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Differential transport properties of two mdr gene products are distinguished by progesterone
C P Yang1, D Cohen, L M Greenberger
1Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461.
Abstract:
P-glycoprotein is an integral membrane protein that is overproduced in multidrug-resistant cells. It is likely to function as an energy-dependent drug efflux pump to maintain intracellular drug concentrations below cytotoxic levels. Individually isolated multidrug-resistant murine cell lines, J7.V1-1 and J7.V3-1, overproduce P-glycoproteins encoded by the mdr1b and mdr1a genes, respectively. The transport properties of these cell lines and the drug binding characteristics of their P-glycoproteins have been compared. It is concluded that 1) the mdr1a gene product is a more efficient efflux pump than the mdr1b gene product, and 2) whereas a single class of vinblastine binding sites is present in J7.V1-1 membrane vesicles, there appears to be two classes of such sites in J7.V3-1 membrane vesicles. The effects of verapamil and progesterone, two compounds that are known to interact with P-glycoprotein, have been analyzed in the two cell lines. Progesterone inhibited drug binding and efflux and increased drug sensitivity to vinblastine with more potency in J7.V1-1 cells than in J7.V3-1 cells. It is concluded that progesterone, but not verapamil, can be used to differentiate the two mdr gene products in the mouse.
Insights
Multidrug resistance involves P-glycoprotein (P-gp) efflux pumps. Mouse cell lines show mdr1a P-gp is a more efficient pump than mdr1b P-gp, with progesterone differentiating their drug interactions.
Area of Science:
- Biochemistry
- Molecular Biology
- Pharmacology
Background:
- P-glycoprotein (P-gp) is an integral membrane protein overproduced in multidrug-resistant cells.
- P-gp functions as an energy-dependent drug efflux pump, maintaining intracellular drug concentrations below cytotoxic levels.
- Murine cell lines J7.V1-1 and J7.V3-1 overproduce P-gp encoded by mdr1b and mdr1a genes, respectively.
Purpose of the Study:
- To compare the transport properties and drug binding characteristics of P-glycoproteins encoded by mdr1a and mdr1b genes.
- To analyze the effects of verapamil and progesterone on drug sensitivity, binding, and efflux in these cell lines.
- To determine if verapamil or progesterone can differentiate between the mdr1a and mdr1b gene products.
Main Methods:
- Comparative analysis of drug transport and binding in multidrug-resistant murine cell lines.
- Utilizing membrane vesicles from J7.V1-1 (mdr1b) and J7.V3-1 (mdr1a) cell lines.
- Assessing the effects of verapamil and progesterone on vinblastine binding and efflux.
Main Results:
- The mdr1a gene product functions as a more efficient efflux pump than the mdr1b gene product.
- J7.V1-1 membrane vesicles exhibit one class of vinblastine binding sites, while J7.V3-1 vesicles show two classes.
- Progesterone demonstrated greater potency in inhibiting drug binding and efflux, and increasing vinblastine sensitivity in J7.V1-1 cells compared to J7.V3-1 cells.
Conclusions:
- The mdr1a gene product is a more efficient P-glycoprotein efflux pump than the mdr1b gene product.
- Distinct vinblastine binding site characteristics exist between the mdr1a and mdr1b P-glycoproteins.
- Progesterone can differentiate the functional properties of the mdr1a and mdr1b gene products, unlike verapamil.