In human
mammary cancer cells,
pro-cathepsin D (pro-Cath-D) is induced by
estrogens and 50% of it is secreted. To determine whether its secretion is characteristic of mammary cells or transformed cells, we compared its production, processing, and glycosylation in primary cultures of normal mammary epithelial cells to those found in
breast cancer cell lines. The cytosolic concentration of total
cathepsin D (precursor and mature
enzyme) measured by
enzyme-linked
immunosorbent assay was 8 times higher in
cancer cells. Its
mRNA level estimated by Northern blot analysis was 8 to 50 times higher and its secretion was 30 times higher in
cancer cells. Using pulse-chase labeling, the cellular processing of pro-Cath-D was altered in
hormone-dependent and -independent
breast cancer cells in comparison to normal cells. This alteration resulted in a lower accumulation of mature
enzyme, while the secretion and cytoplasmic accumulation of pro-Cath-D was greater in
breast cancer cells than in normal cells. NH4Cl increased secretion of the
proenzyme in normal cells but not in
cancer cells. The secreted
proenzyme was markedly heterogeneous and had a more acidic pI in MCF7 cells than in normal mammary cells. These acidic forms disappeared following
endo-beta-N-acetylglucosaminidase H treatment indicating that the structural difference between pro-Cath-D of normal and of
cancer mammary cells was located on high
mannose or hybrid N-linked
oligosaccharides. This difference may be responsible for the altered routing of the pro-Cath-D in
breast cancer cells.