Structure and regulation of the envoplakin gene

Envoplakin, a member of the plakin family of proteins, is a component of desmosomes and the epidermal cornified envelope. To understand how envoplakin expression is regulated, we have analyzed the structure of the mouse envoplakin gene and characterized the promoters of both the human and mouse genes. The mouse gene consists of 22 exons and maps to chromosome 11E1, syntenic to the location of the human gene on 17q25. The exon-intron structure of the mouse envoplakin gene is common to all members of the plakin family: the N-terminal protein domain is encoded by 21 small exons, and the central rod domain and the C-terminal globular domain are coded by a single large exon. The C terminus shows the highest sequence conservation between mouse and human envoplakins and between envoplakin and the other family members. The N terminus is also conserved, with sequence homology extending to Drosophila Kakapo. A region between nucleotides -101 and 288 was necessary for promoter activity in transiently transfected primary keratinocytes. This region is highly conserved between the human and mouse genes and contains at least two different positively acting elements identified by site-directed mutagenesis and electrophoretic mobility shift assays. Mutation of a GC box binding Sp1 and Sp3 proteins or a combined E box and Krüppel-like element interacting with unidentified nuclear proteins virtually abolished promoter activity. 600 base pairs of the mouse upstream sequence was sufficient to drive expression of a beta-galactosidase reporter gene in the suprabasal layers of epidermis, esophagus, and forestomach of transgenic mice. Thus, we have identified a regulatory region in the envoplakin gene that can account for the expression pattern of the endogenous protein in stratified squamous epithelia.