SPECIFIC INDUCTION OF CELL MOTILITY ON LAMININ BY ALPHA-7 INTEGRIN

Laminin, the major glycoprotein of basement membranes, actively suppor ts cell migration in development, tissue repair, tumor growth, metasta sis, and other pathological processes. Previously we have shown that t he locomotion of murine skeletal myoblasts is specifically and signifi cantly enhanced on laminin but not on other matrix proteins. One of th e major laminin receptors of myoblasts is the alpha 7 beta 1 integrin, which was first described in human MeWo melanoma cells and Rugli glio blastoma cells. In order to investigate and directly test the role of the alpha 7 integrin in cell migration on laminin, we expressed the mu rine alpha 7B splice variant in human 293 kidney cells and 530 melanom a cells which cannot migrate on laminin and are devoid of endogenous a lpha 7. Northern blotting of the transfected cells showed that the alp ha 7 mRNA was expressed efficiently, and the protein was detected on t he cell surface by immunofluorescence and fluorescence-activated cell sorter analysis. Cell motility measurements by computer-assisted time- lapse videomicroscopy of the alpha 7-transfected cells revealed an 8-1 0-fold increase in motility on laminin-1 and its E8 fragment, but not on fibronectin. Mock-transfected cells did not migrate significantly o n laminin or on fibronectin, Similarly, transmigration of alpha 7-tran sfected 293 cells through laminin coated filters in a Boyden chamber a ssay was significantly enhanced in comparison to mock-transfected cell s, These findings prove that alpha 7 integrin expression confers a gai n of function-motile phenotype to immobile cells and may be responsibl e for transduction of the laminin-induced cell motility.