Probable protease (By similarity). In placenta, plays a role in promoting giant cell differentiation (PubMed:18776147). Also plays a role in placental spiral artery remodeling by direct degradation of smooth muscle alpha-actin (PubMed:18776147). Localizes to the cytoplasm with a punctate staining pattern indicative of a predominant lysosomal and endosomal localization. Expressed in placenta (PubMed:11829493, PubMed:10885754, PubMed:18776147). Highly expressed in a subset of trophoblast giant cells in the parietal yolk sac and at the outside of the ectoplacental cone (PubMed:10885754). Expressed at highest level in liver with lesser amounts in testis, kidney, heart, lung and brain (PubMed:10885754). Not detected in spleen and skeletal muscle (PubMed:10885754, PubMed:11829493). Not detected in blood, heart, brain, testis, liver, lung, kidney, thymus or uterus (PubMed:11829493). Detected from 5.5 dpc in parietal trophoblast giant cells (PubMed:18776147, PubMed:10885754). Detected at 8.5 dpc in placenta, and shows increased expression level from 13.5 to 19.5 dpc (PubMed:11829493). Belongs to the peptidase C1 family.