Thorngate F E, Raghow R, Wilcox H G, Werner C S, Heimberg M, Elam M B
Department of Pharmacology, University of Tennessee, Memphis 38163.
Proc Natl Acad Sci U S A. 1994 Jun 7;91(12):5392-6. doi: 10.1073/pnas.91.12.5392.
Long-term insulin treatment selectively stimulates secretion of the truncated form of apolipoprotein B (apoB), apoB-48, from primary rat hepatocytes in culture. Chronic treatment with insulin at 400 ng/ml causes a 3-fold increase in total apoB secretion, with apoB-48 making up about 75% of that increase. apo-B-48 is the protein product generated by translation of full-length apoB mRNA which has been modified by a posttranscriptional editing mechanism. Editing changes codon 2153 in the middle of the apoB-100 coding region from CAA, coding for glutamine, to UAA, a translation stop signal. We therefore examined the effect of insulin treatment on the ratio of edited to nonedited apoB mRNA in RNA isolated from primary rat hepatocyte cultures. There was a dramatic shift in the ratio of edited versus nonedited forms of apoB mRNA, from about 1:1 in untreated cells to 7:1 in insulin-treated cells. Insulin exerted a dose-dependent effect on apoB secretion and apoB mRNA editing over the range of insulin concentrations studied (0.4-400 ng/ml). In contrast, oleic acid, which also increased apoB (B-48 and B-100) secretion, had no significant effect on the ratio of apoB-48 to apoB-100 particles secreted and no effect on the proportion of edited apoB mRNA. Neither insulin nor oleic acid affects total apoB mRNA levels as assayed by Northern blot analysis. These data strongly suggest that insulin stimulates biosynthesis and secretion of apoB-48 in rat hepatocytes by regulating the proportion of edited apoB mRNA.
长期胰岛素治疗可选择性刺激原代培养大鼠肝细胞分泌截短形式的载脂蛋白B（apoB），即apoB-48。用400 ng/ml胰岛素进行慢性治疗可使apoB总分泌量增加3倍，其中apoB-48约占增加量的75%。apo-B-48是全长apoB mRNA经转录后编辑机制修饰后翻译产生的蛋白质产物。编辑将apoB-100编码区中部的密码子2153由编码谷氨酰胺的CAA变为翻译终止信号UAA。因此，我们检测了胰岛素治疗对从原代大鼠肝细胞培养物中分离的RNA中编辑型与未编辑型apoB mRNA比例的影响。apoB mRNA编辑型与未编辑型的比例发生了显著变化，从未处理细胞中的约1:1变为胰岛素处理细胞中的7:1。在所研究的胰岛素浓度范围（0.4 - 400 ng/ml）内，胰岛素对apoB分泌和apoB mRNA编辑具有剂量依赖性作用。相比之下，油酸虽然也增加了apoB（B-48和B-100）的分泌，但对分泌的apoB-48与apoB-100颗粒的比例没有显著影响，对编辑型apoB mRNA的比例也没有影响。通过Northern印迹分析检测，胰岛素和油酸均不影响总apoB mRNA水平。这些数据强烈表明，胰岛素通过调节编辑型apoB mRNA的比例来刺激大鼠肝细胞中apoB-48的生物合成和分泌。
