TGF Beta-Induced Apoptosis in B-Lymphocytes

性状（申请人提供）：转化生长因子？(TGF?)和促凋亡Bcl-2家族成员Bim，细胞死亡的Bcl-2相互作用介质，在免疫系统的发育和稳态中起关键作用。有针对性的破坏，在小鼠中，无论是TGF？或Bim基因导致淋巴样和骨髓样细胞的积累、T细胞发育的干扰，并且最终，动物死于系统性自身免疫疾病。这些表型强调了TGF？和Bim在T细胞发育和自身反应性B细胞的阴性选择或克隆缺失中的作用，所述自身反应性B细胞对于正常B淋巴细胞发育和自身耐受性的维持是关键的。我们已经研究了TGF？通过诱导B淋巴细胞凋亡来帮助维持自身耐受性。我们已经证明，TGF？-诱导的细胞死亡是通过Bim的诱导来介导的，这提供了Bim表达水平直接受促凋亡细胞因子影响而不是响应促存活因子（即IL-3、IL-7）撤除或应激诱导而上调的第一个证据。转化生长因子Bim的诱导被证明是Smad 3依赖性的，并且通过存活途径的激活而被消除。我们的初步数据已经确定了两种潜在的TGF？调节剂-介导的Bim诱导、立即早期基因MAPK磷酸酶2（MKP 2）和转录辅助调节因子Runx 1/AML 1。在此，我们希望测试的假设，TGF？通过MAP激酶Erk的失活诱导MKP 2快速靶向现有的Bim水平，导致Bim去磷酸化和逃避泛素介导的蛋白酶体衰变。此外，并持续调制Bim，我们假设，TGF？诱导转录辅助调节因子Runx 1/AML 1，其与Fox 03相互作用以反式激活Bim mRNA表达。有趣的是，Runx 1诱导TGF？是通过非转录机制介导的，该机制涉及通过内部核糖体进入（IRES）机制的翻译调节。因此，TGF？不仅诱导从头Bim mRNA转录，而且确保导致其产物降解的途径被抑制，导致Bim蛋白积累并最终导致细胞介导的细胞死亡。 公共卫生相关性：促凋亡蛋白Bim是B淋巴细胞中细胞死亡的关键调节因子，其表达失调是许多血液恶性肿瘤的基础。这些目标的成功实现将导致更好地了解Bim的调控在转录和翻译后机制。我们的研究可能会确定的因素和重要的调控途径，可用于治疗调节Bim在体内的表达。

DESCRIPTION (provided by applicant): 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. PUBLIC HEALTH RELEVANCE: 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.