Hanawalt DNA Repair Mechanisms

1. Auflage 2012
ISBN: 978-0-323-14232-8
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 832 Seiten

DNA Repair Mechanisms is an account of the proceedings at a major international conference on DNA Repair Mechanisms held at Keystone, Colorado on February 1978. The conference discusses through plenary sessions the overall standpoint of DNA repair. The papers presented and other important documents, such as short summaries by the workshop session conveners, comprise this book. The compilation describes the opposing views, those that agree and dispute about certain topic areas. This book, divided into 15 parts, is arranged according to the proceedings in the conference. The plenary sessions are grouped with the related workshop and poster manuscripts. The first two parts generally tackle repair in terms of its identification and quantification, as well as the models, systems, and perspectives it utilizes. The following parts discuss the various types of repair including base excision, nucleotide excision repair in bacteria, excision repair in mammalian cells, inducible/error-prone repair in prokaryotes, and strand break repair in mammalian cells among others. This reference material looks into the replicative bypass mechanisms in mammalian cells, viral probes, and hereditary repair defects. It explains repair deficiency and human disease, as well as mutagenesis and carcinogenesis. The last part of this book deals with the consequences and effects of DNA repair. This volume is a helpful source of reference for students, teachers, scientists, and researchers in the different fields of genetics, radiology, biochemistry, and environmental biology.

Autoren/Hrsg.

Hanawalt, Philip

Leseproben

REPAIRABLE DAMAGE IN DNA1

Peter A. Cerutti,     Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610

ABSTRACT

Important contributions to the elucidation of the role of DNA repair for cell viability, mutagenesis, malignant transformation and cell degeneration are expected from experiments in which individual DNA lesions of known chemical structure are investigated. This is important in view of the high degree of complexity of the spectrum of lesions which is induced by most physical and chemical agents by and by via the intermediacy of active oxygen species. The formation of thymine damage in baby hamster kidney cells by indirect action was demonstrated for the chemical DNA damaging agents benzo(a)pyrene (B(a)P) and ascorbic acid/Cu2+. It is useful to characterize the biochemical properties of DNA lesions in terms of their and . As a start the excisability of several structurally related arylation products of guanine induced by B(a)P and N-acetoxy-acetylaminofluorene (N-acetoxy-AAF) was determined in the epitheloid human alveolar tumor line A549. The following decreasing scale of excisability was observed: B(a)P-4,5-epoxide adduct C2> B(a)P-4,5-epoxide adduct C1B(a)P-diol-epoxide II-deoxyguanosine > deacetylation product of “major” deoxyguanosine-AAF adduct > B(a)Pdiol-epoxide I-deoxyguanosine > “major” deoxyguanosine-AAF adduct “minor” deoxyguanosine-AAF adduct. For the B(a)P-deoxyguanosine adducts these results suggest an inverse relationship between the excisability of the lesions and the mutagenicity and toxicity of the B(a)P-metabolites by which they are induced in mammalian cells. The effect of the location of the lesions in chromatin on their excisability is discussed.

INTRODUCTION

The elucidation of the role of the repair of DNA damage in cell viability, mutagenesis, malignant transformation and cell degeneration represents a major goal in molecular toxicology. Important contributions to this goal are expected from experimental systems in which of known chemical structure can be investigated. The study of which induce a whole spectrum of lesions and the use of biochemical procedures which do not allow the distinction of individual lesions are less informative. The biochemical and biological effects resulting from the treatment of a cell with a DNA damaging agent are usually a composite of the expression of a multitude of lesions and it is often very difficult or impossible to dissect the contributions made by individual lesions. However, it is the chemical structure of the individual lesions, their abundance and distribution in the genome which determine the mode(s) of lesion processing and ultimately the biological endpoints in a particular cell. With the help of this knowledge it may become possible to analyze multiple lesion situations where lesion interaction may influence repairability and biological expression.

In this article I will first discuss lesion formation and point out the complexity of the spectrum of lesions which are formed in the DNA of intact cells by most physical and chemical damaging agents. I will then describe and define biochemical properties of DNA lesions and, as an example, I will review our present knowledge of the relative excisability of a series of structurally related arylation lesions of guanine. In a final paragraph I will discuss the effects which the intragenomic location of lesions may have on their repairability.

