Structural and Functional Impacts of ER Coactivator Sequential Recruitment.

Area of Science:

• Molecular Biology
• Structural Biology
• Epigenetics

Background:

• Nuclear receptors orchestrate gene transcription through the sequential recruitment of coactivator proteins.
• Estrogen receptor (ER) utilizes a cascade of coactivators, including SRC-3, p300/CBP, and CARM1, with distinct temporal dependencies.

Purpose of the Study:

• To elucidate the structural and functional interplay between sequentially recruited coactivators in estrogen receptor-mediated transcription.
• To investigate the role of CARM1's delayed recruitment in modulating the ER-coactivator complex.

Main Methods:

• Cryo-electron microscopy (cryo-EM) for structural analysis of the ER-coactivator complex.
• Biochemical assays to assess coactivator activities and interactions.
• Histone modification analysis (HAT and methylation) to evaluate functional outcomes.

Main Results:

• CARM1 recruitment to the ER complex is temporally delayed compared to SRC-3 and p300.
• CARM1 interacts with and induces conformational changes in p300, enhancing its HAT activity on histone H3K18.
• This p300 activation promotes CARM1's methyltransferase activity on histone H3R17, amplifying transcriptional output.

Conclusions:

• Sequential coactivator recruitment is critical for ER transcriptional regulation, involving structural crosstalk between early and late factors.
• CARM1's delayed recruitment and its impact on p300 activity reveal a novel mechanism for fine-tuning gene expression.