HRD1的Ufmylation修饰的分子机制及在脂质代谢中的功能研究

Dysfunction of lipid metabolism is associated with diverse metabolic disorders including obesity. Although pathways of lipid metabolism have been generally elucidated, how these pathways are precisely regulated was largely unknown. Endoplasmic reticulum (ER)-associated degradation (ERAD) regulates various metabolic pathways by controlling the protein stability of metabolic enzymes. However, the mechanisms that regulation of ERAD are largely unknown. We previously found that knockdown of UFL1, the E3 ligase of ufmylation pathway, upregulated the protein level of GPAT3, the rate-limiting enzyme of triacylglycerol synthesis. In addition, the lipid accumulation was also increased. We also found that UFL1 mediated ERAD degradation of GPAT3. Further studies confirmed that UFL1 interacted with HRD1, the E3 ubiquitin ligase of ERAD, which resulted in the ufmylation of HRD1. These evidences suggested that the ufmylation of HRD1 may play an important role in fat synthesis.We intend to use molecular biology, biochemical recombination and cell biology to study the molecular mechanisms of lipid metabolism regulated by HRD1 ufmylation, so as to reveal the regulation mode of lipid metabolism and the mechanisms of obesity.

脂质代谢的紊乱是肥胖等一系列代谢疾病的重要原因。尽管脂质代谢的通路已经被基本解析，但具体调控机理的阐述还处于初步阶段。内质网相关降解途径（ERAD）通过控制代谢酶的蛋白稳定性来调节各种代谢途径，但目前对ERAD的调控机制尚不清楚。我们前期的研究发现，敲低类泛素化Ufmylation通路的E3连接酶UFL1后，脂肪合成的限速酶GPAT3的蛋白水平上调，促进脂肪的积累；另外我们发现UFL1能促进GPAT3的ERAD途径降解。进一步的研究证实UFL1能与ERAD中的E3泛素连接酶HRD1相互作用，使HRD1发生Ufmylation修饰。这些证据提示我们HRD1的Ufmylation修饰调节可能在脂肪合成中发挥着重要的作用。我们拟应用分子生物学、生化重组和细胞生物学等方法研究HRD1的Ufmylation修饰调控脂代谢的分子机制，为揭示脂代谢调控方式及揭示肥胖的发生机理做出贡献。

UFM1是一种类泛素样蛋白，其对底物的修饰对后生动物胚胎发育至关重要。虽然UFMylation已经被证实与内质网稳态有关，但其潜在机制和相关的底物在很大程度上尚不清楚。在这里，我们证明内质网相关蛋白降解途径(ER-associated protein degradation，ERAD)的其中一种重要泛素连接酶HRD1,，是UFM1偶联的新底物。HRD1与UFMylation系统组分UFL1和DDRGK1相互作用，在Lys610残基处被UFMylation修饰。在UFL1缺失的细胞中，HRD1的稳定性增加，其泛素化修饰减少。在内质网应激的情况下，HRD1的UFMylation和泛素化修饰随着时间的推移逐渐被抑制。HRD1 Lys610残基突变为精氨酸会削弱其降解未折叠或错误折叠蛋白的能力，从而激活未折叠蛋白反应(unfolded protein response，UPR)。这些结果表明，HRD1的UFMylation修饰有助于ERAD功能并维持内质网稳态。