Biology subjects

Vang Orom, U. A.

Publications and source records attributed to Vang Orom, U. A..

6 recordsLinked to original sources

bioRxiv2026

Fine-tuning m6A and METTL3 levels have profound impact on cellular proliferation and protein synthesis

The RNA modification m6A is the most abundant internal RNA modification in eukaryotic mRNAs and long non-coding RNAs and has been implicated in diverse and important biological processes. Notably, m6A has been associated with both pro and anti-tumorigenic roles depending on cellular and biological context. In basal-like triple negative breast cancer (TNBC), heterozygous loss of the m6A methyltransferase METTL3 and increased levels of the m6A demethylase FTO are associated with poor prognosis and an increased risk of metastasis. Here, using CRISPR generated METTL3 heterozygous knockout TNBC cell lines (MDA-MB-468) and Nanopore direct RNA sequencing, we characterise transcriptome-wide changes in m6A modification patterns following partial loss of METTL3. We reveal that partial loss of global m6A is associated with preferential changes in the methylation status of transcripts involved in translational control, leading to an increase in translational output and proliferative capacity. In contrast, strong pharmacologic inhibition of METTL3 suppresses translation and proliferation. Our findings highlight how m6A levels differentially regulate gene expression in a dose dependent manner and provides a deeper molecular understanding of the RNA modification m6A and its role in fine-tuning translation and affecting both tumorigenesis and cancer progression.

molecular biology↗

bioRxiv2023

m6A RNA modification of mHtt intron 1 regulates the generation of Htt1a in Huntington's Disease

Huntingtons disease (HD) is a dominantly inherited neurodegenerative disorder caused by an expanded, somatically unstable CAG repeat in the first exon of the huntingtin gene (HTT). In the presence of an expanded CAG repeat, huntingtin mRNA undergoes an aberrant processing that generates HTT1a transcripts with exon 1 and intron 1 sequences, which encodes the aggregation-prone and pathogenic HTTexon 1 protein. The regulatory mechanisms that contribute to the production of HTT1a are not fully understood. In a previous transcriptome-wide m6A landscape study performed in Hdh+/Q111 knock-in mice, we have found that the proximal region of intron 1 to exon1-intron 1 splice site in Htt RNA is highly modified by m6A. Several pieces of evidence have demonstrated that m6A is involved in RNA processing and splicing. Therefore, in this study we set out to explore the impact of m6A RNA modifications in the generation of Htt1a. We show in the striatum of Hdh+/Q111 mice that m6A is enriched in intronic sequences 5 to the cryptic poly (A) sites (IpA1 and IpA2) at 680 and 1145 bp into intron 1 as well as in Htt1a polyadenylated mRNA. We also verified the presence of specific m6A-modified sites near the 5 exon1-intron1 splice donor site. Intronic HTT m6A methylation was recapitulated in human samples showing a significantly increased methylation ratio in HD putamen post-mortem samples and in HD fibroblast cell lines from pre-symptomatic and symptomatic patients. In order to test the hypothesis that the m6A modification is involved in mutant Htt RNA processing, we performed a pharmacological inhibition of METTL3 and a targeted demethylation of Htt intron 1 in HD cells using a dCas13-ALKBH5 system. We found that Htt1a transcript levels in HD cells are regulated by METTL3 and by methylation status in Htt intron 1. Site-specific manipulation with an RNA editing system resulted in decreased expression levels of Htt1a, which was accompanied by a reduction in DNA damage, a major hallmark in HD. Finally, we propose that m6A methylation in intron 1 is likely dependent on the expanded CAG repeats. These findings provide insight into the role of m6A in the generation of the aberrantly spliced mutant Htt transcripts with important implications for therapeutic strategies.

neuroscience↗

bioRxiv2023

N4-acetylcytidine (ac4C) promotes mRNA localization to stress granules

Stress granules are an integral part of the stress response that are formed from non-translating mRNAs aggregated with proteins. While much is known about stress granules, the factors that drive their mRNA localization are incompletely described. Modification of mRNA can alter the properties of the nucleobases and affect processes as translation, splicing and localization of individual transcript. Here, we show that the RNA modification N4-acetylcytidine (ac4C) on mRNA associates with transcripts enriched in stress granules and that stress granule localized transcripts with ac4C are particularly translationally regulated. In addition, we show that ac4C on mRNA can mediate co-localization of the protein NOP58 to stress granules. Our results show that acetylation of mRNA regulates localization of both stress-sensitive transcripts and RNA-binding proteins to stress granules and adds to our understanding of the molecular mechanisms responsible for stress granule formation.

