TGF beta-induced apoptosis in B-lymphocytes

描述（由申请人提供）：转化生长因子b （TGFb）是具有免疫调节特性的细胞因子家族的原型，对维持正常的免疫稳态至关重要。在小鼠中靶向破坏TGFb1基因导致一种以自身免疫性疾病典型的进行性多灶性炎症过程为特征的表型。TGFb基因敲除的炎症反应是由淋巴细胞介导的，这表明TGFb在调节淋巴细胞增殖和活化方面发挥重要作用，有助于维持自身耐受性。TGFb通过程序性细胞死亡或凋亡导致B淋巴细胞克隆性缺失来维持自身耐受性的作用已经得到了充分的证实，但尚未得到充分的表征。在这个提议中，我们希望确定TGFb通过诱导B淋巴细胞凋亡来帮助维持自我耐受性的分子机制。我们已经获得了初步结果，证明tgfb诱导的b淋巴细胞凋亡部分是通过其诱导Bcl-2家族成员Bim的促凋亡形式介导的，Bim是Bcl-2细胞死亡的相互作用介质。这是第一次证明直接添加促凋亡诱导剂（TGFb），而不是退出生存因子导致Bim表达增加。TGFb对Bim的诱导是通过Smad3转录介导的，并通过CD40受体诱导的存活途径的激活而被消除。由于先前已经证明Bim的表达受叉头家族（FKHD）转录因子（特别是FKHR-L1）的调控，并且CD40与PI3-K/Akt通路的激活相结合，从而调控FKHR-L1的转录活性，因此我们假设TGFb诱导Bim在B淋巴细胞中的表达和凋亡是通过FKHR-L1和Smad3信号通路之间的协同作用介导的。我们还希望利用基因失活/诱变方法分离出tgfb诱导的新的和以前未表征的细胞凋亡介质。

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.