TGF Beta-Induced Apoptosis in B-Lymphocytes

描述(申请人提供)：转化生长因子？(转化生长因子？)促凋亡蛋白Bim是细胞死亡的相互作用介质，在免疫系统的发育和动态平衡中起着重要作用。在小鼠身上，靶向干扰转化生长因子？或者Bim基因导致淋巴和髓样细胞的积累，扰乱T细胞的发育，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？的重要作用。在T细胞发育和自身反应性B细胞的阴性选择或克隆性删除中，Bim对正常的B淋巴细胞发育和自我耐受的维持至关重要。我们研究了转化生长因子？艾滋病通过诱导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，这首次提供了证据表明Bim的表达水平直接受到促凋亡细胞因子的影响，而不是由于促生存因子(即IL-3、IL-7)的退出或应激诱导而上调。转化生长因子？BIM的诱导被证明是Smad3依赖的，并通过激活生存通路而被取消。我们的初步数据已经确定了两个潜在的调节因子，即即时早期基因MAPK磷酸酶2(MKP2)和转录辅助调节因子RUNX1/AML1。在这里，我们希望检验的假说，转化生长因子？通过使MAP激酶Erk失活，诱导MKP2快速靶向现有的Bim水平，导致Bim去磷酸化，并逃脱泛素介导的蛋白酶体衰退。此外，为了持续调节BIM，我们假设转化生长因子？诱导转录共调控因子RUNX1/AML1与FOX03相互作用，反式激活Bim mRNA的表达。有趣的是，转化生长因子诱导的RUNX1？通过非转录机制介导，涉及通过内部核糖体进入(IRES)机制进行翻译调节。因此，转化生长因子？它不仅能诱导Bim基因的转录，还能抑制导致其降解的途径，导致Bim蛋白积聚，最终导致线粒体介导的细胞死亡。 公共卫生相关性：促凋亡蛋白Bim是B淋巴细胞细胞死亡的关键调节因子，其表达失控是许多血液系统恶性肿瘤的基础。成功地实现这些目标将有助于更好地理解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体内Bim表达的因素和重要的调控途径。

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.