Benanti Jennifer A, Wang Myra L, Myers Hadley E, Robinson Kristin L, Grandori Carla, Galloway Denise A
Program in Cancer Biology, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, C1-015, P. O. Box 19024, Seattle, WA 98109-1024, USA.
Mol Cancer Res. 2007 Nov;5(11):1181-9. doi: 10.1158/1541-7786.MCR-06-0372. Epub 2007 Nov 2.
The transcription factor c-Myc is implicated in the pathogenesis of many cancers. Among the multiple functions of c-Myc, activation of hTert and other genes involved in cellular life span contributes to its role as an oncogene. However, the ability of c-Myc to directly immortalize human cells remains controversial. We show here that overexpression of c-Myc reproducibly immortalizes freshly isolated human foreskin fibroblasts. c-Myc-immortalized cells displayed no gross karyotypic abnormalities but consisted of an oligoclonal population, suggesting that additional events cooperated to achieve immortalization. Levels of p53 and p16 were increased, but both p53-dependent DNA damage response and growth arrest in response to p16 overexpression remained intact. A marked decrease in expression of the tumor suppressor ARF occurred in several independently established c-Myc-immortalized cell lines. Methylation-specific PCR showed that the ARF gene was methylated in immortalized but not early-passage c-Myc cells, whereas p16 was unmethylated in both cell populations. Restoration of ARF expression by treatment with a demethylating agent or overexpression by a retroviral vector coincided with inhibition of proliferation and senescence of c-Myc-immortalized cells. Our findings predict that epigenetic events play a significant role in human tumors that express high levels of c-Myc.
转录因子c-Myc与多种癌症的发病机制有关。在c-Myc的多种功能中，激活hTert及其他参与细胞寿命的基因有助于其发挥癌基因的作用。然而，c-Myc直接使人类细胞永生化的能力仍存在争议。我们在此表明，c-Myc的过表达可重复性地使新鲜分离的人包皮成纤维细胞永生化。c-Myc永生化细胞未显示出明显的核型异常，但由寡克隆群体组成，这表明需要其他事件协同作用才能实现永生化。p53和p16的水平升高，但p53依赖的DNA损伤反应以及对p16过表达的生长停滞反应均保持完整。在几个独立建立的c-Myc永生化细胞系中，肿瘤抑制因子ARF的表达明显降低。甲基化特异性PCR显示，ARF基因在永生化的c-Myc细胞中发生甲基化，而在早期传代的c-Myc细胞中未甲基化，而p16在这两种细胞群体中均未甲基化。用去甲基化剂处理恢复ARF表达或通过逆转录病毒载体过表达ARF，均与抑制c-Myc永生化细胞的增殖和衰老相吻合。我们的研究结果预测，表观遗传事件在表达高水平c-Myc的人类肿瘤中起重要作用。
