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Baranova LA, Emel’yanova VP, Zhornik EV, Minov AM, Naumenko LV, Volotovskii ID. Cloning and analysis of coding cDNA sequence of human leukocyte Csk tyrosine kinase under normal conditions and in choroidal melanoma. BIOL BULL+ 2008. [DOI: 10.1134/s1062359008060022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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2
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O'Shea JJ, Johnston JA, Kehrl J, Koretzky G, Samelson LE. Key molecules involved in receptor-mediated lymphocyte activation. ACTA ACUST UNITED AC 2008; Chapter 11:Unit 11.9A. [PMID: 18432708 DOI: 10.1002/0471142735.im1109as44] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
This unit, along with Unit 11.9B, provides a summary of our current knowledge about various signaling pathways critical to the function of immune cells. Here, our understanding of T cell receptor (TCR)- and B cell receptor (BCR)-mediated signaling is summarized. A schematic representation of immunologically relevant cytokine receptors and the Janus Family Kinases (JAKs) that is activated through these receptors is provided, along with details about molecules involved in interleukin 2 mediated signal transduction.
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Affiliation(s)
- J J O'Shea
- National Institute of Arthritis and Musculoskeletal and Skin Diseases, Bethesda, Maryland, USA
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3
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Abram CL, Lowell CA. The diverse functions of Src family kinases in macrophages. FRONT BIOSCI-LANDMRK 2008; 13:4426-50. [PMID: 18508521 DOI: 10.2741/3015] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Macrophages are key components of the innate immune response. These cells possess a diverse repertoire of receptors that allow them to respond to a host of external stimuli including cytokines, chemokines, and pathogen-associated molecules. Signals resulting from these stimuli activate a number of macrophage functional responses such as adhesion, migration, phagocytosis, proliferation, survival, cytokine release and production of reactive oxygen and nitrogen species. The cytoplasmic tyrosine kinase Src and its family members (SFKs) have been implicated in many intracellular signaling pathways in macrophages, initiated by a diverse set of receptors ranging from integrins to Toll-like receptors. However, it has been difficult to implicate any given member of the family in any specific pathway. SFKs appear to have overlapping and complementary functions in many pathways. Perhaps the function of these enzymes is to modulate the overall intracellular signaling network in macrophages, rather than operating as exclusive signaling switches for defined pathways. In general, SFKs may function more like rheostats, influencing the amplitude of many pathways.
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Affiliation(s)
- Clare L Abram
- Department of Laboratory Medicine, University of California, San Francisco, CA 94143, USA
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4
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Madhusoodanan KS, Guo D, McGarrigle DK, Maack T, Huang XY. Csk mediates G-protein-coupled lysophosphatidic acid receptor-induced inhibition of membrane-bound guanylyl cyclase activity. Biochemistry 2006; 45:3396-403. [PMID: 16519534 PMCID: PMC2519153 DOI: 10.1021/bi052513u] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Natriuretic peptides (NPs) are involved in many physiological processes, including the regulation of vascular tone, sodium excretion, pressure-volume homeostasis, inflammatory responses, and cellular growth. The two main receptors of NP, membrane-bound guanylyl cyclases A and B (GC-A and GC-B), mediate the effects of NPs via the generation of cGMP. NP-stimulated generation of cGMP can be modulated by intracellular processes, whose exact nature remains to be elucidated. Thus, serum and lysophosphatidic acid (LPA), by unknown pathways, have been shown to inhibit the NP-induced generation of cGMP. Here we report that the nonreceptor-tyrosine-kinase Csk is an essential component of the intracellular modulation of atrial natriuretic peptide (ANP)-stimulated activation of GC-A. The genetic deletion of Csk (Csk(-)(/)(-)) in mouse embryonic fibroblasts blocked the inhibitory effect of both serum and LPA on the ANP-stimulated generation of cGMP. Moreover, using a chemical rescue approach, we also demonstrate that the catalytic activity of Csk is required for its modulatory function. Our data demonstrate that Csk is involved in the control of cGMP levels and that membrane-bound guanylyl cyclases can be critically modulated by other receptor-initiated intracellular signaling pathways.
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Affiliation(s)
| | | | | | | | - Xin-Yun Huang
- *X.-Y. H.: To whom correspondence should be addressed, Tel: (212) 746-6362; Fax: (212) 746-8690, E-mail:
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5
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Xu S, Huo J, Tan JEL, Lam KP. Cbp deficiency alters Csk localization in lipid rafts but does not affect T-cell development. Mol Cell Biol 2005; 25:8486-95. [PMID: 16166631 PMCID: PMC1265734 DOI: 10.1128/mcb.25.19.8486-8495.2005] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The ubiquitously expressed transmembrane adaptor Csk-binding protein (Cbp) recruits Csk to lipid rafts, where the latter exerts its negative regulatory effect on the Src family of protein tyrosine kinases. We have inactivated Cbp in the mouse germ line. In contrast to Csk gene inactivation, which leads to embryonic lethality and impaired T-cell development, Cbp-deficient mice were viable and exhibited normal T-cell development but with an increased thymocyte population. In the absence of Cbp, the amount of Csk that localizes to the lipid rafts was greatly reduced. Interestingly, this altered lipid raft localization of Csk did not lead to any detectable biochemical or functional defect in T cells. The T-cell receptor-induced intracellular calcium flux, cell proliferation, and cytokine secretion were not affected by the absence of Cbp. Peripheral T-cell tolerance to superantigen SEB was also largely intact in Cbp-deficient mice. Thus, Cbp is dispensable for T-cell development and activation.
