Chen Ting, Zhang Yu, Guo Wen-Hao, Meng Mao-Bin, Mo Xian-Ming, Lu You
Department of Thoracic Oncology, Cancer Center, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, P. R. China.
Chin J Cancer. 2010 Mar;29(3):270-6. doi: 10.5732/cjc.009.10694.
Radiotherapy (RT) is a major non-surgical modality in the comprehensive treatment for colorectal adenocarcinoma. The radioresistance of cancer stem cells (CSCs) is a key factor that influences therapeutic effectiveness. This study was to investigate the effects of specific chromosome structure and histone modification in CSCs in colorectal adenocarcinoma radioresistance.
Samples were collected from resected human colorectal adenocarcinomas. Subcutaneous colorectal cancer model was established in nude mice. Immunohistochemistry showed that xenografts generated from bulk colorectal cancer cells resembled the original tumor specimen. Flow cytometry was performed to sort CSCs (CD133+) and non-CSCs (CD133-) from both resected samples of colorectal adenocarcinoma and xenograft before and after high single-dose radiation. The markers labeling heterochromatin (H3K9me3, HP1-alpha and H3K4me1) and euchromatin (H3K4me3) in CD133+ and CD133- nucleus were detected by immunofluorescence.
There was distinct difference in chromatin structure between colorectal CSCs (CD133+) and non-CSCs (CD133-). The chromatin displayed compact patches in CD133+ nucleus, but loosely latticed structure in CD133- nucleus; immunofluorescence verified that the compact patches existing in CSCs was generated from heterochromatin construction. In addition, the vacuole-like defect in heterochromatin regions of CSCs was observed within 24 h after exposure to 10 gray (Gy) single-dose RT. Interestingly, this phenomenon was repaired from 96 h, and recovered to dense plaque structure in heterochromatin regions of CSCs after 144 h. However, no significant difference in non-CSCs was observed after RT exception for a loose chromatin structure.
CSCs play a role in radiosensitivity in colorectal cancer. The mechanism may be related to heterochromatin formation and histone methylation.
放射治疗（RT）是结直肠癌综合治疗中的一种主要非手术方式。癌症干细胞（CSCs）的放射抗性是影响治疗效果的关键因素。本研究旨在探讨结直肠癌中CSCs的特定染色体结构和组蛋白修饰对放射抗性的影响。
收集人结直肠癌切除样本。在裸鼠中建立皮下结直肠癌模型。免疫组化显示，由大量结直肠癌细胞生成的异种移植物与原始肿瘤标本相似。在高单次剂量放疗前后，对结直肠癌切除样本和异种移植物进行流式细胞术分选CSCs（CD133+）和非CSCs（CD133-）。通过免疫荧光检测CD133+和CD133-细胞核中标记异染色质（H3K9me3、HP1-α和H3K4me1）和常染色质（H3K4me3）的标志物。
结直肠癌CSCs（CD133+）和非CSCs（CD133-）之间的染色质结构存在明显差异。CD133+细胞核中的染色质呈现紧密斑块，而CD133-细胞核中的染色质呈现松散的格子状结构；免疫荧光证实CSCs中存在的紧密斑块是由异染色质构建产生的。此外，在接受10格雷（Gy）单次剂量RT后24小时内，观察到CSCs异染色质区域出现空泡样缺陷。有趣的是，这种现象在96小时开始修复，并在144小时后恢复到CSCs异染色质区域的致密斑块结构。然而，RT后非CSCs除染色质结构松散外未观察到显著差异。
CSCs在结直肠癌放射敏感性中起作用。其机制可能与异染色质形成和组蛋白甲基化有关。
