To better understand the biochemical mechanisms necessary for prostate cancer invasion and metastases, we studied the expression and interaction of proteolytic enzymes cathepsin D, cathepsin B, urokinase and collagenase IV in human prostate cell lines LNCAP (hormone sensitive) and DU145 (hormone refractory). Cellular fractionation and immunoblotting revealed that both cell lines expressed similar amounts of the 34 kD form of cathepsin D, 72 kD form of collagenase IV and the 55 kD form of urokinase. However, DU145 expressed an increased amount of the 28 kD form of cathepsin B. When E64, a cysteine protease inhibitor was added, a decreased amount of the active cathepsin D was expressed. Furthermore, when cathepsin B was added to concentrated plasma membrane homogenates, urokinase was processed to its active form at 33 kD. E64 inhibited the ability of both cell lines to degrade fibronectin. An in vitro Boyden chamber demonstrated that DU145 was more motile than LNCAP and that preincubation with E64 could decrease motility of both cell lines. We suggest that cathepsin B may promote tumor invasion not only by proteolysis of basement membrane components, but also by activating other proteases.

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