Proteinase inhibitor 6 (PI-6) expression in human skin: induction of PI-6 and a PI-6/proteinase complex during keratinocyte differentiation.
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.
Scott
F L
FL
Department of Medicine, Monash University, Box Hill Hospital 3128, Melbourne, Australia.
Paddle-Ledinek
J E
JE
Cerruti
L
L
Coughlin
P B
PB
Salem
H H
HH
Bird
P I
PI
D000818:Animals; D000911:Antibodies, Monoclonal; D015152:Blotting, Northern; D019556:COS Cells; D002454:Cell Differentiation; D002460:Cell Line; D048429:Cell Size; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D000078404:Epidermal Cells; D004817:Epidermis / Q000201:enzymology / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D015603:Keratinocytes / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism; D007633:Keratins / Q000378:metabolism; D008970:Molecular Weight; D009097:Multienzyme Complexes / Q000378:metabolism; D011487:Protein Conformation; D012697:Serine Endopeptidases / Q000378:metabolism; D015843:Serpins / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D013917:Thrombin / Q000378:metabolism
D000911:Antibodies, Monoclonal; D009097:Multienzyme Complexes; D015843:Serpins; C094472:serpin B6; D007633:Keratins; D012697:Serine Endopeptidases; D013917:Thrombin