42 results on '"Alexandropoulos K"'
Search Results
2. Medullary thymic epithelial cell depletion by conditional deletion of TRAF6 leads to the development of autoimmune hepatitis: W45.005
- Author
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Alexandropoulos, K., Bonito, A. J., and Aloman, C.
- Published
- 2012
3. Erratum: HEF1 is a necessary and specific downstream effector of FAK that promotes the migration of glioblastoma cells
- Author
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Natarajan, M, Stewart, Jr, J E, Golemis, E A, Pugacheva, E N, Alexandropoulos, K, Cox, B D, Wang, W, Grammer, J R, and Gladson, C L
- Published
- 2007
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4. HEF1 is a necessary and specific downstream effector of FAK that promotes the migration of glioblastoma cells
- Author
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Natarajan, M, primary, Stewart, J E, additional, Golemis, E A, additional, Pugacheva, E N, additional, Alexandropoulos, K, additional, Cox, B D, additional, Wang, W, additional, Grammer, J R, additional, and Gladson, C L, additional
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- 2005
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5. Coordinate activation of c-Src by SH3- and SH2-binding sites on a novel p130Cas-related protein, Sin.
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Alexandropoulos, K, primary and Baltimore, D, additional
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- 1996
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6. Proline-rich sequences that bind to Src homology 3 domains with individual specificities.
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Alexandropoulos, K, primary, Cheng, G, additional, and Baltimore, D, additional
- Published
- 1995
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7. Evidence that v-Src-induced phospholipase D activity is mediated by a G protein
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Jiang, H, primary, Alexandropoulos, K, additional, Song, J, additional, and Foster, D A, additional
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- 1994
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8. Evidence that Ha-Ras mediates two distinguishable intracellular signals activated by v-Src.
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Qureshi, S.A., primary, Alexandropoulos, K, additional, Rim, M, additional, Joseph, C.K., additional, Bruder, J.T., additional, Rapp, U.R., additional, and Foster, D.A., additional
- Published
- 1992
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9. Evidence that a G-protein transduces signals initiated by the protein-tyrosine kinase v-Fps
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Alexandropoulos, K., primary, Joseph, C.K., additional, Spangler, R., additional, and Foster, D.A., additional
- Published
- 1991
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10. Cholera toxin induces expression of the immediate-early response gene JE via a cyclic AMP-independent signaling pathway.
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Qureshi, S A, primary, Alexandropoulos, K, additional, Joseph, C K, additional, Spangler, R, additional, and Foster, D A, additional
- Published
- 1991
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11. Influence of element modeling on the predicted seismic performance of an existing RC building
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Dimitrios Vamvatsikos, Alexandropoulos, K., Giannitsas, P., and Zeris, C.
12. Switching antipsychotic treatment in patients with bipolar disorder: reasons and outcome
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Zoumadaki Aikaterini, Vlachveis Georgios, Vartzopoulos Dimitrios, Takant Amir, Stribakos Dimitrios, Stamatakis Nikolaos, Spyropoulos Ioannis, Spinaris Vasileios, Siotis Christos, Marinos Vasileios, Kafalis Georgios, Giouzepas Ioannis, Gevrekis Georgios, Fryssas Georgios, Bargiotas Efthimios, Mougiakos Theodoros, Alexandropoulos Konstantinos, Boubouridis Konstantinos, Charisiadi Marina, Kontou Fotini, Morogiannis Fotios, Vainas Christos, Katsikas Emmanouil, and Grigoriou Panagiotis
- Subjects
Psychiatry ,RC435-571 - Published
- 2006
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13. HEF1 is a necessary and specific downstream effector of FAK that promotes the migration of glioblastoma cells.
- Author
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Natarajan, M, Stewart, J E, Golemis, E A, Pugacheva, E N, Alexandropoulos, K, Cox, B D, Wang, W, Grammer, J R, and Gladson, C L
- Subjects
CELL migration - Abstract
A correction to the article "HEF1 is a necessary and specific downstream effector of FAK that promotes the migration of glioblastoma cells" that was published in the previous issue is presented.
- Published
- 2007
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14. Paraneoplastic hypoglycemia: An overview for optimal clinical guidance.
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Karamanolis NN, Kounatidis D, Vallianou NG, Alexandropoulos K, Kovlakidi E, Kaparou P, Karampela I, Stratigou T, and Dalamaga M
- Abstract
Paraneoplastic hypoglycemia, also known as non-islet cell tumor hypoglycemia (NICTH), is a rare but critical condition occurring in patients with different types of malignancy. This condition is commonly linked to tumors producing insulin-like growth (IGF) factors, particularly IGF-2 and its precursors, which disrupt glucose homeostasis and lead to excessive glucose consumption. The diagnosis typically involves documenting symptomatic hypoglycemia and ruling out other potential causes. Essential diagnostic tools include imaging studies and laboratory tests, specifically measuring IGF-2 levels and the IGF-2:IGF-1 ratio. Treatment strategies for NICTH are multifaceted and may include surgical resection of the tumor if feasible, pharmacological interventions such as corticosteroids to suppress IGF-2 production, or supportive measures to manage acute hypoglycemic episodes. Novel therapeutic approaches targeting IGF-2, such as monoclonal antibodies or siRNA, are also being explored and hold promise for future treatment options. This review aims to enhance understanding of paraneoplastic hypoglycemia, focusing on its pathogenesis and diagnosis, to guide optimal medical treatment., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors. Published by Elsevier Inc.)
- Published
- 2024
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15. Profiling of mouse and human liver diseases identifies targets for therapeutic treatment of autoimmune hepatitis.
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Centa M, Thermidor C, Fiel MI, and Alexandropoulos K
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- Humans, Inflammation, Hepatitis, Autoimmune drug therapy, Non-alcoholic Fatty Liver Disease, Cholangitis, Sclerosing, Liver Diseases, Autoimmune Diseases
- Abstract
Autoimmune hepatitis (AIH), primary sclerosing cholangitis (PSC), and non-alcoholic steatohepatitis (NASH) are chronic liver diseases (CLDs) of distinct etiologies that represent a public health risk with limited therapeutic options. A common feature among CLDs is an aggressive T cell response resulting in destruction of liver tissue and fibrosis. Here, we assessed the presence and nature of T cell inflammation in late-stage human AIH, PSC and NASH and examined whether targeting the T cell response can improve disease pathology in a mouse model (Traf6ΔTEC) of spontaneous AIH. T cell infiltration and ensuing inflammatory pathways were present in human AIH and PSC and to a lesser extent in NASH. However, we observed qualitative differences in infiltrating T cell subsets and upregulation of inflammatory pathways among these diseases, while mouse and human AIH exhibited similar immunogenic signatures. While gene expression profiles differed among diseases, we identified 52 genes commonly upregulated across all diseases that included the JAK3 tyrosine kinase. Therapeutic targeting of chronic AIH with the JAK inhibitor tofacitinib reduced hepatic T cell infiltration, AIH histopathology and associated immune parameters in treated Traf6ΔTEC mice. Our results indicate that targeting T cell responses in established hepatic autoimmune inflammation is a feasible strategy for developing novel therapeutic approaches to treat AIH and possibly other CLDs irrespective of etiology., Competing Interests: Declaration of Competing Interest: The authors have declared that no conflict of interest exists., (Copyright © 2023. Published by Elsevier Inc.)
- Published
- 2023
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16. Impaired central tolerance induces changes in the gut microbiota that exacerbate autoimmune hepatitis.
