Meprin B: transcriptional and posttranscriptional regulation of the meprin beta metalloproteinase subunit in human and mouse cancer cells

Abstract

A novel mRNA isoform encoding the cell surface metalloproteinase meprin beta is expressed in mouse teratocarcinoma cells and in a variety of cultured human cancer cells. In both mouse and human cells, the cancer cell-specific mRNA isoform, referred to as beta', has an extended 5' UTR as compared to the meprin beta mRNA isoform expressed in normal kidney and intestinal epithelium. The work herein aimed to determine the molecular mechanisms for the expression of meprin beta and beta' in normal and cancer cells, respectively. Analysis of the 5' end of the mouse meprin beta gene revealed that the unique sequences in the beta and beta' mRNA isoforms are encoded by separate exons that are alternately spliced, and transcribed from independent promoters. By contrast, the human meprin beta and beta' mRNAs have identical sequences except for 87 additional bases in the 5' UTR sequence of beta', indicating that a single, mixed usage promoter directs expression of the isoforms. The region upstream of the human meprin beta' transcription start site contained elements with homology to the promoters of intestine-specific genes, interspersed with AP-1 and PEA3 elements; the latter were essential to meprin beta' promoter activity in cancer cells. Phorbol myristal acetate increased meprin beta' mRNA levels in cultured human colon cancer cells, providing further evidence that AP-1/PEA3 sites are actively involved in meprin beta' expression.