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Cryo-EM structures reveal the PP2A-B55α and Eya3 interaction that can be disrupted by a peptide inhibitor
Shasha Shi1, Xueni Li1, Christopher Alderman2
1Department of Biochemistry and Molecular Genetics, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA.
Abstract:
We have previously shown that Eya3 recruits PP2A-B55α to dephosphorylate pT58 on Myc, increasing Myc stability and enhancing primary tumor growth of triple-negative breast cancer (TNBC). However, the molecular details of how Eya3 recruits PP2A-B55α remain unclear. Here, we determined the cryo-EM structures of PP2A-B55α bound with Eya3, with an inhibitory peptide B55i, and in its unbound state. These studies demonstrate that Eya3 binds B55α through an extended peptide in the N-terminal domain of Eya3. The Eya3 peptide, PP2A-B55α substrates, and protein-peptide inhibitors including B55i bind to a similar area on the B55α surface, but the molecular details of the binding differ. We further demonstrated that the B55i peptide inhibits the B55α and Eya3 interaction in vitro. The B55i peptide expressed on a plasmid increases Myc pT58 and decreases Myc protein levels in TNBC cells, suggesting the potential of B55i or similar peptides as therapies for TNBC.
Insights
Eya3 protein stability in triple-negative breast cancer (TNBC) is regulated by binding to PP2A-B55α. This interaction is inhibited by the B55i peptide, offering a potential new therapy for TNBC.
Area of Science:
- Molecular biology
- Structural biology
- Cancer research
Background:
- Eya3 protein enhances triple-negative breast cancer (TNBC) growth by stabilizing Myc.
- The mechanism by which Eya3 recruits PP2A-B55α to dephosphorylate Myc remains elusive.
Purpose of the Study:
- To elucidate the molecular details of Eya3 recruitment of PP2A-B55α.
- To investigate the potential of B55i peptide as a therapeutic agent for TNBC.
Main Methods:
- Cryo-electron microscopy (cryo-EM) to determine structures of PP2A-B55α bound with Eya3, B55i peptide, and unbound.
- In vitro assays to assess the inhibitory effect of B55i peptide on Eya3-PP2A-B55α interaction.
- In vivo studies using plasmid-expressed B55i peptide in TNBC cells.
Main Results:
- Cryo-EM structures revealed Eya3 binds PP2A-B55α via an N-terminal peptide.
- Eya3 peptide, PP2A-B55α substrates, and inhibitors like B55i bind to overlapping but distinct sites on B55α.
- B55i peptide demonstrated inhibition of Eya3-PP2A-B55α interaction in vitro and reduced Myc protein levels in TNBC cells.
Conclusions:
- Eya3 interacts with PP2A-B55α through a specific N-terminal peptide, providing structural insights.
- The B55i peptide effectively inhibits this interaction and impacts Myc stability in TNBC cells.
- B55i peptide represents a promising therapeutic strategy for TNBC treatment.
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