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Showing papers by "Richard A. Flavell published in 2003"


PatentDOI
09 Jan 2003-Cell
TL;DR: IRAK-M regulates TLR signaling and innate immune homeostasis and prevents dissociation of IRAK and IRAK-4 from MyD88 and formation of IRAk-TRAF6 complexes.

1,375 citations


Journal ArticleDOI
17 Jul 2003-Nature
TL;DR: The results suggest that multiple dendritic cell types, not just plasmacytoid cells, can act as specialized interferon-producing cells in certain viral infections, and reveal the existence of a TLR-independent pathway for d endritic cell activation that can be the target of viral interference.
Abstract: Type I interferons (IFN-I) are important cytokines linking innate and adaptive immunity. Plasmacytoid dendritic cells make high levels of IFN-I in response to viral infection and are thought to be the major source of the cytokines in vivo. Here, we show that conventional non-plasmacytoid dendritic cells taken from mice infected with a dendritic-cell-tropic strain of lymphocytic choriomeningitis virus make similarly high levels of IFN-I on subsequent culture. Similarly, non-plasmacytoid dendritic cells secrete high levels of IFN-I in response to double-stranded RNA (dsRNA), a major viral signature, when the latter is introduced into the cytoplasm to mimic direct viral infection. This response is partially dependent on the cytosolic dsRNA-binding enzyme protein kinase R and does not require signalling through toll-like receptor (TLR) 3, a surface receptor for dsRNA. Furthermore, we show that sequestration of dsRNA by viral NS1 (refs 6, 7) explains the inability of conventional dendritic cells to produce IFN-I on infection with influenza. Our results suggest that multiple dendritic cell types, not just plasmacytoid cells, can act as specialized interferon-producing cells in certain viral infections, and reveal the existence of a TLR-independent pathway for dendritic cell activation that can be the target of viral interference.

607 citations


Journal ArticleDOI
TL;DR: It is shown that MKK3 and MKK6 are essential for tumor necrosis factor-stimulated p38 MAPK activation, and loss of p38MAPK activation in the mutant cells was associated with defects in growth arrest and increased tumorigenesis.
Abstract: The p38 mitogen-activated protein kinase (MAPK) is activated in vitro by three different protein kinases: MKK3, MKK4, and MKK6. To examine the relative roles of these protein kinases in the mechanism of p38 MAP kinase activation in vivo, we examined the effect of disruption of the murine Mkk3, Mkk4, and Mkk6 genes on the p38 MAPK signaling pathway. We show that MKK3 and MKK6are essential for tumor necrosis factor-stimulated p38 MAPK activation. In contrast, ultraviolet radiation-stimulated p38 MAPK activation was mediated by MKK3, MKK4, and MKK6. Loss of p38 MAPK activation in the mutant cells was associated with defects in growth arrest and increased tumorigenesis. These data indicate that p38 MAPK is regulated by the coordinated and selective actions of three different protein kinases in response to cytokines and exposure to environmental stress.

490 citations


Journal ArticleDOI
TL;DR: These findings show that UCM involves an autocrine or paracrine loop, and indicate that an alternative TLR3-independent, Trif-independent pathway contributes to dsRNA-induced UCM.
Abstract: Both lipopolysaccharide (LPS) and double-stranded RNA (dsRNA) are adjuvants for the adaptive immune response, inducing upregulation of costimulatory molecules (UCM) on antigen-presenting cells. Trif, an adapter protein that transduces signals from Toll-like receptor 4 (TLR4) and TLR3, permits the induction of many cytokines, including interferon-beta, which signals through the type I interferon receptor. We show here that LPS-induced UCM was strictly dependent on the TLR4-->Trif axis, whereas dsRNA-induced UCM was only partly dependent on the TLR3-->Trif axis. But both LPS- and dsRNA-induced UCM were entirely dependent on type I interferon receptor signaling. These findings show that UCM involves an autocrine or paracrine loop, and indicate that an alternative TLR3-independent, Trif-independent pathway contributes to dsRNA-induced UCM.

