Oxygen-Dependent Accumulation of Purine DNA Lesions in Cockayne Syndrome Cells

Abstract

Cockayne Syndrome (CS) is an autosomal recessive neurodegenerative premature aging disorder associated with defects in nucleotide excision repair (NER). Cells from CS patients, with mutations in CSA or CSB genes, present elevated levels of reactive oxygen species (ROS) and are defective in the repair of a variety of oxidatively generated DNA lesions. In this study, six purine lesions were ascertained in wild type (wt) CSA, defective CSA, wtCSB and defective CSB-transformed fibroblasts under different oxygen tensions (hyperoxic 21%, physioxic 5% and hypoxic 1%). In particular, the four 5′,8-cyclopurine (cPu) and the two 8-oxo-purine (8-oxo-Pu) lesions were accurately quantified by LC-MS/MS analysis using isotopomeric internal standards after an enzymatic digestion procedure. cPu levels were found comparable to 8-oxo-Pu in all cases (3–6 lesions/106 nucleotides), slightly increasing on going from hyperoxia to physioxia to hypoxia. Moreover, higher levels of four cPu were observed under hypoxia in both CSA and CSB-defective cells as compared to normal counterparts, along with a significant enhancement of 8-oxo-Pu. These findings revealed that exposure to different oxygen tensions induced oxidative DNA damage in CS cells, repairable by NER or base excision repair (BER) pathways. In NER-defective CS patients, these results support the hypothesis that the clinical neurological features might be connected to the accumulation of cPu. Moreover, the elimination of dysfunctional mitochondria in CS cells is associated with a reduction in the oxidative DNA damage.

How (5′S) and (5′R) 5′,8-Cyclo-2′-Deoxypurines Affect Base Excision Repair of Clustered DNA Damage in Nuclear Extracts of xrs5 Cells? A Biochemical Study

“…CdPus are repaired by NER, which is inhibited or not active in some scenarios, e.g., in mitochondria or diseases with defective NER such as Xeroderma pigmentosum , trichothiodystrophy, or Cockayne syndrome [ 14 , 15 , 16 , 17 , 18 , 19 ]. Interestingly, 5′R diastereomer is repaired more efficiently than 5′S for both, 5′,8-cyclo-2′-deoxyadenosine (cdA) and 5′,8-cyclo-2′-deoxyguanosine (cdG), indicating the biological importance of stereochemistry of cdPus [ 15 ].…”

(5′S) 5′,8-cyclo-2′-deoxyadenosine Cannot Stop BER. Clustered DNA Lesion Studies

“…Noteworthy, cdPus are removed from oligonucleosides by the Nucleotide Excision Repair (NER) system, not by BER, as no cdPu-specific glycosylases are known. The defect in the cellular NER system may lead to an accumulation of DNA damage sites, which causes various clinical manifestations (e.g., Xeroderma Pigmentosum , TrichoThioDystrophy, and Cockayne syndrome) [ 29 , 30 ]. Additionally, the 5′ R and 5′ S diastereomers of cdA strongly influence dU and AP-site incision by uracil-DNA glycosylase (UDG) and human AP-site endonuclease one (hAPE1).…”

Mechanisms of Genome Maintenance in Plants: Playing It Safe With Breaks and Bumps

“…For instance, UV-induced photo products such as pyrimidine dimers and 6-4 PPs that produce significant conformational changes in DNA are key substrates of NER. The serious human disorders caused by inborn genetic defects in NER proteins, such as xeroderma pigmentosum and Cockayne syndrome, demonstrate the significance of this repair process ( Lehmann et al, 2018 ; Krokidis et al, 2020 ). NER eliminates these adducts by making an incision on both sides of the adduct followed by the removal of this incised stretch of DNA through a helicase ( Marteijn et al, 2014 ).…”