Mixed Lineage Kinase Phosphorylates Transcription Factor E47 and Inhibits TrkB Expression to Link Neuronal Death and Survival Pathways
Mixed Lineage Kinase Phosphorylates Transcription Factor E47 and Inhibits TrkB Expression to Link Neuronal Death and Survival Pathways
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DOI：
10.1074/jbc.m109.038729
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发表时间：
2009-11-20
影响因子：
4.8
通讯作者：
Gallego, Carme
中科院分区：
文献类型：
--
作者：
Pedraza, Neus;Rafel, Marta;Gallego, Carme
E47是一种基本的螺旋-环-螺旋转录因子，参与神经元的分化和存活。我们先前已经证明，碱性螺旋-环-螺旋蛋白E47与TrkB基因启动子内的E-box序列结合并激活其转录。TrkB受体的正确表达在脊椎动物神经系统的发育和功能中起着关键作用，TrkB水平的改变与人类的重要疾病有关。在这里，我们显示E47与mlk2相互作用，mlk2是一种参与JNK介导的程序性细胞死亡激活的混合谱系激酶(MLK)。Mlk2在体内以不依赖于JNK的方式增强E47的AD2激活域的磷酸化，并在体外磷酸化AD2的环-螺旋结构中确定的丝氨酸和苏氨酸残基，该结构也包含假定的MLK对接位点。虽然这些残基是mlk2介导的E47失活所必需的，但CEP11004抑制MLKs会导致小脑颗粒神经元和分化中的神经母细胞瘤细胞中TrkB在转录水平上的上调。这些发现使我们能够提出一种新的机制，即MLK通过磷酸化E47的激活结构域来调节TrkB的表达。这种分子联系可以解释为什么MLK抑制剂不仅可以阻止细胞死亡过程的激活，还可以增强细胞存活信号，作为其神经保护潜力的一个关键方面。
E47 is a basic helix-loop-helix transcription factor involved in neuronal differentiation and survival. Wehad previously shown that the basic helix-loop-helix protein E47 binds to E-box sequences within the promoter of the TrkB gene and activates its transcription. Proper expression of the TrkB receptor plays a key role in development and function of the vertebrate nervous system, and altered levels of TrkB have been associated with important human diseases. Here we show that E47 interacts with MLK2, a mixed lineage kinase (MLK) involved in JNK-mediated activation of programmed cell death. MLK2 enhances phosphorylation of the AD2 activation domain of E47 in vivo in a JNK-independent manner and phosphorylates in vitro defined serine and threonine residues within a loop-helix structure of AD2 that also contains a putative MLK docking site. Although these residues are essential for MLK2-mediated inactivation of E47, inhibition of MLKs by CEP11004 causes up-regulation of TrkB at a transcriptional level in cerebellar granule neurons and differentiating neuroblastoma cells. These findings allow us to propose a novel mechanism by which MLK regulates TrkB expression through phosphorylation of an activation domain of E47. This molecular link would explain why MLK inhibitors not only prevent activation of cell death processes but also enhance cell survival signaling as a key aspect of their neuroprotective potential.