Lee Choogon, Weaver David R, Reppert Steven M
Department of Neurobiology, LRB-728, University of Massachusetts Medical School, 364 Plantation Street, Worcester, MA 01605, USA.
Mol Cell Biol. 2004 Jan;24(2):584-94. doi: 10.1128/MCB.24.2.584-594.2004.
The mPER1 and mPER2 proteins have important roles in the circadian clock mechanism, whereas mPER3 is expendable. Here we examine the posttranslational regulation of mPER3 in vivo in mouse liver and compare it to the other mPER proteins to define the salient features required for clock function. Like mPER1 and mPER2, mPER3 is phosphorylated, changes cellular location, and interacts with other clock proteins in a time-dependent manner. Consistent with behavioral data from mPer2/3 and mPer1/3 double-mutant mice, either mPER1 or mPER2 alone can sustain rhythmic posttranslational events. However, mPER3 is unable to sustain molecular rhythmicity in mPer1/2 double-mutant mice. Indeed, mPER3 is always cytoplasmic and is not phosphorylated in the livers of mPer1-deficient mice, suggesting that mPER3 is regulated by mPER1 at a posttranslational level. In vitro studies with chimeric proteins suggest that the inability of mPER3 to support circadian clock function results in part from lack of direct and stable interaction with casein kinase Iepsilon (CKIepsilon). We thus propose that the CKIepsilon-binding domain is critical not only for mPER phosphorylation but also for a functioning circadian clock.
mPER1和mPER2蛋白在生物钟机制中发挥着重要作用，而mPER3则是可有可无的。在此，我们研究了小鼠肝脏中mPER3在体内的翻译后调控，并将其与其他mPER蛋白进行比较，以确定生物钟功能所需的显著特征。与mPER1和mPER2一样，mPER3会发生磷酸化，改变细胞定位，并以时间依赖的方式与其他生物钟蛋白相互作用。与来自mPer2/3和mPer1/3双突变小鼠的行为数据一致，单独的mPER1或mPER2都可以维持有节奏的翻译后事件。然而，mPER3在mPer1/2双突变小鼠中无法维持分子节律性。事实上，mPER3在mPer1缺陷小鼠的肝脏中始终位于细胞质中且未被磷酸化，这表明mPER3在翻译后水平上受mPER1调控。对嵌合蛋白的体外研究表明，mPER3无法支持生物钟功能，部分原因是缺乏与酪蛋白激酶Iε（CKIε）的直接和稳定相互作用。因此，我们提出CKIε结合结构域不仅对mPER磷酸化至关重要，而且对正常运作的生物钟也至关重要。
