Non-duplex G-Quadruplex DNA Structure: A Developing Story from Predicted Sequences to DNA Structure-Dependent...

Area of Science:

• Molecular Biology
• Genetics
• Epigenetics

Background:

• The G-quadruplex (G4) is a non-canonical DNA structure initially found at telomeres and immunoglobulin switch regions.
• Computational predictions suggested a gene regulatory role for G4s, particularly in promoters, challenging the view of their genome-wide presence as mere accidents.

Purpose of the Study:

• To investigate the prevalence and evolutionary conservation of potential G4 (pG4) forming sequences in genomes.
• To explore the functional roles of G4s in gene expression, epigenetic modifications, and their connection to specific proteins.
• To understand the relationship between G4s at telomeres and gene promoters, and the influence of telomere length on G4-mediated gene regulation.

Main Methods:

• Bioinformatic analysis of pG4 sequences across different species' genomes.
• Treatment of human cancer cells with G4-binding ligands to observe gene expression changes.
• Identification and characterization of G4-interacting proteins, such as NM23-H2 and TRF2.
• Analysis of epigenetic modifications in relation to G4 structures and protein binding.

Main Results:

• Potential G4-forming sequences are conserved throughout evolution and prevalent in gene promoters.
• G4-binding ligands induce widespread gene expression changes in cancer cells.
• NM23-H2 interacts with G4s in promoter regions, regulating oncogene transcription (e.g., c-myc).
• TRF2 binds extensively to non-telomeric G4s, and its epigenetic gene regulation is telomere-length dependent.

Conclusions:

• G4s play a significant role in gene regulation and epigenetic modifications, intrinsically linked to DNA sequence and structure.
• The discovery of G4-interacting proteins like NM23-H2 contributes to defining the 'G4-transcriptome'.
• Telomere-associated factor TRF2 connects telomere length to G4-mediated epigenetic regulation at gene promoters, suggesting a unified explanation for G4 prevalence in these distinct genomic regions.