Angiotensin II generation at the cell surface of activated neutrophils: novel cathepsin G-mediated catalytic activity that is resistant to inhibition.
Human neutrophils express inducible, catalytically active cathepsin G on their cell surface. Herein, we report that membrane-bound cathepsin G on intact neutrophils has potent angiotensin II-generating activity. Membrane-bound cathepsin G on activated neutrophils 1) converts both human angiotensin I and angiotensinogen to angiotensin II; 2) expresses angiotensin II-generating activity equivalent to 8.6 +/- 2.3 (+/-SD) x 10(-18) mol of free cathepsin G (5.2 +/- 1.4 x 10(6) molecules)/cell; and 3) has similar high affinity for angiotensin I compared with free cathepsin G (Km = 5.9 x 10(-4) and 4.6 x 10(-4) M; k(cat) = 4.0 and 2.0/s, respectively). In marked contrast to soluble cathepsin G, membrane-bound enzyme was substantially resistant to inhibition by plasma proteinase inhibitors and converted angiotensin I to angiotensin II even in undiluted plasma. There was a striking inverse relationship between inhibitor size and its effectiveness against membrane-bound cathepsin G activity. Alpha1-antichymotrypsin was a markedly ineffective inhibitor of membrane-bound enzyme (IC50 = 2.18 microM and 1.38 nM when tested against 1 nM membrane-bound and free cathepsin G, respectively). These data indicate that membrane-bound cathepsin G expressed on neutrophils is an inducible and mobile angiotensin II-generating system that may exert potent local vasoactive and chemoattractant properties at sites of inflammation.
Owen
C A
CA
Department of Internal Medicine, University of Utah Health Sciences Center, Salt Lake City 84132, USA. caroline.owen@hsc.utah.edu
Campbell
E J
EJ
D000803:Angiotensin I / Q000378:metabolism; D000804:Angiotensin II / Q000378:metabolism*; D002384:Catalysis; D056649:Cathepsin G; D002403:Cathepsins / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D007700:Kinetics; D019272:Leukocyte Elastase / Q000378:metabolism; D053146:Myeloblastin; D018375:Neutrophil Activation / Q000187:drug effects; D009504:Neutrophils / Q000201:enzymology* / Q000378:metabolism; D007703:Peptidyl-Dipeptidase A / Q000378:metabolism; D053491:Proteinase Inhibitory Proteins, Secretory; D011506:Proteins / Q000494:pharmacology; D012697:Serine Endopeptidases / Q000378:metabolism; D015842:Serine Proteinase Inhibitors / Q000502:physiology*; D000514:alpha 1-Antichymotrypsin / Q000494:pharmacology
D053491:Proteinase Inhibitory Proteins, Secretory; D011506:Proteins; D015842:Serine Proteinase Inhibitors; D000514:alpha 1-Antichymotrypsin; D000804:Angiotensin II; D000803:Angiotensin I; D002403:Cathepsins; D007703:Peptidyl-Dipeptidase A; D012697:Serine Endopeptidases; C534094:CTSG protein, human; D056649:Cathepsin G; D019272:Leukocyte Elastase; D053146:Myeloblastin