CircZNF609 regulates microtubule dynamics ad tumorigenicity by sustaining CKAP5 protein levels.

Circular RNAs (circRNAs) are widely expressed in eukaryotes and highly regulated in a myriad of biological processes. While many studies indicate their activity as miRNA and protein sponges, little is known about their ability to directly control mRNA homeostasis. We show that a widely expressed circRNA, circZNF609, directly interacts with several mRNAs and increases their stability and/or translation by favouring the recruitment of the RNA-binding protein ELAVL1. Specifically, the interaction with Ckap5 mRNA, that interestingly overlaps the back-splicing junction, regulates microtubule homeostasis in several cancer cell lines and sustains cell-cycle progression. Finally, we show that circZNF609 downregulation increases the sensitivity to several microtubule-targeting cancer drugs in the regulation of microtubule metabolism and that LNA protectors against the Ckap5 pairing region on circZNF609 phenocopies such activity. These data set an example of how the small effects tuned by circZNF609/Ckap5 mRNA interaction might have potent output in tumour growth and drug response. High-throughput sequencing of total RNA from circ-ZNF609 pull-down experiments performed using two sets of specific biotynilated antisense probes targeting ZNF609 exon 2 and control biotynilated antisense probes targeting LacZ bacterial mRNA.