Depleting hsa_circ_0000567 suppresses acquired gefitinib resistance and proliferation of lung adenocarcinoma cells through regulating the miR-377-3p / ZFX axis: an in vitro and in vivo study

Background. Circular RNAs (circRNAs) expression profile has been reported in lung adenocarcinoma (LUAD) cells resistant to gefitinib, and hsa_circ_0000567 was abnormally upregulated. However, its precise role in gefitinib resistance remains unclarified. Methods. Levels of hsa_circ_0000567, microRNA (miR)-377-3p and zinc finger protein X-linked (ZFX) were detected by real-time quantitative PCR. Direct attachment was confirmed by dual-luciferase reporter assay and RNA immunoprecipitation assay. Gefitinib resistance was measured by MTT assay, colony formation assay, flow cytometry, western blotting, and xenograft in mice. Results. Expression of hsa_circ_0000567 was upreguated in human gefitinib-resistant human LUAD tissues and cells (HCC827/GR and PC9/GR). Clinically, higher hsa_circ_0000567 correlated with advanced tumor burden. Blockage of hsa_circ_0000567 inhibitory concentration suppressed cell viability, half maximal concentration (IC50) value, colony formation ability, and expression of Bcl-2 and proliferating cell nuclear antigen (PCNA) in HCC827/GR and PC9/GR cells under gefitinib treatment or not, accompanied with enhanced apoptosis rate and Bax expression. In vivo, tumor growth of PC9/GR cells untreated and treated with gefitinib was restrained by silencing hsa_circ_0000567. miR-377-3p was directly regulated by hsa_circ_0000567, and then targeted ZFX. Similar to hsa_circ_0000567 knockdown, overexpressing miR-377-3p inhibited chemoresistance in genitinib-resistant LUAD cells in vitro, whereas, depleting miR-377-3p was able to promote gefitinib resistance in spite of hsa_circ_0000567 knockdown. Moreover, restoring ZFX abrogated miR-377-3p-mediated chemosensitivity in genitinib-resistant LUAD cells in vitro. Conclusion. The hsa_circ_0000567/miR-3773p/ZFX axis might contribute to acquired gefitinib resistance in LUAD cells both in vitro and in vivo, suggesting hsa_circ_0000567 as a novel therapeutic target in treatment of gefitinib-resistant LUAD.