Kalyanaraman A, Gnanasampanthapandian D, Shanmughan P, Kishore P, Ramalingam S, Arunachalam R, Jayaraman S, Kaliappan I, Munuswamy-Ramanujam G, Ramachandran I, Sambandam Y, Anbalagan M, Chandrakesan P, Palaniyandi K. Tamoxifen induces stem-like phenotypes and multidrug resistance by altering epigenetic regulators in ERα+ breast cancer cells.
Stem Cell Investig 2020;
7:20. [PMID:
33294429 DOI:
10.21037/sci-2020-020]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2020] [Accepted: 08/25/2020] [Indexed: 12/24/2022] [Imported: 02/21/2025]
Abstract
Background
To understand the mechanism underlying tamoxifen-induced multidrug resistance (MDR) and stem-like phenotypes in breast cancer cells, we treated the MCF-7 cells with 4-hydroxy-tamoxifen (TAM) for 6 months continuously and established MCF-7 tamoxifen resistance (TR) phenotypes.
Methods
In the present study, the following methods were used: cell viability assay, colony formation, cell cycle analysis, ALDEFLUOR assay, mammosphere formation assay, chromatin immunoprecipitation (ChIP) assay, PCR array, western blot analysis and quantitative reverse transcription polymerase chain reaction (QRT-PCR).
Results
The expression of ERα was significantly higher in MCF7-TR cells when compared with parental MCF-7 cells. MCF7-TR cells exposed to TAM showed a significant increase in the proliferation and rate of colony formation. The number of cancer stem cells was higher in MCF7-TR cells as observed by the increase in the number of ALDH+ cells. Furthermore, the number of mammospheres formed from the FACS-sorted ALDH+ cells was higher in MCF7-TR cells. Using PCR array analysis, we were able to identify that the long-term exposure of TAM leads to alterations in the epigenetic and MDR stem cell marker genes. Furthermore, western blot analysis demonstrated elevated levels of Notch-1 expression in MCF-TR cells compared with MCF-7 cells. Chromatin immunoprecipitation (ChIP) assay revealed that Notch-1 enhanced the cyclin D1 expression significantly in these cells. In addition, we observed that MCF7-TR cells were resistant to doxorubicin but not the MCF-7 cells.
Conclusions
In the present study, we conclude that the treatment with tamoxifen induces multiple epigenetic alterations that lead to the development of MDR and stem-like phenotypes in breast cancers. Therefore, our study provides better insights to develop novel treatment regime to control the progression of breast cancer.
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