Alpha7 integrin mediates cell adhesion and migration on specific laminin isoforms.

The laminin-binding alpha7beta1 integrin receptor is expressed at high levels by skeletal and cardiac muscles and by certain melanocytic cells. We have assessed the potential role of the alpha7A/B integrin isoforms in mediating cell adhesion and motility and determined the laminin isoform specificity of this integrin. When MCF-7 breast carcinoma cells, normally nonadherent to laminin 1, were stably transfected with cDNA for mouse alpha7, they adhered with high efficiency and migrated on laminin 1 substrates. Function-perturbing monoclonal antibodies generated to mouse alpha7 subunit blocked both adhesion and migration of alpha7 transfectants on laminin 1 substrates. Additional studies with MCF-7 transfectants revealed that alpha7beta1 binds well to laminin 1 and to a mixture of laminin 2 and 4 but not to laminin 5. Importantly, alpha7beta1 was capable of promoting motility on both laminin 1 and laminin 2/4 substrates. However, MCF-7 cells transfected with cDNA for either alpha7A or alpha7B showed no significant differences in cell adhesion or motility on laminin 1 substrates. Although the role for the alternatively spliced cytoplasmic variants of alpha7 remains unknown, the results establish that alpha7beta1 mediates cell adhesive activities on a restricted number of laminin isoforms.