241 human active and 13 inactive phosphatases in total;
194 phosphatases have substrate data;
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336 protein substrates;
83 non-protein substrates;
1215 dephosphorylation interactions;
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299 KEGG pathways;
876 Reactome pathways;
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last scientific update: 11 Mar, 2019
last maintenance update: 01 Sep, 2023
Cytoplasm Cellmembrane Note=In quiescent T-lymphocytes, itis cytoplasmic Upon TCR activation, it is recruited at the plasmamembrane by interacting with CD247/CD3Z Colocalizes together withRHOH in the immunological synapse RHOH is required for its properlocalization to the cell membrane and cytoskeleton fractions inthe thymocytes (By similarity)
Function (UniProt annotation)
Tyrosine kinase that plays an essential role inregulation of the adaptive immune response Regulates motility,adhesion and cytokine expression of mature T-cells, as well asthymocyte development Contributes also to the development andactivation of primary B-lymphocytes When antigen presenting cells(APC) activate T-cell receptor (TCR), a serie of phosphorylationslead to the recruitment of ZAP70 to the doubly phosphorylated TCRcomponent CD247/CD3Z through ITAM motif at the plasma membraneThis recruitment serves to localization to the stimulated TCR andto relieve its autoinhibited conformation Release of ZAP70 activeconformation is further stabilized by phosphorylation mediated byLCK Subsequently, ZAP70 phosphorylates at least 2 essentialadapter proteins: LAT and LCP2 In turn, a large number ofsignaling molecules are recruited and ultimately lead tolymphokine production, T-cell proliferation and differentiationFurthermore, ZAP70 controls cytoskeleton modifications, adhesionand mobility of T-lymphocytes, thus ensuring correct delivery ofeffectors to the APC ZAP70 is also required for TCR-CD247/CD3Zinternalization and degradation through interaction with the E3ubiquitin-protein ligase CBL and adapter proteins SLA and SLA2Thus, ZAP70 regulates both T-cell activation switch on and switchoff by modulating TCR expression at the T-cell surface Duringthymocyte development, ZAP70 promotes survival and cell-cycleprogression of developing thymocytes before positive selection(when cells are still CD4/CD8 double negative) Additionally,ZAP70-dependent signaling pathway may also contribute to primaryB-cells formation and activation through B-cell receptor (BCR)
Catalytic Activity (UniProt annotation)
ATP + a [protein]-L-tyrosine = ADP + a[protein]-L-tyrosine phosphate
The Ras proteins are GTPases that function as molecular switches for signaling pathways regulating cell proliferation, survival, growth, migration, differentiation or cytoskeletal dynamism. Ras proteins transduce signals from extracellular growth factors by cycling between inactive GDP-bound and active GTP-bound states. The exchange of GTP for GDP on RAS is regulated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Activated RAS (RAS-GTP) regulates multiple cellular functions through effectors including Raf, phosphatidylinositol 3-kinase (PI3K) and Ral guanine nucleotide-dissociation stimulator (RALGDS).
Nuclear factor-kappa B (NF-kappa B) is the generic name of a family of transcription factors that function as dimers and regulate genes involved in immunity, inflammation and cell survival. There are several pathways leading to NF-kappa B-activation. The canonical pathway is induced by tumour necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1) or byproducts of bacterial and viral infections. This pathway relies on IKK- mediated IkappaB-alpha phosphorylation on Ser32 and 36, leading to its degradation, which allows the p50/p65 NF-kappa B dimer to enter the nucleus and activate gene transcription. Atypical pathways are IKK-independent and rely on phosphorylation of IkappaB-alpha on Tyr42 or on Ser residues in IkappaB-alpha PEST domain. The non-canonical pathway is triggered by particular members of the TNFR superfamily, such as lymphotoxin-beta (LT-beta) or BAFF. It involves NIK and IKK-alpha-mediated p100 phosphorylation and processing to p52, resulting in nuclear translocation of p52/RelB heterodimers.
Natural killer (NK) cells are lymphocytes of the innate immune system that are involved in early defenses against both allogeneic (nonself) cells and autologous cells undergoing various forms of stress, such as infection with viruses, bacteria, or parasites or malignant transformation. Although NK cells do not express classical antigen receptors of the immunoglobulin gene family, such as the antibodies produced by B cells or the T cell receptor expressed by T cells, they are equipped with various receptors whose engagement allows them to discriminate between target and nontarget cells. Activating receptors bind ligands on the target cell surface and trigger NK cell activation and target cell lysis. However Inhibitory receptors recognize MHC class I molecules (HLA) and inhibit killing by NK cells by overruling the actions of the activating receptors. This inhibitory signal is lost when the target cells do not express MHC class I and perhaps also in cells infected with virus, which might inhibit MHC class I exprssion or alter its conformation. The mechanism of NK cell killing is the same as that used by the cytotoxic T cells generated in an adaptive immune response; cytotoxic granules are released onto the surface of the bound target cell, and the effector proteins they contain penetrate the cell membrane and induce programmed cell death.
