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Benzo[a]pyrene-resistant MCF-7 human breast cancer cells. A unique aryl hydrocarbon-nonresponsive clone
1Department of Veterinary Physiology and Pharmacology, Texas A&M University, College Station 77843-4466.
Abstract:
Wild-type MCF-7 human breast cancer cells were cultured for 3 months in 1 microM benzo[a]pyrene (BaP), and resistant clones were screened for inducibility of CYP1A1 gene expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). One of the BaP-resistant (BaPR) clones exhibited unique genotypic expression which distinguished it from both wild-type and drug-resistant (AdrR) variant MCF-7 cells. Glutathione levels, glutathione S-transferase activities, estrogen receptor levels, estrogen responsiveness, and expression of the multidrug-resistant MDR1 and MRP mRNA levels were similar in the wild-type and BaPR cells, whereas these parameters were reported to be altered in AdrR cells. In contrast, TCDD induced CYP1A1 gene expression and inhibited selected estrogen-induced responses in wild-type but not BaPR MCF-7 cells. Treatment of wild-type and BaPR cells with [3H]TCDD resulted in formation of the radiolabeled aryl hydrocarbon (Ah) 6 S nuclear receptor complex in both cell lines. The loss of Ah responsiveness in the BaPR variant cells correlated with the failure of the nuclear or transformed cytosolic Ah receptor complex to bind genomic dioxin-responsive elements as determined in gel retardation assays.
Insights
Benzo[a]pyrene-resistant breast cancer cells lose responsiveness to dioxin. This resistance is linked to the aryl hydrocarbon receptor complex failing to bind DNA, impacting gene expression.
Area of Science:
- Cell Biology
- Molecular Toxicology
- Cancer Research
Background:
- Benzo[a]pyrene (BaP) is a polycyclic aromatic hydrocarbon found in environmental pollutants.
- 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a potent environmental toxicant that activates the aryl hydrocarbon receptor (AhR).
- MCF-7 cells are a human breast cancer cell line commonly used in toxicological studies.
Purpose of the Study:
- To investigate the mechanisms of resistance to benzo[a]pyrene (BaP) in MCF-7 human breast cancer cells.
- To determine if BaP resistance affects the inducibility of CYP1A1 gene expression by dioxin (TCDD).
- To characterize the role of the aryl hydrocarbon (Ah) receptor pathway in BaP-resistant cells.
Main Methods:
- Culture of wild-type MCF-7 cells with benzo[a]pyrene (BaP) to generate resistant clones.
- Screening of resistant clones for CYP1A1 gene expression inducibility by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).
- Analysis of glutathione levels, glutathione S-transferase activities, estrogen receptor levels, and multidrug resistance (MDR1 and MRP) mRNA levels.
- Treatment with radiolabeled TCDD and gel retardation assays to assess Ah receptor complex binding to DNA.
Main Results:
- A BaP-resistant (BaPR) clone exhibited unique genotypic expression compared to wild-type and drug-resistant (AdrR) cells.
- Glutathione, GST, estrogen receptor levels, estrogen responsiveness, and MDR1/MRP mRNA levels were similar in wild-type and BaPR cells.
- TCDD induced CYP1A1 gene expression and inhibited estrogen responses in wild-type cells, but not in BaPR cells.
- The Ah receptor complex formed in both cell types, but failed to bind dioxin-responsive elements in BaPR cells.
Conclusions:
- BaP-resistant MCF-7 cells display a loss of aryl hydrocarbon (Ah) receptor responsiveness.
- This loss of responsiveness is attributed to the inability of the Ah receptor complex to bind to genomic dioxin-responsive elements.
- The findings highlight a novel mechanism of resistance involving the Ah receptor pathway in breast cancer cells.