476 citations


Journal ArticleDOI
TL;DR: It is shown by using a CD8+ T cell-mediated model of type 1 diabetes that transforming growth factor (TGF)-β–TGF-β receptor signals are critical for CD4+CD25+ Treg cell regulation of autoreactive islet-specific cytotoxic T lymphocytes.
Abstract: Pancreatic lymph node-derived CD4+CD25+ T regulatory (Treg) cells inhibit in situ differentiation of islet-reactive CD8+ T cells into cytotoxic T lymphocytes, thereby preventing diabetes progression. The mechanism by which these Treg cells suppress anti-islet CD8+ T cells is unknown. Here, we show by using a CD8+ T cell-mediated model of type 1 diabetes that transforming growth factor (TGF)-β–TGF-β receptor signals are critical for CD4+CD25+ Treg cell regulation of autoreactive islet-specific cytotoxic T lymphocytes. Transgenic expression of tumor necrosis factor α from birth to 25 days of age in the islets of B6 mice that constitutively express CD80 on their β cells results in accumulation of CD4+CD25+TGF-β+ cells exclusively in the islets and pancreatic lymph nodes, which delays diabetes progression. In contrast, expression of tumor necrosis factor α until 28 days of age prevents islet accumulation of CD4+CD25+TGF-β+ Treg cells, resulting in acceleration to diabetes. Furthermore, adoptive transfer experiments demonstrated that CD4+CD25+ Treg cells could not control naive or activated isletreactive CD8+ T cells bearing a dominant negative TGF-β receptor type II. Our data demonstrate that, in vivo, TGF-β signaling in CD8+ T cells is critical for CD4+CD25+ Treg cell suppression of isletreactive CD8+ T cells in type 1 diabetes.

437 citations


Journal ArticleDOI
TL;DR: Results show that abrogation of T GF-β signaling in T cells increases atherosclerosis and suggest that TGF-β reduces Atherosclerosis by dampening T cell activation, and inhibition of T cellactivation may represent a strategy for antiatherosclerotic therapy.
Abstract: Increasing evidence suggests that atherosclerosis is an inflammatory disease promoted by hypercholesterolemia. The role of adaptive immunity has been controversial, however. We hypothesized that proatherogenic T cells are controlled by immunoregulatory cytokines. Among them, TGF-beta has been implied in atherosclerosis, but its mechanism of action remains unclear. We crossed atherosclerosis-prone ApoE-knockout mice with transgenic mice carrying a dominant negative TGF-beta receptor II in T cells. The ApoE-knockout mice with disrupted TGF-beta signaling in T cells exhibited a sixfold increase in aortic lesion surface area, a threefold increase in aortic root lesion size, and a 125-fold increase in aortic IFN-gamma mRNA when compared with age-matched ApoE-knockout littermates. When comparing size-matched lesions, those of mice with T cell-specific blockade of TGF-beta signaling displayed increased T cells, activated macrophages, and reduced collagen, consistent with a more vulnerable phenotype. Ab's to oxidized LDL, circulating T cell cytokines, and spleen T cell activity were all increased in ApoE-knockout mice with dominant negative TGF-beta receptors in T cells. Taken together, these results show that abrogation of TGF-beta signaling in T cells increases atherosclerosis and suggest that TGF-beta reduces atherosclerosis by dampening T cell activation. Inhibition of T cell activation may therefore represent a strategy for antiatherosclerotic therapy.

415 citations


Journal ArticleDOI
TL;DR: It is shown that JNK1 is the major isoform responsible for the high level of basal JNK activity in the brain, and targeted deletion of Jnk3 not only reduces the stress-induced J NK activity, but also protects mice from brain injury after cerebral ischemia–hypoxia.
Abstract: c-Jun N-terminal kinase (JNK) signaling is an important contributor to stress-induced apoptosis, but it is unclear whether JNK and its isoforms (JNK1, JNK2, and JNK3) have distinct roles in cerebral ischemia. Here we show that JNK1 is the major isoform responsible for the high level of basal JNK activity in the brain. In contrast, targeted deletion of Jnk3 not only reduces the stress-induced JNK activity, but also protects mice from brain injury after cerebral ischemia–hypoxia. The downstream mechanism of JNK3-mediated apoptosis may include the induction of Bim and Fas and the mitochondrial release of cytochrome c. These results suggest that JNK3 is a potential target for neuroprotection therapies in stroke.

