain uncertain. Here, we demonstrate that natural killer T (NKT) cells in mice and humans play a crucial role in the BCG-induced suppression of IgE responses. BCG-activated murine Valpha14 NKT cells, but not conventional CD4 T cells, selectively express high levels of interleukin (IL)-21, which preferentially induces apoptosis in Bepsilon cells. Signaling from the IL-21 receptor increases the formation of a complex between Bcl-2 and the proapoptotic molecule Bcl-2-modifying factor, resulting in Bepsilon cell apoptosis. Similarly, BCG vaccination induces IL-21 expression by human peripheral blood mononuclear cells (PBMCs) in a partially NKT cell-dependent fashion. BCG-activated PBMCs significantly reduce IgE production by human B cells. These findings provide new insight into the therapeutic effect of BCG in allergic diseases.
Adaptor Proteins, Signal Transducing↗
Toll-like receptor 2 does not contribute to host response during postinfluenza pneumococcal pneumonia.
Influenza A can be complicated by secondary bacterial pneumonia, which is most frequently caused by Streptococcus pneumoniae and associated with uncontrolled pulmonary inflammation. Evidence points to Toll-like receptor (TLR) 2 as a possible mediator of this exaggerated lung inflammation: (1) TLR2 is the most important "sensor" for gram-positive stimuli, (2) TLR2 contributes to S. pneumoniae-induced inflammation, and (3) influenza A enhances TLR2 expression in various cell types. Therefore, the objective of this study was to determine the role of TLR2 in the host response to postinfluenza pneumococcal pneumonia. TLR2 knockout (KO) and wild-type (WT) mice were infected intranasally with influenza A virus. Fourteen days later they were administered with S. pneumoniae intranasally. Influenza was associated with a similar transient weight loss in TLR2 KO and WT mice. Both mouse strains were fully recovered and had completely cleared the virus at Day 14. Importantly, no differences between TLR2 KO and WT mice were detected during postinfluenza pneumococcal pneumonia with respect to bacterial growth, lung inflammation, or cytokine/chemokine concentrations, with the exception of lower pulmonary levels of cytokine-induced neutrophil chemoattractant in TLR2 KO mice. Toll-like receptor 2 does not contribute to host defense during murine postinfluenza pneumococcal pneumonia.
Animals↗
Dectin-1 is required for host defense against Pneumocystis carinii but not against Candida albicans.
Dectin-1 is a C-type lectin involved in the recognition of beta-glucans found in the cell walls of fungi. We generated dectin-1-deficient mice to determine the importance of dectin-1 in the defense against pathogenic fungi. In vitro, beta-glucan-induced cytokine production from wild-type dendritic cells and macrophages was abolished in cells homozygous for dectin-1 deficiency ('dectin-1-knockout' cells). In vivo, dectin-1-knockout mice were more susceptible than wild-type mice to pneumocystis infection, even though their cytokine production was normal. However, pneumocystis-infected dectin-1-knockout macrophages did show defective production of reactive oxygen species. In contrast to those results, wild-type and dectin-1-knockout mice were equally susceptible to candida infection. Thus, dectin-1 is required for immune responses to some fungal infections, as protective immunity to pneumocystis, but not to candida, required dectin-1 for the production of antifungal reactive oxygen species.
Animals↗
Cutting Edge: Pivotal function of Ubc13 in thymocyte TCR signaling.
The Ubc13 E2 ubiquitin-conjugating enzyme is essential for BCR-, TLR-, and IL-1 receptor (IL-1R)-mediated immune responses. Although Ubc13-deficient mice show defects in BCR-, TLR/IL-1R-, or CD40-mediated activation of mitogen-activated protein kinases, the function of Ubc13 in TCR-mediated signaling and responses remains uncertain. To address this, we here generated T cell-specific conditional Ubc13-deficient mice. The frequency of T lymphocytes was severely reduced in spleens from Ubc13-deficient mice. Moreover, Ubc13-deficient thymocytes displayed defective proliferation in response to anti-CD3/CD28 or PMA/ionophore stimulation. Regarding the signal transduction, although NF-kappaB activation was modestly affected, PMA/ionophore-induced activation of Jnk and p38 was profoundly impaired in Ubc13-deficient thymocytes. In addition, PMA/ionophore-mediated ubiquitination of NF-kappaB essential modulator (NEMO)/IkappaB kinase gamma (IKKgamma) and phosphorylation of TGF-beta-activated kinase 1 (TAK1) were nearly abolished in Ubc13-deficient thymocytes. Thus, Ubc13 plays an important role in thymocyte TCR-mediated signaling and immune responses.
Animals↗
Macrophages and myeloid dendritic cells, but not plasmacytoid dendritic cells, produce IL-10 in response to MyD88- and TRIF-dependent TLR signals, and TLR-independent signals.
