lncRNAs transactivate Staufen1-mediated mRNA decay by duplexing with 3'UTRs via Alu elements

Staufen1 (STAU1)-mediated mRNA decay (SMD) degrades translationally active mRNAs that bind the double-stranded (ds)RNA binding protein STAU1 within their 3'-untranslated regions (3'UTRs)1,2. Earlier studies defined the STAU1 binding site (SBS) within ADP ribosylation factor 1 (ARF1) mRNA as a 19-base-pair stem with a 100-nucleotide apex2. However, we were unable to identify comparable structures within the 3'UTRs of other SMD targets. Here we report that SBSs can be formed by imperfect base-pairing between an Alu element within the 3'UTR of an SMD target and another Alu element within a cytoplasmic and polyadenylated long noncoding RNA (lncRNA). Individual lncRNAs can downregulate a subset of SMD targets, and distinct lncRNAs can downregulate the same SMD target. These are previously unappreciated functions for ncRNAs and Alu elements3–5. Not all mRNAs that contain a 3'UTR Alu element are targeted for SMD despite the presence of a complementary lncRNA that targets other mRNAs for SMD. Most known trans-acting RNA effectors consist of fewer than 200 nucleotides and include snoRNAs and microRNAs. Our finding that STAU1 binding to mRNAs can be transactivated by lncRNAs uncovers an unexpected strategy used by cells to recruit proteins to mRNAs and mediate their decay. We name these lncRNAs “half(½)-sbsRNAs”.