Expression of circ-PHC3 enhances ovarian cancer progression via regulation of the miR-497-5p/SOX9 pathway

Interplay of microRNAs and circRNAs in Epithelial Ovarian Cancer

Epithelial ovarian cancer (EOC) with its high death incidence rate is generally detected at advanced stages. During its progression, EOC often develops peritoneal metastasis aggravating the outcomes of EOC patients. Studies on non-coding RNAs (ncRNAs), such as microRNAs (miRNAs) and circular RNAs (circRNAs), have analyzed the impact of miRNAs and circRNAs, along with their interaction among each other, on cancer cells. MiRNAs can act as oncogenes or tumor suppressors modulating post-transcriptional gene expression. There is accumulating evidence that circRNAs apply their stable, covalently closed, continuous circular structures to competitively inhibit miRNA function, and so act as competing endogenous RNAs (ceRNAs). This interplay between both ncRNAs participates in the malignity of a variety of cancer types, including EOC. In the current review, I describe the characteristics of miRNAs and circRNAs, and discuss their interplay with each other in the development, progression, and drug resistance of EOC. Sponging of miRNAs by circRNAs may be used as a biomarker and therapeutic target in EOC.

The role of circRNAs in regulation of drug resistance in ovarian cancer

Ovarian cancer is one of the female reproductive system tumors. Chemotherapy is used for advanced ovarian cancer patients; however, drug resistance is a pivotal cause of chemotherapeutic failure. Hence, it is critical to explore the molecular mechanisms of drug resistance of ovarian cancer cells and to ameliorate chemoresistance. Noncoding RNAs (ncRNAs) have been identified to critically participate in drug sensitivity in a variety of human cancers, including ovarian cancer. Among ncRNAs, circRNAs sponge miRNAs and prevent miRNAs from regulation of their target mRNAs. CircRNAs can interact with DNA or proteins to modulate gene expression. In this review, we briefly describe the biological functions of circRNAs in the development and progression of ovarian cancer. Moreover, we discuss the underneath regulatory molecular mechanisms of circRNAs on governing drug resistance in ovarian cancer. Furthermore, we mention the novel strategies to overcome drug resistance via targeting circRNAs in ovarian cancer. Due to that circRNAs play a key role in modulation of drug resistance in ovarian cancer, targeting circRNAs could be a novel approach for attenuation of chemoresistance in ovarian cancer.

Hsa_circ_0000585 promotes chemoresistance to cis-platin in epithelial cells of ovarian cancer by modulating autophagy

BACKGROUND

Chemoresistance, i.e., resistance to cisplatin (DDP), has been a major obstacle to ovarian cancer treatment. It has been found that circular RNAs (circRNAs) play vital roles in the tumorigenesis various cancers by regulating autophagy, while few studies focusing on cisplatin-resistance ovarian cancer (CROC).

METHODS

The expressions of the circRNAs were detected by qRT-PCR. Short hairpin RNA targeting circRNA was used to explore the biological functions of the circRNA. Cell viability, autophagic flux, immunofluorescence, and xenograft tumors experiments were performed to further illustrate the underlying mechanisms.

RESULTS

Hsa_circ_0000585 was increased in cisplatin-resistant SKOV3/DDP cells. Stably knocking down hsa_circRNA_0000585 expression in SKOV3/DDP cells was established by RNA interference. We found that downregulation of hsa_circ_0000585 significantly enhanced the sensitivity of DDP/SkOV3 cells to DDP. In vivo study, hsa_circRNA_0000585 knockdown significantly decreased tumor volume in nude mice. Under the measurements of western blot and cellular immunofluorescence, hsa_circ_0000585 knockdown significantly inhibited the expression of Beclin1 and P62, indicating the autophagic flux was inhibited. Administrations with autophagic inhibitor "Chloroquine (CQ)" and autophagy activator "QX77" further confirmed that hsa_circ_0000585 knockdown resulted in autophagy inhibition.

CONCLUSIONS

Overall, this study provided a new insight into the role of circRNAs in the mechanism of DDP-resistance in ovarian cancer. Hsa_circRNA_0000585 may be promising therapeutic targets for the enhancement of the sensitivity of ovarian cancer cells to cisplatin-mediated chemotherapy.