Circular RNA circVAPA is up-regulated and exerts oncogenic properties by sponging miR-101 in colorectal cancer

Circular RNAs (circRNAs) are a novel class of non-coding RNAs with distinct properties and diverse physiological and pathological functions. However, the functions of circRNAs in colorectal cancer (CRC) remain elusive. This study aimed to investigate the functional roles of circVAPA in CRC. High-throughput RNA sequencing was performed in 4 paired CRC tissues, and circVAPA (hsa_circ_0006990), was identified as a potential functional circRNA. Using quantitative real-time polymerase chain reaction (qRT-PCR), circVAPA was found to be up-regulated in CRC patients' tissues and plasma. Furthermore, circVAPA level was associated with unfavorable clinicopathologic features in CRC. The area under curve (AUC) of ROC was 0.724, suggesting that plasma level of circVAPA could serve as a promising biomarker for CRC detection. Sanger sequencing confirmed the back-splice junction sequences of circVAPA. Actinomycin D and RNase R treatments suggested that circVAPA was highly stable compared with its linear counterpart, and qRT-PCR for the circVAPA level in nuclear and cytoplasmic fractions indicated that circVAPA was predominantly localized in the cytoplasm. Gain-of-function and loss-of-function studies in CRC cell lines indicated that circVAPA could promote CRC cell proliferation, migration, invasion, and inhibit apoptosis. miRanda software (v3.3a) was used to predict target miRNAs of circVAPA. Moreover, target miRNAs associated with the KEGG pathway of COLORECTAL CANCER (Entry: map05210; https://www.kegg.jp/) were screened using DIANA-miRPath v.3 platform (Reverse Search module; TarBase v7.0 method). The analyses by miRanda and miRPath suggested that circVAPA could potentially bind to hsa-miR101-3p (miR-101) associated with the COLORECTAL CANCER pathway. Luciferase reporter assay confirmed a direct interaction between circVAPA and miR-101. Furthermore, circVAPA had no effect on the expression level of miR-101, and miR-101 over-expression had the similar tumor-suppressing effects as circVAPA silencing. The tumor-promoting effect of circVAPA over-expression could be reversed by the up-regulation of miR-101. These data demonstrated that circVAPA promoted CRC progression by sponging miR-101. In conclusion, we have verified that circVAPA is up-regulated in CRC patients' tissues and plasma, and exerts oncogenic properties by sponging miR-101 in CRC. CircVAPA could serve as a promising biomarker and a therapeutic target for CRC.