Role of nutrients in the regulation of the expression of digestion/absorption-related genes

1.克隆了蔗糖酶-异麦芽糖酶(SI)和乳糖酶-根皮苷水解酶(LPH)两个具有代表性的双糖酶基因的5‘侧翼区。在大鼠LPH基因5‘侧翼区和大鼠SI基因5’侧翼区都存在共同的CDX-2结合元件，分别命名为CE-LPH1和SIF1。在大鼠SI基因的5‘端还存在一个HNF1结合元件，该元件与SI基因表达的日变化有关。比较大鼠空肠葡萄糖转运蛋白(GLUT5、SGLT1、GLUT2)和乳糖酶的表达与核因子表达的发育性变化。断奶后，各类型葡萄糖转运蛋白的表达水平均升高，这与甲状腺激素核受体α-1的表达升高密切相关。随着LPH表达的减少，与CE-LPH1.3结合的核因子的数量也减少。含蔗糖饲料对…大鼠的平行灌胃作用注射放线菌素D后，SI和LPH基因表达在3h内出现更多的升高，并被注射放线菌素D完全消除。在绒毛-隐窝柱诱导开始的部位，SI基因表达水平开始升高，而LPH基因表达水平则在绒毛更顶端和更宽广的部位表达。在所测试的单糖中，果糖引起SI和LPH基因转录的显著增加，同时伴随着SGLT1和GLUT5基因的转录增加。饲喂含有葡萄糖或α-甲基葡萄糖苷(一种非代谢糖)的饲料不会增加SI、LPh和肠道己糖转运体的转录水平。当同时将含有果糖或葡萄糖的溶液灌流到两个连续的空肠插管和灌流环中时，灌流果糖的空肠环的SI和GLUT5的mRNA水平高于灌流葡萄糖的空肠环。核连续分析表明，果糖而不是葡萄糖增加了SI、LPH和GLUT5的转录。使用CE-LPH1和SIF1元件进行的电迁移率漂移分析表明，喂高淀粉饲料的大鼠空肠核提取液比喂低淀粉饲料的大鼠有更高密度的迟滞条带。此外，我们还发现，强迫饲喂果糖饮食会导致二聚体核蛋白(CDX2)与SIF1元件的结合增加，SIF1元件是通过核蛋白的去磷酸化而复制的。较少

1. The 5' flanking regions of two representing disaccharidase genes, i.e., sucrase-isomaltase (SI) and lactase-phlorizin hydrolase (LPH) were cloned. In the 5' flanking region of both rat LPH and rat SI genes, common Cdx-2 binding elements were present and termed as CE-LPH1 and SIF1, respectively. In the 5' region of rat SI gene, a HNF1-binding element was also present which was associated with the diurnal variations in the SI gene expression.2. Developmental changes in the expressions of glucose transporters (GLUT5, SGLT1, GLUT2) and lactase were compared with those of nuclear factors in rat jejunum. After weaning, the mRNA levels of all types of glucose transporters were elevated, which was closely related with the rise in the expression of a thyroid hormone nuclear receptor (TR α-1). The decrease in the expression of LPH was accompanied by a decrease in the amounts of the nuclear factor binding to CE-LPH1.3. Oro-gastric feeding of a sucrose-containing diet to rats caused parallel in … More creases in SI and LPH mRNA levels within 3h, which were completely abolished by an injection of actinomycin D. A difference was observed in the site along the villus-crypt columns where the induction started ; the initial rise in SI mRNA level occurred at the lower villus, whereas that of LPH mRNA level occurred at more apical and broader locus of the villus.4. Among the monosaccharides tested, fructose gave rise to the most prominent increases in the transcripts of SI and LPH genes, which were accompanied by a coordinate rise in the transcripts of SGLT1 and GLUT5 genes. Feeding the diet containing glucose or α-methylglucoside (a non-metabolizable sugar) did not increase the transcript levels of SI, LPH and the intestinal hexose transporters. When a solution containing either fructose or glucose was simultaneously perfused into two consecutive cannulated and irrigated loops of jejunum, the loop perfused with fructose exhibited greater SI and GLUT5 mRNA levels than that perfused with glucose.5. Nuclear run-on assays revealed that fructose, but not glucose, increased the transcription of SI, LPH and GLUT5. Electromobility shift assays using the CE-LPH1 and the SIF1 elements revealed that nuclear extracts from the jejunum of rats fed the high-starch diet gave greater density of retarded bands than those of rats fed the low-starch diet. In addition, we found that force feeding a fructose diet gave rise to an increase in the binding of the dimeric nuclear protein (Cdx2) to the SIF1 element, which was reproduced by dephosphorylation of the nuclear protein. Less