van der Westhuyzen J
Nutr Cancer. 1985;7(3):179-83. doi: 10.1080/01635588509513852.
This paper summarizes recent developments linking methionine metabolism and S-adenosylmethionine to DNA methylation and gene expression in relation to cancer. Methionine, obtained in the diet and synthesized by several reactions in the body, is the sole precursor of S-adenosylmethionine, the primary methyl donor in the body. Disruptions in methionine metabolism and methylation reactions may be involved in cancer processes. S-Adenosylmethionine is involved in, inter alia, the methylation of a small percentage of cytosine bases of DNA. Recent evidence suggests that enzymatic DNA methylation is an important component of gene control and may serve as a silencing mechanism for gene function. Some carcinogens interfere with enzymatic DNA methylation, and thus may allow oncogene activation. Demethylation may be a necessary, but not always sufficient, condition for enhanced transcription. DNA hypomethylation has been observed in many cancer cells and tumors. The hypothesis that oncogenic transformation may be prevented or even reversed by a diet containing excess methionine and/or choline needs to be further investigated.
本文总结了近期将蛋氨酸代谢和S-腺苷甲硫氨酸与癌症相关的DNA甲基化及基因表达联系起来的研究进展。饮食中获取的蛋氨酸以及体内通过多种反应合成的蛋氨酸，是S-腺苷甲硫氨酸的唯一前体，而S-腺苷甲硫氨酸是体内主要的甲基供体。蛋氨酸代谢和甲基化反应的紊乱可能参与癌症进程。S-腺苷甲硫氨酸尤其参与了DNA中一小部分胞嘧啶碱基的甲基化。近期证据表明，酶促DNA甲基化是基因调控的重要组成部分，可能作为基因功能的沉默机制。一些致癌物会干扰酶促DNA甲基化，从而可能导致癌基因激活。去甲基化可能是增强转录的必要条件，但并非总是充分条件。在许多癌细胞和肿瘤中都观察到了DNA低甲基化。通过含有过量蛋氨酸和/或胆碱的饮食预防甚至逆转致癌转化这一假说，有待进一步研究。