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Affiliation(s)
- Shengli Xu
- Laboratory of Immunology, Center for Molecular Medicine, Institute of Molecular and Cell Biology, 61 Biopolis Drive, Lab 6-15, Proteos, Singapore 138673, Singapore
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6
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Grill B, Wilson GM, Zhang KX, Wang B, Doyonnas R, Quadroni M, Schrader JW. Activation/division of lymphocytes results in increased levels of cytoplasmic activation/proliferation-associated protein-1: prototype of a new family of proteins. THE JOURNAL OF IMMUNOLOGY 2004; 172:2389-400. [PMID: 14764709 DOI: 10.4049/jimmunol.172.4.2389] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We purified from activated T lymphocytes a novel, highly conserved, 116-kDa, intracellular protein that occurred at high levels in the large, dividing cells of the thymus, was up-regulated when resting T or B lymphocytes or hemopoietic progenitors were activated, and was down-regulated when a monocytic leukemia, M1, was induced to differentiate. Expression of the protein was highest in the thymus and spleen and lowest in tissues with a low proportion of dividing cells such as kidney or muscle, although expression was high in the brain. The protein was localized to the cytosol and was phosphorylated, which is consistent with a previous report that the Xenopus laevis ortholog was phosphorylated by a mitotically activated kinase (1 ). The cDNA was previously mischaracterized as encoding p137, a 137-kDa GPI-linked membrane protein (2 ). We propose that the authentic protein encoded by this cDNA be called cytoplasmic activation/proliferation-associated protein-1 (caprin-1), and show that it is the prototype of a novel family of proteins characterized by two novel protein domains, termed homology regions-1 and -2 (HR-1, HR-2). Although we have found evidence for caprins only in urochordates and vertebrates, two insect proteins exhibit well-conserved HR-1 domains. The HR-1 and HR-2 domains have no known function, although the HR-1 of caprin-1 appeared necessary for formation of multimeric complexes of caprin-1. Overexpression of a fusion protein of enhanced green fluorescent protein and caprin-1 induced a specific, dose-dependent suppression of the proliferation of NIH-3T3 cells, consistent with the notion that caprin-1 plays a role in cellular activation or proliferation.
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Affiliation(s)
- Brock Grill
- The Biomedical Research Centre, University of British Columbia, Vancouver, British Columbia, Canada
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7
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Abstract
The specificity of the adaptive immune response is, in part, dependent on the clonal expression of the mature T cell receptor (TCR) on T lymphocytes. One mechanism regulating the clonality of the TCR occurs at the level of TCR-beta gene rearrangements during lymphocyte development. Expression of a nascent TCR-beta chain together with pre-Talpha (pTalpha) and CD3 molecules to form the pre-TCR complex, represents a critical checkpoint in T cell differentiation known as beta-selection. Indeed, failure to generate a functionally rearranged TCR-beta chain at this stage of development results in apoptosis. Signals derived from the pre-TCR complex trigger a maturation program within developing thymocytes that includes: rescue from apoptosis; inhibition of further DNA recombination at the TCR-beta gene locus (allowing for the clonality of antigen receptor expression; allelic exclusion); and induction of proliferation and differentiation. The signaling mechanisms that control this developmental program remain largely undefined. Here, we discuss recent evidence investigating the molecular mechanisms that regulate thymocyte differentiation downstream of pre-TCR formation.
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Affiliation(s)
- Alison M Michie
- Department of Immunology and Bacteriology, Western Infirmary, University of Glasgow, Glasgow, Scotland, G11 6NT, UK
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8
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Abstract
Immunoreceptor engagement results in the sequential activation of several classes of protein tyrosine kinases, including the Src and Syk/Zap-70 families. Recent progress has been made in our understanding of the regulation and function of these molecules. First, it was revealed that membrane compartmentation of protein tyrosine kinases may be essential for their proper biological function. Second, Src family kinases were found to act not only as positive regulators, but also as inhibitors of cell activation. Third, it was appreciated that Csk, a potent inhibitor of Src kinases, is regulated by an assortment of protein-protein interactions. Fourth, differences in the regulation of Syk and Zap-70 were observed, suggesting significant distinctions in the purpose of these two kinases in immunoreceptor signaling. And fifth, it was suggested that proximal kinases implicated in immunoreceptor-mediated signal transduction may be regulated by protein degradation via binding to c-Cbl, a ubiquitin ligase.
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Affiliation(s)
- S Latour
- Laboratory of Molecular Oncology, IRCM, 110 Pine Avenue West, H2W 1R7, Montréal, Québec, Canada.
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9
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Ortaldo JR, Bere EW, Hodge D, Young HA. Activating Ly-49 NK receptors: central role in cytokine and chemokine production. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2001; 166:4994-9. [PMID: 11290779 DOI: 10.4049/jimmunol.166.8.4994] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
In an attempt to understand potential novel functions of receptors in vivo, we evaluated gene expression after cross-linking the activating Ly-49D mouse NK receptor. Gene expression was evaluated using a mouse GEM 2 microarray chip (Incyte Genomics, St. Louis, MO). Each chip displays a total of 8734 elements. The strongly induced genes fell into two categories: 1) soluble factors and 2) apoptotic genes. The majority of the strongly induced mRNAs as analyzed by microarray hybridization were chemokine genes. RNase protection assays and chemokine protein production analysis validated the microarray results, as cross-linking the Ly-49D mouse NK receptor induced high levels of IFN-gamma, lymphotactin, macrophage-inflammatory protein (MIP)1alpha, and MIP1beta. This gene expression was specific because other chemokines were not induced by anti-Ly-49D receptors. In addition, a series of pharmacological inhibitors were used to identify the key signaling pathways involved in the cellular response. The primary Ly-49D signaling for IFN-gamma production is predominantly mediated through Src kinase pathways involving membrane proximal events, whereas MIP1alpha and MIP1beta gene induction is more complex and may involve multiple biochemical pathways. Thus, we conclude that a primary role for the activating NK receptors in vivo may be to trigger soluble factor production and regulation of the immune response. This would place NK cells and their activating Ly-49 receptors as important initiators of microbial immunity and key elements of the innate immune system.
