NAR Cancer

Ovarian cancer is the most lethal gynecological malignancy, largely because of late diagnosis and marked genomic instability, with high-grade serous ovarian cancer (HGSOC) representing its most common and aggressive subtype. Amplification of chromosome 8q24.3 is a recurrent event in HGSOC, yet the regulation and clinical relevance of the non-coding RNA output from this locus remain poorly defined. Here, we performed an integrative analysis of 8q24.3-encoded miRNAs in ovarian cancer using copy-number, transcriptomic, isoform-resolved, and clinical data from TCGA and NCBI datasets. We identified pronounced heterogeneity in miRNA abundance and strand usage across this locus. Copy-number gain broadly associated with increased miRNA expression, although this effect was not uniform across all candidates. Intronic miRNAs showed variable coupling with their host genes, indicating that mature miRNA output is shaped by both genomic dosage and post-transcriptional regulation. Isoform-level analysis revealed marked strand asymmetry and regulatory complexity, but did not strengthen copy-number or histotype associations compared with total miRNA measurements. Clinically, higher expression of miR-937, miR-4664, and miR-6849 was associated with improved overall survival in HGSOC. Functional enrichment of validated targets highlighted pathways related to cellular stress responses, senescence, p53 signaling, endocytosis, and metabolic adaptation. Together, these findings define 8q24.3 as a heterogeneous non-coding regulatory hub in ovarian cancer and provide a basis for future mechanistic and biomarker studies.

Long noncoding RNAs (lncRNAs) are important regulators of gene expression and are frequently dysregulated in cancer. The mitotically associated lncRNA MANCR is highly expressed in aggressive cancers and contributes to genomic instability in triple-negative breast cancer (TNBC), but the molecular mechanisms underlying its activity remain poorly defined. Here we integrate computational and experimental approaches to examine the structure and regulatory interactions of MANCR isoforms. Analysis of transcriptomic datasets revealed tumor-type-specific expression patterns for seven MANCR isoforms in breast cancer cell lines. Computational prediction of RNA secondary structures identified conserved structural features across isoforms, suggesting potential functional specialization. We identify p53 as a MANCR-interacting protein through computational docking and RNA immunoprecipitation sequencing (RIP-seq) and demonstrate that MANCR depletion reduces p53-dependent transcriptional activity. Chromatin isolation by RNA purification sequencing (ChIRP-seq) revealed 1, 250 genomic regions associated with MANCR, including enrichment of p53 consensus motifs and GC-rich sequence elements. Motif analysis further identified candidate sequence features associated with MANCR-occupied chromatin regions. Computational prediction of RNA-miRNA interactions identified multiple potential miRNA binding sites across MANCR isoforms, including miR-6756-5p, which targets the androgen receptor (AR). Consistent with this prediction, AR expression decreased following MANCR knockdown in TNBC cells. Together, these results suggest that MANCR isoforms may contribute to transcriptional regulation in TNBC through interactions with chromatin, p53 signaling pathways, and potential miRNA regulatory networks. One Sentence SummaryMitotically-associated lncRNA (MANCR) is prevalent in aggressive cancers interacting with DNA, P53, and miRNAs, to mediate multiple levels of epigenetic transcriptional control in triple negative breast cancer.

BackgroundTumors exhibit substantial cellular and molecular diversity driven by genetic and epigenetic mechanisms. Large-scale profiling efforts have established aberrant DNA methylation as a universal hallmark of cancer. Beyond changes in mean methylation levels, tumor tissues exhibit elevated DNA methylation variability at specific genomic regions within and across tumors. This constitutes a fundamental dimension of cancer epigenomes, reflecting disrupted maintenance of epigenomic states and stochastic drift, which may enable adaptation to the microenvironment, phenotypic plasticity, invasion, disease progression, and treatment resistance. However, the genome-wide organization and functional consequences of DNA methylation variability across cancer types remain incompletely understood. MethodsWe analyzed paired tumor-normal DNA methylation profiles across 16 cancer types to systematically quantify DNA methylation variability. Pan-cancer DNA methylation variability was consistently observed using complementary statistical approaches and multiple modes of data representation. We identified cancer-specific and pan-cancer differentially variable regions and evaluated their associations with genomic features, transcriptional and chromatin regulators, and biological processes. Variability was quantified using three measures per sample: the proportion of intermediately methylated sites (PIM), genome-wide Shannon entropy, and a DNA methylation-based stemness index. Associations with genomic instability, tumor biological features, and clinical outcomes were subsequently assessed. ResultsTumor samples consistently exhibited higher DNA methylation variability than matched normal tissues, reflected by increased dispersion and wider interquartile ranges. Pan-cancer variably methylated regions were depleted in promoters and enriched in open sea regions, in heterochromatic H3K27me3-decorated PRC2-repressed domains, and at enhancers. They preferentially contained motifs for transcription factors involved in developmental regulation. Elevated DNA methylation variability, captured by higher PIM, entropy, and stemness scores, was associated with increased genomic instability manifested by higher aneuploidy, increased DNA break points, a greater fraction of the genome altered, and increased tumor mutational burden, as well as with aggressive tumor features such as lymph node involvement, post-therapy neoplasm events, and elevated hypoxia scores. Importantly, tumors with high DNA methylation variability exhibited significantly worse overall, progression-free, and disease-free survival. ConclusionsDNA methylation variability is a pervasive and clinically relevant feature of tumor epigenomes, reflecting epigenetic and genetic instability, expanded regulatory plasticity, and tumor aggressiveness.

