Human leukocyte elastase and cathepsin G inactivate factor VII by limited proteolysis.

The effect of supernatant from phorbol myristate acetate (PMA) stimulated human polymorphonuclear granulocytes (PMN) on human factor VII was studied in vitro. The supernatant caused a rapid loss in factor VII coagulant activity by the action of human leukocyte elastase (HLE) and cathepsin G in the supernatant, as demonstrated by the use of specific inhibitors of the two serine proteases, respectively. Preincubation of the supernatant with the elastase inhibitor and the cathepsin G inhibitor preserved 80% and 25% of the clotting activity, respectively. Calcium protected factor VII completely from the supernatant mediated inactivation. Cathepsin G and HLE purified from PMN each destroyed the coagulant activity of factor VII when added to a non-plasma system. There were, however, no effect on factor VII activity when cathepsin G was added to plasma. Polyacrylamide gel electrophoresis in the presence of SDS indicated that HLE and cathepsin G cleaved the zymogen in the same manner, producing (a) peptide(s) of low molecular mass and a single large product of 48 kDa. Preincubation of factor VII with calcium ions inhibited the proteolytic action of HLE and cathepsin G. It is suggested that HLE and cathepsin G from activated granulocytes may be partly responsible for the loss in factor VII activity that is observed during sepsis.