Department of Respiratory Medicine, Institute of Clinical Medicine, University of Tsukuba, Tsukuba, Ibaraki, Japan.
Oncogene. 2012 Nov 8;31(45):4768-77. doi: 10.1038/onc.2011.628. Epub 2012 Jan 16.
We previously demonstrated that the transcription factor NF-E2-related factor2 (Nrf2), expressed abundantly in non-small-cell lung cancer (NSCLC) cells, plays a pivotal role in the proliferation and chemoresistance of NSCLC. Here we show that Nrf2-mediated NSCLC cell proliferation is dually regulated by epidermal growth factor receptor (EGFR) signaling and an Nrf2 repressor protein Keap1 (Kelch-like ECH-associated protein-1). NSCLC cells expressing wild-type EGFR and Keap1 genes show enhanced proliferation on stimulation with EGFR ligand under non-stress conditions. Exposure to cigarette smoke extract (CSE) enhanced cell proliferation by modification of the Nrf2/Keap1 interaction. Although EGFR-tyrosine kinase inhibitor (TKI) inhibited the proliferation of these cells, exposure to CSE attenuated its efficacy. In NSCLC cells with Keap1 gene mutations, Nrf2 was constitutively activated owing to dysfunction of Keap1 and cells proliferated independently of EGFR signaling. Furthermore, EGFR-TKI was unable to inhibit their proliferation. In NSCLC cells with EGFR gene mutations, Nrf2 was constitutively activated by EGFR signaling. In these cells, proliferation was largely dependent on the EGFR signaling pathway. Although these cells were highly sensitive to EGFR-TKI, exposure to CSE or knockdown of Keap1 mRNA reduced sensitivity to EGFR-TKI. We found a case of NSCLC showing resistance to EGFR-TKI despite having EGFR-TKI-sensitive EGFR gene mutation because of dysfunctional mutation in Keap1 gene. Results indicate that oxidative stress reduces the anticancer effects of EGFR-TKI in wild-type Keap1 NSCLC cells. Analysis of Keap1 dysfunction may become a novel molecular marker to predict resistance to EGFR-TKI in NSCLC cells having EGFR-TKI-sensitive EGFR mutations. Finally, as the downstream molecule of both EGFR and Keap1 signaling, Nrf2 is an important molecular target for the treatment of NSCLC, where cells have mutations in EGFR, KRAS or Keap1 genes.
我们之前证明，转录因子 NF-E2 相关因子 2（Nrf2）在非小细胞肺癌（NSCLC）细胞中大量表达，在 NSCLC 的增殖和化疗耐药中发挥关键作用。在这里，我们表明 Nrf2 介导的 NSCLC 细胞增殖受到表皮生长因子受体（EGFR）信号和 Nrf2 抑制蛋白 Keap1（Kelch-like ECH-associated protein-1）的双重调节。表达野生型 EGFR 和 Keap1 基因的 NSCLC 细胞在非应激条件下受到 EGFR 配体刺激时显示出增强的增殖。香烟烟雾提取物（CSE）通过修饰 Nrf2/Keap1 相互作用增强细胞增殖。虽然 EGFR 酪氨酸激酶抑制剂（TKI）抑制这些细胞的增殖，但暴露于 CSE 会降低其疗效。在具有 Keap1 基因突变的 NSCLC 细胞中，由于 Keap1 功能障碍，Nrf2 持续激活，细胞增殖独立于 EGFR 信号。此外，EGFR-TKI 无法抑制其增殖。在具有 EGFR 基因突变的 NSCLC 细胞中，Nrf2 被 EGFR 信号持续激活。在这些细胞中，增殖在很大程度上依赖于 EGFR 信号通路。虽然这些细胞对 EGFR-TKI 高度敏感，但暴露于 CSE 或敲低 Keap1 mRNA 会降低对 EGFR-TKI 的敏感性。我们发现一例 NSCLC 尽管具有 EGFR-TKI 敏感的 EGFR 基因突变，但由于 Keap1 基因突变功能失调而对 EGFR-TKI 产生耐药。结果表明，氧化应激降低了野生型 Keap1 NSCLC 细胞中 EGFR-TKI 的抗癌作用。分析 Keap1 功能障碍可能成为预测具有 EGFR-TKI 敏感 EGFR 突变的 NSCLC 细胞对 EGFR-TKI 耐药的新型分子标志物。最后，作为 EGFR 和 Keap1 信号的下游分子，Nrf2 是治疗 EGFR、KRAS 或 Keap1 基因突变的 NSCLC 细胞的重要分子靶点。
