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 600aa EPLIN-alpha and the 759aa EPLIN-beta, are generated from a single gene. In the majority of human breast and prostate cancer cell lines, the expression of EPLIN-alpha 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 EPLIN100kb and consists of 11 exons. The EPLIN-beta mRNA requires all 11 exons, while the EPLIN-alpha mRNA requires Exons 4-11. The transcriptional start sites of EPLIN-alpha were mapped within the third intron by 5' RACE and S1 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-alpha, 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 100bp upstream of the transcriptional start sites of EPLIN-alpha. The activity of 0.7kb EPLIN-alpha promoter reporter construct could be enhanced by activated RhoA, indicating that this serum response element is functional.