Interaction between dietary methionine and methyl donor intake on rat liver betaine-homocysteine methyltransferase gene expression and organization of the human gene
Interaction between dietary methionine and methyl donor intake on rat liver betaine-homocysteine methyltransferase gene expression and organization of the human gene
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DOI：
10.1074/jbc.274.12.7816
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发表时间：
1999-03-19
影响因子：
4.8
通讯作者：
Garrow, TA
中科院分区：
文献类型：
--
作者：
Park, EI;Garrow, TA
我们先前表明，与喂食具有对照水平甲硫氨酸的相同饮食的大鼠相比，当大鼠喂食含有足够胆碱的甲硫氨酸缺乏饮食时，大鼠肝脏甜菜碱-高半胱氨酸甲基转移酶（BHMT）mRNA含量和活性增加1倍（Park，E，I.，Renduchintala，M，S，and Garrow，T，A.（1997）J，Nutr，Biochem.8，541-545），在用补充甜菜碱的甲硫氨酸缺乏饮食喂养的大鼠中观察到进一步的a倍增加，本文报道的营养研究旨在确定当加入蛋氨酸时，其他甲基供体是否会诱导大鼠肝脏BHMT基因表达。并确定蛋氨酸限制程度和甲基供体摄入水平对BHMT表达的关系。因此，给大鼠喂食蛋氨酸和甲基供体组成不同的氨基酸定义的饲料。使用北方、西方和酶活性分析来评价饮食对BHMT表达的影响。类似于当甜菜碱被添加到甲硫氨酸缺乏的饮食中时，甜菜碱的胆碱或锍类似物诱导BHMT表达。饮食诱导的肝脏BHMT活性的诱导是通过其mRNA和免疫可检测蛋白的稳态水平的增加介导的。使用无甲基供体的饮食，我们发现蛋氨酸限制是必需的，但单独不足以高诱导BHMT表达。伴随着蛋氨酸限制，膳食甲基组需要高水平的BHMT诱导，甲基供体摄入量和BHMT诱导之间观察到剂量依赖性关系。此外，甲硫氨酸限制的严重程度影响BHMT诱导的大小。为了研究调控BHMT表达的分子机制，我们克隆了人BHMT基因。该基因跨越约20个DNA碱基，含有8个外显子和7个内含子。利用从人肝和肝癌细胞中分离的RNA，利用5'cDNA末端快速扩增技术，定位了一个主要的转录起始位点，该起始位点位于TATA盒下游26个核苷酸处。
We previously showed that rat liver betaine-homocysteine methyltransferase (BHMT) mRNA content and activity increased l-fold when rats were fed a methionine-deficient diet containing adequate choline, compared with rats fed the same diet with control levels of methionine (Park, E, I., Renduchintala, M, S,, and Garrow, T, A. (1997) J, Nutr, Biochem. 8, 541-545), A further a-fold increase was observed in rats fed the methionine-deficient diet with supplemental betaine, The nutrition studies reported here were designed to determine whether other methyl donors would induce rat liver BHMT gene expression when added to a methionine-deficient diet and to define the relationship between the degree of methionine restriction and level of methyl donor intake on BHMT expression. Therefore, rats were fed amino acid-defined diets varying in methionine and methyl donor composition. The effect of diet on BHMT expression was evaluated using Northern, Western, and enzyme activity analyses. Similar to when betaine was added to a methionine-deficient diet, choline or sulfonium analogs of betaine induced BHMT expression. The diet-induced induction of hepatic BHMT activity was mediated by increases in the steady-state level of its mRNA and immunodetectable protein. Using methyl donor-free diets, we found that methionine restriction was required but alone not sufficient for the high induction of BHMT expression. Concomitant with methionine restriction, dietary methyl groups were required for high levels of BHMT induction, and a dose-dependent relationship was observed between methyl donor intake and BHMT induction. Furthermore, the severity of methionine restriction influenced the magnitude of BHMT induction,To study the molecular mechanisms that regulate the expression of BHMT, we have cloned the human BHMT gene. This gene spans about 20 kilobases of DNA and contains 8 exons and 7 introns, Using RNA isolated from human liver and hepatoma cells, a major transcriptional start site has been mapped using the 5' rapid amplification of cDNA ends technique, and this start site is 26 nucleotides downstream from a putative TATA box.