We have previously reported that mouse plasmacytoid dendritic cells (DC) produce high levels of IL-12p70, whereas bone marrow-derived myeloid DC and splenic DC produce substantially lower levels of this cytokine when activated with the TLR-9 ligand CpG. We now show that in response to CpG stimulation, high levels of IL-10 are secreted by macrophages, intermediate levels by myeloid DC, but no detectable IL-10 is secreted by plasmacytoid DC. MyD88-dependent TLR signals (TLR4, 7, 9 ligation), Toll/IL-1 receptor domain-containing adaptor-dependent TLR signals (TLR3, 4 ligation) as well as non-TLR signals (CD40 ligation) induced macrophages and myeloid DC to produce IL-10 in addition to proinflammatory cytokines. IL-12p70 expression in response to CpG was suppressed by endogenous IL-10 in macrophages, in myeloid DC, and to an even greater extent in splenic CD8alpha(-) and CD8alpha(+) DC. Although plasmacytoid DC did not produce IL-10 upon stimulation, addition of this cytokine exogenously suppressed their production of IL-12, TNF, and IFN-alpha, showing trans but not autocrine regulation of these cytokines by IL-10 in plasmacytoid DC.
Adaptor Proteins, Vesicular Transport↗
Pathological role of Toll-like receptor signaling in cerebral malaria.
Toll-like receptors (TLRs) recognize malaria parasites or their metabolites; however, their physiological roles in malaria infection in vivo are not fully understood. Here, we show that myeloid differentiation primary response gene 88 (MyD88)-dependent TLR signaling mediates brain pathogenesis of severe malaria infection, namely cerebral malaria (CM). A significant number of MyD88-, but not TIR domain containing adaptor-inducing IFN-beta (TRIF)-deficient or wild-type (WT) mice survived CM caused by Plasmodium berghei ANKA (PbA) infection. Although systemic parasitemia was comparable, sequestration of parasite and hemozoin load in the brain blood vessels was significantly lower in MyD88-deficient mice compared with those in TRIF-deficient or WT mice. Moreover, brain-specific pathological changes were associated with MyD88-dependent infiltration of CD8+, CCR5+ T cells and CD11c+ dendritic cells, including CD11c+, NK1.1+ and B220+ cells, and up-regulation of genes such as Granzyme B, Lipocalin 2, Ccl3 and Ccr5. Further studies using mice lacking various TLRs suggest that TLR2 and TLR9, but not TLR4, 5 and 7, were involved in CM. These results strongly suggest that TLR2- and/or TLR9-mediated, MyD88-dependent brain pathogenesis may play a critical role in CM, the lethal complication during PbA infection.
Adaptor Proteins, Vesicular Transport↗
TLR-dependent induction of IFN-beta mediates host defense against Trypanosoma cruzi.
Host resistance to the intracellular protozoan parasite Trypanosoma cruzi depends on IFN-gamma production by T cells and NK cells. However, the involvement of innate immunity in host resistance to T. cruzi remains unclear. In the present study, we investigated host defense against T. cruzi by focusing on innate immunity. Macrophages and dendritic cells (DCs) from MyD88(-/-)TRIF(-/-) mice, in which TLR-dependent activation of innate immunity was abolished, were defective in the clearance of T. cruzi and showed impaired induction of IFN-beta during T. cruzi infection. Neutralization of IFN-beta in MyD88(-/-) macrophages led to enhanced T. cruzi growth. Cells from MyD88(-/-)IFNAR1(-/-) mice also showed impaired T. cruzi clearance. Furthermore, both MyD88(-/-)TRIF(-/-) and MyD88(-/-)IFNAR1(-/-) mice were highly susceptible to in vivo T. cruzi infection, highlighting the involvement of innate immune responses in T. cruzi infection. We further analyzed the molecular mechanisms for the IFN-beta-mediated antitrypanosomal innate immune responses. MyD88(-/-)TRIF(-/-) and MyD88(-/-)IFNAR1(-/-) macrophages and DCs exhibited defective induction of the GTPase IFN-inducible p47 (IRG47) after T. cruzi infection. RNA interference-mediated reduction of IRG47 expression in MyD88(-/-) macrophages resulted in increased intracellular growth of T. cruzi. These findings suggest that TLR-dependent expression of IFN-beta is involved in resistance to T. cruzi infection through the induction of IRG47.
Adaptor Proteins, Vesicular Transport↗
Th17 functions as an osteoclastogenic helper T cell subset that links T cell activation and bone destruction.
In autoimmune arthritis, traditionally classified as a T helper (Th) type 1 disease, the activation of T cells results in bone destruction mediated by osteoclasts, but how T cells enhance osteoclastogenesis despite the anti-osteoclastogenic effect of interferon (IFN)-gamma remains to be elucidated. Here, we examine the effect of various Th cell subsets on osteoclastogenesis and identify Th17, a specialized inflammatory subset, as an osteoclastogenic Th cell subset that links T cell activation and bone resorption. The interleukin (IL)-23-IL-17 axis, rather than the IL-12-IFN-gamma axis, is critical not only for the onset phase, but also for the bone destruction phase of autoimmune arthritis. Thus, Th17 is a powerful therapeutic target for the bone destruction associated with T cell activation.
Animals↗
Cutting edge: Role of TANK-binding kinase 1 and inducible IkappaB kinase in IFN responses against viruses in innate immune cells.
