Chromosome 3: 37493606-37865005; forward strand. Segons omim: 3:37493812 - 37861280.

Exons: 28; Coding exons: 28; Transcript length: 7889 bps; Translation length: 1035 residues.
4 splice variants described (7889, 2282, 609 and 428bp), three of which with protein translation (1035, 632 and 609 aa).

Alpha9-Integrin.

Alpha-integrins, such as Alpha9-Integrin, are cell surface glycoproteins that contain a large N-terminal extracellular domain with 7 conserved repeats of putative metal-binding domains, a transmembrane segment, and a short C-terminal cytoplasmic tail. ITGA9, like ITGA4, lacks the domain I and the post-translational cleavage that usually occurs in the rest of alpha-integrins. Alpha9-Integrin forms a functional heterodimer with beta1-integrin.

ITGA9 expression is widely distributed in normal human epithelia and muscle. For instance, it has been found in airway epithelium, basal layer of squamous epithelium, smooth muscle and skeletal muscle. Furthermore, its expression has been found in hepatocytes, breast tissue, neutrophils and polymorphonuclear leukocytes.

Cell membrane.

Adhesion with extracellular-matrix proteins, cell-cell interactions and signal transduction. ITGA9 has been shown to bind a plethora of ligands: tenascin, VCAM-1, osteopontin, uPAR, plasmin, angiostatin, several ADAMs (ADAM1, ADAM2, ADAM3, ADAM7, ADAM8, ADAM9, ADAM12, ADAM15, ADAM28 and ADAM33), EMILIN1, fibronectin, VEGF-A, VEGF-C and VEGF-D.
Alpha9 knockout mice died from respiratory failure before day 12 after birth and showed chylothorax, defective lymphatic and venous valve morphogenesis, impaired development of neutrophils, improper re-epithelialisation during cutaneous wound-healing, impaired bone resorption and abnormal osteoclasts.
In cancer, the heterodimer alpha9-beta1 has recently been shown to have an oncogenic role by inducing epithelial-mesenchymal transition and cell migration and metastatic ability in several cancers such as glioma, breast, colon and rhabdomyosarcoma. However, other authors have reported a tumour suppressor function for ITGA9 in a wide variety of tumours based on deletion or methylation states in varying percentages of patients. Furthermore, a very small percentage of patients (1%) with point mutations has also been reported.

Alpha- and beta-integrins are completely distinct, with no detectable homology between them. Sequence identity among alpha-integrins is around 45%. All alpha-integrins are thought to have evolved from a common ancestor. Among all alpha-subunits, alpha-9 shows the greatest homology with alpha-4.