Grams B, Harms A, Braun S, Strassburg C P, Manns M P, Obermayer-Straub P
Department of Gastroenterology and Hepatology, Medizinische Hochschule Hannover, Germany.
Arch Biochem Biophys. 2000 May 15;377(2):255-65. doi: 10.1006/abbi.2000.1777.
UDP-Glucuronosyltransferases (UGT) catalyze the glucuronidation of a broad spectrum of endobiotic and xenobiotic substrates. The resulting glucuronides are more hydrophilic, facilitating renal and biliary excretion. Apart from hepatic glucuronidation, high rates of gastrointestinal glucuronidation have been observed. The aim of this study was to characterize the expression of family 1 UGTs (UGT1A) in liver, kidney, and all parts of the rat gastrointestinal tract by reverse transcription polymerase reaction (RT-PCR), Northern blot, and xenobiotic induction experiments. RT-PCR experiments were performed with primers specific for all known rat UGT1A mRNAs. UGT1A1, UGT1A6, and UGT1A7 were expressed in liver, kidney, and the gastrointestinal tract. UGT1A5 transcripts were detected in liver, but not in kidney or gastrointestinal tissue. In contrast, UGT1A2 and UGT1A3 were not expressed in liver or kidney, but were detected in intestine. Low levels of UGT1A3 were detectable in duodenum and jejunum. UGT1A2 was abundantly expressed in the small intestine; expression levels in the stomach and the large intestine were low. Quantitative evaluation of RNA levels by Northern blot revealed expression in gradients, with highest UGT1A mRNA levels in duodenum and decreasing levels in the small and large intestine. Only UGT1A6 was expressed at high levels in the rectum. Rats treated with 3-methylcholanthrene (3-MC) displayed a 10-fold induction of hepatic UGT1A6 and UGT1A7 mRNAs. In gastric tissues and in intestine, induction was 4-fold and 2-fold, respectively. In contrast to the constitutive expression of UGT1A7 in kidney, UGT1A6 was inducible in the liver. Effects of 3-MC on UGT1A1 expression revealed downregulation in the liver and highly variable effects in duodenum and stomach. This study demonstrates tissue-specific expression and tissue-specific induction patterns in rat liver, kidney, and gastrointestinal tract, which may represent the physiological basis of tissue-specific glucuronidation in rats.
尿苷二磷酸葡萄糖醛酸基转移酶（UGT）催化多种内源性和外源性底物的葡萄糖醛酸化反应。生成的葡萄糖醛酸苷具有更高的亲水性，有利于通过肾脏和胆汁排泄。除了肝脏的葡萄糖醛酸化反应外，还观察到胃肠道有较高的葡萄糖醛酸化速率。本研究的目的是通过逆转录聚合酶反应（RT-PCR）、Northern印迹法和外源性诱导实验，来表征大鼠肝脏、肾脏及整个胃肠道中1家族UGT（UGT1A）的表达情况。使用针对所有已知大鼠UGT1A mRNA的特异性引物进行RT-PCR实验。UGT1A1、UGT1A6和UGT1A7在肝脏、肾脏和胃肠道中均有表达。在肝脏中检测到UGT1A5转录本，但在肾脏或胃肠道组织中未检测到。相反，UGT1A2和UGT1A3在肝脏或肾脏中不表达，但在肠道中可检测到。在十二指肠和空肠中可检测到低水平的UGT1A3。UGT1A2在小肠中大量表达；在胃和大肠中的表达水平较低。通过Northern印迹法对RNA水平进行定量评估，结果显示其表达呈梯度变化，十二指肠中UGT1A mRNA水平最高，在小肠和大肠中水平逐渐降低。只有UGT1A6在直肠中高水平表达。用3-甲基胆蒽（3-MC）处理的大鼠肝脏中UGT1A6和UGT1A7 mRNA诱导了10倍。在胃组织和肠道中，诱导倍数分别为4倍和2倍。与UGT1A7在肾脏中的组成型表达不同，UGT1A6在肝脏中可诱导。3-MC对UGT1A1表达的影响显示，肝脏中出现下调，在十二指肠和胃中影响高度可变。本研究证明了大鼠肝脏、肾脏和胃肠道中存在组织特异性表达和组织特异性诱导模式，这可能代表了大鼠组织特异性葡萄糖醛酸化的生理基础。
