Delineation of proteolytic and non-proteolytic functions of the membrane-anchored serine protease prostasin.

The membrane-anchored serine proteases prostasin (PRSS8) and matriptase (ST14) initiate a cell surface proteolytic pathway essential for epithelial function. Mice expressing only catalytically inactive prostasin are viable, unlike prostasin null mice, indicating that at least some prostasin functions are non-proteolytic. Here we used knock-in mice expressing catalytically inactive prostasin (Prss8(Ki/Ki)) to show that the physiological and pathological functions of prostasin vary in their dependence on its catalytic activity. Whereas prostasin null mice exhibited partial embryonic and complete perinatal lethality, Prss8(Ki/Ki) mice displayed normal prenatal and postnatal survival. Unexpectedly, catalytically inactive prostasin caused embryonic lethality in mice lacking its cognate inhibitors HAI-1 (SPINT1) or HAI-2 (SPINT2). Proteolytically inactive prostasin, unlike the wild-type protease, was unable to activate matriptase during placentation. Surprisingly, all essential functions of prostasin in embryonic and postnatal development were compensated for by loss of HAI-1, indicating that prostasin is only required for mouse development and overall viability in the presence of this inhibitor. This study expands our knowledge of non-proteolytic functions of membrane-anchored serine proteases and provides unexpected new data on the mechanistic interactions between matriptase and prostasin in the context of epithelial development.