Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030-3498, USA.
Proc Natl Acad Sci U S A. 2010 Feb 23;107(8):3522-7. doi: 10.1073/pnas.0910179107. Epub 2010 Feb 3.
Tumor-initiating cells (TICs) have been shown both experimentally and clinically to be resistant to radiation and chemotherapy, potentially resulting in residual disease that can lead to recurrence. In this study, we demonstrate that TICs isolated from p53 null mouse mammary tumors repair DNA damage following in vivo ionizing radiation more efficiently than the bulk of the tumor cells. Down-regulation of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) was observed both in fluorescence activated cell sorting (FACS)-isolated TICs as compared to non-TICs and in TIC-enriched mammospheres as compared to primary tumor cells depleted of TICs. This effect was accompanied by increased Akt signaling, as well as by the direct activation of the canonical Wnt/beta-catenin signaling pathway specifically within the TIC subpopulation by phosphorylation of beta-catenin on serine 552. Using limiting dilution transplantation performed on p53 null tumor cells transduced with Wnt reporter lentivirus, we demonstrated that FACS sorting of cells expressing TOP-eGFP resulted in a marked enrichment for TICs. Furthermore, FACS analysis demonstrated that cells with active Wnt signaling overlapped with the TIC subpopulation characterized previously using cell surface markers. Finally, pharmacological inhibition of the Akt pathway in both mammospheres and syngeneic mice bearing tumors was shown to inhibit canonical Wnt signaling as well as the repair of DNA damage selectively in TICs, sensitizing them to ionizing radiation treatment. Thus, these results suggest that pretreatment with Akt inhibitors before ionizing radiation treatment may be of potential therapeutic benefit to patients.
肿瘤起始细胞（TICs）已被实验和临床证明对辐射和化疗具有抗性，可能导致残留疾病，从而导致复发。在这项研究中，我们证明了从 p53 缺失的小鼠乳腺肿瘤中分离的 TIC 在体内电离辐射后修复 DNA 损伤的效率比肿瘤细胞的大部分都高。在荧光激活细胞分选（FACS）分离的 TIC 中与非 TIC 相比，以及在富含 TIC 的乳腺球体中与原发性肿瘤细胞中 TIC 耗尽相比，观察到磷酸酶和张力蛋白同源物缺失的染色体 10（PTEN）下调。这种效应伴随着 Akt 信号的增加，以及通过磷酸化 beta-catenin 的丝氨酸 552，特异性地在 TIC 亚群中直接激活经典的 Wnt/β-catenin 信号通路。通过用 Wnt 报告 lentivirus 转导的 p53 缺失肿瘤细胞进行有限稀释移植，我们证明了对表达 TOP-eGFP 的细胞进行 FACS 分选导致 TIC 明显富集。此外，FACS 分析表明，具有活跃 Wnt 信号的细胞与先前使用细胞表面标志物表征的 TIC 亚群重叠。最后，在乳腺球体和携带肿瘤的同基因小鼠中，用 Akt 途径的药理学抑制剂处理，显示出选择性地抑制 TIC 中的经典 Wnt 信号和 DNA 损伤的修复，使它们对电离辐射治疗敏感。因此，这些结果表明，在电离辐射治疗前用 Akt 抑制剂预处理可能对患者具有潜在的治疗益处。