Immunity to different classes of microorganisms is orchestrated by separate lineages of effector T helper (TH)-cells, which differentiate from naive CD4+ precursor cells in response to cues provided by antigen presenting cells (APC) and include T helper type 1 (Th1) and Th2. Th1 cells are characterized by the transcription factor T-bet and signal transducer and activator of transcription (STAT) 4, and the production of IFN-gamma. These cells stimulate strong cell-mediated immune responses, particularly against intracellular pathogens. On the other hand, transcription factors like GATA-3 and STAT6 drive the generation of Th2 cells that produce IL-4, IL-5 and IL-13 and are necessary for inducing the humoral response to combat parasitic helminths (type 2 immunity) and isotype switching to IgG1 and IgE. The balance between Th1/Th2 subsets determines the susceptibility to disease states, where the improper development of Th2 cells can lead to allergy, while an overactive Th1 response can lead to autoimmunity.
Interleukin (IL)-17-producing helper T (Th17) cells serve as a subset of CD4+ T cells involved in epithelial cell- and neutrophil mediated immune responses against extracellular microbes and in the pathogenesis of autoimmune diseases. In vivo, Th17 differentiation requires antigen presentation and co-stimulation, and activation of antigen presenting-cells (APCs) to produce TGF-beta, IL-6, IL-1, IL-23 and IL-21. This initial activation results in the activation and up-regulation of STAT3, ROR(gamma)t and other transcriptional factors in CD4+ T cells, which bind to the promoter regions of the IL-17, IL-21 and IL-22 genes and induce IL-17, IL-21 and IL-22. In contrast, the differentiation of Th17 cells and their IL-17 expression are negatively regulated by IL-2, Th2 cytokine IL-4, IL-27 and Th1 cytokine IFN-gamma through STAT5, STAT6 and STAT1 activation, respectively. Retinoid acid and the combination of IL-2 and TGF-beta upregulate Foxp3, which also downregulates cytokines like IL-17 and IL-21. The inhibition of Th17 differentiation may serve as a protective strategy to 'fine-tune' the expression IL-17 so it does not cause excessive inflammation. Thus, balanced differentiation of Th cells is crucial for immunity and host protection.
Activation of T lymphocytes is a key event for an efficient response of the immune system. It requires the involvement of the T-cell receptor (TCR) as well as costimulatory molecules such as CD28. Engagement of these receptors through the interaction with a foreign antigen associated with major histocompatibility complex molecules and CD28 counter-receptors B7.1/B7.2, respectively, results in a series of signaling cascades. These cascades comprise an array of protein-tyrosine kinases, phosphatases, GTP-binding proteins and adaptor proteins that regulate generic and specialised functions, leading to T-cell proliferation, cytokine production and differentiation into effector cells.
Primary immunodeficiencies (PIs) are a heterogeneous group of disorders, which affect cellular and humoral immunity or non-specific host defense mechanisms mediated by complement proteins, and cells such as phagocytes and natural killer (NK) cells. These disorders of the immune system cause increased susceptibility to infection, autoimmune disease, and malignancy. Most of PIs are due to genetic defects that affect cell maturation or function at different levels during hematopoiesis. Disruption of the cellular immunity is observed in patients with defects in T cells or both T and B cells. These cellular immunodeficiencies comprise 20% of all PIs. Disorders of humoral immunity affect B-cell differentiation and antibody production. They account for 70% of all PIs.
The dual phosphorylated ITAMs recruit Syk kinase ZAP-70 via their tandem SH2 domains (step 4). ZAP-70 subsequently undergoes phosphorylation on multiple tyrosine residues for further activation. ZAP-70 includes both positive and negative regulatory sites. Tyrosine 493 is a conserved regulatory site found within the activation loop of the kinase domain. This site has shown to be a positive regulatory site required for ZAP-70 kinase activity and is phosphorylated by Lck (step 5). This phosphorylation contributes to the active conformation of the catalytic domain. Later ZAP-70 undergoes trans-autophosphorylation at Y315 and Y319 (step 6). These sites appear to be positive regulatory sites. ZAP-70 achieves its full activation after the trans-autophosphorylation. Activated ZAP-70 along with Lck phosphorylates the multiple tyrosine residues in the adaptor protein LAT (step 7)
In addition to serving as a scaffold via auto-phosphorylation, ZAP-70 also phosphorylates a restricted set of substrates following TCR stimulation - including LAT and SLP-76. These substrates have been recognized to play pivotal role in TCR signaling by releasing second messengers. When phosphorylated, LAT and SLP-76 act as adaptor proteins which serve as nucleation points for the construction of a higher order signalosome: GADS, PLC-gamma1 and GRB2 bind to the LAT on the phosphorylated tyrosine residues (steps 8 and 13). SLP-76 and SOS are then moved to the signalosome by interacting with the SH3 domains of GRB2 and GADS via their proline rich sequences (step 9). Three SLP-76 acidic domain N-term tyrosine residues are phosphorylated by ZAP-70, once SLP-76 binds to GADS (step 10). These phospho-tyrosine residues act as binding sites to the SH2 domains of PLC-gamma1, Vav and Itk (steps 11 and 12).
PLC-gamma1 is activated by dual phosphorylation on the tyrosine residues at positions 771, 783 and 1254 by Itk and ZAP-70 (step 14). Phosphorylated PLC-gamma1 subsequently detaches from LAT and SLP-76 and translocates to the plasma membrane by binding to phosphatidylinositol-4,5-bisphosphate (PIP2) via its PH domain (step 15). PLC-gamma1 goes on to hydrolyse PIP2 to second messengers DAG and IP3. These second messengers are involved in PKC and NF-kB activation and calcium mobilization (step 16)
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