KAI1

KAI1, also known as CD82, is a metastasis suppressor gene that encodes a member of the tetraspanin family of membrane proteins. In humans, CD82 is expressed on the surface of various cell types, including immune and epithelial cells, and plays a role in organizing membrane protein complexes.

Function and mechanism: As a tetraspanin, CD82 contributes to the formation of tetraspanin-enriched microdomains that coordinate signaling receptors, adhesion molecules, and proteases. Through interactions with integrins and other surface receptors, CD82 modulates cell adhesion, migration, and invasion, influencing cytoskeletal organization and signal transduction. In tumor cells, higher CD82 expression is generally associated with reduced metastatic potential, while loss or downregulation of CD82 correlates with increased invasiveness and distant spread.

Clinical relevance: Reduced CD82 expression has been observed in several metastatic cancers, including breast, prostate, gastric, and lung cancers. In experimental models, restoring CD82 expression can suppress metastatic colonization without necessarily inhibiting primary tumor growth, supporting its role as a metastasis suppressor rather than a traditional tumor suppressor. CD82 levels are sometimes evaluated for prognostic information in certain cancer types.

Structure and genetics: The CD82 gene encodes a protein of approximately 23–28 kDa with four transmembrane domains, short cytoplasmic tails, and two extracellular loops. As a member of the tetraspanin superfamily, CD82 participates in diverse protein–protein interactions that regulate cell surface organization and signaling.

See also: tetraspanins, metastasis suppressor genes, CD82 in cancer.