ABSTRACT
@# Objective: To investigate the role and molecular mechanism of miR-520d in reversing the chemoresistance of triple negative breast cancer (TNBC) by regulating autophagy. Methods: Docetaxel (Doc) resistant cell lines MDA-MB-231/Doc and MDA-MB468/Doc were constructed by using human TNBC cell lines MDA-MB-231 and MDA-MB-468 as parental cells, and the cells were divided into blank group (parental cells), control group (drug-resistant group), and miR-520d over-expression group. The expression levels of miR-520d in cells of the blank and drug-resistant groups were detected by qPCR. The Doc-sensitivity of resistant cells over-expressing miR-520d was detected by MTT assay.After MDC staining, the generation of autophagosome in cells was observed under fluorescence microscopy; the number of miR-520d over-expressed resistant cells with positive LC3 expression was observed under confocal microscopy. The luciferase reporter gene assay was used to verify the targeting relationship between miR-520d and Beclin1. The effect of miR-520d mimics on the expression of autophagy-associated protein Beclin1, and LC3Ⅰ, LC3Ⅱ in cells was detected by WB assay. Results: The results of qPCR showed that the expression of miR-520d in the drug-resistant TNBC cells was significantly lower than that of normal cells (P<0.01). In drug-resistant cells over-expressing miR-520d, the Doc-sensitivity was significantly improved, while the autophagy activity was significantly reduced (all P<0.01).At the same time, luciferase experiments demonstrated that Beclin1 was a possible target molecule of miR-520d (P<0.05). WB results showed that the combination of docetaxel and miR-520d mimics reduced the LC3-II/I ratio and the expression of autophagy protein Beclin1 in drug-resistant TNBC cells (all P<0.05). Conclusion: The regulation of miR-520d levels may alter the expression of autophagy protein Beclin1, thereby reversing Doc chemotherapy resistance in TNBC cells.
ABSTRACT
Objective: To study the effect of docetaxet (DOC) combined with 4-AP on human breast can-cer MCF-7 cells and to explore whether 4-AP could strengthen the effect of docetaxel. Methods: MTT assays were performed to investigate the effect of docetaxel, 4-AP and the combination of them on the proliferation of MCF-7 cells. Flow cytometry was employed to detect cell cycles and cell apoptosis after the cells were stained by PI alone or by Annexin-V and PI. Results: Docetaxel could significantly inhibit the proliferation of MCF-7 cells in a dose- and time- dependent manner. 4-AP could inhibit the proliferation of MCF-7 cells and the inhibitory rates were 11.9%±1.7%, 42.1%±3.2%, and 44.2%±1.6% at 24h, 48h and 72h after adding 4-AP. Moreover 4-AP (5mmol/L) could strengthen the effect of docetaxel. 4-AP (25μmol/L) could increase the effect of Docetaxel. Docetaxel at 5μmol/L could significantly increase the percentage of cells at G_2/M (53.58%± 1.44% vs. 8.83%±0.44%, P<0.01) and decrease the percentage of cells at G_0/G_1 (11.48%±0.14% vs. 63.89%±0.98%, P<0.01), indicating that docetaxel blocked MCF-7 cells at G_2/M phase. 4-AP at 5mmol/L could in-crease the percentage of MCF-7 cells at G_0/G_1 and decrease the percentage of cells at G_2/M (0.42%±0.17% vs. 8.83%±0.44%, P<0.05). Docetaxel could significantly increase late apoptosis and death of MCF-7 cells af-ter treatment over 24h (from 6.97%±0.75% to 20.77%±0.75%, P<0.05). Docetaxel combined with 4-AP could increase early apoptosis rate from 4.60%±0.91% to 12.20%±0.82% (P<0.05) and could increase late apopto-sis rate and death rate from 4.60%±0.91% to 12.20%±0.82% (P<0.05). Conclusion: Both docetaxel and 4-AP can inhibit the proliferation of MCF-7 cells. Docetaxel can increase the percentage of cells at G_2/M phase and 4-AP can increase the percentage of cells at G_0/G_1 phase. 4-AP could strengthen the inhibitory effect of docetaxel on the proliferation of MCF-7 cells through inducing cell apoptosis.