Biology subjects

Humphrey, T.

Publications and source records attributed to Humphrey, T..

6 recordsLinked to original sources

bioRxiv2026

A DMT1-dependent iron-endoplasmic reticulum-extracellular matrix axis regulates cancer cell invasion

Intracellular iron homeostasis is increasingly recognized as a regulator of cancer cell behavior, but how iron distribution influences extracellular matrix (ECM) organization and invasion remains poorly understood. Here, we show that loss of divalent metal transporter 1 (DMT1/SLC11A2) disrupts intracellular iron homeostasis and promotes cancer cell invasion through an iron-ER-ECM axis. In MDA-MB-231 cells, DMT1 knockout (KO) reduced total iron content but increased the labile iron pool (LIP) in both 2D and 3D culture models, indicating altered intracellular iron distribution. Across transcriptomic and phenotypic readouts, DMT1-dependent effects were more evident in 3D than in 2D models, with DMT1 KO inducing endoplasmic reticulum (ER) stress and impaired collagen/ECM organization. Functionally, the DMT1-loss phenotype was marked by reduced 2D motility, whereas in 3D spheroid models DMT1 KO cells displayed enhanced invasive outgrowth in both Matrigel and collagen matrices. Iron chelation further modulated this phenotype in a DMT1-dependent manner. Pharmacologic induction of ER stress phenocopied the loose spheroid architecture and invasive behavior, supporting ER stress as a mechanistic link between altered iron handling and ECM destabilization. Together, these findings identify intracellular iron distribution, rather than total iron abundance alone, as a determinant of ECM integrity and context-dependent cancer cell invasion. One Sentence Summary: Iron misrouting, not iron excess, drives ER stress and collagen failure that unleash invasion in triple-negative breast cancer.

cancer biology↗

bioRxiv2026

FABP8/PMP2 is a positive regulator of PNS myelination

Myelin formation in peripheral nerves is orchestrated by axon-derived signals and the ability of Schwann cells to expand lipid-rich membrane. Axonal Neuregulin-1 type III (NRG1t3) is known to promote thicker myelin and is associated with increased lipid abundance in peripheral nerves. NRG1t3 also strongly upregulates peripheral myelin protein 2 (FABP8/PMP2), a fatty acid binding protein in myelinating Schwann cells. Here, we directly tested whether elevating PMP2 in Schwann cells is sufficient to enhance myelin growth in nerves. We generated transgenic mice with Schwann cell-specific PMP2 overexpression and showed that PMP2 overexpression drove significant myelin thickening in peripheral nerves, without altering myelin ultrastructure, impairing nerve conduction, or causing detectable adverse effects despite sustained expression. Strikingly, this hypermyelination occurred without activating canonical promyelinating signaling pathways. Instead, elevated PMP2 selectively enhanced fatty acid uptake in Schwann cells, identifying PMP2 as a dosage sensitive enhancer of myelin growth. These findings suggest that in the absence of axonal signaling-driven upregulation, enhanced PMP2 expression itself promotes myelin membrane expansion and enhanced fatty acid availability that could favor complex lipid synthesis. These findings reveal new role for PMP2 as a regulator for myelin expansion in vivo, highlighting a key link between lipid trafficking and myelin growth.

neuroscience↗

bioRxiv2022

Using canavanine resistance to measure mutation rates in Schizosaccharomyces pombe

