LAUSR

BACKGROUND To investigate the function and mechanism of circular RNA circ_0001658 on gefitinib resistance of non-small cell lung cancer (NSCLC) cells. METHODS Circ_0001658, microRNA (miRNA, miR)-409-3p and twist family bHLH transcription factor 1 (TWIST1) expression levels in NSCLC tissues and cell lines were probed by quantitative real-time PCR and Western blot assays. Cell counting kit-8 assay was adopted to examine the inhibitory effect of different concentrations of gefitinib on the viability of NSCLC cells, with the 50% concentration of inhibition (IC50) value calculated. Besides, BrdU assay and flow cytometry assay were used to detect the proliferative and apoptotic rate of NSCLC cells. What's more, the binding relationships between miR-409-3p and circ_0001658, miR-409-3p and TWIST1 mRNA 3' untranslated region (3' UTR) were confirmed by dual-luciferase reporter gene assay and RNA immunoprecipitation assay. RESULTS Circ_0001658 expression was raised in NSCLC tissue samples and cell lines, which was significantly associated with TNM stage and the differentiation degree of NSCLC tissues. Knocking down circ_0001658 could restrain the viability of NSCLC cells, promote the apoptosis, and reduce the IC50 of gefitinib, while transfection of miR-409-3p inhibitors could partially reverse these impacts. Additionally, circ_0001658 directly targeted miR-409-3p and negatively modulated its expression. TWIST1 was the target of miR-409-3p, which could be indirectly and positively modulated by circ_0001658. Moreover, circ_0001658 expression was negatively interrelated with miR-409-3p expression, while positively correlated with TWIST1 expression in NSCLC samples. CONCLUSION Circ_0001658 promotes the malignant phenotypes and the resistance to gefitinib of NSCLC cells by regulating the miR-409-3p/TWIST1 axis.