TGF Beta-Induced Apoptosis in B-Lymphocytes

项目摘要/摘要： 转化生长因子与促凋亡的Bim、Bcl2家族成员相互作用 细胞死亡的中介物在免疫系统的发育和动态平衡中起着关键作用。目标明确 在小鼠中，无论是转化生长因子基因还是Bim基因的破坏，都会导致淋巴和髓系细胞的聚集， T细胞发育的紊乱，最终导致动物死于系统性自身免疫性疾病。 这些表型强调了转化生长因子β和Bim在T细胞发育中的重要作用。 自身反应性B细胞的选择或克隆性删除对正常B淋巴细胞发育和 保持自我容忍度。我们研究了转化生长因子β促进血管生成的分子机制。 通过诱导B淋巴细胞凋亡来维持自身耐受性。我们已经证明了 转化生长因子β诱导的细胞死亡是通过诱导Bim介导的，为Bim提供了第一个证据 表达水平直接受到促凋亡细胞因子的影响，而不是因此而上调 促生存因子(即IL-3、IL-7)停用或应激诱导。转化生长因子β对BIM的诱导作用 Smad3依赖，并通过激活生存通路而被取消。我们的初步数据确定了两个 转化生长因子β介导的BIM诱导的潜在调节物--即刻早期基因MAPK磷酸酶2 (MKP2)和转录共调控因子RUNX1/AML1。在这里，我们希望检验转化生长因子？的假设 通过使MAP激酶Erk失活，诱导MKP2快速靶向现有的Bim水平，导致 泛素介导的蛋白酶体衰变中Bim的去磷酸化和逃逸。此外，对于 Bim的持续调控，我们假设转化生长因子β诱导了转录辅助调节因子RUNX1/AML1， 它与FOX03相互作用，反式激活Bim mRNA的表达。有趣的是，转化生长因子对RUNX1的诱导 通过非转录机制进行调节，该机制涉及通过内部 核糖体进入(IRES)机制。因此，转化生长因子β不仅能诱导Bim基因转录，而且还能诱导Bim基因转录。 确保导致其产物降解的途径被抑制，从而产生Bim蛋白 积累，最终导致线粒体介导的细胞死亡。项目叙事。 促凋亡蛋白Bim是B淋巴细胞细胞死亡及其非调控表达的关键调节因子 是许多血液系统恶性肿瘤的基础。对这些目标的成功追求将带来更好的 理解Bim在转录和翻译后机制中的调控。我们的 研究可能确定可用于治疗调节的因素和重要的调控途径 在体内表达BIM。

Project Summary/Abstract: Transforming growth factor ¿ (TGF¿) and the pro-apoptotic Bcl-2 family member Bim, Bcl-2 interacting mediator of cell death, play critical roles in the development and homeostasis of the immune system. Targeted disruption, in mice, of either the TGF¿ or Bim gene results in an accumulation of lymphoid and myeloid cells, a perturbation of T cell development, and ultimately, the animals succumb to systemic autoimmune diseases. These phenotypes underscore the essential roles of TGF¿ and Bim in T cell development and in the negative selection or clonal deletion of autoreactive B cells that is critical for normal B lymphocyte development and the maintenance of self tolerance. We have investigated the molecular mechanisms by which TGF¿ aids in maintenance of self tolerance through its induction of apoptosis in B lymphocytes. We have demonstrated that TGF¿-induced cell death is mediated through its induction of Bim, providing the first evidence that Bim expression levels are directly influenced by a pro-apoptotic cytokine rather than being upregulated in response to pro-survival factor (i.e. IL-3, IL-7) withdrawal or stress induction. TGF¿ induction of Bim was shown to be Smad3-dependent and abrogated by activation of survival pathways. Our preliminary data has identified two potential modulators of TGF¿-mediated Bim induction, the immediate early gene MAPK phosphatase 2 (MKP2) and the transcriptional co-regulator Runx1/AML1. Herein, we wish to test the hypotheses that TGF¿ induces MKP2 to rapidly target existing Bim levels by inactivation of the MAP kinase Erk, resulting in dephosphorylation and escape of Bim from ubiquitin-mediated proteasomal decay. Additionally, and for sustained modulation of Bim, we postulate that TGF¿ induces the transcriptional co-regulator Runx1/AML1, which interacts with Fox03 to transactivate Bim mRNA expression. Interestingly, Runx1 induction by TGF¿ is mediated through a non-transcriptional mechanism involving translational regulation through an internal ribosome entry (IRES) mechanism. Thus, TGF¿ not only induces de novo Bim mRNA transcription but also assures that the pathway that results in degradation of its product is inhibited, resulting in Bim protein accumulation and ultimately mitochondrial-mediated cell death. Project Narrative. The pro-apoptotic protein Bim is a key regulator of cell death in B lymphocytes and its deregulated expression underlies many hematological malignancies. The successful pursuit of these aims will lead to a better understanding of the regulation of Bim at both the transcriptional and post-translational mechanisms. Our research may identify factors and important regulatory pathways that could be used therapeutically to modulate Bim expression in vivo.