Multidrug-resistant MCF-7 breast cancer cells contain deficient intracellular calcium pools
Jack S K Chen1, Neeraj Agarwal, Kapil Mehta
1Department of Bioimmunotherapy, The University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
Abstract:
Emergence of resistance to antineoplastic drugs poses a major impediment to the successful treatment of breast cancer. We previously reported that human breast carcinoma MCF-7 cells selected for resistance against doxorubicin (MCF-7/DOX cells) expressed high levels of tissue-type transglutaminase (tTGase), a calcium-dependent protein cross-linking enzyme that plays a role in apoptosis. The purpose of this study was to determine the mechanisms by which MCF-7/DOX cells survive and proliferate despite high levels of tTGase expression. Our results demonstrate that the MCF-7/DOX cells contain deficient intracellular calcium pools, which may explain their ability to survive and tolerate the high levels of tTGase expression. Treatment with thapsigargin failed to induce any significant killing of MCF-7/DOX cells. Similar treatment of the drug-sensitive MCF-7 wild-type (MCF-7/WT) cells, however, induced significant apoptosis. Treatment with the ionophore A23187, on the other hand, killed a large percentage of both the MCF-7/DOX and the MCF-7/WT cells. We also established a revertant cell line, MCF-7/RT, from MCF-7/DOX cells to rule out the involvement of P-glycoprotein (P-gp) in these phenomena. Unlike the MCF-7/DOX cells, the MCF-7/RT cells showed no detectable P-gp expression; the MCF-7/RT cells, however, continued to express high levels of tTGase. Moreover, like MCF-7/DOX cells, the MCF-7/RT cells were highly resistant to thapsigargin-induced apoptosis but were sensitive to the ionophore A23187-induced apoptosis. These results suggest that the resistance of MCF7/DOX cells to thapsigargin is linked to their defective intracellular Ca2+ stores, a notion that was directly confirmed by single-cell spectrofluorometric analysis.
Insights
Breast cancer cells resistant to doxorubicin survive due to deficient intracellular calcium stores, not P-glycoprotein. This resistance impacts apoptosis pathways, offering insights into overcoming antineoplastic drug resistance.
Area of Science:
- Cell Biology
- Cancer Research
- Biochemistry
Background:
- Antineoplastic drug resistance is a major challenge in breast cancer treatment.
- MCF-7/DOX cells, selected for doxorubicin resistance, overexpress tissue-type transglutaminase (tTGase).
- tTGase is a calcium-dependent enzyme involved in apoptosis.
Purpose of the Study:
- To investigate the mechanisms underlying MCF-7/DOX cell survival despite high tTGase levels.
- To determine the role of intracellular calcium pools in drug resistance and apoptosis.
Main Methods:
- Comparison of drug-sensitive (MCF-7/WT) and resistant (MCF-7/DOX) cell lines.
- Treatment with thapsigargin (ER calcium store depletor) and ionophore A23187.
- Establishment and analysis of a P-glycoprotein-negative revertant cell line (MCF-7/RT).
- Single-cell spectrofluorometric analysis of intracellular calcium.
Main Results:
- MCF-7/DOX cells exhibit deficient intracellular calcium pools.
- MCF-7/DOX cells are resistant to thapsigargin-induced apoptosis, unlike MCF-7/WT cells.
- A revertant cell line (MCF-7/RT) lacking P-glycoprotein also showed resistance to thapsigargin, implicating calcium stores, not P-gp.
- Both cell lines were sensitive to ionophore A23187-induced apoptosis.
Conclusions:
- Defective intracellular calcium stores contribute to the resistance of MCF-7/DOX cells to thapsigargin-induced apoptosis.
- P-glycoprotein is not the primary mediator of this specific resistance mechanism.
- Understanding calcium homeostasis is crucial for developing strategies against drug-resistant breast cancer.
