A thyroid hormone response unit formed between the promoter and first intron of the carnitine palmitoyltransferase-Iα gene mediates the liver-specific induction by thyroid hormone
A thyroid hormone response unit formed between the promoter and first intron of the carnitine palmitoyltransferase-Iα gene mediates the liver-specific induction by thyroid hormone
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DOI：
10.1074/jbc.m211062200
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发表时间：
2003-03-07
影响因子：
4.8
通讯作者：
Park, EA
中科院分区：
文献类型：
--
作者：
Jackson-Hayes, L;Song, SL;Park, EA
肉毒碱棕榈酰转移酶-I（CPT-I）催化脂肪酸氧化的速率控制步骤。CPT-I将长链脂肪酰辅酶A转化为酰基肉毒碱，用于跨线粒体膜转运。在甲状腺功能亢进动物的肝脏中，肝脏同种型CPT-1 α的mRNA水平和酶活性大大增加。甲状腺激素（T3）在肝脏中比在非肝组织中更强烈地刺激CPT-Ⅰ α转录。我们已经证明，甲状腺激素受体（TR）结合到一个甲状腺激素反应元件（TRE）位于CPT-Ⅰ α启动子。此外，第一内含子中的元件参与CPT-1 α基因表达的T3诱导，但CPT-1 α内含子单独不能赋予T3应答。我们发现，在+653和+744之间的第一内含子中的序列的缺失降低了CPT-Ia的T3诱导。上游刺激因子（USF）和CCAAT增强子结合蛋白（C/EBP）与该区域内的元件结合，这些因子是T3应答所需的。染色质免疫沉淀试验显示TR和C/EBP与CPT-1 α基因在体内的结合。我们确定TR可以与USF-1，USF-2和C/EBPalpha物理相互作用。产生携带CPT-I α-荧光素酶转基因的转基因小鼠，所述转基因小鼠具有或不具有CPT-I α基因的第一内含子。在这些小鼠系中，第一个内含子是T3诱导以及高水平的肝脏表达所必需的。我们的数据表明，T3刺激CPT-Ialpha基因在肝脏中的表达，通过T3的反应单元组成的TRE的启动子和其他因素，C/EBP和USF，结合在第一个内含子。
Carnitine palmitoyltransferase-I (CPT-I) catalyzes the rate-controlling step of fatty acid oxidation. CPT-I converts long-chain fatty acyl-CoAs to acylcarnitines for translocation across the mitochondrial membrane. The mRNA levels and enzyme activity of the liver isoform, CPT-Ialpha, are greatly increased in the liver of hyperthyroid animals. Thyroid hormone (T3) stimulates CPT-Ialpha transcription far more robustly in the liver than in nonhepatic tissues. We have shown that the thyroid hormone receptor (TR) binds to a thyroid hormone response element (TRE) located in the CPT-Ialpha promoter. In addition, elements in the first intron participate in the T3 induction of CPT-Ialpha gene expression, but the CPT-Ialpha intron alone cannot confer a T3 response. We found that deletion of sequences in the first intron between +653 and +744 decreased the T3 induction of CPT-Ia. Upstream stimulatory factor (USF) and CCAAT enhancer binding proteins (C/EBPs) bind to elements within this region, and these factors are required for the T3 response. The binding of TR and C/EBP to the CPT-Ialpha gene in vivo was shown by the chromatin immunoprecipitation assay. We determined that TR can physically interact with USF-1, USF-2, and C/EBPalpha. Transgenic mice were created that carry CPT-Ialpha-luciferase transgenes with or without the first intron of the CPT-Ialpha gene. In these mouse lines, the first intron is required for T3 induction as well as high levels of hepatic expression. Our data indicate that the T3 stimulates CPT-Ialpha gene expression in the liver through a T3 response unit consisting of the TRE in the promoter and additional factors, C/EBP and USF, bound in the first intron.