title: Signaling complexes and protein-protein interactions involved in the activation of the Ras and phosphatidylinositol 3-kinase pathways by the c-Ret receptor tyrosine kinase.
abstract: Proximal signaling events and protein-protein interactions initiated after activation of the c-Ret receptor tyrosine kinase by its ligand, glial cell line-derived neurotrophic factor (GDNF), were investigated in cells carrying native and mutated forms of this receptor. Mutation of Tyr-1062 (Y1062F) in the cytoplasmic tail of c-Ret abolished receptor binding and phosphorylation of the adaptor Shc and eliminated activation of Ras by GDNF. Phosphorylation of Erk kinases was also greatly attenuated but not eliminated by this mutation. This residual wave of Erk phosphorylation was independent of the kinase activity of c-Ret. Mutation of Tyr-1096 (Y1096F), a binding site for the adaptor Grb2, had no effect on Erk activation by GDNF. Activation of phosphatidylinositol-3 kinase (PI3K) and its downstream effector Akt was also reduced in the Y1062F mutant but not completely abolished unless Tyr-1096 was also mutated. Ligand stimulation of neuronal cells induced the assembly of a large protein complex containing c-Ret, Grb2, and tyrosine-phosphorylated forms of Shc, p85(PI3K), the adaptor Gab2, and the protein-tyrosine phosphatase SHP-2. In agreement with Ras-independent activation of PI3K by GDNF in neuronal cells, survival of sympathetic neurons induced by GDNF was dependent on PI3K but was not affected by microinjection of blocking anti-Ras antibodies, which did compromise neuronal survival by nerve growth factor, suggesting that Ras is not required for GDNF-induced survival of sympathetic neurons. These results indicate that upon ligand stimulation, at least two distinct protein complexes assemble on phosphorylated Tyr-1062 of c-Ret via Shc, one leading to activation of the Ras/Erk pathway through recruitment of Grb2/Sos and another to the PI3K/Akt pathway through recruitment of Grb2/Gab2 followed by p85(PI3K) and SHP-2. This latter complex can also assemble directly onto phosphorylated Tyr-1096, offering an alternative route to PI3K activation by GDNF.
authors.affiliation: Division of Molecular Neurobiology, Department of Neuroscience, Karolinska Institute, 17177 Stockholm, Sweden.
authors.forename: V
authors.initials: V
authors.lastname: Besset
authors.forename: R P
authors.initials: RP
authors.lastname: Scott
authors.forename: C F
authors.initials: CF
authors.lastname: Ibáñez
mesh_terms: D016475:3T3 Cells; D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002867:Chromones / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D029721:Drosophila Proteins; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D051380:GRB2 Adaptor Protein; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D005982:Glutathione Transferase / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008954:Models, Biological; D009025:Morpholines / Q000494:pharmacology; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D055765:Shc Signaling Adaptor Proteins; D015398:Signal Transduction; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D013997:Time Factors; D014443:Tyrosine / Q000737:chemistry; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D002867:Chromones; D029721:Drosophila Proteins; D004791:Enzyme Inhibitors; D051380:GRB2 Adaptor Protein; C495040:Gdnf protein, mouse; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; C495949:Grb2 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D009025:Morpholines; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D055765:Shc Signaling Adaptor Proteins; C528034:Shc1 protein, mouse; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D014443:Tyrosine; D005982:Glutathione Transferase; D019869:Phosphatidylinositol 3-Kinases; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases; C416649:Ret protein, Drosophila; C494999:Ret protein, mouse; D020928:Mitogen-Activated Protein Kinases; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; C516725:Ptpn11 protein, mouse; C509248:Ptpn6 protein, mouse; D018631:ras Proteins