Moscatello D K, Holgado-Madruga M, Emlet D R, Montgomery R B, Wong A J
Department of Microbiology and Immunology, Kimmel Cancer Institute, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
J Biol Chem. 1998 Jan 2;273(1):200-6. 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.
人类肿瘤中最常见的表皮生长因子受体（EGFR）改变是外显子2 - 7缺失。这种受体被称为EGFRvIII，它能使NIH 3T3细胞发生转化，该变体的频繁表达意味着它在体内赋予肿瘤细胞选择性优势。尽管EGFRvIII是一种组成型激活的酪氨酸激酶，但在表达该变体的NIH 3T3细胞中，Ras.GTP水平没有增加，丝裂原活化蛋白激酶活性水平较低。我们研究了磷脂酰肌醇（PI）3激酶是否是EGFRvIII介导转化的效应器。在EGFRvIII转化的细胞中持续存在高水平的PI 3激酶活性，且依赖于受体的激酶活性。在持续激活EGFR 12小时后，丝裂原活化蛋白激酶活性迅速下调至基础水平，而在表达正常EGFR的细胞中，48小时后PI 3激酶活性增加了3倍，在表达EGFRvIII的细胞中增加了8倍。这种活性增加可能反映了与EGFRvIII的结合增强以及新型PI 3激酶同工型存在。用PI 3激酶抑制剂渥曼青霉素和LY294002处理可阻断非锚定依赖性生长和低血清培养基中的生长，还导致EGFRvIII转化细胞的形态逆转。这些结果支持PI 3激酶在这种EGFR变体介导的转化中起重要作用。
