TGF beta-induced apoptosis in B-lymphocytes

描述(由申请人提供)：转化生长因子b(TGFb)是一个细胞因子家族的原型，具有免疫调节特性，对维持正常的免疫稳态至关重要。在小鼠中靶向破坏TGFb1基因导致了一种表型，其特征是自身免疫性疾病典型的进行性多灶性炎症过程。在TGFb基因敲除中的炎症反应是由淋巴细胞介导的，表明TGFb在调节淋巴细胞增殖和激活方面发挥着重要作用，有助于维持自身耐受。TGFb通过程序性细胞死亡或凋亡克隆性删除B淋巴细胞来维持自身耐受性的这种作用已得到很好的证实，但其特征尚不明确。在这项建议中，我们希望确定TGFb通过诱导B淋巴细胞凋亡来帮助维持自身耐受的分子机制。我们已获得的初步结果表明，TGFb诱导的B淋巴细胞凋亡部分是通过其诱导促凋亡形式的Bcl2家族成员Bim、Bcl2相互作用的细胞死亡介质来实现的。这是第一次证明直接加入促凋亡诱导剂(TGFb)而不是撤除生存因子会导致Bim表达增加。TGFb对BIM的诱导是通过Smad3转录介导的，而通过CD40受体诱导的生存通路被激活而被取消。由于先前已经证明Bim的表达受转录因子叉头家族(FKHD)(特别是FKHR-L1)的调控，并且CD40偶联到调节FKHR-L1转录活性的PI3-K/Akt通路的激活，我们假设TGFb诱导B淋巴细胞Bim的表达和凋亡是通过FKHR-L1和SMAD3信号通路之间的协同作用来介导的。我们还希望通过基因失活/突变的方法来分离新的和以前未被描述的TGFb诱导的细胞凋亡的介体。

DESCRIPTION (provided by applicant): Transforming growth factor b (TGFb) is prototypic of a family of cytokines with immunoregulatory properties that are critical to the maintenance of normal immunological homeostasis. Targeted disruption of the TGFb1 gene in mice results in a phenotype characterized as a progressive multifocal inflammatory process typical of autoimmune disease. The inflammatory response in the TGFb-knockout is lymphocyte mediated demonstrating the vital role of TGFb in regulating lymphocyte proliferation and activation, which contribute to the maintenance of self tolerance. This role of TGFb in the maintenance of self tolerance through clonal deletion of B lymphocytes by programmed cell death or apoptosis is fairly well established but poorly characterized. In this proposal we wish to determine the molecular mechanisms by which TGFb aids in maintenance of self tolerance through its induction of apoptosis in B lymphocytes. We have obtained preliminary results demonstrating that TGFb-induced apoptosis in B-lymphocytes is in part mediated through its induction of the pro-apoptotic form of the Bcl-2 family member Bim, Bcl-2 interacting mediator of cell death. This is the first demonstration that direct addition of a pro-apoptotic inducer (TGFb), and not withdrawal of a survival factor results in increased Bim expression. TGFb induction of Bim is transcriptionally mediated through Smad3 and is abrogated by activation of the survival pathway induced through the CD40 receptor. Since it has previously been demonstrated that Bim expression is regulated by the forkhead family (FKHD) of transcription factors (specifically FKHR-L1) and that CD40 couples to activation of the PI3-K/Akt pathway which regulates FKHR-L1 transcriptional activity, we hypothesize that TGFb induced Bim expression and apoptosis in B lymphocytes is mediated through a cooperativity between the FKHR-L1 and the Smad3 signaling pathway. We also wish to isolate novel and previously uncharacterized mediators of TGFb-induced apoptosis using a gene inactivation/mutagenesis approach.