Regulation of SMAD2 Signaling by SMP1 Phosphatase

描述(由申请人提供)：失去转化生长因子-β生长因子诱导的细胞周期停滞是癌症的一个标志。我们的长期目标是了解正常细胞中控制细胞周期进程和细胞分化的基本过程，并阐明失调的转化生长因子-β信号转导在肿瘤发病机制中的作用。转化生长因子-β信号转导通路激活的关键事件之一是细胞表面转化生长因子-β受体对转录因子Smads的磷酸化。虽然磷酸化的Smad直接激活细胞核中的基因反应，但假想的蛋白磷酸酶预计会使磷酸化的Smads去磷酸化，从而关闭转化生长因子-β信号。尽管支持SMAD磷酸酶(SMP)存在的数据，SMPC(S)的身份仍然含糊不清。因此，我们对这一提议的短期策略是鉴定这类磷酸酶，并研究(去)磷酸化对Smads的调节。我们的初步研究已经确定了一种名为SMP1的磷酸酶，它可以与Smad2相互作用并使其去磷酸化。这些数据使我们假设SMP1作为肿瘤抑制基因Smad2的真正磷酸酶，关闭了转化生长因子-β信号。因此，研究SMP1在调节转化生长因子-β信号的肿瘤抑制功能中的生理作用具有重要意义。 我们提出了三个具体目标来检验这一假设。目的：通过进一步鉴定SMP1的磷酸酶活性、检测SMP1-Smad2复合体的相互作用以及确定SMP1介导的Smad2去磷酸化所需的结构特征，来研究SMP1介导的Smad2去磷酸化的分子机制。目的：研究SMP1在转化生长因子-β诱导的哺乳动物细胞周期停滞和非洲爪哇发育过程中组织分化等转化生长因子-β反应中的生理作用。目的3：研究SMP1介导的Smad2去磷酸化在乳腺细胞和肿瘤中的调节作用。进行拟议研究的实验设计将采用广泛的方法，跨越生物学的多个学科，以解决正常细胞功能和癌症发展的基本问题。预期本项目的结果将有助于建立Smad2如何调控的工作理论，并为深入了解转化生长因子-β耐药的机制和SMAD在人类癌症恶性转化和进展中的作用提供依据。 我们提出了一项研究计划，以了解转化生长因子-β和相关的生长因子如何调节正常细胞和癌细胞的细胞功能。研究结果将有助于为合理设计预防和治疗人类癌症和其他疾病的新治疗方法奠定基础。

DESCRIPTION (provided by applicant): Loss of TGF-beta growth factor-induced cell cycle arrest is a hallmark in cancers. Our long-term objective of this application is to understand the fundamental processes controlling cell cycle progression and cell differentiation in normal cells and to elucidate the functions of dysregulated TGF-beta signal transduction as a causal factor in tumor pathogenesis. One of the most critical events in activation of TGF-beta signal transduction pathway is the phosphorylation of transcription factor SMADs by cell surface TGF-beta receptors. While phosphorylated SMADs directly activate the gene responses in the nucleus, hypothetical protein phosphatases are anticipated to dephosphorylate phospho-SMADs and consequently shut down TGF-beta signaling. Despite supporting data for the existence of SMAD phosphatases (SMP), the identity of SMPC(s) remains vague. Therefore, our short-term strategy for this proposal is to identify such phosphatases and investigate the regulation of SMADs by (de)phosphorylation. Our preliminary studies have identified a phosphatase designated SMP1 that can interact with and dephosphorylate SMAD2. These data lead us to hypothesize that SMP1 acts as a bonafide phosphatase for tumor suppressor SMAD2 and shuts down TGF-beta signaling. Thus, it is significantly important to investigate the physiological roles of SMP1 in the regulation of tumor suppressing functions of TGF-beta signaling. We propose three specific aims to test the hypothesis. Aim 1: The molecular mechanisms for SMP1-mediated SMAD2 dephosphorylation will be investigated by further characterizing the phosphatase activity of SMP1, examining the SMP1-SMAD2 complex interaction and determining the structural features required for SMP1- mediated SMAD2 dephosphorylation. Aim 2: We will determine the physiological roles of SMP1 in TGF-beta responses such as TGF-beta-induced cell cycle arrest in mammalian cells and tissue differentiation during Xenopus development. Aim 3: We will examine the regulation of SMP1-mediated SMAD2 dephosphorylation in breast cells and cancers. The experimental design to carry out the proposed research will take on a wide range of approaches that cross the multiple disciplines of biology to address fundamental questions in normal cell functions and cancer development. It is expected that the results obtained from this project will help to establish a working theory for how SMAD2 is regulated and provide insights into the mechanisms of TGF-beta resistance and of SMAD actions in malignant transformation and progression of human cancers. Lay description: We propose a research plan to understand how TGF-beta and related growth factors regulate cell functions in normal versus cancer cells. The results will be pertinent towards development for a foundation for the rational design of novel therapeutic approaches for prevention and treatment of human cancers and other diseases.