Involved in trophoblast cell proliferation and differentiation probably by affecting mitotic cell cycle progression. Proteolytic activity and nuclear localization are essential for its role in cell cycle progression. Expressed in placenta. Expressed in parietal and spiral artery-associated trophoblast giant cells, most abundantly during the phase of trophoblast invasion. From 14.5 dpc onwards, expressed at lower levels in labyrinth trophoblast cells. Expressed in trophoblast stem cells. Expressed in heart, liver and testis. Expressed in adult but not in embryo. Expressed in the placenta from early post-implantation (5.5 dpc) onwards. After 9.5 dpc expression declines. Belongs to the peptidase C1 family.