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| 2. |
- Achour, Cyrinne, 1991-
(author)
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Canonical and non-canonical functions of METTL3 in breast cancer
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Gene expression is spatially and temporally regulated at multiple levels. N6-methyladenosine (m6A) is the most prevalent internal modification in messenger RNA (mRNA) and long noncoding RNA (lncRNAs). m6A plays important roles in multiple cellular processes including stem cell pluripotency, adipogenesis, spermatogenesis, neurogenesis, circadian rhythm and development by modulating RNA splicing, export, stability, degradation and translation. Although aberrant m6A methylation has been reported in various types of cancer, the underlying molecular functions of METTL3, the solely catalytic subunit of the m6A-methylase complex, has yet to be defined.m6A has been recently identified in nascent pre-mRNA, and more specifically intronic m6A has been linked to exon skipping events. The occurrence of impaired alternative splicing (AS) is frequently found during the development of cancer. We performed transcriptome wide analysis in breast cancer cell lines and explored AS events. Our results define an AS signature for breast tumorigenesis. We found that METTL3 modulates AS directly through m6A deposition at the intron-exon junctions or indirectly by the m6A deposition in transcripts encoding for splicing factors and transcription factors. In particular, we show that MYC mRNA harbours the m6A mark, suggesting that METTL3 regulates AS indirectly via the regulation of MYC expression. Indeed, the targets of MYC overlapped with METTL3-associated AS events. Importantly, five of the AS events identified and validated in vitro, are linked to a worse prognosis in breast cancer patients. Additionally, we show that METTL3 enhances the breast cancer phenotype through a dual mechanism depending on its sub-cellular localization. We find that the canonical nuclear function of METTL3 decorates transcripts that are involved in cell proliferation and migration. We observe that METTL3 is highly expressed in the cytoplasmic compartment of breast cancer cells from patients. Remarkably, we uncover that the cytoplasmic METTL3 interacts with subunits of the exocyst, whose subunit EXOC7 has been linked to cell adhesion, migration and invasion. Notably, we show that breast cancer cell lines depleted of METTL3 display less gelatinase activity and invadopodia formation, supporting the role of METTL3 in cell invasion via exocytosis.m6A is a reversible modification, which can be demethylated by the erasers FTO and ALKBH5. Depletion of FTO has been shown to increase the level of m6A in mRNA, however recent studies have reported that FTO could demethylate N6,2´-O-dimethyladenosine (m6Am), adjacent to the 7-methylguanosine cap on mRNA. In the cellular model of colorectal cancer CRC1, depletion of FTO leads to a cancer stem cell phenotype and confers chemotherapy resistance. By performing m6A-RNA immunoprecipitation followed by sequencing (MeRIP), we show that knockdown of FTO in CRC1 cells does not affect the global level of m6A in mRNA but of m6Am level.
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| 3. |
- Achour, Cyrinne, et al.
(author)
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Long non-coding RNA and Polycomb : an intricate partnership in cancer biology
- 2018
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In: Frontiers in Bioscience. - : IMR Press. - 1093-9946 .- 1093-4715. ; 23, s. 2106-2132
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Journal article (peer-reviewed)abstract
- High-throughput analyses have revealed that the vast majority of the transcriptome does not code for proteins. These non-translated transcripts, when larger than 200 nucleotides, are termed long non-coding RNAs (lncRNAs), and play fundamental roles in diverse cellular processes. LncRNAs are subject to dynamic chemical modification, adding another layer of complexity to our understanding of the potential roles that lncRNAs play in health and disease. Many lncRNAs regulate transcriptional programs by influencing the epigenetic state through direct interactions with chromatin-modifying proteins. Among these proteins, Polycomb repressive complexes 1 and 2 (PRC1 and PRC2) have been shown to be recruited by lncRNAs to silence target genes. Aberrant expression, deficiency or mutation of both lncRNA and Polycomb have been associated with numerous human diseases, including cancer. In this review, we have highlighted recent findings regarding the concerted mechanism of action of Polycomb group proteins (PcG), acting together with some classically defined lncRNAs including X-inactive specific transcript (XIST), antisense non-coding RNA in the INK4 locus (ANRIL), metastasis associated lung adenocarcinoma transcript 1 (MALAT1), and HOX transcript antisense RNA (HOTAIR).
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| 4. |
- Achour, Cyrinne, et al.
