泛素连接酶NEDD4在抗体类型转换和CD40信号通路中的调节作用及机制研究

Immunoglobulin class switch, which is essential for humoral immunity, generates changes in the immunoglobulin expressed and the biological effector functions of immunoglobulin molecule without changing its specificity. CD40 is a major in vivo inducer of immunoglobulin class switch and abnormal CD40 signaling resulting immunodeficiency disorder, such as hyper-IgM syndrome. However, the regulation of CD40-mediated class switch is not fully understood and a molecular and biochemical understanding of CD40 signaling is lacking. Here we find that, in vivo and in vitro, E3 ubiquitin ligase NEDD4 is involved in immunoglobulin class switch, CD40-mediated AKT activation, and TRAF3 poly-ubiquitination. Upon these observation, we try to investigate the roles of NEDD4 in thymus-dependent immunoglobulin class switch, B cell survival, B cell proliferation, germinal center formation and plasmacytic differentiation through Nedd4 knockout mice and cells. Furthermore, using co-IP, ubiquitination assay and detecting CD40-mediated signaling, we try to clarify the form of NEDD4-mediated TRAF3 ubiquitination and its contribution to CD40 signaling pathway. In summary, this project propose that through ubiquitinating TRAF3, NEDD4 controls CD40-AKT signaling which regulate B cell immunoglobulin class switch.

抗体类型转换在体液免疫中发挥重要作用，该机制在不改变抗体特异性的情况下转换成不同类型的抗体，继而产生抗体的不同生物学效应。CD40信号通路是B细胞抗体类型转换的重要诱导因素之一，通路异常可导致高IgM血症等免疫缺陷相关疾病。但是，CD40介导的抗体类型转换和CD40信号通路调控机制并不完全清楚。我们前期研究发现：泛素连接酶NEDD4敲除细胞和动物中抗体类型转换能力增强；NEDD4调控CD40介导AKT激活，促进CD40信号通路重要调节蛋白质TRAF3泛素化。在此基础上，本项目拟在敲除动物和细胞水平深入研究NEDD4对B细胞功能的调节作用，包括抗体类型转换、B细胞增殖与存活、生发中心形成和浆细胞分化等。通过免疫共沉淀、泛素化和CD40信号通路激活检测，探讨NEDD4对TRAF3泛素化修饰方式及其对下游信号通路激活的调控机制。本研究有可能发现调控CD40信号通路和B细胞功能的全新分子机制。