LCK Antibody – Mouse Monoclonal

Function: Non-receptor tyrosine-protein kinase that plays an essential role in the selection and maturation of developing T-cells in the thymus and in the function of mature T-cells. Plays a key role in T-cell antigen receptor (TCR)-linked signal transduction pathways. Constitutively associated with the cytoplasmic portions of the CD4 and CD8 surface receptors. Association of the TCR with a peptide antigen-bound MHC complex facilitates the interaction of CD4 and CD8 with MHC class II and class I molecules, respectively, thereby recruiting the associated LCK protein to the vicinity of the TCR/CD3 complex. LCK then phosphorylates tyrosines residues within the immunoreceptor tyrosine-based activation motifs (ITAM) of the cytoplasmic tails of the TCR-gamma chains and CD3 subunits, initiating the TCR/CD3 signaling pathway. Once stimulated, the TCR recruits the tyrosine kinase ZAP70, that becomes phosphorylated and activated by LCK. Following this, a large number of signaling molecules are recruited, ultimately leading to lymphokine production. LCK also contributes to signaling by other receptor molecules. Associates directly with the cytoplasmic tail of CD2, which leads to hyperphosphorylation and activation of LCK. Also plays a role in the IL2 receptor-linked signaling pathway that controls the T-cell proliferative response. Binding of IL2 to its receptor results in increased activity of LCK. Is expressed at all stages of thymocyte development and is required for the regulation of maturation events that are governed by both pre-TCR and mature alpha beta TCR. Phosphorylates other substrates including RUNX3, PTK2B/PYK2, the microtubule-associated protein MAPT, RHOH or TYROBP

By similarity.

Catalytic activity: ATP + a [protein]-L-tyrosine = ADP + a [protein]-L-tyrosine phosphate.

Enzyme regulation: The relative activities of the inhibitory tyrosine-protein kinase CSK and the activating tyrosine-protein phosphatase PTPRC/CD45 determine the level of LCK activity. These interactions allow rapid and efficient activation of LCK in response to TCR stimulation

By similarity. Ref.1

Subunit structure: Binds to the cytoplasmic domain of cell surface receptors, such as AXL, CD2, CD4, CD5, CD8, CD44, CD45 and CD122. Also binds to effector molecules, such as PI4K, VAV1, RASA1, FYB and to other protein kinases including CDK1, RAF1, ZAP70 and SYK. Binds to phosphatidylinositol 3'-kinase (PI3K) from T-lymphocytes through its SH3 domain and to the tyrosine phosphorylated form of KHDRBS1/p70 through its SH2 domain. Interacts with SQSTM1. Interacts with phosphorylated LIME1. Interacts with CBLB and PTPRH. Interacts with RUNX3. Forms a signaling complex with EPHA1, PTK2B AND PI3-KINASE; upon activation by EFNA1 which may regulate T-lymphocytes migration. Associates with ZAP70 and RHOH; these interactions allow LCK-mediated RHOH and CD3 subunit phosphorylations in the presence of functional ZAP70

By similarity. Interacts with Saimiriine herpesvirus 2 TIP. Ref.1

Subcellular location: Cytoplasm

By similarity. Cell membrane; Lipid-anchor; Cytoplasmic side

By similarity. Note: Present in lipid rafts in an inactive form

By similarity.

Tissue specificity: Expressed specifically in lymphoid cells.

Developmental stage: Levels remain relatively constant throughout T-cell ontogeny.

Domain: The SH2 domain mediates interaction with SQSTM1. Interaction is regulated by Ser-59 phosphorylation

By similarity.

Post-translational modification: Autophosphorylated on Tyr-394, increasing enzymatic activity, this site is dephosphorylated by PTN22. Phosphorylated on Tyr-505 by CSK, decreasing activity. Dephosphorylated by PTPRC/CD45. Dephosphorylation at Tyr-394 by PTPN2 negatively regulates T-cells differentiation

By similarity.Myristoylation is required prior to palmitoylation

By similarity.Palmitoylation regulates subcellular location

By similarity.

Sequence similarities: Belongs to the protein kinase superfamily. Tyr protein kinase family.Contains 1 protein kinase domain.Contains 1 SH2 domain.Contains 1 SH3 domain.

Caution: LCK seems to be active in all vertebrates, except in squirrel monkey T-cells, in which it is inactivated. The reason seems to be that squirrel monkeys are the natural host for Saimiriine herpesvirus 2, which is able to efficiently transform T-cells through a mechanism involving viral Tip/ host LCK interaction. Its inactivation may a mechanism that specifically counteracts the transformation effects of viral Tip.