Oxidative stress-mediated epigenetic regulation by G-quadruplexes

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Guanine (G)-rich sequences form G-quadruplex structures, regulating cancer-associated genes.
• These G-quadruplexes are susceptible to oxidative damage, repaired by base excision repair (BER) glycosylases.
• Oxidation within G-quadruplexes impacts gene expression.

Purpose of the Study:

• To investigate how oxidation of guanosine in promoter G-quadruplexes affects gene expression.
• To elucidate the role of the base excision repair pathway, particularly AP endonuclease 1 (APE1/REF1), in this process.

Main Methods:

• In vitro biophysical studies.
• Whole-genome analyses.
• Reporter plasmid assays in cellulo.
• Investigating the interplay between G-quadruplex structure, oxidative damage, and BER.

Main Results:

• Oxidation of guanosine in promoter G-quadruplexes can lead to gene expression up- or downregulation, dependent on location and strand.
• The base excision repair pathway, with a key role for the apurinic (AP) site intermediate and APE1/REF1, mediates these effects.
• APE1/REF1's nuclease activity is paused at G-quadruplexes, while its REF1 function interacts with transcription factors (HIF-1α, AP-1, p53).
• Oxidative stress significantly enhances the regulatory impact of G-rich sequences.

Conclusions:

• G-quadruplexes in gene promoters are sensitive regulatory elements affected by oxidative damage.
• The BER pathway, particularly APE1/REF1, is crucial for mediating gene expression changes induced by oxidative lesions in G-quadruplexes.
• APE1/REF1 acts as a molecular switch, integrating DNA damage signaling with transcriptional regulation.