ABSTRACT
Estrogen receptor α (ERα) is a hormone receptor and key driver for over 70% of breast cancers that has been studied for decades as a transcription factor. Unexpectedly, we discover that ERα is a potent non-canonical RNA-binding protein. We show that ERα RNA binding function is uncoupled from its activity to bind DNA and critical for breast cancer progression. Employing genome-wide cross-linking immunoprecipitation (CLIP) sequencing and a functional CRISPRi screen, we find that ERα-associated mRNAs sustain cancer cell fitness and elicit cellular responses to stress. Mechanistically, ERα controls different steps of RNA metabolism. In particular, we demonstrate that ERα RNA binding mediates alternative splicing of XBP1 and translation of the eIF4G2 and MCL1 mRNAs, which facilitates survival upon stress conditions and sustains tamoxifen resistance of cancer cells. ERα is therefore a multifaceted RNA-binding protein, and this activity transforms our knowledge of post-transcriptional regulation underlying cancer development and drug response.
Subject(s)
Breast Neoplasms/metabolism , Breast Neoplasms/pathology , Drug Resistance, Neoplasm , Estrogen Receptor alpha/metabolism , RNA-Binding Proteins/metabolism , Animals , Base Sequence , Breast Neoplasms/genetics , Cell Line, Tumor , Cell Survival/drug effects , Cell Survival/genetics , Disease Progression , Drug Resistance, Neoplasm/drug effects , Drug Resistance, Neoplasm/genetics , Estrogen Receptor alpha/chemistry , Eukaryotic Initiation Factor-4G/genetics , Eukaryotic Initiation Factor-4G/metabolism , Female , Gene Expression Regulation, Neoplastic/drug effects , Genomics , Humans , Mice, Inbred NOD , Myeloid Cell Leukemia Sequence 1 Protein/genetics , Myeloid Cell Leukemia Sequence 1 Protein/metabolism , Oncogenes , Protein Binding/drug effects , Protein Domains , RNA Splicing/genetics , RNA, Messenger/genetics , RNA, Messenger/metabolism , Stress, Physiological/drug effects , Stress, Physiological/genetics , Tamoxifen/pharmacology , X-Box Binding Protein 1/metabolismABSTRACT
While mutations affecting protein-coding regions have been examined across many cancers, structural variants at the genome-wide level are still poorly defined. Through integrative deep whole-genome and -transcriptome analysis of 101 castration-resistant prostate cancer metastases (109X tumor/38X normal coverage), we identified structural variants altering critical regulators of tumorigenesis and progression not detectable by exome approaches. Notably, we observed amplification of an intergenic enhancer region 624 kb upstream of the androgen receptor (AR) in 81% of patients, correlating with increased AR expression. Tandem duplication hotspots also occur near MYC, in lncRNAs associated with post-translational MYC regulation. Classes of structural variations were linked to distinct DNA repair deficiencies, suggesting their etiology, including associations of CDK12 mutation with tandem duplications, TP53 inactivation with inverted rearrangements and chromothripsis, and BRCA2 inactivation with deletions. Together, these observations provide a comprehensive view of how structural variations affect critical regulators in metastatic prostate cancer.
Subject(s)
Genomic Structural Variation/genetics , Prostatic Neoplasms/genetics , Aged , Aged, 80 and over , BRCA2 Protein/metabolism , Cyclin-Dependent Kinases/metabolism , DNA Copy Number Variations , Exome , Gene Expression Profiling/methods , Genomics/methods , Humans , Male , Middle Aged , Mutation , Neoplasm Metastasis/genetics , Proto-Oncogene Proteins c-myc/genetics , Proto-Oncogene Proteins c-myc/metabolism , Receptors, Androgen/genetics , Receptors, Androgen/metabolism , Tandem Repeat Sequences/genetics , Tumor Suppressor Protein p53/metabolism , Whole Genome Sequencing/methodsABSTRACT
Transfer RNAs (tRNAs) are primarily viewed as static contributors to gene expression. By developing a high-throughput tRNA profiling method, we find that specific tRNAs are upregulated in human breast cancer cells as they gain metastatic activity. Through loss-of-function, gain-of-function, and clinical-association studies, we implicate tRNAGluUUC and tRNAArgCCG as promoters of breast cancer metastasis. Upregulation of these tRNAs enhances stability and ribosome occupancy of transcripts enriched for their cognate codons. Specifically, tRNAGluUUC promotes metastatic progression by directly enhancing EXOSC2 expression and enhancing GRIPAP1-constituting an "inducible" pathway driven by a tRNA. The cellular proteomic shift toward a pro-metastatic state mirrors global tRNA shifts, allowing for cell-state and cell-type transgene expression optimization through codon content quantification. TRNA modulation represents a mechanism by which cells achieve altered expression of specific transcripts and proteins. TRNAs are thus dynamic regulators of gene expression and the tRNA codon landscape can causally and specifically impact disease progression.
