May act as a papain-like cysteine protease inhibitor to modulate the host immune response against tumor cells. Also functions as an inhibitor of UV-induced apoptosis via suppression of the activity of c-Jun NH(2)-terminal kinase (JNK1). Interacts with MAPK8/JNK1. Seems to also be secreted in plasma by cancerous cells but at a low level. Squamous cells. Expressed in some hepatocellular carcinoma (at protein level). Its expression is closely related to cellular differentiation in both normal and malignant squamous cells. Strongly up-regulated in the upper epidermis of sun-exposed skin. Belongs to the serpin family. Ov-serpin subfamily.