去泛素化酶OTUD3在肺腺癌发生中的功能及机制研究

Lung cancer is the leading cause of cancer-related death. Adenocarcinoma, accounting for approximately 40% of all cases, is an important subgroup of lung cancer. Ubiquitylation is a reversible post-translational modification with the roles in determining protein stability. Our partners’ work which published on the Nature Cell Biology in 2015 identified that OTUD3 as a DUB of PTEN and the inactivation of OTUD3 in breast cancer samples promotes the tumorigenesis. However, our previous study indicated that in lung adenocarcinoma samples OTUD3 expression is significantly increased in cancer tissues as compared with the adjacent normal tissues. Meanwhile, OTUD3 induces the anchorage independent growth, tumor formation in xenografts and enhanced the cell migration ability. These suggest a different mechanism. Furthermore, we identified OTUD3 interacts and stabilizes GRP78. In this project, we will characterize the key sites responsible for the interaction, and explore the effect of tumor mutation on their interactions and functions. Besides, we will intensively investigate the ubiquitylation of GRP78 which might explain the reason why GRP78 is expressing high. Through discussing whether the function of OTUD3 is dependent on GRP78, we intend to clarify the correlation of OTUD3 and GRP78 which will help us confirm the function of OTUD3 in tumorigenesis. This project is expected to provide new targets for the treatment of lung adenocarcinoma.

肺癌是发病率和致死率最高的恶性肿瘤，其中肺腺癌是占比高达40%的亚型。泛素化修饰是调节蛋白稳定的可逆的翻译后修饰过程。我们的合作团队2015年发表于自然细胞生物学杂志上的研究表明：去泛素化酶OTUD3可以稳定抑癌因子PTEN，乳腺癌样本中OTUD3的低表达或突变失活促进了乳腺癌的发生发展。但是，我们近期的研究表明，OTUD3在肺腺癌组织中高表达，且促进肺腺癌细胞系的增殖和迁移，暗示着不同的调控机制。初步的机制探索实验表明：OTUD3能结合并稳定促癌蛋白GRP78，提示GRP78为其下游分子。本项目将进一步明确二者的结合位点，同时筛查肺腺癌样本突变；深入精细研究OTUD3调控GRP78的泛素化修饰的机制，解释肺腺癌中GRP78高表达的原因；探讨OTUD3的功能发挥是否依赖于GRP78，阐明OTUD3-GRP78轴在肺腺癌发生发展的作用。本研究有望为肺腺癌的治疗提供潜在的新靶点。

之前的研究表明，去泛素化酶OTUD3通过稳定PTEN蛋白，在乳腺肿瘤的发生中发挥抑制作用，但其在肺癌中的作用尚不清楚。本项目首先确证了体内OTUD3缺失会促进小鼠乳腺癌的发生发展。进一步的组织微阵列分析表明，在人类乳腺癌、肝细胞癌、结肠癌和宫颈癌中，OTUD3的表达水平降低，并伴随着PTEN丰度的降低。而令人惊奇的是，OTUD3缺失能够减慢KrasG12D驱动的肺腺癌(ADC)的发生和发展，同时显著增加小鼠的存活率。此外，OTUD3在人肺癌组织中高表达，其高表达与患者生存率较差显著相关。进一步的机制研究表明，OTUD3与葡萄糖调节蛋白GRP78存在相互作用。具体的机制为，OTUD3通过去除GRP78蛋白的泛素化从而使其稳定。OTUD3的敲低会导致肺癌中GRP78蛋白水平降低、抑制细胞生长和迁移以及肿瘤的发生。总之，本题首次揭示了OTUD3在肺癌中的促癌基因作用，并提示去泛素化酶可在细胞和组织依赖性环境中发挥不同的功能。同时，解析了GRP78在肺腺癌中高表达的机制，完善了其泛素化修饰的研究。本研究通过明确OTUD3-GRP78轴在肺癌发生发展的机制和功能，为肺癌的治疗提供潜在的新靶点。