Proteinase inhibitor 6 (PI-6) expression in human skin: induction of PI-6 and a PI-6/proteinase complex during keratinocyte differentiation

Exp Cell Res. 1998 Dec 15;245(2):263-71. doi: 10.1006/excr.1998.4241.

Abstract

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.

MeSH terms

  • Animals
  • Antibodies, Monoclonal
  • Blotting, Northern
  • COS Cells
  • Cell Differentiation
  • Cell Line
  • Cell Size
  • Cells, Cultured
  • Cytosol / metabolism
  • Epidermal Cells*
  • 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

Substances

  • Antibodies, Monoclonal
  • Multienzyme Complexes
  • Serpins
  • serpin B6
  • Keratins
  • Serine Endopeptidases
  • Thrombin