Jenei Veronika, Andersson Tommy, Jakus Judit, Dib Karim
Institute of Biomolecular Chemistry, Chemical Research Centre, Hungarian Academy of Sciences, Pusztaszeri Street 59-67, 1025 Budapest, Hungary.
Exp Cell Res. 2005 Nov 1;310(2):463-73. doi: 10.1016/j.yexcr.2005.08.010. Epub 2005 Sep 22.
E3B1, a human homologue of the mouse gene product Abi-1, has been implicated in growth-factor-mediated regulation of the small GTPases p21Ras and Rac. E3b1 is a regulator of Rac because it can form a complex with Sos-1 and eps8, and such a Sos-1-e3B1-eps8 complex serves as a guanine nucleotide exchange factor for Rac. In the present study, we found that overexpression of e3B1 in NIH3T3/EGFR cells sensitized EGF-induced activation of Rac1, whereas it had no impact on EGF-induced activation of p21Ras. Remarkably, we found that EGF-induced activation of the p21Ras-related GTPase Rap1 was also sensitized in NIH3T3/EGFR-e3B1 cells. Thus, in NIH3T3/EGFR-e3B1 cells, maximal EGF-induced activation of Rap1 occurs with a dose of EGF much lower than in NIH3T3/EGFR cells. We also report that overexpression of e3B1 in NIH3T3/EGFR cells renders EGF-induced activation of Rap1 completely dependent on Src tyrosine kinases but not on c-Abl. However, EGF-induced tyrosine phosphorylation of the Rap GEF C3G occurred regardless of whether e3B1 was overexpressed or not, and this did not involve Src tyrosine kinases. Accordingly, we propose that overexpression of e3B1 in NIH3T3/EGFR cells leads to mobilization of Src tyrosine kinases that participate in EGF-induced activation of Rap1 and inhibition of cell proliferation.
E3B1是小鼠基因产物Abi-1的人类同源物，已被证明参与生长因子介导的小GTP酶p21Ras和Rac的调节。E3b1是Rac的调节因子，因为它可以与Sos-1和eps8形成复合物，并且这种Sos-1-E3B1-eps8复合物作为Rac的鸟嘌呤核苷酸交换因子。在本研究中，我们发现NIH3T3/EGFR细胞中e3B1的过表达使EGF诱导的Rac1激活敏感化，而对EGF诱导的p21Ras激活没有影响。值得注意的是，我们发现NIH3T3/EGFR-e3B1细胞中EGF诱导的与p21Ras相关的GTP酶Rap1的激活也敏感化。因此，在NIH3T3/EGFR-e3B1细胞中，EGF诱导的Rap1最大激活所需的EGF剂量远低于NIH3T3/EGFR细胞。我们还报告说，NIH3T3/EGFR细胞中e3B1的过表达使EGF诱导的Rap1激活完全依赖于Src酪氨酸激酶而不是c-Abl。然而，无论e3B1是否过表达，EGF诱导的Rap GEF C3G的酪氨酸磷酸化都会发生，并且这与Src酪氨酸激酶无关。因此，我们提出NIH3T3/EGFR细胞中e3B1的过表达导致参与EGF诱导的Rap1激活和细胞增殖抑制的Src酪氨酸激酶的动员。
