Sasaoka T, Langlois W J, Leitner J W, Draznin B, Olefsky J M
Department of Medicine, University of California, San Diego, La Jolla 92093.
J Biol Chem. 1994 Dec 23;269(51):32621-5.
Epidermal growth factor (EGF) treatment causes autophosphorylation of the epidermal growth factor receptor (EGFR) leading to increased guanine nucleotide exchange factor (GEF; Sos) activity and enhanced formation of p21ras-GTP. The connection of the EGFR to p21ras activation can occur through binding of Grb2.Sos complexes to the EGFR or through the adaptor protein Shc via EGFR.Shc.Grb2.Sos multimeric complexes. Therefore, we investigated the importance of Shc in coupling the EGFR to activation of ras GEF (Sos). EGF treatment led to rapid tyrosine phosphorylation of Shc. Although phosphorylated EGFR can bind to both Shc and Grb2, the predominant linkage was observed between EGFR and Shc. Similarly, more Grb2 was associated with Shc than with EGFR after EGF stimulation. Immunoprecipitation of Shc from EGF-stimulated cells removed almost all EGFR-associated Grb2. Furthermore, immunodepletion of Shc proteins from membrane fractions of EGF-stimulated cells removed 93% of the ras GEF activity, whereas, precipitation of EGFR had only a small effect on ras GEF activity. These data indicate that coupling to Shc provides the major pathway linking activated EGFRs to Grb2.Sos and stimulation of the p21ras pathway.
表皮生长因子（EGF）处理会导致表皮生长因子受体（EGFR）发生自身磷酸化，进而使鸟嘌呤核苷酸交换因子（GEF；Sos）活性增加，并增强p21ras-GTP的形成。EGFR与p21ras激活之间的联系可通过Grb2.Sos复合物与EGFR结合，或通过衔接蛋白Shc经EGFR.Shc.Grb2.Sos多聚体复合物来实现。因此，我们研究了Shc在将EGFR与ras GEF（Sos）激活相偶联过程中的重要性。EGF处理导致Shc迅速发生酪氨酸磷酸化。尽管磷酸化的EGFR能与Shc和Grb2都结合，但在EGFR与Shc之间观察到的连接更为主要。同样，EGF刺激后，与Shc相关的Grb2比与EGFR相关的更多。从EGF刺激的细胞中免疫沉淀Shc几乎去除了所有与EGFR相关的Grb2。此外，从EGF刺激的细胞的膜组分中免疫去除Shc蛋白可去除93%的ras GEF活性，而沉淀EGFR对ras GEF活性只有很小的影响。这些数据表明，与Shc偶联提供了将活化的EGFR与Grb2.Sos相连接以及刺激p21ras途径的主要通路。
