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Regulation of the mitogen-activated protein kinase signaling pathway by SHP2
Jess M Cunnick1, Songshu Meng, Yuan Ren
1H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida 33612, USA.
Abstract:
Gab1-SHP2 association is required for Erk mitogen-activated protein kinase activation by several growth factors. Gab1-SHP2 interaction activates SHP2. However, an activated SHP2 still needs to associate with Gab1 to mediate Erk activation. It was unclear whether SHP2 is required to dephosphorylate a negative phosphorylation site on Gab1 or whether SHP2 needs the Gab1 pleckstrin homology (PH) domain to target it to the plasma membrane. We found that expression of a fusion protein consisting of the Gab1 PH domain and an active SHP2 (Gab1PH-SHP2DeltaN) induced constitutive Mek1 and Erk2 activation. Linking the active SHP2DeltaN to the PDK1 PH domain or the FRS2beta myristoylation sequence also induced Mek1 activation. Mek1 activation by Gab1PH-SHP2DeltaN was inhibited by an Src inhibitor and by Csk. Significantly, Gab1PH-SHP2DeltaN induced Src activation. Gab1PH-SHP2DeltaN expression activated Ras, and the Gab1PH-SHP2DeltaN-induced Mek1 activation was blocked by RasN17. These findings suggest that Gab1PH-SHP2DeltaN activated a signaling step upstream of Src and Ras. The SHP2 tyrosine phosphatase activity is essential for the function of the fusion protein. Together, these data show that the Gab1 sequence, besides the PH domain and SHP2 binding sites, is dispensable for Erk activation, suggesting that the primary role of Gab1 association with an activated SHP2 is to target it to the membrane.
Insights
The Gab1 protein targets the SHP2 phosphatase to the cell membrane, which is crucial for activating Erk mitogen-activated protein kinase signaling pathways. This localization is key for growth factor-induced cell responses.
Area of Science:
- Cellular signaling
- Molecular biology
- Signal transduction pathways
Background:
- Gab1 and SHP2 interaction is vital for Erk mitogen-activated protein kinase (MAPK) activation by growth factors.
- Activated SHP2 requires Gab1 association to mediate Erk activation, but the precise mechanism remains unclear.
Purpose of the Study:
- To elucidate the role of Gab1 in SHP2-mediated Erk activation.
- To determine if SHP2 dephosphorylates Gab1 or if Gab1 targets SHP2 to the plasma membrane.
Main Methods:
- Constructed a fusion protein (Gab1PH-SHP2DeltaN) linking the Gab1 pleckstrin homology (PH) domain to active SHP2.
- Investigated Mek1 and Erk2 activation by the fusion protein.
- Utilized Src inhibitors, Csk, and dominant-negative Ras (RasN17) to probe signaling pathways.
Main Results:
- Gab1PH-SHP2DeltaN induced constitutive Mek1 and Erk2 activation.
- Linking active SHP2 to other membrane-targeting sequences (PDK1 PH domain, FRS2beta myristoylation) also activated Mek1.
- Gab1PH-SHP2DeltaN activated Src and Ras, indicating upstream signaling.
- SHP2 tyrosine phosphatase activity was essential for fusion protein function.
Conclusions:
- The Gab1 PH domain targets active SHP2 to the plasma membrane, which is essential for Erk activation.
- Gab1's primary role in this context is membrane localization of SHP2, not dephosphorylation of negative sites.
- Specific Gab1 sequences beyond the PH domain and SHP2 binding sites are dispensable for Erk activation.