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Macrophage-stimulating protein activates Ras by both activation and translocation of SOS nucleotide exchange factor
1Biological Carcinogenesis and Development Program, SAIC/Frederick, MD 21702, USA.
Abstract:
Macrophage-stimulating protein (MSP) is a chemotactic factor that activates the receptor tyrosine kinase RON. The involvement of Ras in MSP-induced signal transduction was investigated. Here we demonstrate that, in RON-transfected MDCK cells, an active GTP-bound form of Ras was rapidly accumulated by MSP treatment and the Ras-guanine nucleotide exchange activity in SOS immunoprecipitates was concomitantly increased. GAP activity was not changed under the same conditions used. Furthermore, the SH2 domain of adaptor protein GRB2, but not Shc, associated with the activated RON-beta chain, and GRB2-SOS complexes translocated from the cytosol to the membrane upon MSP treatment. These results strongly suggest that MSP activates Ras through RON, and that MSP-induced activation of Ras might be controlled by both the enhancement of catalytic exchange activity of SOS and its translocation to the membrane where its target Ras is localized.
Insights
Macrophage-stimulating protein (MSP) activates Ras signaling through the RON receptor tyrosine kinase. This involves increased guanine nucleotide exchange activity of SOS and its membrane translocation, crucial for Ras activation.
Area of Science:
- Molecular Biology
- Cell Signaling
- Biochemistry
Background:
- Macrophage-stimulating protein (MSP) is a known chemotactic factor.
- MSP activates the receptor tyrosine kinase RON, initiating cellular responses.
- The role of Ras signaling in MSP-mediated pathways requires elucidation.
Purpose of the Study:
- To investigate the involvement of Ras in signal transduction pathways activated by MSP.
- To elucidate the specific mechanisms by which MSP influences Ras activation via RON.
Main Methods:
- Utilized RON-transfected MDCK cells for experimental models.
- Assessed Ras-GTP levels and guanine nucleotide exchange activity of SOS.
- Examined the association of adaptor proteins (GRB2, Shc) with activated RON and translocation of GRB2-SOS complexes.
Main Results:
- MSP treatment rapidly increased active GTP-bound Ras.
- Concomitant increase in Ras-guanine nucleotide exchange activity of SOS was observed, without changes in GAP activity.
- The SH2 domain of GRB2, not Shc, associated with activated RON, and GRB2-SOS complexes translocated to the membrane.
Conclusions:
- MSP activates Ras through the RON receptor tyrosine kinase.
- MSP-induced Ras activation is regulated by enhanced catalytic activity of SOS.
- Membrane translocation of GRB2-SOS complexes plays a key role in localizing SOS to activate Ras.