Yu Xinfeng, Li Ruilian, Shi Wenna, Jiang Tao, Wang Yufei, Li Cong, Qu Xianjun
Department of Pharmacology, School of Basic Medical Sciences, Capital Medical University, Beijing, China.
Department of Pharmacology, School of Basic Medical Sciences, Capital Medical University, Beijing, China; Pharmaceutical Department, Tumor Hospital of Shandong Province, Jinan, China.
Biomed Pharmacother. 2016 Feb;77:37-44. doi: 10.1016/j.biopha.2015.11.005. Epub 2015 Dec 12.
Tamoxifen (TAM) and fulvestrant (FUL) represent the major adjuvant therapy to estrogen receptor-alpha positive (ER(+)) breast cancer patients. However, endocrine resistance to TAM and FUL is a great impediment for successful treatment. We hypothesized that miR-21 might alter the sensitivity of breast cancer cells to TAM or FUL by regulating cell autophagy. Using the ER(+) breast cancer cells, we knockdown miR-21.by transfection with miR-21 inhibitor, then the cells were exposed to TAM or FUL and the percentages of apoptosis and autophagy were determined. Knockdown of miR-21 significantly increased the TAM or FUL-induced apoptosis in ER(+) breast cancer cells. Further, silencing of miR-21 in MCF-7 cells enhanced cell autophagy at both basal and TAM or FUL-induced level. The increase of autophagy in miR-21-knockdown MCF-7 cells was also indicated by increase of beclin-1, LC3-II and increased GFP-LC3 dots. Importantly, knockdown of miR-21 contributed to autophagic cell death, which is responsible for part of TAM induced cell death in miR-21 inhibitor-transfected cells. Further analysis suggested that miR-21 inhibitor enhance autophagic cell death through inhibition of PI3K-AKT-mTOR pathway. MiR-21 coordinated the function of autophagy and apoptosis by targeting Phosphatase and tensin homolog (PTEN) through inhibition of PI3K-AKT-mTOR pathway. In conclusion, silencing of miR-21 increased the sensitivity of ER(+) breast cancer cells to TAM or FUL by increasing autophagic cell death. Targeting autophagy-related miRNAs is a potential strategy for overcoming endocrine resistance to TAM and FUL.
他莫昔芬（TAM）和氟维司群（FUL）是雌激素受体α阳性（ER(+)）乳腺癌患者的主要辅助治疗药物。然而，对TAM和FUL的内分泌抵抗是成功治疗的一大障碍。我们推测miR-21可能通过调节细胞自噬来改变乳腺癌细胞对TAM或FUL的敏感性。我们使用ER(+)乳腺癌细胞，通过转染miR-21抑制剂来敲低miR-21，然后将细胞暴露于TAM或FUL中，并测定细胞凋亡和自噬的百分比。敲低miR-21显著增加了ER(+)乳腺癌细胞中TAM或FUL诱导的细胞凋亡。此外，在MCF-7细胞中沉默miR-21可增强基础水平以及TAM或FUL诱导水平的细胞自噬。自噬相关蛋白beclin-1、LC3-II的增加以及绿色荧光蛋白标记的微管相关蛋白1轻链3（GFP-LC3）斑点的增加也表明miR-21敲低的MCF-7细胞中自噬增加。重要的是，敲低miR-21导致自噬性细胞死亡，这是miR-21抑制剂转染细胞中TAM诱导细胞死亡的部分原因。进一步分析表明，miR-21抑制剂通过抑制磷脂酰肌醇-3激酶-蛋白激酶B-哺乳动物雷帕霉素靶蛋白（PI3K-AKT-mTOR）通路增强自噬性细胞死亡。miR-21通过抑制PI3K-AKT-mTOR通路靶向磷酸酶及张力蛋白同源物（PTEN），从而协调自噬和凋亡的功能。总之，沉默miR-21通过增加自噬性细胞死亡提高了ER(+)乳腺癌细胞对TAM或FUL的敏感性。靶向自噬相关的微小RNA是克服对TAM和FUL内分泌抵抗的潜在策略。