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MESH Headings
- Animals
- Antigens, Ly
- Chemokine CCL3
- Chemokine CCL4
- Chemokines/antagonists & inhibitors
- Chemokines/biosynthesis
- Chemokines/genetics
- Cytokines/antagonists & inhibitors
- Cytokines/biosynthesis
- Cytokines/genetics
- Dactinomycin/pharmacology
- Enzyme Inhibitors/pharmacology
- Gene Expression Regulation/immunology
- Humans
- Interferon-gamma/antagonists & inhibitors
- Interferon-gamma/biosynthesis
- Interferon-gamma/genetics
- Killer Cells, Natural/enzymology
- Killer Cells, Natural/immunology
- Killer Cells, Natural/metabolism
- Lectins, C-Type
- Macrophage Inflammatory Proteins/antagonists & inhibitors
- Macrophage Inflammatory Proteins/biosynthesis
- Macrophage Inflammatory Proteins/genetics
- Membrane Glycoproteins/immunology
- Membrane Glycoproteins/metabolism
- Membrane Glycoproteins/physiology
- Mice
- Mice, Inbred C57BL
- Pyrimidines/pharmacology
- RNA, Messenger/antagonists & inhibitors
- RNA, Messenger/biosynthesis
- Receptors, Immunologic/immunology
- Receptors, Immunologic/metabolism
- Receptors, Immunologic/physiology
- Receptors, NK Cell Lectin-Like
- Signal Transduction/immunology
- Transcriptional Activation
- src-Family Kinases/antagonists & inhibitors
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Affiliation(s)
- J R Ortaldo
- Laboratory of Experimental Immunology, National Cancer Institute, Frederick, MD 21701, USA.
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10
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Schmedt C, Tarakhovsky A. Autonomous maturation of alpha/beta T lineage cells in the absence of COOH-terminal Src kinase (Csk). J Exp Med 2001; 193:815-26. [PMID: 11283154 PMCID: PMC2193374 DOI: 10.1084/jem.193.7.815] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The deletion of COOH-terminal Src kinase (Csk), a negative regulator of Src family protein tyrosine kinases (PTKs), in immature thymocytes results in the development of alpha/beta T lineage cells in T cell receptor (TCR) beta-deficient or recombination activating gene (rag)-1-deficient mice. The function of Csk as a repressor of Lck and Fyn activity suggests activation of these PTKs is solely responsible for the phenotype observed in csk-deficient T lineage cells. We provide genetic evidence for this notion as alpha/beta T cell development is blocked in lck(-/)-fyn(-/)- csk-deficient mice. It remains unclear whether activation of Lck and Fyn in the absence of Csk uncouples alpha/beta T cell development entirely from engagement of surface-expressed receptors. We show that in mice expressing the alpha/beta TCR on csk-deficient thymocytes, positive selection is biased towards the CD4 lineage and does not require the presence of major histocompatibility complex (MHC) class I and II. Furthermore, the introduction of an MHC class I-restricted transgenic TCR into a csk-deficient background results in the development of mainly CD4 T cells carrying the transgenic TCR both in selecting and nonselecting MHC background. Thus, TCR-MHC interactions have no impact on positive selection and commitment to the CD4 lineage in the absence of Csk. However, TCR-mediated negative selection of csk-deficient, TCR transgenic cells is normal. These data suggest a differential involvement of the Csk-mediated regulation of Src family PTKs in positive and negative selection of developing thymocytes.
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Affiliation(s)
- C Schmedt
- Laboratory for Lymphocyte Signaling, The Rockefeller University, New York, New York 10021, USA.
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11
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Wiest DL, Berger MA, Carleton M. Control of early thymocyte development by the pre-T cell receptor complex: A receptor without a ligand? Semin Immunol 1999; 11:251-62. [PMID: 10441211 DOI: 10.1006/smim.1999.0181] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Beta-selection refers to a developmental checkpoint linking thymocyte survival to the outcome of antigen receptor gene rearrangement. Immature thymocytes that productively rear-range the gene segments of the TCRbeta locus undergo proliferative expansion and mature to the CD4(+)CD8(+)stage; those failing to do so die by apoptosis. How are these precursor cells alerted that TCRbeta rearrangement has been productive? While it is clear that this process involves signals transduced by a surrogate form of the TCR termed the pre-TCR, it remains unclear how pre-TCR signals are triggered. In this review, we will discuss the implications of recent experimental attempts to address this issue, as well as how pre-TCR activation is linked to the changes in gene expression that underlie thymocyte development.
