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SEA Antagonizes the Imatinib-Meditated Inhibitory Effects on T Cell Activation via the TCR Signaling Pathway

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      The BCR-ABL kinase inhibitor imatinib is highly effective in the treatment of chronic myeloid leukemia (CML). However, long-term imatinib treatment induces immunosuppression, which is mainly due to T cell dysfunction. Imatinib can reduce TCR-triggered T cell activation by inhibiting the phosphorylation of tyrosine kinases such as Lck, ZAP70, LAT, and PLC γ 1 early in the TCR signaling pathway. The purpose of this study was to investigate whether the superantigen SEA, a potent T cell stimulator, can block the immunosuppressive effects of imatinib on T cells. Our data show that the exposure of primary human T cells and Jurkat cells to SEA for 24 h leads to the upregulation of the Lck and ZAP70 proteins in a dose-dependent manner. T cells treated with SEA prior to TCR binding had increased the tyrosine phosphorylation of Lck, ZAP70, and PLC γ 1. Pretreatment with SEA prevents the inhibitory effects of imatinib on TCR signaling, which leads to T cell proliferation and IL-2 production. It is conceivable that SEA antagonizes the imatinib-mediated inhibition of T cell activation and proliferation through the TCR signaling pathway.

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      Most cited references 51

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      The bacterial superantigen and superantigen-like proteins.

      The bacterial superantigens are protein toxins that bind to major histocompatibility complex class II and T-cell receptor to stimulate large numbers of T cells. The majority are produced by the Gram-positive organisms Staphylococcus aureus and Streptococcus pyogenes and are the causative agents in toxic shock syndrome, an acute disease caused by the sudden and massive release of T-cell cytokines into the blood stream. The structure and function of the superantigens has revealed a common architecture that is also shared by another group of staphylococcal virulence factors called the superantigen-like proteins (SSL). Together, this family of structurally related molecules highlights how a common pathogenic organism has employed a simple but adaptable protein to generate an armamentarium of potent defense molecules designed to target of the innate and adaptive immune response.
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        Crystal structures of the kinase domain of c-Abl in complex with the small molecule inhibitors PD173955 and imatinib (STI-571).

        The inadvertent fusion of the bcr gene with the abl gene results in a constitutively active tyrosine kinase (Bcr-Abl) that transforms cells and causes chronic myelogenous leukemia. Small molecule inhibitors of Bcr-Abl that bind to the kinase domain can be used to treat chronic myelogenous leukemia. We report crystal structures of the kinase domain of Abl in complex with two such inhibitors, imatinib (also known as STI-571 and Gleevec) and PD173955 (Parke-Davis). Both compounds bind to the canonical ATP-binding site of the kinase domain, but they do so in different ways. As shown previously in a crystal structure of Abl bound to a smaller variant of STI-571, STI-571 captures a specific inactive conformation of the activation loop of Abl in which the loop mimics bound peptide substrate. In contrast, PD173955 binds to a conformation of Abl in which the activation loop resembles that of an active kinase. The structure suggests that PD173955 would be insensitive to whether the conformation of the activation loop corresponds to active kinases or to that seen in the STI-571 complex. In vitro kinase assays confirm that this is the case and indicate that PD173955 is at least 10-fold more inhibitory than STI-571. The structures suggest that PD173955 achieves its greater potency over STI-571 by being able to target multiple forms of Abl (active or inactive), whereas STI-571 requires a specific inactive conformation of Abl.
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          T-cell receptor proximal signaling via the Src-family kinases, Lck and Fyn, influences T-cell activation, differentiation, and tolerance.

          T-cell development in the thymus and activation of mature T cells in secondary lymphoid organs requires the ability of cells to respond appropriately to environmental signals at multiple stages of their development. The process of thymocyte selection insures a functional T-cell repertoire, while activation of naive peripheral T cells induces proliferation, gain of effector function, and, ultimately, long-lived T-cell memory. The T-cell immune response is initiated upon engagement of the T-cell receptor (TCR) and coreceptor, CD4 or CD8, by cognate antigen/major histocompatibility complexes presented by antigen-presenting cells. TCR/coreceptor engagement induces the activation of biochemical signaling pathways that, in combination with signals from costimulator molecules and cytokine receptors, direct the outcome of the response. Activation of the src-family kinases p56(lck) (Lck) and p59(fyn) (Fyn) is central to the initiation of TCR signaling pathways. This review focuses on our current understanding of the mechanisms by which these two proteins orchestrate T-cell function.

            Author and article information

            1Department of Microbiology and Immunology, Medical College, Jinan University, Guangzhou 510632, China
            2Quanzhou Medical college, Quanzhou 362000, China
            3Institute of Hematology, Medical College, Jinan university, Guangzhou 510632, China
            4Key Laboratory for Regenerative Medicine of Ministry of Education, Guangzhou 510632, China
            Author notes

            Academic Editor: Masahisa Jinushi

            Biomed Res Int
            Biomed Res Int
            BioMed Research International
            Hindawi Publishing Corporation
            2 January 2014
            : 2014
            Copyright © 2014 Guanming Wang et al.

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

            Funded by: National Natural Science Foundation of China
            Award ID: 81270604
            Research Article


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