Anti-hormonal therapies such as selective estrogen receptor modulators like tamoxifen or aromatase inhibitors like letrozole represent a cornerstone for breast cancer prevention and therapy of estrogen receptor-positive breast cancer. Therapeutic monitoring can include blood tests and imaging; however, genetically-based approaches are not yet in practice. Ideally, a test would be able to detect a positive molecular response across different estrogen pathway-suppressive approaches. Circular RNAs are a species of non-coding RNAs detectable in plasma that have been proposed as non-invasive therapeutic biomarkers. To determine whether a set of specific circular RNAs is altered across estrogen-suppressive pathway approaches, we analyzed mammary gland-specific total RNA sequencing data from two individual genetically engineered mouse models (GEMMs) of estrogen pathway-induced breast cancer, with or without exposure to tamoxifen or letrozole. The nf-core/circrna pipeline was used to identify circRNAs that were differentially expressed in response to either tamoxifen or letrozole. We then screened for circRNAs that were differentially regulated by both anti-hormonals. Four up-regulated and 31 down-regulated circRNAs with host genes known to be expressed in human breast epithelial cells were identified as showing reproducible differential regulation in response to anti-hormonal treatment.

Network biology traditionally identifies gene correlations that reflect biological pathways. While LIONESS enables individualized gene networks, the influence of replication timing on these correlations remains unexplored. Replication timing reflects the temporal order of DNA synthesis and is tightly linked to chromatin state, methylation, and transcriptional stability, all of which affect tumor behavior. Integrating replication-timing proxies derived from methylation data therefore offers a bridge between epigenetic state and functional gene coordination, while morphology provides an additional route for inferring gene expression. This is the first study to integrate replication-timing proxies and morphological embeddings into individualized LIONESS gene networks. The aim is to determine how replication timing and morphology derived from bulk methylation and image embeddings influence gene coexpression in pancreatic cancer. Patient-specific networks were generated for basal and classical pancreatic ductal adenocarcinoma subtypes using TCGA data. Results show an 80% AUC for RNA-replication-timing-based subtype prediction modules and a 75% AUC for morphology-based networks. Incorporating replication timing and morphology increased network robustness while maintaining classification performance. Notably, the 80% AUC was achieved using only 17 of the 50 Moffitt genes, with 16 overlapping the PURIST gene set, indicating that replication timing captures clinically relevant regulatory structure. These findings suggest that replication-timing proxies can act as epigenetic indicators of mechanistic gene coordination and may help identify patients with distinct replication stress or chromatin accessibility profiles relevant to therapeutic response.

