INDUCIBLE BINDING OF BIOACTIVE CATHEPSIN-G TO THE CELL-SURFACE OF NEUTROPHILS - A NOVEL MECHANISM FOR MEDIATING EXTRACELLULAR CATALYTIC ACTIVITY OF CATHEPSIN-G

Catalytically active cathepsin G that is bound to the cell surface of human neutrophils may play a variety of roles in normal neutrophil bio logy and in pathobiology associated with inflammation. In this study, we describe expression of neutrophil cell surface-bound cathepsin G in response to TNF-alpha and platelet-activating factor (PAF) under cond itions in which minimal free release of cathepsin G is detected. TNF-a lpha and PAF alone induced modest (two- to threefold) increases in cel l surface-bound cathepsin G, but exhibited a marked dose- and time-dep endent priming effect for subsequent chemoattractant-induced responses (up to 15- to 25-fold increases in cell surface expression). When opt imally primed (TNF-alpha, 100 U/ml, or PAF, 10(-9) M), neutrophils exp ressed five- to sixfold more cell surface-bound cathepsin G, in compar ison with cells exposed to FMLP alone. Priming responses were more rap id with PAF (15 s to 5 min) than with TNF-alpha (1 to 60 min). Optimal ly primed and FMLP-stimulated neutrophils express similar to 160 ng of catalytically active cathepsin G per 10(6) cells, which represents si milar to 11% of the cellular content of unstimulated cells. Cathepsin C binds to the cell surface by a charge-dependent mechanism since: 1) incubation of cells with highly positively charged molecules abrogated agonist-induced up-regulation of the cell surface -expression of cath epsin C and 2) cathepsin G was eluted from the cell surface by high co ncentrations of NaCl, These data indicate that interactions between bi ologically relevant pro-inflammatory cytokines and chemoattractants se rve to markedly up-regulate cell surface-bound cathepsin C. The focuse d catalytic activity of cell surface-bound cathepsin G may alter endot helial and epithelial barriers, promote thrombogenesis, injure extrace llular matrix, and/or facilitate directed migration of neutrophils dur ing inflammation.