Abstract
Cockayne syndrome protein B (CSB) is an ATP-dependent chromatin remodeler that relieves oxidative stress by regulating DNA repair and transcription. CSB is proposed to participate in base-excision repair (BER), the primary pathway for repairing oxidative DNA damage, but exactly how CSB participates in this process is unknown. It is also unclear whether CSB contributes to other repair pathways during oxidative stress. Here, using a patient-derived CS1AN-sv cell line, we examined how CSB is targeted to chromatin in response to menadione-induced oxidative stress, both globally and locus-specifically. We found that menadione-induced, global CSB-chromatin association does not require CSB's ATPase activity and is, therefore, mechanistically distinct from UV-induced CSB-chromatin association. Importantly, poly(ADP-ribose) polymerase 1 (PARP1) enhanced the kinetics of global menadione-induced CSB-chromatin association. We found that the major BER enzymes, 8-oxoguanine DNA glycosylase (OGG1) and apurinic/apyrimidinic endodeoxyribonuclease 1 (APE1), do not influence this association. Additionally, the level of γ-H2A histone family member X (γ-H2AX), a marker for dsDNA breaks, was not increased in menadione-treated cells. Therefore, our results support a model whereby PARP1 localizes to ssDNA breaks and recruits CSB to participate in DNA repair. Furthermore, this global CSB-chromatin association occurred independently of RNA polymerase II-mediated transcription elongation. However, unlike global CSB-chromatin association, both PARP1 knockdown and inhibition of transcription elongation interfered with menadione-induced CSB recruitment to specific genomic regions. This observation supports the hypothesis that CSB is also targeted to specific genomic loci to participate in transcriptional regulation in response to oxidative stress.
Highlights
Cockayne syndrome protein B (CSB) is an ATP-dependent chromatin remodeler that relieves oxidative stress by regulating DNA repair and transcription
We found that poly(ADP-ribose) polymerase 1 (PARP1), a CSB-binding protein, which responds to both single- and double-strand DNA breaks [35, 40], enhances the kinetics of global CSB– chromatin association induced by oxidative stress (Fig. 5)
As we observed no apparent increase in the level of ␥-H2AX, a marker for DNA double-strand breaks, in cells treated for 30 min with menadione (Fig. 1A), these results together support the notion that PARP1 functions in the recruitment of CSB to ssDNA breaks upon oxidative stress (Fig. 7A)
Summary
Poly(ADP-ribose) polymerase 1 (PARP1) promotes oxidative stress–induced association of Cockayne syndrome group B protein with chromatin. Our results support a model whereby PARP1 localizes to ssDNA breaks and recruits CSB to participate in DNA repair This global CSB– chromatin association occurred independently of RNA polymerase II–mediated transcription elongation. Unlike global CSB– chromatin association, both PARP1 knockdown and inhibition of transcription elongation interfered with menadione-induced CSB recruitment to specific genomic regions. This observation supports the hypothesis that CSB is targeted to specific genomic loci to participate in transcriptional regulation in response to oxidative stress. We found that CSB and CTCF reciprocally regulate each other’s site-specific chromatin association in response to oxidative stress and that these two proteins interact directly [20]. We further characterized the mechanisms by which CSB stably associates with chromatin, both globally and locus-in response to oxidative stress
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