CD69

CD69 (Cluster of Differentiation 69) is a human transmembrane C-Type lectin protein encoded by the CD69 gene. It is an early activation marker that is expressed in hematopoietic stem cells, T cells, and many other cell types in the immune system.[5] It is also implicated in T cell differentiation as well as lymphocyte retention in lymphoid organs.

CD69
Available structures
PDBOrtholog search: PDBe RCSB
Identifiers
AliasesCD69, AIM, BL-AC/P26, CLEC2C, EA1, GP32/28, MLR-3, CD69 molecule
External IDsOMIM: 107273 MGI: 88343 HomoloGene: 128584 GeneCards: CD69
Gene location (Human)
Chr.Chromosome 12 (human)[1]
Band12p13.31Start9,752,486 bp[1]
End9,760,901 bp[1]
RNA expression pattern
More reference expression data
Orthologs
SpeciesHumanMouse
Entrez

969

12515

Ensembl

ENSG00000110848

ENSMUSG00000030156

UniProt

Q07108

P37217

RefSeq (mRNA)

NM_001781

NM_001033122

RefSeq (protein)

NP_001772

NP_001028294

Location (UCSC)Chr 12: 9.75 – 9.76 MbChr 6: 129.27 – 129.28 Mb
PubMed search[3][4]
Wikidata
View/Edit HumanView/Edit Mouse

Function

The activation of T lymphocytes and Natural Killer (NK) Cells, both in vivo and in vitro, induces expression of CD69. This molecule, which appears to be the earliest inducible cell surface glycoprotein acquired during lymphoid activation, is involved in lymphocyte proliferation and functions as a signal-transmitting receptor in lymphocytes, including natural killer (NK) cells, and platelets (Cambiaggi et al., 1992) [supplied by OMIM].[6]

Structure and ligands

The gene encoding CD69 is located in the NK gene complex on chromosome 6 and chromosome 12 in mice and humans respectively.[7] Activation signaling pathways in lymphocytes, NK cells, dendritic cells and other cell types upregulate transcription factors, such as NF-κB, ERG-1 (erythroblast transformation-specific related gene-1), and AP-1 (activator protein), in order to promote the transcription of the CD69 gene.[8][7] The CD69 protein is subject to post-translational modifications. Namely, it is differentially glycosylated to produce either a 28 kDa peptide or a 32 kDa peptide. Two of these peptides randomly combine to form a homodimer linked by a disulfide bond.[7] These subunits have a C-type lectin domain (CTLD) that binds ligands, a transmembrane domain, and a cytoplasmic tail that relays signals to the cell interior.[7]

CD69 lacks the characteristic Ca2+ binding residues in CTLDs, indicating that it might bind to proteins rather than carbohydrates, the usual ligand of CTLDs.[9][7] It has been shown that CD69 binds to Gal-1, a carbohydrate binding protein located on some dendritic cells and macrophages, in addition to Myl9/12.[8] Other ligands have yet to be identified. However, it is known that binding of the ligands initiates the Jak/Stat signaling pathway as well as the mTOR/HIF1-α pathway.[9][8][7] CD69 is also known to interact with and mediate S1P and LAT1 receptors, which influence lymphocyte egress in lymphoid organs among other responses.[10][8] More work must be done to fully characterize CD69-ligand interactions as well as CD69's method of transducing intracellular signals.

T cell differentiation

CD69 expression has been associated with both regulatory T cell (Treg), memory T cell and Bcl6 loCD69 hiLZ GC B plasmablast precursors.[11] Treg precursors exit the thymus expressing CD69 and complete differentiation into Treg cells in peripheral tissues when they encounter antigens and other cytokines, like IL-2.[12] Through the JAK/STAT signaling pathway, CD69 activation also induces the production of TGF-β as well as IL-2, which contribute to the differentiation of Treg cells as mentioned above.[8] Furthermore, CD69 is also known to be upregulated by NF-κB signaling at the onset of an immune response. A prolonged immune response is then maintained by the non-canonical NF-κB pathway, which in turn is associated with Treg differentiation.[7]

In addition to Treg differentiation, CD69 is a common marker of precursor and mature resident memory T cells (TRMs) that are localized in peripheral tissues.[13][9] TGF-β is also responsible for the development of TRMs, thus promoting TRM differentiation in a manner similar to Treg differentiation.[14]

Lymphocyte migration

Most lymphocytes express sphingosine-1-phosphate receptors (S1P1-5), which are G protein-coupled receptors located in the cell membrane that bind to the ligand sphingosine-1-phosphate (S1P). S1P is a sphingolipid metabolite that is abundant in the bloodstream and, upon binding to S1P1, promotes lymphocyte egress from lymphoid organs so they can travel to affected tissues.[15][8] However, when a T cell is activated in a lymphoid organ through cytokine and TCR signaling, CD69 is expressed and forms a complex with S1P1 (not S1P3 or S1P5). This association is dependent on the interaction between the CD69 transmembrane domain and helix-4 of S1P1. Following formation of this complex, S1P1 is internalized and is destroyed within the cell, inhibiting its ability to bind S1P and initiate downstream signaling. This in turn results in temporary lymphocyte retention in the lymph organs.[8] It is thought that retention of lymphocytes in the lymph nodes may increase the chance of successful lymphocyte activation, especially if the initial activation signal was weak. Similarly, CD69 expressed in thymocytes following positive selection may ensure that T cells fully mature in the thymus prior to entering circulation.[10]

