Lck

LCK
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 1BHF, 1BHH, 1CWD, 1CWE, 1FBZ, 1H92, 1IJR, 1KIK, 1LCJ, 1LCK, 1LKK, 1LKL, 1Q68, 1Q69, 1QPC, 1QPD, 1QPE, 1QPJ, 1X27, 2IIM, 2OF2, 2OF4, 2OFU, 2OFV, 2OG8, 2PL0, 2ZM1, 2ZM4, 2ZYB, 3AC1, 3AC2, 3AC3, 3AC4, 3AC5, 3AC8, 3ACJ, 3ACK, 3AD4, 3AD5, 3AD6, 3B2W, 3BRH, 3BYM, 3BYO, 3BYS, 3BYU, 3KMM, 3KXZ, 3LCK, 3MPM, 4D8K, 4C3F
Identifiers
Aliases	LCK, LCK proto-oncogene, Src family tyrosine kinase, IMD22, LSK, YT16, p56lck, pp58lck
External IDs	OMIM: 153390 MGI: 96756 HomoloGene: 3911 GeneCards: LCK
Gene location (Human) Chr. Chromosome 1 (human)[1] Band No data available Start 32,251,239 bp[1] End 32,286,165 bp[1]
Gene location (Mouse) Chr. Chromosome 4 (mouse)[2] Band No data available Start 129,548,344 bp[2] End 129,573,641 bp[2]
RNA expression pattern More reference expression data
Gene ontology Molecular function • transferase activity • nucleotide binding • protein kinase activity • CD4 receptor binding • ATPase binding • SH2 domain binding • CD8 receptor binding • phosphatidylinositol 3-kinase binding • protein C-terminus binding • protein binding • identical protein binding • protein phosphatase binding • ATP binding • protein kinase binding • phosphatidylinositol-4,5-bisphosphate 3-kinase activity • kinase activity • protein serine/threonine phosphatase activity • non-membrane spanning protein tyrosine kinase activity • phosphotyrosine residue binding • protein tyrosine kinase activity • T cell receptor binding Cellular component • cytoplasm • cytosol • membrane • extrinsic component of cytoplasmic side of plasma membrane • immunological synapse • extracellular exosome • pericentriolar material • membrane raft • plasma membrane Biological process • B cell receptor signaling pathway • release of sequestered calcium ion into cytosol • hemopoiesis • phosphorylation • transmembrane receptor protein tyrosine kinase signaling pathway • positive regulation of T cell receptor signaling pathway • T cell costimulation • regulation of defense response to virus by virus • platelet activation • T cell differentiation • regulation of cell proliferation • cellular zinc ion homeostasis • regulation of lymphocyte activation • peptidyl-tyrosine autophosphorylation • T cell receptor signaling pathway • positive regulation of intrinsic apoptotic signaling pathway • phosphatidylinositol-mediated signaling • leukocyte migration • positive regulation of T cell activation • protein dephosphorylation • regulation of phosphatidylinositol 3-kinase signaling • innate immune response • phosphatidylinositol phosphorylation • viral process • protein phosphorylation • activation of cysteine-type endopeptidase activity involved in apoptotic process • response to drug • cell migration • peptidyl-tyrosine phosphorylation • interleukin-7-mediated signaling pathway Sources:Amigo / QuickGO
Orthologs
Species	Human	Mouse
Entrez	3932	16818
Ensembl	ENSG00000182866	ENSMUSG00000000409
UniProt	P06239	P06240
RefSeq (mRNA)	NM_001042771 NM_005356 NM_001330468	NM_001162432 NM_001162433 NM_010693
RefSeq (protein)	NP_001036236 NP_001317397 NP_005347	NP_001155904 NP_001155905 NP_034823
Location (UCSC)	Chr 1: 32.25 – 32.29 Mb	Chr 1: 129.55 – 129.57 Mb
PubMed search	[3]	[4]
Wikidata
View/Edit Human View/Edit Mouse

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,^[5][6] 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). Additionally, upon T cell activation, a fraction of kinase active Lck, translocates from outside of lipid rafts (LR) to inside lipid rafts where it interacts with and activates LR-resident Fyn, which is involved in further downstream signaling activation.^[7][8]

The tyrosine phosphorylation cascade initiated by Lck and Fyn 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.

Structure

Lck is a 56-kilodalton protein. The N-terminal tail of Lck is myristoylated and palmitoylated, which tethers the protein to the plasma membrane of the cell. The protein furthermore contains a SH3 domain, a SH2 domain and in the C-terminal part the tyrosine kinase domain. The two main phosphorylation sites on Lck are tyrosines 394 and 505. The former is an autophosphorylation site and is linked to activation of the protein. The latter is phosphorylated by Csk, which inhibits Lck because the protein folds up and binds its own SH2 domain. Lck thus serves as an instructive example that protein phosphorylation may result in both activation and inhibition.

Substrates

Lck tyrosine phosphorylates a number of proteins, the most important of which are the CD3 receptor, CEACAM1, ZAP-70, SLP-76, the IL-2 receptor, Protein kinase C, ITK, PLC, SHC, RasGAP, Cbl, Vav1, and PI3K.

Inhibition

In resting T cells, Lck is constitutively inhibited by Csk phosphorylation on tyrosine 505. Lck is also inhibited by SHP-1 dephosphorylation on tyrosine 394. Lck can also be inhibited by Cbl ubiquitin ligase, which is part of the ubiquitin-mediated pathway.^[9]

Interactions

Lck has been shown to interact with:

See also

• Tyrosine kinase
• T cell

References

Further reading

External links

• lck Kinase at the US National Library of Medicine Medical Subject Headings (MeSH)