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Affiliation(s)
- D L Wiest
- Division of Basic Sciences, Immunobiology Working Group, Fox Chase Cancer Center, 7701 Burholme Ave., Philadelphia, PA 19111, USA
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12
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Plas DR, Williams CB, Kersh GJ, White LS, White JM, Paust S, Ulyanova T, Allen PM, Thomas ML. Cutting Edge: The Tyrosine Phosphatase SHP-1 Regulates Thymocyte Positive Selection. THE JOURNAL OF IMMUNOLOGY 1999. [DOI: 10.4049/jimmunol.162.10.5680] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Abstract
The binding kinetics of the TCR for its interacting ligand and the nature of the resulting signal transduction event determine the fate of a developing thymocyte. The intracellular tyrosine phosphatase SHP-1 is a potential regulator of the TCR signal transduction cascade and may affect thymocyte development. To assess the role of SHP-1 in thymocyte development, we generated T cell-transgenic mice that express a putative dominant negative form of SHP-1, in which a critical cysteine is mutated to serine (SHP-1 C453S). SHP-1 C453S mice that express the 3.L2 TCR transgene are increased in CD4 single positive cells in the thymus and are increased in cells that express the clonotypic TCR. These data suggest that the expression of SHP-1 C453S results in increased positive selection in 3.L2 TCR-transgenic mice and support a role for SHP-1 thymocyte development.
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Affiliation(s)
- David R. Plas
- *Howard Hughes Medical Institute, and
- †Center for Immunology, Department of Pathology, Washington University, St. Louis, MO 63110
| | - Calvin B. Williams
- †Center for Immunology, Department of Pathology, Washington University, St. Louis, MO 63110
| | - Gilbert J. Kersh
- †Center for Immunology, Department of Pathology, Washington University, St. Louis, MO 63110
| | - Lynn S. White
- *Howard Hughes Medical Institute, and
- †Center for Immunology, Department of Pathology, Washington University, St. Louis, MO 63110
| | - J. Michael White
- †Center for Immunology, Department of Pathology, Washington University, St. Louis, MO 63110
| | - Silke Paust
- *Howard Hughes Medical Institute, and
- †Center for Immunology, Department of Pathology, Washington University, St. Louis, MO 63110
| | - Tatiana Ulyanova
- *Howard Hughes Medical Institute, and
- †Center for Immunology, Department of Pathology, Washington University, St. Louis, MO 63110
| | - Paul M. Allen
- †Center for Immunology, Department of Pathology, Washington University, St. Louis, MO 63110
| | - Matthew L. Thomas
- *Howard Hughes Medical Institute, and
- †Center for Immunology, Department of Pathology, Washington University, St. Louis, MO 63110
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13
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Rafnar T, Peebles RS, Brummet ME, Catipović B, Imani F, MacGlashan DW, Marsh DG. Stimulation of the high-affinity IgE receptor results in the tyrosine phosphorylation of a 60 kD protein which is associated with the protein-tyrosine kinase, Csk. Mol Immunol 1998; 35:249-57. [PMID: 9736341 DOI: 10.1016/s0161-5890(98)00028-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The protein tyrosine kinase Csk downregulates the activity of the Src family of kinases and has a negative effect on signal transduction through several Src kinase-associated receptors. Because the Src-family kinase Lyn plays a pivotal role in FcepsilonRI-mediated cellular activation, we examined whether Csk is involved in FcepsilonRI signaling events. Using anti-Csk antibodies and recombinant fusion proteins we detected a single tyrosine-phosphorylated protein of 60 kD (herein referred to as 'p60') that associates with the SH2 domain of Csk after stimulation of the FcepsilonRI. p60 phosphorylation reached a maximum within one minute and remained constant while the receptors were aggregated; disaggregation of the receptors resulted in rapid dephosphorylation of p60. The phosphorylation of p60 was only detected after activation by IgE and antigen and not by stimulation with PMA and/or ionomycin. Phosphorylated p60 was associated entirely with the membrane fraction of the cells. A considerable fraction of Csk was associated with the membrane in both unstimulated and stimulated cells, this fraction did not change upon activation. p60 coprecipitated with Csk from both unstimulated and FcepsilonRI stimulated cells and was phosphorylated by the immunocomplex. Total kinase activity of Csk immunoprecipitates increased upon FcepsilonRI stimulation. p60 did not react with antibodies to a number of known signaling molecules, including the recently cloned, GAP-associated protein, p62dok. Our data demonstrate that Csk associates with a membrane-anchored protein complex that is directly involved in FcepsilonRI signal transduction.
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Affiliation(s)
- T Rafnar
- Division of Clinical Immunology, Johns Hopkins Asthma and Allergy Center, Johns Hopkins University School of Medicine, Baltimore, MD 21224, USA.
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14
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Abstract
Src family protein tyrosine kinases are activated following engagement of many different classes of cellular receptors and participate in signaling pathways that control a diverse spectrum of receptor-induced biological activities. While several of these kinases have evolved to play distinct roles in specific receptor pathways, there is considerable redundancy in the functions of these kinases, both with respect to the receptor pathways that activate these kinases and the downstream effectors that mediate their biological activities. This chapter reviews the evidence implicating Src family kinases in specific receptor pathways and describes the mechanisms leading to their activation, the targets that interact with these kinases, and the biological events that they regulate.
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Affiliation(s)
- S M Thomas
- Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02115, USA.
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15
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Iritani BM, Forbush KA, Farrar MA, Perlmutter RM. Control of B cell development by Ras-mediated activation of Raf. EMBO J 1997; 16:7019-31. [PMID: 9384581 PMCID: PMC1170305 DOI: 10.1093/emboj/16.23.7019] [Citation(s) in RCA: 126] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Cell fate commitment in a variety of lineages requires signals conveyed via p21ras. To examine the role of p21ras in the development of B lymphocytes, we generated transgenic mice expressing a dominant-negative form of Ras in B lymphocyte progenitors, using a novel transcriptional element consisting of the Emu enhancer and the lck proximal promoter. Expression of dominant-negative Ras arrests B cell development at a very early stage, prior to formation of the pre-B cell receptor. Furthermore, an activated form of Raf expressed in the same experimental system could both drive the maturation of normal pro-B cells and rescue development of progenitors expressing dominant-negative Ras. Hence p21ras normally regulates early development of B lymphocytes by a mechanism that involves activation of the serine/threonine kinase Raf.
