CELLULAR GROWTH CONTROL IN HEPATOCARCINOGENESIS

多条证据表明，E2F转录家族 因子在细胞生长控制中很重要：1)E2F家族调节 DNA合成和细胞周期进程所需的许多基因；2) E2F信号转导通路中的突变在许多 癌症；3)E2F家族成员的过度表达可以减缓生长 因子要求和导致致瘤性，提示E2F家族 成员是细胞生长的积极调节者；以及4)增加的 在E2F1基因缺失小鼠身上观察到的肿瘤数量表明 E2F1也可能是一种肿瘤抑制因子。这两个看似矛盾的东西 E2F的功能可能是由于E2F家族成员有能力 转录的激活物和抑制物。细胞周期模型 E2F在细胞生长中发挥积极作用的调控重点 S对E2F靶基因的时相特异性激活，而模型 针对特定于GO期的E2F调用肿瘤抑制功能 抑制E2F靶基因。我们建议用小鼠的肝脏，一口井- 研究细胞调控的活体模型 增殖和致瘤性，以确定E2F的主要作用是否 作为激活剂或抑制物或化学诱导的肝脏发挥作用 肿瘤。我们将利用E2F1无合子小鼠(Aim I)和转基因小鼠 表达显性负E2F1(目标III)的小鼠分析 降低E2F活性的效果。E2F靶基因在小鼠体内的表达 将根据发起人是否受围棋影响最大而有所不同 相抑制或S相激活。这些实验的目标是 确定哪一类E2F靶基因对 介导E2F在肝细胞中的作用。我们将使用转基因技术 表达了E2F1衍生品的小鼠，可以解压围棋相- 特异性转录，但不能激活S阶段特异性转录 E2F靶基因(AIM II)。这一目标的目标是确定它 E2F靶基因的抑制足以导致肿瘤 肝细胞转化。我们还建议在以下方面进行实验(目标IV 我们将识别和描述两类E2F的示例 靶向启动子；这对于理解 我们在动物模型系统中使用的E2F衍生物。总而言之， 我们实验的长期目标是通过 E2F家族在正常肝脏和正常肝脏中介导细胞生长控制 化学诱导的肝癌发生。

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.