CD63 is a tetraspanin, a cell surface-associated membrane protein with four transmembrane domains. CD63 interacts with integrins, cell surface receptors, kinases, and many other proteins. Cell surface expession of CD63 is highly regulated. While CD63 is involved with HIV-1 entry into T-lymphocytes, decreased surface expression of CD63 is associated with an increase in cancer invasiveness and metastasis.
Pols, M.S., et al. (2009) Trafficking and function of the tetraspanin CD63. Exp Cell Res. , 15,315(9):1584-92.