A new mode of DNA binding distinguishes Capicua from other HMG-box factors and explains its mutation patterns in...

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• HMG-box proteins, such as Sox and TCF, bind DNA weakly via their HMG-box domain.
• Distinct auxiliary mechanisms are employed by these factors to enhance DNA binding affinity and specificity.
• Capicua (CIC) is an HMG-box transcriptional repressor involved in Ras/MAPK signaling and cancer.

Purpose of the Study:

• To investigate the DNA-binding mechanism of Capicua (CIC) proteins.
• To determine if the HMG-box alone mediates CIC DNA binding.
• To elucidate the role of other CIC domains in DNA sequence recognition.

Main Methods:

• Biochemical assays to assess DNA binding of CIC domains.
• Site-directed mutagenesis to identify critical binding regions.
• Analysis of CIC binding in Drosophila development and human cells.
• Examination of CIC mutations in human cancers.

Main Results:

• Contrary to assumptions, the CIC HMG-box requires a distant C-terminal motif (C1) for DNA binding.
• The HMG-box and C1 domains form a bipartite structure for specific binding to TGAATGAA-like sites.
• This bipartite binding mechanism is conserved across species and functions independently of dimerization or cofactors.
• Inactivating mutations in the C1 domain are frequent in oligodendroglioma, while preserved in CIC-DUX4 fusion chimeras in sarcomas.

Conclusions:

• CIC proteins employ a unique bipartite DNA-binding mode, distinct from other HMG-box proteins.
• This mechanism ensures precise regulation of CIC target genes during development and in disease.
• The C1 domain's critical role in DNA binding explains its mutation patterns in various cancers, highlighting its oncogenic relevance.