Characterization of cysteine proteases and their endogenous inhibitors in MCF-7 and adriamycin-resistant MCF-7 human breast cancer cells.

The expression of three lysosomal cysteine proteases was examined in a lowly metastatic, MCF-7 human breast cancer cell line and its highly metastatic, Adriamycin-resistant variant, MCF-7/AdrR. While levels of cathepsin H activity were similar in all cell lines at each stage of growth, intracellular cathepsin B and L activities were highest in MCF-7/AdrR. These high levels were accompanied by growth-related increases in acid/pepsin-activatable cathepsin activity in the culture medium. Analyses of endogenous cathepsin B inhibitor activity in control and heat-treated cell homogenates after fractionation by fast protein liquid chromatography suggested that alterations in cystatin-like, cysteine protease inhibitor activities contribute to increased levels of cathepsin activities in metastatic MCF-7/AdrR cells.