We constructed a panel of S. pombe strains expressing DNA polymerase {varepsilon} variants associated with cancer, specifically POLES297F, POLEV411L, POLEL424V, POLES4459F and used these to compare mutation rates determined by canavanine resistance with other selective methods. Canavanine-resistance mutation rates are broadly similar to those seen with reversion of the ade-485 mutation to adenine prototrophy, but lower than 5-fluoroorotic acid (FOA)-resistance rates (inactivation of ura4+ or ura5+ genes). Inactivation of several genes has been associated with canavanine-resistance in S. pombe but surprisingly whole genome sequencing showed that 8/8 spontaneous canavanine-resistance mutants have an R175C mutation in the any1/arn1 gene. This gene encodes a {beta}-arrestin-like protein involved in mediating Pub1 ubiquitylation of target proteins, and the phenotypic resistance to canavanine by this single mutation is similar to that shown by the original "can1-1" strain, which also has the any1R175C mutation. Some of the spontaneous mutants have additional mutations in arginine transporters, suggesting that this may marginally increase resistance to canavanine. The any1R175C strain showed internalisation of the Cat1 arginine transporter, explaining the canavanine-resistance phenotype. In addition, any1R175C cells were elongated compared to wild type. The mitotic activator Cdc25 has been identified as a Pub1 ubiquitylation target, and since Wee1 inhibition of Cdc2 is counteracted by Cdc25, it is likely that Cdc25 ubiquitylation and downregulation by Any1R175C-Pub1 delays mitotic entry

genetics↗

bioRxiv2021

Expression of the cancer-associated DNA polymerase ϵ P286R in fission yeast leads to translesion synthesis polymerase dependent hypermutation and defective DNA replication

Somatic mutations in the proofreading domain of the replicative DNA polymerase {varepsilon} (POLE-exonuclease domain mutations, POLE-EDMs) are frequently found in colorectal and endometrial cancers and, occasionally, in other tumours. POLE-associated cancers typically display hypermutation, microsatellite stability and a unique mutational signature, with a predominance of C > A transversions in the context TCT. To understand better the contribution of hypermutagenesis to tumour development, we have modelled the most recurrent POLE-EDM (POLE-P286R) in Schizosaccharomyces pombe. Whole-genome sequencing analysis revealed that the corresponding pol2-P287R allele also has a strong mutator effect in vivo, with a high frequency of base substitutions and relatively few frameshift mutations. The mutations are equally distributed across different genomic regions, but they occur within an AT-rich context. The most abundant base-pair changes are TCT > TAT transversions and, in contrast to human mutations, TCG > TTG transitions are not elevated, likely due to the absence of cytosine methylation in fission yeast. The pol2-P287R variant has an increased sensitivity to elevated dNTP levels and DNA damaging agents, and shows reduced viability on depletion of the Pfh1 helicase. In addition, S phase is aberrant and RPA foci are elevated, suggestive of persistent ssDNA or DNA damage, and the pol2-P287R mutation is synthetically lethal with rad3 inactivation, indicative of checkpoint activation. Significantly, deletion of genes encoding some translesion synthesis polymerases, most notably Pol {kappa}, partially suppresses pol2-P287R hypermutation, indicating that polymerase switching contributes to this phenotype. AUTHOR SUMMARYCancer is a genetic disease caused by mutations that lead to uncontrolled cell proliferation and other tumour properties. Defects in DNA repair or replication can lead to cancer development by increasing the likelihood that cancer-causing mutations will happen. Here we look at a pathogenic variant of a polymerase involved in genome replication (DNA polymerase POLE-P286R). This variant is associated with highly mutated cancer genomes. By introducing this mutation into the polymerase gene of a model organism, fission yeast, we show that it causes a large increase in single base substitutions, scattered throughout the genome. The sequence context of mutations is similar in fission yeast and humans, suggesting that the yeast model is useful for understanding how POLE-P286R causes such a high mutation rate. Yeast POLE-P286R cells show slow chromosome replication, suggesting that the polymerase has difficulty in copying certain chromosomal regions. Yeast POLE-P286R cells become inviable when the concentration of dNTP building blocks for DNA synthesis is increased, probably because the mutation rate is pushed to an intolerable level. Interestingly, we find that specialised polymerases that are tolerant of DNA damage contribute to the high mutation rate caused by POLE-P286R. These findings have implications for the therapy of POLE-P286R tumours.

