Iwahara Toshinori, Akagi Tsuyoshi, Shishido Tomoyuki, Hanafusa Hidesaburo
Laboratory of Molecular Oncology, Osaka Bioscience Institute, 6-2-4 Furuedai, Suita, Osaka 565-0874, Japan.
Oncogene. 2003 Sep 4;22(38):5946-57. doi: 10.1038/sj.onc.1206633.
CrkII belongs to the adaptor protein family that plays a crucial role in signal transduction. In order to better understand the biological functions of CrkII, we focused on the regulation of gene expression by CrkII. Various transcriptional control elements were examined for their activation by CrkII-expression, and we found that CrkII selectively activates the serum response element (SRE), a transcriptional control element of immediate-early genes. This SRE activation induced by CrkII-overexpression was mediated by the serum response factor (SRF) via Rho. Indeed, we confirmed that the amount of activated Rho was increased in the CrkII-expressing cells. Moreover, we showed that when overexpressed, CrkII induces the cellular transformation of NIH 3T3 cells and that a dominant negative mutant of Rho suppresses this transformation, strongly suggesting that activation of Rho is essential for the transforming activity by CrkII. Furthermore, we also found that CrkII and Galpha12, a member of the heterotrimeric G proteins, synergistically activates Rho as well as the SRF, and that an SH3 mutant of CrkII can inhibit the Galpha12-induced activation of SRF. These results strongly suggest that CrkII is involved in the activation of Rho and SRF by Galpha12. Our study provides strong evidence that Rho activation plays a crucial role in CrkII-mediated signals to induce gene expression and cellular transformation.
CrkII属于衔接蛋白家族，在信号转导中起关键作用。为了更好地理解CrkII的生物学功能，我们聚焦于CrkII对基因表达的调控。我们检测了各种转录控制元件受CrkII表达激活的情况，发现CrkII选择性激活血清反应元件（SRE），即即刻早期基因的转录控制元件。CrkII过表达诱导的这种SRE激活是由血清反应因子（SRF）通过Rho介导的。事实上，我们证实表达CrkII的细胞中活化的Rho量增加。此外，我们表明，过表达时CrkII会诱导NIH 3T3细胞发生细胞转化，并且Rho的显性负性突变体可抑制这种转化，这强烈表明Rho的激活对于CrkII的转化活性至关重要。此外，我们还发现CrkII与异源三聚体G蛋白的成员之一Gα12协同激活Rho以及SRF，并且CrkII的一个SH3突变体可以抑制Gα12诱导的SRF激活。这些结果强烈表明CrkII参与了Gα12对Rho和SRF的激活。我们的研究提供了有力证据，表明Rho激活在CrkII介导的诱导基因表达和细胞转化的信号中起关键作用。
