Influences of diabetes mellitus and insulin resistance on hepatic synthesis of serum paraoxonase 1

1.葡萄糖和胰岛素对人血清对氧磷酶1 （PON1）基因转录的影响：d -葡萄糖，而不是l -葡萄糖或甘露醇，显著增强了HepG2和Huh7人肝癌细胞系PON1的转录活性（报告基因测定）。胰岛素也增强了转录活性，但作用较小。2.葡萄糖和胰岛素对PON1 mRNA和蛋白表达的影响：d -葡萄糖增强Huh7细胞PON1 mRNA表达，而胰岛素不增强。d -葡萄糖也增加了Huh7细胞和人原代肝细胞PON1蛋白的表达（western blotting）。3.葡萄糖诱导PON1基因反活化的机制：蛋白激酶C （PKC）抑制剂双吲哚酰马来酰亚胺部分抑制d -葡萄糖诱导的PON1基因反活化，转录因子Sp1抑制剂mythramycin完全消除反活化。缺失分析显示，包含Sp1结合位点的启动子序列（-269/-97）对反激活至关重要。4.糖尿病大鼠（沙鼠）肝脏PON1表达：与对照组（正常胰岛素水平、正常血糖水平）相比，糖尿病（高胰岛素水平、高血糖水平）动物肝脏PON1表达显著升高。糖尿病前期（高胰岛素血症、血糖正常）动物肝脏PON1表达无明显变化。5.结论：高血糖增加了肝脏PON1的合成，而高胰岛素血症不增加。我们的数据表明，高血糖状态下激活的二酰基甘油- pkc通路通过Sp1激活促进PON1转录。

1.Effects of glucose and insulin on transcription of human serum paraoxonase 1 (PON1) gene : D-glucose, but not L-glucose or mannitol, significantly enhanced PON1 transcriptional activity in both HepG2 and Huh7 human hepatoma cell lines (reporter gene assay). Insulin also enhanced the transcriptional activity, but its effect was minor. 2.Effects of glucose and insulin on PON1 mRNA and protein expressions : D-glucose, but not insulin, enhanced PON1 mRNA expression in Huh7 cells (RT-PCR). D-glucose also increased PON1 protein expression in both Huh7 cells and human primary hepatocytes (western blotting). 3.Mechanism of glucose-induced transactivation of PON1 gene : Bisindolylmaleimide, a protein kinase C (PKC) inhibitor, partially inhibited D-glucose-induced transactivation of PON1 gene, and mythramycin, an inhibitor of transcriptional factor Sp1, completely abrogated the transactivation. Deletion analyses revealed that the promoter sequence (-269/-97) containing Sp1 binding sites was crucial for the transactivation. 4.Hepatic PON1 expression in diabetic Psammomys obesus (sand rat) : Significantly increased PON1 expression in the liver was detected in the diabetic (hyperinsulinemic, hyperglycemic) animals as compared with the control (normoinsulinemic, normoglycemic) animals. The prediabetic (hperinsulinemic, normoglycemic) animals showed no significant change in hepatic PON1 expression. 5.Conclusion : Hyperglycemia, but not hyperinsulinemia, increases hepatic PON1 synthesis. Our data suggest that activated diacylglycerol-PKC pathway under hyperglycemic condition promotes PON1 transcription through Sp1 activation.