Redistribution of lysosomes to the cell surface and secretion of lysosomal proteases appear to be general phenomena in cells that participate in local proteolysis. In the present study, we have determined whether malignant progression affects the intracellular distribution and secretion of the lysosomal protease cathepsin B in three model systems, each of which consists of cell pairs that differ in their degree of malignancy. The intracellular distribution of vesicles staining for cathepsin B was evaluated by immunofluorescent microscopy and the secretion of cathepsin B was evaluated by two complementary techniques: stopped assays of activity secreted into culture media; and continuous assays of activity secreted from viable (≥95%) cells growing on coverslips. We observed that the intracellular distribution of cathepsin B+ vesicles was more peripheral in the cells of higher malignancy in all three model systems and that active cathepsin B was secreted constitutively from these cells. Because an acidic pericellular pH has been shown to induce translocation of lysosomes in macrophages and fibroblasts, we evaluated the intracellular distribution of cathepsin B+ vesicles and secretion of cathepsin B in cell pairs incubated at slightly acidic pH. Acidic pericellular pH induced a redistribution of cathepsin B+ vesicles toward the cell periphery. In the more malignant cells, this resulted with time in reduced intracellular staining for cathepsin B and enhanced secretion of active cathepsin B. Translocation and secretion of cathepsin B were dependent on a functional microtubular system. Both the redistribution of cathepsin B+ vesicles toward the cell surface induced by acidic pH and the constitutive and acidic pH-induced secretion of active cathepsin B could be inhibited by microtubule poisons and stabilizers. We suggest that the redistribution of active cathepsin B to the surface of malignant cells and its secretion may facilitate invasion of these cells.
↵1 This work was supported by USPHS Grants CA 36481 and CA 56586. Development of the MCF-10 human breast epithelial cell lines has been supported by a grant from the Elsa U. Pardee Foundation and the core support grant of the Meyer Prentis Comprehensive Cancer Center of Metropolitan Detroit.
↵2 To whom requests for reprints should be addressed, at the Department of Pharmacology, Wayne State University School of Medicine, 540 E. Canfield, Detroit, MI 48201.
- Received May 11, 1994.
- Accepted October 26, 1994.
- ©1994 American Association for Cancer Research.