CD9 Protein, Mouse (Cell-Free, His)

The CD9 protein, an integral membrane protein associated with integrins, plays a pivotal role in regulating various processes, including sperm-egg fusion, platelet activation and aggregation, and cell adhesion. It is prominently present on the cell surface of oocytes, where it assumes a key role in sperm-egg fusion, potentially by orchestrating multiprotein complexes and influencing membrane morphology essential for the fusion process. In myoblasts, CD9 associates with CD81 and PTGFRN, acting as an inhibitor of myotube fusion during muscle regeneration. Within macrophages, CD9 forms associations with CD9 and beta-1 and beta-2 integrins, preventing macrophage fusion into multinucleated giant cells specialized in ingesting complement-opsonized large particles and impeding the fusion between mononuclear cell progenitors into osteoclasts responsible for bone resorption. CD9 also acts as a receptor for PSG17 and is involved in platelet activation and aggregation, regulating paranodal junction formation. Its role extends to cell adhesion, cell motility, and tumor metastasis, particularly influencing integrin-dependent migration of macrophages, a critical aspect of the inflammatory response in the lung. CD9 forms disulfide-linked homodimers, higher homooligomers, and heterooligomers with other tetraspanin family members. It interacts with integrins ITGAV:ITGB3 and ITGA6:ITGB1, forming complexes with CD81, beta-1, and beta-2 integrins, CD63, CR2/CD21, PTGFRN/CD9P1, and IGSF8, the latter interaction being direct. Additionally, CD9's interaction with PDPN is homophilic and attenuates platelet aggregation and pulmonary metastasis induced by PDPN.