CD9
Description
The CD9 (CD9 molecule) is a protein-coding gene located on chromosome 12.
CD9 is a gene that codes for a protein belonging to the transmembrane 4 superfamily (tetraspanin family). This protein is a cell surface glycoprotein with four transmembrane regions and two extracellular loops containing disulfide bonds. It also has distinct palmitoylation sites that enable interactions with lipids and other proteins. Tetraspanins are involved in various biological processes, including adhesion, motility, membrane fusion, signaling, and protein trafficking. Their ability to interact with numerous proteins, including each other, allows them to play a role in many cellular functions. The palmitoylation sites allow tetraspanins to organize into tetraspanin-enriched microdomains (TEMs), which are thought to be involved in various processes, including exosome biogenesis. CD9 is often used as a marker for exosomes, as it is present on their surface. In some cases, CD9 plays a significant role in the pathogenicity of exosomes. For example, in HIV-1 infection, exosomes can enhance HIV-1 entry through the interaction of tetraspanins CD9 and CD81.
CD9 is an integral membrane protein that interacts with integrins and regulates various cellular processes, including sperm-egg fusion, platelet activation and aggregation, and cell adhesion. It plays a key role in sperm-egg fusion by organizing multiprotein complexes and influencing membrane morphology. In myoblasts, it interacts with CD81 and PTGFRN to inhibit myotube fusion during muscle regeneration. In macrophages, it associates with CD81 and beta-1 and beta-2 integrins, preventing macrophage fusion into multinucleated giant cells. It also prevents fusion between mononuclear cell progenitors into osteoclasts. CD9 serves as a receptor for PSG17 and is involved in platelet activation and aggregation. It regulates paranodal junction formation and is implicated in cell adhesion, cell motility, and tumor metastasis.
CD9 is also known as BTCC-1, DRAP-27, MIC3, MRP-1, TSPAN-29, TSPAN29.
