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lck
Lck (or lymphocyte-specific protein tyrosine kinase) is a 56 kDa protein that is found inside specialized cells of the immune system called lymphocytes. Lck is a tyrosine kinase, which phosphorylates tyrosine residues of certain proteins involved in the intracellular signaling pathways of these lymphocytes. It is a member of the Src family of tyrosine kinases.
== T cell signaling ==
Lck is most commonly found in T cells. It associates with the cytoplasmic tails of the CD4 and CD8 co-receptors on T helper cells and cytotoxic T cells, respectively, to assist signaling from the T cell receptor (TCR) complex. When the T cell receptor is engaged by the specific antigen presented by MHC, Lck acts to phosphorylate the intracellular chains of the CD3 and ζ-chains of the TCR complex, allowing another cytoplasmic tyrosine kinase called ZAP-70 to bind to them. Lck then phosphorylates and activates ZAP-70, which in turn phosphorylates another molecule in the signaling cascade called LAT (short for Linker of Activated T cells), a transmembrane protein that serves as a docking site for a number of other proteins, the most important of which are Shc-Grb2-SOS, PI3K, and phospholipase C (PLC).
The tyrosine phosphorylation cascade initiated by Lck culminates in the intracellular mobilization of calcium (Ca2+) ions and activation of important signaling cascades within the lymphocyte. These include the Ras-MEK-ERK pathway, which goes on to activate certain transcription factors such as NFAT, NF-κB, and AP-1. These transcription factors regulate the production of a plethora of gene products, most notable, cytokines such as Interleukin-2 that promote long-term proliferation and differentiation of the activated lymphocytes.
The function of Lck has been studied using several biochemical methods, including gene knockout (knock-out mice), Jurkat cells deficient in Lck (JCaM1.6), and siRNA-mediated RNA interference.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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