Specific induction of cell motility on laminin by α7 integrin

Abstract

Laminin, the major glycoprotein of basement membranes, actively supports cell migration in development, tissue repair, tumor growth, metastasis, and other pathological processes. Previously we have shown that the locomotion of murine skeletal myoblasts is specifically and significantly enhanced on laminin but not on other matrix proteins. One of the major laminin receptors of myoblasts is the α7β1 integrin, which was first described in human MeWo melanoma cells and Rugli glioblastoma cells. In order to investigate and directly test the role of the α7 integrin in cell migration on laminin, we expressed the murine α7B splice variant in human 293 kidney cells and 530 melanoma cells which cannot migrate on laminin and are devoid of endogenous α7. Northern blotting of the transfected cells showed that the α7 mRNA was expressed efficiently, and the protein was detected on the cell surface by immunofluorescence and fluorescence-activated cell sorter analysis. Cell motility measurements by computer-assisted time-lapse videomicroscopy of the α7-transfected cells revealed an 8-10-fold increase in motility on laminin- 1 and its E8 fragment, but not on fibronectin. Mock-transfected cells did not migrate significantly on laminin or on fibronectin. Similarly, transmigration of α7-transfected 293 cells through laminin-coated filters in a Boyden chamber assay was significantly enhanced in comparison to mock-transfected cells. These findings prove that α7 integrin expression confers a gain of function-motile phenotype to immobile cells and may be responsible for transduction of the laminin-induced cell motility.