cancer biology↗

bioRxiv2018

An essential role for dNTP homeostasis following CDK-induced replication stress

Replication stress is a common feature of cancer cells, and thus a potentially important therapeutic target. Here we show that CDK-induced replication stress is synthetic lethal with mutations disrupting dNTP homeostasis in fission yeast. Wee1 inactivation leads to increased dNTP demand and replication stress through CDK-induced firing of dormant replication origins. Subsequent dNTP depletion leads to inefficient DNA replication, Mus81-dependent DNA damage, and to genome instability. Cells respond to this replication stress by increasing dNTP supply through Set2-dependent MBF-induced expression of Cdc22, the catalytic subunit of ribonucleotide reductase (RNR). Disrupting dNTP synthesis following Wee1 inactivation, through abrogating Set2-dependent H3K36 tri-methylation or DNA integrity checkpoint inactivation results in critically low dNTP levels, replication collapse and cell death, which can be rescued by increasing dNTP levels. These findings support a dNTP supply and demand model in which maintaining dNTP homeostasis is essential to prevent replication catastrophe in response to CDK-induced replication stress.

molecular biology↗

bioRxiv2016

Genome-Wide Fitness Analyses of the Foodborne Pathogen Campylobacter jejuni in In Vitro and In Vivo Models

Infection by Campylobacter is recognised as the most common cause of foodborne bacterial illness worldwide. Faecal contamination of meat, especially chicken, during processing represents a key route of transmission to humans. There is currently no licenced vaccine and no Campylobacter-resistant chickens. In addition, preventative measures aimed at reducing environmental contamination and exposure of chickens to Campylobacter jejuni (biosecurity) have been ineffective. There is much interest in the factors/mechanisms that drive C. jejuni colonisation and infection of animals, and survival in the environment. It is anticipated that understanding these mechanisms will guide the development of effective intervention strategies to reduce the burden of C. jejuni infection. Here we present a comprehensive analysis of C. jejuni fitness during growth and survival within and outside hosts. A comparative analysis of transposon (Tn) gene inactivation libraries in three C. jejuni strains by Tn-seq demonstrated that a large proportion, 331 genes, of the C. jejuni genome is dedicated to (in vitro) growth. An extensive Tn library in C. jejuni M1cam (~10,000 mutants) was screened for the colonisation of commercial broiler chickens, survival in houseflies and under nutrient-rich and-poor conditions at low temperature, and infection of human gut epithelial cells. We report C. jejuni factors essential throughout its life cycle and we have identified genes that fulfil important roles across multiple conditions, including maf3, fliW, fliD, pflB and capM, as well as novel genes uniquely implicated in survival outside hosts. Taking a comprehensive screening approach has confirmed previous studies, that the flagella are central to the ability of C. jejuni to interact with its hosts. Future efforts should focus on how to exploit this knowledge to effectively control infections caused by C. jejuni.\n\nAuthor SummaryCampylobacter jejuni is the leading bacterial cause of human diarrhoeal disease. C. jejuni encounters and has to overcome a wide range of \"stress\" conditions whilst passing through the gastrointestinal tract of humans and other animals, during processing of food products, on/in food and in the environment. We have taken a comprehensive approach to understand the basis of C. jejuni growth and within/outside host survival, with the aim to inform future development of intervention strategies. Using a genome-wide transposon gene inactivation approach we identified genes core to the growth of C. jejuni. We also determined genes that were required during the colonisation of chickens, survival in the housefly and under nutrient-rich and -poor conditions at low temperature, and during interaction with human gut epithelial tissue culture cells. This study provides a comprehensive dataset linking C. jejuni genes to growth and survival in models relevant to its life cycle. Genes important across multiple models were identified as well as genes only required under specific conditions. We identified that a large proportion of the C. jejuni genome is dedicated to growth and that the flagella fulfil a prominent role in the interaction with hosts. Our data will aid development of effective control strategies.

microbiology↗