Kim Jeongyub, Jung Jieun, Lee Su-Jae, Lee Jae-Seon, Park Myung-Jin
Divisions of Radiation Cancer Research, Korea Institute of Radiological and Medical Sciences, Nowon-gu, Seoul 139-706.
Oncol Lett. 2012 Mar;3(3):607-612. doi: 10.3892/ol.2011.531. Epub 2011 Dec 21.
Recent studies have shown that a small subpopulation of stem-like cancer cells within most solid tumors are responsible for the malignancy of aggressive cancer cells, including tumorigenicity and relapse of solid tumors. These tumor cells may be enriched and maintained in vitro in the presence of growth factors (GFs), including epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF), without serum in almost all solid tumor cell lines. In the present study, however, we found that the enrichment of cancer stem-like cells (CSCs) from established cell lines using sphere cultures was achieved efficiently without GFs. Enhanced sphere-forming activity was detected in GF-free cultures compared with GF-containing cultures in MCF7, A549 and U87 cells. Analysis of conditioned media (CM) demonstrated an elevated level of EGF secretion in GF-free CM compared with GF-containing CM in MCF7 cells. By contrast, cells in GF-free CM exhibited almost no secretion of bFGF, whereas cells in GF-containing CM secreted a high level of bFGF. The addition of EGF enhanced sphere formation, whereas bFGF suppressed sphere formation under GF-free conditions in MCF7 cells. Conversely, the addition of bFGF suppressed sphere formation in these cells. Notably, bFGF markedly suppressed EGF receptor (EGFR) expression and EGF secretion in MCF7 and A549 cells. Consistent with this result, EGFR blockade with pharmacological inhibitors significantly suppressed sphere formation in MCF7 and A549 cells under GF-free conditions. Furthermore, the neutralization of EGF also inhibited sphere formation, whereas bFGF neutralization still enhanced sphere formation under these conditions. Together, CSCs may be maintained in a serum-free culture condition without GFs, possibly through autocrine secretion of GFs such as EGF, and the addition of bFGF may not be sufficient for the enrichment of stem-like cancer cells.
最近的研究表明，大多数实体瘤中一小部分干细胞样癌细胞是侵袭性癌细胞恶性特征的根源，包括实体瘤的致瘤性和复发。在几乎所有实体瘤细胞系中，这些肿瘤细胞在存在生长因子（GFs）（包括表皮生长因子（EGF）和碱性成纤维细胞生长因子（bFGF））的情况下，可在无血清条件下于体外富集并维持。然而，在本研究中，我们发现使用球体培养从已建立的细胞系中高效富集癌症干细胞样细胞（CSCs）无需生长因子。与含GF的培养物相比，在MCF7、A549和U87细胞的无GF培养物中检测到增强的球体形成活性。对条件培养基（CM）的分析表明，与MCF7细胞中含GF的CM相比，无GF的CM中EGF分泌水平升高。相比之下，无GF的CM中的细胞几乎不分泌bFGF，而含GF的CM中的细胞分泌高水平的bFGF。在MCF7细胞的无GF条件下，添加EGF可增强球体形成，而bFGF则抑制球体形成。相反，添加bFGF可抑制这些细胞中的球体形成。值得注意的是，bFGF显著抑制MCF7和A549细胞中表皮生长因子受体（EGFR）的表达和EGF分泌。与该结果一致，用药物抑制剂阻断EGFR可在无GF条件下显著抑制MCF7和A549细胞中的球体形成。此外，中和EGF也可抑制球体形成，而在这些条件下中和bFGF仍可增强球体形成。总之，CSCs可能在无GF的无血清培养条件下通过自分泌GF（如EGF）得以维持，并且添加bFGF可能不足以富集干细胞样癌细胞。