ObjectiveRNA adenosine-to-inosine (A-to-I) editing, catalyzed by adenosine deaminases acting on RNA (ADARs), is a pervasive post-transcriptional mechanism that expands transcriptomic and proteomic diversity. However, the global landscape of RNA A-to-I editing, as well as its functional and clinical significance in esophageal squamous cell carcinoma (ESCC), remains largely unexplored. This study aimed to systematically characterize the RNA editome of ESCC and elucidate its biological and clinical significance. MethodsWhole-transcriptome sequencing was performed on 121 primary ESCC tumors, with or without lymph node metastasis, together with matched normal tissues, to construct a high-resolution RNA editome. ADAR1-regulated RNA editing events were identified, and their functional consequences were investigated using integrated transcriptomic, phosphoproteomic, and RNA immunoprecipitation sequencing (RIP-seq) analyses. Associations between CDK13 editing, cGAS-STING-interferon-stimulated gene (ISG) signaling, and patient survival were further evaluated. ResultsA total of 222,020 high-confidence RNA editing sites were identified, of which approximately 98% were A-to-I events, including 124,486 ESCC-specific edits predominantly enriched in introns, 3' untranslated regions, and non-coding RNAs, highlighting a pervasive post-transcriptional regulatory layer. RNA A-to-I editing was extensively remodeled and globally up-regulated in non-metastatic ESCC, whereas only minimal changes were observed during lymph node metastasis, indicating that RNA editing alterations predominantly occur during early tumorigenesis. CDK13 emerged as a recurrent ADAR1 target, with RNA editing inversely correlated with CDK13 expression. ADAR1-mediated CDK13 editing established a positive feedback loop associated with enhanced interferon-stimulated gene (ISG) signaling and poorer survival in non-metastatic ESCC. Mechanistically, partial attenuation of CDK13 induced chronic, tumor cell-intrinsic activation of the cGAS-STING-ISG pathway. Integrated multi-omics analyses further revealed that CDK13 regulates phosphorylation networks governing cytoskeleton organization, intracellular trafficking, RNA homeostasis, and immune signaling. ConclusionRNA A-to-I editing represents a dynamic regulatory mechanism driving early ESCC progression and remodeling tumor cell-intrinsic immune signaling. ADAR1-mediated editing of CDK13 provides a mechanistic link between RNA editing and cGAS-STING-ISG pathway activation, revealing potential therapeutic vulnerabilities and supporting its utility as an early prognostic biomarker in ESCC.

Y-box binding protein 1 (YB-1; YBX1) is a multifunctional DNA- and RNA-binding protein involved in cell cycle regulation, DNA repair, stress adaptation, and therapy resistance. Elevated YBX1 mRNA expression is associated with aggressive disease across multiple cancers, yet its pan-cancer genomic and clinical correlates remain unclear. Here, we performed a comprehensive pan-cancer analysis across 53 datasets spanning 33 tumour types, integrating RNA expression, somatic mutations, copy number, hypoxia, and clinical outcomes. YBX1 was rarely mutated or amplified, indicating that oncogenic relevance is primarily driven by its expression. Tumours with high YBX1 mRNA exhibited a conserved transcriptional program enriched for cell cycle, DNA repair, and chromatin regulation pathways, and were preferentially mutated in genes involved in maintaining genomic stability, including TP53. These tumours were associated with increased mutation burden, fraction of genome altered, homologous recombination deficiency, and elevated hypoxia. Clinically, high YBX1 mRNA associated with advanced stage, higher grade, shorter progression-free survival, and reduced overall survival. Collectively, high YBX1 mRNA expression defines a conserved, genomically unstable, and clinically aggressive tumour state across multiple cancer types.