408 citations


Journal ArticleDOI
28 Nov 2003-Science
TL;DR: A critical role for PSR in early stages of mammalian organogenesis is demonstrated and it is suggested that this receptor may be involved in respiratory distress syndromes and congenital brain malformations.
Abstract: Cells undergoing apoptosis during development are removed by phagocytes, but the underlying mechanisms of this process are not fully understood. Phagocytes lacking the phosphatidylserine receptor (PSR) were defective in removing apoptotic cells. Consequently, in PSR-deficient mice, dead cells accumulated in the lung and brain, causing abnormal development and leading to neonatal lethality. A fraction of PSR knockout mice manifested a hyperplasic brain phenotype resembling that of mice deficient in the cell death-associated genes encoding Apaf-1, caspase-3, and caspase-9, which suggests that phagocytes may also be involved in promoting apoptosis. These data demonstrate a critical role for PSR in early stages of mammalian organogenesis and suggest that this receptor may be involved in respiratory distress syndromes and congenital brain malformations.

404 citations


Journal ArticleDOI
TL;DR: The results suggest a model in which STAT3 has critical roles in the development and regulation of innate immunity, and deletion of STAT3 during hematopoiesis results in abnormalities in myeloid cells and causes Crohn's disease-like pathogenesis.
Abstract: Signal transducer and activator of transcription 3 (STAT3) is a key transcriptional mediator for many cytokines and is essential for normal embryonic development. We have generated a unique strain of mice with tissue-specific disruption of STAT3 in bone marrow cells during hematopoiesis. This specific STAT3 deletion causes death of these mice within 4–6 weeks after birth with Crohn's disease-like pathogenesis in both the small and large intestine, including segmental inflammatory cell infiltration, ulceration, bowel wall thickening, and granuloma formation. Deletion of STAT3 causes significantly increased cell autonomous proliferation of cells of the myeloid lineage, both in vivo and in vitro. Most importantly, Stat3 deletion during hematopoiesis causes overly pseudoactivated innate immune responses. Although inflammatory cytokines, including tumor necrosis factor α and IFN-γ, are overly produced in these mice, the NAPDH oxidase activity, which is involved in antimicrobial and innate immune responses, is inhibited. The signaling responses to lipopolysaccharide are changed in the absence of STAT3, leading to enhanced NF-κB activation. Our results suggest a model in which STAT3 has critical roles in the development and regulation of innate immunity, and deletion of STAT3 during hematopoiesis results in abnormalities in myeloid cells and causes Crohn's disease-like pathogenesis.

399 citations


Journal ArticleDOI
TL;DR: CO provides protection in a murine model of sepsis through modulation of inflammatory cytokine production through the JNK signaling pathway and the transcription factor AP-1.

385 citations


Journal ArticleDOI
01 Dec 2003-Immunity
TL;DR: The formation of CMP and CLP represents the first decisive lineage commitment step, and in this regard it is provided evidence that commitments of CLP/CMP to the DC lineage strictly depend on the interplay of both Flt3L and STAT3 activation.

Journal ArticleDOI
TL;DR: The studies show that low level, exogenous CO attenuates anoxia-reoxygenation (A-R)-induced lung endothelial cell apoptosis and are the first to demonstrate in models of A-R that the anti-apoptotic effects of CO are via modulation of p38 MAPK and caspase 3.

Journal ArticleDOI
TL;DR: It is demonstrated that JNK-stimulated survival signaling can be mediated by JunD, and the JNK/JunD pathway can collaborate with NF-kappaB to increase antiapoptotic gene expression.

Journal ArticleDOI
TL;DR: It is proposed that Salmonella, through the action of SipB, kills macrophages by disrupting mitochondria, thereby inducing autophagy and cell death.
Abstract: Salmonella enterica, the causative agent of food poisoning and typhoid fever, induces programmed cell death in macrophages, a process found to be dependent on a type III protein secretion system, and SipB, a protein with membrane fusion activity that is delivered into host cells by this system. When expressed in cultured cells, SipB caused the formation of and localized to unusual multimembrane structures. These structures resembled autophagosomes and contained both mitochondrial and endoplasmic reticulum markers. A mutant form of SipB devoid of membrane fusion activity localized to mitochondria, but did not induce the formation of membrane structures. Upon Salmonella infection of macrophages, SipB was found in mitochondria, which appeared swollen and devoid of christae. Salmonella-infected macrophages exhibited marked accumulation of autophagic vesicles. We propose that Salmonella, through the action of SipB, kills macrophages by disrupting mitochondria, thereby inducing autophagy and cell death.