Subject(s)
Breast Neoplasms/genetics , Gene Expression Regulation, Neoplastic , RNA, Transfer/metabolism , Animals , Breast Neoplasms/pathology , Cell Line, Tumor , Codon , Disease Progression , Exosome Multienzyme Ribonuclease Complex/genetics , Gene Expression Profiling , Gene Knockdown Techniques , Humans , Lung/pathology , Mice , Neoplasm Invasiveness/genetics , Neoplasm Micrometastasis/genetics , Neoplasm Proteins/biosynthesis , RNA-Binding Proteins/genetics , Regulatory Sequences, Ribonucleic Acid , Ribosomes/metabolism , Xenograft Model Antitumor AssaysABSTRACT
N(6)-methyladenosine (m(6)A) is the most abundant internal modification of messenger RNA. While the presence of m(6)A on transcripts can impact nuclear RNA fates, a reader of this mark that mediates processing of nuclear transcripts has not been identified. We find that the RNA-binding protein HNRNPA2B1 binds m(6)A-bearing RNAs in vivo and in vitro and its biochemical footprint matches the m(6)A consensus motif. HNRNPA2B1 directly binds a set of nuclear transcripts and elicits similar alternative splicing effects as the m(6)A writer METTL3. Moreover, HNRNPA2B1 binds to m(6)A marks in a subset of primary miRNA transcripts, interacts with the microRNA Microprocessor complex protein DGCR8, and promotes primary miRNA processing. Also, HNRNPA2B1 loss and METTL3 depletion cause similar processing defects for these pri-miRNA precursors. We propose HNRNPA2B1 to be a nuclear reader of the m(6)A mark and to mediate, in part, this mark's effects on primary microRNA processing and alternative splicing. PAPERCLIP.
Subject(s)
Adenosine/analogs & derivatives , Heterogeneous-Nuclear Ribonucleoprotein Group A-B/metabolism , RNA Processing, Post-Transcriptional , Adenosine/metabolism , Alternative Splicing , Cell Line, Tumor , Cell Nucleus/metabolism , HEK293 Cells , HeLa Cells , Humans , Methylation , RNA/metabolism , RNA-Binding Proteins/metabolism , TranscriptomeABSTRACT
Upon exposure to stress, tRNAs are enzymatically cleaved, yielding distinct classes of tRNA-derived fragments (tRFs), yielding distinct classes of tRFs. We identify a novel class of tRFs derived from tRNA(Glu), tRNA(Asp), tRNA(Gly), and tRNA(Tyr) that, upon induction, suppress the stability of multiple oncogenic transcripts in breast cancer cells by displacing their 3' untranslated regions (UTRs) from the RNA-binding protein YBX1. This mode of post-transcriptional silencing is sequence specific, as these fragments all share a common motif that matches the YBX1 recognition sequence. Loss-of-function and gain-of-function studies, using anti-sense locked-nucleic acids (LNAs) and synthetic RNA mimetics, respectively, revealed that these fragments suppress growth under serum-starvation, cancer cell invasion, and metastasis by breast cancer cells. Highly metastatic cells evade this tumor-suppressive pathway by attenuating the induction of these tRFs. Our findings reveal a tumor-suppressive role for specific tRNA-derived fragments and describe a molecular mechanism for their action. This transcript displacement-based mechanism may generalize to other tRNA, ribosomal-RNA, and sno-RNA fragments.