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Centa M, Weinstein EG, Clemente JC, Faith JJ, Fiel MI, Lyallpuri R, Herbin O, and Alexandropoulos K
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- Animals, Central Tolerance, Mice, Mice, Inbred C57BL, T-Lymphocytes, Regulatory, Thymus Gland, Gastrointestinal Microbiome, Hepatitis, Autoimmune
- Abstract
Medullary thymic epithelial cells (mTECs) induce T cell tolerance in the thymus through the elimination of self-reactive thymocytes. Commensal bacteria are also critical for shaping T cell responses in the gut and distal organs. We previously showed that mice depleted of mTECs (Traf6ΔTEC) generated autoreactive T cells and developed autoimmune hepatitis (AIH). In this report, we found that Toll-like receptor (TLR)-mediated microbial sensing on liver hematopoietic cells and the gut microbiota contributed to AIH development in Traf6ΔTEC mice. While adoptive transfer of thymic Traf6ΔTEC T cells in immune-deficient mice was sufficient for AIH development, colonization of germ-free mice with Traf6ΔTEC microbiota failed to induce AIH, suggesting that the gut microbiota contributes to but is not sufficient for AIH development. Microbiota-mediated exacerbation of AIH associated with increased numbers of hepatic Foxp3
+ T cells and their increase was proportional to the degree of inflammation. The contribution of the gut microbiota to AIH development associated with an altered microbial signature whose composition was influenced by the qualitative nature of the thymic T cell compartment. These results suggest that aberrant selection of T cells in the thymus can induce changes in the gut microbiota that lead to exacerbation of organ-specific autoimmunity and AIH. Our results add to our understanding of the mechanisms of AIH development and create a platform towards developing novel therapeutic approaches for treating this disease., (Copyright © 2022 Elsevier Ltd. All rights reserved.)- Published
- 2022
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17. Immunology of COVID-19: Current State of the Science.
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Vabret N, Britton GJ, Gruber C, Hegde S, Kim J, Kuksin M, Levantovsky R, Malle L, Moreira A, Park MD, Pia L, Risson E, Saffern M, Salomé B, Esai Selvan M, Spindler MP, Tan J, van der Heide V, Gregory JK, Alexandropoulos K, Bhardwaj N, Brown BD, Greenbaum B, Gümüş ZH, Homann D, Horowitz A, Kamphorst AO, Curotto de Lafaille MA, Mehandru S, Merad M, and Samstein RM
- Subjects
- Animals, COVID-19, Coronavirus Infections diagnosis, Coronavirus Infections pathology, Coronavirus Infections therapy, Disease Susceptibility, Humans, Immunity, Innate, Immunologic Memory, Inflammation immunology, Inflammation virology, Lymphocytes immunology, Myeloid Cells immunology, Pandemics, Pneumonia, Viral diagnosis, Pneumonia, Viral pathology, Pneumonia, Viral therapy, SARS-CoV-2, Betacoronavirus physiology, Coronavirus Infections immunology, Pneumonia, Viral immunology
- Abstract
The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has affected millions of people worldwide, igniting an unprecedented effort from the scientific community to understand the biological underpinning of COVID19 pathophysiology. In this Review, we summarize the current state of knowledge of innate and adaptive immune responses elicited by SARS-CoV-2 infection and the immunological pathways that likely contribute to disease severity and death. We also discuss the rationale and clinical outcome of current therapeutic strategies as well as prospective clinical trials to prevent or treat SARS-CoV-2 infection., Competing Interests: Declaration of Interests N.B. serves as an advisor/board member for Neon, Checkpoint Sciences, Primevax, Novartis, Array BioPharma, Roche, Avidea, Boeringer Ingelheim, Rome Therapeutics, Roswell Park, and the Parker Institute for Cancer Immunotherapy. N.B. receives research support from the Parker Insitute, Novocure, Celldex, Genentech, Oncovir, and Regeneron. M.M. serves as an advisor/board member for Celsius, Pionyr, Compugen, Myeloids and Innate pharma and ad hoc for Takeda. M.M. receives research support from Regeneron, Takeda, and Genentech. A.M. has equity in Gilead Sciences and Regeneron Pharmaceuticals., (Copyright © 2020 Elsevier Inc. All rights reserved.)
- Published
- 2020
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18. Medullary thymic epithelial cells and CD8α + dendritic cells coordinately regulate central tolerance but CD8α + cells are dispensable for thymic regulatory T cell production.
- Author
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Herbin O, Bonito AJ, Jeong S, Weinstein EG, Rahman AH, Xiong H, Merad M, and Alexandropoulos K
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- Animals, Antigen-Presenting Cells immunology, Antigen-Presenting Cells metabolism, Autoimmunity immunology, CD8 Antigens metabolism, Dendritic Cells metabolism, Epithelial Cells metabolism, Flow Cytometry, Immune Tolerance immunology, Lymphocyte Depletion, Mice, Inbred C57BL, Mice, Knockout, Mice, Transgenic, Models, Immunological, Receptors, Immunologic deficiency, Receptors, Immunologic genetics, Receptors, Immunologic immunology, T-Lymphocytes, Regulatory metabolism, Thymus Gland cytology, Thymus Gland immunology, Thymus Gland metabolism, CD8 Antigens immunology, Central Tolerance immunology, Dendritic Cells immunology, Epithelial Cells immunology, T-Lymphocytes, Regulatory immunology
- Abstract
In the thymus, antigen presenting cells (APCs) namely, medullary thymic epithelial cells (mTECs) and thymic dendritic cells (tDCs) regulate T cell tolerance through elimination of autoreactive T cells and production of thymic T regulatory (tTreg) cells. How the different APCs in the thymus share the burden of tolerazing the emerging T cell repertoire remains unclear. For example, while mutations that inhibit mTEC development or function associate with peripheral autoimmunity, the role of tDCs in organ-specific autoimmunity and tTreg cell production remains controversial. In this report we used mice depleted of mTECs and/or CD8α
+ DCs, to examine the contributions of these cell populations in thymic tolerance. We found that while mice depleted of CD8α+ DCs or mTECs were normal or developed liver inflammation respectively, combined depletion of mTECs and CD8α+ DCs resulted in overt peripheral autoimmunity. The autoimmune manifestations in mice depleted of both mTECs and CD8α+ cDCs associated with increased percentages of CD4+ and CD8+ T cells in the thymus. In contrast, while mTEC depletion resulted in reduced percentages of tTreg cells, no additional effect was observed when CD8α+ DCs were also depleted. These results reveal that: 1) mTECs and CD8α+ DCs cooperatively safeguard against peripheral autoimmunity through thymic T cell deletion; 2) CD8α+ DCs are dispensable for tTreg cell production, whereas mTECs play a non-redundant role in this process; 3) mTECs and CD8α+ DCs make unique contributions to tolerance induction that cannot be compensated for by other thymic APCs such as migratory SIRPα+ or plasmacytoid DCs., (Copyright © 2016 Elsevier Ltd. All rights reserved.)- Published
- 2016
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19. Actin polymerization-dependent activation of Cas-L promotes immunological synapse stability.
