Overexpression of enzymes that repair endogenous damage to DNA

Abstract

A significant contribution to human mutagenesis and carcinogenesis may come from DNA damage of endogenous, rather than exogenous, origin. Efficient repair mechanisms have evolved to cope with this. The main repair pathway involved in repair of endogenous damage is DNA base excision repair. In addition, an important contribution is given by O 6 -alkylguanine DNA alkyltranferase, that repairs specifically the miscoding base O 6 -alkylguanine. In recent years, several attempts have been carried out to enhance the efficiency of repair of endogenous damage by overexpressing in mammalian cells single enzymatic activities. In some cases (e.g. O 6 -alkylguanine DNA alkyltransferase or yeast AP endonuclease) this approach has been successful in improving cellular protection from endogenous and exogenous mutagens, while overexpression of other enzymatic activities (e.g. alkyl N-purine glycosylase or DNA polymerase b) were detrimental and even produced a genome instability phenotype. The reasons for these different outcomes are analyzed and alternative enzymatic activities whose overexpression may improve the efficiency of repair of endogenous damage in human cells are proposed.Keywords: DNA repair; endogenous damage; O 6 -alkylguanine DNA alkyltransferase; oxidation; methylation; abasic sites; DNA base excision repair; rate-limiting step; transfection.A significant portion of carcinogenic events may be due to genetic damage of endogenous, rather than environmental, origin. Most endogenous damage originates from products of oxygen dismetabolism (so called reactive oxygen species), from the intrinsic lability of chemical bonds in DNA, from endogenous methylating agents or from DNA replication errors. Several mechanisms have evolved in humans to repair damage to DNA. We have known for several years that, should the repair of damage induced by sunlight be defective (as in the case of the hereditary disorder xeroderma pigmentosum), the probability of skin cancer is increased. [17,18] have appeared in recent years. The aim of this review is to survey and analyze the potential to increase the protective role of repair of endogenous damage against spontaneous mutagenesis and carcinogenesis. In those cases in which data are scant or unavailable, the survey will extend to protection from induced mutagenesis and carcinogenesis. E N D O G E N O U S D A M A G EEndogenous damage affects the primary, rather than the secondary, structure of the double helix. Four general classes of modifications can be envisaged. OxidationThis is due mainly to byproducts of oxygen metabolism and is the subject of current intensive investigation, as some oxidized bases have been shown to be miscoding and formed in huge amounts under physiological conditions [e.g. 8-oxo-7,8-dihydroguanine (8-oxoG), thymine glycol and similar oxidized bases]. Perhaps the most abundant and dangerous of these lesions is 8-oxoG, which frequently mispairs with adenine [2,3]. It has been calculated that approximately 7500 8-oxoG lesions may form daily in a mammalian cell (< 5% ...

Synergic effect of polymorphisms inERCC65′ flanking region andcomplement factor Hon age-related macular degeneration predisposition

“…ERCC6 functions in DNA repair, regardless of whether the repair is transcription coupled or base incision, as a partner in protein complexes (30,40). It has been reported that overexpression of just one element in an enzyme complex can adversely affect the desired end result (41)(42)(43)(44)(45). Even though a statistically identified epistasis does not necessarily mean a biological epistasis (24), prolonged enhanced expression of ERCC6 could result in significant biological epistasis because ERCC6 is known to play an important role in universal transcription by functioning as a component of RNA pol I transcription complex (40).…”

Elevated oxidative stress and DNA damage and repair levels in urinary bladder carcinomas associated with schistosomiasis

“…11,12 Carcinomas result from a progressive accumulation of multiple genetic changes in cells, 13 and there is increasing evidence that endogenous DNA damage is a major etiological factor in human cancers. 14,15 At low concentrations, reactive oxygen species (ROSs) act as intra and intercellular second messengers modulating cellular functions including proliferation, apoptosis and gene expression. 16 When ROSs are produced in excess, as in macrophages and polymorphonuclear cells with microbial infections, 17 they are able to induce oxidatively generated DNA damage, 18 an independent risk factor for cancer often involving p53 gene mutations in humans.…”

Accelerated repair and reduced mutagenicity of oxidative DNA damage in human bladder cells expressing the E. coli FPG protein

“…7,8 The threat to genome integrity represented by oxidized purines could be reduced in human cells by expression of efficient repair activities obtained from heterologous sources. 9 The E. coli formamidopyrimidine DNA glycosylase (FPG) protein differs from hOGG1 under several aspects. hOGG1 only excises from DNA 8-oxoG and FapyG, while FPG fastly releases 8-oxoG, FapyG and FapyA with similar excision kinetics.…”