Identification and Characterization of Hypoxia-Regulated Endothelial Circular RNA
Rationale: Circular RNAs (circRNAs) are non-coding RNAs generated by back-splicing. Back-splicing has been considered a rare event, but recent studies suggest that circRNAs are widely expressed. However, the expression, regulation and function of circRNAs in vascular cells is still unknown.
Objective: Here, we characterize the expression, regulation and function of circRNAs in endothelial cells.
Methods and Results: Endothelial circRNAs were identified by computational analysis of ribo-minus RNA generated from human umbilical venous endothelial cells cultured under normoxic or hypoxic conditions. Selected circRNAs were biochemically characterized, and we found that the majority of them lacks polyadenylation, is resistant to RNase R digestion and localized to the cytoplasm. We further validated the hypoxia-induced circRNAs cZNF292, cAFF1, and cDENND4C as well as the down-regulated cTHSD1 by RT-PCR in cultured endothelial cells. Cloning of cZNF292 validated the predicted back splicing of exon 4 to a new alternative exon 1A. Silencing of cZNF292 inhibited cZNF292 expression and reduced tube formation and spheroid sprouting of endothelial cells in vitro. The expression of pre-mRNA or mRNA of the host gene was not affected by silencing of cZNF292. No validated miRNA binding sites for cZNF292 were detected in Argonaute HITS-CLIP data sets, suggesting that cZNF292 does not act as a microRNA sponge.
Conclusions: We show that the majority of the selected endothelial circRNAs fulfill all criteria of bona fide circRNAs. The circRNA cZNF292 exhibits pro-angiogenic activities in vitro. These data suggest that endothelial circRNAs are regulated by hypoxia and have biological functions.
- Received February 24, 2015.
- Revision received September 15, 2015.
- Accepted September 16, 2015.