Carrasco-Serrano C, Viniegra S, Ballesta J J, Criado M
Department of Neurochemistry, Centro Mixto CSIC-Universidad Miguel, Hernández, San Juan, Alicante, Spain.
J Neurochem. 2000 Mar;74(3):932-9. doi: 10.1046/j.1471-4159.2000.0740932.x.
alpha-Bungarotoxin-sensitive neuronal nicotinic acetylcholine receptors from bovine adrenomedullary chromaffin cells are up-regulated by long-term exposure to phorbol esters. The rise in receptor density is paralleled by an increase in transcripts corresponding to the alpha7 subunit, which is a component of this receptor subtype. Transcriptional activation of the alpha7 subunit gene is evidenced in reporter gene transfection experiments, in which phorbol esters increase alpha7 promoter activity by up to 14-fold. About 80% of this activation is abolished when at least two of the three sites for the immediate-early transcription factor Egr-1, present in the proximal promoter region of the alpha7 subunit gene, are mutated simultaneously. In addition, phorbol esters elevate both Egr-1 mRNA and Egr-1 protein levels in chromaffin cells, whereas electrophoretic mobility shift assays show that the Egr-1 component of the complexes that originate at the alpha7 promoter increases in cells treated with phorbol esters. These results suggest that the transcription factor Egr-1 is involved in triggering expression of alpha-bungarotoxin-sensitive nicotinic receptors in response to external stimuli, such as the ones resulting from phorbol ester treatment, and support our previous hypothesis that the alpha7 subunit gene is one of the specific targets for Egr-1.
长期暴露于佛波酯可上调来自牛肾上腺髓质嗜铬细胞的α-银环蛇毒素敏感型神经元烟碱型乙酰胆碱受体。受体密度的增加与对应α7亚基的转录本增加平行，α7亚基是该受体亚型的一个组成部分。在报告基因转染实验中证实了α7亚基基因的转录激活，其中佛波酯可使α7启动子活性增加高达14倍。当α7亚基基因近端启动子区域中存在的即时早期转录因子Egr-1的三个位点中的至少两个同时发生突变时，这种激活的约80%被消除。此外，佛波酯可提高嗜铬细胞中Egr-1 mRNA和Egr-1蛋白水平，而电泳迁移率变动分析表明，在用佛波酯处理的细胞中，源自α7启动子的复合物中的Egr-1成分增加。这些结果表明，转录因子Egr-1参与触发α-银环蛇毒素敏感型烟碱受体对外界刺激（如佛波酯处理产生的刺激）的表达，并支持我们之前的假设，即α7亚基基因是Egr-1的特定靶点之一。