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Affiliation(s)
- B M Iritani
- Department of Immunology, University of Washington, Seattle, WA 98195, USA
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16
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Honda ZI, Suzuki T, Hirose N, Aihara M, Shimizu T, Nada S, Okada M, Ra C, Morita Y, Ito K. Roles of C-terminal Src kinase in the initiation and the termination of the high affinity IgE receptor-mediated signaling. J Biol Chem 1997; 272:25753-60. [PMID: 9325302 DOI: 10.1074/jbc.272.41.25753] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
As an attempt to analyze the roles of C-terminal Src kinase (Csk) in the high affinity IgE receptor (FcepsilonRI)-mediated signaling, we overexpressed Csk, a membrane-targeted form of Csk (mCsk), and a kinase-defective, membrane-targeted form of Csk (mCsk(-)) in rat basophil leukemia (RBL) 2H3 cells. Specific activity of Lyn at the basal state was decreased in Csk-expressing cells, and further decreased in mCsk-expressing cells. In mCsk(-)-expressing cells, basal specific activity of Lyn was increased, thereby indicating that mCsk(-) functioned as a dominant negative molecule. The onset of FcepsilonRI-mediated Lyn activation was delayed in Csk-expressing cells, and further delayed in mCsk-expressing cells. In mCsk(-)-expressing cells, Lyn activation was rapid and quite long lasting. These findings indicate (i) Csk negatively regulates rapid FcepsilonRI/Lyn coupling, and (ii) Csk activity is potentially required for its termination. The onsets of the series of events including tyrosyl phosphorylation of Syk, mitogen-activated protein (MAP) kinase activation, elevation of intracellular calcium concentration ([Ca2+]i), and histamine release were all stepwisely delayed in Csk-expressing cells and in mCsk-expressing cells. The durations of Syk phosphorylation and MAP kinase activation also closely correlated with those of Lyn activation, but [Ca2+]i elevation and histamine release followed different temporal patterns: the delayed responses in Csk-expressing cells and in mCsk-expressing cells led to sustained [Ca2+]i oscillation and histamine release, while the prompt responses in parent cells and mCsk(-)-expressing cells rapidly subsided. These findings provide further evidence that the initiations of the FcepsilonRI-mediated signals are upstreamly regulated by Src family protein tyrosine kinases and revealed that their terminations are regulated by Lyn-dependent (Syk and MAP kinase) and -independent ([Ca2+]i elevation and histamine release) mechanisms.
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Affiliation(s)
- Z i Honda
- Department of Internal Medicine, Faculty of Medicine, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113, Japan.
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17
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Wan Y, Bence K, Hata A, Kurosaki T, Veillette A, Huang XY. Genetic evidence for a tyrosine kinase cascade preceding the mitogen-activated protein kinase cascade in vertebrate G protein signaling. J Biol Chem 1997; 272:17209-15. [PMID: 9202044 DOI: 10.1074/jbc.272.27.17209] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The signal transduction pathway from heterotrimeric G proteins to the mitogen-activated protein kinase (MAPK) cascade is best understood in the yeast mating pheromone response, in which a serine/threonine protein kinase (STE20) serves as the critical linking component. Little is known in metazoans on how G proteins and the MAPK cascade are coupled. Here we provide genetic and biochemical evidence that a tyrosine kinase cascade bridges G proteins and the MAPK pathway in vertebrate cells. Targeted deletion of tyrosine kinase Csk in avian B lymphoma cells blocks the stimulation of MAPK by Gq-, but not Gi-, coupled receptors. In cells deficient in Bruton's tyrosine kinase (Btk), Gi-coupled receptors failed to activate MAPK, while Gq-coupled receptor-mediated stimulation is unaffected. Taken together with our previous data on tyrosine kinases Lyn and Syk, the Gq-coupled pathway requires tyrosine kinases Csk, Lyn, and Syk, while the Gi-coupled pathway requires tyrosine kinases Btk and Syk to feed into the MAPK cascade in these cells. The central role of Syk is further strengthened by data showing that Syk can bind to purified Lyn, Csk, or Btk.
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Affiliation(s)
- Y Wan
- Department of Physiology, Cornell University Medical College, New York, New York 10021, USA
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18
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Takaki S, Watts JD, Forbush KA, Nguyen NT, Hayashi J, Alberola-Ila J, Aebersold R, Perlmutter RM. Characterization of Lnk. An adaptor protein expressed in lymphocytes. J Biol Chem 1997; 272:14562-70. [PMID: 9169414 DOI: 10.1074/jbc.272.23.14562] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Stimulation of the T cell antigen receptor (TCR) activates a set of non-receptor protein tyrosine kinases that assist in delivering signals to the cell interior. Among the presumed substrates for these kinases, adaptor proteins, which juxtapose effector enzyme systems with the antigen receptor complex, figure prominently. Previous studies suggested that Lnk, a 38-kDa protein consisting of a single SH2 domain and a region containing potential tyrosine phosphorylation sites, might serve to join Grb2, phospholipase C-gamma1, and phosphatidylinositol 3-kinase to the TCR. To elucidate the physiological roles of Lnk in T cell signal transduction, we isolated the mouse Lnk cDNA, characterized the structure of the mouse Lnk gene, and generated transgenic mice that overproduce Lnk in thymocytes. Here we report that although Lnk becomes phosphorylated during T cell activation, it plays no limiting role in the TCR signaling process. Moreover, we have distinguished p38(Lnk) from the more prominent 36-kDa tyrosine phosphoproteins that appear in activated T cells. Together these studies suggest that Lnk participates in signaling from receptors other than antigen receptors in lymphocytes.
