Chondroitin sulfate proteoglycan is a potent enhancer in the processing of procathepsin L

The acceleration effect of chondroitin-4-sulfate(CS-) proteoglycan on the processing of procathepsin L in vitro was investigated using enzyme purified from the culture medium of MLC cells. Procathepsin L was slightly processed even when it was incubated without CS-proteoglycan for 60 min in 50 mm acetate buffer, pH 5.5, and trace amounts of the 31 kDa mature form and 35-38 kDa intermediates of cathepsin L were formed. On the other hand, in the presence of CS-proteoglycan, procathepsin L was completely converted to the mature form within the same 60 minute time period. Moreover, Z-Phe-Arg-MCA hydrolyzing activity was increased significantly by the incubation with CS-proteoglycan, while no considerable increase in the activity was observed during the incubation without CS-proteoglycan. Since the specific cathepsin L inhibitor, CLIK-195, inhibited the processing of procathepsin L accelerated by CS-proteoglycan, the trace amount of cathepsin L activity may participate in the processing. These results suggest that CS-proteoglycan may play a role in accelerating the processing of procathepsin L as an endogenous enhancer in the extracellular environment in vivo.