- Author
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Santos LC, Blair DA, Kumari S, Cammer M, Iskratsch T, Herbin O, Alexandropoulos K, Dustin ML, and Sheetz MP
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- Animals, Calcium metabolism, Cell Adhesion, Crk-Associated Substrate Protein deficiency, Integrins metabolism, Lymphocyte Activation immunology, Mice, Inbred C57BL, Models, Immunological, Phosphorylation, Protein Transport, Receptors, Antigen, T-Cell metabolism, T-Lymphocytes metabolism, Actins metabolism, Crk-Associated Substrate Protein metabolism, Immunological Synapses metabolism, Polymerization
- Abstract
The immunological synapse formed between a T-cell and an antigen-presenting cell is important for cell-cell communication during T-cell-mediated immune responses. Immunological synapse formation begins with stimulation of the T-cell receptor (TCR). TCR microclusters are assembled and transported to the center of the immunological synapse in an actin polymerization-dependent process. However, the physical link between TCR and actin remains elusive. Here we show that lymphocyte-specific Crk-associated substrate (Cas-L), a member of a force sensing protein family, is required for transport of TCR microclusters and for establishing synapse stability. We found that Cas-L is phosphorylated at TCR microclusters in an actin polymerization-dependent fashion. Furthermore, Cas-L participates in a positive feedback loop leading to amplification of Ca
2+ signaling, inside-out integrin activation, and actomyosin contraction. We propose a new role for Cas-L in T-cell activation as a mechanical transducer linking TCR microclusters to the underlying actin network and coordinating multiple actin-dependent structures in the immunological synapse. Our studies highlight the importance of mechanotransduction processes in T-cell-mediated immune responses., Competing Interests: The authors declare no conflict of interest.- Published
- 2016
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20. Monocyte Adhesion and Plaque Recruitment During Atherosclerosis Development Is Regulated by the Adapter Protein Chat-H/SHEP1.
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Herbin O, Regelmann AG, Ramkhelawon B, Weinstein EG, Moore KJ, and Alexandropoulos K
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- Adaptor Proteins, Signal Transducing deficiency, Adaptor Proteins, Signal Transducing genetics, Animals, Antigens, Ly metabolism, Atherosclerosis genetics, Atherosclerosis pathology, Atherosclerosis prevention & control, Bone Marrow Transplantation, Cells, Cultured, Disease Models, Animal, Genotype, Macrophages metabolism, Macrophages pathology, Male, Mice, Inbred C57BL, Mice, Knockout, Monocytes pathology, Neutrophils metabolism, Neutrophils pathology, Phenotype, Receptors, LDL deficiency, Receptors, LDL genetics, Signal Transduction, Vascular Cell Adhesion Molecule-1 metabolism, Adaptor Proteins, Signal Transducing metabolism, Atherosclerosis metabolism, Cell Adhesion, Chemotaxis, Leukocyte, Monocytes metabolism, Plaque, Atherosclerotic
- Abstract
Objective: The chronic inflammation associated with atherosclerosis is caused by lipid deposition followed by leukocyte recruitment to the arterial wall. We previously showed that the hematopoietic cell-specific adaptor protein Cas- and Hef1-associated signal transducer hematopoietic isoform (Chat-H)/SHEP1 regulated lymphocyte adhesion and migration. In this study, we analyzed the role of Chat-H in atherosclerosis development., Approach and Results: Using Chat-H-deficient bone marrow transplantation in low-density lipoprotein receptor-deficient mice, we found that Chat-H regulated atherosclerotic plaque formation. Chat-H deficiency in hematopoietic cells associated with lower plaque complexity and fewer leukocytes in the lesions, whereas myeloid-specific deletion of Chat-H was sufficient for conferring atheroprotection. Chat-H deficiency resulted in reduced recruitment of classical Ly6c(high) and nonclassical Ly6c(low) monocytes to the plaques, which was accompanied by increased numbers of both monocyte subsets in the blood. This associated with defective adhesion of Chat-H-deficient Ly6c(high) and Ly6c(low) monocytes to vascular cell adhesion molecule-1 in vitro and impaired infiltration of fluorescent bead-loaded monocytes to atherosclerotic plaques. In contrast, Chat-H was dispensable for CX3CL1 and CCR1/CCR5-dependent migration of monocytes., Conclusions: Our findings highlight Chat-H as a key protein that regulates atherosclerosis development by controlling monocyte adhesion and recruitment to the plaques and identify a novel target that may be exploited for treating atherosclerosis., Competing Interests: Disclosure. The authors have no conflicting financial interests to disclose., (© 2016 American Heart Association, Inc.)
- Published
- 2016
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21. Microbiota regulate the ability of lung dendritic cells to induce IgA class-switch recombination and generate protective gastrointestinal immune responses.
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Ruane D, Chorny A, Lee H, Faith J, Pandey G, Shan M, Simchoni N, Rahman A, Garg A, Weinstein EG, Oropallo M, Gaylord M, Ungaro R, Cunningham-Rundles C, Alexandropoulos K, Mucida D, Merad M, Cerutti A, and Mehandru S
- Subjects
- Adaptor Proteins, Vesicular Transport genetics, Adaptor Proteins, Vesicular Transport metabolism, Animals, Antigens, CD metabolism, B-Cell Activating Factor genetics, B-Cell Activating Factor metabolism, B-Lymphocytes drug effects, B-Lymphocytes immunology, B-Lymphocytes metabolism, CD24 Antigen metabolism, Cell Movement genetics, Dendritic Cells metabolism, Gastrointestinal Tract metabolism, Gene Expression, Immunoglobulin Class Switching drug effects, Integrin alpha Chains metabolism, Integrins genetics, Integrins metabolism, Macrophages, Alveolar immunology, Macrophages, Alveolar metabolism, Mice, Myeloid Differentiation Factor 88 genetics, Myeloid Differentiation Factor 88 metabolism, Receptors, CCR genetics, Receptors, CCR metabolism, Transforming Growth Factor beta pharmacology, Tretinoin pharmacology, Tumor Necrosis Factor Ligand Superfamily Member 13 genetics, Tumor Necrosis Factor Ligand Superfamily Member 13 metabolism, Dendritic Cells immunology, Gastrointestinal Tract immunology, Gastrointestinal Tract microbiology, Immunoglobulin A genetics, Immunoglobulin A immunology, Immunoglobulin Class Switching genetics, Lung immunology, Microbiota
- Abstract
Protective immunoglobulin A (IgA) responses to oral antigens are usually orchestrated by gut dendritic cells (DCs). Here, we show that lung CD103(+) and CD24(+)CD11b(+) DCs induced IgA class-switch recombination (CSR) by activating B cells through T cell-dependent or -independent pathways. Compared with lung DCs (LDC), lung CD64(+) macrophages had decreased expression of B cell activation genes and induced significantly less IgA production. Microbial stimuli, acting through Toll-like receptors, induced transforming growth factor-β (TGF-β) production by LDCs and exerted a profound influence on LDC-mediated IgA CSR. After intranasal immunization with inactive cholera toxin (CT), LDCs stimulated retinoic acid-dependent up-regulation of α4β7 and CCR9 gut-homing receptors on local IgA-expressing B cells. Migration of these B cells to the gut resulted in IgA-mediated protection against an oral challenge with active CT. However, in germ-free mice, the levels of LDC-induced, CT-specific IgA in the gut are significantly reduced. Herein, we demonstrate an unexpected role of the microbiota in modulating the protective efficacy of intranasal vaccination through their effect on the IgA class-switching function of LDCs., (© 2016 Ruane et al.)
- Published
- 2016
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22. Nuclear export inhibitors avert progression in preclinical models of inflammatory demyelination.
