Functions of an E1A-Associated Cellular Protein

描述(申请人提供)：腺病毒转化蛋白E1a的N-末端区域与几种宿主蛋白结合，这些宿主蛋白的功能对细胞周期控制至关重要。这些蛋白包括P400、P300和高度相关的CBP，视网膜母细胞瘤蛋白(Rb)，以及两个Rb相关蛋白p107和p130。E1a与这些宿主蛋白的相互作用导致细胞生长控制的深刻变化，p300/CBP是一个共激活因子和一个组蛋白乙酰转移酶，它将染色质重塑与转录联系起来。本应用的重点是研究p300在细胞周期调控中的作用，以及E1a与p300的结合如何解除对细胞周期相关的p300功能的调控。最近，本实验室发现静止期细胞中p300的缺失会导致G1期提前退出和c-Myc的上调。相反，静止期细胞中p300的过表达导致c-Myc表达下调，进而抑制S的时相进入。因此，p300通过负调控Myc，防止G1期过早退出，从而在G1期调控细胞周期中发挥重要作用。这些结果为先前报道的病毒癌蛋白如E1A和SV40 Large-T在细胞转化过程中灭活p300功能提供了分子基础。在这里，有人建议研究p300在染色质水平上负向调节c-Myc的机制。具体目的包括确定p300的结构域和活性，Myc启动子特异的转录因子和染色质重塑蛋白在负调控过程中与p300相互作用，以及它们相互作用导致Myc启动子抑制的机制。最后，建议研究EIA失活p300功能导致Myc上调的机制，以及E1A与p300结合如何促进G1退出。P300/CBP是细胞增殖的关键调节因子，具有肿瘤抑制作用。因此，了解该蛋白在细胞周期调控中的功能，以及病毒癌基因产物干扰其功能的机制，将对理解p300介导的生长调控途径具有重要意义。

DESCRIPTION (provided by applicant): The N-terminal region of the adenovirus transforming protein E1A binds to several host proteins whose functions are critical for the cell cycle control. These include p400, p300 and the highly related CBP, Retinoblastoma protein (Rb), and two Rb related proteins p107 and p130. E1A interactions with these host proteins result in profound alterations in cellular growth control, p300/CBP is a coactivator and a histone acetyl transferase that links chromatin remodeling with transcription. The focus of this application is to investigate the roles played by p300 in cell cycle control and to investigate how E1A binding to p300 deregulates the cell cycle related p300 functions. Recently, this laboratory has shown that depletion of p300 in quiescent cells leads to premature G1 exit and upregulation of c-Myc. Conversely, overexpression of p300 in quiescent cells leads to downregulation of c-Myc followed by inhibition of S phase entry. Thus, p300 provides an important function in G1 control of the cell cycle by negatively regulating Myc, and preventing a premature G1 exit. These results provide a molecular basis for the previously documented need for viral oncoproteins such as E1A and SV40 large-T to inactivate the p300 functions during cell transformation. Here, studies are proposed to investigate the mechanism by which p300 negatively regulates c-Myc at the chromatin level. The specific aims include the identification of the domains and activities of p300 that are critical for the negative regulation of Myc, the Myc promoter specific transcription factors and chromatin remodeling proteins that interact with p300 during this negative regulation, and the mechanism of their interactions that results in the repression of the Myc promoter. Finally, studies are proposed to investigate the mechanism by which EIA inactivates p300 functions that leads to Myc upregulation, and how E1A binding to p300 contributes to the G1 exit. p300/CBP is a key regulator of cell proliferation with tumor suppression properties. Therefore, understanding the functions of this protein in cell cycle control, and the mechanism by which viral oncogene products interfere with its functions will be valuable in understanding the p300 mediated growth regulatory pathways.