CD9 Gene: Function, Expression, and Clinical Significance

CD9 is a member of the tetraspanin family, a group of transmembrane proteins that organize membrane microdomains and regulate cell adhesion, migration, proliferation, and signal transduction. CD9 is widely expressed on the surface of various cell types, including platelets, endothelial cells, and many cancer cells. It plays a role in cell fusion, viral entry, and tumor suppression. CD9 is also a marker for exosomes and is implicated in the progression of several cancers, including breast, lung, and colorectal cancer.

Tissue Expression

Cell Line Expression

Hotspot Mutations

Mutation functional classification

• Integrin signaling pathway

• Cell adhesion molecules (CAMs)

• Exosome biogenesis and secretion

• Viral entry into host cell

CD9 is a 228-amino acid tetraspanin protein with four transmembrane domains, two extracellular loops, and short cytoplasmic tails. It localizes to the plasma membrane and is enriched in exosomes. CD9 interacts with integrins, other tetraspanins, and signaling molecules to modulate cell adhesion, migration, and fusion. It is involved in platelet aggregation, sperm-egg fusion, and viral infection. CD9 is frequently downregulated in metastatic cancers, suggesting a tumor suppressor role.