Department of Biochemistry and Molecular Biology, Third Military Medical University, Chongqing, 400038, China.
Department of Clinical Laboratory Medicine, Southwest Hospital, Third Military Medical University, Chongqing, 400038, China.
Clin Transl Oncol. 2019 Aug;21(8):1026-1033. doi: 10.1007/s12094-018-02019-1. Epub 2019 Feb 2.
Flap endonuclease 1 (FEN1) is up-regulated by estrogen (17β-estradiol, E2) and related to cisplatin resistance of human breast cancer cells. Letrozole, an aromatase inhibitor, suppresses the change of testosterone into estrogen and is frequently used to treat breast cancer. However, the effects of letrozole on FEN1 expression and cisplatin sensitivity in breast cancer cells overexpressing aromatase have not been revealed.
The expression of FEN1 and the proteins in ERK/Elk-1 signaling were evaluated by RT-PCR and Western blot. Cisplatin sensitivity was explored through CCK-8 and flow cytometry analysis, respectively. FEN1 siRNAs and FEN1 expression plasmid were transfected into cells to down-regulate or up-regulate FEN1 expression. The promotor activity of FEN1 was detected using luciferase reporter assay.
FEN1 down-regulation improved cisplatin sensitivity of breast cancer cells overexpressing aromatase. Letrozole down-regulated FEN1 expression and increased cisplatin sensitivity. The sensitizing effect of letrozole to cisplatin was dependent on FEN1 down-regulation. FEN1 overexpression could block the sensitizing effect of letrozole to cisplatin. Testosterone up-regulated the promotor activity, protein expression of FEN1, and phosphorylation of ERK/Elk-1, which could be eliminated by both letrozole and MEK1/2 inhibitor U0126. Letrozole down-regulated FEN1 expression in an ERK/Elk-1-dependent manner.
Our findings clearly demonstrate that letrozole improves cisplatin sensitivity of breast cancer cells overexpressing aromatase via down-regulation of FEN1 and suggest that a combined use of letrozole and cisplatin may be a potential treatment protocol for relieving cisplatin resistance in human breast cancer.
核酸内切酶 1（FEN1）可被雌激素（17β-雌二醇，E2）上调，且与人类乳腺癌细胞对顺铂的耐药性有关。来曲唑是一种芳香酶抑制剂，可抑制睾酮转化为雌激素，常用于治疗乳腺癌。然而，来曲唑对过表达芳香酶的乳腺癌细胞中 FEN1 表达和对顺铂敏感性的影响尚未被揭示。
通过 RT-PCR 和 Western blot 评估 FEN1 和 ERK/Elk-1 信号通路中蛋白质的表达。分别通过 CCK-8 和流式细胞术分析来研究顺铂敏感性。通过转染 FEN1 siRNA 和 FEN1 表达质粒下调或上调 FEN1 的表达。使用荧光素酶报告基因检测法检测 FEN1 的启动子活性。
下调 FEN1 可提高过表达芳香酶的乳腺癌细胞对顺铂的敏感性。来曲唑下调 FEN1 的表达并增加顺铂敏感性。来曲唑对顺铂的增敏作用依赖于 FEN1 的下调。FEN1 的过表达可阻断来曲唑对顺铂的增敏作用。睾酮上调 FEN1 的启动子活性、蛋白表达和 ERK/Elk-1 的磷酸化，这可被来曲唑和 MEK1/2 抑制剂 U0126 消除。来曲唑以 ERK/Elk-1 依赖的方式下调 FEN1 的表达。
我们的研究结果清楚地表明，来曲唑通过下调 FEN1 提高了过表达芳香酶的乳腺癌细胞对顺铂的敏感性，并提示来曲唑与顺铂联合使用可能是缓解人类乳腺癌顺铂耐药的一种潜在治疗方案。
