Molecular Haematology and Cancer Biology Unit, Institute of Child Health, University College London, 30 Guilford Street, London WC1N1EH, UK.
BMC Neurosci. 2011 Jul 15;12:69. doi: 10.1186/1471-2202-12-69.
Apoptosis plays a critical role during neuronal development and disease. Developing sympathetic neurons depend on nerve growth factor (NGF) for survival during the late embryonic and early postnatal period and die by apoptosis in its absence. The proapoptotic BH3-only protein Bim increases in level after NGF withdrawal and is required for NGF withdrawal-induced death. The regulation of Bim expression in neurons is complex and this study describes a new mechanism by which an NGF-activated signalling pathway regulates bim gene expression in sympathetic neurons.
We report that U0126, an inhibitor of the prosurvival MEK-ERK pathway, increases bim mRNA levels in sympathetic neurons in the presence of NGF. We find that this effect is independent of PI3-K-Akt and JNK-c-Jun signalling and is not mediated by the promoter, first exon or first intron of the bim gene. By performing 3' RACE and microinjection experiments with a new bim-LUC+3'UTR reporter construct, we show that U0126 increases bim expression via the bim 3' UTR. We demonstrate that this effect does not involve a change in bim mRNA stability and by using PD184352, a specific MEK1/2-ERK1/2 inhibitor, we show that this mechanism involves the MEK1/2-ERK1/2 pathway. Finally, we demonstrate that inhibition of MEK/ERK signalling independently reduces cell survival in NGF-treated sympathetic neurons.
These results suggest that in sympathetic neurons, MEK-ERK signalling negatively regulates bim expression via the 3' UTR and that this regulation is likely to be at the level of transcription. This data provides further insight into the different mechanisms by which survival signalling pathways regulate bim expression in neurons.
细胞凋亡在神经元发育和疾病中起着关键作用。在胚胎晚期和出生后早期，发育中的交感神经元依赖神经生长因子（NGF）存活，在缺乏 NGF 的情况下通过细胞凋亡死亡。促凋亡 BH3 仅蛋白 Bim 在 NGF 撤出后水平增加，并且是 NGF 撤出诱导的死亡所必需的。神经元中 Bim 表达的调控非常复杂，本研究描述了一种新的机制，即 NGF 激活的信号通路调节交感神经元中 bim 基因的表达。
我们报告称，U0126，一种存活 MEK-ERK 通路的抑制剂，在 NGF 存在的情况下增加交感神经元中的 bim mRNA 水平。我们发现，这种效应独立于 PI3-K-Akt 和 JNK-c-Jun 信号，并且不由 bim 基因的启动子、第一外显子或第一内含子介导。通过使用新的 bim-LUC+3'UTR 报告构建体进行 3'RACE 和微注射实验，我们表明 U0126 通过 bim 3'UTR 增加 bim 表达。我们证明这一效应不涉及 bim mRNA 稳定性的变化，并且通过使用 PD184352，一种特异性 MEK1/2-ERK1/2 抑制剂，我们表明这种机制涉及 MEK1/2-ERK1/2 通路。最后，我们证明抑制 MEK/ERK 信号独立于 NGF 处理的交感神经元中的细胞存活。
这些结果表明，在交感神经元中，MEK-ERK 信号通过 3'UTR 负调节 bim 表达，并且这种调节可能在转录水平上进行。该数据提供了进一步的深入了解存活信号通路调节神经元中 bim 表达的不同机制。
