Removal of oxygen free-radical-induced 5′,8-purine cyclodeoxynucleosides from DNA by the nucleotide excision-repair pathway in human cells

Abstract

Exposure of cellular DNA to reactive oxygen species generates several classes of base lesions, many of which are removed by the base excision-repair pathway. However, the lesions include purine cyclodeoxynucleoside formation by intramolecular crosslinking between the C-8 position of adenine or guanine and the 5 position of 2-deoxyribose. This distorting form of DNA damage, in which the purine is attached by two covalent bonds to the sugarphosphate backbone, occurs as distinct diastereoisomers. It was observed here that both diastereoisomers block primer extension by mammalian and microbial replicative DNA polymerases, using DNA with a site-specific purine cyclodeoxynucleoside residue as template, and consequently appear to be cytotoxic lesions. Plasmid DNA containing either the 5 R or 5 S form of 5 ,8-cyclo-2-deoxyadenosine was a substrate for the human nucleotide excision-repair enzyme complex. The R diastereoisomer was more efficiently repaired than the S isomer. No correction of the lesion by direct damage reversal or base excision repair was detected. Dual incision around the lesion depended on the core nucleotide excision-repair protein XPA. In contrast to several other types of oxidative DNA damage, purine cyclodeoxynucleosides are chemically stable and would be expected to accumulate at a slow rate over many years in the DNA of nonregenerating cells from xeroderma pigmentosum patients. High levels of this form of DNA damage might explain the progressive neurodegeneration seen in XPA individuals.endogenous DNA lesions ͉ xeroderma pigmentosum ͉ neurodegeneration

Dynamic two-stage mechanism of versatile DNA damage recognition by xeroderma pigmentosum group C protein

“…The same excision system eliminates other intrastrand crosslinks, produced for example by the antitumor drug cisplatin, and a wide diversity of bulky carcinogen-DNA adducts. In addition, this versatile reaction eliminates a subset of oxidative base lesions like 8,5'-cyclopurine nucleosides, which are not amenable to excision by DNA glycosylases [5,6], as well as DNA adducts formed from lipid peroxidation products such as malondialdehyde [7]. A common feature of these different lesions channeled into the same repair pathway is their ability to cause helical distortions, leading to abnormal oscillations of non-hydrogenbonded nucleotides primarily in the undamaged strand [8].…”

“…Many core factors participating in the GGR reaction are encoded by genes that, when mutated, give rise to xeroderma pigmentosum (XP), an autosomal recessive disorder characterized by photosensitivity, skin atrophy, hyperpigmentation and sunlightinduced skin cancer [1,2]. XP patients also have an increased risk of developing internal tumors and the disease is often associated with neurological manifestations attributable to 5 oxidative damage [5][6][7]. Indeed, various clinical and pathological features of XP patients are similar to those seen in elderly people and, hence, reflect premature aging triggered by the accumulation of unrepaired DNA lesions [11].…”

Effects of NQO1 deficiency on levels of cyclopurines and other oxidative DNA lesions in liver and kidney of young mice

“…19,22,23 Cyclopurines in DNA block mammalian DNA and RNA polymerases, 19,[22][23][24] suggesting that they have significant pathologic consequences in vivo. Because of the presence of the 8,5Ј-covalent bond between the sugar and purine moieties, cyclopurines can be repaired by NER, albeit inefficiently, but not by BER or direct reversal.…”

“…19,22 This type of DNA damage is repaired poorly by NER and not at all by BER. 19,22,23 cA strongly suppresses gene expression in CHO and human cells [22][23][24] and is repaired extremely poorly in NER-deficient CHO cells and in patients with XP, a genetic disease with defective NER. 22,24,25 NQO1 (formerly known as DT diaphorase) is a flavoprotein which catalyzes 2-electron reduction and detoxification of quinones and its derivatives, thereby protecting cells from redox cycling, oxidative stress, mutagenicity and cytotoxicity induced by quinones and its precursors.…”

Clinical implications of the basic defects in Cockayne syndrome and xeroderma pigmentosum and the DNA lesions responsible for cancer, neurodegeneration and aging

“…A recent suggestion that RNA pol II is a universal sensor of DNA damage (Lindsey-Boltz and Sancar, 2007) blurs the distinction between TCR and global repair. The neurological symptoms of CS patients have been ascribed to defective repair in the brain of endogenous oxidative damage that blocks transcription (Kuraoka et al, 2000;Osterod et al, 2002;de Waard et al, 2003;Kyng et al, 2003;Tuo et al, 2003;Cline et al, 2004), but the more common oxidative base damages (8-oxo-G, 5-hydroxycytosine, thymine glycols) do not block transcription and are therefore not the culprits in neurodegeneration (Kathe et al, 2004). CSA and CSB cells are however different in their responses to oxidative damage, despite overlap in clinical symptoms (de Waard et al, 2004;D'Errico et al, 2007).…”