SOX2 Knockdown with Sirna Reverses Cisplatin Resistance in NSCLC by Regulating APE1 Signaling

Abstract Objective: SOX2 is related to drug resistance in many types of cancer, including lung cancer, but the underlying mechanism is still not fully understood. Herein, we investigated the role of SOX2 and its regulatory signaling in cisplatin-treated non-small-cell lung cancer (NSCLC).Methods: Cisplatin-resistant NSCLC A549/CDDP cells, parental A549 cells and NCI-H460 cells were selected for experiments. The effects of SOX2 on cell viability, proliferation, and apoptosis were evaluated in vitro. Western blotting, real-time quantitative PCR (qPCR), immunohistochemistry (IHC), and luciferase reporter assays were used to investigate the underlying mechanism of SOX2. Kaplan-Meier survival analysis and the log-rank test were used to assess the relationship between SOX2 expression levels and patient survival.Results: A549/CDDP cells had marked resistance to cisplatin and stronger colony formation ability than A549 cells. The expression of SOX2 protein or mRNA in A549/CDDP cells was higher than that in A549 cells. Knockdown of SOX2 in A549/CDDP cells induced apoptosis by inhibiting colony formation and decreasing viability, but overexpression of SOX2 reversed these effects. Interestingly, Genomatix software predicted that the APE1 promoter has some SOX2 binding sites, while the SOX2 promoter has no APE1 binding sites. Furthermore, luciferase reporter assays proved that SOX2 could bind the promoter of APE1 in 293T cells. We further verified that SOX2 expression was not affected by small hairpin RNA against APE1 (shAPE1) in A549/CDDP cells. As expected, colony formation was obviously inhibited and apoptosis was strongly enhanced in A549/CDDP cells treated with SOX2 small-interfering RNA (siSOX2) alone or combined with CDDP compared with control cells. Meaningfully, SOX2 expression was variable in 45 advanced NSCLC patients, and patients with high expression of SOX2 survived longer than those with low expression of SOX2.Conclusion: siSOX2 overcomes cisplatin resistance in NSCLC by regulating APE1 signaling, providing a new therapeutic target for overcoming cisplatin resistance in NSCLC patients.