ZAP-70 (Zeta-chain-associated protein kinase 70) is a protein normally expressed near the surface membrane of lymphocytes (T cells, natural killer cells, and a subset of B cells).[5] It is most prominently known to be recruited upon antigen binding to the T cell receptor (TCR), and it plays a critical role in T cell signaling.

Quick Facts Available structures, PDB ...
ZAP70
Available structures
PDBOrtholog search: PDBe RCSB
Identifiers
AliasesZAP70, SRK, STCD, STD, TZK, ZAP-70, zeta chain of T cell receptor associated protein kinase 70kDa, zeta chain of T cell receptor associated protein kinase 70, zeta chain of T-cell receptor associated protein kinase 70, IMD48, ADMIO2
External IDsOMIM: 176947; MGI: 99613; HomoloGene: 839; GeneCards: ZAP70; OMA:ZAP70 - orthologs
Orthologs
SpeciesHumanMouse
Entrez
Ensembl
UniProt
RefSeq (mRNA)

NM_001079
NM_207519
NM_001378594

NM_009539
NM_001289612
NM_001289765
NM_001289766

RefSeq (protein)

NP_001070
NP_997402
NP_001365523

NP_001276541
NP_001276694
NP_001276695
NP_033565

Location (UCSC)Chr 2: 97.71 – 97.74 MbChr 1: 36.8 – 36.82 Mb
PubMed search[3][4]
Wikidata
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ZAP-70 was initially discovered in TCR-stimulated Jurkat cells, an immortal line of human T lymphocytes, in 1991.[6] Its molecular weight is 70 kDa, and it is a member of the protein-tyrosine kinase family and is a close homolog of SYK. SYK and ZAP70 share a common evolutionary origin and split from a common ancestor in the jawed vertebrates. [7] The importance of ZAP-70 in T cell activation was determined when comparing ZAP-70 expression in patients with SCID (severe combined immunodeficiency).[6] ZAP-70 deficient individuals were found to have no functioning T cells in their peripheral blood, suggesting that ZAP-70 is a critical component of T cell activation and development.[6]

ZAP-70 expression in B cells is correlated with the development of chronic lymphocytic leukemia (CLL).

Function

The T cell receptor has no innate enzymatic activity. Due to this, T cell receptors rely on signaling molecules to transduce a signal from the cell membrane. ZAP-70 is a critical cytoplasmic tyrosine kinase that initiates a signal pathway downstream of an activated T cell receptor.[8]

T lymphocytes are activated by engagement of the T cell receptor with processed antigen fragments presented by professional antigen presenting cells (i.e. macrophages, dendritic cells, Langerhans cells and B cells) via the MHC. Upon this activation, the TCR co-receptor CD4 (expressed on T helper cells) or CD8 (expressed on cytotoxic T cells) binds to the MHC, activating the co-receptor associated tyrosine kinase Lck. Lck is moved near the CD3 complex and phosphorylates the tyrosines in the immunoreceptor tyrosine-based activation motifs (ITAMS), creating a docking site for ZAP-70.[9] The most important member of the CD3 family is CD3-zeta, to which ZAP-70 binds (hence the abbreviation). The tandem SH2-domains of ZAP-70 are engaged by the doubly phosphorylated ITAMs of CD3-zeta, which positions ZAP-70 to phosphorylate the transmembrane protein linker for activation of T cells (LAT).[9] Phosphorylated LAT, in turn, serves as a docking site to which a number of signaling proteins bind, including the SH2-domain-containing leukocyte protein of 76 kDa (SLP-76).[9] SLP-76 is also phosphorylated by ZAP-70, which requires its activation by Src family kinases.[10] The final outcome of T cell activation is the transcription of several gene products which allow the T cells to differentiate, proliferate, and secrete a number of cytokines.

Clinical Significance

Due to its role in lymphocyte signaling, ZAP-70 has been associated with several diseases affecting lymphocytes. ZAP-70 expression is a significant indicator of the survival of lymphocytes and has been notably associated with chronic lymphocytic leukemia (CLL).[11] CLL is a cancer that develops from overproduction of B cells in the bone marrow.

In people with CLL, higher levels of ZAP-70 confers a worse prognosis; CLL patients that are positive for the marker ZAP-70 have an average survival of 8 years, whereas those that are negative for ZAP-70 have an average survival of more than 25 years. Many patients, especially older ones, with slowly progressing disease can be reassured and may not need any treatment in their lifetimes.[12] In individuals with CLL, higher levels of ZAP-70 is associated with a higher number of malignant B cells activated.[5] Increased expression of ZAP-70 in B cell malignancies is correlated with increased association between malignant B cells and the immune environment, suggesting a complex role for ZAP-70 in B cell signaling.[5]

In systemic lupus erythematosus, the Zap-70 receptor pathway is missing and the homolog Syk takes its place.[13]

ZAP-70 deficiency results in a form of autosomal recessive immune deficiency named combined immunodeficiency.[14] Patients afflicted with combined immunodeficiency have a normal lymphocyte count, but they have low concentrations of T helper cells and cytotoxic T cells.[14] Patients were also found to have irregular lymphocyte proliferation responses.[14] These effects suggest that a deficiency in ZAP-70 results in decreased rates of T cell activation and subsequent signal transductions.[14]

Interactions

ZAP-70 has been shown to interact with:

See also

References

Further reading

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