Complete nucleotide sequence, origin of isoform and functional characterization of the mouse hepsin gene

Hepsin, a type-IT membrane-associated serine protease, has been implicated in cell growth and development as well as possible initiation of blood coag ulation. Here, we report on the complete nucleotide sequence, functional ch aracterization of key structural features and the promoter of the mouse hep sin gene. The gene has a size of approximate to 17 kb, and is composed of 1 2, 13, or 14 exons depending on alternative intron splicings - one in the 5 '-UTR and the other two in the second intron. The latter two, which occur i n approximately half of the hepsin transcripts. generate a hepsin mRNA spec ies with an extra exon, which is responsible for producing a hepsin isoform with a unique 20-residue sequence inserted in the cytoplasmic portion of h epsin. Most hepsin transcripts have the 5'-UTR intron spliced, and its spli cing can occur independently of the other alternative splicings. The transc riptional initiation site was determined to be 636 bp upstream of the first ATG site in a cytidine-rich region. The 5'-flanking region of hepsin up to nucleotide 274 showed a substantial promoter activity in HepG2 cells, with its expression activity sevenfold higher in the presence of the 5'-UTR int ron sequence in comparison to that without the intron sequence. The basal p romoter region contains potential binding sites for several transcription f actors including SP1, AP2, C/EBP, LF-Al, and E box, which may be responsibl e for ubiquitous, but liver- and kidney-preferred tissue expression of the hepsin gene.