CircEXOC6B Suppresses the Proliferation and Motility and Sensitizes Ovarian Cancer Cells to Paclitaxel Through miR-376c-3p/FOXO3 Axis.

Abstract

Background: Circular RNAs (circRNAs) are regarded as important regulators in the tumorigenesis of multiple cancers. However, the characterization of circRNA exocyst complex component 6B (circEXOC6B) in ovarian cancer is barely known. Materials and Methods: Quantitative real-time polymerase chain reaction (qRT-PCR) was utilized to detect the enrichment of circEXOC6B, microRNA-376c-3p (miR-376c-3p), and forkhead box O3 (FOXO3). Cell proliferation was examined by Cell Counting Kit-8 (CCK8) assay and colony formation assay. Cell metastasis was measured by transwell assays. Western blot assay was conducted to examine the expression of proliferation and metastasis-related proteins and FOXO3. The chemoresistance of ovarian cancer cells was analyzed by CCK8 assay. Flow cytometry was used to detect cell apoptosis. The activities of caspase3 and caspase9 were analyzed through using colorimetric assay kits. The direct interaction between miR-376c-3p and circEXOC6B or FOXO3 was predicted by StarBase software and confirmed by dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay. Murine xenograft assay was conducted to verify the role of circEXOC6B on the paclitaxel (PTX) resistance of ovarian cancer cells in vivo. Results: The level of circEXOC6B was notably decreased in ovarian cancer tissues. Low level of circEXOC6B was associated with malignant pathological characteristics in ovarian cancer patients. CircEXOC6B suppressed the proliferation and motility and decreased the chemoresistance of ovarian cancer cells to PTX. CircEXOC6B functioned through directly targeting and downregulating miR-376c-3p. FOXO3 was a direct target of miR-376c-3p, and the abundance of FOXO3 was regulated by circEXOC6B/miR-376c-3p axis. CircEXOC6B accelerated the PTX sensitivity of ovarian cancer cells through acting as a decoy of miR-376c-3p to upregulate FOXO3 in vivo. Conclusion: CircEXOC6B suppressed the progression and PTX resistance of ovarian cancer cells through sequestering miR-376c-3p, thus enhancing FOXO3 level.