Regulation of Liver by Nuclear Ca2+ Signaling

Ca~(2+)在肝脏中起重要作用。在胞浆中，它调节胆汁分泌、葡萄糖代谢和细胞骨架组织等活动。我们假设，肿瘤中的钙离子反而调节肝脏的生长和再生以及基因转录等过程。因此，核质内钙离子的调控机制具有重要的潜在意义。已有研究表明，核内钙离子被动地跟随胞质内的钙离子，但我们的初步数据表明，核质内的钙离子不受胞浆中钙离子浓度的影响，存在着控制核质内钙离子的核机制。这样的机制反过来又允许对核内钙离子介导的事件进行独立调节。由于肌醇1，4，5-三磷酸(InsP3)受体调节肝细胞中的钙信号，我们的假设将通过以下项目系统地定义肝细胞核钙信号的机制和作用来检验我们的假说：项目A将在完整的肝细胞和肝细胞系中确定核钙库的组织和调节这些库中钙释放的因素。项目B将在单通道水平上描述天然和克隆的肝细胞核InsP3受体的功能和调节。项目C将研究丝裂原活化蛋白激酶(MAPK)磷酸酶-1(MAPK-1)在控制MAPK介导的肝脏特异基因转录事件中的作用，以响应核钙信号。项目D将通过确定与肝脏特异性功能相关的基因如何受钙离子和钙动员胆汁酸调节来研究核钙信号对肝脏基因转录的意义。为了帮助实施这些项目，将建立细胞和分子生物学、细胞成像和管理的核心设施。

Ca2+ plays an important role in the liver. In the cytosol, it regulates activities such as bile secretion, glucose metabolism and cytoskeletal organization. We hypothesize that Ca2+ in the neoplasm instead regulates processes such as hepatic growth and regeneration and gene transcription. The mechanism by which nucleoplasmic Ca2+ is regulated thus is of great potential importance. It has been suggested that nuclear Ca2+ passively follows cytosolic Ca2+, but our preliminary data instead suggest that there is nuclear machinery that allows nucleoplasmic Ca2+ to be controlled independent of the Ca2+ concentration in the cytosol. Such machinery would in turn allow independent regulation of Ca2+- mediated events in the nucleus. Since the inositol 1,4,5,-triphosphate (InsP3) receptor regulates Ca2+ signaling in hepatocytes, our hypothesis will be tested by systematically defining the mechanisms and effects of nuclear Ca2+ signaling in liver through the following projects: Project A The organization of nuclear Ca2+ stores and the factors that regulate release of Ca2+ from these stores will be determined in intact hepatocytes and in liver cell lines. Project B The function and regulation of both native and cloned nuclear InsP3 receptors of hepatocytes will be characterized at the single channel level. Project C The role of the mitogen-activated protein kinase (MAPK) phosphatase-1 (MAPK-1) in controlling MAPK-mediated liver-specific gene transcription events in response to nuclear Ca2+ signals will be examined. Project D The significance of nuclear Ca2+ signals for gene transcription in liver will be examined by determining how genes integral to liver- specific functions are regulated by Ca2+ and by Ca2+-mobilizing bile acids. To help carry out these projects, core facilities will be established for cell and molecular biology, cell imaging, and administration.