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Haines JD, Herbin O, de la Hera B, Vidaurre OG, Moy GA, Sun Q, Fung HY, Albrecht S, Alexandropoulos K, McCauley D, Chook YM, Kuhlmann T, Kidd GJ, Shacham S, and Casaccia P
- Subjects
- Acrylamides administration & dosage, Acrylamides pharmacokinetics, Acrylamides pharmacology, Active Transport, Cell Nucleus drug effects, Animals, Cell Nucleus metabolism, Cells, Cultured, Disease Models, Animal, Disease Progression, Drug Evaluation, Preclinical, Female, Karyopherins antagonists & inhibitors, Karyopherins genetics, Male, Mice, Mice, Inbred C57BL, Mice, Knockout, Neuroprotective Agents administration & dosage, Neuroprotective Agents pharmacokinetics, Proteomics, Rats, Rats, Sprague-Dawley, Receptors, Cytoplasmic and Nuclear antagonists & inhibitors, Receptors, Cytoplasmic and Nuclear genetics, Thiazoles administration & dosage, Thiazoles pharmacokinetics, Thiazoles pharmacology, Treatment Outcome, Exportin 1 Protein, Axons drug effects, Axons metabolism, Axons pathology, Encephalomyelitis, Autoimmune, Experimental drug therapy, Karyopherins metabolism, Neuroprotective Agents pharmacology, Receptors, Cytoplasmic and Nuclear metabolism
- Abstract
Axonal damage has been associated with aberrant protein trafficking. We examined a newly characterized class of compounds that target nucleo-cytoplasmic shuttling by binding to the catalytic groove of the nuclear export protein XPO1 (also known as CRM1, chromosome region maintenance protein 1). Oral administration of reversible CRM1 inhibitors in preclinical murine models of demyelination significantly attenuated disease progression, even when started after the onset of paralysis. Clinical efficacy was associated with decreased proliferation of immune cells, characterized by nuclear accumulation of cell cycle inhibitors, and preservation of cytoskeletal integrity even in demyelinated axons. Neuroprotection was not limited to models of demyelination, but was also observed in another mouse model of axonal damage (that is, kainic acid injection) and detected in cultured neurons after knockdown of Xpo1, the gene encoding CRM1. A proteomic screen for target molecules revealed that CRM1 inhibitors in neurons prevented nuclear export of molecules associated with axonal damage while retaining transcription factors modulating neuroprotection.
- Published
- 2015
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23. Medullary thymic epithelial cells and central tolerance in autoimmune hepatitis development: novel perspective from a new mouse model.
- Author
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Alexandropoulos K, Bonito AJ, Weinstein EG, and Herbin O
- Subjects
- Animals, Mice, T-Lymphocytes, Regulatory immunology, Central Tolerance immunology, Disease Models, Animal, Epithelial Cells pathology, Hepatitis, Autoimmune immunology, Thymus Gland pathology
- Abstract
Autoimmune hepatitis (AIH) is an immune-mediated disorder that affects the liver parenchyma. Diagnosis usually occurs at the later stages of the disease, complicating efforts towards understanding the causes of disease development. While animal models are useful for studying the etiology of autoimmune disorders, most of the existing animal models of AIH do not recapitulate the chronic course of the human condition. In addition, approaches to mimic AIH-associated liver inflammation have instead led to liver tolerance, consistent with the high tolerogenic capacity of the liver. Recently, we described a new mouse model that exhibited spontaneous and chronic liver inflammation that recapitulated the known histopathological and immunological parameters of AIH. The approach involved liver-extrinsic genetic engineering that interfered with the induction of T-cell tolerance in the thymus, the very process thought to inhibit AIH induction by liver-specific expression of exogenous antigens. The mutation led to depletion of specialized thymic epithelial cells that present self-antigens and eliminate autoreactive T-cells before they exit the thymus. Based on our findings, which are summarized below, we believe that this mouse model represents a relevant experimental tool towards elucidating the cellular and molecular aspects of AIH development and developing novel therapeutic strategies for treating this disease.
- Published
- 2015
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24. Cas adaptor proteins organize the retinal ganglion cell layer downstream of integrin signaling.
- Author
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Riccomagno MM, Sun LO, Brady CM, Alexandropoulos K, Seo S, Kurokawa M, and Kolodkin AL
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- Animals, Mice, Mice, Transgenic, Neurons metabolism, Crk-Associated Substrate Protein metabolism, Integrin beta1 metabolism, Laminin metabolism, Retina metabolism, Retinal Ganglion Cells metabolism, Signal Transduction physiology
- Abstract
Stratification of retinal neuronal cell bodies and lamination of their processes provide a scaffold upon which neural circuits can be built. However, the molecular mechanisms that direct retinal ganglion cells (RGCs) to resolve into a single-cell retinal ganglion cell layer (GCL) are not well understood. The extracellular matrix protein laminin conveys spatial information that instructs the migration, process outgrowth, and reorganization of GCL cells. Here, we show that the β1-Integrin laminin receptor is required for RGC positioning and reorganization into a single-cell GCL layer. β1-Integrin signaling within migrating GCL cells requires Cas signaling-adaptor proteins, and in the absence of β1-Integrin or Cas function retinal neurons form ectopic cell clusters beyond the inner-limiting membrane (ILM), phenocopying laminin mutants. These data reveal an essential role for Cas adaptor proteins in β1-Integrin-mediated signaling events critical for the formation of the single-cell GCL in the mammalian retina., (Copyright © 2014 Elsevier Inc. All rights reserved.)
- Published
- 2014
- Full Text
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25. Identification of novel thymic epithelial cell subsets whose differentiation is regulated by RANKL and Traf6.
- Author
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Danzl NM, Jeong S, Choi Y, and Alexandropoulos K
- Subjects
- Aging physiology, Animals, Animals, Newborn, Antigens, Neoplasm metabolism, Biomarkers metabolism, Cell Adhesion Molecules metabolism, Cell Proliferation, Epithelial Cell Adhesion Molecule, Gene Deletion, Mice, Mice, Inbred C57BL, Mice, Transgenic, Models, Biological, T-Lymphocytes cytology, T-Lymphocytes metabolism, Time Factors, Transcription Factors metabolism, AIRE Protein, Cell Differentiation, Epithelial Cells cytology, Epithelial Cells metabolism, RANK Ligand metabolism, TNF Receptor-Associated Factor 6 metabolism, Thymus Gland cytology
- Abstract
Thymic epithelial cells (TECs) are critical for the normal development and function of the thymus. Here, we examined the developmental stages of TECs using quantitative assessment of the cortical and medullary markers Keratin 5 and Keratin 8 (K5 and K8) respectively, in normal and gain/loss of function mutant animals. Gain of function mice overexpressed RANKL in T cells, whereas loss of function animals lacked expression of Traf6 in TECs (Traf6ΔTEC). Assessment of K5 and K8 expression in conjunction with other TEC markers in wild type mice identified novel cortical and medullary TEC populations, expressing different combinations of these markers. RANKL overexpression led to expansion of all medullary TECs (mTECs) and enlargement of the thymic medulla. This in turn associated with a block in thymocyte development and loss of CD4+ CD8+, CD4+ and CD8+ thymocytes. In contrast, Traf6 deletion inhibited the production of most TEC populations including cortical TECs (cTECs), defined by absence of UEA-1 binding and LY51 expression, but had no apparent effect on thymocyte development. These results reveal a large degree of heterogeneity within the TEC compartment and the existence of several populations exhibiting concomitant expression of cortical, medullary and epithelial markers and whose production is regulated by RANKL and Traf6.
- Published
- 2014
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26. Medullary thymic epithelial cell depletion leads to autoimmune hepatitis.
