Functional DNA demethylation is accompanied by chromatin accessibility.

Area of Science:

• Epigenetics
• Cancer Biology
• Chromatin Remodeling

Background:

• DNA methylation inhibitors like 5-aza-2'-deoxycytidine (5-Aza-CdR) are used for myelodysplastic syndrome.
• Global DNA demethylation occurs after 5-Aza-CdR treatment, but its effect on nucleosome occupancy is unclear.

Purpose of the Study:

• To investigate the extent to which DNA demethylation influences nucleosome occupancy.
• To identify potential epigenetic drivers of tumor suppressor gene reactivation in colorectal cancer.

Main Methods:

• Utilized HCT116 colorectal cancer cell line and DKO1 (a derivative engineered for DNA methyltransferase disruption).
• Assessed changes in nucleosome occupancy following 5-Aza-CdR treatment and compared with histone deacetylase inhibitor effects.

Main Results:

• Less than 2% of 5-Aza-CdR-demethylated regions showed altered nucleosome configuration (opened).
• Nucleosome retention was observed at sites of DNA methylation loss.
• Open regions in treated cells and DKO1 cells included promoters of tumor suppressors and under-expressed genes in colorectal cancer.

Conclusions:

• Only a small fraction of demethylated promoters undergo nucleosome remodeling.
• These specific remodeling events may be crucial epigenetic drivers for loss of tumorigenicity.
• Histone deacetylase inhibitors target different chromatin regions than 5-Aza-CdR, highlighting the need for combinatorial therapies.