The Function of Epiplakin - in vitro, in vivo Analysis and Gene Structure of Mouse Epiplakin

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Epiplakin was originally identified as a 450-k Da human epidermal autoantigen that reacted with the serum from an individual with a subepidermal blistering disease. The structural analysis of this protein showed that it is a highly unique member of the plakin family (Fujiwara et al.: J Biol Chem 276: 13340-13347, 2001).In this study, we have isolated human epiplakin gene (EPPK 1) by screening of leukocyte genomic library. The gene was one exon which covers entire open reading frame of epiplakin. The gene was mapped to chromosomal band 8q24.3, which was the same locus of plectin. The gene converged into one locus in mapping excluded the possibility that the genomic clones we isolated are processed pseudogene(s). We amplified the coding region of five COOH-terminal homologous repeats with polymerase chain reaction using DNA from HeLa cells as template and these sequences were compared with those of cDNA derived from HeLa cells. The numbers of different nucleotides between cDNA and the isolated gene were 30 sites, 19 of which might lead amino acid change. The numbers of different nucleotides between cDNA and the amplified product of 3^* strongly conserved region were 40 sites, 30 of which might lead amino acid change. Gene polymorphism between individuals was detected especially in number of trinucleotide (GCC) repeats in the last five homologous repeats. Five, eight or nine GCC repeats-variations and the change of GCC to ACC in some repeats which leads amino acid change (alanine to threonine) were found. After polymerase chain reaction followed by direct sequencing using DNA isolated from nonrelated 15 Japanese, the numbers of GCC repeats in the first repeat of 3^* strongly conserved region were examined. Eight GCC repeats were most frequently detected though five and nine repeats were also found in minor populations. This data indicated the presence of polymorphism of epiplakin gene.