Subject(s)
Breast Neoplasms/pathology , RNA, Small Untranslated/metabolism , Y-Box-Binding Protein 1/antagonists & inhibitors , Y-Box-Binding Protein 1/genetics , Breast Neoplasms/genetics , Breast Neoplasms/metabolism , HEK293 Cells , Humans , Neoplasm Metastasis , Oligonucleotides/pharmacology , RNA, Small Untranslated/analysis , RNA, Small Untranslated/genetics , RNA, Transfer/genetics , RNA, Transfer/metabolism , Sequence Analysis, RNAABSTRACT
Cancer cells frequently alter their lipids to grow and adapt to their environment1-3. Despite the critical functions of lipid metabolism in membrane physiology, signalling and energy production, how specific lipids contribute to tumorigenesis remains incompletely understood. Here, using functional genomics and lipidomic approaches, we identified de novo sphingolipid synthesis as an essential pathway for cancer immune evasion. Synthesis of sphingolipids is surprisingly dispensable for cancer cell proliferation in culture or in immunodeficient mice but required for tumour growth in multiple syngeneic models. Blocking sphingolipid production in cancer cells enhances the anti-proliferative effects of natural killer and CD8+ T cells partly via interferon-γ (IFNγ) signalling. Mechanistically, depletion of glycosphingolipids increases surface levels of IFNγ receptor subunit 1 (IFNGR1), which mediates IFNγ-induced growth arrest and pro-inflammatory signalling. Finally, pharmacological inhibition of glycosphingolipid synthesis synergizes with checkpoint blockade therapy to enhance anti-tumour immune response. Altogether, our work identifies glycosphingolipids as necessary and limiting metabolites for cancer immune evasion.
ABSTRACT
RNA structural switches are key regulators of gene expression in bacteria, but their characterization in Metazoa remains limited. Here, we present SwitchSeeker, a comprehensive computational and experimental approach for systematic identification of functional RNA structural switches. We applied SwitchSeeker to the human transcriptome and identified 245 putative RNA switches. To validate our approach, we characterized a previously unknown RNA switch in the 3' untranslated region of the RORC (RAR-related orphan receptor C) transcript. In vivo dimethyl sulfate (DMS) mutational profiling with sequencing (DMS-MaPseq), coupled with cryogenic electron microscopy, confirmed its existence as two alternative structural conformations. Furthermore, we used genome-scale CRISPR screens to identify trans factors that regulate gene expression through this RNA structural switch. We found that nonsense-mediated messenger RNA decay acts on this element in a conformation-specific manner. SwitchSeeker provides an unbiased, experimentally driven method for discovering RNA structural switches that shape the eukaryotic gene expression landscape.
ABSTRACT
Post-transcriptional regulation of RNA stability is a key step in gene expression control. We describe a regulatory program, mediated by the RNA binding protein TARBP2, that controls RNA stability in the nucleus. TARBP2 binding to pre-mRNAs results in increased intron retention, subsequently leading to targeted degradation of TARBP2-bound transcripts. This is mediated by TARBP2 recruitment of the m6A RNA methylation machinery to its target transcripts, where deposition of m6A marks influences the recruitment of splicing regulators, inhibiting efficient splicing. Interactions between TARBP2 and the nucleoprotein TPR then promote degradation of these TARBP2-bound transcripts by the nuclear exosome. Additionally, analysis of clinical gene expression datasets revealed a functional role for TARBP2 in lung cancer. Using xenograft mouse models, we find that TARBP2 affects tumor growth in the lung and that this is dependent on TARBP2-mediated destabilization of ABCA3 and FOXN3. Finally, we establish ZNF143 as an upstream regulator of TARBP2 expression.
Subject(s)
Lung Neoplasms/metabolism , Neoplasm Proteins/metabolism , RNA Splicing , RNA Stability , RNA, Neoplasm/metabolism , RNA-Binding Proteins/metabolism , ATP-Binding Cassette Transporters/genetics , ATP-Binding Cassette Transporters/metabolism , Animals , Cell Cycle Proteins/genetics , Cell Cycle Proteins/metabolism , Cell Line, Tumor , Forkhead Transcription Factors/genetics , Forkhead Transcription Factors/metabolism , Humans , Lung Neoplasms/genetics , Lung Neoplasms/pathology , Mice , Mice, Inbred NOD , Mice, SCID , Neoplasm Proteins/genetics , RNA, Neoplasm/genetics , RNA-Binding Proteins/genetics , Trans-Activators/genetics , Trans-Activators/metabolismABSTRACT
Blood vessels support tumours by providing nutrients and oxygen, while also acting as conduits for the dissemination of cancer1. Here we use mouse models of breast and lung cancer to investigate whether endothelial cells also have active 'instructive' roles in the dissemination of cancer. We purified genetically tagged endothelial ribosomes and their associated transcripts from highly and poorly metastatic tumours. Deep sequencing revealed that metastatic tumours induced expression of the axon-guidance gene Slit2 in endothelium, establishing differential expression between the endothelial (high Slit2 expression) and tumoural (low Slit2 expression) compartments. Endothelial-derived SLIT2 protein and its receptor ROBO1 promoted the migration of cancer cells towards endothelial cells and intravasation. Deleting endothelial Slit2 suppressed metastatic dissemination in mouse models of breast and lung cancer. Conversely, deletion of tumoural Slit2 enhanced metastatic progression. We identified double-stranded RNA derived from tumour cells as an upstream signal that induces expression of endothelial SLIT2 by acting on the RNA-sensing receptor TLR3. Accordingly, a set of endogenous retroviral element RNAs were upregulated in metastatic cells and detected extracellularly. Thus, cancer cells co-opt innate RNA sensing to induce a chemotactic signalling pathway in endothelium that drives intravasation and metastasis. These findings reveal that endothelial cells have a direct instructive role in driving metastatic dissemination, and demonstrate that a single gene (Slit2) can promote or suppress cancer progression depending on its cellular source.
