Role of chromatin structure modulation by the histone deacetylase inhibitor trichostatin A on the radio-sensitivity of ataxia telangiectasia

RRM1 promotes homologous recombination and radio/chemo-sensitivity via enhancing USP11 and E2F1-mediated RAD51AP1 transcription

Ribonucleotide reductase M1 (RRM1), the catalytic subunit of ribonucleotide reductase, plays a pivotal role in converting ribonucleotides (NTP) into deoxyribonucleotides (dNTP), essential for DNA replication and repair. Elevated RRM1 expression is associated with various human cancers, correlating with poorer prognosis and reduced overall survival rates. Our previous study found that RRM1 will enter the nucleus to promote DNA damage repair. However, the underlying mechanism remains elusive. Here, we unveil a novel role of RRM1 in promoting homologous recombination (HR) by upregulating the expression of RAD51AP1, a critical HR factor, in an E2F1-dependent manner. We demonstrate that RRM1 interacts with USP11 in the cytoplasm, and the recruitment of RRM1 to LaminB1 induced by ionizing radiation (IR) facilitates the binding of USP11 to the nuclear pore complex (NPC), promoting USP11 entry into the nucleus. Upon nuclear translocation, USP11 binds to E2F1 and inhibits the ubiquitin-mediated degradation of E2F1, thereby enhancing the transcriptional expression of RAD51AP1. Moreover, a specific RRM1 mutant lacking amino acids 731-793, crucial for its interaction with USP11 and recruitment to LaminB1, exhibits a dominant-negative effect on RAD51AP1 expression and HR. Truncations of RRM1 fail to inhibit the ubiquitin-mediated degradation of E2F1 and cannot promote the E2F1-mediated transactivation of RAD51AP1. Lastly, the full length of RRM1, not truncations, enhances tumor cells' sensitivity to IR, underscoring its importance in radiotherapy resistance. Collectively, our results suggest a novel function of RRM1 in promoting HR-mediated DSB repair through positive regulation of RAD51AP1 transcription by direct interaction with USP11 and promoting subsequent USP11-mediated deubiquitination of E2F1. Our findings elucidate a previously unknown mechanism whereby RRM1 promotes HR-mediated DNA repair, presenting a potential therapeutic target for cancer treatment.

DNA integrity and ecophysiological responses of Spanish populations of Ulmus glabra to increasing ozone levels

Ulmus glabra is a deciduous tree with a wide distribution in the Eurosiberian region. The southernmost populations, in the Mediterranean area, are fragmented in mountain areas which act as a refugium. These small relict populations can act as sentinel of global change, including climate change and impacts of human activities such as air pollution. Besides, tropospheric ozone (O₃) is an additional stress factor in the Mediterranean region affecting plant physiology and health. Moreover, oxidative stress caused by O₃ could increase DNA damage in plants cells. U. glabra 4-year-old seedlings originated from a natural population growing in the Guadarrama mountain range (central Spain), were exposed in Open Top Chambers to four O₃ treatments: charcoal filtered air, non-filtered air reproducing ambient levels, non-filtered air supplemented with 15 nl l^-1 O₃ and non- filtered air supplemented with 30 nl l^-1 O₃. Ozone effects on the DNA integrity through Comet assay were evaluated and eco-physiological responses were explored as well as. Comet assay showed a significant increase of DNA damage with increasing levels of O₃ after only one-month exposure, when no eco-physiological symptoms of damage could be detected. Comet assay could thus be suggested as a predictive test to detect DNA damage induced in plants by other abiotic stresses as well as to identify tolerant and sensitive species or in preservation strategies of small relict populations. The discovery of a test for an early identification of stressed plants could be important to speed the selection of tolerant individuals for breeding programmes.

Comparing Lymphocyte Radiosensitivity of Prostate Cancer Patients with Healthy Donors Using Micronuclei and Chemical Premature Chromosome Condensation Tests

Background:

Cytogenetic tests are usually used for diagnosing predisposed individuals to cancer by determining their lymphocyte radiosensitivity.

Objective:

To determine the potential role of radiosensitivity in predisposition of prostate cancer by comparing lymphocyte radiosensitivity of prostate cancer patients with healthy donors.

Materials and Methods:

In this experimental study, the blood samples of 10 prostate cancer patients and 10 healthy donors were irradiated to 0.25, 0.5, 1, 2, 4 and 6 Gy ionizing radiation produced by a 6MV Linac. One sample of each group receiving no radiation was regarded as the background. The micronuclei (MN) and chemical premature chromosome condensation (PCC) cytogenetic tests were performed on all samples and the numbers of MN and PCC rings were scored. Dose-response curves were plotted for both healthy and cancerous groups with two tests.

