detection-post-replicative-gaps-accumulation-repair-human-cells-using

Detection of Post-Replicative Gaps Accumulation and Repair in Human Cells Using the DNA Fiber Assay

The DNA fiber assay is a simple and robust method for the analysis of replication fork dynamics, based on the immunodetection of nucleotide analogs that ...

Washington University in St. Louis

Most of the studies on air pollution focus on emissions from fossil fuel burning in urban centers. However, approximately half of the world's population is exposed to air pollution caused by biomass burning emissions. In the Brazilian Amazon population, over 10 million people are directly exposed to high levels of pollutants resulting from deforestation and agricultural fires. This work is the first study to present an integrated view of the effects of inhalable particles present in emissions of biomass burning. Exposing human lung cells to particulate matter smaller than 10 µm (PM), significantly increased the level of reactive oxygen species (ROS), inflammatory cytokines, autophagy, and DNA damage. Continued PM exposure activated apoptosis and necrosis. Interestingly, retene, a polycyclic aromatic hydrocarbon present in PM, is a potential compound for the effects of PM, causing DNA damage and cell death. The PM concentrations observed during Amazon biomass burning were sufficient to induce severe adverse effects in human lung cells. Our study provides new data that will help elucidate the mechanism of PM-mediated lung cancer development. In addition, the results of this study support the establishment of new guidelines for human health protection in regions strongly impacted by biomass burning.

Biomass burning in the Amazon region causes DNA damage and cell death in human lung cells.

Acute treatment with replication-stalling chemotherapeutics causes reversal of replication forks. BRCA proteins protect reversed forks from nucleolytic degradation, and their loss leads to chemosensitivity. Here, we show that fork degradation is no longer detectable in BRCA1-deficient cancer cells exposed to multiple cisplatin doses, mimicking a clinical treatment regimen. This effect depends on increased expression and chromatin loading of PRIMPOL and is regulated by ATR activity. Electron microscopy and single-molecule DNA fiber analyses reveal that PRIMPOL rescues fork degradation by reinitiating DNA synthesis past DNA lesions. PRIMPOL repriming leads to accumulation of ssDNA gaps while suppressing fork reversal. We propose that cells adapt to repeated cisplatin doses by activating PRIMPOL repriming under conditions that would otherwise promote pathological reversed fork degradation. This effect is generalizable to other conditions of impaired fork reversal (e.g., SMARCAL1 loss or PARP inhibition) and suggests a new strategy to modulate cisplatin chemosensitivity by targeting the PRIMPOL pathway.

PRIMPOL-Mediated Adaptive Response Suppresses Replication Fork Reversal in BRCA-Deficient Cells.

TAR DNA-binding protein 43 (TDP-43; also known as TARDBP) is an RNA-binding protein whose aggregation is a hallmark of the neurodegenerative disorders amyotrophic lateral sclerosis and frontotemporal dementia. TDP-43 loss increases DNA damage and compromises cell viability, but the actual function of TDP-43 in preventing genome instability remains unclear. Here, we show that loss of TDP-43 increases R-loop formation in a transcription-dependent manner and results in DNA replication stress. TDP-43 nucleic-acid-binding and self-assembly activities are important in inhibiting R-loop accumulation and preserving normal DNA replication. We also found that TDP-43 cytoplasmic aggregation impairs TDP-43 function in R-loop regulation. Furthermore, increased R-loop accumulation and DNA damage is observed in neurons upon loss of TDP-43. Together, our findings indicate that TDP-43 function and normal protein homeostasis are crucial in maintaining genomic stability through a co-transcriptional process that prevents aberrant R-loop accumulation. We propose that the increased R-loop formation and genomic instability associated with TDP-43 loss are linked to the pathogenesis of TDP-43 proteinopathies.This article has an associated First Person interview with the first author of the paper.

TDP-43 dysfunction results in R-loop accumulation and DNA replication defects.

It is well established that short telomeres activate an ATM-driven DNA damage response that leads to senescence in terminally differentiated cells. However, technical limitations have hampered our understanding of how telomere shortening is signaled in human stem cells. Here, we show that telomere attrition induces ssDNA accumulation (G-strand) at telomeres in human pluripotent stem cells (hPSCs), but not in their differentiated progeny. This led to a unique role for ATR in the response of hPSCs to telomere shortening that culminated in an extended S/G2 cell cycle phase and a longer period of mitosis, which was associated with aneuploidy and mitotic catastrophe. Loss of p53 increased resistance to death, at the expense of increased mitotic abnormalities in hPSCs. Taken together, our data reveal an unexpected dominant role of ATR in hPSCs, combined with unique cell cycle abnormalities and, ultimately, consequences distinct from those observed in their isogenic differentiated counterparts.

Article	Year
Biomass burning in the Amazon region causes DNA damage and cell death in human lung cells. Scientific reports\| PubMed ID: 28883446	2017
PRIMPOL-Mediated Adaptive Response Suppresses Replication Fork Reversal in BRCA-Deficient Cells. Molecular cell\| PubMed ID: 31676232	2020
TDP-43 dysfunction results in R-loop accumulation and DNA replication defects. Journal of cell science\| PubMed ID: 32989039	2020
Telomere erosion in human pluripotent stem cells leads to ATR-mediated mitotic catastrophe. The Journal of cell biology\| PubMed ID: 33851958	2021

Annabel Quinet

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