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c-Cbl is a critical modulator of the Ron tyrosine kinase receptor
Lorenza Penengo1, Chanan Rubin, Yosef Yarden
1Department of Medical Sciences, University of Piemonte Orientale, Novara 28100, Italy.
Abstract:
Ron, the receptor tyrosine kinase (RTK) for the macrophage stimulating protein (MSP), activates multiple signaling pathways by recruiting several positive regulators to a multifunctional docking site. Here we show that stimulation by MSP also recruits a negative regulator, the c-Cbl ubiquitin ligase, to the multifunctional docking site as well as to a juxtamembrane tyrosine autophosphorylation site. c-Cbl recruitment to these two sites results in polyubiquitylation of Ron molecules, which are subsequently sorted for endocytosis and degradation. Both the phosphotyrosine binding domain of c-Cbl and its RING domain are essential for downregulation of Ron. Although Ron and c-Cbl are found also in physical complexes that include Grb2, these associations are insufficient for productive ubiquitylation of Ron. Our results shed light on the mechanism of receptor desensitization mediated by c-Cbl and its binding partner Grb2.
Insights
Macrophage stimulating protein (MSP) receptor Ron is downregulated by c-Cbl ubiquitin ligase. c-Cbl targets Ron for degradation, revealing a key mechanism in receptor desensitization.
Area of Science:
- Cellular signaling
- Receptor tyrosine kinases
- Ubiquitin ligases
Background:
- Ron receptor tyrosine kinase (RTK) activates pathways via positive regulators.
- Macrophage stimulating protein (MSP) is the ligand for Ron.
- Understanding RTK regulation is crucial for cellular signaling research.
Purpose of the Study:
- To investigate the role of negative regulators in Ron receptor desensitization.
- To elucidate the mechanism by which c-Cbl interacts with and regulates Ron.
- To identify the specific domains of c-Cbl involved in Ron ubiquitylation.
Main Methods:
- Co-immunoprecipitation to detect protein-protein interactions.
- Western blotting to analyze protein ubiquitylation and degradation.
- Site-directed mutagenesis to assess the function of c-Cbl domains.
Main Results:
- MSP stimulation recruits c-Cbl ubiquitin ligase to Ron.
- c-Cbl polyubiquitylation of Ron leads to its endocytosis and degradation.
- Both the phosphotyrosine binding and RING domains of c-Cbl are essential for Ron downregulation.
- Grb2 association with Ron and c-Cbl is insufficient for Ron ubiquitylation.
Conclusions:
- c-Cbl acts as a negative regulator of Ron receptor tyrosine kinase.
- c-Cbl-mediated ubiquitylation and degradation are key mechanisms for Ron desensitization.
- This study clarifies the role of c-Cbl and Grb2 in regulating RTK signaling pathways.