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RIPK1 is shown to have a crucial role—independent of its known kinase function—in suppressing epithelial cell apoptosis and necroptosis in mice, thereby regulating homeostasis and preventing inflammation in barrier tissues. RIPK1 both activates and inhibits cell death Receptor-interacting protein 1 kinase (RIPK1) is involved in the activation of various cell death pathways and in the control of inflammatory signalling. Two separate groups reporting in this issue use contrasting techniques to show that as well as promoting cell death, RIPK1 has a paradoxical function in supporting the survival of mouse epithelial cells that is independent of its kinase function. RIPK1 suppresses epithelial cell apoptosis and necroptosis by preventing FADD/caspase-8-mediated apoptosis and RIPK3-dependent necroptosis. These findings, together with genetic data, suggest that RIPK1 is a master regulator of epithelial cell survival, homeostasis and inflammation in the intestine and the skin. Necroptosis has emerged as an important pathway of programmed cell death in embryonic development, tissue homeostasis, immunity and inflammation 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 . RIPK1 is implicated in inflammatory and cell death signalling 9 , 10 , 11 , 12 , 13 and its kinase activity is believed to drive RIPK3-mediated necroptosis 14 , 15 . Here we show that kinase-independent scaffolding RIPK1 functions regulate homeostasis and prevent inflammation in barrier tissues by inhibiting epithelial cell apoptosis and necroptosis. Intestinal epithelial cell (IEC)-specific RIPK1 knockout caused IEC apoptosis, villus atrophy, loss of goblet and Paneth cells and premature death in mice. This pathology developed independently of the microbiota and of MyD88 signalling but was partly rescued by TNFR1 (also known as TNFRSF1A) deficiency. Epithelial FADD ablation inhibited IEC apoptosis and prevented the premature death of mice with IEC-specific RIPK1 knockout. However, mice lacking both RIPK1 and FADD in IECs displayed RIPK3-dependent IEC necroptosis, Paneth cell loss and focal erosive inflammatory lesions in the colon. Moreover, a RIPK1 kinase inactive knock-in delayed but did not prevent inflammation caused by FADD deficiency in IECs or keratinocytes, showing that RIPK3-dependent necroptosis of FADD-deficient epithelial cells only partly requires RIPK1 kinase activity. Epidermis-specific RIPK1 knockout triggered keratinocyte apoptosis and necroptosis and caused severe skin inflammation that was prevented by RIPK3 but not FADD deficiency. These findings revealed that RIPK1 inhibits RIPK3-mediated necroptosis in keratinocytes in vivo and identified necroptosis as a more potent trigger of inflammation compared with apoptosis. Therefore, RIPK1 is a master regulator of epithelial cell survival, homeostasis and inflammation in the intestine and the skin.

The innate immune response involves a variety of inflammatory reactions that can result in inflammatory disease and cancer if they are not resolved and instead are allowed to persist. The effective activation and resolution of innate immune responses relies on the production and posttranscriptional regulation of mRNAs encoding inflammatory effector proteins. The RNA-binding protein HuR binds to and regulates such mRNAs, but its exact role in inflammation remains unclear. Here we show that HuR maintains inflammatory homeostasis by controlling macrophage plasticity and migration. Mice lacking HuR in myeloid-lineage cells, which include many of the cells of the innate immune system, displayed enhanced sensitivity to endotoxemia, rapid progression of chemical-induced colitis, and severe susceptibility to colitis-associated cancer. The myeloid cell-specific HuR-deficient mice had an exacerbated inflammatory cytokine profile and showed enhanced CCR2-mediated macrophage chemotaxis. At the molecular level, activated macrophages from these mice showed enhancements in the use of inflammatory mRNAs (including Tnf, Tgfb, Il10, Ccr2, and Ccl2) due to a lack of inhibitory effects on their inducible translation and/or stability. Conversely, myeloid overexpression of HuR induced posttranscriptional silencing, reduced inflammatory profiles, and protected mice from colitis and cancer. Our results highlight the role of HuR as a homeostatic coordinator of mRNAs that encode molecules that guide innate inflammatory effects and demonstrate the potential of harnessing the effects of HuR for clinical benefit against pathologic inflammation and cancer.

TGF[beta]-activated kinase 1 (TAK1), a member of the mitogen-activated protein kinase kinase kinase (MAP3K) family, is considered a key intermediate in a multitude of innate immune signaling pathways. Yet, the specific role of TAK1 in the myeloid compartment during inflammatory challenges has not been revealed. To address this question, we generated myeloid-specific kinase-dead TAK1 mutant mice. TAK1 deficiency in macrophages results in impaired NF-[kappa]B and JNK activation upon stimulation with lipopolysaccharide (LPS). Moreover, TAK1-deficient macrophages and neutrophils show an enhanced inflammatory cytokine profile in response to LPS stimulation. Myeloid-specific TAK1 deficiency in mice leads to increased levels of circulating IL-1[beta], TNF and reduced IL-10 after LPS challenge and sensitizes them to LPS-induced endotoxemia. These results highlight an antiinflammatory role for myeloid TAK1, which is essential for balanced innate immune responses and host survival during endotoxemia.

