Neuron specific functions of HSV-1 ICP4

描述(由申请人提供)：ICP4既是转录的激活因子，也是转录的抑制因子，这取决于它与病毒启动子和细胞转录机制的相互作用。它对病毒的生长是绝对必要的，主要是因为它的功能是激活大多数病毒基因的转录，达到最终产生后代病毒粒子所需的水平。对ICP4抑制物功能的要求还不是很明确。虽然ICP4可抑制基因已经被识别，但这一功能对病毒生命周期的贡献还不是很清楚。ICP4的DNA结合域有一些氨基末端区域，参与转录的激活和抑制，并且在1-疱疹病毒的ICP4类似物中是保守的。在完整的ICP4分子的背景下，这些区域对组织培养或体内非神经细胞中的病毒生长或基因表达几乎没有贡献。然而，在缺少羧基末端激活区的情况下，氨基末端的突变体在激活和/或抑制方面存在缺陷。这表明ICP4分子的多个区域通过指定在某些细胞类型中可能是多余的而在其他细胞类型中不是多余的活动来促进其功能。此外，对于一种细胞类型的生长不重要的保守区域可能指定了另一种细胞类型唯一需要的活动。我们实验室的研究表明，ICP4的某些区域是神经细胞所需的，而不是其他类型的细胞。来自其他实验室的研究表明，在神经元中产生的病毒基因表达与在非神经元细胞中的不同。这是单纯疱疹病毒生物学中一个研究很少的方面，可能对我们理解单纯疱疹病毒如何进入潜伏期并从潜伏期重新激活至关重要。这一探索性项目的目标是确定ICP4的保守结构域，这些结构域在细胞培养中是必不可少的，但在神经元或体内的病毒生命周期的某些方面是必需的，并开始阐明病毒基因表达和已知ICP4活性所需的分子基础。这些研究还可能阐明在神经元中观察到的不同基因表达模式的基础。

DESCRIPTION (provided by applicant): ICP4 is both an activator and repressor of transcription depending on how it interacts with a viral promoter and the cellular transcription machinery. It is absolutely required for viral growth largely because it functions to activate the transcription of most viral genes to levels required for the ultimate production of progeny virions. The requirement for the repressor function of ICP4 is less well defined. While ICP4- repressible genes have been identified, the contribution of this function to the viral life cycle is not well understood. There are regions amino terminal to the DNA binding domain of ICP4 that are involved in both activation and repression of transcription and are conserved among the ICP4 analogs of 1-herpesviruses. In the context of the intact ICP4 molecule, these regions contribute little to viral growth or gene expression in tissue culture or in non-neuronal cells in vivo. However in the absence of the carboxyl-terminal activation region, mutants in the amino terminus are defective in activation and/or repression. This suggests that multiple regions of the ICP4 molecule contribute to its functions by specifying activities that may be redundant in some cell types and not others. In addition conserved regions that are not important for growth in one cell type may specify an activity that is uniquely required in another cell type. Studies from our lab suggest that there are domains of ICP4 that are required in neuronal cells and not other cell types. Studies from other labs suggest that the productive viral gene expression in neurons differs from that in non-neuronal cells. This is a very understudied aspect of HSV biology that may be crucial for our understanding of how HSV enters and reactivates from latency. The goals of this exploratory project are to identify conserved domains of ICP4 that are dispensable in cell culture, but are required for aspects of the virus life cycle in neurons or in vivo, and to begin to elucidate the molecular basis for the requirements in terms of virus gene expression and known ICP4 activities. These studies may also shed light on the basis for the different patterns of gene expression observed in neurons.