MicroRNAs control translation initiation by inhibiting eukaryotic initiation factor 4E/cap and poly(A) tail function

Abstract

MicroRNAs (miRNAs) repress translation of target mRNAs by interaction with partially mismatched sequences in their 3 UTR. The mechanism by which they act on translation has remained largely obscure. We examined the translation of mRNAs containing four partially mismatched miRNA-binding sites in the 3 UTR in HeLa cells cotransfected with a cognate miRNA. The mRNAs were prepared by in vitro transcription and were engineered to employ different modes of translation initiation. We find that the 5 cap structure and the 3 poly(A) tail are each necessary but not sufficient for full miRNA-mediated repression of mRNA translation. Replacing the cap structure with an internal ribosome entry site from either the cricket paralysis virus or the encephalomyocarditis virus impairs miRNA-mediated repression. Collectively, these results demonstrate that miRNAs interfere with the initiation step of translation and implicate the cap-binding protein eukaryotic initiation factor 4E as a molecular target. mRNA translation ͉ cap structure ͉ processing bodies ͉ mRNA decay ͉ short interfering RNA

On the origin and functions of RNA-mediated silencing: from protists to man

“…Plant miRNAs are also methylated on the ribose of the last nucleotide, a modification presumably involved in protecting miRNAs from 3′ end uridylation and degradation, whereas animal miRNAs do not appear to be modified Yu et al 2005). Mechanistically, most animal miRNAs are only partly complementary to their targets and mediate silencing primarily by translational repression, although localization to the processing bodies may also affect RNA stability (Humphreys et al 2005;Liu et al 2005b;Pillai et al 2005;Wienholds and Plasterk 2005;Zamore and Haley 2005). In contrast, most plant miRNAs have near-perfect complementarity to their targets and trigger predominantly mRNA cleavage (Carrington and Ambros 2003;Schwab et al 2005).…”

The role of microRNAs (miRNA) in circadian rhythmicity

“…This pairing may either lead to mRNA degradation, or can affect the efficiency of translation by either promoting the ribosomal drop-off from the mRNA, or inhibiting the formation of 80S ribosome at the beginning of the translation (Humphreys et al 2005;Pillai et al 2005;Nottrott et al 2006;Petersen et al 2006). It was shown that miRNAs can also affect the stability of mRNA by de-adenylation and de-capping of the target mRNA (BehmAnsmant et al 2006;Giraldez et al 2006;Mishima et al 2006;Wu et al 2006).…”

MicroRNAs and genomic instability

“…This so called 'seed sequence' [29][30][31] has been used to attempt the bioinformatic matching of miRNAs and gene targets, however, as the sequence nucleotide constraints for other parts of the miRNA-target interaction are much weaker and are much less well defined this has proven to be difficult [10,32]. The role of miRNAs in the regulation of gene expression is primarily thought to be through repression of translation, however, there is conflicting evidence as to whether miRNA activity is mediated through effects on the initiation of translation and/or termination [33][34][35].…”