Cell surface-bound elastase and cathepsin G on human neutrophils: a novel, non-oxidative mechanism by which neutrophils focus and preserve catalytic activity of serine proteinases.

Abstract

Abstract. Serine proteinases of human polymorphonuclear neutrophils play an important role in neutrophilmediated proteolytic events; however, the non-oxidative mechanisms by which the cells can degrade extracellular matrix in the presence of proteinase inhibitors have not been elucidated. Herein, we provide the first report that human neutrophils express persistently active cell surface-bound human leukocyte elastase and cathepsin G on their cell surface. Unstimulated neutrophils have minimal cell surface expression of these enzymes; however, phorbol ester induces a 30-fold increase. While exposure of neutrophils to chemoattractants (fMLP and C5a) stimulates modest (two-to threefold) increases in cell surface expression of serine proteinases, priming with concentrations of lipopolysaccharide as low as 100 fg/ml leads to striking (up to 10-fold) increase in chemoattractant-induced cell surface expression, even in the presence of serum proteins. LPSprimed and fMLP-stimulated neutrophils have ~100 ng of cell surface human leukocyte elastase activity per 106 cells. Cell surface-bound human leukocyte elastase is catalytically active, yet is remarkably resistant to inhibition by naturally occurring proteinase inhibitors. These data indicate that binding of serine proteinases to the cell surface focuses and preserves their catalytic activity, even in the presence of proteinase inhibitors. Upregulated expression of persistently active cell surfacebound serine proteinases on activated neutrophils provides a novel mechanism to facilitate their egress from the vasculature, penetration of tissue barriers, and recruitment into sites of inflammation. Dysregulation of the cell surface expression of these enzymes has the potential to cause tissue destruction during inflammation.

Role of neutrophil elastase in hypersecretion in asthma

“…These studies are compatible with the results of a recent study describing the binding of elastase to the neutrophil plasma membrane [24]. The studies by OWEN et al [25] showed the importance of surface-bound elastase and of the pericellular environment in determining the enzymatic activity of elastase in tissues.…”

The cell biology of leukocyte-mediated proteolysis

“…Membrane-bound HLE exhibits striking catalytic activity against fibronectin and type IV collagen [49,80], indicating that this form of the enzyme may play important roles in penetration of tissue barriers during cellular migration. Membrane-bound CG has potent capacity to convert the biologically inactive peptide angiotensin I to angiotensin II [81], which regulates vascular smooth muscle tone, vascular permeability, and mononuclear cell chemotaxis.…”

“…In marked contrast to HLE and CG that are freely released from leukocytes, membrane-bound HLE and CG are remarkably resistant to inhibition by naturally occurring proteinase inhibitors [80,81]. It is noteworthy that membrane-bound CG can convert angiotensin I to angiotensin II even in undiluted plasma [81].…”

“…Rather, HLE and CG become bound to the external surface of the plasma membrane [48,49,80]. Unstimulated PMN express minimal amounts of membrane-bound HLE or CG.…”

“…Unstimulated PMN express minimal amounts of membrane-bound HLE or CG. Priming of cells with cytokines [such as tumor necrosis factor ␣ (TNF-␣), platelet-activating factor (PAF) or lipopolysaccharide (LPS)] followed by stimulation with chemoattractants (fMLP or IL-8) results in optimal (up to 20-fold) increases in cell surface expression of HLE and CG, and optimally activated cells express ϳ200 ng of each proteinase/10 6 cells [48,49,80].…”