Proteinase Inhibitor 6 (PI-6) Expression in Human Skin: Induction of PI-6 and a PI-6/Proteinase Complex during Keratinocyte Differentiation

• Published in: Experimental cell research Vol. 245; no. 2; pp. 263 - 271
• Main Authors: Scott, Fiona L., Paddle-Ledinek, Joanna E., Cerruti, Loretta, Coughlin, Paul B., Salem, Hatem H., Bird, Phillip I.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15-12-1998
• Subjects: Animals; Antibodies, Monoclonal; Blotting, Northern; Cell Differentiation; Cell Line; Cell Size; Cells, Cultured; COS Cells; Cytosol - metabolism; Epidermis - cytology; Epidermis - enzymology; Epidermis - metabolism; Gene Expression Regulation; Humans; Keratinocytes - cytology; Keratinocytes - enzymology; Keratinocytes - metabolism; Keratins - metabolism; Molecular Weight; Multienzyme Complexes - metabolism; Protein Conformation; Serine Endopeptidases - metabolism; Serpins - chemistry; Serpins - genetics; Serpins - immunology; Serpins - metabolism; Thrombin - metabolism
• ISSN: 0014-4827; 1090-2422
• DOI: 10.1006/excr.1998.4241

Proteinase inhibitor 6 (PI-6) is a 42-kDa intracellular protein present in epithelial cells and endothelial cells. It is capable of inhibiting a number of serine proteinases, including trypsin and chymotrypsin. In this study we examined PI-6 expression in human skin and its primary cell type, the keratinocyte. By immunohistochemical analysis, PI-6 staining is absent from the basal cells, weak in the spinous layer, and strongest in the granulosa layer of human epidermis. Immunoblotting of cultured primary keratinocytes revealed that PI-6 production increases 24-fold on differentiation. Analysis of an immortalized keratinocyte cell line, HaCat, showed a 5-fold increase in PI-6 mRNA and a 7-fold increase in PI-6 protein upon differentiation, and indirect immunofluorescence revealed that this is due to an increase in the number of differentiated cells expressing high levels of PI-6. Of particular interest is the appearance of a preformed complex between PI-6 and an endogenous serine proteinase in differentiating HaCat cells, which was detected by a monoclonal antibody demonstrated to preferentially recognize PI-6 in complex with a proteinase. This identification of a PI-6/proteinase complex is the first example of a serpin bound to a proteinase in keratinocytes. We postulate that a physiological role of PI-6 is to regulate a serine proteinase associated with keratinocyte differentiation.