INTEGRIN-ALPHA-6-BETA-4 COMPLEX IS LOCATED IN HEMIDESMOSOMES, SUGGESTING A MAJOR ROLE IN EPIDERMAL-CELL BASEMENT-MEMBRANE ADHESION

The alpha-6/beta-4 complex is a member of the integrin family of adhesion receptors. It is found on a variety of epithelial cell types, but is most strongly expressed on stratified squamous epithelia. Fluorescent antibody staining of human epidermis suggests that the beta-4 subunit is strongly localized to the basal region showing a similar distribution to that of the 230-kD bullous pemphigoid antigen. The alpha-6 subunit is also strongly localized to the basal region but in addition is present over the entire surfaces of basal cells and some cells in the immediate suprabasal region. By contrast staining for beta-1, alpha-2, and alpha-3 subunits was very weak basally, but strong on all other surfaces of basal epidermal cells. These results suggest that different integrin complexes play differing roles in cell-cell and cell-matrix adhesion in the epidermis. Immunoelectron microscopy showed that the alpha-6/beta-4 complex at the basal epidermal surface is strongly localized to hemidesmosomes. This result provides the first well-characterized monoclonal antibody markers for hemidesmosomes and suggests that the alpha-6/beta-4 complex plays a major role in epidermal cell-basement membrane adhesion. We suggest that the cytoplasmic domains of these transmembrane glycoproteins may contribute to the structure of hemidesmosomal plaques. Immunoultrastructural localization of the BP antigen suggests that it may be involved in bridging between hemidesmosomal plaques and keratin intermediate filaments of the cytoskeleton.