(author)
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Long Noncoding RNAs as Players in Breast Tumorigenesis
- 2020
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In: The chemical biology of long noncoding RNAs. - Cham : Springer. - 9783030447427 - 9783030447458 - 9783030447434 ; , s. 385-403
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Book chapter (peer-reviewed)abstract
- Comprehensive analysis of the mammalian genome uncovered the discovery of pervasive transcription of large RNA transcripts that do not code for proteins, namely, long noncoding RNAs (lncRNAs). LncRNAs play important roles in the regulation of gene expression from integration of chromatin remodeling complexes to transcriptional and posttranscriptional regulation of protein-coding genes. Application of next-generation sequencing technologies to cancer transcriptomes has revealed that aberrant expression of lncRNAs is associated with tumor progression and metastasis. Although thousands of lncRNAs have been shown to be dysregulated in different cancer types, just few of them have been fully characterized. In this book chapter, we aim to highlight recent findings of the mechanistic function of lncRNAs in breast cancer and summarize key examples of lncRNAs that are misregulated during breast tumorigenesis. We have categorized breast cancer–associated lncRNA according to their contribution to tumor suppression or tumor progression based on recent studies. Because some of them are expressed in a specific molecular breast cancer subtype, we have outlined lncRNAs that can potentially serve as diagnostic and prognostic markers, in which expression is linked to chemotherapy resistance. Finally, we have discussed current limitations and perspectives on potential lncRNA targets for use in therapies against breast cancer.
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| 5. |
- Achour, Cyrinne, et al.
(author)
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METTL3 regulates breast cancer-associated alternative splicing switches
- 2023
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In: Oncogene. - : Nature Publishing Group. - 0950-9232 .- 1476-5594. ; 42, s. 911-925
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Journal article (peer-reviewed)abstract
- Alternative splicing (AS) enables differential inclusion of exons from a given transcript, thereby contributing to the transcriptome and proteome diversity. Aberrant AS patterns play major roles in the development of different pathologies, including breast cancer. N6-methyladenosine (m6A), the most abundant internal modification of eukaryotic mRNA, influences tumor progression and metastasis of breast cancer, and it has been recently linked to AS regulation. Here, we identify a specific AS signature associated with breast tumorigenesis in vitro. We characterize for the first time the role of METTL3 in modulating breast cancer-associated AS programs, expanding the role of the m6A-methyltransferase in tumorigenesis. Specifically, we find that both m6A deposition in splice site boundaries and in splicing and transcription factor transcripts, such as MYC, direct AS switches of specific breast cancer-associated transcripts. Finally, we show that five of the AS events validated in vitro are associated with a poor overall survival rate for patients with breast cancer, suggesting the use of these AS events as a novel potential prognostic biomarker.
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| 7. |
- Aguilo, Francesca, et al.
(author)
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Coordination of m(6)A mRNA Methylation and Gene Transcription by ZFP217 Regulates Pluripotency and Reprogramming.
- 2015
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In: Cell Stem Cell. - : Elsevier BV. - 1934-5909 .- 1875-9777. ; 17:6, s. 689-704
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Journal article (peer-reviewed)abstract
- Epigenetic and epitranscriptomic networks have important functions in maintaining the pluripotency of embryonic stem cells (ESCs) and somatic cell reprogramming. However, the mechanisms integrating the actions of these distinct networks are only partially understood. Here we show that the chromatin-associated zinc finger protein 217 (ZFP217) coordinates epigenetic and epitranscriptomic regulation. ZFP217 interacts with several epigenetic regulators, activates the transcription of key pluripotency genes, and modulates N6-methyladenosine (m(6)A) deposition on their transcripts by sequestering the enzyme m(6)A methyltransferase-like 3 (METTL3). Consistently, Zfp217 depletion compromises ESC self-renewal and somatic cell reprogramming, globally increases m(6)A RNA levels, and enhances m(6)A modification of the Nanog, Sox2, Klf4, and c-Myc mRNAs, promoting their degradation. ZFP217 binds its own target gene mRNAs, which are also METTL3 associated, and is enriched at promoters of m(6)A-modified transcripts. Collectively, these findings shed light on how a transcription factor can tightly couple gene transcription to m(6)A RNA modification to ensure ESC identity.
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| 8. |
- Aguilo, Francesca, et al.
