A triple helix stabilizes the 3' ends of long noncoding RNAs that lack poly(A) tails

Titelangaben

Wilusz, Jeremy E. ; JnBaptiste, Courtney K. ; Lu, Laura Y. ; Kuhn, Claus-D. ; Joshua-Tor, Leemor ; Sharp, Phillip A.:
A triple helix stabilizes the 3' ends of long noncoding RNAs that lack poly(A) tails.
In: Genes & Development. Bd. 26 (2012) Heft 21 . - S. 2392-2407.
ISSN 1549-5477
DOI: https://doi.org/10.1101/gad.204438.112

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Abstract

The MALAT1 (metastasis-associated lung adenocarcinoma transcript 1) locus is misregulated in many human cancers and produces an abundant long nuclear-retained noncoding RNA. Despite being transcribed by RNA polymerase II, the 3' end of MALAT1 is produced not by canonical cleavage/polyadenylation but instead by recognition and cleavage of a tRNA-like structure by RNase P. Mature MALAT1 thus lacks a poly(A) tail yet is expressed at a level higher than many protein-coding genes in vivo. Here we show that the 3' ends of MALAT1 and the MEN beta long noncoding RNAs are protected from 3'-5' exonucleases by highly conserved triple helical structures. Surprisingly, when these structures are placed downstream from an ORF, the transcript is efficiently translated in vivo despite the lack of a poly(A) tail. The triple helix therefore also functions as a translational enhancer, and mutations in this region separate this translation activity from simple effects on RNA stability or transport. We further found that a transcript ending in a triple helix is efficiently repressed by microRNAs in vivo, arguing against a major role for the poly(A) tail in microRNA-mediated silencing. These results provide new insights into how transcripts that lack poly(A) tails are stabilized and regulated and suggest that RNA triple-helical structures likely have key regulatory functions in vivo.