Characterization of the human EPLIN (Epithelial Protein Lost in Neoplasm) gene reveals distinct promoters for the two EPLIN isoforms

EPLIN is a novel LIM domain protein that co-localizes to the actin stress fibers and focal adhesion plaques. We previously have demonstrated that two isoforms, the 600 aa EPLIN-alpha and the 759 aa EPLIN-beta, are generated from a single gene. In the majority of human breast and prostate cancer cell lines, the expression of EPLIN-a is significantly reduced, while the expression of EPLIN-beta is either up-regulated or unchanged. To understand the basis of this differential regulation, we have determined the organization of the human EPLIN gene. The human EPLIN gene spans > 100 kb and consists of 11 exons. The EPLIN-beta mRNA requires all 11 exons, while the EPLIN-a mRNA requires Exons 4-11. The transcriptional start sites of EPLIN-a were mapped within the third intron by 5' RACE and Si nuclease protection. Similarly, the 5' ends of EPLIN-beta were mapped upstream of Exon 1. The DNA sequences flanking the EPLIN-alpha or EPLIN-beta transcriptional start sites were capable of stimulating the expression of promoter reporter constructs. Interestingly, the endogenous transcription of EPLIN-a, but not EPLIN-beta, could be stimulated by serum, indicating that the expression of two EPLIN isoforms can be independently regulated. A consensus serum response element was present within 100 bp upstream of the transcriptional start sites of EPLIN-alpha. The activity of 0.7 kb EPLIN-alpha promoter reporter construct could be enhanced by activated RhoA, indicating that this serum response element is functional. (C) 2000 Elsevier Science B.V. All rights reserved.