PI13, a novel keratinocyte-associated member of the ovalbumin (ov) family of serpins showing a predominant expression in cells of the human keratinocyte cell line HaCaT and in lesional keratinocytes from psoriatic skin. Initially identified as a UV-repressible gene in HaCaT cells , this novel serpin is also called 'HaCaT UV-repressible serpin,' or hurpin.Sequence analysis predicted that the 391-amino acid protein contains an inhibitory serpin hinge region, a reactive site loop near the C terminus, and a penultimate serine residue found in all ov-serpin family members. Northern blot analysis detected a 3.3-kb transcript in normal oral mucosa but not in tumor-derived oral mucosa; no expression was detected in any other tissue tested. Expression in squamous carcinoma and head and neck tumor cell lines compared with normal oral mucosa.