Some research has shown that S1P1 and CD69 co-regulate so that when CD69 is in greater abundance, it results in the removal of S1P1 from the membrane as mentioned above.[10] However, if S1P1 is more abundant than CD69, as would be the case in mature T cells, CD69 membrane localization is reduced. In this manner, regulation of CD69 and S1P1 expression and localization jointly impact lymphocyte egress and migration.[10]

gollark: ```(angel -97392)(tit-for-tat -83669)(devil -85670)(time-machine -78224)(tat-for-tit -112052)(grudger -68152)(random-choice -104122)(apl -97870)(angry-tit-for-tat -92851)(forgiving-grudge -66681)(meapiometics -79127)```
gollark: ```scheme(define get-repeated-score (lambda (strategy accumulator counter) (if (= counter 0) accumulator (get-repeated-score strategy (+ accumulator (get-strategy-scores strategy)) (- counter 1)))))(define get-all-scores (lambda () (define helper (lambda (x) (write (list (car x) (get-repeated-score x 0 49))) (newline))) (map helper strategies)))```Put in this if you want cool BIGGER scores.
gollark: By somewhat narrow margins, but it consistently beats the normal grudger.
gollark: And my slightly improved grudger... wins utterly, great.
gollark: I'll make it run 50 times and sum them.

See also

References
  1. GRCh38: Ensembl release 89: ENSG00000110848 - Ensembl, May 2017
  2. GRCm38: Ensembl release 89: ENSMUSG00000030156 - Ensembl, May 2017
  3. "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  4. "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  5. Ziegler SF, Ramsdell F, Alderson MR (September 1994). "The activation antigen CD69". Stem Cells. 12 (5): 456–65. doi:10.1002/stem.5530120502. PMID 7804122.
  6. "Entrez Gene: CD69 CD69 molecule".
  7. Radulovic K, Niess JH (2015). "CD69 is the crucial regulator of intestinal inflammation: a new target molecule for IBD treatment?". Journal of Immunology Research. 2015: 497056. doi:10.1155/2015/497056. PMC 4352431. PMID 25759842.
  8. Cibrián D, Sánchez-Madrid F (June 2017). "CD69: from activation marker to metabolic gatekeeper". European Journal of Immunology. 47 (6): 946–953. doi:10.1002/eji.201646837. PMC 6485631. PMID 28475283.
  9. Kimura MY, Hayashizaki K, Tokoyoda K, Takamura S, Motohashi S, Nakayama T (July 2017). "Crucial role for CD69 in allergic inflammatory responses: CD69-Myl9 system in the pathogenesis of airway inflammation". Immunological Reviews. 278 (1): 87–100. doi:10.1111/imr.12559. PMID 28658550.
  10. Cyster JG, Schwab SR (2012). "Sphingosine-1-phosphate and lymphocyte egress from lymphoid organs". Annual Review of Immunology. 30: 69–94. doi:10.1146/annurev-immunol-020711-075011. PMID 22149932.
  11. Ise, Wataru (April 17, 2018). "T Follicular Helper Cell-Germinal Center B Cell Interaction Strength Regulates Entry into Plasma Cell or Recycling Germinal Center Cell Fate". Immunity. 48 (4): 702–715.e4. doi:10.1016/j.immuni.2018.03.027. PMID 29669250.
  12. González-Amaro R, Marazuela M (April 2016). "T regulatory (Treg) and T helper 17 (Th17) lymphocytes in thyroid autoimmunity". Endocrine. 52 (1): 30–8. doi:10.1007/s12020-015-0759-7. PMID 26475497.
  13. Farber DL, Yudanin NA, Restifo NP (January 2014). "Human memory T cells: generation, compartmentalization and homeostasis". Nature Reviews. Immunology. 14 (1): 24–35. doi:10.1038/nri3567. PMC 4032067. PMID 24336101.
  14. Mueller SN, Mackay LK (February 2016). "Tissue-resident memory T cells: local specialists in immune defence". Nature Reviews. Immunology. 16 (2): 79–89. doi:10.1038/nri.2015.3. PMID 26688350.
  15. Garris CS, Blaho VA, Hla T, Han MH (July 2014). "Sphingosine-1-phosphate receptor 1 signalling in T cells: trafficking and beyond". Immunology. 142 (3): 347–53. doi:10.1111/imm.12272. PMC 4080950. PMID 24597601.

Further reading
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