circRNA-TBC1D4, circRNA-NAALAD2 and circRNA-TGFBR3: Selected Key circRNAs in Neuroblastoma and Their Associations with Clinical Features.

Objective: The roles of circRNAs in neuroblastoma (NB) are unclear. We used next-generation sequencing to detect the circRNA expression profiles in NB to identify the key circRNAs and analyzed the relationships between the circRNAs and clinical features.

Methods: Five paired neuroblastoma tumor and adjacent normal fetal adrenal medulla samples were collected for high-throughput RNA sequencing. Bioinformatics analysis was performed for functional annotation of the host genes of differentially expressed circRNAs. Validation of dysregulated circRNAs was performed by real-time quantitative reverse transcription polymerase chain reaction. The relationships between the key circRNAs and clinical features were analyzed. In addition, overexpression of key circRNAs in an NB cell line, as well as cell proliferation assays, colony formation assays and cell migration assays, was conducted to investigate the biological functions of key circRNAs.

Results: A total of 4704 differentially expressed circRNAs were found, including 2462 up-regulated and 2242 down-regulated circRNAs. According to our previous studies, the predicted target circRNAs of miR-21 involved in tumorigenic signaling pathways were selected, including circRNA-TBC1D4, circRNA-NAALAD2 and circRNA-TGFBR3. These circRNAs were associated with clinical features, and the circRNA expression was significantly lower (P < 0.05) in the NB tissues than in normal adrenal tissues. Overexpression of circRNA-TBC1D4 promotes NB cell migration, but not proliferation and colony-formation in vitro.

Conclusion: We suggest that circRNA-TBC1D4, circRNA-NAALAD2 and circRNA-TGFBR3 may be cancer suppressor genes, which act by sponging miR-21 in NB. Further investigations are needed to elucidate the underlying mechanism.