- Author
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Bonito AJ, Aloman C, Fiel MI, Danzl NM, Cha S, Weinstein EG, Jeong S, Choi Y, Walsh MC, and Alexandropoulos K
- Subjects
- Adoptive Transfer, Animals, Antibodies, Antinuclear metabolism, Disease Models, Animal, Epithelial Cells immunology, Hepatitis, Autoimmune immunology, Humans, Immune Tolerance, Liver immunology, Liver metabolism, Liver pathology, Mice, Mice, Inbred C57BL, Mice, Transgenic, Plasma Cells pathology, T-Lymphocytes immunology, T-Lymphocytes transplantation, T-Lymphocytes, Regulatory immunology, TNF Receptor-Associated Factor 6 deficiency, TNF Receptor-Associated Factor 6 genetics, Thymus Gland immunology, Epithelial Cells pathology, Hepatitis, Autoimmune pathology, Thymus Gland pathology
- Abstract
TRAF6, an E3 ubiquitin protein ligase, plays a critical role in T cell tolerance by regulating medullary thymic epithelial cell (mTEC) development. mTECs regulate T cell tolerance by ectopically expressing self-antigens and eliminating autoreactive T cells in the thymus. Here we show that mice with mTEC depletion due to conditional deletion of Traf6 expression in murine thymic epithelial cells (Traf6ΔTEC mice) showed a surprisingly narrow spectrum of autoimmunity affecting the liver. The liver inflammation in Traf6ΔTEC mice exhibited all the histological and immunological characteristics of human autoimmune hepatitis (AIH). The role of T cells in AIH establishment was supported by intrahepatic T cell population changes and AIH development after transfer of liver T cells into immunodeficient mice. Despite a 50% reduction in natural Treg thymic output, peripheral tolerance in Traf6ΔTEC mice was normal, whereas compensatory T regulatory mechanisms were evident in the liver of these animals. These data indicate that mTECs exert a cell-autonomous role in central T cell tolerance and organ-specific autoimmunity, but play a redundant role in peripheral tolerance. These findings also demonstrate that Traf6ΔTEC mice are a relevant model with which to study the pathophysiology of AIH, as well as autoantigen-specific T cell responses and regulatory mechanisms underlying this disease.
- Published
- 2013
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27. Thymic epithelial cells: antigen presenting cells that regulate T cell repertoire and tolerance development.
- Author
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Alexandropoulos K and Danzl NM
- Subjects
- Animals, Antigen Presentation immunology, Autoantigens immunology, Epithelial Cells cytology, Humans, Immune Tolerance, Antigen-Presenting Cells immunology, Epithelial Cells immunology, T-Lymphocytes immunology, Thymus Gland cytology
- Abstract
During thymocyte development bone marrow-derived precursors in the thymus undergo a series of differentiation steps to produce self-tolerant, mature T lymphocytes. The thymus contains two functionally distinct anatomical compartments, consisting of a centrally located medulla surrounded by the thymic cortex. These compartments in turn are comprised of two major cellular components: (1) the T lymphoid compartment of developing thymocytes and (2) the thymic stroma consisting mainly of thymic epithelial cells (TECs). These epithelial cells are further separated into cortical and medullary TECs (cTECs and mTECs) based on their localization within the thymic cortex or medulla respectively. Reciprocal interactions between thymocytes and epithelial cells are required for the development of both cellular components into a functional thymic organ. Thymocytes provide trophic factors for the development of a complex three-dimensional epithelial cell network, while epithelial cells regulate T cell development through expression and presentation of self-antigens on major histocompatibility molecules. Our work focuses on how thymic epithelial cells regulate T cell development and function and on elucidating the mechanisms of thymic epithelial cell differentiation. Here we review current knowledge and provide our own insight into the development, differentiation and antigen presenting properties of TECs. We focus specifically on how mTECs regulate T cell repertoire selection and central tolerance.
- Published
- 2012
- Full Text
- View/download PDF
28. Regulation of medullary thymic epithelial cell differentiation and function by the signaling protein Sin.
- Author
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Danzl NM, Donlin LT, and Alexandropoulos K
- Subjects
- Adaptor Proteins, Signal Transducing, Animals, Autoimmunity immunology, Cell Differentiation immunology, Cell Differentiation physiology, Epithelial Cells cytology, Epithelial Cells drug effects, Epithelial Cells immunology, Fibroblast Growth Factor 7 pharmacology, Homeostasis, Immune Tolerance, Immunologic Memory, Immunosuppression Therapy, Inflammation etiology, Major Histocompatibility Complex, Mice, Mice, Knockout, Mice, Nude, Phosphoproteins genetics, Receptors, Antigen, T-Cell immunology, Signal Transduction drug effects, Signal Transduction immunology, T-Lymphocytes immunology, Thymus Gland drug effects, Phosphoproteins physiology, Thymus Gland cytology, Thymus Gland immunology
- Abstract
Medullary thymic epithelial cells (mTECs) play an important role in T cell tolerance and prevention of autoimmunity. Mice deficient in expression of the signaling protein Sin exhibit exaggerated immune responses and multitissue inflammation. Here, we show that Sin is expressed in the thymic stroma, specifically in mTECs. Sin deficiency led to thymic stroma-dependent autoimmune manifestations shown by radiation chimeras and thymic transplants in nude mice, and associated with defective mTEC-mediated elimination of thymocytes in a T cell receptor transgenic model of negative selection. Lack of Sin expression correlated with a disorganized medullary architecture and fewer functionally mature mTECs under steady-state conditions. Additionally, Sin deficiency inhibited the expansion of mTECs in response to in vivo administration of keratinocyte growth factor (KGF). These results identify Sin as a novel regulator of mTEC development and T cell tolerance, and suggest that Sin is important for homeostatic maintenance of the medullary epithelium in the adult thymus.
- Published
- 2010
- Full Text
- View/download PDF
29. Regulation of T-lymphocyte physiology by the Chat-H/CasL adapter complex.
- Author
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Alexandropoulos K and Regelmann AG
- Subjects
- Animals, Cell Adhesion, Crk-Associated Substrate Protein chemistry, Crk-Associated Substrate Protein immunology, Humans, Mice, Nerve Tissue Proteins chemistry, Nerve Tissue Proteins immunology, Protein Interaction Domains and Motifs physiology, Receptors, Antigen, T-Cell metabolism, Signal Transduction immunology, Crk-Associated Substrate Protein metabolism, Leukocyte Rolling, Nerve Tissue Proteins metabolism, Protein Multimerization, T-Lymphocytes physiology
- Abstract
The Cas family of proteins consists of at least four members implicated in the regulation of diverse cellular processes such as cell proliferation, adhesion, motility, and cancer cell metastasis. Cas family members have conserved C-termini that mediate constitutive heterotypic interactions with members of a different group of proteins, the NSP family. Both the Cas and NSP proteins have conserved domains that mediate protein-protein interactions with other cytoplasmic intermediates. Signaling modules assembled by these proteins in turn regulate signal transduction downstream of a variety of receptors including integrin, chemokine, and antigen receptors. T lymphocytes express the NSP protein NSP3/Chat-H and the Cas protein Hef1/CasL, which are found in a constitutive complex in naive T cells. We recently showed that Chat-H and Hef1/CasL regulate integrin-mediated adhesion and promote T-cell migration and trafficking downstream of activated chemokine receptors. It is currently unclear if the Chat-H/CasL module also plays a role in antigen receptor signaling. Here we review our current knowledge of how Chat-H and Hef1/CasL regulate T-cell physiology and whether this protein complex plays a functional role downstream of T-cell receptor activation.
- Published
- 2009
- Full Text
- View/download PDF
30. The hematopoietic isoform of Cas-Hef1-associated signal transducer regulates chemokine-induced inside-out signaling and T cell trafficking.