Subject(s)
Breast Neoplasms/metabolism , Breast Neoplasms/pathology , Endothelium/metabolism , Intercellular Signaling Peptides and Proteins/metabolism , Lung Neoplasms/metabolism , Lung Neoplasms/pathology , Neoplasm Metastasis , Nerve Tissue Proteins/metabolism , Toll-Like Receptor 3/metabolism , Animals , Chemotaxis , Disease Models, Animal , Disease Progression , Endothelial Cells/metabolism , Female , Humans , Intercellular Signaling Peptides and Proteins/genetics , Male , Mice , Neoplasm Metastasis/genetics , Nerve Tissue Proteins/genetics , RNA, Double-Stranded , Receptors, Immunologic/genetics , Receptors, Immunologic/metabolism , Signal Transduction , Toll-Like Receptor 3/deficiency , Toll-Like Receptor 3/genetics , Tumor Cells, Cultured , Roundabout ProteinsABSTRACT
Ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) expression correlates with poor prognosis in many cancers, and we previously discovered that ENPP1 is the dominant hydrolase of extracellular cGAMP: a cancer-cell-produced immunotransmitter that activates the anticancer stimulator of interferon genes (STING) pathway. However, ENPP1 has other catalytic activities and the molecular and cellular mechanisms contributing to its tumorigenic effects remain unclear. Here, using single-cell RNA-seq, we show that ENPP1 in both cancer and normal tissues drives primary breast tumor growth and metastasis by dampening extracellular 2'3'-cyclic-GMP-AMP (cGAMP)-STING-mediated antitumoral immunity. ENPP1 loss-of-function in both cancer cells and normal tissues slowed primary tumor growth and abolished metastasis. Selectively abolishing the cGAMP hydrolysis activity of ENPP1 phenocopied ENPP1 knockout in a STING-dependent manner, demonstrating that restoration of paracrine cGAMP-STING signaling is the dominant anti-cancer mechanism of ENPP1 inhibition. Finally, ENPP1 expression in breast tumors deterministically predicated whether patients would remain free of distant metastasis after pembrolizumab (anti-PD-1) treatment followed by surgery. Altogether, ENPP1 blockade represents a strategy to exploit cancer-produced extracellular cGAMP for controlled local activation of STING and is therefore a promising therapeutic approach against breast cancer.
Subject(s)
Breast Neoplasms , Female , Humans , Breast Neoplasms/genetics , Breast Neoplasms/pathology , Immunity, Innate , Membrane Proteins/genetics , Membrane Proteins/metabolism , Phosphoric Diester Hydrolases/genetics , Phosphoric Diester Hydrolases/metabolism , Pyrophosphatases/metabolismABSTRACT
Eukaryotic transfer RNAs can become selectively fragmented upon various stresses, generating tRNA-derived small RNA fragments. Such fragmentation has been reported to impact a small fraction of the tRNA pool and thus presumed to not directly impact translation. We report that oxidative stress can rapidly generate tyrosine-tRNAGUA fragments in human cells-causing significant depletion of the precursor tRNA. Tyrosine-tRNAGUA depletion impaired translation of growth and metabolic genes enriched in cognate tyrosine codons. Depletion of tyrosine tRNAGUA or its translationally regulated targets USP3 and SCD repressed proliferation-revealing a dedicated tRNA-regulated growth-suppressive pathway for oxidative stress response. Tyrosine fragments are generated in a DIS3L2 exoribonuclease-dependent manner and inhibit hnRNPA1-mediated transcript destabilization. Moreover, tyrosine fragmentation is conserved in C. elegans. Thus, tRNA fragmentation can coordinately generate trans-acting small RNAs and functionally deplete a tRNA. Our findings reveal the existence of an underlying adaptive codon-based regulatory response inherent to the genetic code.
