Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore, Karnataka, India.
Oncogene. 2012 Apr 12;31(15):1896-909. doi: 10.1038/onc.2011.378. Epub 2011 Aug 29.
Emerging evidence suggests that cancers arise in stem/progenitor cells. Yet, the requirements for transformation of these primitive cells remains poorly understood. In this study, we have exploited the 'mammosphere' system that selects for primitive mammary stem/progenitor cells to explore their potential and requirements for transformation. Introduction of Simian Virus 40 Early Region and hTERT into mammosphere-derived cells led to the generation of NBLE, an immortalized mammary epithelial cell line. The NBLEs largely comprised of bi-potent progenitors with long-term self-renewal and multi-lineage differentiation potential. Clonal and karyotype analyses revealed the existence of heterogeneous population within NBLEs with varied proliferation, differentiation and sphere-forming potential. Significantly, injection of NBLEs into immunocompromised mice resulted in the generation of invasive ductal adenocarcinomas. Further, these cells harbored a sub-population of CD44(+)/CD24(-) fraction that alone had sphere- and tumor-initiating potential and resembled the breast cancer stem cell gene signature. Interestingly, prolonged in vitro culturing led to their further enrichment. The NBLE cells also showed increased expression of stemness and epithelial to mesenchymal transition markers, deregulated self-renewal pathways, activated DNA-damage response and cancer-associated chromosomal aberrations-all of which are likely to have contributed to their tumorigenic transformation. Thus, unlike previous in vitro transformation studies that used adherent, more differentiated human mammary epithelial cells our study demonstrates that the mammosphere-derived, less-differentiated cells undergo tumorigenic conversion with only two genetic elements, without requiring oncogenic Ras. Moreover, the striking phenotypic and molecular resemblance of the NBLE-generated tumors with naturally arising breast adenocarcinomas supports the notion of a primitive breast cell as the origin for this subtype of breast cancer. Finally, the NBLEs represent a heterogeneous population of cells with striking plasticity, capable of differentiation, self-renewal and tumorigenicity, thus offering a unique model system to study the molecular mechanisms involved with these processes.
新出现的证据表明，癌症起源于干细胞/祖细胞。然而，这些原始细胞转化的要求仍知之甚少。在这项研究中，我们利用了“乳腺球体”系统来选择原始的乳腺干细胞/祖细胞，以探索它们的潜力和转化的要求。将猴病毒 40 早期区和 hTERT 导入乳腺球体衍生的细胞中，导致了 NBLE 的产生，这是一种永生化的乳腺上皮细胞系。NBLE 主要由具有长期自我更新和多谱系分化潜力的双潜能祖细胞组成。克隆和核型分析显示，NBLE 内存在具有不同增殖、分化和球体形成能力的异质群体。重要的是，将 NBLE 注射到免疫缺陷小鼠中会导致侵袭性导管腺癌的产生。此外，这些细胞还存在一个 CD44(+)/CD24(-)亚群，该亚群仅具有球体和肿瘤起始能力，并且类似于乳腺癌干细胞的基因特征。有趣的是，体外长期培养会导致其进一步富集。NBLE 细胞还表现出更高的干性和上皮间质转化标志物的表达、失调的自我更新途径、激活的 DNA 损伤反应和与癌症相关的染色体异常——所有这些都可能促成了它们的肿瘤转化。因此，与之前使用贴壁、更分化的人乳腺上皮细胞的体外转化研究不同，我们的研究表明，乳腺球体衍生的、分化程度较低的细胞在仅需要两个遗传元件的情况下发生肿瘤转化，而不需要致癌 Ras。此外，NBLE 产生的肿瘤与自然发生的乳腺腺癌在表型和分子上惊人的相似，支持了原始乳腺细胞是这种乳腺癌亚型起源的观点。最后，NBLE 代表了具有惊人可塑性的细胞异质性群体，能够分化、自我更新和致瘤，因此为研究这些过程涉及的分子机制提供了一个独特的模型系统。