TGFβ-activated kinase 1 (TAK1), a member of the mitogen-activated protein kinase kinase kinase (MAP3K) family, is considered a key intermediate in a multitude of innate immune signaling pathways. Yet, the specific role of TAK1 in the myeloid compartment during inflammatory challenges has not been revealed. To address this question, we generated myeloid-specific kinase-dead TAK1 mutant mice. TAK1 deficiency in macrophages results in impaired NF-κB and JNK activation upon stimulation with lipopolysaccharide (LPS). Moreover, TAK1-deficient macrophages and neutrophils show an enhanced inflammatory cytokine profile in response to LPS stimulation. Myeloid-specific TAK1 deficiency in mice leads to increased levels of circulating IL-1β, TNF and reduced IL-10 after LPS challenge and sensitizes them to LPS-induced endotoxemia. These results highlight an antiinflammatory role for myeloid TAK1, which is essential for balanced innate immune responses and host survival during endotoxemia.

TGFβ-activated kinase 1 (TAK1), a member of the mitogen-activated protein kinase kinase kinase (MAP3K) family, is considered a key intermediate in a multitude of innate immune signaling pathways. Yet, the specific role of TAK1 in the myeloid compartment during inflammatory challenges has not been revealed. To address this question, we generated myeloid-specific kinase-dead TAK1 mutant mice. TAK1 deficiency in macrophages results in impaired NF-κB and JNK activation upon stimulation with lipopolysaccharide (LPS). Moreover, TAK1-deficient macrophages and neutrophils show an enhanced inflammatory cytokine profile in response to LPS stimulation. Myeloid-specific TAK1 deficiency in mice leads to increased levels of circulating IL-1β, TNF and reduced IL-10 after LPS challenge and sensitizes them to LPS-induced endotoxemia. These results highlight an antiinflammatory role for myeloid TAK1, which is essential for balanced innate immune responses and host survival during endotoxemia.TGFβ-activated kinase 1 (TAK1), a member of the mitogen-activated protein kinase kinase kinase (MAP3K) family, is considered a key intermediate in a multitude of innate immune signaling pathways. Yet, the specific role of TAK1 in the myeloid compartment during inflammatory challenges has not been revealed. To address this question, we generated myeloid-specific kinase-dead TAK1 mutant mice. TAK1 deficiency in macrophages results in impaired NF-κB and JNK activation upon stimulation with lipopolysaccharide (LPS). Moreover, TAK1-deficient macrophages and neutrophils show an enhanced inflammatory cytokine profile in response to LPS stimulation. Myeloid-specific TAK1 deficiency in mice leads to increased levels of circulating IL-1β, TNF and reduced IL-10 after LPS challenge and sensitizes them to LPS-induced endotoxemia. These results highlight an antiinflammatory role for myeloid TAK1, which is essential for balanced innate immune responses and host survival during endotoxemia.

The \"1\" in \"TAK1\" was replaced with an \"L.\" The correct title is: \"Myeloid TAK1 Acts as a Negative Regulator of the LPS Response and Mediates Resistance to Endotoxemia\". Eftychi C, Karagianni N, Alexiou M, Apostolaki M, Kollias G (2012) Myeloid TAK1 Acts as a Negative Regulator of the LPS Response and Mediates Resistance to Endotoxemia. PLoS ONE 7(2): e31550. doi:10.1371/journal.pone.0031550 Citation: Eftychi C, Karagianni N, Alexiou M, Apostolaki M, Kollias G (2012) Correction: Myeloid Takl Acts as a Negative Regulator of the LPS Response and Mediates Resistance to Endotoxemia.

