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Gastrin induces tyrosine phosphorylation of Shc proteins and their association with the Grb2/Sos complex
C Seva1, A Kowalski-Chauvel, J S Blanchet
1INSERM U.151., Institut Louis Bugnard, CHU Rangueil, Toulouse, France.
Abstract:
Gastrin/CCKB G protein-coupled receptors have been shown to mediate proliferative effects of their endogenous ligands. In the present study, we examined the signal transduction mechanisms linked to the G/CCKB receptor occupancy. We report here that gastrin stimulates MAP kinase activation in a dose- and time-dependent manner, a pathway known to play a key role in cell proliferation. We also characterized the molecular events, upstream of p21-Ras, that may link the MAP kinase pathway to G/CCKB receptors. Gastrin induced a rapid and transient increase in tyrosine phosphorylation of several proteins including the 2 isoforms (46 and 52 kDa) of the adaptor protein Shc. Phosphorylated Shc subsequently associated with a complex that includes Grb2 and the p21-Ras activator, Sos. Our results also indicate that Sos becomes phosphorylated in response to gastrin as shown by a reduction in electrophoretic mobility of the protein. Tyrosine phosphorylation of Shc and subsequent complex formation with Grb2 and Sos appear to be a common mechanism by which tyrosine kinase receptors and the G/CCKB G protein-coupled receptor stimulate the Ras-dependent MAP kinase pathway.
Insights
Gastrin stimulates the MAP kinase pathway, crucial for cell proliferation, by activating the CCK-B receptor. This involves Shc protein tyrosine phosphorylation and subsequent complex formation with Grb2 and Sos, linking the receptor to Ras activation.
Area of Science:
- Cellular signaling
- Molecular biology
- G protein-coupled receptors
Background:
- Gastrin/cholecystokinin B (CCK-B) receptors are G protein-coupled receptors known to mediate cellular proliferation.
- Understanding the specific signal transduction pathways activated by CCK-B receptor occupancy is essential for elucidating its role in cellular processes.
Purpose of the Study:
- To investigate the signal transduction mechanisms downstream of gastrin/CCK-B receptor activation.
- To identify the molecular events linking CCK-B receptor occupancy to the mitogen-activated protein kinase (MAPK) pathway.
Main Methods:
- Dose- and time-dependent stimulation of MAP kinase activation by gastrin.
- Analysis of protein tyrosine phosphorylation, specifically of the Shc adaptor protein.
- Investigation of protein-protein interactions involving Shc, Grb2, and Sos.
Main Results:
- Gastrin significantly stimulates MAP kinase activation in a dose- and time-dependent manner.
- Gastrin induces rapid tyrosine phosphorylation of Shc adaptor protein isoforms (46 and 52 kDa).
- Phosphorylated Shc forms a complex with Grb2 and the Ras activator Sos, which also undergoes phosphorylation.
Conclusions:
- Gastrin/CCK-B receptor activation stimulates the Ras-dependent MAP kinase pathway.
- Tyrosine phosphorylation of Shc and subsequent complex formation with Grb2/Sos is a key mechanism linking CCK-B receptors to Ras activation.
- This pathway is shared with tyrosine kinase receptors, suggesting a common signaling mechanism for proliferation.