TP53 mutations occur in 80-90% of triple-negative breast cancers (TNBCs) and drive genomic instability and metastatic progression. Poly (ADP-ribose) polymerase (PARP) is critical for DNA repair and replication fork stability. How oncogenic signaling influences PARP function to sustain proliferation during replication stress remains unclear. Mutant p53 (mtp53) R273H associates tightly with chromatin, forms complexes with PARP, and enhances PARP recruitment to replication forks [1-3]. The C-terminal region of mtp53 mediates mtp53-PARP and mtp53-Poly (ADP-ribose) (PAR) interactions that facilitate S phase progression [4, 5]. The PARP inhibitor talazoparib (TAL) combined with the alkylating agent temozolomide (TMZ) produces synergistic cytotoxicity selectively in mtp53, but not wild-type p53 (wtp53), breast cancer cells and organoids. Herein we evaluated the mechanism of mtp53-associated cell death and tested if this could translate to a preclinical xenograft model. We found that TMZ+TAL treatment induced elevated cleaved PARP and {gamma}H2AX and reduced the metastasis-promoting oncoprotein MDMX. In orthotopic xenografts expressing mtp53 R273H, but not wtp53, combination therapy significantly decreased circulating tumor cells (CTCs) and lung metastases. Transcriptomic profiling of tumors from combination treated animals demonstrated downregulation of MDMX, VEGF, and NF-{kappa}B, consistent with the observed suppression of CTCs and lung metastasis, and increased {gamma}H2AX, indicative of replication stress in mtp53 xenografts. Inhibition of metastasis was also observed in mtp53 R273H WHIM25 and p53-undetectable WHIM6 TNBC patient-derived xenografts (PDX). The mtp53 C-terminal domain (347-393) demonstrated a critical tumor promoting function, as CRISPR-mediated deletion impaired replication fork progression, tumor growth, and metastatic dissemination. DNA fiber combing showed that expression of full-length mtp53 R273H, but not C-terminal deleted {Delta}347-393, supported sustained single-stranded DNA gaps (ssGAPs) following Poly (ADP-ribose) glycohydrolase (PARG) inhibition. These findings support that mtp53 uses C-terminal amino acids to exploit PARP to enable replication stress adaptation and that mtp53 is a predictive biomarker for combined PARP inhibitor and DNA damaging therapies targeting TNBC. Significance statementTP53 mutations are the most common genetic alterations in TNBC and a major driver of replication stress and metastasis. This study shows that missense mutant p53 uses C-terminal amino acids to reprogram PARP activity to maintain tumor cell survival under replication stress. We demonstrate that p53 status governs the response to combined PARP inhibitor (PARPi) and DNA-damaging chemotherapy, establishing an additional molecular basis beyond BRCA1 mutations for treating TNBC with PARPi therapy. These findings reveal a previously unrecognized mechanism by which the mutant p53-PARP axis enables replication stress tolerance and drives cancer metastasis. We show mutation of p53 in TNBC provides an additional biomarker-guided framework to improve PARPi therapeutic outcomes.

The microRNAs miR-15a and miR-16 are key regulators of the anti-apoptotic oncogene BCL2, playing a significant role in tumorigenesis. These miRNAs function as tumor suppressors by directly targeting BCL2, whose overexpression contributes to cell survival and resistance to therapy in multiple malignancies, including chronic lymphocytic leukemia (CLL). The downregulation or deletion miR-15a/miR-16-1 cluster located on chromosome 13q occurs in about 50% of CLL patients and leads to the overexpression of the oncogenic BCL2, contributing to the survival and proliferation of cancer cells. In this confirmatory study, we provide additional evidence supporting the mechanism by which these miRNAs mediate the inhibition of BCL2 translation, leading to reduced levels of BCL2 protein with no significant effect on BCL2 mRNA degradation. This mechanism has been previously established as a critical pathway in the regulation of apoptosis, particularly in cancer cells where BCL2 overexpression is often associated with resistance to cell death. Our findings reinforce the notion that miRNAs, such as miR-15 and miR-16, bind to the 3-UTR of BCL2 messenger RNA (mRNA), specifically repressing its translation without inducing mRNA degradation. The results from our study align with previous research, confirming that the miRNA-mediated inhibition of BCL2 translation serves as a precise regulatory mechanism that targets protein synthesis rather than mRNA stability. These findings highlight the role of miRNAs in fine-tuning post-transcriptional gene regulation, offering a targeted approach to downregulate oncogenic proteins like BCL2 without disrupting the underlying mRNA, which could be leveraged for more refined therapeutic strategies.

Fusion transcripts are composed of hybrid RNA consisting of transcripts from two distinct genes and can arise from physical linking of genes at the DNA level, splicing or read-through transcription. In addition, there are also fusion transcripts that can occur between a protein coding gene and long non-coding RNAs. Systemic detection of all fusion transcripts at the RNA-level is important in the identification of potential therapeutic drug targets as well as biomarkers for detection, classification, and subtyping of cancer. We used long-read third-generation sequencing of RNA, Iso Sequencing to identify fusion transcripts in Mantle Cell Lymphoma (MCL) cell lines. Our results revealed widespread transcript diversity in MCL. The majority of the long-read transcripts were novel. Some of the thousands of novel transcripts we identified were fusion transcripts. These fusion transcripts had some of the longest transcripts in the MCL transcriptome. We identified the fusion junction of several select fusion transcripts involving protein coding genes including the well-known and widely expressed CTBS::GNG5 and validated their presence using other techniques. Furthermore, we also identified and validated a novel fusion transcript between the multifunctional, m6A methylation writer, RBM15, and LAMTOR5:AS, a long noncoding RNA. Use of the chemical compound, JT-607, an inhibitor of CPSF73/CPSF3 which affects both alternative polyadenylation and read-through transcription resulted in increased expression of the RBM15::LAMTOR5:AS fusion transcript. Our analysis suggests that RBM15::LAMTOR5:AS and many fusion transcripts we identified are intrachromosomal. Since the origin, significance and impact of many fusion transcripts remain unknown, our results support using an unbiased approach to identify fusion transcripts. This will help us to fully comprehend the complexity of the human transcriptome in normal biology and in disease.

