Department of Tumor Biology, H, Lee Moffitt Cancer Center and Research Institute, 12902 Magnolia Drive, Tampa, FL, 33612, USA.
Mol Cancer. 2012 Sep 25;11:73. doi: 10.1186/1476-4598-11-73.
Cancer stem cells are thought to be responsible for the initiation and progression of cancers. In non-small cell lung cancers (NSCLCs), Hoechst 33342 dye effluxing side population (SP) cells are shown to have stem cell like properties. The oncogenic capacity of cancer stem-like cells is in part due to their ability to self-renew; however the mechanistic correlation between oncogenic pathways and self-renewal of cancer stem-like cells has remained elusive. Here we characterized the SP cells at the molecular level and evaluated its ability to generate tumors at the orthotopic site in the lung microenvironment. Further, we investigated if the self-renewal of SP cells is dependent on EGFR mediated signaling.
SP cells were detected and isolated from multiple NSCLC cell lines (H1650, H1975, A549), as well as primary human tumor explants grown in nude mice. SP cells demonstrated stem-like properties including ability to self-renew and grow as spheres; they were able to generate primary and metastatic tumors upon orthotopic implantation into the lung of SCID mice. In vitro study revealed elevated expression of stem cell associated markers like Oct4, Sox2 and Nanog as well as demonstrated intrinsic epithelial to mesenchymal transition features in SP cells. Further, we show that abrogation of EGFR, Src and Akt signaling through pharmacological or genetic inhibitors suppresses the self-renewal growth and expansion of SP-cells and resulted in specific downregulation of Sox2 protein expression. siRNA mediated depletion of Sox2 significantly blocked the SP phenotype as well as its self-renewal capacity; whereas other transcription factors like Oct4 and Nanog played a relatively lesser role in regulating self-renewal. Interestingly, Sox2 was elevated in metastatic foci of human NSCLC samples.
Our findings suggest that Sox2 is a novel target of EGFR-Src-Akt signaling in NSCLCs that modulates self-renewal and expansion of stem-like cells from NSCLC. Therefore, the outcome of the EGFR-Src-Akt targeted therapy may rely upon the expression and function of Sox2 within the NSCLC-CSCs.
癌症干细胞被认为是癌症发生和发展的根源。在非小细胞肺癌（NSCLC）中，Hoechst 33342 染料外排侧群（SP）细胞表现出类似干细胞的特性。癌干细胞样细胞的致癌能力部分归因于其自我更新的能力；然而，致癌途径与癌干细胞样细胞自我更新之间的机制相关性仍然难以捉摸。在这里，我们从分子水平上对 SP 细胞进行了表征，并评估了其在肺微环境中同源部位生成肿瘤的能力。此外，我们还研究了 SP 细胞的自我更新是否依赖于 EGFR 介导的信号转导。
从多种 NSCLC 细胞系（H1650、H1975、A549）以及在裸鼠中生长的原发性人肿瘤外植体中检测和分离出 SP 细胞。SP 细胞表现出类似干细胞的特性，包括自我更新和生长为球体的能力；它们能够在将其原位植入 SCID 小鼠肺部后生成原发性和转移性肿瘤。体外研究表明，SP 细胞中高水平表达干细胞相关标志物，如 Oct4、Sox2 和 Nanog，并表现出内在的上皮到间充质转化特征。此外，我们还表明，通过药理学或遗传抑制剂阻断 EGFR、Src 和 Akt 信号通路可抑制 SP 细胞的自我更新生长和扩增，并导致 Sox2 蛋白表达的特异性下调。Sox2 的 siRNA 介导耗竭显著阻断了 SP 表型及其自我更新能力；而其他转录因子，如 Oct4 和 Nanog，在调节自我更新方面的作用相对较小。有趣的是，Sox2 在人类 NSCLC 样本的转移灶中升高。
我们的研究结果表明，Sox2 是 NSCLC 中 EGFR-Src-Akt 信号通路的一个新靶点，调节 NSCLC 中干细胞样细胞的自我更新和扩增。因此，EGFR-Src-Akt 靶向治疗的结果可能依赖于 NSCLC-CSCs 中 Sox2 的表达和功能。
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