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      S1P Lyase Regulation of Thymic Egress and Oncogenic Inflammatory Signaling

      review-article
      1 , 2 , 2 , 2 ,
      Mediators of Inflammation
      Hindawi

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          Abstract

          Sphingosine-1-phosphate (S1P) is a potent lipid signaling molecule that regulates pleiotropic biological functions including cell migration, survival, angiogenesis, immune cell trafficking, inflammation, and carcinogenesis. It acts as a ligand for a family of cell surface receptors. S1P concentrations are high in blood and lymph but low in tissues, especially the thymus and lymphoid organs. S1P chemotactic gradients are essential for lymphocyte egress and other aspects of physiological cell trafficking. S1P is irreversibly degraded by S1P lyase (SPL). SPL regulates lymphocyte trafficking, inflammation and other physiological and pathological processes. For example, SPL located in thymic dendritic cells acts as a metabolic gatekeeper that controls the normal egress of mature T lymphocytes from the thymus into the circulation, whereas SPL deficiency in gut epithelial cells promotes colitis and colitis-associated carcinogenesis (CAC). Recently, we identified a complex syndrome comprised of nephrosis, adrenal insufficiency, and immunological defects caused by inherited mutations in human SGPL1, the gene encoding SPL. In the present article, we review current evidence supporting the role of SPL in thymic egress, inflammation, and cancer. Lastly, we summarize recent progress in understanding other SPL functions, its role in inherited disease, and SPL targeting for therapeutic purposes.

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          Most cited references137

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          Lymphocyte egress from thymus and peripheral lymphoid organs is dependent on S1P receptor 1.

          Adaptive immunity depends on T-cell exit from the thymus and T and B cells travelling between secondary lymphoid organs to survey for antigens. After activation in lymphoid organs, T cells must again return to circulation to reach sites of infection; however, the mechanisms regulating lymphoid organ exit are unknown. An immunosuppressant drug, FTY720, inhibits lymphocyte emigration from lymphoid organs, and phosphorylated FTY720 binds and activates four of the five known sphingosine-1-phosphate (S1P) receptors. However, the role of S1P receptors in normal immune cell trafficking is unclear. Here we show that in mice whose haematopoietic cells lack a single S1P receptor (S1P1; also known as Edg1) there are no T cells in the periphery because mature T cells are unable to exit the thymus. Although B cells are present in peripheral lymphoid organs, they are severely deficient in blood and lymph. Adoptive cell transfer experiments establish an intrinsic requirement for S1P1 in T and B cells for lymphoid organ egress. Furthermore, S1P1-dependent chemotactic responsiveness is strongly upregulated in T-cell development before exit from the thymus, whereas S1P1 is downregulated during peripheral lymphocyte activation, and this is associated with retention in lymphoid organs. We find that FTY720 treatment downregulates S1P1, creating a temporary pharmacological S1P1-null state in lymphocytes, providing an explanation for the mechanism of FTY720-induced lymphocyte sequestration. These findings establish that S1P1 is essential for lymphocyte recirculation and that it regulates egress from both thymus and peripheral lymphoid organs.
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            Sphingosine-1-phosphate: an enigmatic signalling lipid.

            The evolutionarily conserved actions of the sphingolipid metabolite, sphingosine-1-phosphate (S1P), in yeast, plants and mammals have shown that it has important functions. In higher eukaryotes, S1P is the ligand for a family of five G-protein-coupled receptors. These S1P receptors are differentially expressed, coupled to various G proteins, and regulate angiogenesis, vascular maturation, cardiac development and immunity, and are important for directed cell movement.
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              Endocytosis and signalling: intertwining molecular networks.

              Cell signalling and endocytic membrane trafficking have traditionally been viewed as distinct processes. Although our present understanding is incomplete and there are still great controversies, it is now recognized that these processes are intimately and bidirectionally linked in animal cells. Indeed, many recent examples illustrate how endocytosis regulates receptor signalling (including signalling from receptor tyrosine kinases and G protein-coupled receptors) and, conversely, how signalling regulates the endocytic pathway. The mechanistic and functional principles that underlie the relationship between signalling and endocytosis in cell biology are becoming increasingly evident across many systems.
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                Author and article information

                Contributors
                Journal
                Mediators Inflamm
                Mediators Inflamm
                MI
                Mediators of Inflammation
                Hindawi
                0962-9351
                1466-1861
                2017
                3 December 2017
                : 2017
                : 7685142
                Affiliations
                1Department of Biochemistry, All India Institute of Medical Sciences (AIIMS) Bhopal, Madhya Pradesh 462020, India
                2Children's Hospital Oakland Research Institute and UCSF Benioff Children's Hospital Oakland, 5700 Martin Luther King Jr. Way, Oakland, CA 94609, USA
                Author notes

                Academic Editor: Alice Alessenko

                Author information
                http://orcid.org/0000-0002-4894-919X
                Article
                10.1155/2017/7685142
                5733215
                a9051802-a51d-4fe9-810f-cf94ce7b7ccf
                Copyright © 2017 Ashok Kumar et al.

                This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 12 May 2017
                : 13 September 2017
                Funding
                Funded by: National Institutes of Health
                Award ID: CA129438
                Funded by: Swim Across America Foundation
                Funded by: Madhya Pradesh Council of Science & Technology
                Award ID: A/RD/RP-2/2015-16/50
                Funded by: Science and Engineering Research Board
                Award ID: SB/YS/LS-184/2013
                Categories
                Review Article

                Immunology
                Immunology

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