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Imaging G-protein Coupled Receptor (GPCR)-mediated Signaling Events that Control Chemotaxis of Dictyostelium Discoideum
Published on: September 20, 2011
Cyclic AMP signalling in Dictyostelium: G-proteins activate separate Ras pathways using specific RasGEFs
Helmut Kae1, Arjan Kortholt, Holger Rehmann
1Department of Microbiology and Immunology, University of British Columbia, 3540-2350 Health Sciences Mall, Vancouver, British Columbia V6T 1Z3, Canada.
EMBO Reports
|March 24, 2007
Summary
Two Ras guanine nucleotide exchange factors (RasGEFs) in Dictyostelium show specific targets. RasGEFA activates RasC, while RasGEFR activates RasG, enabling distinct cellular responses to cyclic AMP signals.
Area of Science:
- Cellular signaling
- Molecular biology
- Biochemistry
Background:
- Ras guanine nucleotide exchange factors (RasGEFs) are crucial regulators of Ras signaling pathways.
- Mammalian RasGEFs often exhibit broad substrate specificity, making pathway regulation complex.
- Understanding RasGEF specificity is key to deciphering how single upstream signals control diverse cellular processes.
Purpose of the Study:
- To investigate the substrate specificity of two RasGEFs, RasGEFA and RasGEFR, in Dictyostelium development.
- To determine if specific RasGEFs regulate distinct Ras proteins (RasC and RasG) and their downstream pathways.
Main Methods:
- In vivo analysis of Ras protein activation in Dictyostelium mutants lacking specific RasGEFs (gefA and gefR).
- In vitro assays measuring GDP release from purified RasC and RasG proteins by purified RasGEFA and RasGEFR.
- Monitoring downstream cellular functions like chemotaxis and adenylyl cyclase activation.
Main Results:
- RasGEFA specifically activated RasC, essential for adenylyl cyclase activation, but not RasG.
- RasGEFR specifically activated RasG, crucial for chemotaxis, but not RasC.
- In vitro GDP release assays confirmed the specific interactions: RasGEFA with RasC and RasGEFR with RasG.
Conclusions:
- RasGEFA and RasGEFR exhibit distinct substrate specificities for RasC and RasG, respectively.
- This specificity allows a single upstream signal (cyclic AMP) to diverge into independent pathways regulating different cellular functions.
- The findings provide a molecular mechanism for signal diversification mediated by specific RasGEF-Ras interactions.
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