Journal ArticleDOI
01 Jul 2003-Immunity
TL;DR: Investigation of the global locus-specific regulation of these genes using BAC transgenic mice containing the murine Th2 cytokine cluster carrying an IL4 promoter-luciferase reporter suggested the presence of an LCR in the locus.

Journal ArticleDOI
01 Dec 2003-Immunity
TL;DR: The results indicate that distinct microbial signals activate innate immune responses in an ordered, step-wise fashion, providing a mechanism to specify and modulate antimicrobial effector functions.

Journal ArticleDOI
TL;DR: It is shown that embryonic fibroblasts from Syt VII–deficient mice are less susceptible to trypanosome invasion, and defective in lysosomal exocytosis and resealing after wounding, which suggests defective plasma membrane repair in tissues under mechanical stress may favor the development of inflammatory autoimmune disease.
Abstract: Members of the synaptotagmin family have been proposed to function as Ca2+ sensors in membrane fusion. Syt VII is a ubiquitously expressed synaptotagmin previously implicated in plasma membrane repair and Trypanosoma cruzi invasion, events which are mediated by the Ca2+-regulated exocytosis of lysosomes. Here, we show that embryonic fibroblasts from Syt VII–deficient mice are less susceptible to trypanosome invasion, and defective in lysosomal exocytosis and resealing after wounding. Examination of mutant mouse tissues revealed extensive fibrosis in the skin and skeletal muscle. Inflammatory myopathy, with muscle fiber invasion by leukocytes and endomysial collagen deposition, was associated with elevated creatine kinase release and progressive muscle weakness. Interestingly, similar to what is observed in human polymyositis/dermatomyositis, the mice developed a strong antinuclear antibody response, characteristic of autoimmune disorders. Thus, defective plasma membrane repair in tissues under mechanical stress may favor the development of inflammatory autoimmune disease.

Journal ArticleDOI
TL;DR: The data suggest that hyperoxia generates reactive oxygen species (ROS), which mediates cell death of lung epithelium via ERK1/2 MAPK activation, and functions upstream of caspase activation in lung epithelial cells.
Abstract: Therapy with high oxygen concentrations (hyperoxia) is often necessary to treat patients with respiratory failure. However, hyperoxia may exacerbate the development of acute lung injury, perhaps by increasing lung epithelial cell death. Therefore, interrupting lung epithelial cell death is an important protective and therapeutic strategy. In the present study, hyperoxia (95% O2) results in murine lung epithelium cell death by DNA-laddering, terminal deoxynucleotidyltransferase dUTP nick end labeling, and Annexin V–fluorescein isothiocyanate flow cytometry assay. We show that hyperoxia increases superoxide production, as assessed by nicotinamide adenine dinucleotide phosphate reduced (NADPH) oxidase activity and flow cytometric assay, and increases phospho–extracellular signal-regulated kinase (ERK)1/2 by Western blot analysis. These processes are inhibited by a reactive oxygen species inhibitor, diphenylene iodonium (DPI), and by an inhibitor of the mitogen-activated protein (MAP) or ERK kinase (MEK)/ERK1...

Journal ArticleDOI
TL;DR: It is demonstrated that carbon monoxide (CO), a byproduct released during the degradation of heme by HO, plays a major role in mediating the cytoprotection against oxidant-induced lung injury and exerts potent anti-inflammatory effects.
Abstract: The stress-inducible gene heme oxygenase (HO-1) has previously been shown to provide cytoprotection against oxidative stress. The mechanism(s) by which HO-1 provides this cytoprotection is poorly understood. We demonstrate here that carbon monoxide (CO), a byproduct released during the degradation of heme by HO, plays a major role in mediating the cytoprotection against oxidant-induced lung injury. We show in vitro that CO protects cultured epithelial cells from hyperoxic damage. By using dominant negative mutants and mice deficient in the genes for the various MAP kinases, we demonstrate that the cytoprotective effects of CO are mediated by selective activation of the MKK3/p38β protein MAP kinase pathway. In vivo, our experiments demonstrate that CO at a low concentration protects the lungs, extends the survival of the animals, and exerts potent anti-inflammatory effects with reduced inflammatory cell influx into the lungs and marked attenuation in the expression of pro-inflammatory cytokines.

