Widespread localisation of long noncoding RNAs to ribosomes: Distinguishing features and evidence for regulatory roles.

Abstract

The function of long noncoding RNAs (lncRNAs) depends on their location within the cell. While most studies to date have concentrated on their nuclear roles in transcriptional regulation, evidence is mounting that lncRNA also have cytoplasmic roles. Here we comprehensively map the cytoplasmic and ribosomal lncRNA population in a human cell. Three-quarters (74%) of lncRNAs are detected in the cytoplasm, the majority of which (62%) preferentially cofractionate with polyribosomes. Ribosomal lncRNA are highly expressed across tissues, under purifying evolutionary selection, and have cytoplasmic-to-nuclear ratios comparable to mRNAs and consistent across cell types. LncRNAs may be classified into three groups by their ribosomal interaction: non-ribosomal cytoplasmic lncRNAs, and those associated with either heavy or light polysomes. A number of mRNA-like features destin lncRNA for light polysomes, including capping and 5′UTR length, but not cryptic open reading frames or polyadenylation. Surprisingly, exonic retroviral sequences antagonise recruitment. In contrast, it appears that lncRNAs are recruited to heavy polysomes through basepairing to mRNAs. Finally, we show that the translation machinery actively degrades lncRNA. We propose that light polysomal lncRNAs are translationally engaged, while heavy polysomal lncRNAs are recruited indirectly. These findings point to extensive and reciprocal regulatory interactions between lncRNA and the translation machinery.