Alpha 6 beta 4 integrin heterodimer is a component of hemidesmosomes

Antisera that recognize the alpha 6 and beta 4 subunits of integrins were found by immunoelectron microscopy to localize to hemidesmosomes in the basal cells of mouse corneal epithelium. Immunoprecipitation experiments using extracts of metabolically labeled corneal epithelial cells indicate that the primary alpha 6-subunit-containing integrin heterodimer present is alpha 6 beta 4 and not alpha 6 beta 1. Here we extend previous studies to report that by immunofluorescence microscopy the alpha 6 integrin subunit colocalizes with bullous pemphigoid antigen and type VII collagen in newly forming hemidesmosomes in the developing 17-day fetal rabbit eye. Neither the composition of the anchoring filaments, which span the region between the hemidesmosomal plaque and the lamina densa of basement membrane where the globular domain of type VII collagen is located, nor the extracellular ligand of alpha 6 beta 4 is known. Once anchoring filament proteins are identified, it will be of interest to determine whether any bind to alpha 6 beta 4.