Let‐7a‐regulated translational readthrough of mammalian AGO1 generates a microRNA pathway inhibitor. (22nd July 2019)

• Record Type: Journal Article
• Authors: Singh, Anumeha; Manjunath, Lekha E; Kundu, Pradipta; Sahoo, Sarthak; Das, Arpan; Suma, Harikumar R; Fox, Paul L; Eswarappa, Sandeep M
• Is Part Of: EMBO journal. Volume 38:Number 16(2019)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2019-07-22
• Subjects: Argonaute -- let‐7a -- miRNA -- translational readthrough; Molecular biology -- Periodicals; 572.805
• DOI: 10.15252/embj.2018100727
• Languages: English
• ISSNs: 0261-4189

Abstract

Abstract: Translational readthrough generates proteins with extended C‐termini, which often possess distinct properties. Here, we have used various reporter assays to demonstrate translational readthrough of AGO1 mRNA. Analysis of ribosome profiling data and mass spectrometry data provided additional evidence for translational readthrough of AGO1 . The endogenous readthrough product, Ago1x, could be detected by a specific antibody both in vitro and in vivo . This readthrough process is directed by a cis sequence downstream of the canonical AGO1 stop codon, which is sufficient to drive readthrough even in a heterologous context. This cis sequence has a let‐7a miRNA‐binding site, and readthrough is promoted by let‐7a miRNA. Interestingly, Ago1x can load miRNAs on target mRNAs without causing post‐transcriptional gene silencing, due to its inability to interact with GW182. Because of these properties, Ago1x can serve as a competitive inhibitor of miRNA pathway. In support of this, we observed increased global translation in cells overexpressing Ago1x. Overall, our results reveal a negative feedback loop in the miRNA pathway mediated by the translational readthrough product of AGO1 . Synopsis: Ago proteins load miRNAs and siRNAs onto their target mRNAs and cause post‐transcriptional gene silencing. A translational readthrough in AGO1 mRNA results in a longer isoform termed Ago1x, which can load miRNAs onto their target mRNAs, but cannot cause post‐transcriptional gene silencing. AGO1 mRNA undergoes translational readthrough. Let‐7a miRNA promotes translational readthrough of AGO1 mRNA. Ago1x loads miRNAs onto target mRNAs. Ago1x cannot repress translation of target mRNAs due to its inability to interact with GW182. Abstract : A novel Ago1 isoform loads miRNAs onto target mRNAs, but cannot cause post‐transcriptional gene silencing due to inability to bind the essential cofactor GW182.