ACID-ACTIVATED INSULIN-LIKE-GROWTH-FACTOR BINDING-PROTEIN PROTEASE ACTIVITY OF CATHEPSIN-D IN NORMAL AND MALIGNANT PROSTATIC EPITHELIAL-CELLS AND SEMINAL PLASMA

In this study, we demonstrate insulin-like growth factor binding prote in (IGFBP) acid proteolysis in conditioned media (CM) from normal and malignant primary cultures of prostatic epithelial cells, prostatic ce ll lines, and in seminal plasma. We further demonstrate the absence of such activity in CM from prostatic stromal cells. Radio-labeled ICFBP s (1-6) were incubated with various acidified CM and seminal plasma. N one of these media showed IGFBP proteolytic activity at neutral pH, bu t all CM from prostatic epithelial cells (PC-E) demonstrated strong IG FBP proteolysis at acidic pH. No acid-activated proteolysis was observ ed in the CM from stromal cell cultures. In order to ascertain the rol e of cathepsin D, anticathepsin antibodies were used to immunodeplete the media of the selected enzymes prior to incubation with IGFBPs. Dep letion of cathepsin D greatly reduced the proteolytic activity of the PC-E CM. Additionally, purified cathepsin D yielded a digestion patter n identical to that produced by prostatic cell CM and seminal plasma, following acidic incubation with IGFBP-3. Remarkably, the proteolytic pattern generated by seminal plasma, when incubated with IGFBP-3 at ne utral pH, corresponded to that produced by prostate-specific antigen ( PSA), demonstrating the interpolation of both neutral and acid proteas es from prostate cells into seminal plasma. In conclusion, prostatic e pithelial cells secrete acid-specific IGFBP protease(s) related to cat hepsin D. Although no significant statistical difference was observed in the degree of acid-specific proteolysis in the media from normal ve rsus malignant primary epithelial cell cultures, physiological charact eristics of the malignant state might facilitate increased cathepsin D activity. We suspect this proteolysis may play a role in prostatic ce ll proliferation and invasive tumor growth. (C) 1997 Wiley-Liss, Inc.