Regulation of B Lymphocyte Survival and Differentiation by HSH2

描述(申请人提供)：本申请的目的是阐明新的接头蛋白HSH2(造血SH2蛋白)在调节B淋巴细胞生物学中的生理作用。我们实验室的研究表明，HSH2在脾B细胞中以低基础水平表达，其表达是在刺激结合促进生存和分化的不同受体家族的刺激下诱导的，包括CD40L、IL-4、LPS、CpG DMA和BLyS(BAFF)。HSH2表达的上调依赖于核因子-β的激活，并与包括Bcl-xL上调在内的生存反应的启动有关。观察到逆转录病毒介导的HSH2在BCR连接后发生凋亡的WEHI-231B细胞系中的表达，以提高存活率和线粒体的稳定性。同样，WEHI-231细胞对CD40介导的信号反应的存活率增加与HSH2表达的上调直接相关。尽管HSH2没有显著改变BCR-近端信号转导，但它被观察到维持线粒体的稳定性，这与其阻止Bim上调BCR信号的能力有关。此外，HSH2被发现与抗凋亡蛋白HAX-1相互作用，HAX-1具有跨膜区域，以线粒体膜外膜为靶标。初步研究表明，HSH2与HAX-1之间的相互作用对HSH2的抗凋亡活性具有重要作用。因此，HSH2和HAX-1可能共同发挥调节线粒体完整性和细胞存活的作用。为了进一步阐明HSH2在调节B淋巴细胞存活/分化中的生理作用，人们提出了三个具体的目标：1)确定HSH2在B淋巴细胞发育、体内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；3)确定HSH2与HAX-1相互作用在调节线粒体稳定性方面的功能重要性。由于HSH2的表达是在许多已知促进B细胞存活和分化的关键刺激作用下诱导的，这种接头蛋白很可能在调节B细胞的动态平衡和免疫功能方面发挥重要作用。因此，这些研究将为维持B淋巴细胞存活和死亡之间的平衡导致体液效应细胞分化的分子机制提供新的见解，并将为与B细胞功能异常相关的疾病的病因和进展提供见解，包括癌症和自身免疫。

DESCRIPTION (provided by applicant): The goal of this application is to elucidate the physiological role of the novel adaptor protein HSH2 (Hematopoietic 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-?B and correlates with initiation of a survival response that includes up-.regulation of Bcl-XL. 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 possesses a 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.