HD4, A 180 KDA BULLOUS PEMPHIGOID ANTIGEN, IS A MAJOR TRANSMEMBRANE GLYCOPROTEIN OF THE HEMIDESMOSOME

Hemidesmosomes (HDs) constitute a major cellular apparatus for substratum adhesion in stratified and complex epithelia. A large number of components participate in their construction. HD4, a 180 kDa polypeptide, which is one of the major constituents of the isolated HD fraction, has been suggested to be a glycoprotein, is probably identical to the 180 kDa bullous pemphigoid (BP) antigen [Owaribe, K., Nishizawa, Y., & Franke, W.W. (1991) Exp. Cell Res. 192, 622-630]. By using a sensitive method for detection of glycoproteins, HD4 was confirmed to be a major glycoprotein in cytoskeletal fractions of certain cultured epithelial cells as well as in the HD fraction. To further characterize HD4, we prepared two groups of monoclonal antibodies (mAbs), one recognizing extracellular parts of the HD4 molecule (group I) and the other recognizing intracellular ones (group II). In cultured keratinocytes, type I mAbs, as well as BP autoantibodies that recognize both 230 and 180 kDa polypeptides, stained living cells while type II mAbs did not. The two mAbs exhibited identical staining patterns in fixed cells. HD4 molecules proved partially susceptible to collagenase and Dispase digestion, which removed epitopes of type I mAbs but not those of type II. Immunoelectron microscopy revealed the epitopes of group I mAbs to be localized in the extracellular region of HDs, whereas those of group II were on the cytoplasmic side. These results indicate that the HD4 (BP180) molecule is a major transmembrane glycoprotein with collagen domains in its extracellular portion.