German M S, Wang J
Hormone Research Institute, University of California, San Francisco 94143-0534.
Mol Cell Biol. 1994 Jun;14(6):4067-75. doi: 10.1128/mcb.14.6.4067-4075.1994.
The beta cells in the pancreatic islets of Langerhans increase insulin gene transcription in response to increased glucose concentration. We have mapped sequences within the rat insulin I gene 5'-flanking DNA (rInsI promoter) that direct this transcriptional response to glucose. When linked to chloramphenicol acetyltransferase and expressed in cultured beta cells, no single mutation of the rInsI promoter removes its ability to respond to glucose, although several mutations cause marked reductions in basal chloramphenicol acetyltransferase expression. A 50-bp sequence isolated from the rInsI promoter, the Far-FLAT minienhancer, can confer glucose responsiveness to nonresponsive promoters. Fine mapping of this minienhancer further localizes a glucose response to the sequence GGCCATCTGGCC, or the Far element. Nuclear extracts from islets grown in various glucose concentrations demonstrate a glucose-stimulated increase in a protein complex that binds the Far element and contains the transcription factors Pan-1 and Pan-2. Overexpression of intact or partially deleted Pan-1 ablates the Far-directed transcriptional response to glucose. We conclude that the full glucose response of the insulin promoter involves the interaction of multiple sequence elements. Part of this response, however, results from activation of a complex binding at the Far element.
胰岛中的β细胞会根据葡萄糖浓度的升高增加胰岛素基因转录。我们已绘制出大鼠胰岛素I基因5'-侧翼DNA（rInsI启动子）中指导这种对葡萄糖转录反应的序列。当与氯霉素乙酰转移酶相连并在培养的β细胞中表达时，rInsI启动子的单个突变均未消除其对葡萄糖反应的能力，尽管有几个突变导致基础氯霉素乙酰转移酶表达显著降低。从rInsI启动子分离出的一个50 bp序列，即远侧翼激活转录增强子（Far-FLAT微型增强子），可赋予无反应性启动子葡萄糖反应性。对该微型增强子的精细定位进一步将葡萄糖反应定位到序列GGCCATCTGGCC，即远元件。在不同葡萄糖浓度下生长的胰岛的核提取物显示，一种与远元件结合并包含转录因子Pan-1和Pan-2的蛋白质复合物在葡萄糖刺激下增加。完整的或部分缺失的Pan-1的过表达消除了对远元件的葡萄糖定向转录反应。我们得出结论，胰岛素启动子的完全葡萄糖反应涉及多个序列元件的相互作用。然而，这种反应的一部分是由远元件处结合的复合物的激活引起的。