- Author
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Regelmann AG, Danzl NM, Wanjalla C, and Alexandropoulos K
- Subjects
- Adaptor Proteins, Signal Transducing immunology, Animals, Enzyme Activation physiology, Immunoblotting, Integrins immunology, Integrins metabolism, Mice, Mice, Inbred C57BL, Protein Isoforms immunology, Protein Isoforms metabolism, RNA, Small Interfering, Signal Transduction immunology, T-Lymphocytes immunology, rap1 GTP-Binding Proteins immunology, rap1 GTP-Binding Proteins metabolism, Adaptor Proteins, Signal Transducing metabolism, Cell Adhesion immunology, Chemotaxis, Leukocyte immunology, Models, Immunological, T-Lymphocytes metabolism
- Abstract
Leukocyte migration and trafficking is dynamically regulated by various chemokine and adhesion molecules and is vital to the proper function of the immune system. We describe a role for the Cas and Hef-1-associated signal transducer in hematopoietic cells (Chat-H) as a critical regulator of T lymphocyte migration, by using lentivirus-mediated RNA interference (RNAi). Impaired migration of Chat-H-depleted cells coincided with defective inside-out signaling shown by diminished chemokine-induced activation of the Rap-1 GTPase and integrin-mediated adhesion. Localization of Chat-H to the plasma membrane, association with its binding partner Crk-associated substrate in lymphocytes (CasL), and Chat-H-mediated CasL serine-threonine phosphorylation were required for T cell migration. These results identify Chat-H as a critical signaling intermediate acting upstream of Rap1 to regulate chemokine-induced adhesion and migration.
- Published
- 2006
- Full Text
- View/download PDF
31. Deficiency in expression of the signaling protein Sin/Efs leads to T-lymphocyte activation and mucosal inflammation.
- Author
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Donlin LT, Danzl NM, Wanjalla C, and Alexandropoulos K
- Subjects
- Adaptor Proteins, Signal Transducing, Animals, B-Lymphocytes immunology, CD4-Positive T-Lymphocytes immunology, Enterocolitis genetics, Granuloma genetics, Intestinal Mucosa pathology, Liver pathology, Male, Mice, Mice, Knockout, Phosphoproteins deficiency, Phosphoproteins genetics, Receptors, Interleukin-2 analysis, Signal Transduction, Enterocolitis immunology, Lymphocyte Activation, Phosphoproteins physiology, T-Lymphocytes immunology
- Abstract
Our studies have concentrated on elucidating the role of the signaling protein Sin in T-lymphocyte function. We have previously shown that Sin overexpression inhibits T-lymphocyte development and activation. Here we show that Sin-deficient mice exhibit exaggerated immune responses characterized by enhanced cytokine secretion and T-cell-dependent antibody production. Excessive T-cell responses in young mice correlate with spontaneous development of inflammatory lesions in different organs of aged Sin(-/-) mice, particularly the small intestine. The intestinal inflammation is characterized by T- and B-cell infiltrates in the lamina propria, which correlate with crypt enlargement and marked villus expansion and/or damage. Similar to the human intestinal inflammatory disorder Crohn's disease (CD), and in contrast to most mouse models of mucosal inflammation, inflammatory lesions in the gastrointestinal tract of Sin(-/-) mice are restricted to the small bowel. Taken together, these results suggest that Sin regulates immune system and T-lymphocyte function and that immune system dysfunction in the absence of Sin may underlie the pathogenesis of tissue-specific inflammation and enteropathies such as CD.
- Published
- 2005
- Full Text
- View/download PDF
32. The adapter molecule Sin regulates T-cell-receptor-mediated signal transduction by modulating signaling substrate availability.
- Author
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Xing L, Donlin LT, Miller RH, and Alexandropoulos K
- Subjects
- Animals, Base Sequence, DNA, Complementary genetics, Gene Expression, Humans, Jurkat Cells, Lymphocyte Activation, Mice, Mice, Inbred C57BL, Mice, Transgenic, Models, Biological, Phospholipase C gamma, Phosphorylation, Protein Isoforms genetics, Protein Isoforms metabolism, Proteins genetics, Recombinant Proteins genetics, Recombinant Proteins metabolism, Retinoblastoma-Like Protein p130, Signal Transduction, Transcriptional Activation, Type C Phospholipases antagonists & inhibitors, Proteins metabolism, Receptors, Antigen, T-Cell metabolism, T-Lymphocytes immunology, T-Lymphocytes metabolism
- Abstract
Engagement of the T-cell receptor (TCR) results in the activation of a multitude of signaling events that regulate the function of T lymphocytes. These signaling events are in turn modulated by adapter molecules, which control the final functional output through the formation of multiprotein complexes. In this report, we identified the adapter molecule Sin as a new regulator of T-cell activation. We found that the expression of Sin in transgenic T lymphocytes and Jurkat T cells inhibited interleukin-2 expression and T-cell proliferation. This inhibitory effect was specific and was due to defective phospholipase C-gamma (PLC-gamma) phosphorylation and activation. In contrast to other adapters that become phosphorylated upon TCR stimulation, Sin was constitutively phosphorylated in resting cells by the Src kinase Fyn and bound to signaling intermediates, including PLC-gamma. In stimulated cells, Sin was transiently dephosphorylated, which coincided with transient dissociation of Fyn and PLC-gamma. Downregulation of Sin expression using Sin-specific short interfering RNA oligonucleotides inhibited transcriptional activation in response to TCR stimulation. Our results suggest that endogenous Sin influences T-lymphocyte signaling by sequestering signaling substrates and regulating their availability and/or activity in resting cells, while Sin is required for targeting these intermediates to the TCR for fast signal transmission during stimulation.
- Published
- 2004
- Full Text
- View/download PDF
33. Sin: good or bad? A T lymphocyte perspective.
- Author
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Alexandropoulos K, Donlin LT, Xing L, and Regelmann AG
- Subjects
- Animals, Cellular Apoptosis Susceptibility Protein metabolism, Crk-Associated Substrate Protein, Lymphocyte Activation, Mice, Models, Genetic, Phosphoproteins chemistry, Phosphoproteins genetics, Phosphoproteins metabolism, Retinoblastoma-Like Protein p130, T-Lymphocytes enzymology, src Homology Domains, src-Family Kinases metabolism, Phosphoproteins physiology, Proteins, T-Lymphocytes immunology
- Abstract
Stimulation of T cells through their antigen receptor induces a multitude of signaling networks that regulate T cell activation in the form of cytokine production and T cell proliferation. Multiple signal integration sites exist along these pathways in the form of multiprotein signaling complexes, the formation of which is facilitated by adapter and scaffold molecules. In recent years a number of adapter and scaffold molecules have been described in T cells and shown to play an integral part in T cell function. Among these molecules are proteins that function as positive or negative regulators of T cell activation downstream of the activated T cell receptor (TCR). Here, we discuss the role of a small family of multiadapter proteins on T cell activation, the p130Cas family, with emphasis on one of its members, Sin (Src-interacting protein). Our results suggest that Sin inhibits thymocyte development and T cell activation and is a novel negative regulator of T lymphocyte function.
- Published
- 2003
- Full Text
- View/download PDF
34. Defective thymocyte maturation by transgenic expression of a truncated form of the T lymphocyte adapter molecule and Fyn substrate, Sin.
