Cdc42-Specific GTPase-Activating Protein Rga1 Squelches Crosstalk between the High-Osmolarity Glycerol (HOG) and
Jesse C Patterson1,2, Louise S Goupil1,3, Jeremy Thorner1
1Department of Molecular and Cell Biology, Division of Biochemistry, Biophysics and Structural Biology, University of California, Berkeley, CA 94720, USA.
Biomolecules
|October 23, 2021
Summary
Yeast uses distinct pathways for stress and mating. Rga1 prevents the stress pathway from activating the mating pathway by regulating Cdc42, ensuring signaling accuracy.
Area of Science:
- Cellular signaling
- Molecular biology
- Yeast genetics
Background:
- Eukaryotes employ specific mitogen/messenger-activated protein kinase (MAPK) pathways for distinct cellular responses.
- In yeast, hyperosmotic stress activates MAPK Hog1, while mating pheromones activate MAPK Fus3 and Kss1.
- Shared upstream components like Cdc42 GTPase necessitate mechanisms to prevent cross-pathway activation.
Purpose of the Study:
- To identify factors maintaining signaling fidelity during hypertonic stress by preventing cross-pathway activation.
- To understand the role of Rga1 in regulating Cdc42 activity and preventing MAPK crosstalk.
Main Methods:
- Unbiased genetic selection for yeast mutants exhibiting mating pathway activation under hyperosmotic stress.
- Analysis of truncated RGA1 alleles and their effect on MAPK pathway activation.
- Investigation of Rga1's interaction with Cdc42 and its regulation by phosphorylation (Cdc28, Hog1, PP2A).
Main Results:
- Truncated Rga1 alleles lacking the catalytic domain allowed mating MAPK activation during hyperosmotic stress.
- Rga1 down-regulates Cdc42 in the high-osmolarity glycerol (HOG) pathway, not the mating pathway.
- Rga1 activation involves dephosphorylation by Cdc28 and is promoted by Hog1 blocking Cdc28 phosphorylation.
Conclusions:
- Rga1 acts as a GTPase-activating protein (GAP) for Cdc42, contributing to signal insulation and preventing HOG pathway crosstalk to the mating pathway.
- Rga1's function involves limiting the availability of GTP-bound Cdc42 under hypertonic stress, acting as a 'kinetic proofreading' mechanism.
- Hog1 promotes Rga1 activation by inhibiting its inhibitory phosphorylation by Cdc28, thereby maintaining signaling specificity.
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