circRAB3IP modulates cell proliferation by reorganizing gene expression and mRNA processing in a paracrine manner [HUVEC_EVs_OE]

Circular RNAs are endogenous long-lived and abundant non-coding species. Despite their prevalence, only few circRNAs have been dissected mechanistically as regards their function to date. Here, we catalogued nascent RNA-enriched circRNAs from primary human cells and focus on circRAB3IP to assign to it a role in sustaining cellular homeostasis. We combine “omics” and functional experiments to show how circRAB3IP depletion deregulates hundreds of genes, suppress cell cycle progression, and brings about senescence-like gene expression changes. Conversely, excess circRAB3IP delivered to endothelial cells via exosomes suffices for accelerating their cell division. We attribute these effects to widespread changes in isoform usage that stem from the interplay between circRAB3IP and the general splicing factor SF3B1. Together, our findings link the maintenance of cell homeostasis to the tightly regulated titers of a single circRNA. Overall design: circRAB3IP-piggyBAC HEK293 cells were grown in exosome-depleted medium and induced and selected with additionally induced with 3 µg/ml of doxycycline (DOX, Sigma) and 400 µg/ml of G418 (Sigma). After 48h, the medium was used for purification of extracellular vesicles which were used to treat normal grown HUVEC cells for 24h. HUVECs were then collected for RNA extraction and RNA sequencing.