Walther-Straub-Institut of Pharmacology and Toxicology, Ludwig-Maximilians University of Munich, Goethestrasse 33, 80336 Munich, Germany.
J Pharmacol Exp Ther. 2012 Jul;342(1):41-52. doi: 10.1124/jpet.112.192757. Epub 2012 Mar 27.
Morphine-induced signaling via opioid receptors (ORs) in dorsal root ganglia (DRG) neurons, the spinal cord, and various brain regions has been shown to modulate gene activity. Hitherto, little attention has been paid to extracellular signal-regulated kinases-1/2 (ERK-1/2)-mediated activation of the serum response factor (SRF) and ternary complex factors (TCFs) such as the E twenty six-like transcription factor-1 (ELK-1) in this context. Using TCF/SRF-dependent reporter gene constructs, a specific ERK-1/2 inhibitor and a dominant-negative ELK-1 mutant, we show herein that morphine activates ELK-1 via ERK-1/2 in DRG-derived F11 cells endogenously expressing μ and δ ORs. Previous studies with glioma cell lines such as NG108-15 cells attributed morphine-induced gene expression to the activation of the cAMP-responsive element binding protein (CREB). Thus, we also analyzed morphine-dependent activation of CREB in F11 and NG108-15 cells. In contrast to the CREB stimulation found in NG108-15 cells, we observed an inhibitory effect of morphine in F11 cells, indicating cell type-specific regulation of CREB by morphine. To obtain data about putative target genes of morphine-induced ELK-1/SRF activation, we analyzed mRNA levels of 15 ELK-1/SRF-dependent genes in cultured rat DRG neurons and F11 cells. We identified the early growth response protein-4 (EGR-4) as the strongest up-regulated gene in both cell types and observed ELK-1 activity-dependent activation of an EGR-4-driven reporter in F11 cells. Overall, we reveal an important role of ELK-1 for morphine-dependent gene induction in DRG-derived cells and propose that ELK-1 and EGR-4 contribute to the effects of morphine on neuronal plasticity.
阿片受体（ORs）在背根神经节（DRG）神经元、脊髓和各种脑区诱导的吗啡信号转导已被证明可调节基因活性。迄今为止，人们很少关注细胞外信号调节激酶-1/2（ERK-1/2）介导的血清反应因子（SRF）和三元复合物因子（TCFs）如 E 二十六个样转录因子-1（ELK-1）的激活在这种情况下。使用 TCF/SRF 依赖性报告基因构建体、一种特定的 ERK-1/2 抑制剂和显性负 ELK-1 突变体，我们在此表明吗啡通过 DRG 衍生的 F11 细胞中内源性表达的μ和δ ORs 激活 ELK-1。先前使用神经胶质瘤细胞系（如 NG108-15 细胞）的研究将吗啡诱导的基因表达归因于 cAMP 反应元件结合蛋白（CREB）的激活。因此，我们还分析了 F11 和 NG108-15 细胞中吗啡依赖性 CREB 激活。与在 NG108-15 细胞中发现的 CREB 刺激相反，我们在 F11 细胞中观察到吗啡的抑制作用，表明吗啡对 CREB 的细胞类型特异性调节。为了获得吗啡诱导的 ELK-1/SRF 激活的推定靶基因的相关数据，我们分析了培养的大鼠 DRG 神经元和 F11 细胞中 15 个 ELK-1/SRF 依赖性基因的 mRNA 水平。我们确定早期生长反应蛋白-4（EGR-4）是两种细胞类型中最强上调的基因，并观察到 F11 细胞中 ELK-1 活性依赖性的 EGR-4 驱动报告基因的激活。总体而言，我们揭示了 ELK-1 在 DRG 衍生细胞中吗啡依赖性基因诱导中的重要作用，并提出 ELK-1 和 EGR-4 有助于吗啡对神经元可塑性的影响。
