Human periplakin: Genomic organization in a clonally unstable region of chromosome 16p with an abundance of repetitive sequence elements

Periplakin, a member of the plakin family of proteins, has been recently ch aracterized by cDNA cloning, and the corresponding gene, PPL, has been mapp ed to human chromosome 16p13.3 (Aho et at, 1998, Genomics 48: 242-247), Per iplakin has also been shown to serve as an autoantigen in a malignancy-asso ciated autoimmune blistering disease, paraneoplastic pemphigus (Mahoney et al., 1998, J. Invest. Dermatol. 111: 308-313). In this study, we have eluci dated the intron-exon organization of human PPL and characterized its promo ter region. The flanking 5' sequences were rich in G and C (similar to 80%) and included multiple AP2 sites and a SP1 site, while no canonical TATA or CCAAT sequences were found. The functionality of the upstream sequences (- 709 to +135) as a promoter in cultured epidermal keratinocytes was detected by a CAT reporter gene, and a limited region (-382 to +135) showed activit y in cultured dermal fibroblasts, attesting to cell-type specificity of the promoter. The genomic organization, including the intron-exon borders, was determined by direct nucleotide sequencing of human genomic P1 clones. Com parative analysis of cDNA and genomic sequences revealed that PPL consists of 22 exons, with the distribution of exons in PPL being consistent with th at of other plakin genes: 21 small exons, separated by large introns, encod e the amino-terminal globular domain, and 1 large exon encodes the entire r od and the tail domains. Characterization of four P1 clones spanning the PP L locus revealed multiple Alu repeats, 20 of them within 33 kb of the entir ely sequenced segments (0.60/kb), in addition to numerous MLR and L1 elemen ts. These repetitive elements could lead to the clonal instability detected throughout the genomic P1 clones and may give rise to the genomic rearrang ements possibly underlying the paraneoplastic pemphigus. (C) 1999 Academic Press.