Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA.
Science. 2010 Jan 22;327(5964):463-6. doi: 10.1126/science.1180067.
At the core of the mammalian circadian clock is a negative feedback loop in which the dimeric transcription factor CLOCK-BMAL1 drives processes that in turn suppress its transcriptional activity. To gain insight into the mechanisms of circadian feedback, we analyzed mouse protein complexes containing BMAL1. Receptor for activated C kinase-1 (RACK1) and protein kinase C-alpha (PKCalpha) were recruited in a circadian manner into a nuclear BMAL1 complex during the negative feedback phase of the cycle. Overexpression of RACK1 and PKCalpha suppressed CLOCK-BMAL1 transcriptional activity, and RACK1 stimulated phosphorylation of BMAL1 by PKCalpha in vitro. Depletion of endogenous RACK1 or PKCalpha from fibroblasts shortened the circadian period, demonstrating that both molecules function in the clock oscillatory mechanism. Thus, the classical PKC signaling pathway is not limited to relaying external stimuli but is rhythmically activated by internal processes, forming an integral part of the circadian feedback loop.
在哺乳动物的生物钟核心是一个负反馈回路，其中二聚体转录因子 CLOCK-BMAL1 驱动的过程反过来抑制其转录活性。为了深入了解生物钟反馈的机制，我们分析了含有 BMAL1 的小鼠蛋白复合物。在循环的负反馈阶段，激活的蛋白激酶 C 受体 1（RACK1）和蛋白激酶 C-α（PKCalpha）以节律方式被募集到核 BMAL1 复合物中。RACK1 和 PKCalpha 的过表达抑制了 CLOCK-BMAL1 的转录活性，并且 RACK1 在体外刺激 PKCalpha 对 BMAL1 的磷酸化。成纤维细胞中内源性 RACK1 或 PKCalpha 的耗竭缩短了生物钟周期，表明这两种分子都在时钟振荡机制中发挥作用。因此，经典的 PKC 信号通路不仅限于传递外部刺激，而是被内部过程周期性激活，成为生物钟反馈回路的一个组成部分。
