Project description:Nonsense-mediated mRNA decay (NMD) is a conserved co-translational mRNA surveillance and turnover pathway across eukaryotes. NMD has a central role in degrading defective mRNAs and also regulates the stability of a significant portion of the transcriptome. The pathway is organized around UPF1, an RNA helicase that can interact with several NMD-specific factors. In human cells, degradation of the targeted mRNAs begins with a cleavage event that requires the recruitment of the SMG6 endonuclease to UPF1. Previous studies have identified functional links between SMG6 and UPF1, but the underlying molecular mechanisms have remained elusive. In this work, we used mass spectrometry, structural biology and biochemical approaches to identify and characterize a conserved short linear motif in SMG6 that interacts with the cysteine/histidine-rich (CH) domain of UPF1. Unexpectedly, we found that the UPF1-SMG6 interaction is precluded when the UPF1 CH domain is engaged with another NMD factor, UPF2. Based on cryo-EM data, we propose that the formation of distinct SMG6-containing and UPF2-containing NMD complexes may be dictated by the RNA-binding status of UPF1. Our findings rationalize a key event in the metazoan NMD quality control pathway and progress our understanding of mechanisms regulating activity and guiding substrate recognition by the SMG6 endonuclease.
Project description:RNA helicases are important regulators of gene expression that act by remodeling RNA secondary structures and as RNA-protein interactions. Here, we demonstrate that MOV10 has an ATP-dependent 5' to 3' in vitro RNA unwinding activity and determine the RNA-binding sites of MOV10 and its helicase mutants using PAR-CLIP. We find that MOV10 predominantly binds to 3' UTRs upstream of regions predicted to form local secondary structures and provide evidence that MOV10 helicase mutants are impaired in their ability to translocate 5' to 3' on their mRNA targets. MOV10 interacts with UPF1, the key component of the nonsense-mediated mRNA decay pathway. PAR-CLIP of UPF1 reveals that MOV10 and UPF1 bind to RNA in close proximity. Knockdown of MOV10 resulted in increased mRNA half-lives of MOV10-bound as well as UPF1-regulated transcripts, suggesting that MOV10 functions in UPF1-mediated mRNA degradation as an RNA clearance factor to resolve structures and displace proteins from 3' UTRs. Flp-In T-REx HEK293 cells expressing FLAG/HA-tagged MOV10 WT, MOV10 K530A, MOV10 D645N and UPF1 were used to determine the protein-RNA interaction sites of RNA helicases MOV10 and UPF1 as well as MOV10 inactive variants using PAR-CLIP in combination with next generation sequencing. mRNA half-life changes of MOV10-targeted mRNA were determined by measuring mRNA half-lives by mRNA sequencing of mock and MOV10-depleted HEK293 cells.
Project description:RNA sequencing of heterozygote or Tudor domain contian protein 6 (TDRD6) knockout round spermatid cells. Chromatoid bodies (CBs) are germ cell-specific organelles of largely unknown function. CBs harbor various RNA species, RNA-associated proteins and proteins of the tudor domain family such as TDRD6. Proteome analysis of purified CBs revealed components of the nonsense-mediated mRNA decay machinery such as UPF1. TDRD6 is essential for UPF1 localization to CBs, for UPF1-UPF2 interaction, and for assembly of UPFs and other RNA binding proteins into super-complexes. In absence of TDRD6, the association of some mRNAs with UPF1 is impaired, and the long 3’ UTR-stimulated but not the exon junction complex-stimulated pathway of NMD is distorted. Reduced association of mRNAs with UPF1 correlated with increased stability and presence in polysome fractions, i.e. enhanced translational activity. Thus, we define CBs as sites of UPF1-dependent mRNA degradation and provide evidence for the requirement for NMD in spermiogenesis. This function of CBs depends on TDRD6-promoted assembly of mRNA decay enzymes within mRNPs.
