MOLECULAR-GENETIC STUDIES OF A HUMAN EPIDERMAL AUTOANTIGEN (THE 180-KD BULLOUS PEMPHIGOID ANTIGEN BP180) - IDENTIFICATION OF FUNCTIONALLY IMPORTANT SEQUENCES WITHIN THE BP180 MOLECULE AND EVIDENCE FOR AN INTERACTION BETWEEN BP180 AND ALPHA-6 INTEGRIN/

The 180-kD bullous pemphigoid autoantigen (BP180) is a component of th e hemidesmosome, a cell-matrix connector. This protein is oriented in a type II fashion in the membrane of the hemidesmosome and is a hybrid collagen (classified as type XVII). We have analyzed the fate of vari ous mutant BP180 molecules transfected into several different cell typ es. A protein, D1, lacking the collagen-like extracellular domains of BP180 polarizes normally in 804G epithelial cells and colocalizes with other hemidesmosomal components in the plane of the basal cell surfac e. However, deletion of a stretch of 36 amino acids located at the NH2 terminus of D1 induces an apical polarization of the protein (D1-36N) in the cell surface of 804G cells. Deletion of the 27-amino acid nonc ollagenous extracellular domain that is located immediately after the membrane spanning domain of BP180 results in a failure of D1-27C prote in to codistribute with other hemidesmosomal components despite its ba sal localization in transfected 804G cells. In FG cells, which lack th eir own BP180, transfected D1 protein localizes with the alpha 6 beta 4 integrin heterodimer. In HT1080 cells, which do not possess BP180 or beta 4 integrin, D1 protein localizes with alpha 6 beta 4 integrin wh ile both the D1-27C and D1-36N proteins do not. Moreover, D1 protein c oprecipitates with alpha 6 integrin from extracts of HT1080 transfecta nts. Taken together, these results suggest that the NH2-terminal domai n of BP180 determines polarization of BP180 while the noncollagenous e xtracellular domain of BP180 stabilizes its interactions with other he midesmosomal components, such as alpha 6 integrin. Perturbation of thi s latter domain by human bullous pemphigoid autoantibodies may explain the loss of epidermal cell-dermis attachment that characterizes the B P disease.