(1) FORMATION OF DNA LESIONS BY DIRECT AND INDIRECT ACTION

The list of DNA damaging agents is long and the list of DNA lesions which they produce is even longer. There is hardly an atom on the purine and pyrimidine rings of DNA which has not been shown to react with some physical or chemical damaging agent. Often it is possible to predict the type of lesions which are likely to be formed from basic chemical principles, e.g. a majority of ultimate chemical damaging agents possess electrophilic properties and react with the electron-rich centers of the heterocyclic bases in nucleophilic displacement reactions (1). Valuable information about the structure of DNA lesions can be obtained from experiments with mono- and polynucleotides but reliable data concerning the relative abundance and distribution of the lesions can only be obtained in experiments with intact cells. Most experiments with chemical agents use highly radioactive compounds in order to be able to detect the introduction of radioactive substituents on the DNA bases (or the backbone) at low levels of damage. However, an important class of DNA lesions escapes detection under these conditions. There are a number of chemical DNA damaging agents of considerable importance to biochemical and medical research which may exert at least part of their action via the formation of reactive oxygen species. Most of these agents, e.g. 4-nitroquinoline-N-oxide (2), streptonigrin(3), adriamycin, mitomycin C(4), benzo(a)pyrene (B(a)P) (5), possess or are metabolically activated to quinone-like structures. In many cell systems they can participate in one-electron redox cycles which lead to the formation of highly reactive oxygen radical species such as superoxide- and hydroxyl-radicals which are expected to induce DNA lesions of the type produced by radiation. Oxygen radical species may also be responsible for the chromosomal damage induced by ascorbic acid plus Cu2+. The formation of DNA strand-breakage by some of these agents has been clearly demonstrated in component, systems but not in intact cells where drug-induced breaks have to be distinguished from breaks introduced as a consequence of DNA repair.

Hydroxyl- and superoxide- radicals are formed as a consequence of water radiolysis by ionizing radiation. Hydroxyl radicals have been shown to induce thymine damage(8,9) and DNA strand breaks(10) in intact cells and they are mostly responsible for the lethal action of aerobic gamma- and x-rays(11). This type of radiation action which is mediated via oxygen radical species is referred to as “indirect action”. In contrast, energy deposition into the DNA target is referred to as “direct action” of ionizing radiation. Similarly, active oxygen species are also formed by far-ultraviolet light by water photolysis and by near–ultraviolet light by photodynamic action and photodissociation of hydrogen peroxide(12, 13). The type of DNA lesions formed by active oxygen species is expected to be closely related regardless of whether they are formed by ionizing radiation, ultraviolet light or in a redox system involving a chemical agent. Therefore, it may be useful to expand the terminology developed for ionizing radiation to include ultraviolet light and chemical agents and we are proposing the following definitions:

DIRECT ACTION: attack of DNA by the primary agent or a chemical derivative of the primary agent.

INDIRECT ACTION: (of ionizing radiation, ultraviolet radiation or a chemical) attack of DNA by active oxygen species which are formed by the reaction of the primary agent with a non-DNA target.

In general, direct action is expected to predominate for most chemical damaging agents and for far–ultraviolet light while indirect action represents the major intracellular reaction mechanism for ionizing radiation. There is great variation in the structure of DNA lesions induced by direct chemical action. In contrast, a similar spectrum of lesions is expected to be introduced by indirect action of physical and chemical agents. They include: single- and double–strand breaks, products of the 5,6-dihydroxy-dihydrothymine type, damage at the thymine - methyl group, damage involving the other DNA bases, DNA-DNA, DNA–RNA and DNA–protein cross links.

Evidence for indirect action of ultraviolet light and the chemical damaging agents ascorbic acid/Cu2+ and benzo-(a)pyrene (B(a)P) in intact mammalian cells has recently been obtained in our laboratory. The formation of products of the 5,6-dihydroxy-dihydrothymine type (tuv) and the abstraction of tritium from thymine–methyl [3H] was observed in HeLa cells upon irradiation with monochromatic light at 240, 260, 280, 313 and 365 nm. The efficiency of formation of tuv type products was comparable to thymine photodimerization in the near ultraviolet at 313nm(12). There is little doubt that these lesions are formed by indirect action of ultraviolet light. The formation of [3H]H2O in baby hamster kidney cells (BHK) which had been prelabeled in their DNA with thymine–methyl [3H] was observed upon treatment with 2×10-3M ascorbic acid/2×10-5M Cu2+. It was estimated that after 4 hours of incubation approximately 0.2% of all thymine–methyl groups had reacted with hydroxyl-radicals yielding 5-Methylene–uracil radicals and water (M. Ide and P. Cerutti, unpublished)....