Upregulation of miR-34c after silencing E2F transcription factor 1 inhibits paclitaxel combined with cisplatin resistance in gastric cancer cells.

MicroRNA 34c (miR-34c) has been reported to be associated with malignant types of cancer, however, it remains unknown whether miR-34c is involved in chemoresistance in gastric cancer (GC). To investigate the effect of miR-34c and its upstream transcription factor E2F1 on paclitaxel combined with cisplatin resistance in GC cells. Paired GC tissues and adjacent normal tissues were randomly sampled from 74 GC patients. miR-34c and E2F1 were detected by real-time quantitative PCR (qPCR) and Western blot. In addition, the drug resistance of GC cells to paclitaxel and cisplatin was induced by concentration gradient increasing methods, and changes in miR-34c and E2F1 during this process were measured. Furthermore, E2F1 and miR-34c overexpression or underexpression vectors were constructed and transfected into drug-resistant GC cells. MTT was employed to test the sensitivity of cells to paclitaxel combined with cisplatin, qPCR was adopted to detect the expression of miR-34c, Western blot was applied to detect the expression levels of E2F1, drug resistance-related proteins and apoptosis-related proteins, and flow cytometry was used for the determination of cell apoptosis and cell cycle status. E2F1 was overexpressed while miR-34c was underexpressed in GC. After inducing GC cells to be resistant to paclitaxel and cisplatin, E2F1 expression increased while miR-34c expression decreased. Both silencing E2F1 and over-expressing miR-34c could increase the sensitivity of drug-resistant GC cells to paclitaxel combined with cisplatin, promote cell apoptosis and inhibit cell proliferation. Among which, silencing E2F1 could reduce the expression of drug resistance-related proteins and apoptosis-related proteins, while over-expression of miR-34c could upregulate the expression of apoptosis-related proteins without affecting the expression of MDR-1, MRP and other drug resistance-related proteins. Rescue experiments demonstrated that inhibiting miR-34c could significantly weaken the sensitization of drug resistant cells, and Si E2F1 to paclitaxel combined with cisplatin. E2F1 inhibits miR-34c to promote the proliferation of GC cells and enhance the resistance to paclitaxel combined with cisplatin, and silencing E2F1 is conducive to improving the efficacy of paclitaxel combined with cisplatin in GC cells.

Zheng H ，Wang JJ ，Yang XR ，Yu YL ... -  《-》

Overexpression of E2F1 in human gastric carcinoma is involved in anti-cancer drug resistance.

Yan LH ，Wei WY ，Cao WL ，Zhang XS ，Xie YB ，Xiao Q ... -  《BMC CANCER》

Regulation of microtubule-associated protein tau (MAPT) by miR-34c-5p determines the chemosensitivity of gastric cancer to paclitaxel.

Wu H ，Huang M ，Lu M ，Zhu W ，Shu Y ，Cao P ，Liu P ... -  《-》

miR-135a promotes gastric cancer progression and resistance to oxaliplatin.

Yan LH ，Chen ZN ，Li-Li ，Chen J ，Wei WE ，Mo XW ，Qin YZ ，Lin Y ，Chen JS ... -  《Oncotarget》

Reversal of multidrug resistance in gastric cancer cells by E2F-1 downregulation in vitro and in vivo.

Transcription Factor E2F-1 plays a critical role in cell cycle regulation and other biological processes in cells. However whether or not it is involved in the multi-drug resistance (MDR) process of gastric cancer has not been fully elucidated yet. To explore the role of E2F-1 in the MDR process of gastric cancer in vitro and in vivo, a cisplatin-resistant gastric cancer cell line with stable downregulation of E2F-1 was established. E2F-1 shRNA led to downregulation of endogenous E2F-1 mRNA and protein. It significantly promoted the sensitivity of SGC7901/DDP cells to cisplatin, doxorubicin, and fluorouracil. Flow cytometry confirmed that the percentage of apoptotic cells increased after E2F-1 downregulation. This notion was further supported by the observation that downregulation of E2F-1 blocked entry into the S-phase of the cell cycle. Furthermore, downregulation of E2F-1 significantly increased intracellular accumulation of doxorubicin. In addition, we determined the in vivo effects of E2F-1 small interfering RNA (shRNA) on tumor size, and apoptotic cells in tumor tissues were detected by deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling and hematoxylin and eosin staining. In molecular studies, semiquantitative RT-PCR and western blotting revealed that E2F-1 downregulation could inhibit expression of MDR1, MRP, Bcl-2/Bax, c-Myc, Skp2, Survivin, and Cyclin D1. E2F-1 may be involved in regulating multiple signaling pathways in reversing MDR, suggesting that E2F-1 may represent a novel target for gastric cancer therapy.

Yan LH ，Wang XT ，Yang J ，Kong FB ，Lian C ，Wei WY ，Luo W ，Xie YB ，Xiao Q ... -  《-》