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Bromodomain protein Brd4 binds to GTPase-activating SPA-1, modulating its activity and subcellular localization
Andrea Farina1, Masakazu Hattori, Jun Qin
1Laboratory of Molecular Growth Regulation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2753, USA.
Molecular and Cellular Biology
|October 1, 2004
Summary
Bromodomain-containing protein 4 (Brd4) interacts with signal-induced proliferation-associated protein 1 (SPA-1), a Rap GTPase-activating protein (GAP). This interaction regulates cell cycle progression and is crucial for cell division.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Bromodomain-containing protein 4 (Brd4) is a chromatin-binding protein regulating cell cycle progression.
- Signal-induced proliferation-associated protein 1 (SPA-1) is a Rap GTPase-activating protein (GAP).
Purpose of the Study:
- To identify novel interaction partners of Brd4.
- To investigate the functional significance of the interaction between Brd4 and SPA-1.
Main Methods:
- Immunopurification and mass spectrometry to identify interacting proteins.
- Bifluorescence complementation assay to confirm nuclear interaction.
- Assays to evaluate Rap GAP activity and cell cycle progression.
Main Results:
- SPA-1 was identified as a Brd4-interacting protein.
- Brd4 enhances the Rap GAP activity of SPA-1.
- Coexpression of Brd4 and SPA-1 is required for proper cell cycle progression.
Conclusions:
- Brd4 and SPA-1 interact in the nucleus, with Brd4 modulating SPA-1's GAP activity.
- A balanced interaction between Brd4 and SPA-1 in the G2 phase is essential for cell division.
- This study reveals a novel link between Brd4 and GTPase-dependent mitogenic signaling.