CD63

CD63 antigen is a is_associated_with::protein that in humans is encoded by the CD63 is_associated_with::gene. CD63 is mainly associated with membranes of intracellular vesicles, although cell surface expression may be induced.

Allergy Diagnosis
CD63 is a good marker for flow cytometric quantification of in vitro activated basophils for diagnosis of IgE-mediated allergy. The test is commonly designated as basophil activation test (BAT).

Research
Initially, deletion and point mutants were used to investigate the role of the C-terminus, which contains a putative lysosomal-targeting/internalisation motif (GYEVM). C-terminal mutants showed increased surface expression and decreased intracellular localisation relative to CD63Wt. Antibody induced internalisation was reduced in C-terminal deletion mutants and abolished in G→A and Y→A mutants, showing the crucial role of these residues in internalisation.

CD63 is extensively and variably glycosylated and the EC2 region contain three potential N-linked glycosylation sites (N130, N150 and N172). Mutants N130A and N150A were similar to hCD63Wt with respect to intracellular localisation and internalisation. However, the hCD63N172A mutant showed a mainly cell surface localisation and low internalisation. Expression of a mutant lacking all three glycosylation sites was very unstable. It was speculated that the reduced internalisation of CD63N172A might be due to changes in its interaction with cell surface molecules. Immunoprecipitation experiments showed some evidence of a protein (100kDa) associating with CD63N172A, but this was not consistent. However, an association between CD63Wt and β2 integrin (CD18) was shown by co-internalisation of these proteins. Interactions with CD63 may therefore affect the trafficking and function of β2 integrins. Recent work by other groups suggests that CD63 functions as an “adaptor”, controlling the functions of interacting proteins such as integrins, by inducing their internalisation. Our findings indicate that CD63 glycosylation status can affect this role (2).

A recent investigation showed that expression of CD63 positively correlates with the invasiveness of is_associated_with::ovarian cancer.

Interactions
CD63 has been shown to interact with is_associated_with::CD117 and CD82.