Project description:Polyomaviruses are a family of small DNA tumor viruses that includes several pathogenic human members, including Merkel cell polyomavirus, BK virus and JC virus. As is characteristic of DNA tumor viruses, gene expression in polyomaviruses is temporally regulated into an early phase, consisting of the viral regulatory proteins, and a late phase, consisting of the viral structural proteins. Previously, the late transcripts expressed by the prototypic polyomavirus simian virus 40 (SV40) were reported to contain several adenosines bearing methyl groups at the N6 position (m6A), although the precise location of these m6A residues, and their phenotypic effects, have not been investigated. Here, we first demonstrate that overexpression of the key m6A reader protein YTHDF2 induces more rapid viral replication, and larger viral plaques, in SV40 infected BSC40 cells, while mutational inactivation of the endogenous YTHDF2 gene, or the m6A methyltransferase METTL3, has the opposite effect, thus suggesting a positive role for m6A in the regulation of SV40 gene expression. To directly test this hypothesis, we mapped sites of m6A addition on SV40 transcripts and identified two m6A sites on the viral early transcripts and eleven m6A sites on the late mRNAs. Using synonymous mutations, we inactivated the majority of the m6A sites on the SV40 late mRNAs and observed that the resultant viral mutant replicated more slowly than wild type SV40. Alternative splicing of SV40 late mRNAs was unaffected by the reduction in m6A residues and our data instead suggest that m6A enhances the translation of viral late transcripts. Together, these data argue that the addition of m6A residues to the late transcripts encoded by SV40 plays an important role in enhancing viral gene expression and, hence, replication.
Project description:N6-methyladenosine (m6A) is the most abundant internal modification in eukaryotic messenger RNAs (mRNAs), and plays important roles in cell differentiation and organism development. It regulates multiple steps throughout the RNA life cycle including RNA processing, translation, and metabolism, via the recognition by selective binding proteins. In cytoplasm, m6A binding protein YTHDF1 facilitates translation of m6A-modified mRNAs, and YTHDF2 accelerates the decay of m6A-modified transcripts. The biological function of YTHDF3, another cytoplasmic m6A binder of the YTH domain family, remains unknown. Here, we report that YTHDF3 promotes protein synthesis in synergy with YTHDF1, and affects methylated mRNA decay mediated by YTHDF2. Cells deficient in all of YTHDF proteins experience the most dramatic accumulation of the m6A-methylated transcripts. These results indicate that in cytoplasm, YTHDF proteins act in an integrated and cooperative network to accelerate metabolism of m6A-modified mRNAs. The combinative and dynamic nature of YTHDF proteins may collectively impact fundamental biological processes and diseases related to m6A RNA methylation.
Project description:To replicate in the host, HIV-1 must produce RNA and protein, and this depends cellular factors that also control gene expression. Recently, it has been shown that novel components of this machinery post-transcriptionally modify mRNAs with direct consequences for their structure and stability. The most common among these modifications is the addition of a methyl group to the N6 position of adenosine, termed m6A methylation. Here we are interested the interface of HIV-1 with this posttranscriptional mRNA modification pathway. We show that viral transcripts harbor a number of discrete methylation sites and are bound at those sites by these YTHDF proteins. These sites are conserved among distinct HIV-1 isolates and are observed during viral replication in numerous cell types. With reporter assays we also show that these sites stabilize mRNAs when compared to similar sequences mutated to be incapable of methylation. We further show that overexpression of these reader proteins boosts viral protein expression.