Project description:Mature mRNAs undergo quality control during translation that may lead to RNA degradation by triggering the nonsense mediated decay (NMD) pathway. Aberrant translation due to features such as the presence of a premature stop codon downstream on an exon-exon junction or an intron in the 3'UTR activates NMD. However, many of the features that lead to the activation of this pathway are unclear. UPF1, an RNA helicase, is the core NMD factor. UPF1 forms a multi-protein complex by recruiting a series of factors and other protein complexes in a process that depends on the UPF1 phosphorylation-dephosphorylation cycle. Among the factors recruited by UPF1, SMG5-SMG7 and SMG6 have critical importance in executing NMD. The SMG5-SMG7 heterodimer induces the exonucleolytic degradation of the mRNA, which depends on the recruitment of deadenylation factors. SMG6 has endonucleolytic activity and cleaves the targeted transcript close to the stop codon. The redundancy between the exonucleolytic and endonucleolytic paths to achieve degradation during NMD has been previously reported in the literature. To investigate the apparent redundancy between SMG5-SMG7 and SMG6 activity and to further understand the features that lead to the activation of NMD, we have generated two clones of SMG7 knockout human cells using CRISPR-Cas9. We generated mRNA-Sequencing data for control and both SMG7 KO clones with additional siRNA-mediated knockdown of Luciferase (Luc) as control, SMG5 or SMG6.
Project description:RNA sequencing of heterozygote or Tudor domain contian protein 6 (TDRD6) knockout round spermatid cells. Chromatoid bodies (CBs) are germ cell-specific organelles of largely unknown function. CBs harbor various RNA species, RNA-associated proteins and proteins of the tudor domain family such as TDRD6. Proteome analysis of purified CBs revealed components of the nonsense-mediated mRNA decay machinery such as UPF1. TDRD6 is essential for UPF1 localization to CBs, for UPF1-UPF2 interaction, and for assembly of UPFs and other RNA binding proteins into super-complexes. In absence of TDRD6, the association of some mRNAs with UPF1 is impaired, and the long 3â UTR-stimulated but not the exon junction complex-stimulated pathway of NMD is distorted. Reduced association of mRNAs with UPF1 correlated with increased stability and presence in polysome fractions, i.e. enhanced translational activity. Thus, we define CBs as sites of UPF1-dependent mRNA degradation and provide evidence for the requirement for NMD in spermiogenesis. This function of CBs depends on TDRD6-promoted assembly of mRNA decay enzymes within mRNPs. RNA was extracted from quadruplicate samples and libraries generated for sequencing using the NEBNext Ultra Directional RNA Library Prep Kit (New England Biolabs) at the Deep Sequencing Group SFB 655, Biotechnology Center of Technische Universität Dresden. After enrichment and XP bead (Agencourt AMPure Kit; Beckman Coulter, Inc.) purification, quality control was done using Fragment AnalyzerTM (Advanced Analytical). The bar-coded libraries were equimolarly pooled and subjected to 76 bp single-end sequencing on Illumina HiSeq 2000, resulting in an average of 33 million reads per sample.
Project description:A majority of metazoan mRNAs are under microRNA (miRNA)/Argonaute (Ago)-mediated control of RNA stability at the post-transcriptional level. Although the molecular mechanism of the miRNA-mediated repression of target mRNAs through Ago/TNRC6 pathway have been largely elucidated, however, the existence of alternative TNRC6-independent miRNA-mediated post-transcriptional gene regulation pathway remains unknown. Here, we suggest that endogenous miRNAs (endo-miRNAs) can downregulate the target mRNAs via the alternative molecular pathway, Ago-associated UPF1/SMG7, core mediators of nonsense-mediated mRNA decay. Global analyses of mRNAs in a response to UPF1 RNA interference in miRNA-deficient cells reveal that 3’UTR-length-dependent mRNA decay by UPF1 requires endo-miRNA targeting via CUG motif. The repression of miRNA targets is more additively or synergistically accomplished by combination of Ago2 and UPF1 through UPF1-associated SMG7, recruiting CCR4-NOT deadenylase complex, in TNRC6-independent manner. We expect that the new miRNA-mediated mRNA decay pathway enables the miRNA targeting to become more predictable and expand the miRNA-mRNA regulatory network.
