Tremblay Isabelle, Paré Emanuel, Arsenault Dominique, Douziech Mélanie, Boucher Marie-Josée
Department of Medicine, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec, Canada.
PLoS One. 2013 Dec 31;8(12):e85502. doi: 10.1371/journal.pone.0085502. eCollection 2013.
Activation of the NOTCH receptors relies on their intracellular proteolysis by the gamma-secretase complex. This cleavage liberates the NOTCH intracellular domain (NIC) thereby allowing the translocation of NIC towards the nucleus to assemble into a transcriptional platform. Little information is available regarding the regulatory steps operating on NIC following its release from the transmembrane receptor up to its association with transcriptional partners. Interfering with these regulatory steps might potentially influences the nuclear outcome of NOTCH signalling. Herein, we exploited a reliable model to study the molecular events occurring subsequent to NOTCH1 cleavage. In pancreatic cancer cells, pulse of NOTCH1 activation led to increased expression of NOTCH target genes namely HES1 and c-MYC. We uncovered that, upon its release, the NOTCH1 intracellular domain, NIC1, undergoes a series of post-translational modifications that include phosphorylation. Most interestingly, we found that activation of the MEK/ERK pathway promotes HES1 expression. Inhibition of the gamma-secretase complex prevented the MEK/ERK-induced HES1 expression suggesting a NOTCH-dependent mechanism. Finally, higher levels of NIC1 were found associated with its transcriptional partners [CBF1, Su(H) and LAG-1] (CSL) and MASTERMIND-LIKE 1 (MAML1) upon MEK/ERK activation providing a potential mechanism whereby the MEK/ERK pathway promotes expression of NOTCH target genes. For the first time, our data exposed a signalling pathway, namely the MEK/ERK pathway that positively impacts on NOTCH nuclear outcome.
NOTCH受体的激活依赖于γ-分泌酶复合物对其进行的细胞内蛋白水解。这种切割释放出NOTCH细胞内结构域（NIC），从而使NIC能够向细胞核转运，组装成一个转录平台。关于NIC从跨膜受体释放后直至与转录伙伴结合这一过程中的调控步骤，目前所知甚少。干扰这些调控步骤可能会潜在地影响NOTCH信号传导的核内结果。在此，我们利用一个可靠的模型来研究NOTCH1切割后发生的分子事件。在胰腺癌细胞中，NOTCH1激活脉冲导致NOTCH靶基因HES1和c-MYC的表达增加。我们发现，NOTCH1细胞内结构域NIC1在释放后会经历一系列包括磷酸化在内的翻译后修饰。最有趣的是，我们发现MEK/ERK途径的激活促进HES1的表达。γ-分泌酶复合物的抑制阻止了MEK/ERK诱导的HES1表达，提示存在一种NOTCH依赖性机制。最后，在MEK/ERK激活后，发现较高水平的NIC1与其转录伙伴[CBF1、Su(H)和LAG-1]（CSL）以及类主调控分子1（MAML1）相关联，这为MEK/ERK途径促进NOTCH靶基因表达提供了一种潜在机制。我们的数据首次揭示了一条对NOTCH核内结果有正向影响的信号通路，即MEK/ERK途径。
