Molecular identification and characterization of novel membrane-bound metalloprotease, the soluble secreted form of which hydrolyzes a variety of vasoactive peptides

One class of zinc metalloproteases, represented by neutral endopeptidase 24.11 and endothelin-converting enzyme, has been shown to be involved in proteolytic activation or inactivation of many regulatory peptides. Here, we report molecular cloning and characterization of a novel member of this type II membrane-bound metalloprotease family, termed soluble secreted endopeptidase (SEP). Alternative splicing results in the generation of another transcript, SEPDelta, which lacks a 69-base pair nucleotide segment following the transmembrane helix, Both SEP and SEPDelta mRNA are detected in all mouse tissues examined. Transfection of an SEP cDNA expression construct resulted in the expression of the membrane-bound form of SEP in the early secretory pathway as well as the soluble secreted form of the enzyme in the culture medium. In contrast, transfection of the SEPDelta cDNA only results in the expression of the membrane-bound form. In vitro enzymological analysis of the recombinant soluble form of SEP demonstrated that it hydrolyzes a variety of vasoactive peptides, including endothelin-1, atrial natriuretic peptide, and angiotensin I. This activity of SEP was inhibited by phosphoramidon and the neutral endopeptidase 24.11 specific inhibitor thiorphan, but it was only partially inhibited by the endothelin-converting enzyme specific inhibitor FR901533. These findings suggest that SEP is a novel metalloprotease that possesses a broad substrate specificity and that it may be involved in the metabolism of biologically active peptides intracellulary as well as extracellularly.