SENP2在漿細胞所扮演的角色

Abstract

SUMOylation是一種可逆的後轉譯修飾，它進行類似ubiquitin修飾的方式與將SUMO (Small Ubiquitin-like modifier) 與特定蛋白上的lysine支鍊形成共價鍵，進而修飾目標蛋白質來影響參與在各種生物現象之蛋白質的功能、如轉錄、轉譯、癌症、發育、病毒複製等等。此論文主要探討的主題為促成SUMOylation的可逆性的蛋白酶SENPs (SUMO-specific Sentrin Protease)，在漿細胞分化的過程中所扮演的角色，實驗室之前的研究發現，Blimp-1 (B lymphocyte－ induced maturation protein-1) 這個決定B細胞能否分化成漿細胞極其重要的蛋白，它的SUMOylation對於B細胞能否成功的分化成漿細胞是重要的。而SENP2具有去掉被加以SUMO的能力，但因為SUMO-Specific Sentrin protease 2 (SENP2)在免疫系統上的功能尚未被研究，而且以傳統基因剔除的方式將Senp2 於老鼠剔除會導致小鼠胚胎發育時死亡，為此我們將Senp2f/f的小鼠，與CD19-Cre背景的小鼠交配得到只有在B細胞中刪除Senp2的小鼠作研究。結果發現在經由活體免疫之後，B細胞剔除Senp2的老鼠生產出顯著且高量的IgG抗體種類轉移和親合力成熟。此外、我們也在活體外培養脾臟B220+ 細胞佐以不同細胞激素刺激來模仿漿細胞分化的過程，也發現與活體內相同的結果。因此，我們可以確定Senp2在調控漿細胞分泌免疫球蛋白的過程中會扮演重要的角色，而進一步尋找因Senp2被剔除導致抗體生產的目標蛋白則是未來研究的方向。

SUMOylation is one of the post-translational modifications (PTMs) that can be reversibly modified and involves in the regulation of diverse biological processes such as transcription, replication, chromosome segregation, carcinogenesis, and viral replication. Protein SUMOylation is modified by a family of small ubiquitin-related modifier (SUMO) proteins, and such post-translational modification is coined because it shares structure akin to ubiquitins as well as similar enzymatic cascades involving serial actions of E1 activating enzyme, E2 conjugating enzyme, and E3 protein ligase. The diverse biological process mediated by SUMOylation is reversible and reversibility of SUMOylation hinges on a family of proteases called SENPs. The function of SUMO-specific sentrin protease 2 (SENP2) in immune system is yet been elucidated. It’s been reported that conventional knockout of Senp2 in mice results in embryonic lethal. In this thesis, I focused on the study of the function of SENP2 in B cell differentiation. The terminal differentiation of B cells into plasma cells is recognized as the basis of humoral immunity that requires the expression of the master regulator—Blimp-1. Our previous study has shown that Blimp-1 can be specifically modified by SUMO1 through PIAS1 (SUMO E3 ligase) in plasma cell differentiation, and the SUMOylation of Blimp-1 is required for plasma cell differentiation. It is thus conceivable to propose that SUMOylation may affect plasma cell differentiation. Here,we crossed Senp2f/f mice with the mice carrying Cre recombinase under the regulation of CD19 promoter (CD19Cre+/-) to generate Senp2 conditional knockout (CKO) mice in which Senp2 is deleted specifically in B cells. We observed that CKO mice are equipped with stronger antibody secretion ability in both T-dependent immunization and T-independent immunization in vivo as well as the ex vivo culture systems that mimic T-dependent immunization stimulated with IL-21, α-CD40, and α-IgM, T-independent immunization stimulated with LPS, and class switch recombination stimulated with LPS and IL-4. These findings suggest that Senp2 plays a role in controlling the antibody class switch in B cells.