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Immunocytochemical localization of P170 at the plasma membrane of multidrug-resistant human cells
M C Willingham1, N D Richert, M M Cornwell
1Laboratory of Molecular Biology, National Cancer Institute, Bethesda, MD 20892.
Abstract:
P170 (P-glycoprotein) is a membrane protein found in high levels in multidrug-resistant cultured cell lines. We have localized this protein using monoclonal antibody MRK16 by immunofluorescence and electron microscopy in the multidrug-resistant human carcinoma cell line KB-C4. The P170 determinant recognized by antibody MRK16 was found on drug-resistant KB-C4 cells, but not on parental drug-sensitive KB-3-1 cells. The determinant was present on the external surface of the plasma membrane and on the luminal side of Golgi stack membranes. P170 was excluded from coated pits at the plasma membrane and absent from endocytic vesicles and lysosomes. This determinant was detected only in small amounts in the endoplasmic reticulum. The high protein concentration of P170 in the plasma membrane is consistent with a role of this protein as a drug efflux pump at the cell surface.
Insights
P-glycoprotein (P170) is highly concentrated on the cell surface of multidrug-resistant cancer cells, suggesting its role as a drug efflux pump. This localization was confirmed using immunofluorescence and electron microscopy in resistant KB-C4 cells.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- P-glycoprotein (P170) is a membrane protein associated with multidrug resistance in cancer cells.
- High levels of P170 are found in multidrug-resistant cell lines, but its precise localization is key to understanding its function.
Purpose of the Study:
- To localize P-glycoprotein (P170) in multidrug-resistant human carcinoma cells (KB-C4) using the monoclonal antibody MRK16.
- To determine the cell surface and intracellular distribution of P170 in relation to drug resistance.
Main Methods:
- Immunofluorescence microscopy
- Electron microscopy
- Use of monoclonal antibody MRK16 to detect P170 determinant
Main Results:
- P170 determinant was detected on drug-resistant KB-C4 cells but not on drug-sensitive parental KB-3-1 cells.
- P170 was localized on the external surface of the plasma membrane and the luminal side of Golgi stack membranes.
- P170 was excluded from coated pits, endocytic vesicles, and lysosomes, with minimal presence in the endoplasmic reticulum.
Conclusions:
- The high concentration of P170 on the plasma membrane supports its role as a cell surface drug efflux pump.
- Understanding P170 localization provides insights into mechanisms of multidrug resistance in cancer.