Distinctive Functions of α6β4 and Other Integrins in Epithelial Cells

This chapter discusses the aspects of structure and function of β4, β1, and αV integrins that are relevant to epithelial cells. Integrin α6β4 acts as a link between basement membrane and the intermediate filament cytoskeleton in epithelial cells. A proper identification of the α6β4 ligand will be an important step that may clarify many aspects of the molecular interactions between epithelial cells and basement membranes. Several laboratories concurrently produced evidence that α6β4 in epithelial cells is physically associated with structures termed hemidesmosomes. It has been speculated that α6β4 has a role in catalyzing the reorganization of hemidesmosomal components, perhaps after the recognition of a ligand in the basement membrane. Although α6β4 is diffusely distributed throughout the cytoplasm of migrating epithelial cells, as soon as migration halts, it becomes quickly polarized to the basal surface in areas of contact with the basement membrane. In addition, there is a consistent distribution of expression in carcinomas from a variety of sources. Interestingly, α6β4 appears to be expressed in carcinoma cells whether or not the normal tissue of origin is α6β4 positive.