Testicular germ cell tumours (TGCTs) are the most common cancer in young males and are considered curable if they respond to platinum-based therapy. However, a significant number of refractory patients develop metastatic disease and the lack targeted therapy remains an unmet clinical need. To identify novel therapeutic targets, we investigated the epigenetic instability of TGCTs and characterised novel oncogenic gene networks regulated by transposable elements (TEs)-derived long noncoding RNAs (lncRNAs) which are controlled by PIWI-interacting RNAs (piRNAs). A TGCT-specific piRNA signature was identified by bioinformatics analysis of the The Cancer Genome Atlas (TCGA) TGCT dataset and analysis of piRNAs mapped to active LINE1 sequences identified piR-hsa-7221 as a transcriptional regulator of the lncRNA CASC9 in seminoma tumours. We show that piR-hsa-7221 binds to a complementary LINE1 LIPA5 sequence and regulates the expression of CASC9 driven by the LINE1 antisense promoter. Therefore, loss of piR-hsa-7221 drives the upregulation and oncogenic activity of CASC9, which as is impaired after silencing, leading to reduced cancer cell proliferation and invasion, as well as increased sensitivity to cisplatin treatment. These effects are associated with the regulation of the cell cycle, developmental pathways, extracellular matrix, hormone metabolism and immune responses, highlighting WNT signalling as a significant downstream target. Therefore, this novel epigenetic mechanism provides new insights into the role of piRNA-mediated regulation of oncogenic lncRNAs derived from active transposable elements. Importantly, the identification of piR-hsa-7221 and the lncRNA CASC9, together with the associated gene networks highlights novel therapeutic targets for the treatment of seminoma TGCTs.

Extrachromosomal DNA (ecDNA) has emerged as a critical mediator of oncogene amplification and transcriptional dynamics in aggressive cancers, yet its contribution to chemotherapy resistance in vivo remains incompletely understood. This study investigates the contribution of ecDNA-associated molecular features to predictive chemotherapy resistance in TNBC. We analyzed RNA-seq data from 4T1 TNBC cells and 4T1 bulk tumors at different growth stages (1-, 3-, and 6-week) to identify differentially expressed ecDNA alterations. We then utilized molecular docking tools to predict ecDNA protein-drug interactions and employed machine learning (ML) models to predict ecDNA-associated therapeutic resistance. Our results revealed changes in global gene expression, including expression of ecDNA-associated genes, that continued over time, with significant molecular remodeling observed at six weeks. Additionally, we found gradual accumulation of mutations in ecDNA genes, which may have contributed to reduced drug binding affinity, indicating potential resistance. ML models generated stable, high-confidence classifications of resistant phenotypes, consistently identifying ecDNA burden and prevalence as dominant predictive features of drug resistance. Drug specific predictions further highlighted elevated resistance probabilities for paclitaxel and doxorubicin, whereas hydroxyurea, which depletes ecDNA, showed reduced resistance probabilities, indicating potential roles of ecDNA in chemoresistance. This study provides new insights into temporal remodeling of ecDNA within TNBC tumors over time and their potential association with drug resistance.

