Negative control of circadian clock regulator E4BP4 by casein kinase Iε-mediated phosphorylation
Negative control of circadian clock regulator E4BP4 by casein kinase Iε-mediated phosphorylation
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DOI：
10.1016/j.cub.2004.05.043
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发表时间：
2004-06-08
期刊：
影响因子：
9.2
通讯作者：
Fukada, Y
中科院分区：
文献类型：
--
作者：
Doi, M;Okano, T;Fukada, Y
生物钟基因的光依赖性转录调控是生物钟的关键步骤[1]。E4 bp 4是鸡松果体中的光诱导基因[2]，其编码抑制鸡松果体时钟基因cPer 2转录的bZIP蛋白[2，3]。在这里，我们证明了E4 BP 4蛋白的长期光周期依赖性积累与早上cPer 2上升期的延迟在时间上是协调的。E4 BP 4逐渐磷酸化，然后与诱导的cPer 2表达平行消失。E4 BP 4的特征揭示了Ser 182，一个位于Ser/Thr簇的氨基末端边界的磷酸化受体位点，其形成酪蛋白激酶1 β（CK 1 β）的磷酸化基序。CK 1 ε催化E4 BP 4磷酸化导致E4 BP 4水平的蛋白酶体蛋白水解依赖性降低，而E4 BP 4核积累被CK 1 ε以激酶活性不依赖的方式减弱。CK 1 ε介导的翻译后调节伴随着E4 BP 4执行的转录抑制的减少。这些结果不仅证明了E4 BP 4功能的磷酸化依赖性调节机制，而且还强调了CK 1 β作为E4 BP 4介导的cPer 2抑制的负调节因子的作用。
Light-dependent transcriptional regulation of clock genes is a crucial step in the entrainment of the circadian clock [1]. E4bp4 is a light-inducible gene in the chick pineal gland [2], and it encodes a bZIP protein that represses transcription of cPer2, a chick pineal clock gene [2,3]. Here, we demonstrate that prolonged light period-dependent accumulation of E4BP4 protein is temporally coordinated with a delay of the rising phase of cPer2 in the morning. E4BP4 was phosphorylated progressively and then disappeared in parallel with induced cPer2 expression. Characterization of E4BP4 revealed Ser182, a phosphoacceptor site located at the amino-terminal border of the Ser/Thr cluster, which forms the phosphorylation motifs for casein kinase 1epsilon (CK1epsilon). CK1epsilon physically associated with E4BP4 and phosphorylated it. CK1epsilon-catalyzed phosphorylation of E4BP4 resulted in proteasomal proteolysis-dependent decrease of E4BP4 levels, while E4BP4 nuclear accumulation was attenuated by CK1epsilon in a kinase activity-independent manner. CK1epsilon-mediated posttranslational regulation was accompanied by reduction of the transcriptional repression executed by E4BP4. These results not only demonstrate a phosphorylation-dependent regulatory mechanism for E4BP4 function but also highlight the role of CK1epsilon as a negative regulator for E4BP4-mediated repression of cPer2.