CREB/ATF PROTEINS AND HEPATOCYTE GROWTH CONTROL

致癌病毒在定义参与细胞生长控制的细胞调控网络方面具有无价的价值。乙肝病毒X蛋白(Px)参与了肝细胞癌的发生，是一种双重转录激活子；Px激活ras-RAF-MAPK和JNK途径，并通过直接相互作用增加bZip转录因子，包括CREB、ATF2和ATF3的转录效率。CREB介导cAMP的转录反应，是有丝分裂途径的下游效应因子，调节c-fos的表达，在发育中是必不可少的。ATF2在发育过程中也是必不可少的，是应激激活通路的下游效应器。ATF3在再生肝中表达，在应激反应和EIA转化的细胞中被诱导。因此，我们的假设是，这些bZip蛋白介导了PX诱导的肝癌发生的细胞效应。我们的长期目标是定义CREB/ATF/PX相互作用的结构和功能方面。目的1通过描绘CREB(BZip)相互作用所需的最小的功能Px区域，研究CREB(BZip)/Px相互作用的机制。目的2和3研究CREB和ATF2在PX介导的转化中的重要性以及CREB/ATF/PX相互作用在肝癌发生中的功能意义。这些目标将利用条件的，Px表达的，永生化的肝细胞系来解决，在这些细胞系中，Px的表达与致癌转化有关。我们的研究将确定：目的2：PX在转化过程中激活的有丝分裂通路和在PX诱导的转化过程中调控的细胞基因；目的3：CREB和ATF2在PX介导的转化中的作用：a)通过构建CREB和ATF2活性减弱的细胞系；以及b)通过检测Px在细胞核中的作用在细胞转化中的作用。这些研究将阐明CREB(BZip)/PX相互作用的机制，CREB/ATF蛋白在肝细胞生长控制中的作用，并为PX介导的肝癌的发生提供相关的见解。研究Px改变基因表达的机制可能会对了解肝细胞致癌转化的一般过程产生重要的影响。

Oncogenic viruses have been invaluable in defining cellular regulatory networks involved in cell growth control. The Hepatitis B virus X protein (pX), implicated in hepatocarcinogenesis, is a dual activator of transcription; pX activates the ras-raf-MAPK and JNK pathways, and by direct interaction, pX increases the transcriptional efficacy of bZip transcription factors, including CREB, ATF2 and ATF3. CREB mediates the transcriptional response of cAMP, is the downstream effector of mitogenic pathways, regulates c-fos expression, and is essential in development. ATF2 is also essential in development and the downstream effector of the stress-activated pathways. ATF3 is expressed in regenerating liver, is induced in response to stress and in EIA-transformed cells. Accordingly, our hypothesis is that these bZip proteins mediate cellular effects of pX-induced hepatocarcinogenesis. Our long-term goal is to define structural and functional aspects of CREB/ATF/pX interactions. Aim 1 examines the mechanism of CREB(bZip)/pX interactions by delineating a minimal, functional pX region required for CREB(bZip) interaction. Aims 2 and 3 examine the importance of CREB and ATF2 in pX-mediated transformation and the functional significance of CREB/ATF/pX interactions in hepatocarcinogenesis. These aims will be addressed employing conditional, pX-expressing, immortalized hepatocyte cell lines in which pX expression is linked to oncogenic transformation. Our studies will define: Aim 2: the mitogenic pathways activated by pX during transformation and cellular genes deregulated during pX-induced transformation; Aim 3: the role of CREB and ATF2 in pX-mediated transformation: a) by constructing cell lines in which the activity of CREB and ATF2 is attenuated; and b) by examining the role of pX in the nucleus during cellular transformation. These studies will elucidate the mechanism of CREB(bZip)/pX interactions, the role of CREB/ATF proteins in growth control in hepatocytes, and provide insights relevant to pX-mediated hepatocarcinogenesis. Studies on the mechanism of altered gene expression by pX are likely to yield important insights into the general process of oncogenic transformation in hepatocytes.