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Description

CD9 antigen (UniProt: P21926, also known as 5H9 antigen, Cell growth-inhibiting gene 2 protein, Leukocyte antigen MIC3, Motility-related protein, MRP-1, Tetraspanin-29, Tspan-29, p24) is encoded by the CD9 (also known as MIC3, TSPAN29, IG2) gene (Gene ID: 928) in human. CD9 is a multi-pass membrane glycoprotein of the tetraspanin (TM4SF) family. It is expressed in a variety of hematopoietic and epithelial cells. It displays strong expression in platelets where it mediates platelet activation and aggregation upon binding to monoclonal antibodies. CD9 induces cell-cell adhesion, platelet aggregation, and B cell development and is shown to associate with CD63, CD81, CD82, and CD36 and to bind to beta-1 integrins. CD9 activation of platelets is reported to be mediated by the Fc y RII (CD32) molecule. Downregulation of CD9 correlates with tumor progression in some forms of cancer. It can hamper metastasis formation by inhibiting integrin-mediated motility. Lower expression of CD9 are associated with weaker matrix adhesion and diffuse tumor cell growth in vitro.