Transforming activity of receptor tyrosine kinase tyro3 is mediated, at least in part, by the PI3 kinase-signaling pathway.
Protein tyrosine phosphorylation is an integral part of cytokine-induced proliferation and differentiation of hematopoietic cells. The authors previously reported cloning and characterization of the receptor tyrosine kinase Tif, also termed Tyro3. Using the yeast 2-hybrid technology, they recently identified that the p85 subunit of phosphatidylinositol 3-kinase (PI3 kinase) interacted with the cytoplasmic domain of Tyro3. On treatment with epidermal growth factor (EGF), NIH3T3 cells expressed EGFR/Tyro3 (a fusion receptor with the extracellular domain from epidermal growth factor receptor and the transmembrane and cytoplasmic domains from Tyro3), and EGFR/Tyro3 was rapidly phosphorylated on tyrosine residues. The interaction between Tyro3 and p85 was also confirmed by glutathione S-transferase (GST) pull-down experiments. Co-immunoprecipitation followed by Western blot analysis revealed that PI3 kinase was associated with and phosphorylated by the activated Tyro3. Tyro3-associated PI3 kinase exhibited an enhanced kinase activity. In addition, EGF treatment of EGFR/Tyro3-expressing cells led to enhanced phosphorylation of Akt, a downstream component of PI3 kinase. Treatment of NIH3T3 cells expressing a full length of rat Tyro-3, but not NIH3T3 cells, with protein S also resulted in phosphorylation of Akt. Soft agar colony assays showed that the addition of EGF to EGFR/Tyro3-transfected cells, but not to the parental NIH3T3 cells, resulted in a concentration-dependent increase in the formation of anchorage-independent colonies. Tyro3-mediated transformation of NIH3T3 cells was significantly blocked by wortmannin, a PI3 kinase-specific inhibitor. Results of these combined studies strongly suggested that the oncogenic transforming ability of Tyro3 was mediated at least in part by the PI3 kinase pathway. (Blood. 2000;95:633-638)
Lan
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Z
Departments of Internal Medicine and Cell Biology, Neurobiology, and Anatomy, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA.
Wu
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Li
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Wu
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S
Lu
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Xu
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Dai
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D016475:3T3 Cells; D000818:Animals; D002471:Cell Transformation, Neoplastic; D003001:Cloning, Molecular; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics* / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D015398:Signal Transduction; D014162:Transfection; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
D066246:ErbB Receptors; D019869:Phosphatidylinositol 3-Kinases; D020794:Receptor Protein-Tyrosine Kinases; D011993:Recombinant Fusion Proteins; D001616:beta-Galactosidase; C084944:TYRO3 protein, human