The SFL activity secreted by metastatic carcinoma cells is related to laminin 5 and mediates cell scattering in an integrin-independent manner

We have previously reported that an in vivo-selected metastatic variant of NBT-II rat carcinoma cells, M-NBT-II, produces and secretes a factor with c ell-scattering activity, SFL, that is potentially involved in tumor progres sion. This biological activity was purified and characterized as a laminin 5 (LN5) -related protein. This SFL/LN5 protein consists of the alpha 3, bet a 3 and gamma 2 chains of expected sizes. Laminin 5 is a multifunctional se creted glycoprotein thought to be involved in cell adhesion and migration, mainly via its interaction with alpha 3 beta 1 and alpha 6 beta 4 integrins , SFL/LN5, and purified human laminin 5, induced the scattering and motilit y of MDCK cells and the formation of actin stress fibers and focal contacts in A549 cells. These events were dependent on activation of the small GTP- binding protein Rho, cry colocalized with vinculin in the focal contacts of activated cells whereas alpha 3 and alpha 6 integrins did not. Blocking an tibodies directed against alpha 3 and alpha 6 integrins or the laminin 5 in tegrin-binding site did not abolish SFL/LN5 biological activity, which, in contrast, was completely inhibited by heparin, Thus, SFL/LN5 activity in ep ithelial cell scattering and cytoskeletal reorganization is probably indepe ndent of integrin receptors.