选择性自噬在细胞能量代谢、应激反应、细胞生存等过程中起重要的调控作用。我们前期研究发现肺癌细胞中泛素连接酶NEDD4与自噬体蛋白LC3及自噬受体SQSTM1相互作用并泛素化SQSTM1。敲低NEDD4导致肺癌细胞选择性自噬体形成受阻和功能缺陷，并抑制细胞增殖和迁移。本项目基于这些新的发现，将从四个方面对NEDD4通过泛素化SQSTM1调控选择性自噬以及肺癌发生发展进行系统的研究：（1）确定该泛素化对SQSTM1分子结构功能的调节机理；（2）确定该泛素化对选择性自噬前体及自噬体形成和功能的调控机理；（3）确定该泛素化在肺癌细胞增殖和迁移中的作用；（4）确定该泛素化在裸鼠肺癌细胞移植肿瘤生长和转移中的作用。通过这些研究，揭示NEDD4泛素化信号调控选择性自噬的分子机制，确定NEDD4介导的SQSTM1泛素化在肺癌肿瘤生物学中的作用，为肺癌靶向治疗提供新的靶标途径。

Selective autophagy plays essential roles in regulation of metabolic and oxidative stress and multiple pathological processes. Ubiquitination has been demonstrated as a crucial biochemical modification for autophagosomal cargo recognition and recruitment in selective autophagy. However, the role of ubiquitination in regulation of autophagy receptor function remains largely unexplored. Our recent studies have found that the HECT E3 ubiquitin ligase NEDD4 interacts with the key autophagosomal protein LC3 and autophagy receptor SQSTM1 (also named as p62) and ubiquitinates SQSTM1. Knockdown of NEDD4 impaired starvation- or rapamycin-induced autophagy, significantly reduced formation of autophagosomes, and caused aggregation of LC3- and SQSTM1-positive autophagosomes in cells. Furthermore, NEDD4 is also required for lung cancer cell proliferation and migration. These data indicate an important role of NEDD4 in selective autophagy and raise a possible connection between the NEDD4-dependent ubiquitination of SQSTM1and lung tumor growth and progression. However, the mechanism and signaling pathways regulating selective autophagy by NEDD4 and the connection between selective autophagy and lung cancer are largely unknown. Thus, this proposal is to determine the molecular mechanism by which NEDD4 regulates selective autophagic processes, the lung cancer cell proliferation and migration, and lung tumor growth and metastasis through ubiquitination of SQSTM1. Our working hypothesis is that NEDD4 modifies the molecular structure of SQSTM1 by ubiquitination for facilitating interaction of SQSTM1 with its down-stream signaling molecules, activating selective autophagic process, promoting lung tumor growth and metastasis. To test the hypothesis, four specific aims will be investigated: (1) to determine the role of the NEDD4-mediated ubiquitination in regulating molecular structure and function of SQSTM1; (2) to determine the role of the NEDD4-mediated ubiquitination of SQSTM1 in regulating localization and transport of autophagosomes; (3) to determine the role of the NEDD4-mediated ubiquitination of SQSTM1 in facilitating lung cancer cell proliferation and migration; and (4) to determine the effect of NEDD4-mediated ubiquitination of SQSTM1 on xenograft tumor growth and metastasis in a nude mouse model. Through these studies, we expect to elucidate the molecular mechanism by which NEDD4 regulates selective autophagy by ubiquitination of SQSTM1 and define a new ubiquitination signaling pathway promoting lung tumorigenesis and progression.