Department of Hematology and Medical Oncology, Emory University School of Medicine and Winship Cancer Institute, Atlanta, GA, USA.
Cancer Biol Ther. 2012 Mar;13(5):272-80. doi: 10.4161/cbt.18923. Epub 2012 Mar 1.
Eukaryotic translation initiation factor 4E (eIF4E) is the rate-limiting factor for cap-dependent translation initiation, which is known to regulate oncogenesis. Elevated eIF4E and its negative impact on prognosis in human non-small cell lung cancer (NSCLC) have been reported previously. However, its potential as a therapeutic target and role in regulation of sensitivity to EGFR inhibitors is an area of ongoing investigations. In this study, we detected increased levels of eIF4E in 16 human NSCLC cell lines compared with their normal bronchial epithelial cells. Consistently, human tissue array analysis showed that eIF4E expression was significantly higher in human NSCLC tissues than normal tissues. Inhibition of eIF4E using eIF4E siRNA inhibited the growth and invasion of NSCLC cells. These data suggest that eIF4E overexpression plays a crucial role in positive regulation of the growth and invasion of NSCLC cells. By proteomics, we found that eIF4E levels were elevated in erlotinib-resistant cell lines compared with the sensitive parental cell line. In agreement, assembly of the eIF4F cap complex and several oncogenic proteins regulated by the cap-dependent translation mechanism, were also increased in erlotinib-resistant cells. Thus, erlotinib-resistant cells exhibit elevated eIF4E expression and cap-dependent translation. Inhibition of eIF4F with different means (e.g., gene knockdown) downregulated c-Met expression and partially restored cell sensitivity to erlotinib, suggesting that elevated eIF4E contributes to development of erlotinib resistance, likely through positive regulation of c-Met expression. Taken together, we suggest that elevated eIF4E in NSCLC cells is associated with proliferation, invasion and acquired erlotinib resistance.
真核翻译起始因子 4E(eIF4E)是帽依赖翻译起始的限速因子,已知其可调节致癌作用。先前已有报道称,eIF4E 升高及其对人类非小细胞肺癌(NSCLC)预后的负面影响。然而,eIF4E 作为治疗靶点的潜力及其在调节表皮生长因子受体抑制剂敏感性方面的作用是正在研究的一个领域。在这项研究中,我们检测到与正常支气管上皮细胞相比,16 个人类 NSCLC 细胞系中的 eIF4E 水平升高。一致地,人类组织阵列分析显示,eIF4E 在人类 NSCLC 组织中的表达明显高于正常组织。使用 eIF4E siRNA 抑制 eIF4E 可抑制 NSCLC 细胞的生长和侵袭。这些数据表明,eIF4E 过表达在 NSCLC 细胞的生长和侵袭的正调控中起关键作用。通过蛋白质组学,我们发现与敏感亲本细胞系相比,厄洛替尼耐药细胞系中的 eIF4E 水平升高。一致地,帽依赖性翻译机制调节的 eIF4F 帽复合物和几种致癌蛋白的组装也在厄洛替尼耐药细胞中增加。因此,厄洛替尼耐药细胞表现出升高的 eIF4E 表达和帽依赖性翻译。使用不同方法(例如基因敲低)抑制 eIF4F 下调 c-Met 表达并部分恢复细胞对厄洛替尼的敏感性,表明升高的 eIF4E 有助于厄洛替尼耐药的发展,可能通过对 c-Met 表达的正调控。总之,我们认为 NSCLC 细胞中升高的 eIF4E 与增殖、侵袭和获得的厄洛替尼耐药有关。