Center for Medical Genetics, School of Life Sciences, Central South University, Changsha 410078, Hunan, P. R. China.
Hunan Key Laboratory of Animal Models for Human Diseases, Changsha 410078, Hunan, P. R. China.
Nucleic Acids Res. 2020 Aug 20;48(14):7944-7957. doi: 10.1093/nar/gkaa601.
Circadian clocks are endogenous oscillators that control ∼24-hour physiology and behaviors in virtually all organisms. The circadian oscillator comprises interconnected transcriptional and translational feedback loops, but also requires finely coordinated protein homeostasis including protein degradation and maturation. However, the mechanisms underlying the mammalian clock protein maturation is largely unknown. In this study, we demonstrate that necdin, one of the Prader-Willi syndrome (PWS)-causative genes, is highly expressed in the suprachiasmatic nuclei (SCN), the pacemaker of circadian clocks in mammals. Mice deficient in necdin show abnormal behaviors during an 8-hour advance jet-lag paradigm and disrupted clock gene expression in the liver. By using yeast two hybrid screening, we identified BMAL1, the core component of the circadian clock, and co-chaperone SGT1 as two necdin-interactive proteins. BMAL1 and SGT1 associated with the N-terminal and C-terminal fragments of necdin, respectively. Mechanistically, necdin enables SGT1-HSP90 chaperone machinery to stabilize BMAL1. Depletion of necdin or SGT1/HSP90 leads to degradation of BMAL1 through the ubiquitin-proteasome system, resulting in alterations in both clock gene expression and circadian rhythms. Taken together, our data identify the PWS-associated protein necdin as a novel regulator of the circadian clock, and further emphasize the critical roles of chaperone machinery in circadian clock regulation.
昼夜节律钟是内源性振荡器，几乎在所有生物体中控制着约 24 小时的生理和行为。昼夜节律振荡器由相互连接的转录和翻译反馈环组成，但还需要精细协调的蛋白质稳态，包括蛋白质降解和成熟。然而，哺乳动物时钟蛋白成熟的机制在很大程度上是未知的。在这项研究中，我们证明了神经钙黏蛋白（necdin）是普拉德-威利综合征（PWS）致病基因之一，在哺乳动物昼夜节律钟的起搏器视交叉上核（SCN）中高度表达。necdin 缺失的小鼠在 8 小时提前时差范式中表现出异常行为，并在肝脏中破坏时钟基因表达。通过使用酵母双杂交筛选，我们鉴定了 BMAL1，即昼夜节律钟的核心组成部分，以及共伴侣 SGT1 作为与 necdin 相互作用的两种蛋白。BMAL1 和 SGT1 分别与神经钙黏蛋白的 N 端和 C 端片段结合。从机制上讲，necdin 使 SGT1-HSP90 伴侣机制能够稳定 BMAL1。necdin 或 SGT1/HSP90 的耗竭会导致 BMAL1 通过泛素-蛋白酶体系统降解，从而导致时钟基因表达和昼夜节律的改变。总之，我们的数据确定了与 PWS 相关的蛋白神经钙黏蛋白是昼夜节律钟的一种新型调节剂，并进一步强调了伴侣机制在昼夜节律钟调节中的关键作用。