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Affiliation(s)
- S Takaki
- Howard Hughes Medical Institute, University of Washington, Seattle, Washington 98195, USA
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19
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Kokron CM, Bonilla FA, Oettgen HC, Ramesh N, Geha RS, Pandolfi F. Searching for genes involved in the pathogenesis of primary immunodeficiency diseases: lessons from mouse knockouts. J Clin Immunol 1997; 17:109-26. [PMID: 9083888 DOI: 10.1023/a:1027322314256] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- C M Kokron
- Division of Immunology, Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115-5724, USA
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20
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Davidson D, Chow LM, Veillette A. Chk, a Csk family tyrosine protein kinase, exhibits Csk-like activity in fibroblasts, but not in an antigen-specific T-cell line. J Biol Chem 1997; 272:1355-62. [PMID: 8995444 DOI: 10.1074/jbc.272.2.1355] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The Csk family of tyrosine protein kinases comprises two members named Csk and Chk. These enzymes phosphorylate the carboxyl-terminal tyrosine of Src-related kinases in vitro, thereby repressing their activity. Csk has been found to be necessary for normal embryonic development, and to be a potent negative regulator of antigen receptor signaling in T-lymphocytes. As the functions of Chk in mammalian cells are not known, we examined its ability to carry out Csk-like functions in vivo. Like p50csk, Chk reduced the elevated phosphotyrosine levels and the augmented activity of Src family kinases in Csk-deficient fibroblasts. Contrary to Csk, however, Chk was inefficient at repressing antigen receptor-induced signals in a T-cell line (BI-141). We also noted that Chk, but not Csk, failed to stably associate with cellular membranes following addition of a membrane targeting signal to its amino terminus. This observation suggested that Chk may contain dominant targeting sequences disallowing its recruitment to cellular membranes. Hence, these data demonstrate that Chk can mediate some, but not all, Csk-related functions in vivo. Moreover, they suggest that the "restricted" function of Chk may relate at least in part to its inability to be recruited to certain cellular locales.
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Affiliation(s)
- D Davidson
- McGill Cancer Centre, McGill University, Montréal, Canada
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21
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Palacios R, Imhof BA. Primitive lymphohematopoietic precursor cell lines generated in culture from day 7 early-mid-primitive streak stage mouse embryo. EMBO J 1996; 15:6869-76. [PMID: 9003763 PMCID: PMC452513] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
During mouse development, the first lymphohematopoietic precursor cells and myeloid or erythroid cell lineage-determined cells can be detected in the yolk sac at days 8-8.5 of gestation. The characteristics of the cells that give rise to these yolk sac primitive lymphohematopoietic cells and the molecular events controlling this process remain poorly defined. We show here that cell suspensions from day 7 early-mid-primitive streak stage embryo proper generated early immature PgP-1+ Joro 177+ Lin- hematopoietic cells and some Mac-1+ myeloid and TER 119+ erythroid cells after co-culture with the yolk sac-derived stromal cell line YS6 without addition of exogenous cytokines. Purified Lin- hematopoietic cells generated in these cultures did not express genes known to be transcribed at early stages of lymphoid, myeloid or erythroid cell differentiation and were able to give rise to T and B lymphocytes, myeloid cells and erythroid cells after appropriate further induction in vitro. Several cell lines were established in culture with a mixture of four cytokines from the PgP-1+ Joro 177+ Lin- cell population. The cell lines shared phenotypic and genotypic characteristics with the PgP-1+ Joro 177+ Lin- cell population generated in culture from day 7 embryo proper and they were able to reconstitute the lymphohematopoietic system of irradiated mice. Taken together these results support a model of lymphohematopoiesis in which cells from day 7 early-mid-primitive streak mouse embryo proper migrate and colonize the visceral yolk sac. There they generate primitive lymphohematopoietic precursor cells and the first erythroid and myeloid hematopoietic cells under the influence of yolk sac stromal cells like the YS6 cells described here.
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Affiliation(s)
- R Palacios
- The Department of Immunology, The University of Texas M.D. Anderson Cancer Center, Houston 77030, USA
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22
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Cloutier JF, Veillette A. Association of inhibitory tyrosine protein kinase p50csk with protein tyrosine phosphatase PEP in T cells and other hemopoietic cells. EMBO J 1996; 15:4909-18. [PMID: 8890164 PMCID: PMC452228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
p50csk is a tyrosine protein kinase (TPK) that represses the activity of Src family TPKs. We previously showed that Csk is a potent negative regulator of antigen receptor signaling in T lymphocytes and that its Src homology (SH) 3 and SH2 domains are required to inhibit these signals. To test the idea that the Csk SH3 and SH2 domains mediate interactions with other cellular proteins, we attempted to identify Csk-associated polypeptides using the yeast two-hybrid system. The results of our experiments demonstrated that Csk physically associates with PEP, a protein tyrosine phosphatase (PTP) expressed in hemopoietic cells. Further analyses revealed that this interaction was mediated by the Csk SH3 domain and by a proline-rich region (PPPLPERTP) in the non-catalytic C-terminal portion of PEP. The association between Csk and PEP was documented in transiently transfected Cos-1 cells and in a variety of cells of hemopoietic lineages, including T cells. Additional analyses demonstrated that the association between Csk and PEP is highly specific. Together, these data indicated that PEP may be an effector and/or a regulator of p50csk in T cells and other hemopoietic cells. Moreover, they allowed the identification of PEP as the first known ligand for the Csk SH3 domain.
