Laminin 5 deposition regulates keratinocyte polarization and persistent migration

Repair of wounded epidermis requires both keratinocyte migration and deposition of laminin 5 over exposed dermal collagen. To understand the coupling between leading cell migration and laminin 5 deposition, we developed a novel migration assay using time-lapse microscopy. We demonstrate that in migrating, human keratinocytes the deposition of laminin 5 promoted 'processive migration', characterized by stable cell polarization that was tightly coupled to persistent, linear migration in the absence of a chemotactic gradient. Processive migration required deposition of laminin 5, which was restricted to the rear of the polar cell. Integrin alpha3beta1 interacted with these laminin 5 deposits at contact sites that did not require actin-dependent cross-linking. Further, we show that the migrating cells switched adhesion by integrin alpha2beta1 on collagen at the front of the cell to integrin alpha3beta1 on exogenous laminin 5 at the rear of the cell. Along with this switch of integrin usage was the removal of collagen from sites under the cell that precisely correlated with deposition of laminin 5. Processive migration was blocked with suppressors of microtubule dynamics (nocodazole and taxol) or rottlerin, a PKC-delta inhibitor, These drugs were also shown to block deposition of laminin 5 but, surprisingly, constitutive secretion was unimpaired, suggesting deposition was a regulated event. Thus, at the front of the cell, the leading lamellipodium was stabilized through integrin interactions in focal complexes with the exogenous substratum. However, at the rear of the cell, stable cell polarization and linear migration was promoted by laminin 5 deposits and integrin alpha3beta1.