title: Inducible binding of bioactive cathepsin G to the cell surface of neutrophils. A novel mechanism for mediating extracellular catalytic activity of cathepsin G.
abstract: Catalytically active cathepsin G that is bound to the cell surface of human neutrophils may play a variety of roles in normal neutrophil biology 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 conditions in which minimal free release of cathepsin G is detected. TNF-alpha and PAF alone induced modest (two- to threefold) increases in cell surface-bound cathepsin G, but exhibited a marked dose- and time-dependent priming effect for subsequent chemoattractant-induced responses (up to 15- to 25-fold increases in cell surface expression). When optimally primed (TNF-alpha, 100 U/ml, or PAF, 10(-9) M), neutrophils expressed five- to sixfold more cell surface-bound cathepsin G, in comparison with cells exposed to FMLP alone. Priming responses were more rapid with PAF (15 s to 5 min) than with TNF-alpha (1 to 60 min). Optimally primed and FMLP-stimulated neutrophils express approximately 160 ng of catalytically active cathepsin G per 10(6) cells, which represents approximately 11% of the cellular content of unstimulated cells. Cathepsin G 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 cathepsin G and 2) cathepsin G was eluted from the cell surface by high concentrations of NaCl. These data indicate that interactions between biologically relevant pro-inflammatory cytokines and chemoattractants serve to markedly up-regulate cell surface-bound cathepsin G. The focused catalytic activity of cell surface-bound cathepsin G may alter endothelial and epithelial barriers, promote thrombogenesis, injure extracellular matrix, and/or facilitate directed migration of neutrophils during inflammation.
mesh_terms: D056649:Cathepsin G; D002403:Cathepsins / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004790:Enzyme Induction; D006801:Humans; D008565:Membrane Proteins / Q000096:biosynthesis; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism*; D010972:Platelet Activating Factor / Q000494:pharmacology; D011485:Protein Binding; D012697:Serine Endopeptidases; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D008565:Membrane Proteins; D010972:Platelet Activating Factor; D014409:Tumor Necrosis Factor-alpha; D009240:N-Formylmethionine Leucyl-Phenylalanine; D002403:Cathepsins; D012697:Serine Endopeptidases; C534094:CTSG protein, human; D056649:Cathepsin G