Triplex structures induce DNA double strand breaks via replication fork collapse in NER deficient cells

Area of Science:

• Genetics
• Molecular Biology
• DNA Repair

Background:

• DNA structural alterations can impede replication fork stability, leading to DNA damage and genomic instability.
• Polypurine mirror repeat sequences form endogenous triplex structures, triggering DNA damage responses.
• Nucleotide excision repair (NER) proteins are implicated in recognizing and repairing DNA triplex structures.

Purpose of the Study:

• To investigate the impact of chromosomal triplex structures on DNA replication fork progression.
• To determine the role of NER proteins, specifically XPA and XPC, in processing triplex-induced DNA damage.
• To elucidate the mechanisms by which cells respond to triplex-induced genomic instability.

Main Methods:

• Utilized triplex-forming oligonucleotides to induce chromosomal triplexes in cells.
• Assessed DNA replication fork progression and double-strand break (DSB) induction.
• Compared DSB accumulation in NER-proficient versus NER-deficient (XPA, XPC) cells.
• Investigated the role of H2AX phosphorylation in apoptosis signaling.

Main Results:

• Chromosomal triplexes perturb DNA replication forks, leading to fork collapse and DSBs.
• NER-deficient cells, particularly XPC-deficient cells, accumulate more DSBs in the presence of triplexes.
• Apoptosis, mediated by H2AX phosphorylation, can mitigate the deleterious effects of triplex-induced genomic instability in the absence of XPA or XPC.

Conclusions:

• Damage recognition by XPC and XPA is essential for maintaining replication fork integrity.
• XPC and XPA play critical roles in preventing replication fork collapse induced by DNA triplexes.
• NER proteins are vital for preventing genomic instability arising from endogenous DNA triplex structures.