ACTIVATION OF PROUROKINASE BY CATHEPSIN-G IN THE PRESENCE OF GLUCOSAMINOGLYCANS

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.