CREB/ATF PROTEINS AND HEPATOCYTE GROWTH CONTROL

在定义细胞生长控制中涉及的细胞调节网络方面，致癌病毒是无价的。参与肝癌发生的乙肝病毒X蛋白（pX）是转录的双重激活因子；pX激活ras-raf-MAPK和JNK通路，通过直接相互作用，pX提高了bZip转录因子的转录效率，包括CREB、ATF2和ATF3。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表达，在发育中至关重要。ATF2在发育和应激激活途径的下游效应中也是必不可少的。ATF3在再生肝脏中表达，在应激反应和eia转化细胞中被诱导。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交互的结构和功能方面。目的1通过描绘CREB（bZip）相互作用所需的最小功能pX区域来研究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。这些目标将通过有条件的、表达pX的、永生化的肝细胞细胞系来解决，其中pX的表达与致癌转化有关。我们的研究将定义：目标2：在转化过程中被pX激活的有丝分裂途径和在pX诱导的转化过程中细胞基因的失调；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；b)通过检测在细胞转化过程中pX在细胞核中的作用。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介导的肝癌发生提供相关的见解。对pX改变基因表达的机制的研究，可能对肝细胞致癌转化的一般过程有重要的认识。

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.