Project description:N6-methyladenosine (m6A) is the most prevalent internal modification present in the mRNA of all higher eukaryotes. Here we present that m6A is selectively recognized by human YTH domain family (YTHDF2) protein to regulate mRNA degradation. By using crosslinking and immunoprecipitation, we have identified over 4000 substrate RNA of YTHDF2 with conserved core motif of G(m6A)C. We further estabilshed the role of YTHDF2 in RNA metabolism by a combination of ribosome profiling, RNA sequencing, m6A level quantification and cell-based imaging: the C-terminal domain of YTHDF2 selectively binds to m6A of mRNA and the N-terminal domain is responsive for localizing mRNA from translatable pool to processing body where mRNA decay occurs. PAR-CLIP and RIP was used to identify YTHDF2 binding sites followed by ribosome profling and RNA seq to assess the consequences of YTHDF2 siRNA knock-down
Project description:Oxaliplatin as a first-line drug frequently causes the chemo-resistance on colorectal cancer (CRC). N6-methyladenosine (m6A) methylation has been largely acknowledged in multiple biological functions. However, the molecular mechanisms underlying the m6A methylation in modulating anticancer drug resistance in CRC are still obscure. In present study, RIP-seq was conducted to investigate the occupancy of N6-methyladenosine RNA binding protein 3 (YTHDF3) served as “readers” that can recognize m6A modification site in HCT116 cells with oxaliplatin resistance (HCT116R). Then, YTHDF3 was knockdown by siRNA in HCT116 cells with oxaliplatin resistance, and RIP-seq was further conducted to investigate m6A methylation of HCT116, HCT116R and HCT116R cells with YTHDF3 knockdown.
Project description:As the crucial m6A reader, YTHDF2 usually degrades the target mRNAs by recognizing the m6A modified sites, consequently altering m6A levels of each mRNA. In this study, we used m6A MeRIP sequencing to detect the m6A modification alterations in prostate cancer (PCa) cell line after knocking down YTHDF2 and identify how YTHDF2 promote the PCa progression by mediating the mRNA degradation in m6A-dependent way.
Project description:Brain metastasis is a major cause of cancer mortality, but its molecular mechanisms are severely understudied. We found that YTHDF3 overexpression clinically correlates with brain metastases in breast cancer patients and is required for brain metastasis. Silencing YTHDF3 suppressed the brain metastasis of breast cancer cells in vitro and in vivo. Integrated transcriptome and m6A-seq analysis revealed alter expression of selected YTHDF3 target genes, including ST6GALNAC5, GJA1, and EGFR by promoting m6A-dependent translation of these target transcripts. Our work uncovers an essential role of YTHDF3 in controlling the interaction between cancer cells and brain microenvironment, thereby gaining brain metastatic competence.
Project description:We found that the proliferation and differentiation capabilities of NSPCs decrease significantly in Ythdf2 null mutants.To explore the underlying molecular mechanism, we performed transcriptomics and well-established m6A-methylome analyses of NSPCs dervied from wild type and Ythdf2-/- embryo brains. RNA-seq data revealed that expressions of genes enriched in neural development pathways were significantly disturbed. The inhibitory genes, like Flrt2, Ptprd, et al. in regulation of JAK-STAT cascade, which contributes to the neuroprotection and neurite outgrowth, showed increased gene expressions and m6A enrichment by m6A-seq. We identified that without the recognizing and binding of Ythdf2, the degradation of neuron differentiation related m6A-modified mRNAs were delayed in Ythdf2-/-, thereby disturbing the proliferation and differentiation of NSPCs. In summary, our findings uncovered that Ythdf2 modulates neural developmental via regulating the clearance of mRNA targets.
Project description:N6-methyladenosine (m6A), the most abundant reversible modification on eukaryote messenger RNA, is recognized by a series of readers, including the YT521-B homology domain family (YTHDF) proteins, which are coupled to perform physiological functions. Here, we report that YTHDF2 and YTHDF3, but not YTHDF1, are required for reprogramming of somatic cells into induced pluripotent stem cells (iPSCs). Mechanistically, we found that YTHDF3 recruits the PAN2-PAN3 deadenylase complex and conduces to reprogramming by promoting mRNA clearance of somatic genes, including Tead2 and Tgfb1, which parallels the activity of the YTHDF2-CCR4-NOT deadenylase complex. Ythdf2/3 deficiency further represses mesenchymal-to-epithelial transition (MET) and chromatin silencing at loci containing the TEAD motif, contributing to decreased reprogramming efficiency. Moreover, RNA interference of Tgfb1 or the Hippo signaling effectors Yap1, Taz, and Tead2 rescues Ythdf2/3-defective reprogramming. Overall, YTHDF2/3 couple RNA deadenylation and regulation with the clearance of somatic genes provides insights into iPSC reprogramming at the posttranscriptional level.