Human CD9 Antigen (CD9) Protein

Background

CD9 is a member of the tetraspanin superfamily, a group of transmembrane proteins involved in various biological processes, particularly in cell adhesion, migration, proliferation, and signaling. CD9 is ubiquitously expressed on the surface of various cell types, including platelets, leukocytes, epithelial cells, endothelial cells, and germ cells. It plays a critical role in cell-cell interactions, especially in the context of immune responses, reproduction, cancer metastasis, and viral infection. One of the unique features of tetraspanins, including CD9, is their ability to organize membrane microdomains known as tetraspanin-enriched microdomains (TEMs). These microdomains function as platforms that regulate the spatial organization of other membrane proteins such as integrins, growth factor receptors, and co-receptors, thus modulating their signaling activity. CD9, in particular, interacts with several key molecules, including integrins (α6β1, α3β1), epidermal growth factor receptor (EGFR), and immunoglobulin superfamily proteins.