Cragg Mark S, Kuroda Junya, Puthalakath Hamsa, Huang David C S, Strasser Andreas
The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia.
PLoS Med. 2007 Oct;4(10):1681-89; discussion 1690. doi: 10.1371/journal.pmed.0040316.
The epidermal growth factor receptor (EGFR) plays a critical role in the control of cellular proliferation, differentiation, and survival. Abnormalities in EGF-EGFR signaling, such as mutations that render the EGFR hyperactive or cause overexpression of the wild-type receptor, have been found in a broad range of cancers, including carcinomas of the lung, breast, and colon. EGFR inhibitors such as gefitinib have proven successful in the treatment of certain cancers, particularly non-small cell lung cancers (NSCLCs) harboring activating mutations within the EGFR gene, but the molecular mechanisms leading to tumor regression remain unknown. Therefore, we wished to delineate these mechanisms.
We performed biochemical and genetic studies to investigate the mechanisms by which inhibitors of EGFR tyrosine kinase activity, such as gefitinib, inhibit the growth of human NSCLCs. We found that gefitinib triggered intrinsic (also called "mitochondrial") apoptosis signaling, involving the activation of BAX and mitochondrial release of cytochrome c, ultimately unleashing the caspase cascade. Gefitinib caused a rapid increase in the level of the proapoptotic BH3-only protein BIM (also called BCL2-like 11) through both transcriptional and post-translational mechanisms. Experiments with pharmacological inhibitors indicated that blockade of MEK-ERK1/2 (mitogen-activated protein kinase kinase-extracellular signal-regulated protein kinase 1/2) signaling, but not blockade of PI3K (phosphatidylinositol 3-kinase), JNK (c-Jun N-terminal kinase or mitogen-activated protein kinase 8), or AKT (protein kinase B), was critical for BIM activation. Using RNA interference, we demonstrated that BIM is essential for gefitinib-induced killing of NSCLC cells. Moreover, we found that gefitinib-induced apoptosis is enhanced by addition of the BH3 mimetic ABT-737.
Inhibitors of the EGFR tyrosine kinase have proven useful in the therapy of certain cancers, in particular NSCLCs possessing activating mutations in the EGFR kinase domain, but the mechanisms of tumor cell killing are still unclear. In this paper, we demonstrate that activation of the proapoptotic BH3-only protein BIM is essential for tumor cell killing and that shutdown of the EGFR-MEK-ERK signaling cascade is critical for BIM activation. Moreover, we demonstrate that addition of a BH3 mimetic significantly enhances killing of NSCLC cells by the EGFR tyrosine kinase inhibitor gefitinib. It appears likely that this approach represents a paradigm shared by many, and perhaps all, oncogenic tyrosine kinases and suggests a powerful new strategy for cancer therapy.
表皮生长因子受体（EGFR）在细胞增殖、分化和存活的调控中发挥关键作用。在包括肺癌、乳腺癌和结肠癌在内的多种癌症中，已发现EGF-EGFR信号通路异常，如导致EGFR过度活跃的突变或引起野生型受体过表达的突变。吉非替尼等EGFR抑制剂已被证明在治疗某些癌症方面取得成功，尤其是在EGFR基因内具有激活突变的非小细胞肺癌（NSCLC），但导致肿瘤消退的分子机制仍不清楚。因此，我们希望阐明这些机制。
我们进行了生化和遗传学研究，以探究EGFR酪氨酸激酶活性抑制剂（如吉非替尼）抑制人NSCLC生长的机制。我们发现吉非替尼触发了内在（也称为“线粒体”）凋亡信号，涉及BAX的激活和细胞色素c从线粒体的释放，最终引发半胱天冬酶级联反应。吉非替尼通过转录和翻译后机制使促凋亡的仅含BH3结构域的蛋白BIM（也称为BCL2样11）水平迅速升高。用药理抑制剂进行的实验表明，阻断MEK-ERK1/2（丝裂原活化蛋白激酶激酶-细胞外信号调节蛋白激酶1/2）信号通路对BIM激活至关重要，而阻断PI3K（磷脂酰肌醇3激酶）、JNK（c-Jun氨基末端激酶或丝裂原活化蛋白激酶8）或AKT（蛋白激酶B）则不然。使用RNA干扰，我们证明BIM对吉非替尼诱导的NSCLC细胞杀伤至关重要。此外，我们发现添加BH3模拟物ABT-737可增强吉非替尼诱导的凋亡。
EGFR酪氨酸激酶抑制剂已被证明在某些癌症的治疗中有用，特别是在EGFR激酶结构域具有激活突变的NSCLC中，但肿瘤细胞杀伤机制仍不清楚。在本文中，我们证明促凋亡的仅含BH3结构域的蛋白BIM的激活对肿瘤细胞杀伤至关重要，并且EGFR-MEK-ERK信号级联的关闭对BIM激活至关重要。此外，我们证明添加BH3模拟物可显著增强EGFR酪氨酸激酶抑制剂吉非替尼对NSCLC细胞的杀伤作用。看来这种方法可能代表了许多甚至所有致癌酪氨酸激酶共有的一种模式，并为癌症治疗提出了一种强有力的新策略。
