核内LC3调控细胞自噬的机制研究

Autophagy, a highly conserved process in eukaryotic cells, is a lysosome-dependent cellular degradation pathway involved in many physiological and pathological situations. This process is mainly carried out in the cytoplasm and roughly consists of occurrence of isolation membrane, formation of autophagosomes and fusion of autophagosome with lysosome. In our preliminary work, we have found that LC3, a very important autophagy-related protein involved in the formation and maturation of autophagosomes and used widely as a marker for autophagosomes, is expressed strongly in the nucleus of many types of animal cells. During autophagy, nuclear LC3 undergoes translocation form the nucleus to the cytoplasm, and this translocation is essential for autophagosome formation. Based on the preliminary data, in this study, we aim to investigate the molecular mechanism underlying the necessity of LC3 nuclear localization, regulation and significance of LC3 translocation by focusing on the posttranslational modification especially the acetylation and deacetylation of LC3. We are also interested in the identification of regulatory machinery for LC3 translocation.

细胞自噬是真核细胞中高度保守的溶酶体依赖性的蛋白质降解途径，参与真核细胞的多种生理病理过程。从自噬前体的发生到自噬泡的形成，以及自噬泡与溶酶体的融合，其全部过程都在细胞质中完成。但有研究提示细胞核内的某些蛋白修饰系统对细胞自噬具有重要的调控作用。前期研究中我们发现，在自噬泡形成和成熟中发挥重要作用的自噬相关分子LC3在多种动物细胞核内有强烈表达。自噬发生时，细胞核内LC3移位至细胞质，并且该核-质移位过程为细胞自噬所必需。本项目拟在前期结果的基础上，进一步研究LC3定位于核内的必要性和LC3核-质移位在细胞自噬中的意义和机制。重点分析自噬时LC3分子的翻译后修饰改变，明确该修饰改变与LC3核-质移位和LC3与自噬泡膜结合的关系，并进而解析LC3翻译后修饰和出核的调控机制。

在自噬体形成和成熟中发挥重要作用的自噬相关分子LC3 在多种动物细胞核内有强烈表达，但其在核内定位和核内LC3在细胞自噬中的作用不明确。我们发现饥饿诱导自噬发生时，核内LC3移至细胞质，该核质移位为细胞自噬所必需。我们利用分子细胞学和生化学方法，深入研究了LC3定位于核内的必要性和LC3核质移位在细胞自噬中的意义和机制。我们发现，饥饿诱导自噬时，核内LC3被脱乙酰化酶Sirt1在K49和K51位点脱乙酰化；脱乙酰化使得核内LC3与核内蛋白DOR相互作用并移位细胞质；只有脱乙酰化的LC3才能在胞质与Atg7相互作用，完成其脂质化，从而在自噬体形成中发挥其重要作用。这些研究结果，阐明了核内LC3及其乙酰化修饰在自噬中的作用，解决了自噬领域内长期存在的科学问题，对进一步认识自噬启动的分子机制有重要意义。