Activation of pro-urokinase by cathepsin G in the presence of glucosaminoglycans

Abstract

Summary The effect of extracellular matrix glycosaminoglycans (GAGs) on the activity of cathepsin G (Cat G) was investigated. Heparin inhibited the amidolytic activity of Cat G with some peptidyl substrates, whereas it enhanced the activity with others. The effect on Cat G activity was observed with high M r heparin as well as with fractions of relatively low M r . This is in contrast to the effect of heparin on the activity of human leukocyte elastase (HLE) where the effect was observed only with high M r fractions. The Cat G-mediated activation of pro-u-PA was also investigated. In agreement with previous observations (Learmonth et al. Fibrinolysis 1992; 6 (suppl 4): 113–116) we found that Cat G cleaved pro-u-PA primarily in the epidermal growth factor-like domain, and secondarily at, or close to the activation site. Our results showed that the interaction between Cat G and pro-u-PA was strongly enhanced by heparin, and that 75% conversion into an active u-PA form could be obtained. Stimulation of Cat G-catalyzed activation of pro-u-PA was also observed with heparan sulphate and chondroitin sulphate A, B and C. The effect of various fractions of heparin was investigated and shown to depend strongly on the M r with little or no stimulation of the low-M r fractions. We propose that a substantial amount of active u-PA with impaired receptor binding may accumulate under some conditions as a result of influx and activation of neutrophils.