- Author
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Donlin LT, Roman CA, Adlam M, Regelmann AG, and Alexandropoulos K
- Subjects
- Adaptor Proteins, Vesicular Transport biosynthesis, Animals, Apoptosis genetics, Apoptosis immunology, Carrier Proteins biosynthesis, Carrier Proteins physiology, Cell Differentiation genetics, Cell Differentiation immunology, Cell Survival genetics, Cell Survival immunology, Female, Gene Expression Regulation immunology, Growth Inhibitors genetics, Growth Inhibitors physiology, Humans, JNK Mitogen-Activated Protein Kinases, Mice, Mice, Inbred C57BL, Mice, Inbred CBA, Mice, Knockout, Mice, Transgenic, Mitogen-Activated Protein Kinase 3, Mitogen-Activated Protein Kinases antagonists & inhibitors, Mitogen-Activated Protein Kinases metabolism, Phosphoproteins biosynthesis, Phosphorylation, Proto-Oncogene Proteins biosynthesis, Proto-Oncogene Proteins physiology, Proto-Oncogene Proteins c-fyn, Receptors, Antigen, T-Cell metabolism, Sequence Deletion, Substrate Specificity, T-Lymphocytes immunology, T-Lymphocytes pathology, Thymus Gland immunology, Thymus Gland pathology, Transgenes immunology, src-Family Kinases physiology, Adaptor Proteins, Signal Transducing, Adaptor Proteins, Vesicular Transport genetics, Carrier Proteins genetics, Membrane Proteins, Phosphoproteins genetics, Proto-Oncogene Proteins genetics, T-Lymphocytes metabolism, Thymus Gland metabolism
- Abstract
Adapter molecules that promote protein-protein interactions play a central role in T lymphocyte differentiation and activation. In this study, we examined the role of the T lymphocyte-expressed adapter protein and Src kinase substrate, Sin, on thymocyte function using transgenic mice expressing an activated, truncated allele of Sin (SinDeltaC). We found that SinDeltaC expression led to reduced numbers of CD4(+) and CD8(+) single-positive cells and reduced thymic cellularity due to increased thymocyte apoptosis. Because the adapter properties of Sin are mediated by tyrosine-based motifs and given that Sin is a substrate for Src tyrosine kinases, we examined the involvement of these kinases in the inhibitory effects of SinDeltaC. We found that in transgenic thymocytes, SinDeltaC was constitutively phosphorylated by the Src kinase Fyn, but not by the related kinase Lck. Using SinDeltaC and fyn(-/-) animals, we also found that the expression of Fyn was required for the inhibitory effect of SinDeltaC on thymocyte apoptosis but not for SinDeltaC-mediated inhibition of T cell maturation. The inhibitory effect of SinDeltaC on thymocyte maturation correlated with defective activation of the mitogen-activated protein kinase extracellular signal-regulated kinase. Our results suggest that the Sin mutant inhibits thymocyte differentiation through Fyn-dependent and -independent mechanisms and that endogenous Sin may be an important regulator of thymocyte development.
- Published
- 2002
- Full Text
- View/download PDF
35. c-SRC mediates neurite outgrowth through recruitment of Crk to the scaffolding protein Sin/Efs without altering the kinetics of ERK activation.
- Author
-
Yang LT, Alexandropoulos K, and Sap J
- Subjects
- Animals, Enzyme Activation, Epidermal Growth Factor metabolism, Fluorescent Antibody Technique, Kinetics, PC12 Cells, Phosphorylation, Proto-Oncogene Proteins c-crk, Rats, Receptor-Like Protein Tyrosine Phosphatases, Class 4, Signal Transduction physiology, Tyrosine metabolism, src-Family Kinases metabolism, Genes, src physiology, Mitogen-Activated Protein Kinases metabolism, Neurites physiology, Neurons physiology, Protein Tyrosine Phosphatases physiology, Proto-Oncogene Proteins metabolism, Receptors, Cell Surface
- Abstract
SRC family kinases have been consistently and recurrently implicated in neurite extension events, yet the mechanism underlying their neuritogenic role has remained elusive. We report that epidermal growth factor (EGF) can be converted from a non-neuritogenic into a neuritogenic factor through moderate activation of endogenous SRC by receptor-protein-tyrosine phosphatase alpha (a physiological SRC activator). We show that such a qualitative change in the response to EGF is not accompanied by changes in the extent or kinetics of ERK induction in response to this factor. Instead, the pathway involved relies on increased tyrosine phosphorylation of, and recruitment of Crk to, the SRC substrate Sin/Efs. The latter is a scaffolding protein structurally similar to the SRC substrate Cas, tyrosine phosphorylation of which is critical for migration in fibroblasts and epithelial cells. Expression of a dominant negative version of Sin interfered with receptor-protein-tyrosine phosphatase alpha/EGF- as well as fibroblast growth factor-induced neurite outgrowth. These observations uncouple neuritogenic signaling in PC12 cells from sustained activation of ERK kinases and for the first time identify an effector of SRC function in neurite extension.
- Published
- 2002
- Full Text
- View/download PDF
36. c-Src signaling induced by the adapters Sin and Cas is mediated by Rap1 GTPase.
- Author
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Xing L, Ge C, Zeltser R, Maskevitch G, Mayer BJ, and Alexandropoulos K
- Subjects
- Adaptor Proteins, Signal Transducing, Alleles, Amino Acid Substitution, Crk-Associated Substrate Protein, Humans, Ligands, Mitogen-Activated Protein Kinase 1 metabolism, Mitogen-Activated Protein Kinase 3, Mitogen-Activated Protein Kinases metabolism, Neoplasm Proteins physiology, Oncogenes, Peptide Fragments metabolism, Phosphorylation, Protein Processing, Post-Translational, Proto-Oncogene Proteins physiology, Proto-Oncogene Proteins c-crk, Proto-Oncogene Proteins pp60(c-src) genetics, Recombinant Fusion Proteins physiology, Retinoblastoma-Like Protein p130, Sequence Deletion, Transcriptional Activation physiology, Tumor Cells, Cultured, src Homology Domains, Drosophila Proteins, Insect Proteins physiology, MAP Kinase Signaling System physiology, Phosphoproteins physiology, Proteins, Proto-Oncogene Proteins pp60(c-src) physiology, rap1 GTP-Binding Proteins physiology
- Abstract
Oncogenic Src proteins have been extensively studied to gain insight into the signaling mechanisms of Src. To better understand signaling through wild-type Src, we used an approach that involves activation of Src signaling through the binding of physiologic ligands to the Src SH3 domain. To this end, we used full-length and truncated versions of the multiadapter molecules Cas and Sin to activate c-Src, and we examined the intracellular pathways that mediate Src signaling under these conditions. We show that although all proteins bind to and are phosphorylated by c-Src, quantitative differences exist in the ability of the different ligands to activate c-Src signaling. In addition, we show that Sin- and Cas-induced Src signaling, as assayed by transcriptional activation, is exclusively mediated through a pathway that involves the adapter Crk and the GTP-binding protein Rap1. These data are in contrast to previous observations showing Ras to mediate signaling downstream of transforming Src alleles. In our system, we found that signaling through the oncogenic SrcY527 mutant is indeed mediated by Ras. In addition, we found that Rap1 also mediates oncogenic Src signaling. Our results show for the first time that Rap1 mediates c-Src kinase signaling and reveal mechanistic differences in the signaling properties of wild-type and transforming Src proteins.
- Published
- 2000
- Full Text
- View/download PDF
37. A nuclear tyrosine kinase becomes a cytoplasmic oncogene.
- Author
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Baltimore D, Ren R, Cheng G, Alexandropoulos K, and Cicchetti P
- Subjects
- Animals, Cell Nucleus enzymology, Cytoplasm genetics, Cell Transformation, Neoplastic, Protein-Tyrosine Kinases physiology, Proto-Oncogene Proteins c-abl physiology
- Published
- 1995
- Full Text
- View/download PDF
38. Ha-Ras functions downstream from protein kinase C in v-Fps-induced gene expression mediated by TPA response elements.
