Structural and functional studies of integrin receptors in cultured human keratinocytes

In human keratinocytes cultured in conditions which allow differentiation and stratification and which are suitable to reconstitute a fully functional epidermis, the integrin α₆β₄ and two members of the β₁ integrin family (α₂β₁ and α₃β₁) were polarized to the basal and lateral domains of the plasma membrane both in growing colonies and in the reconstituted epidermis. Conversely, α_vβ₅ integrin was expressed at the basal surface in growing and migrating but not in stationary keratinocytes. The integrin α₆β₄ was organized in patches and spots corresponding to F-actin-free submembraneous areas and did not colocalize to focal contacts; moreover, α₆β₄ colocalized with patches of laminin deposited underneath the ventral membrane of individual cells. The two β₁ laminin receptor integrins (α₂β₁ and α₃β₁) were never found in the basal domain but matched the lateral position of vinculin (but not talin), cingulin and desmoplakins. Only the integrin complex α_vβ₅ was associated with talin- and vinculin-containing focal adhesions mostly in the peripheral cells of expanding keratinocyte colonies and in coincidence with fibronectin strands. The topography of β₁ and β₄ integrins reflects a functional role in adhesion and in the maintenance of the state of aggregation of cultured keratinocytes since lateral aggregation was impaired by antibodies to β₁ whereas antibodies to β₄ prevented cell-matrix adhesion.