Biology subjects

Achour, C.

Publications and source records attributed to Achour, C..

5 recordsLinked to original sources

bioRxiv2026

EOLA1 functions in nucleotide salvage through deacetylating free N4-acetylcytidine

RNA-based medicines rely on modified nucleotides to promote immune evasion and in vivo efficacy. Nucleotides generated from RNA degradation are either exported or recycled through metabolically favorable salvage pathways, though whether modified nucleotides are efficiently recycled remains unclear. N4-acetylcytidine (acC) is a naturally occurring modification in rRNA and tRNA that has shown promise in therapeutic mRNA applications. However, N4-acetylation impairs cytidine deamination, the first step in cytidine salvage. Here, we investigate the endogenous mechanisms that enable acC metabolism. Through sensitive sequence and structural analyses, we identify the uncharacterized human ASCH domain protein EOLA1 as a key acC deacetylase in nucleotide salvage. EOLA1 inactivation leads to free intracellular acC accumulation and increased cytotoxicity upon nucleotide export inhibition. While steady-state acC levels in cellular RNAs remain unchanged, EOLA1-dependent regulation of free acC is evident basally and is exacerbated by exogenous mRNA delivery. Proteomic analyses place EOLA1 in proximity to ribosomal proteins, adjacent to endogenous acC sources. In vitro assays confirm EOLA1 specificity for acC, and structural analysis reveals a narrow nucleotide-binding pocket consistent with mononucleotide selectivity. These findings identify EOLA1 as a bona fide acC eraser and uncover a previously unrecognized pathway for recycling modified nucleotides with relevance to therapeutic RNA design.

molecular biology↗

bioRxiv2025

Peroxiredoxin 1 safeguards the nucleolar genome from oxidative damage

Peroxiredoxin 1 (PRDX1) is a highly conserved, thiol-dependent peroxidase that rapidly scavenges reactive oxygen species to modulate redox signaling. PRDX1-null mice exhibited genomic instability, shortened lifespan, and accelerated tumorigenesis, including development of lymphomas, sarcomas, and carcinomas. Despite extensive characterization of these phenotypes, the molecular mechanism by which PRDX1 loss causes genomic instability remains poorly understood. Here we show that PRDX1 deficiency alters nucleolar morphology, impairs RNA Polymerase I (POL-I)-dependent transcription of pre-ribosomal RNAs and triggers nucleolar genomic instability. This oxidative stress-induced nucleolar dysfunction promotes the stability of secondary DNA structures, such as RNA-DNA hybrids and G-quadruplex DNA, contributing to nucleolar genomic instability. We demonstrate that PRDX1 loss reduces nascent rRNA levels and impairs rRNA processing, further affecting ribosome biogenesis. Mechanistically, we established that PRDX1 loss triggers activation of the nucleolar DNA damage response including activation of DNA repair kinase ATM and the nucleolar factor TCOF1 within the nucleolus, and recruitment of the MRE11-RAD50-NBS1 (MRN) complex subunit NBS1 to ribosomal DNA (rDNA) loci. NBS1 accumulation correlates with the repression of rDNA transcription by POL-I, potentially delaying rRNA synthesis, and safeguarding the nucleolar genome from further oxidative damage. Collectively, these findings uncover a previously unrecognized, but critical role, for PRDX1 in maintaining nucleolar integrity and ribosomal biogenesis through redox-dependent regulation of rDNA transcription and processing machinery.

molecular biology↗

bioRxiv2025

METTL3 regulates exocytosis independently of m6A

RNA modification pathways are often mis-regulated in various cancers, with N6-methyladenosine (m6A) having a pivotal role in cancer progression and metastasis. Methyltransferase-like 3 (METTL3), a core component of the m6A methyltransferase complex, functions not only as an m6A writer but also promotes tumorigenesis through m6A-independent mechanisms. Here, we show that METTL3 is mislocalized to the cytoplasm in breast cancer tumors from patients, contributing to the oncogenic phenotype. Cytoplasmic METTL3 interacts with EXOC7, a key regulator of exocytosis, promoting its stabilization. Additionally, METTL3 regulates m6A-dependent alternative splicing of EXOC7. Silencing METTL3 impairs vesicle trafficking and the breast cancer secretome - effects that do not rely on its enzymatic activity but instead involve METTL3-mediated stabilization of EXOC7 and potentially other exocyst components. Furthermore, METTL3 knockdown impairs invadopodia formation, collagen matrix invasion, and focal adhesion morphology in vitro, while inhibition of METTL3 catalytic activity does not. Our findings uncover non-catalytic roles of METTL3 in regulating exocytosis and the cancer secretome.

molecular biology↗

bioRxiv2022

METTL3 regulates breast cancer-associated alternative splicing switches

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 PHF5A and 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.

cell biology↗

bioRxiv2019

tRNA 2-O-methylation modulates small RNA silencing and life span in Drosophila.

2-O-methylation (Nm) represents one of the most common RNA modifications. Nm affects RNA structure and function with crucial roles in various RNA-mediated processes ranging from RNA silencing, translation, self versus non-self recognition to viral defense mechanisms. Here, we identify two novel Nm methyltransferases (Nm-MTases) in Drosophila melanogaster (CG7009 and CG5220) as functional orthologs of yeast TRM7 and human FTSJ1, respectively. Genetic knockout studies together with MALDI-TOF mass spectrometry and RiboMethSeq mapping revealed that CG7009 is responsible for methylating the wobble position in tRNAPhe, tRNATrp and tRNALeu, while subsequently, CG5220 methylates position C32 in the same tRNAs and targets also additional tRNAs. CG7009 or CG5220 mutant animals were viable and fertile but exhibited various phenotypes such as life span reduction, small RNA pathways dysfunction and increased sensitivity to RNA virus infections. Our results provide the first detailed characterization of two TRM7 family members in Drosophila and uncover a molecular link between enzymes catalysing Nm at specific tRNAs and small RNA-induced gene silencing pathways.

molecular biology↗