Malignant transformation alters intracellular trafficking of lysosomal cathepsin D in human breast epithelial cells

Increased expression and alteration of intracellular trafficking of lysosomal cathepsins have been reported in malignant tumors, or in cells transformed by the transfection with the ras oncogene. In the present study, immortal MCF-10A human breast epithelial cells were transformed with the mutated ras oncogene. Both cell lines were investigated for changes in the intracellular localization of lysosomal cathepsin D and lamp-1 (lysosome- associated membrane protein) employing specific antibodies and confocal immunofluorescence microscopy. The results revealed that staining for cathepsin D along with for lamp-1 was mostly localized in the perinuclear region of MCF-10A cells. In contrast, the staining for these proteins was found to be widely distributed throughout the cytoplasm and at the cell periphery in MCF-10AneoT cells. The organization of microtubules, but not actin, appeared to differ between MCF-10A cells and their oncogenic ras transfectants. When the microtubules were depolymerized by treatment of MCF- 10A cells with nocodazole, vesicles containing the lysosomal cathepsin D were dispersed in the cytoplasm and translocation of these vesicles to the cell periphery was observed. The intracellular localization of cathepsin D in the nocodazole-treated MCF-10A cells seemed to be similar to that observed in the oncogenic ras transfectants of these cells. When taxol, which inhibits microtubule depolymerization, was added to the culture medium of neoT cells, a polymerized microtubule network was observed, and the reclustering of cathepsin D and lamp-1 occurred in a unidirectional manner towards the perinuclear region. These findings support a model in which cytoskeletal microtubule organization is closely related to the trafficking of lysosomes/endodomes, and in which oncogenic ras interferes with such organization in human breast epithelial cells.