HEPATOCYTE NUCLEAR FACTORS IN LIVER REGENERATION

肝脏是为数不多的能够完全 在细胞受到毒素、病毒、 感染或组织切除。本提案的长期目标是 了解增殖和肝细胞特异性 转录因子介导肝再生过程中的复制。 肝细胞特异性基因表达的转录调控依赖于 多个DNA结合位点的组合相互作用 不同的肝细胞核因子（HNF）。肝脏再生 损伤后的肝细胞增殖 加上持续表达肝细胞特异性基因所需的 体内平衡，同时减少细胞的转录， 可能干扰肝细胞复制的特定基因。虽然 这种转录下降的机制仍然存在 由于没有特征，切割同源结构域HNF-6蛋白可能是 参与，因为它是少数肝细胞特异性转录之一， 这些因子在肝再生过程中表达减少。 此外，许多潜在的HNF-6靶基因在细胞凋亡过程中下降。 肝再生，其中几种可能抑制肝细胞复制。 将产生转基因小鼠系，其中HFN-6降低。 可以防止肝再生过程中的表达。我们将会用这些 小鼠来检验HFN-6表达未减少的假设， 抑制肝再生。即刻早期基因表达 已知在肝再生过程中诱导的 进入细胞周期的G1期。但 转录机制介导肝细胞的后期阶段 复制并不完全清楚。进一步探讨在 肝细胞周期进程中的转录过程 再生，我们将改变肝细胞表达的翼状螺旋 HNF-3/叉头同源物-11（HFH-11）基因。HFH-11是一个候选者 参与细胞周期进程的转录因子，因为其 表达在肝细胞周期中短暂再激活， 增殖，和推定的HFH-11结合位点存在于细胞中， 周期调节基因，如c-myc、c-myb、TGF α、细胞周期蛋白B1和 细胞周期蛋白D1。我们将产生具有条件性靶向HFH的小鼠- 成人肝细胞和肝再生研究中的11个基因破坏 将使我们能够验证HFH-11 表达是肝细胞复制所必需的。功能获得 在转基因小鼠中进行的研究被提出来检查是否过早 肝再生过程中肝细胞表达HFH-11导致 增殖肝细胞的细胞周期动力学改变。评估 这些转基因小鼠在肝肿瘤中形成肝结节 升级模型将允许我们调查是否持续 HFH-11的肝细胞表达增加了 肝细胞癌理解转录机制 介导肝脏再生的基因可以让我们识别出 在肝纤维化过程中可能被破坏的途径， 肝硬化

The liver is one of the few adult organs capable of completely regenerating itself in response to cellular injury from toxins, viral infections or tissue removal. The long term goal of this proposal is to understand the role of proliferation- and hepatocyte-specific transcription factors mediating replication during liver regeneration. Transcriptional regulation of hepatocyte-specific gene expression relies on combinatorial interaction of multiple DNA binding sites by several distinct hepatocyte nucleus factors (HNF). Regeneration of the liver following injury involves a balance between hepatocyte proliferation plus sustained expression of hepatocyte-specific genes required for homeostasis and simultaneously diminishing the transcription of cell- specific genes that may interfere with hepatocyte replication. Although the mechanisms involved in this transcriptional decline remain uncharacterized, the cut-homeodomain HNF-6 protein is likely to be involved because it is one of the few hepatocyte-specific transcription factors whose expression is reduced during liver regeneration. Furthermore, a number of potential HNF-6 target genes decline during liver regeneration, several of which may inhibit hepatocyte replication. A transgenic mouse line will be generated in which decreased HFN-6 expression during liver regeneration can be prevented. We will use these mice to test the hypothesis that undiminished HFN-6 expression is inhibitory to liver regeneration. The immediate early gene expression that is induced during liver regeneration is known to mediate hepatocyte progression into the G1 stage of the cell-cycle. However, the transcriptional mechanisms mediating the later stages of hepatocyte replication are not completely understood. To further examine transcriptional processes underlying cell cycle progression during liver regeneration, we will alter hepatocyte expression of the winged helix HNF-3/fork head homolog-11 (HFH-11) gene. HFH-11 is a candidate transcription factor involved in cell cycle progression because its expression is transiently reactivated during the period of hepatocyte proliferation, and putative HFH-11 binding sites are present in cell- cycle regulatory genes such as c-myc, c-myb, TGFalpha, cyclin B1 and cyclin D1. We will generate mice possessing a conditional targeted HFH- 11 gene disruption in adult hepatocytes and liver regeneration studies with these mice will allow us to test the hypothesis that HFH-11 expression is necessary for hepatocyte replication. Gain of function studies in transgenic mice are proposed to examine whether premature hepatocyte expression of HFH-11 during liver regeneration results in altered cell cycle kinetics of proliferating hepatocytes. Assessment of these transgenic mice for development of liver nodules in a liver tumor promotion model will allow us to investigate whether continuous hepatocyte expression of HFH-11 increases the incidence of hepatocellular carcinoma. An understanding of transcriptional mechanisms which mediate liver regeneration may allow us to identify regulatory pathways that are potentially disrupted during liver fibrosis and cirrhosis.