molecular biology↗

bioRxiv2023

Identification and prediction of G-quadruplex RNA-binding proteins with roles in transcription and phase separation

RNA-binding proteins are central for many biological processes and their large-scale identification has demonstrated a broad range of functions. RNA G-quadruplexes are important regulatory elements occurring in both coding and non-coding transcripts, yet our knowledge of their structure-based interactions is limited. Here starting from theoretical prediictions, we show experimentally that a large number of chromatin-binding proteins bind to RNA G-quadruplexes and we classify these based on their RNA G-quadruplex-binding potential. Combining experimental identification of nuclear RNA G-quadruplex-binding proteins with computational analysis, we create a prediction tool that can assign probability score for a protein that it binds RNA G-quadruplexes. We show that predicted G-quadruplex RNA-binding proteins exhibit high degree of protein disorder and hydrophilicity, and suggest involvement in both transcription and phase-separation into membrane-less organelles, particularly the nucleolus. Finally, we present this tool as a web application for estimating RNA G4-binding propensity for proteins of interest at http://service.tartaglialab.com/new_submission/clever_G4_classifier.

molecular biology↗

bioRxiv2021

Nuclear RNA-acetylation can be erased by the deacetylase SIRT7

A large number of RNA modifications are known to affect processing and function of rRNA, tRNA and mRNA 1. The N4-acetylcytidine (ac4C) is the only known RNA acetylation event and is known to occur on rRNA, tRNA and mRNA 2,3. RNA modification by acetylation affects a number of biological processes, including translation and RNA stability 2. For a few RNA methyl modifications, a reversible nature has been demonstrated where specific writer proteins deposit the modification and eraser proteins can remove them by oxidative demethylation 4-6. The functionality of RNA modifications is often mediated by interaction with reader proteins that bind dependent on the presence of specific modifications 1. The NAT10 acetyltransferase has been firmly identified as the main writer of acetylation of cytidine ribonucleotides, but so far neither readers nor erasers of ac4C have been identified 2,3. Here we show, that ac4C is bound by the nucleolar protein NOP58 and deacetylated by SIRT7, for the first time demonstrating reversal by another mechanism than oxidative demethylation. NOP58 and SIRT7 are involved in snoRNA function and pre-ribosomal RNA processing 7-10, and using a NAT10 deficient cell line we can show that the reduction in ac4C levels affects both snoRNA sub-nuclear localization and pre-rRNA processing. SIRT7 can deacetylate RNA in vitro and endogenous levels of ac4C on snoRNA increase in a SIRT7 deficient cell line, supporting its endogenous function as an RNA deacetylase. In summary, we identify the first eraser and reader proteins of the RNA modification ac4C, respectively, and suggest an involvement of RNA acetylation in snoRNA function and pre-rRNA processing.

molecular biology↗

bioRxiv2020

Determination of primary microRNA processing in clinicalsamples by targeted pri-miR-sequencing

MicroRNA expression is important for gene regulation and deregulated microRNA expression is often observed in disease such as cancer. The processing of primary microRNA transcripts is an important regulatory step in microRNA biogenesis. Due to low expression level and association with chromatin primary microRNAs are challenging to study in clinical samples where input material is limited. Here, we present a high-sensitivity targeted method to determine processing efficiency of several hundred primary microRNAs from total RNA using as little as 500 thousand Illumina HiSeq sequencing reads. We validate the method using RNA from HeLa cells and show the applicability to clinical samples by analyzing RNA from normal liver and hepatocellular carcinoma. We identify 24 primary microRNAs with significant changes in processing efficiency from normal liver to hepatocellular carcinoma, among those the highly expressed miRNA-122 and miRNA-21, demonstrating that differential processing of primary microRNAs is occurring and could be involved in disease. With our method presented here we provide means to study pri-miRNA processing in disease from clinical samples.

molecular biology↗