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Affiliation(s)
- J F Cloutier
- McGill Cancer Centre, McGill University, Montreal, Canada
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23
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Abstract
Src is the best understood member of a family of 9 tyrosine kinases that regulates cellular responses to extracellular stimuli. Activated mutants of Src are oncogenic. Using Src as an example, and referring to other Src family members where appropriate, this review describes the structure of Src, the functions of the individual domains, the regulation of Src kinase activity in the cell, the selection of substrates, and the biological functions of Src. The review concentrates on developments in the last 6-7 years, and cites data resulting from the isolation and characterization of Src mutants, crystallographic studies of the structures of SH2, SH3 and tyrosine kinase domains, biochemical studies of Src kinase activity and binding properties, and the biology of transgenic and knockout mouse strains.
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Affiliation(s)
- M T Brown
- Fred Hutchinson Cancer Research Center, Seattle, WA 98104, USA
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24
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Catipović B, Schneck JP, Brummet ME, Marsh DG, Rafnar T. Csk is constitutively associated with a 60-kDa tyrosine-phosphorylated protein in human T cells. J Biol Chem 1996; 271:9698-703. [PMID: 8621646 DOI: 10.1074/jbc.271.16.9698] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The protein-tyrosine kinase Csk is one of the main down-regulators of the Src family of kinases. Csk may be involved in the down-regulation of T cell receptor (TCR) signaling by C-terminal tyrosine phosphorylation of Lck and Fyn; however, it is not known how Csk activity is regulated or how it targets these Src family members. We used Jurkat T cells and normal human T cells to examine proteins that bind to the SH2 domain of Csk. In both Jurkat and normal T cells, the Src homology 2 (SH2) domain of Csk bound constitutively to a tyrosine-phosphorylated protein of 60 kDa (p60). The 60-kDa protein was detected in Csk immunoprecipitates from both unstimulated and CD3-stimulated cells. In addition to p60, a protein of 190 kDa coprecipitated with Csk, and both proteins were phosphorylated on tyrosine residues by the immunocomplex. Small amounts of GTPase-activating protein (GAP) were detected in anti-Csk immunoprecipitates, suggesting that p60 may be a GAP-associated protein. Our data demonstrate that the SH2 domain of Csk specifically associates with at least two tyrosine-phosphorylated proteins in normal human T cells, that this association is independent of TCR/CD3 activation, and that Csk may be a part of a multiprotein complex containing GAP.
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Affiliation(s)
- B Catipović
- Division of Clinical Immunology, Johns Hopkins Asthma and Allergy Center, The John Hopkins University School of Medicine, Baltimore, Maryland 21224, USA
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25
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Abstract
The earliest steps along the pathway leading to T cells in mice and humans are reviewed. These are the steps between the multipotent hemopoietic stem cell (HSC) and the fully committed precursors undergoing T cell receptor (TCR) gene rearrangement. At this level significant differences between adult and fetal lymphopoiesis have been demonstrated. The extent of lymphoid commitment of precursors within bone marrow is still unresolved, although HSCs clearly undergo developmental changes before migration to the thymus. Both multipotent and T-restricted precursors have now been isolated from fetal blood, suggesting both may seed the thymus. Within the thymus, several minute but discrete populations of T precursors precede the stage of TCR gene rearrangement. They include precursors that are not exclusively T-lineage committed, although they are distinct from HSCs. These precursors have a potential to form NK cells, B cells, dendritic cells, and sometimes other myeloid cells. Some factors that control early lymphoid development are discussed, including IL-7 and the Ikaros transcription factors. These will eventually help to clarify the process of T-lineage commitment.
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Affiliation(s)
- K Shortman
- Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria, Australia
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26
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Abstract
B lymphopoiesis is regulated by multiple signals from stromal cell contact, soluble cytokines, antigen, and T helper cells. In vitro and biochemical experiments have implicated tyrosine kinases as key components of many of these signaling pathways. Genetic analysis of the role of these tyrosine kinases has been facilitated by recent advance in transgenic and gene targeting technology as well as by the identification of the genetic basis of several human and murine immune deficiencies. This review discusses the effect of gain and loss of function mutations of selected tyrosine kinases and their regulators and substrates on B cell development and function.
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Affiliation(s)
- A Satterthwaite
- Department of Microbiology and Molecular Genetics, University of California, Los Angeles 90095-1662, USA
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27
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Affiliation(s)
- J Chen
- Department of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA
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28
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Spanopoulou E. Cellular and molecular analysis of lymphoid development using Rag-deficient mice. Int Rev Immunol 1996; 13:257-88. [PMID: 8884425 DOI: 10.3109/08830189609061752] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The establishment of a functional immune system with diverse antigen receptors is dependent on the V(D)J recombination activating gene products Rag-1 and Rag-2. These two proteins constitute the key lymphoid components required for the activation of antigen receptor rearrangement. Both Rag-1 and Rag-2 are required for the catalysis of the initial stages of V(D)J recombination. Thus, functional disruption of either the Rag-1 or Rag-2 genes by homologous recombination, leads to immunodeficiency due to lymphoid arrest at a stage prior to the recombination of the antigen receptor loci. In Rag-deficient mice, both B- and T-cell differentiation is eliminated due to the absence of antigen receptors. Lymphoid development can be restored by the introduction of rearranged antigen receptor transgenes that give rise to monoclonal populations of fully mature B- or T-cells. The absence of the major conventional populations of B- and T-cells from the Rag-deficient mice provided an excellent background for studying the molecular and cellular mechanisms of lymphoid differentiation. The Rag-deficient background has been used as a system for: the functional analysis of Rag-1 and Rag-2; studying the developmental functions of antigen receptors and other molecules of the immune system; the molecular analysis of the early stages of the B- and T-cell lineages; the co-development of lymphocytes with stroma cells; the identification of minor subpopulations of the developing immune system; the involvement of lymphoid populations in the onset of pathogenesis. In addition, the development of the "blastocyst complementation assay" methodology, based on the phenotype of the Rag-/- mice, allowed the functional analysis of numerous lymphoid specific components.
