Crettaz M, Muller-Wieland D, Kahn C R
Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts.
Biochemistry. 1988 Jan 12;27(1):495-500. doi: 10.1021/bi00401a071.
The molecular mechanisms of induction of tyrosine aminotransferase (TAT) by insulin were studied in the well-differentiated rat hepatoma cell line Fao. Incubation of Fao cells with insulin resulted in a 2-fold increase in TAT activity and TAT mRNA measured by Northern blot analysis with an oligonucleotide probe to the 5' end of the gene. The effect of insulin on TAT activity had a lag period of 30-60 min and was maximal within 4-5 h. The insulin effect on TAT mRNA was rapid, half-maximal after 15 min, and complete within 1-2 h. Insulin dose-response curves for stimulation of TAT activity and TAT mRNA were almost identical. TAT mRNA levels and enzyme activity were also stimulated by anti-insulin receptor antibodies and dexamethasone but not by wheat germ agglutinin, concanavalin A, or phytohemagglutin. The effect of insulin on the TAT gene was further investigated by measuring the relative rate of transcription in isolated nuclei using genomic TAT clones. Insulin produced a 1.5-1.7-fold increase in the production of TAT RNA transcripts. Dexamethasone induced both TAT activity and TAT mRNA to a comparable extent. In the presence of dexamethasone, insulin produced an additional 2-fold stimulation of TAT activity but had no additional effect on the abundance of TAT mRNA. These data provide direct evidence that insulin can increase TAT activity by at least two distinct mechanisms: insulin alone appears to increase TAT activity and TAT mRNA due to a stimulation of the TAT gene transcription rate; while in the presence of glucocorticoids, insulin increases TAT activity but not TAT mRNA, suggesting an insulin effect at the posttranscriptional level.
在分化良好的大鼠肝癌细胞系Fao中研究了胰岛素诱导酪氨酸转氨酶（TAT）的分子机制。用胰岛素孵育Fao细胞，通过用针对该基因5'端的寡核苷酸探针进行Northern印迹分析，发现TAT活性和TAT mRNA增加了2倍。胰岛素对TAT活性的影响有30 - 60分钟的延迟期，在4 - 5小时内达到最大值。胰岛素对TAT mRNA的影响迅速，15分钟后达到最大值的一半，在1 - 2小时内达到完全效应。刺激TAT活性和TAT mRNA的胰岛素剂量反应曲线几乎相同。抗胰岛素受体抗体和地塞米松也能刺激TAT mRNA水平和酶活性，但麦胚凝集素、伴刀豆球蛋白A或植物血凝素则不能。通过使用基因组TAT克隆测量分离细胞核中的相对转录速率，进一步研究了胰岛素对TAT基因的影响。胰岛素使TAT RNA转录本的产生增加了1.5 - 1.7倍。地塞米松在相当程度上诱导了TAT活性和TAT mRNA。在地塞米松存在的情况下，胰岛素使TAT活性额外增加了2倍，但对TAT mRNA丰度没有额外影响。这些数据提供了直接证据，表明胰岛素可以通过至少两种不同机制增加TAT活性：单独的胰岛素似乎由于刺激TAT基因转录速率而增加TAT活性和TAT mRNA；而在糖皮质激素存在的情况下，胰岛素增加TAT活性但不增加TAT mRNA，这表明胰岛素在转录后水平起作用。
