Biology subjects

Barbour, J. A.

Publications and source records attributed to Barbour, J. A..

6 recordsLinked to original sources

bioRxiv2025

A tumor necrosis factor-α responsive cryptic promoter drives overexpression of the human endogenous retrovirus ERVK-7

Endogenous retroviruses (ERVs) shape human genome functionality and influence disease pathogenesis, including cancer. ERVK-7, a significant ERV, acts as an immune modulator and prognostic marker in lung adenocarcinoma (LUAD). Although ERVK-7 overexpression has been linked to the amplification of the 1q22 locus in approximately 10% of LUAD cases, it predominantly arises from alternative regulatory mechanisms. Our findings indicate that the canonical 5 long terminal repeat (LTR) of ERVK-7 is methylated and inactive, necessitating the use of alternative upstream promoters. We identified two novel transcripts, ERVK-7.long and ERVK-7.short, arising from distinct promoters located 2.8 kb and 13.8 kb upstream of the 5LTR of ERVK-7, respectively. ERVK-7.long is predominantly overexpressed in LUAD. Through comprehensive epigenetic mapping and single-cell transcriptomics, we demonstrate that ERVK-7.long activation is predetermined by cell lineage, specifically in small airway epithelial cells (SAECs), where its promoter displays tumor-specific H3K4me3 modifications. Single-cell RNA sequencing further reveals a distinct enrichment of ERVK-7.long in LUAD tumor cells and alveolar type 2 epithelial cells, underscoring a cell-type-specific origin. Additionally, inflammatory signaling significantly influences ERVK-7 expression; TNF- enhances ERVK-7.long, while interferon signaling preferentially augments ERVK-7.short by differential recruitment of NF-{kappa}B/RELA and IRF to their respective promoters. This differential regulation clarifies the elevated ERVK-7 expression in LUAD compared to lung squamous cell carcinoma (LUSC). Our study elucidates the complex regulatory mechanisms governing ERVK-7 in LUAD and proposes these transcripts as potential biomarkers and therapeutic targets, offering new avenues to improve patient outcomes.

cancer biology↗

bioRxiv2023

Integrating long-read RNA sequencing improves locus-specific quantification of transposable element expression

Transposable elements (TEs) can influence human diseases by disrupting genome integrity, yet their quantification has been challenging due to the repetitive nature of these sequences across the genome. We developed LocusMasterTE, a method that integrates long-read with short-read RNA-seq to increase the accuracy of TE expression quantification. By incorporating fractional transcript per million (TPM) values from long-read sequencing data into an expectation-maximization (EM) algorithm, LocusMasterTE reassigns multi-mapped reads, enhancing accuracy in short-read-based TE quantification. Validated with simulated and human datasets, LocusMasterTE holds promise for revealing new insights into TE functions through precise quantification.

genomics↗

bioRxiv2022

XPD protects CTCF-Cohesin binding sites from somatic mutagenesis

Xeroderma pigmentosum group D (XPD) is a DNA helicase with critical functions in transcription initiation and nucleotide excision repair. Missense mutations in XPD are putative drivers in around 10% of bladder cancers (BLCA), but the associated mutational process remains poorly understood. Here, we examine the somatic mutational landscape of XPD wild-type (n=343) and mutant (n=39) BLCA whole genomes. The genome-wide distribution of somatic mutations is significantly altered in XPD mutants, affecting both APOBEC and non-APOBEC associated mutational processes. Specifically, XPD mutants are enriched in T[C>T]N mutations (SBS2) with altered correlation with replication timing. At a locoregional genomic level, mutant XPD BLCA had striking T>G mutation hotspots at CTCF-cohesin binding sites (CBS) with evidence linking XPD to genomic uracil repair. Leveraging differential distribution of somatic mutations, we developed a machine-learning model for predicting pathogenic XPD mutations, which we validated in an independent TCGA cohort with 100% accuracy. Our model enabled the discovery of missed XPD mutation calls and uncovered pathogenic non-hotspot XPD mutations in bladder cancer. Our study reveals how XPD mutations redistribute somatic mutations in cancer genomes and provides a genome sequencing approach to differentiate driver and passenger XPD mutations.

