Abundant capped RNAs are derived from mRNA cleavage at 3’UTR G-Quadruplexes

Abstract

SummaryThe 3’ untranslated region (3’UTR) plays a crucial role in determining mRNA stability, localisation, translation and degradation. Cap analysis gene expression (CAGE), a method for the detection of capped 5’ ends of mRNAs, additionally reveals a large number of apparently 5’ capped RNAs derived from 3’UTRs. Here we provide the first direct evidence that these 3’UTR-derived RNAs are indeed capped and often more abundant than the corresponding full-length mRNAs. By using a combination of AGO2 enhanced individual nucleotide resolution UV crosslinking and immunoprecipitation (eiCLIP) and CAGE following siRNA knockdowns, we find that these 3’UTR-derived RNAs likely originate from AGO2-mediated cleavage, and most often occur at locations with potential to form RNA-G-quadruplexes and are enriched by RNA-binding protein UPF1. High-resolution imaging and long-read sequencing analysis validates several 3’UTR-derived RNAs, demonstrates their abundance and shows that they tend not to co-localise with the parental mRNAs. We also find that production of 3’UTR-derived RNA could explain the previously reported role of a 3’UTR G-quadruplex in regulating the production of APP protein. Taken together, we provide new insights into the origin and abundance of 3’UTR-derived RNAs, show the utility of CAGE-seq for their quantitative detection, and provide a rich dataset for exploring new biology of a poorly understood new class of RNAs.