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Immunoelectron microscopy of the receptor for urokinase plasminogen activator and cathepsin D in the human breast cancer cell line MDA‐MB‐231
Author(s) -
Bastholm LONE,
Elling FOLMER,
BrÜNner NILS,
Nielsen MORTEN H.
Publication year - 1994
Publication title -
apmis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.909
H-Index - 88
eISSN - 1600-0463
pISSN - 0903-4641
DOI - 10.1111/j.1699-0463.1994.tb04876.x
Subject(s) - urokinase receptor , immunoelectron microscopy , microbiology and biotechnology , cathepsin d , cytoplasm , chemistry , vesicle , plasminogen activator , receptor , cell , biology , biochemistry , endocrinology , immunology , enzyme , immunohistochemistry , membrane
Receptors for urokinase‐type plasminogen activator (uPAR) are present on the surface of many cell types and appear to be the key determinant controlling extracellular proteolysis catalyzed by the urokinase‐type plasminogen activator (uPA). Receptor‐bound uPA may be inhibited by the specific inhibitors PAI‐1 and PAI‐2, and the complex thus formed may subsequently be internalized and degraded in lysosomes. Biochemical evidence has recently indicated that also uPAR is internalized with the uPA/uPAI complex. We report here the subcellular localization of uPAR and cathepsin D in the MDA‐MB‐231 human breast cancer cell line studied by immuno‐electron microscopy of ultrathin cryosections using single or double immunostaining techniques. Cell surface uPAR was preferentially localized at cell‐cell junctions; cytoplasmic uPAR was inside large vesicles of different morphology and in flat Golgi saccules. A number of vesicles also contained cathepsin D. The uPAR was exclusively membrane‐bound at the cell surface and in cytoplasmic vesicles without cathepsin D. In lysosomal vesicles with both cathepsin D and u‐PAR, uPAR was probably degraded as it was observed in the luminal contents.