Campbell Family Cancer Research Institute, University of Toronto, Ontario Cancer Institute/Princess Margaret Hospital, Toronto, Ontario, Canada.
Cancer Res. 2010 Nov 1;70(21):8748-59. doi: 10.1158/0008-5472.CAN-10-0944. Epub 2010 Oct 12.
MYC regulates a myriad of genes controlling cell proliferation, metabolism, differentiation, and apoptosis. MYC also controls the expression of DNA double-strand break (DSB) repair genes and therefore may be a potential target for anticancer therapy to sensitize cancer cells to DNA damage or prevent genetic instability. In this report, we studied whether MYC binds to DSB repair gene promoters and modulates cell survival in response to DNA-damaging agents. Chromatin immunoprecipitation studies showed that MYC associates with several DSB repair gene promoters including Rad51, Rad51B, Rad51C, XRCC2, Rad50, BRCA1, BRCA2, DNA-PKcs, XRCC4, Ku70, and DNA ligase IV. Endogenous MYC protein expression was associated with increased RAD51 and KU70 protein expression of a panel of cancer cell lines of varying histopathology. Induction of MYC in G(0)-G(1) and S-G(2)-M cells resulted in upregulation of Rad51 gene expression. MYC knockdown using small interfering RNA (siRNA) led to decreased RAD51 expression but minimal effects on homologous recombination based on a flow cytometry direct repeat green fluorescent protein assay. siRNA to MYC resulted in tumor cell kill in DU145 and H1299 cell lines in a manner independent of apoptosis. However, MYC-dependent changes in DSB repair protein expression were not sufficient to sensitize cells to mitomycin C or ionizing radiation, two agents selectively toxic to DSB repair-deficient cells. Our results suggest that anti-MYC agents may target cells to prevent genetic instability but would not lead to differential radiosensitization or chemosensitization.
MYC 调控着众多控制细胞增殖、代谢、分化和凋亡的基因。MYC 还控制着 DNA 双链断裂 (DSB) 修复基因的表达，因此可能成为抗癌治疗的潜在靶点，使癌细胞对 DNA 损伤敏感或防止遗传不稳定性。在本报告中，我们研究了 MYC 是否与 DSB 修复基因启动子结合，并调节细胞对 DNA 损伤剂的存活反应。染色质免疫沉淀研究表明，MYC 与包括 Rad51、Rad51B、Rad51C、XRCC2、Rad50、BRCA1、BRCA2、DNA-PKcs、XRCC4、Ku70 和 DNA 连接酶 IV 在内的几种 DSB 修复基因启动子结合。内源性 MYC 蛋白表达与多种不同组织病理学的癌细胞系中 RAD51 和 KU70 蛋白表达的增加有关。在 G(0)-G(1) 和 S-G(2)-M 细胞中诱导 MYC 表达导致 Rad51 基因表达上调。使用小干扰 RNA (siRNA) 敲低 MYC 导致 RAD51 表达下降，但对基于流式细胞术直接重复绿色荧光蛋白测定的同源重组的影响最小。针对 MYC 的 siRNA 导致 DU145 和 H1299 细胞系中的肿瘤细胞死亡，这种方式与细胞凋亡无关。然而，MYC 依赖性 DSB 修复蛋白表达的改变不足以使细胞对丝裂霉素 C 或电离辐射敏感，这两种药物对 DSB 修复缺陷细胞具有选择性毒性。我们的结果表明，抗 MYC 药物可能靶向细胞以防止遗传不稳定性，但不会导致差异放射敏感性或化学敏感性。
