PROTEINASE-3 - A NEUTROPHIL PROTEINASE WITH ACTIVITY ON PLATELETS

Purified proteinase 3 (PR3) devoid of any elastase (HLE) and cathepsin C (Cat.G) contaminants, was prepared from azurophilic granules of hum an polymorphonuclear neutrophils by using a novel procedure. Although unable to induce platelet activation (up to 25 mu g/ml) by itself, PR3 at a concentration as low as 2.5 mu g/ml enhanced the platelet respon se to a concomitantly added threshold concentration of Cat.G, a recogn ized platelet agonist. In the presence of 10 mu g/ml PR3, aggregation and degranulation of platelets induced by Cat.G were 43.2 +/- 5.9% and 27.1 +/- 1.9% as compared with 5.5 +/- 2.9% and 4.2 +/- 1.5% (n = 4) for Cat.G alone. This enhancing effect by PR3 was also observed with c ollagen and a cyclic endoperoxide analogue, and was inhibited by eglin C and elafin, two PR3 inhibitors. Associated with the removal of acti vity by a anti-PR3 mAb and the lack of effect of the secretory leukocy te proteinase inhibitor, these data demonstrated that the effect is sp ecifically related to the enzymatic activity of PR3. It is hypothesize d that this mechanism could play a role in the polymorphonuclear neutr ophil-mediated platelet activation, an event already known to be depen dent on Cat.G and HLE. This is supported by the fact that the associat ion of PR3 and HLE, at concentrations ineffective by themselves, was a ble to potentiate Cat.G-induced platelet activation.