Serra D, Bellido D, Asins G, Arias G, Vilaró S, Hegardt F G
Unit of Biochemistry, School of Pharmacy, University of Barcelona, Spain.
Eur J Biochem. 1996 Apr 1;237(1):16-24. doi: 10.1111/j.1432-1033.1996.0016n.x.
Mitochondrial 3-hydroxy-3-methylglutaryl-CoA (HOMeGlt-CoA) synthase regulates ketogenesis in the liver of adult rat and in the intestine and liver of neonatal animals but whose mechanisms of regulation have not been fully defined. To investigate transcriptional control of this gene in intestine and liver of suckling rats a quantitative PCR amplification of the pre-mRNA (heteronuclear RNA), compose of part of the first exon and of the first intron, was carried out. Results show that the intestinal pre-mRNA for mitochondrial HOMeGlt-CoA synthase from suckling rats follows a pattern that is nearly identical to that of mature mRNA, with maximum levels on the ninth postnatal day then decreasing smoothly so that at weaning there is no transcriptional activity. Mitochondrial HOMeGlt-CoA synthase protein follows a pattern that is identical to the pre-mRNA and mature mRNA, suggesting no translational regulation. The changes in transcriptional activity are not produced by the presence of an alternative promoter, since the transcription-initiation site is identical in several tissues assayed, including intestine and liver. Enterocytes are the only intestinal cells that express this ketogenic enzyme, as deduced from immunolocalization experiments. The mature intestinal protein is located in mitochondria and not in the cytosol, which coincides with what is found in liver. By using analogous techniques we conclude that hepatic pre-mRNA of mitochondrial HOMeGlt-CoA synthase from suckling rats follows a pattern of expression identical to that of mature hepatic mRNA, which also suggests a transcriptional modulation of this gene in the liver of neonatal rats.
线粒体3-羟基-3-甲基戊二酰辅酶A（HOMeGlt-CoA）合酶调节成年大鼠肝脏以及新生动物肠道和肝脏中的生酮作用，但其调节机制尚未完全明确。为了研究哺乳大鼠肠道和肝脏中该基因的转录调控，我们对由第一个外显子的一部分和第一个内含子组成的前体mRNA（不均一核RNA）进行了定量PCR扩增。结果显示，哺乳大鼠线粒体HOMeGlt-CoA合酶的肠道前体mRNA呈现出与成熟mRNA几乎相同的模式，在出生后第9天达到最高水平，然后平稳下降，以至于在断奶时没有转录活性。线粒体HOMeGlt-CoA合酶蛋白的模式与前体mRNA和成熟mRNA相同，表明不存在翻译调控。转录活性的变化并非由替代启动子的存在所致，因为在所检测的包括肠道和肝脏在内的多个组织中，转录起始位点是相同的。免疫定位实验推断，肠上皮细胞是肠道中唯一表达这种生酮酶的细胞。成熟的肠道蛋白位于线粒体而非细胞质中，这与在肝脏中的情况一致。通过使用类似技术，我们得出结论，哺乳大鼠线粒体HOMeGlt-CoA合酶的肝脏前体mRNA呈现出与成熟肝脏mRNA相同的表达模式，这也表明该基因在新生大鼠肝脏中存在转录调控。
