LINE-1 hypomethylation in a choline-deficiency-induced liver cancer in rats: dependence on feeding period.
LINE-1 hypomethylation in a choline-deficiency-induced liver cancer in rats: dependence on feeding period.
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DOI：
10.1155/jbb/2006/17142
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发表时间：
2006
影响因子：
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通讯作者：
Floyd, Robert A.
中科院分区：
文献类型：
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作者：
Asada, Kiyoshi;Kotake, Yashige;Asada, Rumiko;Saunders, Deborah;Broyles, Robert H.;Towner, Rheal A.;Fukui, Hiroshi;Floyd, Robert A.
慢性喂养甲基供体（蛋氨酸，胆碱，叶酸和维生素B12）缺乏的饮食诱导大鼠肝细胞癌形成。以往的研究表明，在该模型中，各种癌症相关基因的启动子CpG岛异常甲基化。此外，在甲基供体缺乏饮食喂养的大鼠中的整体基因组含有比对照肝脏更少量的5-甲基胞嘧啶。据推测，超过90%的所有5-甲基胞嘧啶位于转座子的CpG岛内，包括长/短散布的核苷酸元件（LINE和SINE）。认为LINE-1中的5-甲基胞嘧啶限制了逆转录转座子被激活和转录的能力;因此，LINE-1的低甲基化程度可能是其他肿瘤相关基因中异常甲基化以及基因组不稳定性的替代标志物。此外，LINE-1甲基化状态已被证明是全基因组甲基化的良好指标。在这项研究中，我们确定了胞嘧啶甲基化状态的LINE-1重复序列的大鼠喂养胆碱缺乏（CD）的饮食不同的持续时间，并比较这些大鼠喂养胆碱充足（CS）的饮食。LINE-1的甲基化状态通过联合亚硫酸氢盐限制性分析（COBRA）方法评估，其中使用凝胶电泳定量亚硫酸氢盐修饰和RsaI切割的DNA的量。在CD肝脏的LINE-1中观察到作为喂养时间的函数的进行性低甲基化;即，总胞嘧啶（甲基化和未甲基化）中胞嘧啶的量从11.1%（1周）增加到19.3%（56周），而在对照CS肝脏中，它从9.2%增加到12.9%。肿瘤组织中的低甲基化水平略高于非肿瘤周围组织（6%）。本研究结果还表明，年龄是影响胞嘧啶甲基化程度的一个因素。
Chronic feeding of methyl-donor (methionine, choline, folic acid, and vitamin B12) deficient diet induces hepatocellular carcinoma formation in rats. Previous studies have shown that promoter CpG islands in various cancer-related genes are aberrantly methylated in this model. Moreover, the global genome in methyl-donor-deficient diet fed rats contains a lesser amount of 5-methylcytosine than control livers. It is speculated that more than 90% of all 5-methylcytosines lie within the CpG islands of the transposons, including the long/short interspersed nucleotide elements (LINE and SINE). It is considered that the 5-methylcytosines in LINE-1 limit the ability of retrotransposons to be activated and transcribed; therefore, the extent of hypomethylation of LINE-1 could be a surrogate marker for aberrant methylation in other tumor-related genes as well as genome instability. Additionally, LINE-1 methylation status has been shown to be a good indicator of genome-wide methylation. In this study, we determined cytosine methylation status in the LINE-1 repetitive sequences of rats fed a choline-deficient (CD) diet for various durations and compared these with rats fed a choline-sufficient (CS) diet. The methylation status of LINE-1 was assessed by the combined bisulfite restriction analysis (COBRA) method, where the amount of bisulfite-modified and RsaI-cleaved DNA was quantified using gel electrophoresis. Progressive hypomethylation was observed in LINE-1 of CD livers as a function of feeding time; that is, the amount of cytosine in total cytosine (methylated and unmethylated) increased from 11.1% (1 week) to 19.3% (56 weeks), whereas in the control CS livers, it increased from 9.2% to 12.9%. Hypomethylation in tumor tissues was slightly higher (6%) than the nontumorous surrounding tissue. The present result also indicates that age is a factor influencing the extent of cytosine methylation.