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      Induction of pathogenic Th17 cells by inducible salt sensing kinase SGK1

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          Abstract

          Th17 cells are highly proinflammatory cells critical for clearing extracellular pathogens and for induction of multiple autoimmune diseases 1 . IL-23 plays a critical role in stabilizing and reinforcing the Th17 phenotype by increasing expression of IL-23 receptor (IL-23R) and endowing Th17 cells with pathogenic effector functions 2, 3 . However, the precise molecular mechanism by which IL-23 sustains the Th17 response and induces pathogenic effector functions has not been elucidated. Here, we used transcriptional profiling of developing Th17 cells to construct a model of their signaling network and nominate major nodes that regulate Th17 development. We identified serum glucocorticoid kinase-1 (SGK1), a serine-threonine kinase 4 , as an essential node downstream of IL-23 signaling. SGK1 is critical for regulating IL-23R expression and stabilizing the Th17 cell phenotype by deactivation of Foxo1, a direct repressor of IL-23R expression. SGK1 has been shown to govern Na + transport and salt (NaCl) homeostasis in other cells 5, 6, 7, 8 . We here show that a modest increase in salt concentration induces SGK1 expression, promotes IL-23R expression and enhances Th17 cell differentiation in vitro and in vivo, accelerating the development of autoimmunity. Loss of SGK1 abrogated Na +-mediated Th17 differentiation in an IL-23-dependent manner. These data demonstrate that SGK1 plays a critical role in the induction of pathogenic Th17 cells and provides a molecular insight into a mechanism by which an environmental factor such as a high salt diet triggers Th17 development and promotes tissue inflammation.

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          Most cited references16

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          Significance analysis of time course microarray experiments.

          Characterizing the genome-wide dynamic regulation of gene expression is important and will be of much interest in the future. However, there is currently no established method for identifying differentially expressed genes in a time course study. Here we propose a significance method for analyzing time course microarray studies that can be applied to the typical types of comparisons and sampling schemes. This method is applied to two studies on humans. In one study, genes are identified that show differential expression over time in response to in vivo endotoxin administration. By using our method, 7,409 genes are called significant at a 1% false-discovery rate level, whereas several existing approaches fail to identify any genes. In another study, 417 genes are identified at a 10% false-discovery rate level that show expression changing with age in the kidney cortex. Here it is also shown that as many as 47% of the genes change with age in a manner more complex than simple exponential growth or decay. The methodology proposed here has been implemented in the freely distributed and open-source edge software package.
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            Protein kinase SGK mediates survival signals by phosphorylating the forkhead transcription factor FKHRL1 (FOXO3a).

            Serum- and glucocorticoid-inducible kinases (SGKs) form a novel family of serine/threonine kinases that are activated in response to a variety of extracellular stimuli. SGKs are related to Akt (also called PKB), a serine/threonine kinase that plays a crucial role in promoting cell survival. Like Akt, SGKs are activated by the phosphoinositide-3 kinase (PI3K) and translocate to the nucleus upon growth factor stimulation. However the physiological substrates and cellular functions of SGKs remained to be identified. We hypothesized that SGKs regulate cellular functions in concert with Akt by phosphorylating common targets within the nucleus. The best-characterized nuclear substrates of Akt are transcription factors of the Forkhead family. Akt phosphorylates Forkhead transcription factors such as FKHRL1, leading to FKHRL1's exit from the nucleus and the consequent shutoff of FKHRL1 target genes. We show here that SGK1, like Akt, promotes cell survival and that it does so in part by phosphorylating and inactivating FKHRL1. However, SGK and Akt display differences with respect to the efficacy with which they phosphorylate the three regulatory sites on FKHRL1. While both kinases can phosphorylate Thr-32, SGK displays a marked preference for Ser-315 whereas Akt favors Ser-253. These findings suggest that SGK and Akt may coordinately regulate the function of FKHRL1 by phosphorylating this transcription factor at distinct sites. The efficient phosphorylation of these three sites on FKHRL1 by SGK and Akt appears to be critical to the ability of growth factors to suppress FKHRL1-dependent transcription, thereby preventing FKHRL1 from inducing cell cycle arrest and apoptosis. These findings indicate that SGK acts in concert with Akt to propagate the effects of PI3K activation within the nucleus and to mediate the biological outputs of PI3K signaling, including cell survival and cell cycle progression.
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              The transcription of FOXO genes is stimulated by FOXO3 and repressed by growth factors.

              FOXO (Forkhead box O) transcription factors induce cell growth arrest and apoptosis, which can be prevented by FOXO phosphorylation by AKT in response to growth factors such as platelet-derived growth factors (PDGF) and insulin-like growth factor I (IGF-I). In addition to this well characterized post-translational modification, we showed that FOXO1, FOXO3, and FOXO4 were also regulated at the transcriptional level. PDGF, fibroblast growth factors (FGF), and IGF-I repressed the expression of FOXO genes in human fibroblasts. This process was sensitive to phosphatidylinositol 3-kinase inhibition by LY294002. FOXO1-specific shRNA decreased FOXO1 mRNA expression and enhanced fibroblast proliferation, mimicking the effects of growth factors. Conversely, ectopic FOXO3 activation blocked the proliferation of fibroblasts and induced the expression of FOXO1, FOXO4, and p27-KIP1. Using luciferase reporter assays and chromatin immunoprecipitations, we identified a conserved FOXO-binding site in the promoter of the FOXO1 gene, which was required for regulation by PDGF, and mediated the up-regulation of FOXO1 by itself and by FOXO3. Altogether, our results suggest that the expression of FOXO1 and FOXO4 genes is stimulated by FOXO3 and possibly by other FOXO factors in a positive feedback loop, which is disrupted by growth factors.
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                Author and article information

                Journal
                0410462
                6011
                Nature
                Nature
                Nature
                0028-0836
                1476-4687
                12 February 2013
                06 March 2013
                25 April 2013
                25 October 2013
                : 496
                : 7446
                : 513-517
                Affiliations
                [1 ]Center for Neurologic Diseases, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA 02115
                [2 ]Broad Institute of MIT and Harvard, 7 Cambridge Center, Cambridge, Massachusetts 02142
                [3 ]Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02140
                Author notes
                [# ]to whom correspondence should be addressed: aregev@ 123456broad.mit.edu (AR), vkuchroo@ 123456rics.bwh.harvard.edu (VK)
                [4]

                These authors contributed equally to this study.

                Article
                NIHMS443495
                10.1038/nature11984
                3637879
                23467085
                fcbdf225-5448-4dd4-932a-de772382a3b4

                Users may view, print, copy, download and text and data- mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use: http://www.nature.com/authors/editorial_policies/license.html#terms

                History
                Funding
                Funded by: National Institute of Neurological Disorders and Stroke : NINDS
                Award ID: R01 NS045937 || NS
                Funded by: National Human Genome Research Institute : NHGRI
                Award ID: P50 HG006193 || HG
                Funded by: National Institute of Allergy and Infectious Diseases Extramural Activities : NIAID
                Award ID: P01 AI073748 || AI
                Funded by: National Institute of Allergy and Infectious Diseases Extramural Activities : NIAID
                Award ID: P01 AI045757 || AI
                Funded by: National Cancer Institute : NCI
                Award ID: DP1 CA174427 || CA
                Funded by: Howard Hughes Medical Institute :
                Award ID: || HHMI_
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