Revisiting the Role of CD63 as Pro-Tumorigenic or Anti-Tumorigenic Tetraspanin in Cancers and its Theragnostic Implications

Cluster of differentiation antigen 63 (CD63) belongs to a superfamily of proteins, usually defined as tetraspanins which are known to transverse the bilayer membranes four times. The expression of CD63 has been shown to get altered in several cancers, where it has been demonstrated to act as both a tumor promoter and tumor suppressor. The present review describes the mechanism of how CD63 promotes tumor formation in certain cancer types while inhibiting in some other specific cancers. Glycosylation, a post-translational process plays a significant role in regulating the expression and function of these membrane proteins. Being a crucial exosomal flag protein, CD63 has been found to get involved in endosomal cargo sorting as well as the production of extracellular vesicles. Increased expression of exosomal CD63 derived from advanced tumors has demonstrated its role in promoting metastasis. CD63 also regulates the characteristic and function of stem cells on which they get expressed. This particular tetraspanin has been discovered to participate in gene fusion to perform distinctive roles in certain specific cancer types like breast cancer and pigmented epithelioid melanocytoma. Furthermore, this review mentions twelve different microRNAs obtained from miRDB that might target CD63. A few theragnostic uses of this membrane protein are also discussed. Thereby, the review indicates that further studies on CD63 might prove it to be an effective therapeutic target in different cancers in the coming future.