Project description:Nonsense-mediated mRNA decay (NMD) controls gene expression by eliminating mRNAs with premature or aberrant translation termination. Degradation of NMD substrates is initiated by the central NMD factor UPF1, which recruits the endonuclease SMG6 and the deadenylation-promoting SMG5/7 complex. Here we map transcriptome-wide sites of SMG6-mediated endocleavage via 3′ fragment capture and degradome sequencing.
Project description:The X-linked DDX3X gene encodes an ATP-dependent DEAD-box RNA helicase frequently altered in various human cancers including melanomas. Despite its important roles in translation and splicing, how DDX3X dysfunction specifically rewires gene expression in melanoma remains completely unknown. Here we uncover a DDX3X-driven post-transcriptional program that dictates melanoma phenotype and poor disease prognosis. Through an unbiased analysis of translating ribosomes we identified the microphtalmia-associated transcription factor, MITF, as a key DDX3X translational target that directs a proliferative-to-metastatic phenotypic switch in melanoma cells. Mechanistically, DDX3X controls MITF mRNA translation via an internal ribosome entry site (IRES) embedded within the 5’ untranslated region. Through this exquisite translation-based regulatory mechanism, DDX3X steers MITF protein levels dictating melanoma metastatic potential in vivo and response to targeted therapy. Together these findings unravel a post-transcriptional layer of gene regulation that may provide a unique therapeutic vulnerability in aggressive male melanomas.
Project description:Analysis of miRNA-targeted cellular NMD substrates in HeLa cell. The hypothesis tested in the present study was that endogenous NMD substrates containing long 3' untranslated region may targeted for miRNA. Results provide important information expanding the roles of miRISC in the posttranscriptional regulation of gene expression: a new cross-talk between miRNA-mediated gene silencing and NMD. ABSTRACT: Imperfect base-pairing between microRNA (miRNA) and the 3â-untranslated region (3âUTR) of target mRNA triggers translational repression of the target mRNA. Here, we provide evidence that human Argonaute 2 (Ago2) targets cap-binding protein (CBP)80/20- and exon junction complex (EJC)-bound mRNAs and inhibits nonsense-mediated mRNA decay (NMD), which is tightly restricted to CBP80/20-bound mRNAs. Furthermore, microarray analyses reveal that a subset of cellular transcripts, which are expected to be targeted for NMD, is stabilized by miRNA-mediated gene silencing. The regulation of NMD by miRNAs will shed light on a new post-transcriptional regulation mechanism of gene expression in mammalian cells Total RNA obtained from HeLa cells with downregulation of Ago2 or Ago2/UPF1 by siRNA. The up- or down-regulated transcripts were compared to control siRNA treated HeLa cell RNA extract. Significant transcripts were confirmed by replication.
Project description:RNA helicases are important regulators of gene expression that act by remodeling RNA secondary structures and as RNA-protein interactions. Here, we demonstrate that MOV10 has an ATP-dependent 5' to 3' in vitro RNA unwinding activity and determine the RNA-binding sites of MOV10 and its helicase mutants using PAR-CLIP. We find that MOV10 predominantly binds to 3' UTRs upstream of regions predicted to form local secondary structures and provide evidence that MOV10 helicase mutants are impaired in their ability to translocate 5' to 3' on their mRNA targets. MOV10 interacts with UPF1, the key component of the nonsense-mediated mRNA decay pathway. PAR-CLIP of UPF1 reveals that MOV10 and UPF1 bind to RNA in close proximity. Knockdown of MOV10 resulted in increased mRNA half-lives of MOV10-bound as well as UPF1-regulated transcripts, suggesting that MOV10 functions in UPF1-mediated mRNA degradation as an RNA clearance factor to resolve structures and displace proteins from 3' UTRs. Flp-In T-REx HEK293 cells expressing FLAG/HA-tagged MOV10 WT, MOV10 K530A, MOV10 D645N and UPF1 were sequenced. mRNA half-life data under GSE56751.