Association of c-myc overexpression and hyperproliferation with arsenite-induced malignant transformation
Association of c-myc overexpression and hyperproliferation with arsenite-induced malignant transformation
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DOI：
10.1006/taap.2001.9253
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发表时间：
2001-09-15
影响因子：
3.8
通讯作者：
Waalkes, MP
中科院分区：
文献类型：
--
作者：
Chen, H;Liu, J;Waalkes, MP
许多研究将砷暴露与包括肝脏在内的各种组织中的人类癌症联系起来。然而，无机砷从未被明确地证明是一种动物致癌物，其致癌机制仍不明确。我们以前的研究表明，慢性（大于或等于18周），低水平（125至500纳米）暴露于砷诱导恶性转化在正常非致瘤大鼠肝上皮细胞系（TRL 1215），这些慢性砷暴露（CAsE）细胞接种到裸鼠后产生侵袭性和转移性肿瘤。此外，先前的异常基因表达的微阵列筛选分析显示，在暴露于500 nM亚砷酸盐的CAsE细胞中，几种癌基因过表达，包括原癌基因c-myc的显著过表达，以及与细胞增殖相关的基因。因此，为了更好地理解砷致癌的机制，我们研究了c-myc过表达在砷诱导的细胞转化中的作用。通过RT-PCR在转录水平和蛋白质印迹分析的翻译产物证实了c-myc的上调。进一步的分析表明，亚砷酸盐产生显着增加的稳态表达的c-myc的时间和浓度依赖性的方式在恶性转化过程中。c-myc表达水平与CAsE细胞接种裸鼠后的肿瘤形成高度相关（r = 0.988），也与基因组DNA低甲基化高度相关（r = 0.997）。CAsE细胞表现出较高的细胞增殖率，且与砷暴露水平相关。c-myc的表达与细胞过度增殖密切相关（r = 0.961）。与增强的增殖一致，增殖细胞核抗原和细胞周期蛋白DI在CAsE细胞中过表达。总之，一个突出的c-myc，在肝癌发生过程中频繁激活的基因的过度表达，是强烈相关的几个事件可能与砷诱导的恶性转化，包括过度增殖，DNA低甲基化和肿瘤形成接种到裸鼠。这些相关性提供了令人信服的证据c-myc过表达是砷诱导的恶性转化在这个模型系统中的重要机制。
Numerous studies link arsenic exposure to human cancers in a variety of tissues, including the liver. However, inorganic arsenic has never been unequivocally shown to be an animal carcinogen, and its carcinogenic mechanism remains undefined. Our previous studies indicate that chronic (greater than or equal to 18 weeks), low-level (125 to 500 nM) exposure to arsenite induces malignant transformation in the normally nontumorigenic rat liver epithelial cell line (TRL 1215), and these chronic arsenic-exposed (CAsE) cells produce invasive and metastatic tumors upon inoculation into nude mice. In addition, a prior microarray screening analysis of aberrant gene expression showed several oncogenes were overexpressed in CAsE cells exposed to 500 nM arsenite, including a prominent overexpression of the protooncogene c-myc, as well as genes related to cell proliferation. Thus, to better understand the mechanism of arsenic carcinogenesis, we studied the role of c-myc overexpression in arsenite-induced cell transformation. The upregulation of c-myc was confirmed by RT-PCR at the transcription level and by Western blot analysis for the translation product. Further analysis showed that arsenite produced significant increases in the steady-state expression of c-myc in a time- and concentration-dependent manner during the malignant transformation process. The level of c-myc expression was highly correlated (r = 0.988) with tumor formation after inoculation of CAsE cells into nude mice and was also highly correlated (r = 0.997) with genomic DNA hypomethylation. CAsE cells showed a high cell proliferation rate in a fashion related to the level of arsenic exposure. The expression of c-myc was highly correlated with cellular hyperproliferation (r = 0.961). Consistent with the enhanced proliferation both proliferating cell nuclear antigen and cyclin DI were overexpressed in CAsE cells. In summary, a prominent overexpression of c-myc, a gene frequently activated during hepatocarcinogenesis, is strongly correlated with several events possibly associated with arsenic-induced malignant transformation, including hyperproliferation, DNA hypomethylation and tumor formation upon inoculation into nude mice. These correlations provide convincing evidence c-myc overexpression is mechanistically important in arsenic-induced malignant transformation in this model system.