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FTO-mediated cytoplasmic m6Am demethylation adjusts stem-like properties in colorectal cancer cell
IGF, Univ. Montpellier, CNRS, INSERM, Montpellier, France.
LIRMM, Univ. Montpellier, CNRS, Montpellier, France.
IGF, Univ. Montpellier, CNRS, INSERM, Montpellier, France; Stellate Therapeutics, Paris, France.
IGF, Univ. Montpellier, CNRS, INSERM, Montpellier, France.
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2021 (English)In: Nature Communications, E-ISSN 2041-1723, Vol. 12, no 1, article id 1716Article in journal (Refereed) Published
Abstract [en]

Cancer stem cells (CSCs) are a small but critical cell population for cancer biology since they display inherent resistance to standard therapies and give rise to metastases. Despite accruing evidence establishing a link between deregulation of epitranscriptome-related players and tumorigenic process, the role of messenger RNA (mRNA) modifications in the regulation of CSC properties remains poorly understood. Here, we show that the cytoplasmic pool of fat mass and obesity-associated protein (FTO) impedes CSC abilities in colorectal cancer through its N6,2’-O-dimethyladenosine (m6Am) demethylase activity. While m6Am is strategically located next to the m7G-mRNA cap, its biological function is not well understood and has not been addressed in cancer. Low FTO expression in patient-derived cell lines elevates m6Am level in mRNA which results in enhanced in vivo tumorigenicity and chemoresistance. Inhibition of the nuclear m6Am methyltransferase, PCIF1/CAPAM, fully reverses this phenotype, stressing the role of m6Am modification in stem-like properties acquisition. FTO-mediated regulation of m6Am marking constitutes a reversible pathway controlling CSC abilities. Altogether, our findings bring to light the first biological function of the m6Am modification and its potential adverse consequences for colorectal cancer management.

Place, publisher, year, edition, pages
Nature Publishing Group, 2021. Vol. 12, no 1, article id 1716
National Category
Cell and Molecular Biology
Identifiers
URN: urn:nbn:se:umu:diva-181801DOI: 10.1038/s41467-021-21758-4ISI: 000631927600001Scopus ID: 2-s2.0-85102687058OAI: oai:DiVA.org:umu-181801DiVA, id: diva2:1540927
Available from: 2021-03-30 Created: 2021-03-30 Last updated: 2023-09-05Bibliographically approved
In thesis
1. Canonical and non-canonical functions of METTL3 in breast cancer
Open this publication in new window or tab >>Canonical and non-canonical functions of METTL3 in breast cancer
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Kanoniska och icke-kanoniska funktioner av METTL3 vid bröstcancer
Abstract [en]

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.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2022. p. 83
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 2235
Keywords
RNA modification, METTL3, m6A, alternative splicing, exocyst, breast cancer
National Category
Biochemistry and Molecular Biology Cell Biology
Identifiers
urn:nbn:se:umu:diva-201050 (URN)978-91-7855-908-4 (ISBN)978-91-7855-909-1 (ISBN)
Public defence
2022-12-13, Major Groove, Department of molecular biology, University hospital area, building 6L, Umeå, 09:00 (English)
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Serieuppgift saknas i publikationen.

Available from: 2022-11-22 Created: 2022-11-16 Last updated: 2023-12-11Bibliographically approved

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Achour, CyrinneAguilo, Francesca

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