PERICELLULAR PH AFFECTS DISTRIBUTION AND SECRETION OF CATHEPSIN-B IN MALIGNANT-CELLS

Redistribution of lysosomes to the cell surface and secretion of lysos omal proteases appear to be general phenomena in cells that participat e in local proteolysis. In the present study, we have determined wheth er malignant progression affects the intracellular distribution and se cretion of the lysosomal protease cathepsin B in three model systems, each of which consists of cell pairs that differ in their degree of ma lignancy, The intracellular distribution of vesicles staining for cath epsin B was evaluated by immunofluorescent microscopy and the secretio n of cathepsin B was evaluated by two complementary techniques: stoppe d assays of activity secreted into culture media; and continuous assay s of activity secreted from viable (greater than or equal to 95%) cell s growing on coverslips. We observed that the intracellular distributi on 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 pericellu lar pH has been shown to induce translocation of lysosomes in macropha ges and fibroblasts, we evaluated the intracellular distribution of ca thepsin B+ vesicles and secretion of cathepsin B in cell pairs incubat ed at slightly acidic pH. Acidic pericellular pH induced a redistribut ion of cathepsin B+ vesicles toward the cell periphery, In the more ma lignant cells, this resulted with time in reduced intracellular staini ng for cathepsin B and enhanced secretion of active cathepsin B+ Trans location and secretion of cathepsin B were dependent on a functional m icrotubular system, Both the redistribution of cathepsin B+ vesicles t oward the cell surface induced by acidic pH and the constitutive and a cidic pH-induced secretion of active cathepsin B could be inhibited by microtubule poisons and stabilizers, We suggest that the redistributi on of active cathepsin B to the surface of malignant cells and its sec retion may facilitate invasion of these cells.