Hypoxia is a defining feature of the solid tumour microenvironment and a major determinant of therapeutic response. Hypoxia-inducible factors (HIFs) are central regulators of transcriptional reprogramming under hypoxic stress. Hypoxia can paradoxically elicit both tumour-promoting and tumour-suppressive outcomes, suggesting regulatory mechanisms beyond canonical HIF-dependent pathways. Emerging evidence indicates that hypoxia-responsive RNAs (HRRs) may also be regulated independently of HIFs, with posttranscriptional stabilization playing a critical determinant of hypoxic adaptation. Cytoplasmic mRNA recapping mediated by the cytoplasmic capping enzyme (cCE) has recently emerged as an important post-transcriptional regulatory process, yet its role in hypoxia-driven RNA regulation remains poorly understood. Here, we aimed to identify novel HRRs that modulate cellular adaptability to hypoxia and to determine whether these transcripts are regulated by cCE. Using CoCl2-induced hypoxia, we observed a significant reduction in osteosarcoma cell aggressiveness, characterized by decreased proliferation, clonogenic survival, and migratory capacity. Transcriptomic profiling of hypoxic osteosarcoma cells identified RORA and KCTD16 as significantly upregulated and function as suppressors of tumour cell aggressiveness. Integrative in-silico CAGE tag analysis followed by cap-specific biochemical assays confirmed that both transcripts are post-transcriptionally stabilized by cCE. Mechanistically, hypoxia-induced stabilization of HIF1 transcriptionally elevated RORA and KCTD16 expression, while cCE further reinforced their stability post-transcriptionally. Stabilization of these cCE-targeted HRRs resulted in suppression of the oncogenic proliferation driver c-Myc, thereby attenuating the aggressive phenotype of hypoxic osteosarcoma cells. Collectively, our findings identify cCE as a previously unrecognized post-transcriptional regulator in hypoxia biology and reveal a RNA-centric mechanism by which hypoxia can restrain tumour aggressiveness.

BackgroundLong non-coding RNAs (lncRNAs) have emerged as key regulators of tumor biology, however, thus far none have translated to cancer therapies. The lncRNA MALAT1 is overexpressed in more than 20 cancers, including breast cancer and has been shown to function via various mechanisms in a context-dependent manner, in 2D cell lines and mouse models. However, its functional role and therapeutic potential have not been evaluated in clinically relevant patient-derived models. MethodsWe investigated the therapeutic potential of a MALAT1-targeting antisense oligonucleotide (ASO) for breast cancer, using clinically relevant 3D human patient-derived organoids (PDOs) and PDO-xenograft (PDO-X) models. We systematically evaluated the efficiency of MALAT1-targeting ASOs using a biobank of 28 PDO models. Using three independent PDO-X models of triple negative breast cancer (TNBC), we targeted MALAT1 in vivo to study its impact on transcription, alternative splicing, stromal remodeling and metastasis. ResultsAcross PDO-X models, MALAT1 depletion reproducibly drove widespread alternative splicing changes across all event types, particularly intron retention events, accompanied by modest gene expression alterations. Differentially spliced transcripts were enriched for targets of shared cancer-associated transcription factors, and MALAT1 knockdown altered the relative abundance of previously unannotated splicing isoforms. Beyond tumor-intrinsic effects, tumor-specific MALAT1 depletion induced a consistent reduction in macrophage-associated gene signatures and reduced lung metastatic burden. ConclusionsOur data define MALAT1s multifaceted role in TNBC, coordinating alternative splicing, transcriptional fine-tuning, tumor-stroma crosstalk, and metastatic progression. Our study provides strong preclinical evidence supporting MALAT1-targeted ASO therapy and establishes PDO-X models as a clinically relevant platform for functional interrogation of TNBC therapies.

tRNA-derived fragments (tRFs) are relatively recently discovered class of small RNAs implicated in gene-regulatory processes in diverse biological contexts but there have been very few reports of a clear phenotypic role of these small RNAs in cancer progression. By analyzing small RNA-seq data from The Cancer Genome Atlas (TCGA), we found that high expression of three 3' tRFs (tRF-3a), tRF-3009a, tRF-3021a or tRF-3030a, is significantly associated with poor overall survival in low-grade glioma (LGG). In glioblastoma cells, tRF-3009a, tRF-3021a and tRF-3030a enhance cell invasion and migration but tRF-3021a was uniquely required for cell proliferation and suppression of apoptosis. Interestingly, tRF-3021a knockdown decreases global protein synthesis prior to and independent of apoptosis. These data indicate that tRF-3021a supports glioma cell survival and particularly protein synthesis while promoting cellular invasion and migration. Given its association with poor outcome in LGG patients, tRF-3021a represents a promising biomarker and potential therapeutic target in gliomas and these results provide a foundation for future studies to define its molecular interactors and downstream pathways controlling protein synthesis and apoptosis in cancer cells. ImplicationtRF-3021a promotes malignant glioma phenotypes, sustains global protein synthesis and prevents spontaneous apoptosis, motivating efforts to evaluate it as a biomarker and therapeutic target.

