Sequence-specific DNA binding by MYC/MAX to low-affinity non-E-box motifs

Area of Science:

• Molecular Biology
• Genomics
• Cancer Biology

Background:

• The MYC oncoprotein is a transcription factor crucial for cell growth and proliferation.
• MYC functions as a heterodimer with MAX, binding to Enhancer box (E-box) DNA sequences.
• Previous studies suggested MYC:MAX binds DNA non-specifically, recognizing E-box variants.

Purpose of the Study:

• To identify additional non-canonical DNA binding sites for MYC:MAX.
• To characterize the binding affinity and sequence specificity of MYC:MAX.
• To understand the impact of MYC levels on DNA binding in vivo.

Main Methods:

• High-throughput in vitro protein-binding microarrays.
• Electrophoretic mobility-shift assays (EMSAs).
• Bioinformatic analyses of MYC-bound genomic loci in vivo.

Main Results:

• Identified hexameric motifs preferentially bound by MYC/MAX, including the low-affinity sequence AACGTT.
• Found that 87% of MYC-bound genomic sites contain top MYC:MAX-bound motifs.
• Demonstrated that high MYC/MAX concentrations are required for binding to low-affinity sites, and elevated MYC levels preferentially increase occupancy at these sites.

Conclusions:

• MYC binds diverse DNA motifs with a broad range of affinities in a sequence-specific and dose-dependent manner.
• MYC overexpression may have more selective effects on the tumor transcriptome than previously assumed.
• These findings refine our understanding of MYC's transcriptional regulatory network in cancer.