Ohkubo Yusuke, Arima Masafumi, Arguni Eggi, Okada Seiji, Yamashita Kimihiro, Asari Sadaki, Obata Shintaro, Sakamoto Akemi, Hatano Masahiko, O-Wang Jiyang, Ebara Masaaki, Saisho Hiromitsu, Tokuhisa Takeshi
Department of Developmental Genetics (H2), Graduate School of Medicine, Chiba University, Chiba, Japan.
J Immunol. 2005 Jun 15;174(12):7703-10. doi: 10.4049/jimmunol.174.12.7703.
Expression of B lymphocyte-induced maturation protein 1 (Blimp-1) transcription factor is essential for promoting B cell differentiation into plasma cells. However, a critical transcription factor for Blimp-1 expression in activated B cells is unclear. When splenic B cells were stimulated with CD40 ligand (CD40L) and IL-4, terminal differentiation was induced in the B cells from c-fos transgenic (H2-c-fos) mice but barely in those from control littermates and from c-fos-deficient mice. AP-1 family and Blimp-1 mRNAs were transiently induced in the control B cells, and overexpression of c-Fos induced a sufficient amount of Blimp-1 for terminal differentiation in the H2-c-fos B cells. When normal and c-fos-deficient B cells were stimulated with LPS, a sufficient amount of Blimp-1 for terminal differentiation was induced in those B cells. However, expression of c-fos/AP-1 family mRNAs in LPS-stimulated normal B cells was similar to that of normal B cells stimulated with CD40L and IL-4. EMSA and chromatin immunoprecipitation assays using the AP-1-binding DNA sequence in the murine Blimp-1 promoter region demonstrated that AP-1-binding activity in nuclear protein of LPS-stimulated normal B cells was prolonged more than that in normal B cells stimulated with CD40L and IL-4. Furthermore, the percentage of CD138(+) B cells within germinal center B cells in the spleen and the number of Ab-forming cells in the bone marrow of H2-c-fos mice was larger than that of control mice 12 days after immunization. Thus, although c-Fos is not essential for Blimp-1 expression, c-Fos/AP-1 positively regulates Blimp-1 expression and terminal differentiation of activated B cells.
B淋巴细胞诱导成熟蛋白1（Blimp-1）转录因子的表达对于促进B细胞分化为浆细胞至关重要。然而，活化B细胞中Blimp-1表达的关键转录因子尚不清楚。用CD40配体（CD40L）和IL-4刺激脾B细胞时，c-fos转基因（H2-c-fos）小鼠的B细胞可诱导终末分化，而对照同窝小鼠和c-fos缺陷小鼠的B细胞几乎不发生终末分化。对照B细胞中AP-1家族和Blimp-1 mRNA被短暂诱导，而c-Fos的过表达在H2-c-fos B细胞中诱导出足够量的Blimp-1以实现终末分化。用脂多糖（LPS）刺激正常和c-fos缺陷的B细胞时，这些B细胞中可诱导出足够量的用于终末分化的Blimp-1。然而，LPS刺激的正常B细胞中c-fos/AP-1家族mRNA的表达与用CD40L和IL-4刺激的正常B细胞相似。使用小鼠Blimp-1启动子区域中AP-1结合DNA序列进行的电泳迁移率变动分析（EMSA）和染色质免疫沉淀分析表明，LPS刺激的正常B细胞核蛋白中的AP-1结合活性比用CD40L和IL-4刺激的正常B细胞延长得更多。此外，免疫后12天，H2-c-fos小鼠脾脏生发中心B细胞中CD138(+) B细胞的百分比和骨髓中抗体形成细胞的数量均高于对照小鼠。因此，尽管c-Fos对于Blimp-1的表达并非必不可少，但c-Fos/AP-1可正向调节活化B细胞的Blimp-1表达和终末分化。
