Alvarez L, Avila M A, Mato J M, Castaño J G, Varela-Nieto I
Instituto de Investigaciones Biomédicas del Consejo Superior de Investigaciones Cientificas, Facultad de Medicina, Universidad Autónoma de Madrid, Spain.
Mol Endocrinol. 1991 Aug;5(8):1062-8. doi: 10.1210/mend-5-8-1062.
The ability of an inositol phosphate-glycan (IPG) to mimic the effects of insulin on regulation of the expression of specific mRNAs was studied in isolated hepatocytes from normal and diabetic rats. Incubation of normal liver cells with IPG (10 microM) during 90 min produced a 5-fold decrease in phosphoenolpyruvate carboxykinase (PEPCK) mRNA levels, which had been previously increased about 10-fold by incubation with 8-bromo-cAMP (0.1 mM). The effect of IPG was dose dependent and could not be reproduced by galactose, glucosamine, or myo-inositol. IPG reduction of PEPCK mRNA is primarily due to a decrease in the rate of transcription of the gene, as judged by nuclear run-on transcription experiments performed in rat hepatoma H4IIE cells. In hepatocytes isolated from diabetic rats, treatment with 5 microM IPG for 15 min caused a 4-fold induction in the expression of alpha 2-microglobulin mRNA concomitantly with a 2.5-fold decrease in the level of PEPCK mRNA. Cleavage of IPG with nitrous acid abolished both the increase and the decrease in specific mRNAs levels. Glycosyl-phosphatidylinositol, the lipid precursor of IPG, did not modify either PEPCK or alpha 2-microglobulin mRNA levels. These data indicate that both positive and negative effects of insulin on the regulation of gene expression are mimicked by IPG.
在从正常大鼠和糖尿病大鼠分离出的肝细胞中，研究了肌醇磷酸聚糖（IPG）模拟胰岛素对特定mRNA表达调控作用的能力。用IPG（10微摩尔）孵育正常肝细胞90分钟，可使磷酸烯醇丙酮酸羧激酶（PEPCK）mRNA水平降低5倍，而此前用8-溴-cAMP（0.1毫摩尔）孵育可使其升高约10倍。IPG的作用呈剂量依赖性，半乳糖、氨基葡萄糖或肌醇无法重现这种作用。通过在大鼠肝癌H4IIE细胞中进行的核转录实验判断，IPG降低PEPCK mRNA主要是由于该基因转录速率下降。在从糖尿病大鼠分离出的肝细胞中，用5微摩尔IPG处理15分钟，可使α2-微球蛋白mRNA表达诱导4倍，同时PEPCK mRNA水平降低2.5倍。用亚硝酸切割IPG可消除特定mRNA水平的升高和降低。IPG的脂质前体糖基磷脂酰肌醇不会改变PEPCK或α2-微球蛋白mRNA水平。这些数据表明，IPG可模拟胰岛素对基因表达调控的正向和负向作用。
