BACKGROUND: Circular RNAs (circRNAs) are covalently closed single-stranded RNAs with multiple biological functions. CircRNA.0007127 is derived from the carbon catabolite repression 4-negative on TATA-less (CCR4-NOT) complex subunit 2 (CNOT2), which was found to regulate tumor cell apoptosis through caspase pathway. METHODS: Potential circRNA.0007127 target microRNAs (miRNAs) were analyzed by miRanda, TargetScan, and RNAhybrid software, and the miRNAs with binding sites for apoptosis-related genes were screened. The roles of circRNA.0007127 and its downstream target, microRNA (miR)‍-513a-5p, were validated by quantitative real-time polymerase chain reaction (qPCR), flow cytometry, mitochondrial membrane potential, immunofluorescence, western blot, and caspase-8 (CASP8) protein activity in vitro in H₂O₂-induced K-562 cells. The circRNA.‍0007127‍‒‍miR-513a-5p and CASP8‍‒‍miR-513a-5p interactions were verified by luciferase reporter assays. RESULTS: Silencing circRNA.0007127 decreased cell apoptosis by inhibiting CASP8 pathway activation in K-562 cells. Compared with the control group, the expression of CASP8 was reduced by 50% and the 43-kD fragment of CASP8 protein was significantly reduced (P≤0.05). The luciferase reporting assay showed that circRNA.0007127 combined with miR-513a-5p or CASP8, with extremely significant differences (P≤0.001). The overexpression of miR-513a-5p inhibited the gene expression level of CASP8 in a human myeloid leukemia cell model (75% change) and the level of a 43-kD fragment of CASP8 protein (P≤0.01). The rescue experiment showed that cotransfection with circRNA.0007127 small-interfering RNA (siRNA) and the miR-513a-5p inhibitor increased CASP8 gene expression and the apoptosis rate, suggesting that the miR-513a-5p inhibitor is a circRNA.0007127 siRNA antagonist. CONCLUSIONS: CircRNA.0007127 regulates K-562 cell apoptosis through the miR-513a-5p/CASP8 axis, which can serve as a novel powerful molecular target for K-562 cells.

Cowanin, a xanthone derivative extracted from the Garcinia fusca plant, has been recognized for various biological activities including, antimicrobial, anti-inflammatory, and anticancer activities. However, the mechanism to induce cancer cell death in cancer cells remains to be fully elucidated. Our previous report showed that other xanthones from these plants could act as histone deacetylase inhibitors (HDACi), so we deeply analyzed the role of cowanin, a major compound of G.fusca, and investigated through the mode of cell death both apoptosis and autophagy that have never been reported. As a result, it was demonstrated that cowanin indicated the role of HDACi as other xanthones. The molecular docking analysis showed that cowanin could interact within the catalytic pocket region of HDAC class I (HDAC2, 8) and II (HDAC4, 7) proteins and inhibit their activity. Also, the level of protein expression of HDAC2, 4, 7, and 8 was distinctly decreased, and the level of histone H3 and H4 acetylation increased in cowanin treated cells. For the mode of cell death, cowanin demonstrated both apoptosis and autophagy activation in Jurkat cells. Besides, cowanin significantly suppressed phosphorylation of PI3K, Akt, and mTOR signaling. Therefore, these findings revealed that cowanin represents a new promising candidate for development as an anticancer agent by inducing apoptosis and autophagy via PI3K/AKT/mTOR pathway and effectively inhibiting HDAC activity.