Journal ArticleDOI
TL;DR: These data are the first to demonstrate that CO has an antiapoptotic effect by inhibiting Fas/Fas ligand, caspases, proap optotic Bcl-2 proteins, and cytochrome c release via the MKK3/p38α MAPK pathway.

Journal ArticleDOI
TL;DR: It is shown that JNK is required for the normal regulation of AP-1 by TNF, and the JNK signal transduction pathway is therefore essential forAP-1 transcription factor regulation in cells exposed to TNF.
Abstract: The c-Jun NH(2)-terminal kinase (JNK) is activated by the cytokine tumor necrosis factor (TNF). This pathway is implicated in the regulation of AP-1-dependent gene expression by TNF. To examine the role of the JNK signaling pathway, we compared the effects of TNF on wild-type and Jnk1(-/-) Jnk2(-/-) murine embryo fibroblasts. We show that JNK is required for the normal regulation of AP-1 by TNF. The JNK-deficient cells exhibited decreased expression of c-Jun, JunD, c-Fos, Fra1, and Fra2; decreased phosphorylation of c-Jun and JunD; and decreased AP-1 DNA binding activity. The JNK-deficient cells also exhibited defects in the regulation of the AP-1-related transcription factor ATF2. These changes were associated with marked defects in TNF-regulated gene expression. The JNK signal transduction pathway is therefore essential for AP-1 transcription factor regulation in cells exposed to TNF.

Journal ArticleDOI
TL;DR: Data indicate that Kv1.3 channels may participate in the pathways that regulate body weight and that channel inhibition increases basal metabolic rate, which is significantly higher in knockout animals.
Abstract: Voltage-gated potassium (Kv) channels regulate cell membrane potential and control a variety of cellular processes. Kv1.3 channels are expressed in several tissues and believed to participate in cell volume regulation, apoptosis, T cell activation and renal solute homeostasis. Examination of Kv1.3-deficient mice (Kv1.3(-/-)), generated by gene targeting, revealed a previously unrecognized role for Kv1.3 in body weight regulation. Indeed, Kv1.3(-/-) mice weigh significantly less than control littermates. Moreover, knockout mice are protected from diet-induced obesity and gain significantly less weight than littermate controls when placed on a high-fat diet. While food intake did not differ significantly between Kv1.3(-/-) and controls, basal metabolic rate, measured at rest by indirect calorimetry, was significantly higher in knockout animals. These data indicate that Kv1.3 channels may participate in the pathways that regulate body weight and that channel inhibition increases basal metabolic rate.

Journal ArticleDOI
TL;DR: It is shown that a soluble activity derived from endothelia and dependent on STAT3 is critical for suppression of interferon γ, and this data define STAT3 signaling within endothelium as a critical antiinflammatory mediator and provide new insight to the protective function of ECs in inflammation.
Abstract: Endothelial cells (ECs) are believed to be an important component in the protection from lipopolysaccharide (LPS)-induced endotoxic shock. However, the cellular and molecular mechanism is not well defined. Here, we report that signal transducer and activator of transcription (STAT) 3 is an essential regulator of the antiinflammatory function of ECs in systemic immunity. Because STAT3 deficiency results in early embryonic lethality, we have generated mice with a conditional STAT3 deletion in endothelium (STAT3 E � / � ). STAT3 E � / � mice are healthy and fertile, and isolated ECs initiate normal tube formation in vitro. Conditional endothelial but not organ-specific (i.e., hepatocyte or cardiomyocyte) STAT3 knockout mice show an increased susceptibility to lethality after LPS challenge. The LPS response in STAT3 E � / � mice shows exaggerated inflammation and leukocyte infiltration in multiple organs combined with elevated activity of serum alanine aminotransferase and aspartate aminotransferase, indicating organ damage. Concomitantly, proinflammatory cytokines are produced at an exaggerated level and for a prolonged period. This defect cannot be explained by lack of antiinflammatory cytokines, such as interleukin 10 and transforming growth factor � . Instead, we have shown that a soluble activity derived from endothelia and dependent on STAT3 is critical for suppression of interferon � . These data define STAT3 signaling within endothelia as a critical antiinflammatory mediator and provide new insight to the protective function of ECs in inflammation.

