Prostasin is a glycosylphosphatidylinositol-anchored active serine protease

A recombinant human prostasin serine protease was expressed in several huma n cell lines. Subcellular fractionation showed that this serine protease is synthesized as a membrane-bound protein while a free-form prostasin is sec reted into the culture medium, Prostasin was identified in nuclear and memb rane fractions. Membrane-bound prostasin can be released by phosphatidylino sitol-specific phospholipase C treatment, or labeled by [H-3]ethanolamine, indicating a glycosylphosphatidylinositol anchorage. A prostasin-binding pr otein was identified in mouse and human seminal vesicle fluid. Both the sec reted and the membrane-bound prostasin were able to form a covalently linke d 82-kDa complex when incubated with seminal vesicle fluid. The complex for mation between prostasin and the prostasin-binding protein was inhibited by a prostasin antibody, heparin, and serine protease inhibitors. Prostasin's serine protease activity was inhibited when bound to the prostasin-binding protein in mouse seminal vesicle fluid. This study indicates that prostasi n is an active serine protease in its membrane-bound form.