- Author
-
Alexandropoulos K, Qureshi SA, and Foster DA
- Subjects
- 3T3 Cells, Animals, Chloramphenicol O-Acetyltransferase genetics, GTP-Binding Proteins physiology, Mice, Mutation, Fusion Proteins, gag-onc pharmacology, Gene Expression Regulation drug effects, Genes, ras, Protein Kinase C physiology, Protein-Tyrosine Kinases, Tetradecanoylphorbol Acetate pharmacology
- Abstract
v-Fps activates promoters under the control of the 12-O-tetradecanoyl phorbol 13-acetate (TPA) response element (TRE). The induction of TRE-mediated transcription by v-Fps was sensitive to a dominant-negative mutant of Ha-Ras. An activated derivative of Ha-Ras, v-Ha-Ras, also activated TRE-mediated transcription. v-Fps-induced TRE-mediated gene expression was sensitive to depleting cells of protein kinase C (PKC), whereas v-Ha-Ras-induced TRE-mediated transcription was insensitive to PKC depletion, suggesting that Ha-Ras functions downstream from PKC in v-Fps-induced TRE-mediated gene expression. Consistent with this hypothesis, the induction of TRE-mediated gene expression by phorbol esters that activate PKC directly was blocked by the dominant-negative Ha-Ras mutant. Thus, v-Fps-induced activation of TRE-mediated gene expression is via an intracellular signaling mechanism that is dependent upon both PKC and Ha-Ras and Ha-Ras functions downstream from PKC.
- Published
- 1993
39. The induction of Egr-1 expression by v-Fps is via a protein kinase C-independent intracellular signal that is sequentially dependent upon HaRas and Raf-1.
- Author
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Alexandropoulos K, Qureshi SA, Bruder JT, Rapp U, and Foster DA
- Subjects
- Animals, Avian Sarcoma Viruses, Cell Line, Cell Line, Transformed, Cell Transformation, Viral, Early Growth Response Protein 1, Enzyme Activation, Fusion Proteins, gag-onc physiology, Gene Expression Regulation, Mutation, Promoter Regions, Genetic, Protein Kinase C physiology, Proto-Oncogene Proteins genetics, Proto-Oncogene Proteins c-raf, Rats, Recombinant Fusion Proteins biosynthesis, DNA-Binding Proteins biosynthesis, Immediate-Early Proteins, Oncogene Protein p21(ras) physiology, Protein-Tyrosine Kinases physiology, Proto-Oncogene Proteins physiology, Signal Transduction, Transcription Factors biosynthesis
- Abstract
Activating the protein-tyrosine kinase activity of v-Fps leads to the rapid transcriptional activation of the Egr-1 gene, which encodes a mitogen-responsive transcription factor. Activation of Egr-1 by v-Fps was insensitive to protein kinase C depletion, suggesting that a protein kinase C-independent signal activated by v-Fps leads to the induction of Egr-1. Expression of v-Fps in transient expression assays induced Egr-1 promoter activation. v-HaRas and v-Raf also activated the Egr-1 promoter. To characterize HaRas and Raf-1 involvement in v-Fps-induced Egr-1 expression, we used recently characterized dominant negative mutants of HaRas and Raf-1. v-Fps-induced Egr-1 promoter activation was inhibited by the dominant negative mutants of both HaRas and Raf-1. v-HaRas-induced Egr-1 promoter activation was blocked by the negative Raf-1 mutant; however, v-Raf-1-induced Egr-1 promoter activation was unaffected by the inhibitory HaRas mutant. These data suggest that v-Fps activates a protein kinase C-independent intracellular signaling pathway that is dependent on both HaRas and Raf-1, where Raf-1 functions downstream of HaRas.
- Published
- 1992
40. v-Fps-responsiveness in the Egr-1 promoter is mediated by serum response elements.
- Author
-
Alexandropoulos K, Qureshi SA, Rim M, Sukhatme VP, and Foster DA
- Subjects
- 3T3 Cells, Animals, Cell Line, Early Growth Response Protein 1, Gene Expression Regulation, Mice, Mutation, Plasmids, Rats, Serum Response Factor, Transfection, DNA-Binding Proteins genetics, DNA-Binding Proteins metabolism, Fusion Proteins, gag-onc metabolism, Immediate-Early Proteins, Nuclear Proteins metabolism, Promoter Regions, Genetic, Protein-Tyrosine Kinases metabolism, Transcription Factors genetics, Transcription Factors metabolism
- Abstract
Egr-1, a mitogen-responsive transcription factor, is rapidly induced by v-Fps in the absence of protein synthesis. Thus, Egr-1 is a primary response to the protein-tyrosine kinase activity of v-Fps. To determine the v-Fps-responsive elements in the Egr-1 promoter, deletion mutants of the Egr-1 promoter were used in transient expression assays. A v-Fps expression vector was contransfected into NIH 3T3 cells with chloramphenicol acetyl transferase (CAT) gene expression vectors under the control of the Egr-1 promoter or the Egr-1 promoter containing various deletions. Responsiveness to v-Fps was restricted to a region that contained repeated CC(A/T)6GG sequences, known as CArG boxes. CArG boxes form the core of serum response element (SREs). v-Fps-induced Egr-1 promoter activation was lost by sequential removal of four tandemly repeated SREs. This region, containing four SREs, was found to be sufficient for maximal Egr-1 induction by v-Fps when placed upstream from a heterologous promoter. Individual SREs from this region were able to respond to v-Fps, however, the activation of the individual SREs was lower than that observed for the clustered SREs. These data suggest that v-Fps-responsiveness in the Egr-1 promoter is mediated by SREs.
- Published
- 1992
- Full Text
- View/download PDF
41. Sustained induction of egr-1 by v-src correlates with a lack of fos-mediated repression of the egr-1 promoter.
- Author
-
Qureshi SA, Rim MH, Alexandropoulos K, Berg K, Sukhatme VP, and Foster DA
- Subjects
- 3T3 Cells, Animals, DNA-Binding Proteins genetics, Early Growth Response Protein 1, Mice, Transcription Factors genetics, Transcription, Genetic, DNA-Binding Proteins metabolism, Gene Expression Regulation physiology, Genes, fos physiology, Genes, src physiology, Immediate-Early Proteins, Transcription Factors metabolism
- Abstract
Serum stimulation of quiescent fibroblasts leads to a transient induction of the transcription factor egr-1. However, the induction of egr-1 by v-src was found to be sustained rather than transient. The proto-oncogene fos has been reported to be co-regulated with egr-1 and to repress serum-induced egr-1 expression. We found that c-fos prevents v-src-induced gene expression regulated by the egr-1 promoter. Thus, the sustained induction of egr-1 by v-src could be explained by a lack of c-fos induction by v-src. Consistent with this hypothesis, egr-1 and c-fos were co-induced by serum, but not by v-src, in Balb/c 3T3 cells; v-src did not induce c-fos expression in these cells. We propose that sustained expression of egr-1 induced by v-src in Balb/c 3T3 cells is due to a lack of c-fos down-regulation of egr-1.
- Published
- 1992
42. Reduction in temporal lobe size in siblings with schizophrenia: a magnetic resonance imaging study.
- Author
-
Dauphinais ID, DeLisi LE, Crow TJ, Alexandropoulos K, Colter N, Tuma I, and Gershon ES
- Subjects
- Adult, Female, Humans, Male, Schizophrenia genetics, Magnetic Resonance Imaging, Schizophrenia pathology, Temporal Lobe pathology
- Abstract
Twenty-eight individuals with familial schizophrenia, from 16 unrelated families (12 sibling pairs and 4 individuals whose siblings refused scanning), and 21 normal control subjects were examined by cerebral magnetic resonance imaging (MRI). Measurements of the cerebrum, temporal lobes, and cerebral lateral ventricles were obtained using consecutive coronal sections containing these structures. Temporal lobe volume was significantly decreased by approximately 10% in these early onset schizophrenic siblings compared with normal controls. These findings add to recent post-mortem and neuroradiological evidence for morphological alteration in the temporal lobes in schizophrenia.
- Published
- 1990
- Full Text
- View/download PDF
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