Regulation of B Lymphocyte Survival and Differentiation by HSH2

描述（由申请人提供）：本申请的目的是阐明新型接头蛋白HSH2（造血SH2蛋白）在B淋巴细胞生物学调节中的生理作用。我们实验室进行的研究表明，HSH2在脾B细胞中以较低的基础水平表达，其表达是在与促进生存和分化的不同受体家族结合的刺激下诱导的，这些受体家族包括CD40L、IL-4、LPS、CpG DMA和BAFF。HSH2表达的上调依赖于NF-？B，并与生存反应的启动相关，包括向上。Bcl-XL的调控。逆转录病毒介导的HSH2在因BCR连接而发生凋亡的WEHI-231 B细胞系中表达，可提高存活和线粒体稳定性。同样，WEHI-231细胞对cd40介导的信号的存活增强与HSH2表达上调直接相关。尽管HSH2没有显著改变BCR-近端信号转导，但观察到它维持了线粒体的稳定性，这与它在BCR信号响应中阻断Bim上调的能力有关。此外，HSH2被发现与抗凋亡蛋白HAX-1相互作用，HAX-1具有一个跨膜区域，将其靶向到线粒体外膜。初步研究表明，HSH2与HAX-1的相互作用对HSH2的抗凋亡活性起重要作用。因此，HSH2和HAX-1可能共同调节线粒体完整性和细胞存活。为了进一步阐明HSH2在B淋巴细胞存活/分化调控中的生理作用，我们提出了三个具体目标：1)确定HSH2在B淋巴细胞发育、稳态和免疫功能中的生理作用；2)阐明HSH2在共刺激下调控Bim表达的作用；3)确定HSH2和HAX-1相互作用在调节线粒体稳定性中的功能重要性。由于HSH2的表达是在对许多已知促进B细胞存活和分化的关键刺激的反应中诱导的，因此这种衔接蛋白可能在调节B细胞稳态和免疫功能方面发挥重要作用。因此，这些研究将为维持B淋巴细胞生存和死亡之间的平衡，导致分化为体液效应细胞的分子机制提供新的见解，并将为与异常B细胞功能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.