Gadd45a promotes DNA demethylation through TDG

Area of Science:

• Epigenetics
• Molecular Biology
• Genetics

Background:

• Growth arrest and DNA-damage-inducible protein 45 (Gadd45) family members are linked to DNA demethylation in vertebrates.
• The precise role of Gadd45 in the demethylation process remained unclear.

Purpose of the Study:

• To elucidate the mechanism by which Gadd45a contributes to active DNA demethylation.
• To investigate the interaction between Gadd45a and the DNA demethylation machinery.

Main Methods:

• Reporter gene assays in HEK293T cells to assess demethylation activity.
• Co-immunoprecipitation to study protein interactions between Gadd45a and thymine DNA glycosylase (TDG).
• Analysis of DNA methylation, 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC) levels in Gadd45a/b knockout mouse embryonic stem cells.

Main Results:

• Gadd45a enhances DNA demethylation mediated by TDG and Ten-eleven-translocation (Tet) enzymes.
• Gadd45a physically interacts with TDG and increases the removal of 5fC and 5caC by TDG.
• Gadd45a/Gadd45b knockout mouse ES cells exhibit hypermethylation at TDG target loci, with enrichment of 5fC.

Conclusions:

• Gadd45a promotes active DNA demethylation through its interaction with and enhancement of TDG activity.
• Gadd45a is integrated into the Tet-initiated oxidative DNA demethylation pathway.
• TDG activity is essential for the demethylation effects attributed to Gadd45a.