CD81 Gene: Function, Expression, and Disease Associations | Biomedical Resource

CD81 is a member of the tetraspanin family, characterized by four transmembrane domains. It is a cell surface glycoprotein involved in a wide range of cellular processes including cell adhesion, motility, signaling, and immune responses. CD81 is a component of the CD19/CD21 signal transduction complex on B cells, playing a critical role in B cell activation and antibody production. It also serves as a receptor for the hepatitis C virus (HCV) envelope protein E2, facilitating viral entry into hepatocytes. Additionally, CD81 is implicated in cancer progression, where its expression can modulate tumor cell invasion and metastasis.

Tissue Expression

Cell Line Expression

Hotspot Mutations

Mutation functional classification

• B cell receptor signaling pathway

• Hepatitis C virus entry pathway

• Integrin signaling pathway

• Tetraspanin-enriched microdomain organization

CD81 is a 236-amino acid tetraspanin protein with four transmembrane domains, a small extracellular loop (SEL) and a large extracellular loop (LEL). The LEL is critical for interactions with viral glycoproteins and other cellular proteins. CD81 forms complexes with integrins, other tetraspanins, and signaling molecules, organizing membrane microdomains that facilitate signal transduction. It is heavily glycosylated and palmitoylated, which influences its localization and function. CD81 is essential for B cell function, as it partners with CD19 and CD21 to lower the threshold for B cell activation. In the liver, CD81 is a key entry factor for HCV, binding to the E2 glycoprotein and initiating clathrin-mediated endocytosis. Its role in cancer is context-dependent, with studies showing both tumor-promoting and tumor-suppressive effects depending on the tissue and microenvironment.