Subject(s)
Codon/genetics , Protein Biosynthesis/genetics , RNA, Transfer/genetics , Tyrosine/genetics , Animals , Caenorhabditis elegans/genetics , Cell Line , Cell Proliferation/genetics , HEK293 Cells , Humans , Oxidative Stress/genetics , Ubiquitin-Specific Proteases/geneticsABSTRACT
This corrects the article DOI: 10.1038/nature25465.
ABSTRACT
Using a functional model of breast cancer heterogeneity, we previously showed that clonal sub-populations proficient at generating circulating tumour cells were not all equally capable of forming metastases at secondary sites. A combination of differential expression and focused in vitro and in vivo RNA interference screens revealed candidate drivers of metastasis that discriminated metastatic clones. Among these, asparagine synthetase expression in a patient's primary tumour was most strongly correlated with later metastatic relapse. Here we show that asparagine bioavailability strongly influences metastatic potential. Limiting asparagine by knockdown of asparagine synthetase, treatment with l-asparaginase, or dietary asparagine restriction reduces metastasis without affecting growth of the primary tumour, whereas increased dietary asparagine or enforced asparagine synthetase expression promotes metastatic progression. Altering asparagine availability in vitro strongly influences invasive potential, which is correlated with an effect on proteins that promote the epithelial-to-mesenchymal transition. This provides at least one potential mechanism for how the bioavailability of a single amino acid could regulate metastatic progression.
Subject(s)
Asparagine/metabolism , Breast Neoplasms/metabolism , Breast Neoplasms/pathology , Neoplasm Metastasis/pathology , Animals , Asparaginase/metabolism , Asparaginase/therapeutic use , Asparagine/deficiency , Aspartate-Ammonia Ligase/genetics , Aspartate-Ammonia Ligase/metabolism , Biological Availability , Breast Neoplasms/enzymology , Breast Neoplasms/genetics , Cell Line, Tumor , Disease Models, Animal , Disease Progression , Epithelial-Mesenchymal Transition/genetics , Female , Humans , Lung Neoplasms/enzymology , Lung Neoplasms/metabolism , Lung Neoplasms/pathology , Lung Neoplasms/secondary , Male , Mice , Neoplasm Invasiveness/pathology , Prognosis , Prostatic Neoplasms/enzymology , Prostatic Neoplasms/genetics , Prostatic Neoplasms/metabolism , Prostatic Neoplasms/pathology , RNA Interference , Reproducibility of ResultsABSTRACT
Post-transcriptional deregulation is a defining feature of metastatic cancer. While many microRNAs have been implicated as regulators of metastatic progression, less is known about the roles and mechanisms of RNA-binding proteins in this process. We identified muscleblind-like 1 (MBNL1), a gene implicated in myotonic dystrophy, as a robust suppressor of multiorgan breast cancer metastasis. MBNL1 binds the 3' untranslated regions (UTRs) of DBNL (drebrin-like protein) and TACC1 (transforming acidic coiled-coil containing protein 1)-two genes that we implicate as metastasis suppressors. By enhancing the stability of these genes' transcripts, MBNL1 suppresses cell invasiveness. Consistent with these findings, elevated MBNL1 expression in human breast tumors is associated with reduced metastatic relapse likelihood. Our findings delineate a post-transcriptional network that governs breast cancer metastasis through RNA-binding protein-mediated transcript stabilization.
