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衔接蛋白HSH 2（造血SH 2蛋白）在B淋巴细胞生物学调节中的生理作用。在我们实验室进行的研究已经证明，HSH 2在脾B细胞中以低基础水平表达，并且其表达响应于结合促进存活和分化的不同受体家族的刺激而被诱导，所述受体家族包括CD 40 L、IL-4、LPS、CpG DMA和BLyS（BAFF）。HSH 2表达的上调被证明是依赖于NF-？B，并与包括上调Bcl-XL的存活应答的起始相关。在WEHI-231 B细胞系中，观察到逆转录病毒介导的HSH 2表达增强了存活和线粒体稳定性，WEHI-231细胞系响应于BCR连接而经历凋亡。类似地，响应于CD 40介导的信号传导的WEHI-231细胞的增强的存活与HSH 2表达的上调直接相关。尽管HSH 2不显著改变BCR近端信号转导，但观察到其维持线粒体稳定性，这与其阻断Bim响应BCR信号转导的上调的能力相关。此外，发现HSH 2与抗凋亡蛋白HAX-1相互作用，HAX-1具有将其靶向线粒体外膜的跨膜区域。初步研究表明，HSH 2和HAX-1之间的相互作用对于HSH 2的抗凋亡活性是重要的。因此，HSH 2和HAX-1可能共同起作用以调节线粒体完整性和细胞存活。为了进一步阐明HSH 2在调节B淋巴细胞存活/分化中的生理作用，提出了三个具体目标：1）确定HSH 2在B淋巴细胞发育、稳态和免疫功能中的生理作用; 2）阐明HSH 2在响应共刺激调节Bim表达中的作用;以及3）确定HSH 2和HAX-1之间的相互作用在调节线粒体稳定性中的功能重要性。因为HSH 2表达是响应于已知促进B细胞存活和分化的许多关键刺激而诱导的，所以这种衔接蛋白可能在调节B细胞稳态和免疫功能中起重要作用。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（包括癌症和自身免疫）的病因学和进展提供见解。

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.