The neuron-specific Rai (ShcC) adaptor protein inhibits apoptosis by coupling Ret to the phosphatidylinositol 3-kinase/Akt signaling pathway.
Rai is a recently identified member of the family of Shc-like proteins, which are cytoplasmic signal transducers characterized by the unique PTB-CH1-SH2 modular organization. Rai expression is restricted to neuronal cells and regulates in vivo the number of postmitotic sympathetic neurons. We report here that Rai is not a common substrate of receptor tyrosine kinases under physiological conditions and that among the analyzed receptors (Ret, epidermal growth factor receptor, and TrkA) it is activated specifically by Ret. Overexpression of Rai in neuronal cell lines promoted survival by reducing apoptosis both under conditions of limited availability of the Ret ligand glial cell line-derived neurotrophic factor (GDNF) and in the absence of Ret activation. Overexpressed Rai resulted in the potentiation of the Ret-dependent activation of phosphatidylinositol 3-kinase (PI3K) and Akt. Notably, increased Akt phosphorylation and PI3K activity were also found under basal conditions, e.g., in serum-starved neuronal cells. Phosphorylated and hypophosphorylated Rai proteins form a constitutive complex with the p85 subunit of PI3K: upon Ret triggering, the Rai-PI3K complex is recruited to the tyrosine-phosphorylated Ret receptor through the binding of the Rai PTB domain to tyrosine 1062 of Ret. In neurons treated with low concentrations of GDNF, the prosurvival effect of Rai depends on Rai phosphorylation and Ret activation. In the absence of Ret activation, the prosurvival effect of Rai is, instead, phosphorylation independent. Finally, we showed that overexpression of Rai, at variance with Shc, had no effects on the early peak of mitogen-activated protein kinase (MAPK) activation, whereas it increased its activation at later time points. Phosphorylated Rai, however, was not found in complexes with Grb2. We propose that Rai potentiates the MAPK and PI3K signaling pathways and regulates Ret-dependent and -independent survival signals.
Pelicci
Giuliana
G
Department of Experimental Oncology, European Institute of Oncology, 20141 Milan, Italy. pgpelicci@ieo.it
Troglio
Flavia
F
Bodini
Alessandra
A
Melillo
Rosa Marina
RM
Pettirossi
Valentina
V
Coda
Laura
L
De Giuseppe
Antonio
A
Santoro
Massimo
M
Pelicci
Pier Giuseppe
PG
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017209:Apoptosis; D002454:Cell Differentiation; D002470:Cell Survival; D029721:Drosophila Proteins; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000378:metabolism; D051380:GRB2 Adaptor Protein; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D018813:Multiple Endocrine Neoplasia Type 2a; D009414:Nerve Growth Factors / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D009474:Neurons / Q000166:cytology; D009479:Neuropeptides; D016716:PC12 Cells; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D051096:Proto-Oncogene Proteins c-ret; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D055765:Shc Signaling Adaptor Proteins; D015398:Signal Transduction; D000071427:Src Homology 2 Domain-Containing, Transforming Protein 3; D013379:Substrate Specificity; D018909:src Homology Domains
D048868:Adaptor Proteins, Signal Transducing; D029721:Drosophila Proteins; D066246:ErbB Receptors; D051380:GRB2 Adaptor Protein; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D020928:Mitogen-Activated Protein Kinases; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011506:Proteins; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases; D055765:Shc Signaling Adaptor Proteins; D000071427:Src Homology 2 Domain-Containing, Transforming Protein 3; C495041:Gdnf protein, rat; C495950:Grb2 protein, rat; C485683:Shc3 protein, rat; C416649:Ret protein, Drosophila; C495001:Ret protein, rat; C494920:Akt1 protein, rat