TGF Beta-Induced Apoptosis in B-Lymphocytes

描述（由申请人提供）：转化生长因子？（TGF?）和促凋亡的Bcl-2家族成员Bim， Bcl-2细胞死亡的相互作用介质，在免疫系统的发育和稳态中起关键作用。在小鼠中，有针对性地破坏TGF？或Bim基因导致淋巴细胞和骨髓细胞的积累，T细胞发育的扰动，最终，动物屈服于系统性自身免疫性疾病。这些表型强调了TGF？在T细胞发育和自身反应性B细胞的负选择或克隆缺失中，Bim是正常B淋巴细胞发育和维持自我耐受性的关键。我们研究了TGF？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TGF？-诱导的细胞死亡是通过诱导Bim介导的，这提供了第一个证据，证明Bim表达水平直接受到促凋亡细胞因子的影响，而不是响应促生存因子（即IL-3、IL-7）的退出或应激诱导而上调。TGF吗?研究表明，Bim的诱导依赖于smad3，并通过激活生存途径而被消除。我们的初步数据已经确定了TGF？-介导的Bim诱导、即时早期基因MAPK磷酸酶2 （MKP2）和转录共调控因子Runx1/AML1。在此，我们希望检验TGF？通过MAP激酶Erk的失活，诱导MKP2快速靶向现有的Bim水平，导致Bim去磷酸化并逃避泛素介导的蛋白酶体衰变。此外，为了持续调制Bim，我们假设TGF？诱导转录共调控因子Runx1/AML1，与Fox03相互作用，反激活Bim mRNA表达。有趣的是，TGF？是通过非转录机制介导的，包括通过内部核糖体进入（IRES）机制进行翻译调节。因此,TGF吗?不仅诱导从头开始的Bim mRNA转录，而且还确保导致其产物降解的途径被抑制，导致Bim蛋白积累，最终导致线粒体介导的细胞死亡。

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.