MECHANISM OF CYTOKINE INDUCED B CELL DIFFERENTIATION

本项目的长期目标是了解 在终末分化和细胞周期控制的基础 B细胞向浆细胞的分化。体内，终末 B细胞分化的特征在于IG合成增加 和分泌，减少表面IG和MHC H类表达， 形态成熟和细胞周期停滞。尽管有这些知识， 其基本机制尚未得到很好的理解。白细胞介素-6（IL-6） 在晚期B细胞分化中具有生理作用，这是显而易见的 通过在转基因小鼠中过度表达 IL-6和继发性IG反应的缺陷在IL-6缺乏的 小鼠我们已经证明，刺激人B淋巴母细胞样细胞 与IL-6在体外重演了B细胞终末的主要标志 体内分化。本提案的目的是阐明 IL-6信号转导调节IG的机制 在B细胞中合成。 IL-6信号被认为是由两个 途径：快速和短暂的JakStat途径， 潜在转录因子Stat 3的激活， Statl，和更稳定的NF-IL 6途径，涉及碱性- 亮氨酸拉链转录因子NF-IL 6。尽管如此 尽管有丰富的信息，但两个关键问题仍未解决。 一个是关于这两种途径之间的关系， 另一个是确定启动子特异性， 每一条路。根据我们的初步研究， 假设短暂的Jak-Stat通路和 稳定的NF-IL 6途径在功能上偶联， 对IL-6的生理反应，通过顺序激活 NF-IL 6，激活和抑制下游基因 根据NF-IL 6同种型的比例， 为了验证这一点， 假设，我们建议（l）阐明之间的耦合 Jak-Stat途径和NF-IL 6途径，通过测定 需要Stat 3和Stat 1以及丝氨酸 用于立即激活NF-IL-6的磷酸化 （2）确定NF-IL 6和Jun在 稳定的IL-6信号传导，和（3）研究生理性的 NF-IL 6亚型在调节IG合成中的作用 通过研究IG启动子的激活和抑制， 体外和体内NF-IL 6同种型。这些研究应 提供了重要的洞察机制， 免疫系统中细胞因子信号传导的基础， B细胞的终末分化。

The long term goal of this project is to understand the mechanism that underlies differentiation and cell cycle control during terminal differentiation of B cells to plasma cells. In vivo, terminal differentiation of B cells is characterized by increases in Ig synthesis and secretion, reduction in surface Ig and MHC class H expression, morphological maturation and cell cycle arrest. Despite this knowledge, the underlying mechanism is not well understood. Interluekin-6 (IL-6) has a physiologic role in late stage B cell differentiation, as evident by the development of plasmacytosis in transgenic mice overexpressing IL-6 and by the deficiencies in secondary Ig responses in IL-6-deficient mice. We have shown that stimulation of human B lymphoblastoid cells with IL-6 in vitro recapitulates the major hallmarks of B cell terminal differentiation in vivo. The objective of this proposal is to elucidate the mechanism by which IL-6 signals are transduced to regulate Ig synthesis in B cells. The IL-6 signals are thought to be transduced by two pathways: the rapid and transient JakStat pathway involving activation of the latent transcription factors Stat3 and Statl, and a more stable NF-IL6 pathway involying the basic- leucine zipper transcription factor NF-IL6. Despite this wealth of information, two crucial issues remain unresolved. One concerns the relationship between the two pathways and the other the determination of the promoter specificity in each pathway. Based on our preliminary studies, we hypothesize that the transient Jak-Stat pathway and the stable NF-IL6 pathways are functionally coupled for physiologic responses to IL-6 by sequential activation of NF-IL6, which activates and inhibits downstream genes according to the ratio of NF-IL6 isoforms and by dimerization between NF-IL6 and Jun. To test this hypothesis, we propose to (l) elucidate the coupling between the Jak-Stat pathway and the NF-IL6 pathway, by determining the requirement of Stat3 and Statl and serine phosphorylation for the immediate activation of the NF-IL-6 promoter, (2) determine the roles of NF-IL6 and Jun in stable IL-6 signaling, and (3) investigate the physiologic roles of NF-IL6 isoforms in the regulation of Ig - synthesis by studying the activation and inhibition of Ig promoters by NF-IL6 isoforms in vitro and in vivo. These studies should provide significant insight into the the mechanisms that underlie cytokine signaling in the immune system and terminal differentiation of B cells.