Molecular consequences of deletion of the cytoplasmic domain of bullous pemphigoid 180 in a patient with predominant features of epidermolysis bullosa simplex

Bullous pemphigoid antigen 2 (BP180; COL17A1) collagen gene mutations typically result in nonlethal junctional epidermolysis bullosa. We have identified a patient, who had phenotypic features of mainly epidermolysis bullosa simplex and evidence for both intraepidermal and junctional blister formation. Mutation analysis disclosed compound heterozygous mutations in the COL17A1 gene, leading to deletion of Ile-18 to Asn-407 from the intracellular domain of BP180, BP180(Delta18-407). To gain insight into the mechanisms underlying the phenotype, we have investigated the functional consequences of this truncation in BP180. The results demonstrate that: (1) in cultured keratinocytes of the patient, the assembly of hemidesmosomes, and their linkage with intermediate filaments are impaired; (2) BP180(Delta18-407) is not capable of binding to the hemidesmosomal components BP230, plectin, and the beta4 subunit of the alpha6beta4 integrin in yeast two-hybrid assays; (3) BP180(Delta18-407) is recruited into hemidesmosome-like structures in both normal and BP180-deficient transfected keratinocytes when ectopically expressed, suggesting that the extracellular domain of BP180(Delta18-407) determines its topogenic fate; and, finally (4) the proteolytic shedding of the extracellular domain of BP180(Delta18-407) is not impaired in transfected COS-7 cells. Collectively, the data demonstrate that the truncation of the intracellular domain of BP180 impairs the organization of hemidesmosomes, affecting both the mechanical stability of basal keratinocytes and dermoepidermal cohesion.