Circular RNAs are differentially expressed in prostate cancer and are potentially associated with resistance to enzalutamide

Abstract

Most forms of castration-resistant prostate cancer (CRPC) are dependent on the androgen receptor (AR) for survival. While, enzalutamide provides a substantial survival benefit, it is not curative and many patients develop resistance to therapy. Although not yet fully understood, resistance can develop through a number of mechanisms, such as AR copy number gain, the generation of splice variants such as AR-V7 and mutations within the ligand binding domain (LBD) of the AR. circular RNAs (circRNAs) are a novel type of non-coding RNA, which can regulate the function of miRNA, and may play a key role in the development of drug resistance. circRNAs are highly resistant to degradation, are detectable in plasma and, therefore may serve a role as clinical biomarkers. In this study, AR-V7 expression was assessed in an isogenic model of enzalutamide resistance. The model consisted of age matched control cells and two sub-line clones displaying varied resistance to enzalutamide. circRNA profiling was performed on the panel using a high throughout microarray assay. Bioinformatic analysis identified a number of differentially expressed circRNAs and predicted five miRNA binding sites for each circRNA. miRNAs were stratified based on known associations with prostate cancer, and targets were validated using qPCR. Overall, circRNAs were more often down regulated in resistant cell lines compared with control (588 vs . 278). Of particular interest was hsa_circ_0004870, which was down-regulated in enzalutamide resistant cells (p ≤ 0.05, vs . sensitive cells), decreased in cells that highly express AR (p ≤ 0.01, vs . AR negative), and decreased in malignant cells (p ≤ 0.01, vs . benign). The associated parental gene was identified as RBM39 , a member of the U2AF65 family of proteins. Both genes were down-regulated in resistant cells (p < 0.05, vs . sensitive cells). This is one of the first studies to profile and demonstrate discrete circRNA expression patterns in an enzalutamide resistant cell line model of prostate cancer. Our data suggests that hsa_circ_0004870, through RBM39 , may play a critical role in the development of enzalutamide resistance in CRPC.

<p>Biological Roles and Mechanisms of Circular RNA in Human Cancers</p>

“…11 CircRNAs may also play a key role in the development of drug resistance. Recently, multiple studies have highlighted the key roles of ncRNAs in chemoresistance of cancer, such as HCC, 142,249 lung cancer, 250,251 gastric cancer, 252,253 breast cancer, 254,255 multiple myeloma, 256 acute myeloid leukemia, 234 prostate cancer, 257 bladder cancer, 258 among others. The up-to-date information regarding the role of circRNAs in the resistance of tumors to chemotherapy has been recently summarized with multiple mechanisms, such as modulating various regulatory pathways and processes including the ceRNA regulatory network axis, EMT process, regulation of ABC transporters, apoptosis, autophagy, and CSCs, among others although many physiological processes and biological signaling pathways through which circRNAs are involved in drug resistance still remained unknown.…”

Anti-antioxidant impacts of circZNF609 silence in HaCaT cells through regulating miR-145

“…CircRNAs are new stars in the field of RNA research. They are believed to be critical in the occurrence and development of a wide range of human diseases, for instance acute ischaemic stroke [26], psoriasis [27] and even tumours [28]. Moreover, circRNA may remove the inhibitory effect of a miRNA on its targeted gene, raise the expression of the targeted gene, thereby regulating a series of pathophysiological processes.…”

Functions and mechanisms of circular RNAs in cancer radiotherapy and chemotherapy resistance

“…Hsa_circ_0004870, derived from the RBM39 gene, is one of the significantly down-regulated circRNAs. It likely enhances chemoresistance by regulating the splicing of U2 small nuclear RNA auxiliary factor 65 (U2AF65) [147]. Silencing of circRNA Foxo3 (circFoxo3 or hsa_circis_0006404) increases the survival of androgen-enhanced prostate cancer cells and represses apoptosis while enhancing resistance to docetaxel.…”