Related Experiment Videos
Effect of P-glycoprotein expression on sensitivity to hormones in MCF-7 human breast cancer cells
R Clarke1, S Currier, O Kaplan
1Vincent T. Lombardi Cancer Research Center, Georgetown University Medical School, Washington, D.C. 20007.
Background:
Data obtained from studies of primary human breast cancers and established cell lines indicate that overexpression of the MDR1 gene (also known as PGY1) is associated with decreased expression of steroid hormone receptors and increased expression of epidermal growth factor (EGF) receptors. Other study results indicate that both progestins and triphenylethylene antiestrogens may be substrates for P-glycoprotein, the product of the MDR1 gene. These findings together suggest an association between overexpression of the MDR1 gene and cross-resistance to progestin and antiestrogen therapies.
Purpose:
This study was designed to determine (a) the ability of MDR1 expression to alter tumor sensitivity to hormone therapy and (b) the role of MDR1 expression in expression of functional hormone receptors in human breast cancer.
Methods:
We transduced MCF-7 cells with MDR1 complementary DNA, using a retroviral vector directing the constitutive expression of the MDR1 gene. Transduced cells (MCF-7MDR1) were examined for ability to produce P-glycoprotein, expression of steroid hormone receptors, and responsivity to antiestrogens. For comparison, we used MCF-7ADR human breast cancer cells, which overexpress MDR1 and have also lost the requirement for 17 beta-estradiol supplementation to form tumors in nude mice. We also investigated the level of EGF-R mRNA expression by using a sensitive RNase protection analysis.
Results:
MCF-7MDR1 cells retained both estrogen receptor and progesterone receptor expression as well as sensitivity to 4-hydroxytamoxifen. Expression of the estrogen-inducible pS2 and EGF receptor genes was similar in parental MCF-7 and transduced MCF-7MDR1 cells. EGF receptor expression was increased, and pS2 expression was lost (undetectable) in MCF-7ADR cells.
Conclusions:
The data indicate that overexpression of the MDR1 gene alone confers a multidrug-resistant phenotype, but it does not directly result in either cross-resistance to antiestrogens or a loss of steroid hormone receptor expression.
Implications:
MCF-7MDR1 cells provide an important model for study of the interactions of cytotoxic drugs, hormones, and the MDR1 glycoprotein in human hormone-responsive breast cancer cells.
Insights
Overexpression of the MDR1 gene confers multidrug resistance but does not directly cause cross-resistance to antiestrogens or loss of hormone receptors in breast cancer cells. MCF-7MDR1 cells offer a model for studying drug-hormone interactions.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- MDR1 gene (PGY1) overexpression is linked to reduced steroid hormone receptors and increased EGF receptors in breast cancer.
- MDR1 gene product, P-glycoprotein, may transport progestins and antiestrogens, suggesting cross-resistance.
- Existing data suggest a correlation between MDR1 overexpression and resistance to hormone therapies.
Purpose of the Study:
- To investigate if MDR1 expression influences tumor sensitivity to hormone therapy.
- To determine the role of MDR1 expression in functional hormone receptor expression in human breast cancer.
Main Methods:
- MCF-7 cells were transduced with MDR1 cDNA using a retroviral vector for constitutive MDR1 expression (MCF-7MDR1).
- MCF-7MDR1 cells were assessed for P-glycoprotein production, steroid hormone receptor expression, and antiestrogen responsiveness.
- EGF receptor (EGF-R) mRNA expression was analyzed using RNase protection assays.
Main Results:
- MCF-7MDR1 cells maintained estrogen and progesterone receptor expression and sensitivity to 4-hydroxytamoxifen.
- Estrogen-inducible pS2 and EGF receptor gene expression remained similar between parental MCF-7 and MCF-7MDR1 cells.
- MCF-7ADR cells showed increased EGF receptor expression and lost pS2 expression.
Conclusions:
- MDR1 gene overexpression alone results in a multidrug-resistant phenotype.
- Overexpression of MDR1 does not directly lead to cross-resistance to antiestrogens or loss of steroid hormone receptors.
- MCF-7MDR1 cells serve as a valuable model for studying interactions between MDR1, hormones, and cytotoxic drugs in breast cancer.