Department of Surgery, University Medical Center Utrecht, Heidelberglaan 100, Utrecht, The Netherlands.
Neoplasia. 2010 Jun;12(6):443-52. doi: 10.1593/neo.92088.
Epidermal growth factor receptor (EGFR)-targeting therapeutics have shown efficacy in the treatment of colorectal cancer patients. Clinical studies have revealed that activating mutations in the KRAS protooncogene predict resistance to EGFR-targeted therapy. However, the causality between mutant KRAS and resistance to EGFR inhibition has so far not been demonstrated. Here, we show that deletion of the oncogenic KRAS allele from colorectal tumor cells resensitizes those cells to EGFR inhibitors. Resensitization was accompanied by an acquired dependency on the EGFR for maintaining basal extracellular signal-regulated kinase (ERK) activity. Deletion of oncogenic KRAS not only resensitized tumor cells to EGFR inhibition but also promoted EGF-induced NRAS activation, ERK and AKT phosphorylation, and c-FOS transcription. The poor responsiveness of mutant KRAS tumor cells to EGFR inhibition and activation was accompanied by a reduced capacity of these cells to bind and internalize EGF and by a failure to retain EGFR at the plasma membrane. Of 16 human colorectal tumors with activating mutations in KRAS, 15 displayed loss of basolateral EGFR localization. Plasma membrane localization of the EGFR could be restored in vitro by suppressing receptor endocytosis through Rho kinase inhibition. This caused an EGFR-dependent increase in basal and EGF-stimulated ERK phosphorylation but failed to restore tumor cell sensitivity to EGFR inhibition. Our results demonstrate a causal role for oncogenic KRAS in desensitizing tumor cells not only to EGFR inhibitors but also to EGF itself.
表皮生长因子受体 (EGFR)-靶向治疗在治疗结直肠癌患者方面显示出疗效。临床研究表明，KRAS 原癌基因的激活突变预测对 EGFR 靶向治疗的耐药性。然而，突变 KRAS 与对 EGFR 抑制的耐药性之间的因果关系迄今尚未得到证明。在这里，我们表明从结直肠肿瘤细胞中删除致癌 KRAS 等位基因可使这些细胞对 EGFR 抑制剂重新敏感。重新敏感伴随着对 EGFR 的获得性依赖，以维持基础细胞外信号调节激酶 (ERK) 活性。致癌 KRAS 的缺失不仅使肿瘤细胞重新敏感于 EGFR 抑制，而且还促进了 EGF 诱导的 NRAS 激活、ERK 和 AKT 磷酸化以及 c-FOS 转录。突变 KRAS 肿瘤细胞对 EGFR 抑制和激活的反应不佳伴随着这些细胞结合和内化 EGF 的能力降低，以及 EGFR 在质膜上的保留能力降低。在 16 个具有 KRAS 激活突变的人类结直肠肿瘤中，有 15 个显示出基底外侧 EGFR 定位丧失。通过抑制受体内吞作用通过 Rho 激酶抑制在体外可恢复 EGFR 的质膜定位。这导致 EGFR 依赖性基础和 EGF 刺激的 ERK 磷酸化增加，但未能恢复肿瘤细胞对 EGFR 抑制的敏感性。我们的结果表明，致癌 KRAS 不仅使肿瘤细胞对 EGFR 抑制剂而且对 EGF 本身脱敏具有因果关系。
