Abstract
Clinical resistance to chemotherapeutic agents is one of the major hindrances in the treatment of human cancers. EHZ2 is involved in drug resistance and is overexpressed in drug-resistant cancer cell lines. In this study, we investigated the effects of EHZ2 on cisplatin -resistance in A549/DDP and AGS/DDP cells. EHZ2 mRNA and protein were found to be significantly overexpressed in A549/DDP and AGS/DDP cells, compared to parental cells. EHZ2 siRNA successfully silenced EHZ2 mRNA and protein expression. Proliferation was inhibited and drug resistance to cisplatin was improved. Flow cytometry showed that silencing of EHZ2 arrested A549/DDP and AGS/DDP cells in the G0/G1 phase, increasing apoptosis, rh-123 fluorescence intensity and caspase-3/8 activities. Silencing of EHZ2 also significantly reduced the mRNA and protein expression levels of cyclin D1 and MDR1,while up-regulating p15, p21, p27 and miR-218 in A549/DPP cells. Furthermore, silencing of EHZ2 also significantly increased the expression level of tumor suppressor factor miR-218. We also found down-regulating EHZ2 expression increased methylation in A549/DDP and AGS/DDP cells. This study demonstrates that drug resistance can be effectively reversed in human cisplatin-resistant lung and gastric cancer cells through delivery of siRNAs targeting EHZ2.
Highlights
Lung cancer is the most common malignant tumor and currently the cancer causing the highest mortality worldwide (Gadgeel et al, 2013)
AGS cell line were purchased from ATCC; MTS, Rh-123 and RT-PCR kits were purchased from Promega; cisplatin was purchased from Sigma-Aldrich; EZH2 siRNA and related reagents were purchased from Cell Signaling Technology; PI cell cycle determination kit, Annexin V-FITC/PI kit and Caspase-3/8 activity kit were purchased from BD; various monoclonal antibodies were purchased from SantaCruz; ECL immunoblotting substrate kit was purchased from Millipore; flow cytometry: BD; microplate reader: Thermo; PCR instrument: Thermo
Some studies have shown that EZH2 plays important roles in cancer development and progression and in chemotherapeutic drug resistance of some types of tumors, the studies on its potential roles in cisplatin resistance of non-small cell lung cancer (NSCLC) and gastric cancer are few
Summary
Lung cancer is the most common malignant tumor and currently the cancer causing the highest mortality worldwide (Gadgeel et al, 2013). In the past 2 decades, targeted therapy has made great success with cancer genomics and molecular biology; taking the small-molecule drugs for the treatment of NSCLC for examples: epidermal growth factor receptor (EGFR) inhibitors gefitinib and erlotinib (Jang et al, 2014), EGFR monoclonal antibody cetuximab (Janjigian et al, 2014), vascular endothelial growth factor (VEGF) monoclonal antibody bevacizumab (Powell et al, 2013); the examples for the treatment of gastric cancer include human epidermal growth factor receptor 2 (Her 2) monoclonal antibody trastuzumab (Zheng et al, 2014) and vascular endothelial cell growth factor receptor (VEGFR) monoclonal antibody ramucirumab (Wadhwa et al, 2014) These targeted drugs have very clear therapeutic indications that can only benefit patients with positive specific biomarkers. Some studies showed that EZH2 played positive roles in cisplatin-resistant ovarian cancers (Hu et al, 2010; Tamgue et al, 2013) and 5-Fu-resistant liver cancers (Zhang et al, 2013) This study investigated the effects of EZH2 on cisplatin resistance in NSCLC and gastric cancer and preliminarily probed its molecular mechanisms
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