Novel Adapter Proteins that Link the Human GM-CSF Receptor to the Phosphatidylino-sitol 3-Kinase and Shc/Grb2/ras Signaling Pathways
We have used a human GM-CSF-dependent hematopoietic cell line that responds to physiological concentrations of hGM-CSF to analyze a set of signaling events that occur in normal myelopoiesis and whose deregulation may lead to leukemogenesis. Stimulation of these cells with hGM-CSF induced the assembly of multimeric complexes that contained known and novel phosphotyrosyl proteins. One of the new proteins was a major phosphotyrosyl substrate of 76–85 kDa (p80) that was directly associated with the p85 subunit of phosphatidylinositol (PI) 3-kinase through the SH2 domains of p85. p80 also associated with the β subunit of the activated hGM-CSF receptor, and assembly of this complex correlated with activation of PI 3-kinase. A second phosphotyrosyl protein we identified, pi40, associated with the She and Grb2 adapter proteins by direct binding to a novel phosphotyrosine-interacting domain located at the N-terminus of She, and to the SH3 domains of Grb2, respectively. The Shc/pl40/Grb2 complex was found to be constitutively activated in acute myeloid leukemia cells, indicating that activation of this pathway may be a necessary step in the development of some leukemias. The p80/p85/PI 3-kinase and the Shc/Grb2/pl40 complexes were tightly associated with Src family kinases, which were prime candidates for phosphorylation of She, p80, pl40 and other phosphotyrosyl substrates pesent in these complexes. Our studies suggest that p80 and pl40 may link the hGM-CSF receptor to the PI 3-kinase and Shc/Grb2/ras signaling pathways, respectively, and that abnormal activation of hGM-CSF-dependent targets may play a role in leukemogenesis.
KeywordsAcute Myeloid Leukemia Acute Myeloid Leukemia Cell NPXY Motif Oncogenic Tyrosine Kinase Grb2 Adapter Protein
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