Results:

There was a significant difference between the numbers of MN within each group due to different levels of radiation doses. There was also a significant difference between the two groups in all identical doses, with the exception of 6 Gy. The chemical PCC test indicated a significant difference between the scored PCC rings in each group at doses higher than 0.25 Gy. However, no differences were noted between the healthy donors and prostate cancer patients receiving the same level of doses.

Conclusion:

MN test can be considered as a reliable indicator of predisposition of prostate cancer. On the other hand, the chemical PCC test could not differentiate between healthy donors and prostate cancer patients at the dose range examined in this study.

Genome-Protecting Compounds as Potential Geroprotectors

Throughout life, organisms are exposed to various exogenous and endogenous factors that cause DNA damages and somatic mutations provoking genomic instability. At a young age, compensatory mechanisms of genome protection are activated to prevent phenotypic and functional changes. However, the increasing stress and age-related deterioration in the functioning of these mechanisms result in damage accumulation, overcoming the functional threshold. This leads to aging and the development of age-related diseases. There are several ways to counteract these changes: 1) prevention of DNA damage through stimulation of antioxidant and detoxification systems, as well as transition metal chelation; 2) regulation of DNA methylation, chromatin structure, non-coding RNA activity and prevention of nuclear architecture alterations; 3) improving DNA damage response and repair; 4) selective removal of damaged non-functional and senescent cells. In the article, we have reviewed data about the effects of various trace elements, vitamins, polyphenols, terpenes, and other phytochemicals, as well as a number of synthetic pharmacological substances in these ways. Most of the compounds demonstrate the geroprotective potential and increase the lifespan in model organisms. However, their genome-protecting effects are non-selective and often are conditioned by hormesis. Consequently, the development of selective drugs targeting genome protection is an advanced direction.

On the Complexity of Mechanisms and Consequences of Chromothripsis: An Update

In the present review, we focus on the phenomenon of chromothripsis, a new type of complex chromosomal rearrangements. We discuss the challenges of chromothripsis detection and its distinction from other chromoanagenesis events. Along with already known causes and mechanisms, we introduce aberrant epigenetic regulation as a possible pathway to chromothripsis. We address the issue of chromothripsis characteristics in cancers and benign tumours, as well as chromothripsis inheritance in cases of its occurrence in germ cells, zygotes and early embryos. Summarising the presented data on different phenotypic effect of chromothripsis, we assume that its consequences are most likely determined not by the chromosome shattering and reassembly themselves, but by the genome regions involved in the rearrangement.

In vitro evaluation of cytotoxic and genotoxic effects of Di(2-ethylhexyl)-phthalate (DEHP) on European sea bass (Dicentrarchus labrax) embryonic cell line

Marine litter is extensively distributed in the marine environment, and plastic debris, of which litter is mostly composed, can be a major source of pollutants. Among them, Di(2-ethylhexyl)-phthalate (DEHP) is the most abundantly used plastic additive, and it has been reported to affect biochemical processes both in humans and wildlife; however, studies on its toxicological effects on marine organisms are still scarce. In this survey, we studied the cytotoxic, genotoxic, and mutagenic effects of DEHP in European sea bass embryonic cell line (DLEC) by applying specific in vitro tests. Results showed a significant decrease in cell viability starting at 0.01 mM of DEHP after 24 h together with a significant increase in apoptosis and necrosis, morphological changes and cell detachment. Consistently, we detected a moderate increase in DNA strand breaks from 0.02 mM, and a dose-dependent increase in of micronucleus frequency from 0.01 mM, accompanied by a significant inhibition of cell proliferation, which suggested a possible aneugenic effect of this phthalate. Our results demonstrate that in vitro exposure to DEHP had a dose-dependent cytotoxic and genotoxic effects in DLEC cell line, encouraging further investigation into its effects in in vivo and/or ex vivo cell systems of marine organisms.

Emerging Perspectives on DNA Double-strand Breaks in Neurodegenerative Diseases

DNA double-strand breaks (DSBs) are common events that were recognized as one of the most toxic lesions in eukaryotic cells. DSBs are widely involved in many physiological processes such as V(D)J recombination, meiotic recombination, DNA replication and transcription. Deregulation of DSBs has been reported in multiple diseases in human beings, such as the neurodegenerative diseases, with which the underlying mechanisms are needed to be illustrated. Here, we reviewed the recent insights into the dysfunction of DSB formation and repair, contributing to the pathogenesis of neurodegenerative disorders including Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD) and ataxia telangiectasia (A-T).