Department of Cancer Biology, Dana-Farber Cancer Institute and Department of Pathology, Harvard Medical School, Boston, MA 02115, USA.
Int J Oncol. 2012 Nov;41(5):1855-62. doi: 10.3892/ijo.2012.1602. Epub 2012 Aug 22.
Members of the Ras protooncogene family are mutated in approximately 75% of colon cancers. The Raf kinases (Raf-1, b-Raf and a-Raf) directly interact with Ras and serve as mediators of mitogenic signals. Expression of the constitutively active alleles of Raf or Ras gene families results in oncogenesis in a number of model systems. Previous studies emphasized the importance of Raf-1 and b-Raf in preventing apoptosis in addition to their roles in cell growth. In the present study, we examined whether inhibition of the Raf-1 or b-Raf kinase decreases cell growth and increases apoptosis in colon cancer cells. c-Raf and b-Raf were depleted in colon cancer cell lines, such as HCT116, HT29 and Colo205, containing Ras or b-Raf mutations by RNA interference (RNAi). The results showed that colon cancer cells with activating Ras mutations undergo apoptosis following Raf-1 inhibition, as determined by cell cycle analysis and the release of cytochrome c. Moreover, in b-Raf mutant colon cancers, the inhibition of b-Raf as compared to Raf-1 is crucial for cancer cell death. There is increasing evidence for both MEK-independent Raf signaling and Raf-independent MEK signaling. Thus, we investigated whether targeting multiple points of the mitogen-activated protein kinase (MAPK) pathway with a MEK inhibitor and Raf RNAi increases cancer cell death. The results showed that combination therapy, inhibiting Raf and MEK kinases simultaneously, increased apoptosis in colon cancer cells. Taken together, our data demonstrate that combination therapy targeting the MAPK pathway at two distinct points, Raf kinase and MEK, has greater efficacy in increasing cancer cell death and is likely to improve therapeutic outcomes for patients.
Ras 原癌基因家族的成员在大约 75%的结肠癌中发生突变。 Raf 激酶（Raf-1、b-Raf 和 a-Raf）直接与 Ras 相互作用，作为有丝分裂信号的介质。 Raf 或 Ras 基因家族的组成性激活等位基因的表达导致许多模型系统中的致癌作用。以前的研究强调了 Raf-1 和 b-Raf 在除了在细胞生长中的作用之外，在防止细胞凋亡中的重要性。在本研究中，我们研究了 Raf-1 或 b-Raf 激酶的抑制是否会减少结肠癌细胞的生长并增加细胞凋亡。通过 RNA 干扰 (RNAi)，在含有 Ras 或 b-Raf 突变的结肠癌细胞系（如 HCT116、HT29 和 Colo205）中耗尽 c-Raf 和 b-Raf。结果表明，具有激活 Ras 突变的结肠癌细胞在 Raf-1 抑制后经历细胞凋亡，如细胞周期分析和细胞色素 c 的释放所确定的。此外，在 b-Raf 突变的结肠癌中，与 Raf-1 相比，b-Raf 的抑制对于癌细胞死亡至关重要。有越来越多的证据表明 Raf 信号传导和 Raf 独立的 MEK 信号传导均不依赖于 MEK。因此，我们研究了用 MEK 抑制剂和 Raf RNAi 靶向丝裂原活化蛋白激酶 (MAPK) 途径的多个点是否会增加癌细胞死亡。结果表明，联合治疗，同时抑制 Raf 和 MEK 激酶，增加了结肠癌细胞的凋亡。总之，我们的数据表明，针对 MAPK 途径的两个不同点，Raf 激酶和 MEK，的联合治疗在增加癌细胞死亡方面更有效，可能改善患者的治疗效果。
