Rozakis-Adcock M, Fernley R, Wade J, Pawson T, Bowtell D
Division of Molecular and Developmental Biology, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.
Nature. 1993 May 6;363(6424):83-5. doi: 10.1038/363083a0.
Many tyrosine kinases, including the receptors for hormones such as epidermal growth factor (EGF), nerve growth factor and insulin, transmit intracellular signals through Ras proteins. Ligand binding to such receptors stimulates Ras guanine-nucleotide-exchange activity and increases the level of GTP-bound Ras, suggesting that these tyrosine kinases may activate a guanine-nucleotide releasing protein (GNRP). In Caenorhabditis elegans and Drosophila, genetic studies have shown that Ras activation by tyrosine kinases requires the protein Sem-5/drk, which contains a single Src-homology (SH) 2 domain and two flanking SH3 domains. Sem-5 is homologous to the mammalian protein Grb2, which binds the autophosphorylated EGF receptor and other phosphotyrosine-containing proteins such as Shc through its SH2 domain. Here we show that in rodent fibroblasts, the SH3 domains of Grb2 are bound to the proline-rich carboxy-terminal tail of mSos1, a protein homologous to Drosophila Sos. Sos is required for Ras signalling and contains a central domain related to known Ras-GNRPs. EGF stimulation induces binding of the Grb2-mSos1 complex to the autophosphorylated EGF receptor, and mSos1 phosphorylation. Grb2 therefore appears to link tyrosine kinases to a Ras-GNRP in mammalian cells.
许多酪氨酸激酶，包括表皮生长因子（EGF）、神经生长因子和胰岛素等激素的受体，通过Ras蛋白传递细胞内信号。配体与这类受体的结合会刺激Ras鸟嘌呤核苷酸交换活性，并增加结合GTP的Ras水平，这表明这些酪氨酸激酶可能激活一种鸟嘌呤核苷酸释放蛋白（GNRP）。在秀丽隐杆线虫和果蝇中，遗传学研究表明酪氨酸激酶激活Ras需要蛋白质Sem-5/drk，它含有一个单一的Src同源（SH）2结构域和两个侧翼SH3结构域。Sem-5与哺乳动物蛋白Grb2同源，Grb2通过其SH2结构域结合自身磷酸化的EGF受体和其他含磷酸酪氨酸的蛋白，如Shc。我们在此表明，在啮齿动物成纤维细胞中，Grb2的SH3结构域与mSos1富含脯氨酸的羧基末端尾巴结合，mSos1是一种与果蝇Sos同源的蛋白。Sos是Ras信号传导所必需的，并且含有一个与已知Ras-GNRP相关的中央结构域。EGF刺激诱导Grb2-mSos1复合物与自身磷酸化的EGF受体结合，以及mSos1磷酸化。因此，Grb2似乎在哺乳动物细胞中将酪氨酸激酶与Ras-GNRP联系起来。
