Foxo3 activity promoted by non-coding effects of circular RNA and Foxo3 pseudogene in the inhibition of tumor growth and angiogenesis

It has recently been shown that the upregulation of a pseudogene specific to a protein-coding gene could function as a sponge to bind multiple potential targeting microRNAs (miRNAs), resulting in increased gene expression. Similarly, it was recently demonstrated that circular RNAs can function as sponges for miRNAs, and could upregulate expression of mRNAs containing an identical sequence. Furthermore, some mRNAs are now known to not only translate protein, but also function to sponge miRNA binding, facilitating gene expression. Collectively, these appear to be effective mechanisms to ensure gene expression and protein activity. Here we show that expression of a member of the forkhead family of transcription factors, Foxo3, is regulated by the Foxo3 pseudogene (Foxo3P), and Foxo3 circular RNA, both of which bind to eight miRNAs. We found that the ectopic expression of the Foxo3P, Foxo3 circular RNA and Foxo3 mRNA could all suppress tumor growth and cancer cell proliferation and survival. Our results showed that at least three mechanisms are used to ensure protein translation of Foxo3, which reflects an essential role of Foxo3 and its corresponding non-coding RNAs.