ITGA9 encodes integrin subunit alpha 9, which forms heterodimeric cell surface receptors with beta-1 subunit to mediate cell adhesion and signaling. The ITGA9:ITGB1 complex serves as a receptor for multiple extracellular matrix proteins including VCAM1, cytotactin, and osteopontin 1. The protein functions as a crucial regulator of cellular processes including proliferation, migration, and adhesion across diverse tissue types. In vascular smooth muscle cells, ITGA9:ITGB1 represses calcium influx and sensitivity, thereby inhibiting vasocontraction through SVEP1 interaction 1. ITGA9 serves as a specific surface marker for SOX9+ sclerotomal progenitors during skeletal development and can distinguish peritubular myoid cells from Leydig cells in testicular tissue 23. In pathological contexts, ITGA9 exhibits complex roles in cancer biology, with abnormal expression linked to tumor proliferation, metastasis, and angiogenesis across multiple cancer types 4. In breast cancer, ITGA9 expression is frequently downregulated through CpG methylation 5. Conversely, ITGA9 overexpression in acute myeloid leukemia enables niche-independent maintenance of leukemia stem cells through osteopontin binding and serves as a prognostic marker 6. The protein also functions in endothelial cell regulation, inhibiting proliferation and migration in psoriatic conditions 7.