CD93

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CD93 molecule
Identifiers
Symbols CD93 ; C1QR1; C1qR(P); C1qRP; CDw93; ECSM3; MXRA4; dJ737E23.1
External IDs OMIM120577 MGI106664 HomoloGene7823 GeneCards: CD93 Gene
RNA expression pattern
PBB GE CD93 202878 s at tn.png
PBB GE CD93 202877 s at tn.png
More reference expression data
Orthologs
Species Human Mouse
Entrez 22918 17064
Ensembl ENSG00000125810 ENSMUSG00000027435
UniProt Q9NPY3 O89103
RefSeq (mRNA) NM_012072 NM_010740
RefSeq (protein) NP_036204 NP_034870
Location (UCSC) Chr 20:
23.06 – 23.07 Mb
Chr 2:
148.44 – 148.44 Mb
PubMed search [1] [2]

CD93 (Cluster of Differentiation 93) is a protein that in humans is encoded by the CD93 gene.[1][2][3] CD93 is a C-type lectin transmembrane receptors which play a role not only in cell–cell adhesion processes but also in host defence.[3]

Family[edit]

CD93 belongs to the Group XIV C-Type lectin family, a group containing two other members, endosialin (CD248) and thrombomodulin, a well characterized anticoagulant. All of them contain a C-type lectin domain, a series of epidermal growth factor like domains (EGF), a highly glycosylated mucin-like domain, a unique transmembrane domain and a short cytoplasmic tail. Due to their strong homology and their close proximity on chromosome 20, CD93 has been suggested to have arisen from the thrombomodulin gene through a duplication event

Expression[edit]

CD93 was originally identified in mice as an early B cell marker through the use of AA4.1 monoclonal antibody.[citation needed] Then this molecule was shown to be expressed on an early population of hematopoietic stem cells, which give rise to the entire spectrum of mature cells in the blood. Now CD93 is known to be expressed by a wide variety of cells such as platelets, monocytes, microglia and endothelial cells. In the immune system CD93 is also expressed on neutrophils, activated macrophages, B cell precursors until the T2 stage in the spleen, a subset of dendritic cells and of natural killer cells. Molecular characterization of CD93 revealed that this protein is identical with C1qRp, a human protein identified as a putative C1q receptor.[4] C1q belongs to the complement activation proteins and plays a major role in the activation of the classical pathway of the complement, which leads to the formation of the membrane attack complex. C1q is also involved in other immunological processes such as enhancement of bacterial phagocytosis, clearance of apoptotic cells or neutralisation of virus. Strikingly, it has been shown that anti-C1qRp significantly reduced C1q enhanced phagocytosis. A more recent study confirmed that C1qRp is identical to CD93 protein, but failed to demonstrate a direct interaction between CD93 and C1q under physiological conditions. Recently it has been shown that CD93 is re-expressed during the late B cell differentiation and CD93 can be used in this context as a plasma cell maturation marker.

Function[edit]

CD93 was initially thought to be a receptor for C1q, but now is thought to instead be involved in intercellular adhesion and in the clearance of apoptotic cells. The intracellular cytoplasmic tail of this protein contains two highly conserved domains which may be involved in CD93 function. Indeed, the highly charged juxtamembrane domain has been found to interact with moesin, a protein known to play a role in linking transmembrane proteins to the cytoskeleton and in the remodelling of the cytoskeleton. This process appears crucial for both adhesion, migration and phagocytosis, three functions in which CD93 may be involved.

In the context of late B cell differentiation, CD93 has been shown to be important for the maintenance of high antibody titres after immunization and in the survival of long-lived plasma cells in the bone marrow. Indeed, CD93 deficient mice failed to maintain high antibody level upon immunization and present a lower amount of antigen specific plasma cells in the bone marrow.

See also[edit]

References[edit]

  1. ^ Nepomuceno RR, Henschen-Edman AH, Burgess WH, Tenner AJ (February 1997). "cDNA cloning and primary structure analysis of C1qR(P), the human C1q/MBL/SPA receptor that mediates enhanced phagocytosis in vitro". Immunity 6 (2): 119–29. doi:10.1016/S1074-7613(00)80419-7. PMID 9047234. 
  2. ^ Webster SD, Park M, Fonseca MI, Tenner AJ (January 2000). "Structural and functional evidence for microglial expression of C1qR(P), the C1q receptor that enhances phagocytosis". J. Leukoc. Biol. 67 (1): 109–16. PMID 10648005. 
  3. ^ a b "Entrez Gene: CD93 CD93 molecule". 
  4. ^ McGreal EP, Ikewaki N, Akatsu H, Morgan BP, Gasque P (May 2002). "Human C1qRp is identical with CD93 and the mNI-11 antigen but does not bind C1q". J. Immunol. 168 (10): 5222–32. doi:10.4049/jimmunol.168.10.5222. PMID 11994479. 

Further reading[edit]

External links[edit]