cDNA Cloning, Genomic Structure, and Chromosome Mapping of the Human Epithelial Membrane Protein CL-20 Gene (EMP1), a Member of the PMP22 Family

CL-20is a novel gene encoding a protein that is structurally related to but distinct from the peripheral myelin protein PMP22. Like PMP22, CL-20 is likely to play important roles in the regulation of cell proliferation, differentiation, and cell death. In this study, we describe the cloning and sequencing of a cDNA encoding the human homologue of CL-20 and characterize the genomic structure of this gene. ThehCL-20gene (HGMW-approved symbol EMP1) encodes a protein of 157 amino acids that exhibits 76% identity to the rabbit CL-20 and to the rat EMP-1, which have been described recently, and 39% identity to human PMP22. CL-20 contains four hydrophobic domains, suggesting that it is an integral membrane protein. In particular the second hydrophobic domain encoded within the fourth exon is highly conserved among CL-20, EMP-1, and PMP22, suggesting a functional role for this region. CL-20 mRNA is abundant in squamous-differentiated bronchial epithelial cells; however, low levels of CL-20 mRNA can be detected in several human tissues by Northern analysis. Retinoic acid, which inhibits squamous differentiation, represses CL-20 expression in normal human bronchial epithelial cells. The genomic structure of thehCL-20gene was analyzed using a P1 vector containing this gene. ThehCL-20gene contains five exons about 0.2, 0.12, 0.1, 0.14, and 2.2 kb and four introns about 15, 1.9, 0.1, and 0.7 kb. We have mapped thehCL-20gene to chromosome 12p12 by fluorescencein situhybridization.