Subject(s)
Breast Neoplasms/physiopathology , Gene Expression Regulation, Neoplastic , RNA-Binding Proteins/metabolism , Animals , Breast Neoplasms/genetics , Cell Line , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , HEK293 Cells , Humans , Microfilament Proteins/metabolism , Microtubule-Associated Proteins/metabolism , Neoplasm Invasiveness/genetics , Neoplasm Metastasis , Protein Binding , Protein Stability , RNA-Binding Proteins/genetics , Recurrence , Transendothelial and Transepithelial Migration/geneticsABSTRACT
BACKGROUND: Despite advances in early detection and therapies, cancer is still one of the most common causes of death worldwide. Since each tumor is unique, there is a need to implement personalized care and develop robust tools for monitoring treatment response to assess drug efficacy and prevent disease relapse. MAIN BODY: Recent developments in liquid biopsies have enabled real-time noninvasive monitoring of tumor burden through the detection of molecules shed by tumors in the blood. These molecules include circulating tumor nucleic acids (ctNAs), comprising cell-free DNA or RNA molecules passively and/or actively released from tumor cells. Often highlighted for their diagnostic, predictive, and prognostic potential, these biomarkers possess valuable information about tumor characteristics and evolution. While circulating tumor DNA (ctDNA) has been in the spotlight for the last decade, less is known about circulating tumor RNA (ctRNA). There are unanswered questions about why some tumors shed high amounts of ctNAs while others have undetectable levels. Also, there are gaps in our understanding of associations between tumor evolution and ctNA characteristics and shedding kinetics. In this review, we summarize current knowledge about ctNA biology and release mechanisms and put this information into the context of tumor evolution and clinical utility. CONCLUSIONS: A deeper understanding of the biology of ctDNA and ctRNA may inform the use of liquid biopsies in personalized medicine to improve cancer patient outcomes.
Subject(s)
Cell-Free Nucleic Acids , Neoplasms , Neoplastic Cells, Circulating , Humans , Cell-Free Nucleic Acids/genetics , Clinical Relevance , Neoplasms/pathology , Biomarkers, Tumor/genetics , Biology , RNAABSTRACT
Compared to coding sequences, untranslated regions of the transcriptome are not well conserved, and functional annotation of these sequences is challenging. Global relationships between nucleotide composition of 3' UTR sequences and their sequence conservation have been appreciated since mammalian genomes were first sequenced, but the functional relevance of these patterns remain unknown. We systematically measured the effect on gene expression of the sequences of more than 25,000 RNA-binding protein (RBP) binding sites in primary mouse T cells using a massively parallel reporter assay. GC-rich sequences were destabilizing of reporter mRNAs and come from more rapidly evolving regions of the genome. These sequences were more likely to be folded in vivo and contain a number of structural motifs that reduced accumulation of a heterologous reporter protein. Comparison of full-length 3' UTR sequences across vertebrate phylogeny revealed that strictly conserved 3' UTRs were GC-poor and enriched in genes associated with organismal development. In contrast, rapidly evolving 3' UTRs tended to be GC-rich and derived from genes involved in metabolism and immune responses. Cell-essential genes had lower GC content in their 3' UTRs, suggesting a connection between unstructured mRNA noncoding sequences and optimal protein production. By reducing gene expression, GC-rich RBP-occupied sequences act as a rapidly evolving substrate for gene regulatory interactions.
Subject(s)
3' Untranslated Regions , Base Composition , Conserved Sequence , Gene Expression Regulation , Gene Expression , Genes, Reporter , RNA, Messenger/genetics , Animals , Base Sequence , Evolution, Molecular , GC Rich Sequence , Humans , Mice , Nucleic Acid Conformation , RNA Stability , RNA, Messenger/chemistryABSTRACT
Small nuclear RNAs (snRNAs) are core spliceosome components and mediate pre-mRNA splicing. Here we show that snRNAs contain a regulated and reversible nucleotide modification causing them to exist as two different methyl isoforms, m1 and m2, reflecting the methylation state of the adenosine adjacent to the snRNA cap. We find that snRNA biogenesis involves the formation of an initial m1 isoform with a single-methylated adenosine (2'-O-methyladenosine, Am), which is then converted to a dimethylated m2 isoform (N6,2'-O-dimethyladenosine, m6Am). The relative m1 and m2 isoform levels are determined by the RNA demethylase FTO, which selectively demethylates the m2 isoform. We show FTO is inhibited by the oncometabolite D-2-hydroxyglutarate, resulting in increased m2-snRNA levels. Furthermore, cells that exhibit high m2-snRNA levels show altered patterns of alternative splicing. Together, these data reveal that FTO controls a previously unknown central step of snRNA processing involving reversible methylation, and suggest that epitranscriptomic information in snRNA may influence mRNA splicing.
