HCMV GPCR functions during latency and reactivation

人巨细胞病毒(HCMV)是一种广泛传播的病原体，感染美国大多数人口。这种病毒对发育中的胎儿以及缺乏有效免疫系统的儿童和成人构成重大威胁，往往会导致严重疾病和死亡。一旦个人感染了巨细胞病毒，病毒就会在造血室中潜伏或静止，终生与宿主在一起。在严重的免疫应激时期，病毒重新激活到其活跃状态，从而允许传播和随后的疾病。除了免疫幼稚和血清阴性的器官移植受者外，初次感染HCMV很少会导致疾病，相反，重新激活会导致显著的并发症。因此，为了预防巨细胞病毒相关疾病，我们必须对病毒的潜伏期和重新激活有一个完整的了解。在潜伏期，HCMV编码四种病毒G蛋白偶联受体(VGPCRs)中的三种：US28、UL33和UL78。我们之前已经证明，US28介导的信号是建立和维持潜伏期所必需的，并调节特定细胞靶点的表达，这些靶点调节主要立即早期(MIE)基因座，这是潜伏期到溶血期开关的主要调节因子。我们的发现还揭示了UL33和UL78需要从潜伏期有效地重新激活病毒。因此，我们假设vGPCRs调节特定的宿主信号通路，以调节潜伏期和重新激活之间的平衡。为了探索这一假设，我们将利用新的方法结合我们的病毒重组库，以及体外和体外潜伏期模型系统。在目标1中，我们将定义US28介导的信号转导的潜在机制，以及这如何影响潜伏期期间沉默因子到MIE基因座的招募。在目标2中，我们将确定UL33信号如何影响MIE基因座的反式激活和随后的重新激活，以及US28和UL78之间的相互作用如何扭转潜伏复制到裂解复制的平衡。总之，本文提出的实验将有助于更好地理解vGPCRs在潜伏期和再激活过程中的生物学功能，为未来研究开发预防HCMV再激活和疾病的新疗法奠定基础。

Human cytomegalovirus (HCMV) is a wide-spread pathogen, infecting the majority of the population in the United States. This virus poses a significant threat to developing fetuses as well as to children and adults who lack a competent immune system, often causing severe disease and mortality. Once individuals acquire an HCMV infection, the virus remains with the host for life, in a latent or quiescent state in the hematopoietic compartment. During times of severe immunological stress, the virus reactivates to its active state, allowing for dissemination and subsequent disease. With the exception of the immuno-naïve and sero-negative organ transplant recipients, primary infection with HCMV rarely causes disease, but rather it is reactivation that leads to significant complications. Thus, to prevent HCMV-associated disease, we must gain a complete understanding of viral latency and reactivation. During latency, HCMV encodes three of the four viral G protein-coupled receptors (vGPCRs): US28, UL33, and UL78. We previously showed US28-mediated signaling is required for establishing and maintaining latency and modulates the expression of specific cellular targets that regulate the Major Immediate Early (MIE) locus, a master regulator in the latent-to-lytic switch. Our findings also reveal a requirement for UL33 and UL78 for efficient viral reactivation from latency. Therefore, we hypothesize the vGPCRs modulate specific host signaling pathways to regulate the balance between latency and reactivation. To explore this hypothesis, we will take advantage of novel approaches coupled with our arsenal of viral recombinants, as well as both in vitro and ex vivo latency model systems. In Aim 1, we will define mechanisms underlying US28-mediated signaling and how this impacts the recruitment of silencing factors to the MIE locus during latency. In Aim 2, we will determine how UL33 signaling impacts the transactivation of the MIE locus and subsequent reactivation, as well as delineate how the interaction between US28 and UL78 tips the balance from latent-to-lytic replication. In sum, the experiments proposed herein will lead to a greater understanding of the vGPCRs’ biological functions during latency and reactivation, laying the foundation for future studies to develop novel therapeutics to prevent HCMV reactivation and disease.