Wicksteed Barton, Alarcon Cristina, Briaud Isabelle, Lingohr Melissa K, Rhodes Christopher J
Pacific Northwest Research Institute, 720 Broadway, Seattle, WA 98122-4302, USA.
J Biol Chem. 2003 Oct 24;278(43):42080-90. doi: 10.1074/jbc.M303509200. Epub 2003 Aug 18.
Proinsulin biosynthesis is regulated in response to nutrients, most notably glucose. In the short term (</=2h) this is due to increases in the translation of pre-existing mRNA. However, prolonging glucose stimulation (24 h) also increases preproinsulin mRNA levels. It has been proposed that secreted insulin from the pancreatic beta-cell regulates its own synthesis through a positive autocrine feedback mechanism. Here the comparative contributions of translation and mRNA levels on the levels of proinsulin biosynthesis were examined in isolated pancreatic islets. Also, the autocrine role of insulin upon four beta-cell functions (insulin secretion, proinsulin translation, preproinsulin mRNA levels, and total protein synthesis) was investigated in parallel. The results showed that proinsulin biosynthesis is regulated, in the short term (1 h), solely at the level of translation, through an approximately 6-fold increase in response to glucose (2.8 mm versus 16.7 mm glucose). In the longer term, when preproinsulin mRNA levels have increased approximately 2-fold, a corresponding increase was observed in the fold response of proinsulin translation to a stimulatory glucose concentration (>/=10-fold). Importantly, neither exogenously added nor secreted insulin were found to play any role in regulating insulin secretion, proinsulin translation, preproinsulin mRNA levels, or total protein synthesis. The results presented here indicate that long term nutritional state sets the preproinsulin mRNA level in the beta-cell at which translation control regulates short term changes in rates of proinsulin biosynthesis in response to glucose, but this is not mediated by any autocrine effect of insulin.
胰岛素原的生物合成受营养物质调节，最显著的是葡萄糖。在短期内（≤2小时），这是由于已有mRNA翻译增加所致。然而，延长葡萄糖刺激时间（24小时）也会增加胰岛素原前体mRNA水平。有人提出，胰腺β细胞分泌的胰岛素通过正性自分泌反馈机制调节其自身合成。在此，研究了分离的胰岛中翻译和mRNA水平对胰岛素原生物合成水平的相对贡献。同时，还并行研究了胰岛素对β细胞的四种功能（胰岛素分泌、胰岛素原翻译、胰岛素原前体mRNA水平和总蛋白合成）的自分泌作用。结果显示，在短期内（1小时），胰岛素原生物合成仅在翻译水平受到调节，对葡萄糖（2.8 mM对16.7 mM葡萄糖）的反应增加约6倍。在较长时期内，当胰岛素原前体mRNA水平增加约2倍时，观察到胰岛素原翻译对刺激葡萄糖浓度（≥10倍）的反应倍数相应增加。重要的是，未发现外源性添加的胰岛素或分泌的胰岛素在调节胰岛素分泌、胰岛素原翻译、胰岛素原前体mRNA水平或总蛋白合成中起任何作用。此处给出的结果表明，长期营养状态设定了β细胞中胰岛素原前体mRNA的水平，在该水平上，翻译控制调节胰岛素原生物合成速率对葡萄糖的短期变化，但这并非由胰岛素的任何自分泌作用介导。
