Department of Internal Medicine III, Technische Universität München, Munich, Germany.
Departments of Genetics and Pediatrics, Stanford University, Stanford, CA, USA.
Oncogene. 2015 Jan 29;34(5):578-88. doi: 10.1038/onc.2013.592. Epub 2014 Feb 10.
Lung cancer is the leading cause of cancer-related deaths worldwide. Recently, we have shown that Notch1 inhibition resulted in substantial cell death of non-small cell lung cancer (NSCLC) cells in vitro. New compounds targeting Notch signal transduction have been developed and are now being tested in clinical trials. However, the tumorigenic role of individual Notch receptors in vivo remains largely unclear. Using a Kras(G12D)-driven endogenous NSCLC mouse model, we analyzed the effect of conditional Notch1 and Notch2 receptor deletion on NSCLC tumorigenesis. Notch1 deficiency led to a reduced early tumor formation and lower activity of MAPK compared with the controls. Unexpectedly, Notch2 deletion resulted in a dramatically increased carcinogenesis and increased MAPK activity. These mice died significantly earlier due to rapidly growing tumor burden. We found that Notch1 regulates Ras/MAPK pathway via HES1-induced repression of the DUSP1 promoter encoding a phosphatase specifically suppressing pERK1/2. Interestingly, Notch1 but not Notch2 ablation leads to decreased HES1 and DUSP1 expression. However, Notch2-depleted tumors showed an appreciable increase in β-catenin expression, a known activator of HES1 and important lung cancer oncogene. Characteristically for β-catenin upregulation, we found that the majority of Notch2-deficient tumors revealed an undifferentiated phenotype as determined by their morphology, E-Cadherin and TTF1 expression levels. In addition, these carcinomas showed aggressive growth patterns with bronchus invasion and obstruction. Together, we show that Notch2 mediates differentiation and has tumor suppressor functions during lung carcinogenesis, whereas Notch1 promotes tumor initiation and progression. These data are further supported by immunohistochemical analysis of human NSCLC samples showing loss or downregulation of Notch2 compared with normal lung tissue. In conclusion, this is the first study characterizing the in vivo functions of Notch1 and Notch2 in Kras(G12D)-driven NSCLC tumorigenesis. These data highlight the clinical importance of a thorough understanding of Notch signaling especially with regard to Notch-targeted therapies.
肺癌是全球癌症相关死亡的主要原因。最近，我们已经证明 Notch1 抑制可导致非小细胞肺癌 (NSCLC) 细胞在体外大量死亡。新的靶向 Notch 信号转导的化合物已经被开发出来，并正在临床试验中进行测试。然而，个体 Notch 受体在体内的致瘤作用在很大程度上仍不清楚。使用 Kras(G12D)驱动的内源性 NSCLC 小鼠模型，我们分析了条件性 Notch1 和 Notch2 受体缺失对 NSCLC 肿瘤发生的影响。与对照组相比，Notch1 缺陷导致早期肿瘤形成减少和 MAPK 活性降低。出乎意料的是，Notch2 缺失导致致癌作用显著增加和 MAPK 活性增加。这些小鼠由于肿瘤负荷迅速增加而死亡显著提前。我们发现 Notch1 通过 HES1 诱导的 DUSP1 启动子抑制来调节 Ras/MAPK 通路，DUSP1 编码一种专门抑制 pERK1/2 的磷酸酶。有趣的是，Notch1 但不是 Notch2 缺失导致 HES1 和 DUSP1 表达减少。然而，Notch2 耗尽的肿瘤显示出 β-catenin 表达的显著增加，β-catenin 是 HES1 的已知激活剂和重要的肺癌致癌基因。典型的 β-catenin 上调，我们发现大多数 Notch2 缺陷型肿瘤由于其形态、E-Cadherin 和 TTF1 表达水平而呈现未分化表型。此外，这些癌表现出具有支气管侵袭和阻塞的侵袭性生长模式。总之，我们表明 Notch2 在肺肿瘤发生过程中介导分化并具有肿瘤抑制功能，而 Notch1 促进肿瘤起始和进展。这些数据进一步得到了人类 NSCLC 样本的免疫组织化学分析的支持，与正常肺组织相比，这些样本显示 Notch2 的缺失或下调。总之，这是首次描述 Notch1 和 Notch2 在 Kras(G12D)驱动的 NSCLC 肿瘤发生中的体内功能的研究。这些数据强调了全面了解 Notch 信号的临床重要性，特别是在 Notch 靶向治疗方面。
