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Histone tails decrease N7-methyl-2'-deoxyguanosine depurination and yield DNA-protein cross-links in nucleosome core
Kun Yang1, Daeyoon Park2, Natalia Y Tretyakova3
1Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218.
Summary
Monofunctional alkylating agents create DNA damage, forming histone-DNA cross-links and slowing abasic site formation within nucleosomes. These DNA-protein cross-links may contribute to the cytotoxicity of these agents.
Area of Science:
- Molecular Biology
- DNA Damage and Repair
- Epigenetics
Background:
- Monofunctional alkylating agents alkylate DNA primarily at the N7 position of 2'-deoxyguanosine.
- Methylated DNA lesions, like N7-methyl-2'-deoxyguanosine (MdG), are persistent and primarily thought to lead to abasic (AP) site formation.
- The reactivity and biological consequences of MdG within the nucleosome structure are not fully understood.
Purpose of the Study:
- To investigate the reactivity of N7-methyl-2'-deoxyguanosine (MdG) within nucleosome core particles (NCPs).
- To determine the impact of histone proteins on MdG depurination and cross-linking.
- To explore the potential role of these interactions in the cytotoxicity of alkylating agents.
Main Methods:
- Studied MdG reactivity in isolated nucleosome core particles (NCPs) and free DNA.
- Utilized histone variants to identify the role of charged amino acids in modulating MdG reactivity.
- Employed mass spectrometry to detect histone-MdG cross-links in cellular chromatin.
Main Results:
- MdG depurination is significantly slower in NCPs compared to free DNA, with rate reduction correlating to proximity to histone tails.
- Positively charged amino acids within histone tails are responsible for decreasing the abasic site formation rate from MdG.
- Histone tails form reversible DNA-protein cross-links (DPCs) with MdG at the C8 position, which were also detected in MMS-treated cells.
- These processes were observed in randomly damaged NCPs, indicating they are general mechanisms.
Conclusions:
- Nucleosome structure, particularly histone tails, modulates the repair pathway of alkylated DNA by slowing depurination.
- Formation of DNA-protein cross-links between histones and MdG is a novel, previously unreported consequence of monofunctional alkylating agents.
- These DPCs may represent a significant, uncharacterized contributor to the cytotoxicity of common alkylating agents like MMS and temozolomide.