Department of Developmental and Regenerative Biology, Medical Research Institute, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8510, Japan.
J Biol Chem. 2012 Mar 9;287(11):8318-26. doi: 10.1074/jbc.M111.308908. Epub 2012 Jan 20.
The stress kinase mitogen-activated protein kinase kinase 7 (MKK7) is a specific activator of c-Jun N-terminal kinase (JNK), which controls various physiological processes, such as cell proliferation, apoptosis, differentiation, and migration. Here we show that genetic inactivation of MKK7 resulted in an extended period of oscillation in circadian gene expression in mouse embryonic fibroblasts. Exogenous expression in cultured mammalian cells of an MKK7-JNK fusion protein that functions as a constitutively active form of JNK induced phosphorylation of PER2, an essential circadian component. Furthermore, JNK interacted with PER2 at both the exogenous and endogenous levels, and MKK7-mediated JNK activation increased the half-life of PER2 protein by inhibiting its ubiquitination. Notably, the PER2 protein stabilization induced by MKK7-JNK fusion protein reduced the degradation of PER2 induced by casein kinase 1ε. Taken together, our results support a novel function for the stress kinase MKK7 as a regulator of the circadian clock in mammalian cells at steady state.
应激激酶丝裂原活化蛋白激酶激酶 7（MKK7）是 c-Jun N 端激酶（JNK）的特异性激活剂，它控制着各种生理过程，如细胞增殖、凋亡、分化和迁移。在这里，我们发现 MKK7 的基因失活导致小鼠胚胎成纤维细胞中昼夜节律基因表达的周期延长。在培养的哺乳动物细胞中外源表达一种 MKK7-JNK 融合蛋白，它作为 JNK 的组成性激活形式，诱导 PER2 的磷酸化，PER2 是一个基本的昼夜节律成分。此外，JNK 在内外源水平上均与 PER2 相互作用，MKK7 介导的 JNK 激活通过抑制 PER2 的泛素化来增加 PER2 蛋白的半衰期。值得注意的是，MKK7-JNK 融合蛋白诱导的 PER2 蛋白稳定减少了酪蛋白激酶 1ε 诱导的 PER2 降解。总之，我们的研究结果支持应激激酶 MKK7 在哺乳动物细胞的稳态下作为昼夜钟调节剂的新功能。
