Angiostatin, a potent endogenous inhibitor of angiogenesis, is generated by
cancer-mediated proteolysis of
plasminogen. The culture medium of human prostate
carcinoma cells, when incubated with
plasminogen at a variety of pH values, generated
angiostatic peptides and
miniplasminogen. The
enzyme(s) responsible for this reaction was purified and identified as
procathepsin D. The purified
procathepsin D, as well as
cathepsin D, generated two
angiostatic peptides having the same NH(2)-terminal amino acid sequences and comprising kringles 1-4 of
plasminogen in the pH range of 3.0-6.8, most strongly at pH 4.0 in vitro. This reaction required the concomitant conversion of
procathepsin D to catalytically active pseudocathepsin D. The conversion of pseudocathepsin D to the mature
cathepsin D was not observed by the prolonged incubation. The affinity-purified
angiostatic peptides inhibited angiogenesis both in vitro and in vivo. Importantly,
procathepsin D secreted by human
breast carcinoma cells showed a significantly lower
angiostatin-generating activity than that by human prostate
carcinoma cells. Since deglycosylated
procathepsin D from both prostate and
breast carcinoma cells exhibited a similar low
angiostatin-generating activity, this discrepancy appeared to be attributed to the difference in
carbohydrate structures of
procathepsin D molecules between the two cell types. The seminal vesicle fluid from patients with prostate
carcinoma contained the mature
cathepsin D and
procathepsin D, but not pseudocathepsin D, suggesting that pseudocathepsin D is not a normal intermediate of
procathepsin D processing in vivo. The present study provides evidence for the first time that
cathepsin D secreted by human prostate
carcinoma cells is responsible for
angiostatin generation, thereby causing the prevention of
tumor growth and angiogenesis-dependent growth of
metastases.