Identification of a 450-kDa human epidermal autoantigen as a new member of the plectin family

The serum from an individual with a subepidermal blistering disease was previously shown to recognize a 450-kDa epidermal autoantigen. The molecular structure of this antigen was investigated by screening a human keratinocyte cDNA library with the patient's serum. One clone, with a 276-bp cDNA insert, that encoded an epitope recognized by the serum was isolated. Rabbit polyclonal antibodies that were prepared against the corresponding fusion protein recognized the 450-kDa epidermal antigen and stained the basal keratinocytes in human epidermis. This clone was used for further screening of the original keratinocyte and HeLa cell cDNA libraries. Two different, but closely related, 0.8- and 2.0-kb cDNAs were isolated, and their deduced amino acid sequences indicated that the encoded proteins belonged to the plectin family. Northern blot analysis of total RNA from human keratinocytes with these cDNA inserts as probes detected RNAs of similar to 12-13 kb. The 0.8-kb cDNA hybridized to polyadenylated RNA species from human skeletal muscle, heart, lung, and kidney, whereas the 2.0-kb cDNA hybridized to transcripts present only in kidney and lung. Southern blot analysis of genomic DNA from the human placenta revealed similar, but not identical, patterns of hybridization with the 0.8- and 2.0-kb cDNAs. Data suggest that the 0.8- and 2.0-kb cDNAs encode two different proteins but are derived from the same gene.