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Coordinated Expression of Retained Introns and Poison Exons in Renal Cell Carcinoma

ABSTRACT: Coordinated intron retention and poison exon inclusion define a subset of kidney tumors by introducing premature stop codons that typically trigger nonsense-mediated decay (NMD). In this study we investigate how mTOR activity modulates these NMD targets, revealing that mTOR inhibition increases the expression of transcripts bearing retained introns and poison exons in certain patient-derived tumors. Our findings show that tumors with low NMD and mTOR activities are more aggressive and have worse outcomes yet display pronounced immune infiltration, highlighting a potential role for these RNA isoforms in shaping tumor progression and immune responses.

ORGANISM(S): Homo sapiens

PROVIDER: GSE289050 | GEO | 2025/05/08

REPOSITORIES: GEO

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Human introns contain conserved tissue-specific cryptic poison exons

Project description:Eukaryotic cells express a large number of transcripts from a single gene due to alternative splicing. Despite hundreds of thousands of splice isoforms being annotated in databases, it has been reported that the current exon catalogs remain incomplete. At the same time, introns of human protein-coding genes contain a large number of evolutionarily conserved elements with unknown function. Here, we explore the possibility that some of them represent cryptic exons that are expressed in rare conditions. We identified a group of cryptic exons that are similar to the annotated exons in terms of evolutionary conservation and RNA-seq read coverage in the GTEx dataset. Most of them were poison, i.e. generated an NMD isoform upon inclusion, and many showed signs of tissue-specific and cancer-specific expression and regulation. We performed RNA-seq in A549 cell line treated with cycloheximide to inactivate NMD, and confirmed using qPCR that seven of eight exons tested are, indeed, expressed. This study shows that introns of human protein-coding genes contain cryptic poison exons, which reside in conserved intronic regions and remain not fully annotated due to insufficient representation in RNA-seq libraries.

2024-11-20 | GSE270310 | GEO

Coordinated Expression of Retained Introns and Poison Exons in Renal Cell Carcinoma

Project description:Coordinated Expression of Retained Introns and Poison Exons in Renal Cell Carcinoma

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Human introns contain conserved tissue-specific cryptic poison exons

Project description:Human introns contain conserved tissue-specific cryptic poison exons

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Human introns contain conserved tissue-specific cryptic poison exons.

Project description:Eukaryotic cells express a large number of transcripts from a single gene due to alternative splicing. Despite hundreds of thousands of splice isoforms being annotated in databases, it has been reported that the current exon catalogs remain incomplete. At the same time, introns of human protein-coding (PC) genes contain a large number of evolutionarily conserved elements with unknown function. Here, we explore the possibility that some of them represent cryptic exons that are expressed in rare conditions. We identified a group of cryptic exons that are similar to the annotated exons in terms of evolutionary conservation and RNA-seq read coverage in the Genotype-Tissue Expression dataset. Most of them were poison, i.e. generated an nonsense-mediated decay (NMD) isoform upon inclusion, and many showed signs of tissue-specific and cancer-specific expression and regulation. We performed RNA-seq in A549 cell line treated with cycloheximide to inactivate NMD and confirmed using quantitative polymerase chain reaction that seven of eight exons tested are, indeed, expressed. This study shows that introns of human PC genes contain cryptic poison exons, which reside in conserved intronic regions and remain not fully annotated due to insufficient representation in RNA-seq libraries.

| S-EPMC11632617 | biostudies-literature

Nonsense-mediated decay of alternative precursor mRNA splicing variants is a major determinant of the eukaryotic steady state transcriptome

Project description:Nonsense-mediated mRNA decay (NMD) is a eukaryotic surveillance pathway that recognizes aberrant transcripts arising from mutations and transcriptional mistakes. Moreover, differential transcript processing such as alternative precursor mRNA splicing (AS) can generate NMD substrates, however, the extent of coupled AS and NMD remained unclear. To investigate NMD targeting of AS variants, we performed transcriptome-wide splicing studies using Arabidopsis thaliana single and double mutants in the NMD factor homologues UPF1 and UPF3, as well as samples treated with the translation inhibitor cycloheximide (CHX). Our analyses revealed that at least 17.5% of all multi-exon, protein-coding genes produce splicing variants of all major types that are targeted by NMD, with a significant fraction originating from the splicing of cryptic introns. Furthermore, accumulation of many intron-retained mRNAs in the mutants, but not in response to CHX suggests the action of distinct routes of NMD with variable impact of translation. Importantly, 92.3% of the NMD-responsive mRNAs exhibit classical NMD-eliciting features, supporting their authenticity as direct targets. NMD-dependent AS variants are linked to diverse biological functions, including the poison exon-mediated regulation of signaling and posttranslational protein modification components. In addition to mRNAs, numerous non-coding RNAs as well as newly identified transcripts derived from intergenic regions were shown to be NMD responsive. In summary, our comprehensive analysis of AS-coupled NMD provides strong evidence for a major function of this pathway in shaping the transcriptome, having fundamental implications in gene regulation and quality control of transcript processing steps in higher eukaryotes. Comparison of gene expression and alternative splicing patterns in control and nonsense-mediated decay (NMD)-impaired Arabidopsis seedlings

