Hsa_circ_0017639 regulates cisplatin resistance and tumor growth via acting as a miR-1296-5p molecular sponge and modulating sine oculis homeobox 1 expression in non-small cell lung cancer

Cisplatin (DDP)-induced chemoresistance is an important reason for the failure of non-small cell lung cancer (NSCLC) treatment. Circular RNAs (circRNAs) participate in the chemoresistance of diverse cancers. However, the function of hsa_circ_0017639 (circ_0017639) in the DDP resistance of NSCLC is unclear. Forty-one NSCLC samples (21 DDP-resistant samples and 20 DDP-sensitive samples) were utilized in the research. The relative expression levels of some genes were determined by real-time quantitative polymerase chain reaction (RT-qPCR). 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) assay for half-maximal inhibitory concentration (IC(50)) value of DDP and cell viability, colony formation and 5-ethynyl-2’-deoxyuridine (EDU) assays for cell proliferation, flow cytometry assay for cell apoptosis, transwell assay for cell invasion and wound-healing assay for cell migration were performed. The regulation mechanism of circ_0017639 was demonstrated by a dual-luciferase reporter assay. We observed higher levels of circ_0017639 in DDP-resistant NSCLC samples and cells. Functionally, circ_0017639 silencing decreased tumor growth and elevated DDP sensitivity in vivo and induced apoptosis, repressed proliferation, invasion, and migration of DDP-resistant NSCLC cells in vitro. Mechanically, circ_0017639 modulated sine oculis homeobox 1 (SIX1) expression via sponging microRNA (miR)-1296-5p. Also, miR-1296-5p inhibitor restored circ_0017639 knockdown-mediated impacts on cell DDP resistance in DDP-resistant NSCLCs. Furthermore, SIX1 overexpression counteracted the inhibiting impact of miR-1296-5p upregulation on DDP resistance and malignant phenotypes of DDP-resistant NSCLC cells. In conclusion, circ_0017639 conferred DDP resistance and promoted tumor growth via elevating SIX1 expression through sequestering miR-1296-5p in NSCLC, providing a new mechanism for understanding the chemoresistance and progression of NSCLC.