Mechanism and regulation of protein kinase functions in HSV nuclear egress

甲型疱疹病毒编码两种蛋白激酶，它们是致病的关键调节因子pUS3和pUL13。PUS3在感染过程中具有多种功能，包括促进核外泄、保护细胞免于凋亡、促进病毒蛋白合成、抑制免疫系统的抗原递呈等。因此，对pUS3活性的调控是非常有意义的，既是理解疱疹病毒感染的分子生物学的工具，也是探索基于抑制其各种活性的抗病毒疗法的途径。据报道，pUS3激酶活性既受自身磷酸化的调节，也受另一种疱疹病毒编码的激酶pUL13的磷酸化调节。有趣的是，pUL13对pUS3活性的调节似乎影响了一些pUS3功能，但不影响其他功能。具体地说，pUS3似乎至少对病毒衣壳从细胞核出口的部分活性是必需的，但对于保护受感染的细胞免受一些促凋亡刺激()来说并不是必需的。这些观察结果突出表明，我们对pUL13和pUS3之间的相互作用的理解存在两个非常重大的差距。首先，目前尚不清楚哪些pUS3功能受pUL13调控，以及UL13依赖功能与UL13独立功能的区别。我们提出了一个简单的假设，即pUS3被pUL13磷酸化后，通过调节其进入细胞核的途径来特异性地调节其核功能。第二，pUL13对pUS3的调控机制和功能意义尚不清楚。已知pUL13使pUS3磷酸化，但目前尚不清楚这种磷酸化是否对pUL13调节pUS3是必要的。最近发表的对HSV感染细胞的蛋白质组学分析表明，pUL13在S139处使pUS3磷酸化。我们将使用遗传学方法来验证S139是pUL13调控pUS3的关键残基的假设，然后测试S139磷酸化对病毒生长和传播的意义。

Alphaherpesviruses encode two proteins kinases that are critical regulators of pathogenesis, pUS3 and pUL13. pUS3 has multiple functions in infection including facilitation of nuclear egress, protection from apoptosis, promotion of viral protein synthesis, and inhibition of antigen presentation to the immune system. The regulation of the activity of pUS3 is, therefore, of great interest, both as a tool for understanding the molecular biology of herpesvirus infections, and as an avenue for exploring antiviral therapies based on inhibition of its various activities. pUS3 kinase activity has been reported to be regulated both by autophosphorylation and by phosphorylation by another herpesvirus-encoded kinase, pUL13. Intriguingly, regulation of pUS3 activity by pUL13 appears to affect some pUS3 functions, but not others. Specifically, it appears to be necessary for at least some of the activities of pUS3 in egress of virus capsids from the nucleus, but not for protection of infected cells from some pro-apoptotic stimuli (). These observations highlight two very significant gaps in our understanding of the interaction between pUL13 and pUS3. First, it is unclear which pUS3 functions are regulated by pUL13, and what distinguished UL13-dependent from UL13-independent functions. We propose the simple hypothesis that phosphorylation of pUS3 by pUL13 specifically regulates its nuclear functions by regulating its access to the nucleus. Second, the mechanism and functional significance of pUL13 regulation of pUS3 is unclear. It is known that pUL13 phosphorylates pUS3, but it is not clear whether this phosphorylation is necessary for pUL13 regulation of pUS3. A recently published proteomic analysis of HSV infected cells suggests that pUL13 phosphorylates pUS3 at S139. We will use a genetic approach to test the hypothesis that S139 is the critical residue for regulation of pUS3 by pUL13, and then to test the significance of S139 phosphorylation for viral growth and spread.