MotivationSingle cell RNAseq (scRNAseq) is an ideal tool to characterize the heterogeneity within the tumor microenvironment, however, accurate identification of tumor cells can be a challenge. Reference-based methods can be inaccurate, if reference datasets are even available. Current purpose-built methods can be inaccurate, particularly with highly heterogeneous tumor types. Improved methods are needed. We explored the use of genetic variants to distinguish tumor from normal cells within scRNAseq data. ResultsWe characterized the limitations inherent to calling variants from scRNAseq data, quantifying how data sparsity precludes genetic distance calculation between single cells. As a novel workaround, we pooled data from transcriptionally similar cell clusters to call high quality variants and then calculated pairwise differences between cell populations and performed hierarchical clustering. We quantified confidence in genetic divergence between tumor and normal cell populations using bootstrapping. We performed extensive validation to assess accurate identification of tumor cells using ground-truth datasets. Application of our method to human scRNAseq samples highlighted the utility of our approach and revealed how mutational burden influences successful tumor cell identification. Improved cell type assignment in scRNAseq data will facilitate analysis of tumor samples and, in turn, accelerate our understanding of the mechanisms underlying tumor progression and reveal potential biological vulnerabilities that can be exploited to develop improved treatment options. Availability and implementationOur method is publicly available as an R package: SCANBIT (Single Cell Altered Nucleotide Based Inference of Tumor) https://github.com/kidcancerlab/scanBit.

The non-canonical translation of specific mRNAs has been implicated in oncogenesis and cancer progression. We previously identified eukaryotic Initiation Factor 5B (eIF5B) as a key factor in Internal Ribosome Entry Site (IRES)-mediated translation of a subset of mRNAs encoding anti-apoptotic proteins. Here, we demonstrate that EIF5B is predominantly expressed in cancer cells compared to other cell types in the Oral Squamous Cell Carcinoma (OSCC) microenvironment. Higher EIF5B mRNA and protein expression are associated with poor patient outcomes. We show that eIF5B depletion in OSCC cells blunted pro-growth, pro-inflammatory, and pro-angiogenic signaling pathways and significantly increased TNF-related apoptosis-inducing ligand (TRAIL)-induced cell death. This is achieved through decreased translation of mRNAs encoding critical factors associated with OSCC pathophysiology. Importantly, the level of interaction of eIF5B with tRNAiMet was significantly higher in OSCC cells compared to non-cancerous fibroblasts. This suggests that OSCC cells (but not non-cancerous fibroblasts) rely heavily on eIF5B for translation initiation. In an in vivo flank xenograft model using nude mice, eIF5B knockdown in UMSCC-29 cells led to a significant reduction in tumor volume compared to control tumors. Also, the immunohistochemical analysis of the xenografted tumor sections demonstrated decreased staining intensity of critical factors associated with OSCC pathophysiology in eIF5B-depleted tumors relative to controls. Collectively, our data demonstrate that OSCC cells are uniquely dependent on eIF5B-tRNA interactions to sustain translation of pro-survival mRNAs. Targeting eIF5B disrupts these oncogenic programs, sensitizing OSCC cells to apoptosis and suppressing pro-angiogenic and pro-growth signaling.

Hypertranscription and transcription-replication conflicts (TRCs) are frequent features of cancer cells. RAS oncogenes promote hypertranscription to allow cell growth and proliferation, which can the lead to TRCs. Here, we report that hyperactivation of the PI3K-AKT signalling pathway is required for TRCs induced by RAS oncogenes. Oncogenic HRAS causes more TRCs than oncogenic KRAS or BRAF, because HRAS hyperactivates PI3K. PI3K hyperactivation is associated with in glycogen synthase kinase-3{beta} (GSK3{beta}) inhibition, increased E2F and MYC transcription programmes, increased nascent transcription of ribosome biogenesis genes and small nucleolar RNAs (snoRNA) expression. Small molecule inhibition of PI3K signalling prevents RAS-induced replication stress, and small molecule PI3K activation promotes replication stress. RAS-induced TRCs require a cooperation of MAPK and Pi3K signalling, S phase entry and hypertranscription. Our findings suggest a mechanistic explanation for replication stress variability between RAS activation models and identify PI3K pathway activation as a potential new determinant of TRCs in cancer.

