Regulation of SMAD2 Signaling by SMP1 Phosphatase

描述（由申请人提供）：TGF-β生长因子诱导的细胞周期停滞的丧失是癌症的标志。本申请的长期目标是了解控制正常细胞中细胞周期进展和细胞分化的基本过程，并阐明作为肿瘤发病机制中的因果因素的失调的TGF-β信号转导的功能。TGF-β信号转导通路激活中最关键的事件之一是细胞表面TGF-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，但预期假设的蛋白磷酸酶使磷酸化SMAD去磷酸化，从而关闭TGF-β信号传导。尽管有支持SMAD磷酸酶（SMP）存在的数据，但SMPC的身份仍然模糊。因此，我们的短期战略，这一建议是确定这样的磷酸酶和调查的SMADs（去）磷酸化的调节。我们的初步研究已经确定了一个磷酸酶命名为SMP 1，可以与SMAD 2相互作用和去磷酸化。这些数据使我们假设SMP 1作为肿瘤抑制因子SMAD 2的真正磷酸酶并关闭TGF-β信号传导。因此，研究SMP 1在调节TGF-β信号传导的肿瘤抑制功能中的生理作用是非常重要的。 我们提出了三个具体的目标来检验假设。目标1：将通过进一步表征SMP 1的磷酸酶活性、检查SMP 1-SMAD 2复合物相互作用并确定SMP 1介导的SMAD 2去磷酸化所需的结构特征来研究SMP 1介导的SMAD 2去磷酸化的分子机制。目标二：我们将确定SMP 1在TGF-β反应中的生理作用，如TGF-β诱导的哺乳动物细胞细胞周期停滞和非洲爪蟾发育过程中的组织分化。目的3：我们将研究乳腺细胞和癌症中SMP 1介导的SMAD 2去磷酸化的调节。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中的基本问题。预计从该项目获得的结果将有助于建立SMAD 2如何调节的工作理论，并提供对TGF-β抗性机制和SMAD在人类癌症恶性转化和进展中作用的见解。 铺设说明：我们提出了一项研究计划，以了解TGF-β和相关生长因子如何调节正常细胞与癌细胞的细胞功能。研究结果将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.