DNA methylation shapes transcription factor binding beyond canonical CpG contexts

Area of Science:

• Epigenetics
• Molecular Biology
• Genomics

Background:

• Cytosine methylation is a crucial epigenetic mark regulating gene expression by influencing transcription factor (TF) binding.
• Current research primarily focuses on fully methylated CpG sites, overlooking the functional importance of non-CpG and hemimethylation, especially in stem cells and neurons.
• The precise effects of these alternative methylation patterns on TF-DNA interactions are not well understood due to limitations in existing assay methods.

Purpose of the Study:

• To systematically investigate the impact of various cytosine methylation contexts (CpG, non-CpG, hemimethylation) on the binding affinity and specificity of human TFs.
• To characterize how methylation state, position, and strand orientation influence TF-DNA interactions.
• To explore the in vivo relevance of identified methylation-sensitive TF binding sites within the genome.

Main Methods:

• Utilized chemically synthesized DNA libraries with position-specific 5-methylcytosines (5mC) in different methylation contexts.
• Employed high-throughput protein-binding microarrays to profile the binding of 18 human TFs from 11 structural families.
• Performed genomic analyses to assess the occurrence of methylation-sensitive sequences in regulatory elements across diverse cell types.

Main Results:

• Demonstrated extensive sensitivity of TFs to DNA methylation, including significant binding to non-CpG and hemimethylated sites.
• Observed that 5-methylcytosine can either enhance TF binding by creating new contacts or reduce it through steric hindrance, altering TF-DNA affinity.
• Identified methylation-sensitive sequences within genomic enhancers and regulatory elements, showing cell-type-specific methylation patterns.

Conclusions:

• Uncovered a significant, previously underappreciated layer of TF-DNA recognition influenced by diverse cytosine methylation patterns.
• Expanded the understanding of epigenetic regulation, highlighting the functional importance of non-CpG and hemimethylation in controlling gene transcription.
• Provided a foundation for further research into the complex interplay between DNA methylation and TF binding in various biological contexts.