Meyer S, LaBudda K, McGlade J, Hayman M J
Department of Microbiology, State University of New York, Stony Brook 11794-5222.
Mol Cell Biol. 1994 May;14(5):3253-62. doi: 10.1128/mcb.14.5.3253-3262.1994.
The epidermal growth factor receptor, EGFR, has been implicated in cell transformation in both mammalian and avian species. The v-ErbB oncoprotein is an oncogenic form of the chicken EGFR. The tyrosine kinase activity of this oncoprotein is required for transformation, but no transformation-specific cellular substrates have been described to date. Recently activation of the ras signal transduction pathway by the EGFR has been shown to involve the Shc and Grb2 proteins. In this communication, we demonstrate that the Shc proteins are phosphorylated on tyrosine residues and are complexed with Grb2 and the chicken EGFR following ligand activation of this receptor. In fibroblasts and erythroid cells transformed by the avian erythroblastosis virus (AEV) strains H and ES4, the Shc proteins are found to be constitutively phosphorylated on tyrosine residues. The tyrosine-phosphorylated forms of the AEV strain H v-ErbB protein are found in a complex with Shc and Grb2, but the Shc proteins do not bind to the AEV strain ES4 v-ErbB protein. Mutant forms of the v-ErbB protein (in which several of the tyrosines that become autophosphorylated have been deleted by truncation) are unable to transform erythroid cells but can still transform fibroblasts. Analysis of cells transformed by one of these mutants revealed that the truncated v-ErbB protein could no longer bind to either Shc or Grb2, but this oncoprotein still gave rise to tyrosine-phosphorylated Shc proteins that complexed with Grb2 and led to activation of mitogen-activated protein (MAP) kinase. The results suggest that stable binding of Grb2 and Shc to the v-ErbB protein is not necessary to activate this signal transduction pathway and assuming that the mutant activate MAP kinase in erythroid cells in a manner similar to that of fibroblasts, that activation of this pathway is not sufficient to transform erythroid cells.
表皮生长因子受体（EGFR）在哺乳动物和禽类细胞转化过程中均发挥作用。v-ErbB癌蛋白是鸡EGFR的致癌形式。该癌蛋白的酪氨酸激酶活性是细胞转化所必需的，但迄今为止尚未发现转化特异性细胞底物。最近研究表明，EGFR激活ras信号转导途径涉及Shc和Grb2蛋白。在本报告中，我们证明，在该受体的配体激活后，Shc蛋白在酪氨酸残基上发生磷酸化，并与Grb2和鸡EGFR形成复合物。在由禽成红细胞增多症病毒（AEV）H株和ES4株转化的成纤维细胞及红细胞中，Shc蛋白在酪氨酸残基上持续磷酸化。AEV H株v-ErbB蛋白的酪氨酸磷酸化形式与Shc和Grb2形成复合物，但Shc蛋白不与AEV ES4株v-ErbB蛋白结合。v-ErbB蛋白的突变形式（其中几个自磷酸化的酪氨酸已被截断删除）无法转化红细胞，但仍可转化成纤维细胞。对其中一种突变体转化的细胞分析表明，截短的v-ErbB蛋白不再与Shc或Grb2结合，但该癌蛋白仍能产生与Grb2形成复合物并导致丝裂原活化蛋白（MAP）激酶激活的酪氨酸磷酸化Shc蛋白。结果表明，Grb2和Shc与v-ErbB蛋白的稳定结合对于激活该信号转导途径并非必要，并且假设突变体在红细胞中激活MAP激酶的方式与成纤维细胞类似，那么该途径的激活不足以转化红细胞。