2013-10-01 | E-GEOD-41432 | biostudies-arrayexpress

Alkaloids modify the poison frog proteome

Project description:Poison frogs sequester chemical defenses from their diet of leaf litter arthropods for defense against predation. Little is known about the physiological adaptations that confer this unusual bioaccumulation ability. We conducted an alkaloid-feeding experiment with the Diablito poison frog (Oophaga sylvatica) to determine how quickly alkaloids are accumulated and how toxins modify frog physiology using quantitative proteomics. Diablito frogs rapidly accumulated the alkaloid decahydroquinoline within four days, and dietary alkaloid exposure modified protein abundance in the intestines, liver, and skin. Many proteins that increased in abundance with toxin accumulation are plasma glycoproteins, including the complement system and the toxin-binding protein saxiphilin. Other protein classes that change in abundance with toxin accumulation are membrane proteins involved in small molecule transport and metabolism. Overall, this work shows poison frogs can rapidly accumulate alkaloids, which alter carrier protein abundance, initiate an immune response, and alter small molecule transport and metabolism dynamics across tissues

2021-01-25 | PXD021216 | Pride

An essential role for the ultra-conserved poison exon of Tra2b in fertility in mice (RNA-seq)

Project description:Alternative splicing-induced inclusion of poison exons containing in-frame stop codons is a mechanism that can be used to attenuate gene expression. Poison exon have been implicated in cancer, but how they operate within the context of normal development and physiology is poorly understood. Several splicing regulator genes, including Tra2b, contain ultra-conserved poison exons that function within regulatory loops to fine-tune their activity. To investigate the physiological role of poison exons in vivo, we created mice lacking either Tra2b or its poison exon, specifically during spermatogenesis to reveal both are essential for male fertility. The mouse Tra2b gene is essential for mitotic proliferation of germ cells, whereas, in contrast, the Tra2b poison exon is critically required during meiosis and not needed by mitotically proliferating cell populations within the germline. Poison exon deletion causes infertility, with a block in male meiotic prophase where Tra2β protein expression levels normally increase. Deletion of the Tra2b poison exon changes expression patterns of genes important for meiosis and splicing patterns of Tra2β target exons, suggesting Tra2b poison exon splicing prevents meiotic cells accumulating toxic levels of Tra2b expression. Our data provide a new physiological explanation for Tra2b poison exon ultra-conservation and indicate the importance of evaluating poison exon function within a physiological context.

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An essential role for the ultra-conserved poison exon of Tra2b in fertility in mice (iCLIP-seq)

2024-12-19 | GSE235083 | GEO

Conserved intronic secondary structures with concealed branch sites regulate alternative splicing of poison exons

Project description:Alternative splicing (AS) generates large amounts of RNA isoforms and dramatically increases the complexities of transcriptomes and proteomes. However, it remains unclear how RNA structures contribute to AS regulation. Here, we systematically search transcriptomes for secondary structures with concealed branch-sites (BSs) in the alternatively spliced introns and predict thousands from six organisms, of which many are evolutionarily conserved. Intriguingly, a highly conserved stem-loop structure with concealed BSs is found in animal SF3B3 genes and colocalizes with a downstream poison exon (PE). Destabilization of this structure allows increased usage of the branch sites and results in enhanced PE inclusion in both human and Drosophila cells, leading to decreased expression of SF3B3. Through an RNAi screen of 28 RNA-binding proteins, we find that this stem-loop structure is sensitive to U2 and U2-associated proteins. Furthermore, we find that SF3B3 also facilitates DNA repair and protects genome stability by enhancing interaction between ERCC6/CSB and arrested RNA polymerase II. Importantly, both Drosophila and human cells with the secondary structure mutated by genome editing exhibit altered DNA repair in vivo. This study provides a novel and common mechanism for AS regulation of PEs and reveals a physiological function of SF3B3 in DNA repair.

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