Constitutive Activation of Phosphatidylinositol 3-Kinase by a Naturally Occurring Mutant Epidermal Growth Factor Receptor

• Published in: The Journal of biological chemistry Vol. 273; no. 1; pp. 200 - 206
• Main Authors: Moscatello, David K., Holgado-Madruga, Marina, Emlet, David R., Montgomery, R. Bruce, Wong, Albert J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 02.01.1998; American Society for Biochemistry and Molecular Biology
• Subjects: 3T3 Cells; Adaptor Proteins, Signal Transducing; Animals; Cell Division; Cell Line, Transformed; Down-Regulation; Enzyme Activation; ErbB Receptors - genetics; ErbB Receptors - metabolism; Mice; Mutation; Phosphatidylinositol 3-Kinases - metabolism; Phosphoproteins - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.273.1.200

The most frequently found alteration of the epidermal growth factor receptor (EGFR) in human tumors is a deletion of exons 2–7. This receptor, termed EGFRvIII, can transform NIH 3T3 cells, and the frequent expression of this variant implies that it confers a selective advantage upon tumor cells in vivo. Although EGFRvIII is a constitutively activated tyrosine kinase, there is no increase in Ras·GTP levels and low levels of mitogen-activated protein kinase activity in NIH 3T3 cells expressing this variant. We investigated whether phosphatidylinositol (PI) 3-kinase was an effector in transformation by the EGFRvIII. High levels of PI 3-kinase activity were constitutively present in EGFRvIII-transformed cells and were dependent upon the kinase activity of the receptor. While mitogen-activated protein kinase activity was quickly down-regulated to basal levels after 12 h of continuous EGFR activation, there was a 3-fold increase in PI 3-kinase activity in cells expressing normal EGFR and an 8-fold increase in cells expressing EGFRvIII after 48 h. This increased activity may reflect enhanced binding to EGFRvIII and the presence of novel PI 3-kinase isoforms. Treatment with the PI 3-kinase inhibitors wortmannin and LY294002 blocked both anchorage-independent growth and growth in low serum media and also resulted in morphological reversion of EGFRvIII-transformed cells. These results support an essential role for PI 3-kinase in transformation by this EGFR variant.