CELLULAR GROWTH CONTROL IN HEPATOCARCINOGENESIS

几条证据表明，E2 F转录家族 在细胞生长控制中重要的因子：1）E2 F家族调节 DNA合成和细胞周期进程所需的许多基因; 2） E2 F信号转导途径中的突变在许多人中发现， 3）E2 F家族成员的过度表达可以减缓生长 因子的需求，并导致致瘤性，这表明E2 F家族， 成员是细胞生长的正调节剂;和4）增加 在E2 F1缺失小鼠中观察到的肿瘤数量表明 E2 F1也可能是一种肿瘤抑制因子。这两个看似矛盾的 E2 F的功能可能是由于E2 F家族成员的能力， 转录的激活子和抑制子。细胞周期模型 E2 F在细胞生长中的调节作用集中在 E2 F靶基因的S期特异性激活，而 激活E2 F的肿瘤抑制功能，聚焦于GO期特异性 抑制E2 F靶基因。我们建议用老鼠的肝脏，一种- 用于研究细胞调节的表征的体内模型 增殖和致瘤性，以确定E2 F的主要作用是否是 作为激活剂或抑制剂或化学诱导的肝脏 肿瘤形成我们将利用E2 F1缺失小鼠（Aim I）和转基因小鼠（Aim I）。 表达显性阴性E2 F1（Aim III）的小鼠，以分析 降低E2 F活性的作用。这些小鼠中E2 F靶基因表达 取决于启动子是否受GO影响最大 期阻遏或S期激活。这些实验的目的是 为了确定哪类E2 F靶基因对E2 F的表达最关键， 介导E2 F在肝细胞中的作用。我们将使用转基因的 表达E2 F1衍生物的小鼠，其可以抑制GO期- 特异性转录，但不能激活S期特异性转录 E2 F靶基因（Aim II）。本目标的目标是确定 E2 F靶基因的去阻遏足以引起肿瘤性 肝细胞的转化。我们还提出了实验（目标IV）， 我们将识别和描述两类E2 F的示例 目标启动子;这对于理解 我们在动物模型系统中使用的E2 F衍生物。总的来说， 我们实验的长期目标是通过 其中E2 F家族介导正常肝脏中的细胞生长控制， 化学诱导的肝癌。

Several lines of evidence suggest that the E2F family of transcription factors is important in cell growth control: 1) the E2F family regulates many genes required for DNA synthesis and cell cycle progression; 2) mutations in the E2F signal transduction pathway are found in many cancers; 3) over-expression of E2F family members can alleviate growth factor requirements and lead to tumorigenicity, suggesting that E2F family members are positive regulators of cell growth; and 4) the increased number of tumors that are observed in a E2F1 nullizygous mouse suggests that E2F1 may also be a tumor suppressor. These two seemingly conflicting functions of E2F are likely due to the ability of E2F family members to be both activators and repressors of transcription. Models for cell cycle regulation in which E2F mediates a positive role in cell growth focus on the S phase-specific activation of E2F target genes, whereas models that invoke a tumor suppressor function for E2F focus on the GO phase-specific repression of E2F target genes. We propose to use the mouse liver, a well- characterized in vivo model for studying the regulation of cell proliferation and tumorigenicity, to determine if the main role of E2F is to function as an activator or a repressor or chemically-induced liver neoplasia. We will utilize E2F1 nullizygous mice (Aim I) and transgenic mice that express a dominant negative E2F1 (Aim III) to analyze the effects of reducing E2F activity. E2F target gene expression in these mice will differ depending on whether the promoter is most influenced by GO phase repression or S phase activation. The goals of these experiments are to determine which category of E2F target genes is most critical for mediating the role of E2F in the hepatocyte. We will use a transgenic mouse that expressed and E2F1 derivative that can derepress GO phase- specific transcription but cannot activate S phase-specific transcription of E2F target genes (Aim II). The goals of this Aim are to determine it derepression of E2F target genes is sufficient to cause neoplastic transformation of hepatocytes. We also propose experiments (Aim IV) in which we will identify and characterize examples of the two classes of E2F target promoters; this is essential for understanding the phenotype of the E2F derivatives that we are using in our animal model systems. In summary, the long-term goals of our experiments are to determine the mechanism by which the E2F family mediates cell growth control in both normal liver and chemically-induced hepatocarcinogenesis.