Med1 in Liver Metabolism, Regeneration and Cancer

描述（申请人提供）：肝脏通过协调碳水化合物、脂肪和蛋白质代谢的生化途径，在能量稳态中起关键作用，并表现出固有的代偿再生能力，以恢复部分失去的代谢功能。然而，肝脏细胞增殖和代谢是如何相互联系和协同调节的尚不清楚。在这种情况下，转录辅激活因子Med1（也称为PBP/TRAP220/DRIP205）是哺乳动物中介复合物的一个关键亚基，与核激素受体和转录因子CCAAT/增强子结合蛋白-¿（CEBPB）相互作用，对肝脏发育和代谢至关重要。中介复合物是RNA聚合酶II （PoI II）转录基因表达所必需的。有条件Med1零突变的研究已经证实，Med1是脂肪酸氧化和葡萄糖代谢所必需的。Med1还控制肝脏再生和肝细胞癌（HCC）的发展，因为缺乏Med1的肝细胞不能再生，不能产生肝脏肿瘤。这项拟议的研究基于令人兴奋的初步研究，这些研究表明，腺病毒驱动的Med1 （adeno-Med1）在小鼠肝脏中的过表达可以刺激肝细胞DNA的复制和再生。基因表达谱显示Med1上调了许多对脂肪生成和糖异生很重要的基因。当这些过程不受约束时，与代谢异常和癌症有关。我们的初步数据表明Med1被能量传感器腺苷单磷酸（AMP）活化蛋白激酶（AMPK）磷酸化。鉴于核受体和转录因子CEBPB和叉头盒蛋白M1 （FOXM1）在肝细胞的代谢和增殖中起着至关重要的作用，增加Med1的表达是同时增强其功能的有效途径。我们之所以关注Med1，是因为它是肝脏再生所必需的，并且本身就足以诱导肝细胞增殖。因此，我们假设Med1整合了肝细胞增殖和代谢的调节，其持续且不受约束的过表达加速了肝脏肿瘤的发生。我们的目标是明确Med1是肝脏再生和代谢功能的关键调节因子，有助于肝脏肿瘤的发生，并阐明其分子机制。我们的具体目标是：1)描述Med1在肝细胞中过表达诱导肝细胞增殖的机制；2)确定ampk介导的磷酸化如何调节med1介导的细胞增殖和代谢功能；3)建立Med1在肝细胞中有条件表达的转基因小鼠模型，证实Med1过表达可增强肝细胞增殖和肝癌发生。这些研究将确立转录辅激活因子Med1在肝细胞增殖、代谢和肝癌发生中的关键作用，并揭示Med1相关的信号介质有望成为新疗法的靶点。

DESCRIPTION (provided by applicant): The liver plays a pivotal role in energy homeostasis by orchestrating biochemical pathways of carbohydrate, fat, and protein metabolism and exhibits inherent compensatory regeneration capacity to regain partially lost metabolic functions. It is unclear, however, as to how cell proliferation and metabolism are interconnected and coregulated in liver. In this context, transcription coactivator Med1 (also known as PBP/TRAP220/DRIP205), a key subunit of the mammalian Mediator complex, interacts with nuclear hormone receptors and transcription factor CCAAT/enhancer-binding protein-¿ (CEBPB) that are critical for liver development and metabolism. The Mediator complex is necessary for the expression of RNA polymerase II (PoI II)-transcribed genes. Studies with conditional Med1 null mutation have established that Med1 is required for fatty acid oxidation and glucose metabolism. Med1 also controls liver regeneration and the development of hepatocellular carcinoma (HCC), in that hepatocytes lacking Med1 fail to regenerate and fail to give rise to liver tumors. The proposed research is based on exciting preliminary studies showing that adenovirally-driven overexpression of Med1 (adeno-Med1) in mouse liver stimulates hepatocyte DNA replication and regeneration. Gene expression profiling revealed that Med1 upregulates many genes that are important for lipogenesis and gluconeogenesis. These processes, when unconstrained, are linked to metabolic abnormalities and cancer. Our preliminary data indicate that Med1 is phosphorylated by energy sensor, adenosine monophosphate (AMP)-activated protein kinase (AMPK). Given that nuclear receptors and transcription factors CEBPB and forkhead box protein M1 (FOXM1), play critical roles in metabolism and proliferation of hepatocytes, increased expression of Med1 is an efficient way to simultaneously enhance their function. We focus on Med1 because it is necessary for liver regeneration and sufficient by itself for inducing hepatocellular proliferation. Therefore, we hypothesize that Med1 integrates the regulation of liver cell proliferation and metabolism and its persistent and unconstrained overexpression accelerates liver tumorigenesis. Our objective is to firmly establish that Med1 is a pivotal regulator of liver regeneration, and metabolic functions that contribute to liver tumorigenesis and elucidate the molecular mechanisms. Our specific aims are to: 1) delineate the mechanisms by which Med1 overexpression in hepatocytes induces liver cell proliferation; 2) determine how Med1-mediated functions of cell proliferation and metabolism are regulated by AMPK-mediated phosphorylation; and 3) characterize and use a transgenic mouse model in which Med1 can be expressed conditionally in hepatocytes to establish that overexpression of Med1 augments hepatocellular proliferation and hepatocarcinogenesis. These studies will establish the critical role of transcription coactivator Med1 in hepatocellular proliferation, metabolism, and hepatocarcinogenesis, and reveal Med1-associated signaling mediators that have promise as targets for new therapies.