Hsa_circ_0000231 Accelerates Cell Autophagy and Promotes Cell Proliferation and Invasion of Colorectal Cancer via miR-140-3p/Bcl-2 Axis

Accumulating evidence indicated that circular RNAs (circRNAs) directly sponge to microRNAs (miRNAs),(miRNAs), which in turn regulate the gene expression and affect the malignancy behavior at the posttranscriptional level. However, the expression levels, function, and mechanism of circ_0000231 in colorectal cancer (CRC) are largely unknown. The expression levels of circ_0000231, miR-140-3p, and Bcl-2 in 110 CRC tissues and matched normal colorectal tissues were detected by qRT-PCR method. circ_0000231 and Bcl-2 were suppressed by siRNA, and miR-140-3p was overexpressed by RNA mimics in CRC cell lines. The function-based experiments were conducted to detect the proliferation and migratory abilities in CRC cell lines. RNA pull-down, RNA immunoprecipitation (RIP), and dual-fluorescence reporter assay were conducted to verify the association among circ_0000231, miR-140-3p, and Bcl-2. Western blot analysis and mRFP-GFP-LC3 adenovirus were used to detect the autophagy level affected by circ_0000231, miR-140-3p, and Bcl-2 axis. Downregulated circ_0000231 significantly suppressed the proliferation and migratory abilities of CRC cells by suppressing autophagy and promoting G0/G1 phase arrest. Furthermore, RNA pull-down, RIP, and dual-fluorescence reporter assays confirmed that circ_0000231 regulates the expression of Bcl-2 by directly targeting miR-140-3p. More importantly, circ_0000231 promoted the levels of autophagy via the miR-140-3p/Bcl-2 axis in CRC. Our study demonstrated that circ_0000231, as a tumor promotor, enhances the level of autophagy by regulating Bcl-2 via targeting miR-140-3p. Moreover, circ_0000231 might serve as a diagnostic and prognostic indicator and a novel molecular target for CRC therapy.