FDH: A Novel Determinant of Tumor Suppression

该提案的总体目标是表征新的肿瘤抑制活性 一种关键的代谢酶并确定转化代谢效应的机制 进入增殖调节。 FDH（10-甲酰四氢叶酸脱氢酶） 不可逆地转化 10-甲酰四氢叶酸，这是从头嘌呤的重要底物 生物合成四氢叶酸。通过消耗这种底物，FDH 可以限制 嘌呤生物合成。这会干扰 DNA/RNA 生物合成和 DNA 修复。 由于这种关键的代谢功能，癌细胞中 FDH 的下调会 是有利于生存的。事实上，我们最初已作出重要的观察，外佣是 通过启动子在肿瘤中强烈且普遍地下调 超甲基化。我们进一步证明FDH的中等表达 FDH 缺陷的癌细胞会诱导细胞凋亡。相比之下，非癌细胞 对高水平的酶不敏感。因此，有人提出癌细胞 沉默 FDH 基因以避免细胞毒性。表型效应的研究 FDH 缺陷肿瘤细胞中正常 FDH 表达的重新激活进一步 探索了 JNK1/2 和 p53 作为 FDH 诱导的细胞凋亡信号传导的关键成分，并且 确定 DHFR 和叶酸补充作为增殖救援因素。 重要的是，一种通过细胞内叶酸调节将 FDH 连接到 发现了细胞运动的控制。当前的提案扩展了以前的研究 FDH 和相关叶酸的抗增殖机制，直接与 p53 相互作用 并评估其在小鼠模型中的体内作用。我们的中心假设是 FDH 通过启动子高甲基化下调是重要手段之一 哪些恶性肿瘤比正常细胞具有促生存优势。我们进一步建议 FDH通过多种机制发挥监管作用。具体目标是 探究这些机制并检验我们的假设是：（1）研究功能 FDH 与细胞质中 p53 肿瘤抑制蛋白的相互作用。 (2) 确定 使用 FDH 缺陷小鼠观察 FDH 沉默对肿瘤发生/进展的影响 模型。 FDH 在癌细胞存活/叶酸诱导中的关键作用的研究 疾病发作时的压力，将为了解恶性疾病提供重要的见解 过程本身并将关键代谢途径的失调与癌症疾病联系起来 为恶性转化的诊断建立新的目标。

The overall goal of this proposal is to characterize the novel tumor suppressor activity of a key metabolic enzyme and determine the mechanisms transforming metabolic effects into regulation of proliferation. FDH (10-formyltetrahydrofolate dehydrogenase) irreversibly converts 10-formyltetrahydrofolate, an essential substrate for de novo purine biosynthesis, to tetrahydrofolate. Through depletion of this substrate, FDH can restrict purine biosynthesis. This interferes with DNA/RNA biosynthesis and DNA repair. Because of this critical metabolic function, down-regulation of FDH in cancer cells would be pro-survival. Indeed, we have initially made the important observation that FDH is strongly and ubiquitously down-regulated in tumors through the promoter hypermethylation. We have further demonstrated that moderate FDH expression in FDH-deficient cancer cells induces apoptotic cell death. In contrast, non-cancer cells are insensitive to high levels of the enzyme. Therefore, it is proposed that cancer cells silence the FDH gene in order to escape cytotoxicity. Studies of phenotypic effects upon reactivation of normal FDH expression in FDH-deficient tumor cells have further explored JNK1/2 and p53 as key components of FDH-induced apoptotic signaling, and determined DHFR and folate supplementation as proliferation rescue factors. Importantly, a novel pathway linking FDH, through intracellular folate regulation, to control of cell motility, was discovered. The current proposal extends previous studies of antiproliferative mechanisms of FDH, and related folates, to direct interaction with p53 and evaluation of its role in vivo in mouse model. Our central hypothesis is that FDH down-regulation through promoter hypermethylation is one of the important means by which malignancies gain pro-survival advantage over normal cells. We further suggest that FDH exerts its regulatory effects through multiple mechanisms. The Specific Aims to probe these mechanisms and test our hypothesis are: (1) Investigate the functional interaction of FDH with p53 tumor suppressor protein in cytoplasm. (2) Determine the impact of FDH silencing on tumor initiation/progression using FDH deficient mouse model. Investigation of the critical role of FDH, in cancer cell survival/induction of folate stress at the onset of the disease, will provide important insight into the malignant process itself and link deregulation of key metabolic pathways to cancer disease, as well as establish new targets for diagnostics of the malignant transformation.