DNA Damage in Nijmegen Breakage Syndrome Cells Leads to PARP Hyperactivation and Increased Oxidative Stress

Harald Krenzlin,Martin Digweed,Petra Wessendorf,Alexander Bürkle,Kathrin Weidele,Bastian Salewsky,Ilja Demuth

doi:10.1371/journal.pgen.1002557

Harald Krenzlin, Martin Digweed + Show 5 more

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https://doi.org/10.1371/journal.pgen.1002557

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Abstract

Nijmegen Breakage Syndrome (NBS), an autosomal recessive genetic instability syndrome, is caused by hypomorphic mutation of the NBN gene, which codes for the protein nibrin. Nibrin is an integral member of the MRE11/RAD50/NBN (MRN) complex essential for processing DNA double-strand breaks. Cardinal features of NBS are immunodeficiency and an extremely high incidence of hematological malignancies. Recent studies in conditional null mutant mice have indicated disturbances in redox homeostasis due to impaired DSB processing. Clearly this could contribute to DNA damage, chromosomal instability, and cancer occurrence. Here we show, in the complete absence of nibrin in null mutant mouse cells, high levels of reactive oxygen species several hours after exposure to a mutagen. We show further that NBS patient cells, which unlike mouse null mutant cells have a truncated nibrin protein, also have high levels of reactive oxygen after DNA damage and that this increased oxidative stress is caused by depletion of NAD+ due to hyperactivation of the strand-break sensor, Poly(ADP-ribose) polymerase. Both hyperactivation of Poly(ADP-ribose) polymerase and increased ROS levels were reversed by use of a specific Poly(ADP-ribose) polymerase inhibitor. The extremely high incidence of malignancy among NBS patients is the result of the combination of a primary DSB repair deficiency with secondary oxidative DNA damage.

Highlights

Genetic cancer susceptibility disorders, such as Xeroderma pigmentosum and Fanconi anemia, generally have deficiencies in DNA repair and cell cycle regulation leading to tumour initiation
Evolution has led to highly complex networks of DNA repair enzymes, which for the majority of individuals are extremely effective in keeping our DNA intact
Several genetic disorders can be attributed to such DNA repair deficiencies and have the common feature of increased tumor incidence as the major life-threatening symptom

Summary

Introduction

Genetic cancer susceptibility disorders, such as Xeroderma pigmentosum and Fanconi anemia, generally have deficiencies in DNA repair and cell cycle regulation leading to tumour initiation. The specific mutagen sensitivities underlying these disorders define a set of enzymes and pathways involved in the DNA damage response. These pathways clearly overlap and components in one pathway can be critically involved in another. The nucleotide excision repair pathway mutated in Xeroderma pigmentosum is required for the repair of interstrand crosslinks, to which Fanconi anemia patient cells are sensitive [1]. The proteins mutated in these four disorders are all involved in the sensing and repair of DNA double-strand breaks (DSB). It has been repeatedly shown that AT patient cells and knockout mice have increased oxidative stress [2,3,4] which could contribute to clinical progression of the disease

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