PRMT5 is a type II arginine methyltransferase that forms an active complex with methylosome protein WDR77 (MEP50) to catalyze the symmetric dimethylation (SDMA) of arginine residues in proteins that regulate biological roles including apoptosis, DNA damage response and RNA processing. Some of the best characterized PRMT5 substrates are the small nuclear ribonucleoproteins SNRPB, SNRPD1 and SNRPD3, which are critical for spliceosome assembly and RNA splicing fidelity. MTAP-deleted cancers exhibit increased sensitivity to PRMT5 inhibition due to elevated levels of methylthioadenosine (MTA), a natural inhibitor of PRMT5. This vulnerability is exploited by MTA-cooperative PRMT5 inhibitors, exemplified by TNG908 and TNG462 which selectively target PRMT5 in MTAP-deleted cells while sparing MTAP-wildtype (WT) cells. Consistent with this mechanism, treatment with TNG908 in preclinical studies induces widespread splicing alterations in MTAP-deleted cancer models, with minimal effects in MTAP-WT cells. These splicing changes are consistent across diverse MTAP-deleted tumor types, including glioblastoma, pancreatic, and non-small cell lung cancer, indicating a histology-agnostic response to PRMT5 inhibition. Moreover, treatment of MTAP-WT cells with exogenous MTA mimics the splicing alterations observed with PRMT5 inhibition, as does pharmacologic inhibition of MTAP further supporting a mechanistic link between MTA accumulation, PRMT5 modulation, and aberrant splicing. Given that MTAP deletions occur in approximately 10-15% of human cancers, the identification of a robust RNA splicing signature offers a valuable pharmacodynamic biomarker for monitoring the activity of PRMT5 inhibitors. This splicing-based readout may also serve as a predictive biomarker of therapeutic response, offering greater specificity than global SDMA levels. Collectively these data suggest that a PRMT5-dependent RNA splicing signature can monitor the pharmacodynamic activity of MTA-cooperative PRMT5 inhibitors in MTAP-deleted cells.

Epigenetic dysregulation is a common feature of cancer and creates selective vulnerabilities arising from an increased reliance on chromatin-based mechanisms that sustain malignant transcriptional states. While many chromatin regulators are broadly required for cellular viability, others function in a context-dependent manner across distinct oncogenic settings, tissue lineages, and differentiation states. Moreover, chromatin regulators often operate within multi-subunit complexes; thus, epigenetic vulnerabilities emerge from coordinated complex activities rather than single genes. Here, we integrate large-scale genetic dependency maps from human cancer cell lines with curated epigenetic complex annotations to perform a systematic, multivariate analysis of complex-level epigenetic dependencies across cancer lineages. Our analysis reveals that dependencies frequently cluster among functionally related chromatin complexes and that biologically related cancer types share similar dependency patterns, consistent with shared underlying epigenetic requirements. Focusing on melanoma, we identify multiple enriched epigenetic complex dependencies, including complexes previously associated with recurrent genetic alterations or melanocyte lineage regulation, as well as a previously unrecognized vulnerability involving the H3K4 methyltransferase complex Set1C/COMPASS. This dependency is not restricted to a specific melanoma differentiation state, but genetic depletion of CXXC1 (a complex-specific subunit) shows that CXXC1-dependent melanoma cells require Set1C/COMPASS activity to maintain global H3K4 trimethylation (H3K4me3) and proliferation. Integrative modeling links Set1C/COMPASS dependency to MYC- and E2F-driven transcriptional programs, which are suppressed upon complex inhibition. Together, this work combines integrative, multivariate analysis of lineage-enriched epigenetic dependencies with genetic perturbation, transcriptional profiling, and single-cell analysis to uncover an enriched epigenetic dependency on Set1C/COMPASS in melanoma cells. Author SummaryCancer cells often rely on abnormal regulation of gene activity to support uncontrolled growth and survival. This regulation is controlled not only by genetic mutations, but also by epigenetic mechanisms, chemical and structural modifications to DNA and its associated proteins that determine which genes are turned on or off. Several therapies that target epigenetic regulators have shown promise, particularly in blood cancers. However, identifying which epigenetic mechanisms are most important in specific cancers remains challenging, especially because epigenetic regulators frequently work together as multi-protein complexes. In this study, we combine large-scale public datasets with computational modeling to systematically identify lineage-enriched epigenetic vulnerabilities across many cancer types. We found that certain epigenetic complexes are selectively important in specific cancer lineages. In melanoma, an aggressive skin cancer, we identified a previously unrecognized dependence on a protein complex that modifies chromatin at gene promoters. We show that disrupting this complex impairs gene programs that drive cell division and blocks cancer cell growth. Our findings reveal a lineage-specific epigenetic vulnerability in melanoma and demonstrate how integrative computational approaches can uncover new targets for potential cancer therapy studies.