(author)
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Deposition of 5-Methylcytosine on Enhancer RNAs Enables the Coactivator Function of PGC-1α
- 2016
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In: Cell Reports. - : Elsevier BV. - 2211-1247. ; 14:3, s. 479-492
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Journal article (peer-reviewed)abstract
- The Peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α) is a transcriptional co-activator that plays a central role in adapted metabolic responses. PGC-1α is dynamically methylated and unmethylated at the residue K779 by the methyltransferase SET7/9 and the Lysine Specific Demethylase 1A (LSD1), respectively. Interactions of methylated PGC-1α[K779me] with the Spt-Ada-Gcn5-acetyltransferase (SAGA) complex, the Mediator members MED1 and MED17, and the NOP2/Sun RNA methytransferase 7 (NSUN7) reinforce transcription, and are concomitant with the m(5)C mark on enhancer RNAs (eRNAs). Consistently, loss of Set7/9 and NSun7 in liver cell model systems resulted in depletion of the PGC-1α target genes Pfkl, Sirt5, Idh3b, and Hmox2, which was accompanied by a decrease in the eRNAs levels associated with these loci. Enrichment of m(5)C within eRNA species coincides with metabolic stress of fasting in vivo. Collectively, these findings illustrate the complex epigenetic circuitry imposed by PGC-1α at the eRNA level to fine-tune energy metabolism.
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| 9. |
- Aguilo, Francesca, et al.
(author)
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Long Non-coding RNA ANRIL and Polycomb in Human Cancers and Cardiovascular Disease
- 2016
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In: Long non-coding RNAs in human disease. - Cham : Springer. - 9783319239064 - 9783319239071 ; , s. 29-39
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Book chapter (peer-reviewed)abstract
- The long non-coding RNA CDKN2B-AS1, commonly referred to as the Antisense Non-coding RNA in the INK4 Locus (ANRIL), is a 3.8-kb-long RNA transcribed from the short arm of human chromosome 9 on p21.3 that overlaps a critical region encompassing three major tumor suppressor loci juxtaposed to the INK4b-ARF-INK4a gene cluster and the methyl-thioadenosine phosphorylase (MTAP) gene. Genome-wide association studies have identified this region with a remarkable and growing number of disease-associated DNA alterations and single nucleotide polymorphisms, which corresponds to increased susceptibility to human disease. Recent attention has been devoted on whether these alterations in the ANRIL sequence affect its expression levels and/or its splicing transcript variation, and in consequence, global cellular homeostasis. Moreover, recent evidence postulates that ANRIL not only can regulate their immediate genomic neighbors in cis, but also has the capacity to regulate additional loci in trans. This action would further increase the complexity for mechanisms imposed through ANRIL and furthering the scope of this lncRNA in disease pathogenesis. In this chapter, we summarize the most recent findings on the investigation of ANRIL and provide a perspective on the biological and clinical significance of ANRIL as a putative biomarker, specifically, its potential role in directing cellular fates leading to cancer and cardiovascular disease.
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| 10. |
- Aguilo, Francesca, et al.
(author)
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Long noncoding RNA, polycomb, and the ghosts haunting INK4b-ARF-INK4a expression.
- 2011
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In: Cancer Research. - 0008-5472 .- 1538-7445. ; 71:16
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Journal article (peer-reviewed)abstract
- Polycomb group proteins (PcG) function as transcriptional repressors of gene expression. The important role of PcG in mediating repression of the INK4b-ARF-INK4a locus, by directly binding to the long noncoding RNA (lncRNA) transcript antisense noncoding RNA in the INK4 locus (ANRIL), was recently shown. INK4b-ARF-INK4a encodes 3 tumor-suppressor proteins, p15(INK4b), p14(ARF), and p16(INK4a), and its transcription is a key requirement for replicative or oncogene-induced senescence and constitutes an important barrier for tumor growth. ANRIL gene is transcribed in the antisense orientation of the INK4b-ARF-INK4a gene cluster, and different single-nucleotide polymorphisms are associated with increased susceptibility to several diseases. Although lncRNA-mediated regulation of INK4b-ARF-INK4a gene is not restricted to ANRIL, both polycomb repressive complex-1 (PRC1) and -2 (PRC2) interact with ANRIL to form heterochromatin surrounding the INK4b-ARF-INK4a locus, leading to its repression. This mechanism would provide an increased advantage for bypassing senescence, sustaining the requirements for the proliferation of stem and/or progenitor cell populations or inappropriately leading to oncogenesis through the aberrant saturation of the INK4b-ARF-INK4a locus by PcG complexes. In this review, we summarize recent findings on the underlying epigenetic mechanisms that link PcG function with ANRIL, which impose gene silencing to control cellular homeostasis as well as cancer development.
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