Cathepsin B Efficiently Activets the Soluble and the Tumor Cell Receptor-Bound Form of the Proenzyme Urokinase-Type Plasminogen Activator (Pro-Upa)

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Abstract
Tumor cell invasion and metastasis is a multifactorial process, which at each step may require the action, of proteolytic enzymes such as collagenase, cathepsins, plasmin, or plasminogen activators 1,2. An enzymatically inactive proenzyme form of the urokinase-type plasminogen activator (pro-uPA) is secreted by tumor cells 1,3. Cathepsin B, a cysteine-dependent protease, which is elevated in tumors, plays a regulatory role in collagen degradation, since it can convert inactive procollagenase IV to its enzymatically active form 4. We demonstrate that cathepsin B has the capacity to efficiently convert soluble or tumor cell receptor-bound pro-uPA to enzymatically active two-chain uPA. Thus, the cellular protease cathepsin B may substitute for the plasma protease plasmin in the activation of pro-uPA released by tumor cells.

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