Subject(s)
Adenosine/analogs & derivatives , Alpha-Ketoglutarate-Dependent Dioxygenase FTO/physiology , RNA, Small Nuclear/biosynthesis , Adenosine/biosynthesis , Adenosine/metabolism , Alpha-Ketoglutarate-Dependent Dioxygenase FTO/metabolism , Alternative Splicing , Animals , HEK293 Cells , Humans , Male , Methylation , Mice , Mice, Knockout , RNA Precursors/genetics , RNA Processing, Post-Transcriptional/genetics , RNA, Messenger/biosynthesis , RNA, Messenger/genetics , RNA, Small Nuclear/metabolismABSTRACT
The first step in the biogenesis of microRNAs is the processing of primary microRNAs (pri-miRNAs) by the microprocessor complex, composed of the RNA-binding protein DGCR8 and the type III RNase DROSHA. This initial event requires recognition of the junction between the stem and the flanking single-stranded RNA of the pri-miRNA hairpin by DGCR8 followed by recruitment of DROSHA, which cleaves the RNA duplex to yield the pre-miRNA product. While the mechanisms underlying pri-miRNA processing have been determined, the mechanism by which DGCR8 recognizes and binds pri-miRNAs, as opposed to other secondary structures present in transcripts, is not understood. Here we find in mammalian cells that methyltransferase-like 3 (METTL3) methylates pri-miRNAs, marking them for recognition and processing by DGCR8. Consistent with this, METTL3 depletion reduced the binding of DGCR8 to pri-miRNAs and resulted in the global reduction of mature miRNAs and concomitant accumulation of unprocessed pri-miRNAs. In vitro processing reactions confirmed the sufficiency of the N(6)-methyladenosine (m(6)A) mark in promoting pri-miRNA processing. Finally, gain-of-function experiments revealed that METTL3 is sufficient to enhance miRNA maturation in a global and non-cell-type-specific manner. Our findings reveal that the m(6)A mark acts as a key post-transcriptional modification that promotes the initiation of miRNA biogenesis.
Subject(s)
Adenosine/analogs & derivatives , MicroRNAs/chemistry , MicroRNAs/metabolism , RNA Processing, Post-Transcriptional , Adenosine/metabolism , Base Sequence , Cell Line , Gene Expression Regulation , Humans , Methylation , Methyltransferases/deficiency , Methyltransferases/metabolism , Molecular Sequence Data , Nucleic Acid Conformation , RNA-Binding Proteins/metabolism , Substrate SpecificityABSTRACT
Aberrant regulation of RNA stability has an important role in many disease states. Deregulated post-transcriptional modulation, such as that governed by microRNAs targeting linear sequence elements in messenger RNAs, has been implicated in the progression of many cancer types. A defining feature of RNA is its ability to fold into structures. However, the roles of structural mRNA elements in cancer progression remain unexplored. Here we performed an unbiased search for post-transcriptional modulators of mRNA stability in breast cancer by conducting whole-genome transcript stability measurements in poorly and highly metastatic isogenic human breast cancer lines. Using a computational framework that searches RNA sequence and structure space, we discovered a family of GC-rich structural cis-regulatory RNA elements, termed sRSEs for structural RNA stability elements, which are significantly overrepresented in transcripts displaying reduced stability in highly metastatic cells. By integrating computational and biochemical approaches, we identified TARBP2, a double-stranded RNA-binding protein implicated in microRNA processing, as the trans factor that binds the sRSE family and similar structural elements--collectively termed TARBP2-binding structural elements (TBSEs)--in transcripts. TARBP2 is overexpressed in metastatic cells and metastatic human breast tumours and destabilizes transcripts containing TBSEs. Endogenous TARBP2 promotes metastatic cell invasion and colonization by destabilizing amyloid precursor protein (APP) and ZNF395 transcripts, two genes previously associated with Alzheimer's and Huntington's disease, respectively. We reveal these genes to be novel metastasis suppressor genes in breast cancer. The cleavage product of APP, extracellular amyloid-α peptide, directly suppresses invasion while ZNF395 transcriptionally represses a pro-metastatic gene expression program. The expression levels of TARBP2, APP and ZNF395 in human breast carcinomas support their experimentally uncovered roles in metastasis. Our findings establish a non-canonical and direct role for TARBP2 in mammalian gene expression regulation and reveal that regulated RNA destabilization through protein-mediated binding of mRNA structural elements can govern cancer progression.