Regulation of B Lymphocyte Survival and Differentiation by HSH2

这项建议的目的是阐明新的接头蛋白HSH2的生理作用 (JHSH2蛋白)在B淋巴细胞生物学调节中的作用。在我们实验室进行的研究 已经证明HSH2在脾B细胞中低基础水平表达，其表达是 刺激与促进存活的不同受体家族结合而诱导 分化包括CD40L、IL-4、内毒素、CpG、DMA和BLyS(BAFF)。HSH2基因表达上调 被证明依赖于核因子-ICB的激活，并与启动生存反应有关， 包括上调bc-xi的表达。逆转录病毒介导的HSH2在WEHI-231 B细胞系中的表达 在BCR结扎后发生细胞凋亡，观察到可提高存活率和线粒体 稳定性。同样，CD40介导的直接信号转导可提高WEHI-231细胞的存活率 与HSH2表达上调相关。尽管HSH2不会显著改变BCR-近端 信号转导，它被观察到维持线粒体的稳定性，这与它的能力有关。 阻断Bim的上调以响应BCR信号。此外，还发现HSH2与 抗凋亡蛋白HAX-1，它具有一个跨膜的区域，以其外部为靶点 线粒体膜。初步研究表明，HSH2与HAX-1之间的相互作用是 对HSH2的抗细胞凋亡活性很重要。因此，HSH2和HAX-1可能共同发挥作用 调节线粒体完整性和细胞存活。为了进一步阐明HSH2的生理作用， 调节B淋巴细胞的存活/分化，已经提出了三个具体的目标，将：1) 确定HSH2在B淋巴细胞发育、动态平衡和免疫功能中的生理作用； 2)阐明HSH2在共刺激反应中调节Bim表达的作用； 确定HSH2和HAX-1相互作用在线粒体调控中的功能重要性 稳定性。因为HSH2的表达是在对许多已知的关键刺激做出反应时诱导的 促进B细胞的存活和分化，这种适配蛋白很可能在调节中发挥重要作用 B细胞动态平衡与免疫功能。因此，这些研究将为我们提供对 维持B淋巴细胞存活和死亡之间平衡的分子机制导致 分化为体液效应细胞，将有助于深入了解疾病的病因和进展 与B细胞功能异常有关，包括癌症和自身免疫。

The goal of this proposal is to elucidate the physiological role of the novel adaptor protein HSH2 (JHematopoietic SH2 protein) in regulation of B lymphocyte biology. Studies conducted in our laboratory have demonstrated that HSH2 is expressed at low basal levels in splenic B cells and that its expression is induced in response to stimuli that bind to distinct families of receptors that promote survival and differentiation, including CD40L, IL-4, LPS, CpG DMA and BLyS (BAFF). Up-regulation of HSH2 expression was shown to be dependent on activation of NF-icB and correlates with initiation of a survival responsethat includes up-.regulation of Bcl-Xi.. Retroviral-mediated expression of HSH2 in the WEHI-231 B cell line, which undergoes apoptosis in response to BCR ligation, was observed to enhance survival and mitochondrial stability. Similarly, enhanced survival of WEHI-231 cells in response to CD40-mediated signaling directly correlated with up-regulation of HSH2 expression. Although HSH2 does not significantly alter BCR-proximal signal transduction, it was observed to maintain mitochondrial stability and this correlated with its ability to block up-regulation of Bim in response to BCR signaling. Moreover, HSH2 was found to interact with the anti-apoptotic protein HAX-1, which possessesa membrane-spanning region that targets it to the outer mitochondrial membrane. Preliminary studies have shown that the interaction between HSH2 and HAX-1 is important for the anti-apoptotic activity of HSH2. Therefore, HSH2 and HAX-1 may function together to regulate mitochondrial integrity and cell survival. To further elucidate the physiological role of HSH2 in regulation of B lymphocyte survival/differentiation, three specific aims have been proposed that will: 1) determine the physiological role of HSH2 in B lymphocyte development, homeostasis and immune function; 2) elucidate the role that HSH2 plays in regulating Bim expression in response to co-stimulation; and 3) determine the functional importance of the interaction between HSH2 and HAX-1 in regulating mitochondrial stability. Because HSH2 expression is induced in response to many of the key stimuli that are known to promote B cell survival and differentiation, this adaptor protein is likely to play an important role in regulating B cell homeostasis and immune function. Therefore, these studies will provide novel insight into the molecular mechanisms that maintain the balance between B lymphocyte survival and death leading to differentiation into humoral effector cells and will provide insight into the etiology and progression of diseases associated with aberrant B cell function, including cancer and autoimmunity.