A global DNA repair mechanism involving the Cockayne syndrome B (CSB) gene product can prevent the in vivo accumulation of endogenous oxidative DNA base damage

Abstract

The Cockayne syndrome B (CSB) gene product is involved in the repair of various types of base modifications in actively transcribed DNA sequences. To investigate its significance for the repair of endogenous oxidative DNA damage, homozygous csb 7/7 /ogg1 7/7 double knockout mice were generated. These combine the deficiency of CSB with that of OGG1, a gene coding for the mammalian repair glycosylase that initiates the base excision repair of 7,8-dihydro-8-oxoguanine (8-oxoG). Compared to ogg1 7/7 mice, csb 7/7 /ogg1 7/7 mice were found to accumulate with age severalfold higher levels of oxidited purine modifications in hepatocytes, splenocytes and kidney cells. In contrast, the basal (steady-state) levels of oxidative DNA modifications in cells from csb 7/7 mice were not different from those in wild-type mice and did not increase with age. The analysis of the repair rates of additional oxidative DNA base modifications induced by photosensitization in immortalized embryonic fibroblasts was in accordance with these findings: compared to wild-type cells, the global repair was only slightly affected in csb 7/7 cells, more compromised in ogg1 7/7 cells, but virtually absent in csb 7/7 /ogg1 7/7 cells. An inhibition of transcription by a-amanitin did not block the Csbdependent repair in ogg1 7/7 fibroblasts. The influence of Csb on the global repair of 8-oxoG was not detectable in assays with total protein extracts and in a shuttle vector system. The data indicate a role for Csb in the removal of 8-oxoG from the overall genome that is independent of both Ogg1-mediated base excision repair and regular transcription.

The role of CSA in the response to oxidative DNA damage in human cells

“…The similar impairment of 8-OH-Gua repair reported in the absence of CSB (reviewed by Licht et al, 2003) or CSA (this study) suggests that these proteins act in the same pathway. We favor the hypothesis that the acceleration of repair at early repair times mediated by CSB (Osterod et al, 2002) or CSA (this study) reflects the role of CS proteins in the regulation of chromatin structure (for instance by ubiquitination and/or acetylation of histones) (Citterio et al, 2000;Groisman et al, 2003;Newman et al, 2006). CS-mediated chromatin remodeling activity might increase the accessibility of DNA damage to the repair machinery.…”

“…However, the defect of CS-B cells in oxidative damage response extends beyond the level of TCR. CS-B human and murine cells are hypersensitive to ionizing radiation (IR) and other oxidants (Tuo et al, 2001;de Waard et al, 2003) and are impaired in the repair of oxidatively induced DNA lesions (Dianov et al, 1999;Tuo et al, 2001Tuo et al, , 2003Osterod et al, 2002). Whether CSA is involved in oxidative DNA damage response is still an open question.…”

The role of Cockayne Syndrome group B (CSB) protein in base excision repair and aging

“…CSB also stimulates the expression of mtOGG1, but it has not yet been possible to demonstrate that the CSB protein is actually present in mitochondria. Finally, data from Epe and coworkers suggests that CSB may play a role in an OGG1 independent removal of 8-oxoG from the general genome (Osterod et al, 2002).…”

“…It is argued that the TCR deficiency of oxidative damage could be responsible for the progressive neurological disorders seen in CS patients (de Waard et al, 2003;Laposa et al, 2007;Osterod et al, 2002;Pastoriza-Gallego et al, 2007). This area of study has been filled with controversy, but one model proposes that the TCR of oxidative damage would be due to the arrest of RNA polymerases at oxidative DNA base lesions.…”

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).…”