Journal ArticleDOI
TL;DR: The findings suggest the ischemic activation of p38-MAPK contributing to myocardial injury is by TAB1-associated autophosphorylation, rather than through dual phosphorylation by MAPK kinase 3 (MKK3).
Abstract: The ischemic activation of p38α mitogen-activated protein kinase (p38α-MAPK) is thought to contribute to myocardial injury. Under other circumstances, activation is through dual phosphorylation by MAPK kinase 3 (MKK3). Therefore, the mkk3−/− murine heart should be protected during ischemia. In retrogradely perfused mkk3−/− and mkk3+/+ mouse hearts subjected to 30 minutes of global ischemia and 120 minutes of reperfusion, infarction/risk volume was similar (50±5 versus 51±4, P =0.93, respectively), as was intraischemic p38-MAPK phosphorylation (10 minutes ischemia as percent basal, 608±224 versus 384±104, P =0.43, respectively). This occurred despite undetectable activation of MKK3/6 in mkk3−/− hearts. However, tumor necrosis factor (TNF)-induced p38-MAPK phosphorylation was markedly diminished in mkk3−/− vs mkk3+/+ hearts (percent basal, 127±23 versus 540±267, respectively, P =0.04), suggesting an MKK-independent activation mechanism by ischemia. Hence, we examined p38-MAPK activation by TAB1-associated autophosphorylation. In wild-type mice and mkk3−/− mice, the p38-MAPK catalytic site inhibitor SB203580 (1 μmol/L) diminished phosphorylation during ischemia versus control (10 minutes ischemia as percent basal, 143±2 versus 436±96, P =0.003, and 122±25 versus 623±176, P =0.05, respectively) and reduced infarction volume (infarction/risk volume, 57±5 versus 36±3, P <0.001, and 50±5 versus 29±3, P =0.003, respectively) but did not alter TNF-induced activation, although in homogenates of ischemic hearts but not TNF-exposed hearts, p38-MAPK was associated with TAB1. Furthermore, adenovirally expressed wild-type and drug-resistant p38α-MAPK, lacking the SB203580 binding site, was phosphorylated when H9c2 myoblasts were subjected to simulated ischemia. However, SB203580 (1 μmol/L) did not prevent the phosphorylation of resistant p38α-MAPK. These findings suggest the ischemic activation of p38-MAPK contributing to myocardial injury is by TAB1-associated autophosphorylation.

Journal ArticleDOI
01 Jun 2003-Immunity
TL;DR: In this article, the authors examined the transcriptional mechanisms by which ICOS regulates Th2 differentiation and selective IL-4 expression by effector T cells and found impaired expression of c-Maf transcription factor functionally associated with the IL 4 defect in ICOS(-/-) cells.

Journal ArticleDOI
TL;DR: It is demonstrated that although JNK does play a role in transformation in vitro, JNK is not required for tumor development in vivo and this conclusion is consistent with the presence in human tumors of loss-of-function mutations in the JNK pathway.
Abstract: The c-Jun NH2-terminal kinase (JNK) phosphorylates and activates members of the activator protein-1 (AP-1) group of transcription factors and is implicated in oncogenic transformation. To examine the role of JNK, we investigated the effect of JNK deficiency on Ras-stimulated transformation. We demonstrate that although JNK does play a role in transformation in vitro, JNK is not required for tumor development in vivo. Importantly, the loss of JNK expression resulted in substantial increases in the number and growth of tumor nodules in vivo. Complementation assays demonstrated that this phenotype was caused by JNK deficiency. These data demonstrate that, in contrast to expectations, the normal function of JNK may be to suppress tumor development in vivo. This conclusion is consistent with the presence in human tumors of loss-of-function mutations in the JNK pathway.