molecular biology↗

bioRxiv2021

Gene expression is a poor predictor of the metabolite abundance in cancer cells

Metabolic reprogramming is a hallmark of cancer characterized by global changes in metabolite levels. However, compared with the study of gene expression, profiling of metabolites in cancer samples remains relatively understudied. We obtained metabolomic profiling and gene expression data from 454 human solid cancer cell lines across 24 cancer types from the Cancer Cell Line Encyclopedia (CCLE) database, to evaluate the feasibility of inferring metabolite levels from gene expression data. For each metabolite, we trained multivariable LASSO regression models to identify gene sets that are most predictive of the level of each metabolite profiled. Even when accounting for cell culture conditions or cell lineage in the model, few metabolites could be accurately predicted. In some cases, the inclusion of the upstream and downstream metabolites improved prediction accuracy, suggesting that gene expression is a poor predictor of steady-state metabolite levels. Our analysis uncovered a single robust relationship between the expression of nicotinamide N-methyltransferase (NNMT) and 1-methylnicotinamide (MNA), however, this relationship could only be validated in cancer samples with high purity, as NNMT is not expressed in immune cells. Together, our findings reveal the challenge of inferring metabolite levels from metabolic enzyme levels and suggest that direct metabolomic profiling is necessary to study metabolism in cancer.

bioinformatics↗

bioRxiv2020

Deficiency in DNA mismatch repair of methylation damage is a major mutational process in cancer

DNA mismatch repair (MMR) is essential for maintaining genome integrity with its deficiency predisposing to cancer1. MMR is well known for its role in the post-replicative repair of mismatched base pairs that escape proofreading by DNA polymerases following cell division2. Yet, cancer genome sequencing has revealed that MMR deficient cancers not only have high mutation burden but also harbour multiple mutational signatures3, suggesting that MMR has pleotropic effects on DNA repair. The mechanisms underlying these mutational signatures have remained unclear despite studies using a range of in vitro4,5 and in vivo6 models of MMR deficiency. Here, using mutation data from cancer genomes, we identify a previously unknown function of MMR, showing that the loss of non-canonical replication-independent MMR activity is a major mutational process in human cancers. MMR is comprised of the MutS (MSH2/MSH6) and MutL (MLH1/PMS2) complexes7. Cancers with deficiency of MutS exhibit mutational signature contributions distinct from those deficient of MutL. This disparity is attributed to mutations arising from the unrepaired deamination of 5-methylcytosine (5mC), i.e. methylation damage, as opposed to replicative errors by DNA polymerases induced mismatches. Repair of methylation damage is strongly associated with H3K36me3 chromatin but independent of binding of MBD4, a DNA glycosylase that recognise 5mC and can repair methylation damage. As H3K36me3 recruits MutS, our results suggest that MutS is the essential factor in mediating the repair of methylation damage. Cell line models of MMR deficiency display little evidence of 5mC deamination-induced mutations as their rapid rate of proliferation limits for the opportunity for methylation damage. We thus uncover a non-canonical role of MMR in the protection against methylation damage in non-dividing cells.

genomics↗

bioRxiv2019

Mutational processes of distinct POLE exonuclease domain mutants drive an enrichment of a specific TP53 mutation in colorectal cancer

Cancer genomes with mutations in the exonuclease domain of Polymerase Epsilon (POLE) present with an extraordinarily high somatic mutation burden. In vitro studies have shown that distinct POLE mutants exhibit different polymerase activity and yet, how these POLE mutants generate mutations across cancer genomes and influence driver events remains poorly understood. Here we analyzed 7,345 colorectal cancer samples, including nine whole genome sequenced samples harboring POLE mutations. Our analysis identified differential mutation spectra across the mutants including methylation-independent enrichment of C>T mutations in POLE V411L. In contrast, analysis of other genomic regions showed similar mutation profiles across the different POLE mutants. Notably, we found that POLE mutants with the TP53 R213* mutation, caused by a TT[C>T]GA substitution, have significantly higher relative frequency of this mutational context compared with samples without this mutation. This finding demonstrates that variations in underlying mutation spectra can increase the likelihood of specific driver mutation formation.

genomics↗