α9β1 Integrin in melanoma cells can signal different adhesion states for migration and anchorage

Cell surface integrins are the primary receptors for cell migration on extracellular matrix, and exist in several activation states regulated in part by ectodomain conformation. The α9 integrin subunit, which pairs only with β1, has specific roles in the immune system and may regulate cell migration. Melanoma cells express abundant α9β1 integrin, and its role in cell migration was assessed. Ligands derived from Tenascin-C and ADAM12 supported α9β1 integrin-mediated cell attachment and GTP-Rac dependent migration, but not focal adhesion formation. Manganese ions induced α9β1 integrin- and Rho kinase-dependent focal adhesion and stress fibre formation, suggesting that the activation status of α9β1 integrin was altered. The effect of manganese ions in promoting focal adhesion formation was reproduced by β1 integrin activating antibody. The α9β1 integrin translocated to focal adhesions, where active β1 integrin was also detected by conformation-specific antibodies. Focal adhesion assembly was commensurate with reduced cell migration. Endogenous α9β1 integrin-mediated adhesion was sensitive to the PP1 chemical inhibitor and an inhibitor of endosomal vesicle recycling, but not inhibitors of protein kinase C or the small GTPase Rho. Our results demonstrated that although α9β1 integrin can induce and localise to focal adhesions in a high activation state, its intermediate activity state normally supports cell adhesion consistent with migration.