Molecular cloning and characterization of a cDNA encoding canine type VII collagen non-collagenous (NC1) domain, the target antigen of autoimmune disease epidermolysis bullosa acquisita (EBA).

Type VII collagen, the major component of anchoring fibrils, serves as tight adhesion of skin basement membrane zone (BMZ) through its amino-terminal non-collagenous (NC1) domain. The NC1 domain is targeted by autoantibodies of an acquired blistering skin disease termed epidermolysis bullosa acquisita (EBA) naturally occurring in humans and dogs. We cloned the full-length canine type VII collagen NC1 domain cDNA and delineated its molecular and immunological characteristics. The canine NC1 domain cDNA consists of 3759 nucleotides encoding for 1253 amino acids, with a molecular mass of approx. 134 kDa and a 17 amino acid signal peptide. The expression of canine type VII collagen was confirmed by Northern blot analysis and by a rabbit antibody raised against a 17 amino acid peptide deduced from canine NC1 sequence. Comparison of canine NC1 with the corresponding human sequence indicated 86.7% and 87.6% identity at the nucleotide and deduced amino acid levels respectively. The protein homology reached greater than 95% within two immunodominant epitope areas. Furthermore, human EBA autoantibodies and a rabbit anti-human NC1 cross-reacted with canine skin BMZ and the newly synthesized canine type VII collagen. The molecular and immunological identities between human and canine NC1 domains suggest that NC1 may be critical for the EBA development.