The role of cathepsin L in malignant transformation.

Procathepsin L is the major excreted protein of malignantly transformed mouse fibroblasts and it is one of the major acid cysteine proteases in mammalian cells. The broad general protease activity of cathepsin L against a variety of extracellular matrix proteins as well as other intracellular protein substrates, and its regulation by factors which stimulate growth, suggest that it contributes to the transformed phenotype. Possible functions in antigen processing, invasiveness, metastasis, and turnover of intracellular and secreted proteins involved in growth regulations have been proposed.