DNA damage, repair and the improvement of cancer therapy - A tribute to the life and research of Barbara Tudek

Professor Barbara Tudek received the Frits Sobels Award in 2019 from the European Environmental Mutagenesis and Genomics Society (EEMGS). This article presents her outstanding character and most important lines of research. The focus of her studies covered alkylative and oxidative damage to DNA bases, in particular mutagenic and carcinogenic properties of purines with an open imidazole ring and 8-oxo-7,8-dihydroguanine (8-oxoGua). They also included analysis of mutagenic properties and pathways for the repair of DNA adducts of lipid peroxidation (LPO) products arising in large quantities during inflammation. Professor Tudek did all of this in the hope of deciphering the mechanisms of DNA damage removal, in particular by the base excision repair (BER) pathway. Some lines of research aimed at discovering factors that can modulate the activity of DNA damage repair in hope to enhance existing anti-cancer therapies. The group's ongoing research aims at deciphering the resistance mechanisms of cancer cell lines acquired following prolonged exposure to photodynamic therapy (PDT) and the possibility of re-sensitizing cells to PDT in order to increase the application of this minimally invasive therapeutic method.

ERCC1-deficient cells and mice are hypersensitive to lipid peroxidation

Lipid peroxidation (LPO) products are relatively stable and abundant metabolites, which accumulate in tissues of mammals with aging, being able to modify all cellular nucleophiles, creating protein and DNA adducts including crosslinks. Here, we used cells and mice deficient in the ERCC1-XPF endonuclease required for nucleotide excision repair and the repair of DNA interstrand crosslinks to ask if specifically LPO-induced DNA damage contributes to loss of cell and tissue homeostasis. Ercc1^-/- mouse embryonic fibroblasts were more sensitive than wild-type (WT) cells to the LPO products: 4-hydroxy-2-nonenal (HNE), crotonaldehyde and malondialdehyde. ERCC1-XPF hypomorphic mice were hypersensitive to CCl₄ and a diet rich in polyunsaturated fatty acids, two potent inducers of endogenous LPO. To gain insight into the mechanism of how LPO influences DNA repair-deficient cells, we measured the impact of the major endogenous LPO product, HNE, on WT and Ercc1^-/- cells. HNE inhibited proliferation, stimulated ROS and LPO formation, induced DNA base damage, strand breaks, error-prone translesion DNA synthesis and cellular senescence much more potently in Ercc1^-/- cells than in DNA repair-competent control cells. HNE also deregulated base excision repair and energy production pathways. Our observations that ERCC1-deficient cells and mice are hypersensitive to LPO implicates LPO-induced DNA damage in contributing to cellular demise and tissue degeneration, notably even when the source of LPO is dietary polyunsaturated fats.

Catalytic activities of Werner protein are affected by adduction with 4-hydroxy-2-nonenal

4-Hydroxy-2-nonenal (HNE) is a reactive α,β-unsaturated aldehyde generated during oxidative stress and subsequent peroxidation of polyunsaturated fatty acids. Here, Werner protein (WRN) was identified as a novel target for modification by HNE. Werner syndrome arises through mutations in the WRN gene that encodes the RecQ DNA helicase which is critical for maintaining genomic stability. This hereditary disease is associated with chromosomal instability, premature aging and cancer predisposition. WRN appears to participate in the cellular response to oxidative stress and cells devoid of WRN display elevated levels of oxidative DNA damage. We demonstrated that helicase/ATPase and exonuclease activities of HNE-modified WRN protein were inhibited both in vitro and in immunocomplexes purified from the cell extracts. Sites of HNE adduction in human WRN were identified at Lys577, Cys727, His1290, Cys1367, Lys1371 and Lys1389. We applied in silico modeling of the helicase and RQC domains of WRN protein with HNE adducted to Lys577 and Cys727 and provided a potential mechanism of the observed deregulation of the protein catalytic activities. In light of the obtained results, we postulate that HNE adduction to WRN is a post-translational modification, which may affect WRN conformational stability and function, contributing to features and diseases associated with premature senescence.

[Cytofluorometric analysis of chosen markers of apoptosis CD95/CD95L (Fas/FasL) in thyroid tissues from young patients with Graves' disease and Hashimoto's thyroiditis]

BACKGROUND

Apoptosis, one of the forms of programmed cell death, is a physiologic process of cell death that is central to normal development and occurs in response to a variety of physiologic and pathophysiologic stimuli. In the thyroid, abnormal apoptotic activity may be involved in a variety of diseases such as Hashimoto thyroiditis and Graves disease. The aim of this study was to estimate the expression of chosen apoptotic molecules CD95 (Fas) and CD95L (FasL) on the surface of thyroid follicular cells in application of mouse monoclonal antibodies #64 which recognized B antigen regions of thyroid peroxidase (TPO) and infiltrating inflammatory cells.

MATERIAL AND METHODS

The investigation was performed on thyroid cells isolated from surgically treated thyroid tissues of 15 patients with Graves' disease (GD), 15 patients with a nontoxic multinodular goiter (NTMG) and 15 aspirates obtained by FNAB from patients with Hashimoto thyroiditis (HT). The thyrocytes were identified by an indirect method: in the first stage we added mouse monoclonal autoantibodies specific for TPO (mAb #64) regions and in the second stage we conjugated this complex with rabbit anti-mouse antibodies IgG (Fab')2 with FITC. In the next step the cellular suspension was completed with suitably well-chosen two-colour monoclonal antibodies marked (PE or PerCP) (Becton Dickinson) directed against suitable apoptotic (Fas/FasL) molecules. All investigations were performed by flow cytometry using Coulter EPICS XL apparatus.

RESULTS

The percentages of thyroid cells were estimated with expression of region B antigenic TPO in reference to individual apoptotic molecules. The analysis of Fas and FasL expression in thyroid tissues revealed significantly increased percentage of intrathyroidal T cells with CD95+ (p<0.005, p<0.001), CD95L+ (p<0.02, p<0.01) and both CD95/CD95L (ns, p<0.05) expression in comparison to percentages of T cells in patients with HT and NTMG. In addition, on the surface of thyroid follicular cells in patients with GD (p<0.01, p<0.01) and NTMG (p<0.001, p<0.004) we observed a lower percentage of thyrocytes with CD95 and CD95L molecules than in cases with HT. The expression of both apoptotic molecules on thyroid cells was higher (18%) in patients with HT in comparison to the percentages of positive cells in patients with GD (p<0.02, p<0.002) and NTMG, 8% and 1%, respectively.

CONCLUSIONS

We conclude that alterations in the expression of death receptors and their ligands on the surface of thyroid follicular cells may play a role in the regulation of apoptosis in thyroid autoimmune disorders.