Mechanisms and Functions of SMAD2 Degradation

转化生长因子-β（transforming growth factor-beta，TFG-beta）超家族成员是多功能的生长因子，在后生动物体内控制着广泛的细胞反应。 TGF-β抑制大多数上皮细胞和造血细胞的生长，并调节间充质细胞产生细胞外基质。 对TGF-β的抗增殖反应性的丧失通常被认为是肿瘤进展的主要步骤。 本申请的长期目标是了解TGF-β抗增殖信号通路的改变如何导致人类疾病中生长控制的失调的分子基础。本申请的一般策略是关注肿瘤抑制因子Smad 2的泛素/蛋白酶体依赖性降解的机制。Smad 2是一种重要的TGF-β信号转导子，通过转录依赖机制抑制细胞增殖。然而，Smad 2的精确调控仍然是个谜。 该提议的统一假设是泛素/蛋白酶体途径通过特异性泛素E3连接酶靶向Smad 2降解。 为了验证这一假设，我们将研究Smad 2降解的机制，由一个新发现的泛素E3连接酶称为Smurf 2和调查的Smurf 2活性失调Smad 2降解的生理后果。 提出了三个具体目标：1。明确Smurf 2介导的Smad 2降解的分子机制。 将确定Smurf 2和Smad 2之间的物理相互作用、相互作用所需的结构域以及底物选择性的分子基础。 2.研究Smurf 2介导的Smad 2降解对TGF-β信号传导的生理影响。将测试Smurf 2介导的Smad 2降解如何影响TGF-β诱导的细胞周期停滞和非洲爪蟾早期胚胎发育期间的Smad 2信号传导。 3.检查上皮细胞中Smurf 2-Smad 2降解的调节。分子和生物化学方法将被用来定义Smurf 2介导的Smad 2降解的细胞机制，并分析正常细胞和癌细胞中的Smad 2降解差异。这些研究将有助于建立TGF-β诱导的生长抑制过程中泛素化介导的Smad 2周转的工作理论，并了解Smad在人类癌症恶性转化和进展中的作用机制。 最后，该结果可能为合理设计癌症预防和治疗的新治疗方法提供基础。

Members of transforming growth factor-beta (TFG-beta) superfamily are multifunctional growth factors that control a broad range of cellular responses in metazoan organism. TGF- betas inhibit the growth of most epithelial and hematopoietic cells and regulates the production of extracellular matrix by mesenchymal cells. Loss of the antiproliferative responsiveness to TGF-beta is often considered as a major step in tumor progression. The long-term objective of this application is to understand the molecular basis of how alterations in TGF-beta antiproliferative signaling pathways lead to deregulation of growth control in human diseases. The general strategy of this application is to focus on the mechanism of ubiquitin/proteasome- dependent degradation of tumor suppressor Smad2. Smad2 is an important TGF-beta signal transducer that inhibits cell proliferation though transcription-dependent mechanisms. However, the precise regulation of Smad2 remains enigmatic. The unifying hypothesis of this proposal is that ubiquitin/proteasome pathway targets Smad2 for degradation through a specific ubiquitin E3 ligase. To test this hypothesis, we will study the mechanism of Smad2 degradation by a newly identified ubiquitin E3 ligase called Smurf2 and investigate the physiological consequences of deregulation of Smurf2 activity in Smad2 degradation. Three Specific Aims are proposed: 1. Define the molecular mechanism of Smurf2-mediated Smad2 degradation. The physical interaction between Smurf2and Smad2, the structural domains required for the interaction, and the molecular basis for substrate selectivity will be determined. 2. Investigate the physiological impact of Smurf2-mediated Smad2 degradation in TGF- beta signaling. It will be tested how Smurf2-mediated Smad2 degradation affects Smad2 signaling during TGF-beta induced cell cycle arrest and Xenopus early embryonic development. 3. Examine the regulation of Smurf2-Smad2 degradation in epithelial cells. Molecular and biochemical approaches will be used to define the cellular mechanism of Smurf2-mediated Smad2 degradation and to analyze differential Smad2 degradation in normal and cancer cells. The proposed studies should help to establish a working theory for ubiquitination-mediated Smad2 turnover during TGF- beta-induced growth inhibition and to understand the mechanisms of Smad actions in malignant transformation and progression of human cancers. Finally, the result may provide a foundation of the rational design of novel therapeutic approaches for cancer prevention and treatment.