蛋白酶体激活因子通过负调控Sirtuin参与细胞自噬和核糖体胁迫的新功能发现和机制研究

NAD-dependent deacetylase, sirtuin, constitute a family of severn genes (SirT1-SirT7). SirT1 deacetylates a variety of proteins including p53, E2F1 and NFkB in addition to histones, participates in a wide arrange of cellular processes such as gene silence, cell cycle, apoptosis and energy metabolism. SirT1 function is important for targeting in cancer and aging therapy. SirT1 has been reported to activate autophagy. However, little is known with respect to the molecular mechanisms by which SirT1 is regulated and what impact these regulations in turn may have on SirT1 involved cellular processes such as autophagy. We recently found that PA28γ, a 20S proteasome activator, binds to SirT1 and SirT7, and enhances their degradation. Intriguingly, knockdown and knockout of PA28γ increase autophagy under normal and starvation conditions. Furthermore, overexpression of PA28γ induces ribosomal stress, and ribosomal stress induces SirT7 degradation and its interaction with PA28γ. We thus plan to study novel functions of protoeasome activator PA28γ in regulating autophagy and ribosomal stress by targeting Sirtuin proteins degradation. The proposed study will have significant impact on human diseases such as cancer and aging.

Sirtuin是一类依赖NAD的去乙酰化酶，有7个成员（SirT1~SirT7）。SirT1能去乙酰化修饰组蛋白、p53、E2F1、NF-kB等, 在基因沉默、细胞周期、凋亡、能量代谢调节等方面有重要作用，是抗肿瘤和抗衰老药物研究重要靶点。近期发现SirT1有诱导自噬的功能。但SirT1降解机制，及SirT1诱导自噬的功能是如何被调控的，却很少了解。我们发现，蛋白酶体激活因子PA28γ能结合SirT1和SirT7，并促进它们的降解；PA28γ基因敲除和RNAi-干扰后，细胞自噬明显加强； PA28γ缺失能进一步增加营养限制诱导的自噬发生；过量表达PA28γ能诱导核糖体胁迫发生；核糖体胁迫能明显降低SirT7，并增强PA28γ-SirT7结合。我们计划通过研究PA28γ对SirT1和SirT7蛋白降解作用，探讨PA28γ在细胞自噬和核糖体胁迫方面的新功能，为抗肿瘤和抗衰老研究提供新思路。

保持细胞的能量代谢如糖脂稳态对细胞在生理和病理胁迫状态下维持存活及保持功能非常重要。细胞能量稳态受到一些调控基因表达、蛋白质生成与降解、糖脂转运及代谢的关键因子和信号通路调控。越来越多的研究证明，细胞内存在一种泛素化非依赖的蛋白酶体系统可启动能量非依赖的蛋白质降解，但该系统一直缺乏研究。在该项目研究中，我们研究了ATP和非泛素依赖的REGγ蛋白酶体在能量代谢调控中的作用，发现REGγ缺失可诱发自噬依赖的脂肪降解，并抵抗高脂诱发脂肪肝形成（Cell metabolism 2013）。REGγ蛋白酶体有可能通过核糖体转录调控核糖体生成和能量代谢，REGγ缺失可增敏糖代谢抑制剂饿死肿瘤的效果，说明REGγ是研究肿瘤“饿死”治疗的分子靶标。再有，我们也研究了REGγ的相互作用蛋白，并发现REGγ蛋白与脂代谢总调节因子—KLF14结合并促进其降解。有意思的是，我们发现KLF14缺失会诱发基因组不稳定并导致肿瘤发生（Nature Communications 2015）。目前，我们正在深入研究REGγ是否在能量胁迫状态下干预细胞能量。我们的研究为肿瘤及代谢紊乱疾病治疗提供了新机制和新分子靶标。