Accumulation of true single strand breaks and AP sites in base excision repair deficient cells

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Single-strand breaks (SSBs) are common DNA lesions.
• Existing alkaline assays for SSBs often yield false positives due to alkali-labile sites.
• Methoxyamine, an acidic O-hydroxylamine, can detect DNA damage but requires neutralization.

Purpose of the Study:

• To develop a convenient and specific assay for detecting DNA single-strand breaks (SSBs).
• To overcome limitations of existing alkaline-based SSB detection methods.
• To investigate DNA damage in polymerase beta null cells.

Main Methods:

• Development of a novel OTX-AGE assay using a neutral O-hydroxylamine (OTX).
• OTX stabilizes abasic (AP) sites, preventing alkaline incision while allowing DNA denaturation.
• Application of the OTX-AGE assay to DT40 and polymerase beta null cells exposed to methyl methanesulfonate (MMS).
• Validation using NAD(P)H depletion assay and ARP-slot blot assay for AP sites.

Main Results:

• The OTX-AGE assay successfully detected time-dependent increases in SSBs in both cell lines.
• Polymerase beta null cells exhibited more extensive SSB formation compared to parental cells.
• MMS exposure led to a significant, time-dependent increase in AP sites, with higher levels in Pol beta null cells.
• Findings were corroborated by NAD(P)H depletion and ARP-slot blot assays.

Conclusions:

• OTX-AGE is a facile and specific method for assessing SSB formation, overcoming false positives from alkali-labile sites.
• The assay is applicable to various cell types and DNA damaging agents.
• Polymerase beta plays a role in repairing DNA damage, as evidenced by increased SSBs and AP sites in null cells.