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Published on: May 3, 2018
Regulation of cyclin-substrate docking by a G1 arrest signaling pathway and the Cdk inhibitor Far1
Patricia A Pope1, Samyabrata Bhaduri1, Peter M Pryciak1
1Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
Abstract:
Eukaryotic cell division is often regulated by extracellular signals. In budding yeast, signaling from mating pheromones arrests the cell cycle in G1 phase. This arrest requires the protein Far1, which is thought to antagonize the G1/S transition by acting as a Cdk inhibitor (CKI), although the mechanisms remain unresolved. Recent studies found that G1/S cyclins (Cln1 and Cln2) recognize Cdk substrates via specific docking motifs, which promote substrate phosphorylation in vivo. Here, we show that these docking interactions are inhibited by pheromone signaling and that this inhibition requires Far1. Moreover, Far1 mutants that cannot inhibit docking are defective at cell-cycle arrest. Consistent with this arrest function, Far1 outcompetes substrates for association with G1/S cyclins in vivo, and it is present in large excess over G1/S cyclins during the precommitment period where pheromone can impose G1 arrest. Finally, a comparison of substrates that do and do not require docking suggests that Far1 acts as a multimode inhibitor that antagonizes both kinase activity and substrate recognition by Cln1/2-Cdk complexes. Our findings uncover a novel mechanism of Cdk regulation by external signals and shed new light on Far1 function to provide a revised view of cell-cycle arrest in this model system.
Insights
Mating pheromones arrest budding yeast cell division via Far1 protein. Far1 inhibits G1/S cyclins from recognizing substrates, revealing a novel cell cycle regulation mechanism.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Eukaryotic cell division is regulated by extracellular signals.
- Mating pheromones in budding yeast arrest the cell cycle at G1 phase.
- Far1 protein is crucial for this arrest, potentially acting as a cyclin-dependent kinase inhibitor (CKI).
Purpose of the Study:
- To elucidate the mechanism by which Far1 mediates cell cycle arrest.
- To investigate the role of G1/S cyclin-substrate docking interactions in pheromone-induced arrest.
- To understand how Far1 antagonizes G1/S cyclin-Cdk complexes.
Main Methods:
- Investigated pheromone signaling effects on G1/S cyclin-substrate docking in vivo.
- Utilized Far1 mutants defective in docking inhibition.
- Assessed Far1 and G1/S cyclin association and relative abundance.
- Compared docking-dependent and independent substrates.
Main Results:
- Pheromone signaling inhibits G1/S cyclin-substrate docking, requiring Far1.
- Far1 mutants unable to inhibit docking show defects in cell cycle arrest.
- Far1 outcompetes substrates for G1/S cyclin binding and is in excess during arrest.
- Far1 acts as a multimode inhibitor, affecting both kinase activity and substrate recognition.
Conclusions:
- Uncovered a novel mechanism of cyclin-dependent kinase regulation by external signals.
- Revised understanding of Far1 function in pheromone-induced G1 cell cycle arrest.
- Demonstrated Far1's role in antagonizing G1/S cyclin-Cdk substrate recognition and activity.
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