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Affiliation(s)
- E Spanopoulou
- Mount Sinai School of Medicine, New York, NY 10029, USA
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29
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Mittrücker HW, Pfeffer K, Schmits R, Mak TW. T-lymphocyte development and function in gene-targeted mutant mice. Immunol Rev 1995; 148:115-50. [PMID: 8825285 DOI: 10.1111/j.1600-065x.1995.tb00096.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- H W Mittrücker
- Department of Medical Biophysics, University of Toronto, Ontario, Canada
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30
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Cloutier JF, Chow LM, Veillette A. Requirement of the SH3 and SH2 domains for the inhibitory function of tyrosine protein kinase p50csk in T lymphocytes. Mol Cell Biol 1995; 15:5937-44. [PMID: 7565746 PMCID: PMC230845 DOI: 10.1128/mcb.15.11.5937] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Previous studies from our laboratory have shown that the cytosolic tyrosine protein kinase p50csk is involved in the negative regulation of T-cell activation (L.M. L. Chow, M. Fournel, D. Davidson, and A. Veillette, Nature [London] 365:156-160, 1993). This function most probably reflects the ability of Csk to phosphorylate the inhibitory carboxy-terminal tyrosine of p56lck and p59fynT, two Src-related enzymes abundantly expressed in T lymphocytes. Herein, we have attempted to better understand the mechanisms by which Csk participates in the inhibitory phase of T-cell receptor signalling. Our results demonstrated that the Src homology 3 (SH3) and SH2 domains of p50csk are crucial for its negative impact on T-cell receptor-mediated signals. As these two sequences were not essential for phosphorylation of the carboxy-terminal tyrosine of a Src-like product in yeast cells, we postulated that they mediate protein-protein interactions allowing the recruitment of p50csk in the vicinity of activated Lck and/or FynT in T cells. In complementary studies, it was observed that linkage of a constitutive membrane targeting signal to the amino terminus of Csk rescued the deleterious impact of a point mutation in the SH2 domain of p50csk. This observation suggested that the SH2 sequence is in part necessary to translocate p50csk from the cytoplasm to the plasma membrane, where Src-related enzymes are located. Nevertheless, constitutive membrane localization was unable to correct the effect of complete deletion of the SH3 or SH2 sequence, implying that these domains provide additional functions necessary for the biological activity of p50csk.
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Affiliation(s)
- J F Cloutier
- McGill Cancer Centre, McGill University, Montréal, Québec, Canada
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31
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Hanke JH, Pollok BA, Changelian PS. Role of tyrosine kinases in lymphocyte activation: targets for drug intervention. Inflamm Res 1995; 44:357-71. [PMID: 8846193 DOI: 10.1007/bf01797862] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Recent developments in our understanding of lymphocyte receptor-associated signalling events have offered many new potential targets for modifying antigen and cytokine receptor signalling events in immune-related diseases such as allergy, autoimmunity and transplant rejection. As discussed below, these targets are largely tissue-restricted and are functionally confined to a limited set of receptors. Therefore, it is anticipated that selective inhibitors of these signalling events would offer safe and effective therapies for immunologically-based diseases. First, we review T and B cell antigen receptor signalling as targets for inhibiting lymphocyte responses. Second, targets in lymphocyte cytokine receptor signalling pathways are discussed. Finally, we review strategies for inhibition of receptor signalling.
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Affiliation(s)
- J H Hanke
- Pfizer Central Research, Groton, CT 06340, USA
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32
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Kerner JD, Appleby MW, Mohr RN, Chien S, Rawlings DJ, Maliszewski CR, Witte ON, Perlmutter RM. Impaired expansion of mouse B cell progenitors lacking Btk. Immunity 1995; 3:301-12. [PMID: 7552995 DOI: 10.1016/1074-7613(95)90115-9] [Citation(s) in RCA: 254] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Mutations in the gene encoding the protein tyrosine kinase Btk are associated with the human B cell immunodeficiency X-linked agammaglobulinemia (XLA). In the mouse, a point mutation in the Btk pleckstrin homology domain segregates with a milder X-linked immunodeficiency (xid). To assess the importance of Btk function in murine lymphopoiesis, we generated multiple embryonic stem cell clones bearing a targeted disruption of the btk gene and examined their potential to produce lymphocytes in both C57BL/6 and RAG2-/- host chimeric animals. These mice provide a complementary set of in vivo competition assays that formally establish the genetic basis for the xid phenotype. Although the null mutation yields a phenotype quite similar to that of xid, it also compromises expansion of B cell precursors. Our results suggest that the murine and human consequences of Btk deficiency differ only quantitatively, and represent the same disease process.
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Affiliation(s)
- J D Kerner
- Department of Immunology, University of Washington, Seattle 98195, USA
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