Structural proteomics defines a sequential priming mechanism for the progesterone receptor.

Area of Science:

• Molecular biology
• Structural biology
• Cancer research

Background:

• Progesterone receptor (PR) has two isoforms, PR-A and PR-B, crucial for cellular signaling.
• Disrupted PR signaling is linked to breast cancer via interactions with co-regulatory proteins (CoRs).
• The precise molecular details of how PR isoforms interact with CoRs are not well understood.

Purpose of the Study:

• To investigate the sequential binding mechanism of PR isoforms and CoRs (SRC3 and p300) on target DNA.
• To elucidate the structural basis of PR-CoR interactions at a peptide level.
• To understand how antagonist binding affects PR-CoR interactions.

Main Methods:

• Structural mass spectrometry was employed to analyze purified full-length PR and intact CoRs.
• Complexes were studied on target DNA to mimic physiological conditions.
• Peptide-level analysis provided insights into protein-protein interactions.

Main Results:

• Selective binding of CoR NR-boxes by PR was observed.
• Unique interaction surfaces between PR and CoRs were identified during complex assembly.
• Antagonist-bound PR maintained persistent CoR interactions, contrary to established models.

Conclusions:

• This study provides a structural framework for understanding sequential CoR binding to PR.
• The findings offer a peptide-level perspective on the progesterone receptor transcriptional complex organization.
• Observed persistent CoR interactions with antagonist-bound PR challenge classical models of nuclear receptor regulation.