The name "Pancreasin" because it is transcribed strongly in the pancreas. This secreted, tryptic serine protease, also known as Marapsin or PRSS27 (Protease, serine, 27), is a member of the peptidase S1 family. Pancreasin is inhibited by benzamidine and leupeptin but resists several classic inhibitors of trypsin. Marapsin was constitutively expressed in nonkeratinizing stratified squamous epithelia of human esophagus, tonsil, cervix, larynx, and cornea. In fact, marapsin was the second most strongly up-regulated protease in psoriatic lesions, where expression was localized to the upper region of the hyperplastic epidermis. Similarly, in the hyperproliferative epithelium of regenerating murine skin wounds, marapsin localized to the suprabasal layers, where keratinocytes undergo squamous differentiation. Marapsin's restricted expression, localization, and cytokine-inducible expression suggest a role in the terminal differentiation of keratinocytes in hyperproliferating squamous epithelia.