Vielhaber E, Eide E, Rivers A, Gao Z H, Virshup D M
Department of Oncological Sciences, Huntsman Cancer Institute, University of Utah, Salt Lake City 84132, USA.
Mol Cell Biol. 2000 Jul;20(13):4888-99. doi: 10.1128/MCB.20.13.4888-4899.2000.
The molecular oscillator that keeps circadian time is generated by a negative feedback loop. Nuclear entry of circadian regulatory proteins that inhibit transcription from E-box-containing promoters appears to be a critical component of this loop in both Drosophila and mammals. The Drosophila double-time gene product, a casein kinase I epsilon (CKIepsilon) homolog, has been reported to interact with dPER and regulate circadian cycle length. We find that mammalian CKIepsilon binds to and phosphorylates the murine circadian regulator mPER1. Unlike both dPER and mPER2, mPER1 expressed alone in HEK 293 cells is predominantly a nuclear protein. Two distinct mechanisms appear to retard mPER1 nuclear entry. First, coexpression of mPER2 leads to mPER1-mPER2 heterodimer formation and cytoplasmic colocalization. Second, coexpression of CKIepsilon leads to masking of the mPER1 nuclear localization signal and phosphorylation-dependent cytoplasmic retention of both proteins. CKIepsilon may regulate mammalian circadian rhythm by controlling the rate at which mPER1 enters the nucleus.
维持昼夜节律时间的分子振荡器是由一个负反馈环产生的。抑制含E盒启动子转录的昼夜节律调节蛋白进入细胞核似乎是果蝇和哺乳动物中这个环的关键组成部分。果蝇双倍时间基因产物，一种酪蛋白激酶Iε（CKIε）同源物，已被报道与dPER相互作用并调节昼夜周期长度。我们发现哺乳动物CKIε与小鼠昼夜节律调节因子mPER1结合并使其磷酸化。与dPER和mPER2不同，单独在HEK 293细胞中表达的mPER1主要是一种核蛋白。两种不同的机制似乎会延迟mPER1进入细胞核。首先，mPER2的共表达导致mPER1 - mPER2异二聚体形成和细胞质共定位。其次，CKIε的共表达导致mPER1核定位信号被掩盖以及两种蛋白的磷酸化依赖性细胞质滞留。CKIε可能通过控制mPER1进入细胞核的速率来调节哺乳动物的昼夜节律。