The innate immune response involves a variety of inflammatory reactions that can result in inflammatory disease and cancer if they are not resolved and instead are allowed to persist. The effective activation and resolution of innate immune responses relies on the production and posttranscriptional regulation of mRNAs encoding inflammatory effector proteins. The RNA-binding protein HuR binds to and regulates such mRNAs, but its exact role in inflammation remains unclear. Here we show that HuR maintains inflammatory homeostasis by controlling macrophage plasticity and migration. Mice lacking HuR in myeloid-lineage cells, which include many of the cells of the innate immune system, displayed enhanced sensitivity to endotoxemia, rapid progression of chemical-induced colitis, and severe susceptibility to colitis-associated cancer. The myeloid cell-specific HuR-deficient mice had an exacerbated inflammatory cytokine profile and showed enhanced CCR2-mediated macrophage chemotaxis. At the molecular level, activated macrophages from these mice showed enhancements in the use of inflammatory mRNAs (including Tnf, Tgfb, Il10, Ccr2, and Ccl2) due to a lack of inhibitory effects on their inducible translation and/or stability. Conversely, myeloid overexpression of HuR induced posttranscriptional silencing, reduced inflammatory profiles, and protected mice from colitis and cancer. Our results highlight the role of HuR as a homeostatic coordinator of mRNAs that encode molecules that guide innate inflammatory effects and demonstrate the potential of harnessing the effects of HuR for clinical benefit against pathologic inflammation and cancer. with turnover or promoting destabilization in some of its targets, through synergies with suppressive RBPs, microRNAs, and associated factors (18-22). Overexpression of HuR in mouse macrophages blocks the translation of selective inflammatory mRNAs, suggesting that it could act as negative regulator of pathologic inflammation (19). Furthermore, developmental deletions of HuR in mice demonstrated its involvement in cellular differentiation, maturation, and migration (23-25), potentially also affecting inflammatory responses. Here we aim to clarify the role of HuR in inflammation by genetic ablation in innate immune cells and to uncover its function in macrophage control and migration that is required for the maintenance of inflammatory homeostasis and protection against cancer.

Analysis of the Type 2 Diabetes-Associated Single Nucleotide Polymorphisms in the Genes IRS1 , KCNJ11 , and PPARG2 in Type 1 Diabetes Christina Eftychi 1 , Joanna M.M. Howson 1 , Bryan J. Barratt 1 , Adrian Vella 1 , Felicity Payne 1 , Deborah J. Smyth 1 , Rebecca C.J. Twells 1 , Neil M. Walker 1 , Helen E. Rance 1 , Eva Tuomilehto-Wolf 2 , Jaakko Tuomilehto 2 3 , Dag E. Undlien 4 , Kjersti S. Rønningen 5 , Cristian Guja 6 , Constantin Ionescu-Tı̂irgovişte 6 , David A. Savage 7 and John A. Todd 1 1 Juvenile Diabetes Research Foundation/Wellcome Trust Diabetes and Inflammation Laboratory, Cambridge Institute for Medical Research, University of Cambridge, Cambridge, U.K 2 Diabetes and Genetic Epidemiology Unit, National Public Health Institute, University of Helsinki, Helsinki, Finland 3 Department of Public Health, University of Helsinki, Helsinki, Finland 4 Institute of Medical Genetics, Ulleval University Hospital, University of Oslo, Oslo, Norway 5 Laboratory of Molecular Epidemiology, Division of Epidemiology, Norwegian Institute of Public Health, Oslo, Norway 6 Clinic of Diabetes, Institute of Diabetes, Nutrition and Metabolic Diseases, Bucharest, Romania 7 Department of Medical Genetics, Queen’s University Belfast, Belfast City Hospital, Belfast, Northern Ireland Address correspondence and reprint requests to John A. Todd, JDRF/WT Diabetes and Inflammation Laboratory, Cambridge Institute for Medical Research, Wellcome Trust/MRC Building, Hills Rd., Cambridge CB2 2XY, U.K. E-mail: john.todd{at}cimr.cam.ac.uk Abstract It has been proposed that type 1 and 2 diabetes might share common pathophysiological pathways and, to some extent, genetic background. However, to date there has been no convincing data to establish a molecular genetic link between them. We have genotyped three single nucleotide polymorphisms associated with type 2 diabetes in a large type 1 diabetic family collection of European descent: Gly972Arg in the insulin receptor substrate 1 (IRS1) gene, Glu23Lys in the potassium inwardly-rectifying channel gene ( KCNJ11 ), and Pro12Ala in the peroxisome proliferative-activated receptor γ2 gene ( PPARG2 ). We were unable to confirm a recently published association of the IRS1 Gly972Arg variant with type 1 diabetes. Moreover, KCNJ11 Glu23Lys showed no association with type 1 diabetes ( P > 0.05). However, the PPARG2 Pro12Ala variant showed evidence of association (RR 1.15, 95% CI 1.04–1.28, P = 0.008). Additional studies need to be conducted to confirm this result. ICAM1, intercellular adhesion molecule 1 IRS1, insulin receptor substrate 1 KCNJ11, potassium inwardly rectifying channel gene PPARγ, peroxisome proliferator-activated receptor γ PPARG2, peroxisome proliferator-activated receptor γ2 gene SNP, single nucleotide polymorphism TDT, transmission/disequilibrium test Footnotes Accepted October 31, 2003. Received October 3, 2003. DIABETES