TANK-binding kinase 1 (TBK1) and inducible IkappaB kinase (IKK-i) are involved in the activation of transcription factors inducing the production of type I IFNs. Although TBK1, but not IKK-i, is critical for LPS-induced IFN induction, the role of these kinases in the responses against viral infection is yet to be determined. In this study, we show that type I IFN production against various RNA viruses was completely abrogated in conventional dendritic cells (DCs) and macrophages induced from fetal liver cells lacking both TBK1 and IKK-i, whereas considerable amounts of IFN were produced in cells lacking either of them. Microarray analysis revealed that various IFN-inducible genes were also regulated by the kinases. In contrast, Fms-like tyrosine kinase 3 ligand-induced DCs produced IFN-alpha even in the absence of both TBK1 and IKK-i. Thus, these two kinases are essential and compensate each other for the regulation of IFN responses in innate immune cells except plasmacytoid DCs.
Animals↗
5'-Triphosphate RNA is the ligand for RIG-I.
The structural basis for the distinction of viral RNA from abundant self RNA in the cytoplasm of virally infected cells is largely unknown. We demonstrated that the 5'-triphosphate end of RNA generated by viral polymerases is responsible for retinoic acid-inducible protein I (RIG-I)-mediated detection of RNA molecules. Detection of 5'-triphosphate RNA is abrogated by capping of the 5'-triphosphate end or by nucleoside modification of RNA, both occurring during posttranscriptional RNA processing in eukaryotes. Genomic RNA prepared from a negative-strand RNA virus and RNA prepared from virus-infected cells (but not from noninfected cells) triggered a potent interferon-alpha response in a phosphatase-sensitive manner. 5'-triphosphate RNA directly binds to RIG-I. Thus, uncapped 5'-triphosphate RNA (now termed 3pRNA) present in viruses known to be recognized by RIG-I, but absent in viruses known to be detected by MDA-5 such as the picornaviruses, serves as the molecular signature for the detection of viral infection by RIG-I.
Animals↗
Roles of the small intestine for induction of toll-like receptor 4-mediated innate resistance in naturally acquired murine toxoplasmosis.
Peroral infection of Toxoplasma gondii is thought to reflect the typical infection route of naturally acquired toxoplasmosis in humans. We have investigated possible differential roles of toll-like receptor 2 (TLR2) and TLR4 in host defense against naturally acquired murine toxoplasmosis. After peroral inoculation of T. gondii ME49 cysts, TLR4-deficient C3H/HeJ mice were more susceptible to infection than wild-type (WT) C3H/HeN mice, as shown by increased cyst number and low production of cytokines, which are the key factors in protective immunity. When mice were inoculated by intra-peritoneal inoculation of T. gondii, there were no significant differences in the number of brain cysts and cytokine productions between C3H/HeJ and C3H/HeN mice. Histopathologic examination revealed severe inflammation in the small intestine of C3H/HeJ (TLR4-deficient) mice, while an increased number of TLR4-positive mononuclear cells was found in C3H/HeN (WT) mice. To confirm these phenomena, TLR2(-/-) or TLR4(-/-) mice were infected perorally with T. gondii cysts. TLR4(-/-) mice were more susceptible to infection compared with TLR2(-/-) and C57BL/6 mice. Nuclear factor-kappa B activation through TLR4 agonistic activity of T. gondii ME49 was demonstrated by luciferase assay using stably expressing mouse (m) TLR2 or mTLR4/mMD-2 transfectants. We demonstrate here for the first time that innate immune recognition by TLR4 is involved in protective mechanisms against peroral infection with T. gondii ME49. These results suggest that the small intestine plays an important role in the induction of innate immunity in naturally acquired toxoplasmosis.
Animals↗
Dual role of MyD88 in rapid clearance of relapsing fever Borrelia spp.
Relapsing fever Borrelia spp. undergo antigenic variation, achieve high levels in blood, and require rapid production of immunoglobulin M (IgM) for clearance. MyD88-deficient mice display defective clearance of many pathogens; however, the IgM response to persistent infection is essentially normal. Therefore, MyD88(-/-) mice provided a unique opportunity to study the effect of nonantibody, innate host defenses to relapsing fever Borrelia. Infected MyD88(-/-) mice harbored extremely high levels of B. hermsii in the blood compared to wild-type littermates. In the comparison of MyD88(-/-) mice and B- and T-cell-deficient scid mice, two features stood out: (i) bacterial numbers in blood were at least 10-fold greater in MyD88(-/-) mice than scid mice, even though the production of IgM still occurred in MyD88(-/-) mice; and (ii) many of the MyD88(-/-) mice were able to exert partial clearance, although with delayed kinetics relative to wild-type mice, a feature not seen in scid mice. Further analysis revealed a delay in the IgM response to lipoproteins expressed by the original inoculum; however, by 6 days of infection antibodies were produced in MyD88(-/-) mice that could clear spirochetemia in scid mice. While these results indicated that the production of IgM was delayed in MyD88(-/-) mice, they also point to a second, antibody-independent role for MyD88 signaling in host defense to relapsing fever Borrelia. This second defect was apparent only when antibody levels were limiting.
Animals↗