Meng Songshu, Chen Zhengming, Munoz-Antonia Teresita, Wu Jie
Molecular Oncology Program, H. Lee Moffitt Cancer Center and Research Institute, 12902 Magnolia Drive, Tampa, FL 33612, USA.
Biochem J. 2005 Oct 1;391(Pt 1):143-51. doi: 10.1042/BJ20050229.
Three members of Gab family docking proteins, Gab1, Gab2 and Gab3, have been identified in humans. Previous studies have found that the hepatocyte growth factor preferentially utilizes Gab1 for signalling, whereas Bcr-Abl selectively signals through Gab2. Gab1-SHP2 interaction has been shown to mediate ERK (extracellular-signal-regulated kinase) activation by EGF (epidermal growth factor). However, it was unclear whether EGF selectively utilizes Gab1 for signalling to ERK and whether Gab2 is dispensable in cells where Gab1 and Gab2 are co-expressed. Using T47D and MCF-7 human breast carcinoma cells that express endogenous Gab1 and Gab2, we examined the role of these docking proteins in EGF-induced ERK activation. It was found that EGF induced a similar amount of SHP2-Gab1 and SHP2-Gab2 complexes. Expression of either SHP2-binding defective Gab1 or Gab2 mutant blocked EGF-induced ERK activation. Down-regulation of either Gab1 or Gab2 by siRNAs (small interfering RNAs) effectively inhibited the EGF-stimulated ERK activation pathway and cell migration. Interestingly, the inhibitory effect of Gab1 siRNA could be rescued not only by expression of an exogenous mouse Gab1 but also by an exogenous human Gab2 and vice versa, but not by IRS1 (insulin receptor substrate 1). These results reveal that Gab2 plays a pivotal role in the EGF-induced ERK activation pathway and that it can complement the function of Gab1 in the EGF signalling pathway. Furthermore, Gab1 and Gab2 are critical signalling threshold proteins for ERK activation by EGF.
在人类中已鉴定出Gab家族对接蛋白的三个成员，即Gab1、Gab2和Gab3。先前的研究发现，肝细胞生长因子优先利用Gab1进行信号传导，而Bcr-Abl则通过Gab2选择性地进行信号传导。Gab1与SHP2的相互作用已被证明可介导表皮生长因子（EGF）激活细胞外信号调节激酶（ERK）。然而，尚不清楚EGF是否选择性地利用Gab1向ERK发出信号，以及在同时表达Gab1和Gab2的细胞中Gab2是否可有可无。我们使用表达内源性Gab1和Gab2的T47D和MCF-7人乳腺癌细胞，研究了这些对接蛋白在EGF诱导的ERK激活中的作用。结果发现，EGF诱导产生的SHP2-Gab1和SHP2-Gab2复合物数量相似。SHP2结合缺陷型Gab1或Gab2突变体的表达均阻断了EGF诱导的ERK激活。通过小分子干扰RNA（siRNA）下调Gab1或Gab2均可有效抑制EGF刺激的ERK激活途径和细胞迁移。有趣的是，Gab1 siRNA的抑制作用不仅可以通过表达外源性小鼠Gab1来挽救，还可以通过外源性人Gab2来挽救，反之亦然，但不能通过胰岛素受体底物1（IRS1）来挽救。这些结果表明，Gab2在EGF诱导的ERK激活途径中起关键作用，并且它可以在EGF信号通路中补充Gab1的功能。此外，Gab1和Gab2是EGF激活ERK的关键信号阈值蛋白。