Journal ArticleDOI
TL;DR: This paper showed that mice lacking the Ro protein develop an autoimmune syndrome characterized by anti-ribosome antibodies, anti-chromatin antibodies, and glomerulonephritis, and showed that Ro-/- mice display increased sensitivity to irradiation with UV light.
Abstract: Antibodies against a conserved RNA-binding protein, the Ro 60-kDa autoantigen, occur in 24-60% of all patients with systemic lupus erythematosus. Anti-Ro antibodies are correlated with photosensitivity and cutaneous lesions in these patients and with neonatal lupus, a syndrome in which mothers with anti-Ro antibodies give birth to children with complete congenital heart block and photosensitive skin lesions. In higher eukaryotes, the Ro protein binds small RNAs of unknown function known as Y RNAs. Because the Ro protein also binds misfolded 5S rRNA precursors, it is proposed to function in a quality-control pathway for ribosome biogenesis. Consistent with a role in the recognition or repair of intracellular damage, an orthologue of Ro in the radiation-resistant eubacterium Deinococcus radiodurans contributes to survival of this bacterium after UV irradiation. Here, we show that mice lacking the Ro protein develop an autoimmune syndrome characterized by anti-ribosome antibodies, anti-chromatin antibodies, and glomerulonephritis. Moreover, in one strain background, Ro-/- mice display increased sensitivity to irradiation with UV light. Thus, one function of this major human autoantigen may be to protect against autoantibody development, possibly by sequestering defective ribonucleoproteins from immune surveillance. Furthermore, the finding that mice lacking the Ro protein are photosensitive suggests that loss of Ro function could contribute to the photosensitivity associated with anti-Ro antibodies in humans.

Journal ArticleDOI
TL;DR: It is found that ICOS knockout mice on the DBA/1 background were completely resistant to collagen-induced arthritis and exhibited absence of joint tissue inflammation, suggesting novel means for treating patients with rheumatoid arthritis.
Abstract: CD4+ helper Th cells play a major role in the pathogenesis of rheumatoid arthritis. Th cell activation, differentiation, and immune function are regulated by costimulatory molecules. Inducible costimulator (ICOS) is a novel costimulatory receptor expressed on activated T cells. We, as well as others, recently demonstrated its importance in Th2 cytokine expression and Ab class switching by B cells. In this study, we examined the role of ICOS in rheumatoid arthritis using a collagen-induced arthritis model. We found that ICOS knockout mice on the DBA/1 background were completely resistant to collagen-induced arthritis and exhibited absence of joint tissue inflammation. These mice, when immunized with collagen, exhibited reduced anti-collagen IgM Ab’s in the initial stage and IgG2a Ab’s at the effector phase of collagen-induced arthritis. Furthermore, ICOS regulates the in vitro and in vivo expression of IL-17, a proinflammatory cytokine implicated in rheumatoid arthritis. These data indicate that ICOS is essential for collagen-induced arthritis and may suggest novel means for treating patients with rheumatoid arthritis.

Journal ArticleDOI
TL;DR: It is proposed that Ro plays a general role in small RNA quality control and that this function is important for cell survival after ultraviolet irradiation.

Journal ArticleDOI
TL;DR: Results show that ECSit functions as an essential component in two important signal transduction pathways and establishes a novel role for Ecsit as a cofactor for Smad proteins in the Bmp signaling pathway.
Abstract: Bone morphogenetic proteins (Bmps) are members of the transforming growth factor beta (TGFbeta) superfamily that play critical roles during mouse embryogenesis. Signaling by Bmp receptors is mediated mainly by Smad proteins. In this study, we show that a targeted null mutation of Ecsit, encoding a signaling intermediate of the Toll pathway, leads to reduced cell proliferation, altered epiblast patterning, impairment of mesoderm formation, and embryonic lethality at embryonic day 7.5 (E7.5), phenotypes that mimic the Bmp receptor type1a (Bmpr1a) null mutant. In addition, specific Bmp target gene expression is abolished in the absence of Ecsit. Biochemical analysis demonstrates that Ecsit associates constitutively with Smad4 and associates with Smad1 in a Bmp-inducible manner. Together with Smad1 and Smad4, Ecsit binds to the promoter of specific Bmp target genes. Finally, knock-down of Ecsit with Ecsit-specific short hairpin RNA inhibits both Bmp and Toll signaling. Therefore, these results show that Ecsit functions as an essential component in two important signal transduction pathways and establishes a novel role for Ecsit as a cofactor for Smad proteins in the Bmp signaling pathway.