Modification of Host Chemokine Responses by Human Cytomegalovirus

描述(申请人提供)：人类巨细胞病毒(HCMV)是疱疹病毒科家族的成员，它操纵宿主免疫系统并建立终身潜伏感染。这种与宿主的成功共存是由病毒蛋白的产生所介导的，这种蛋白模仿正常的免疫调节器，如细胞因子、趋化因子和趋化因子受体。人巨细胞病毒编码四种与人类趋化因子受体相似的蛋白质：US27、US28、UL33和UL78。US28和UL33都表现出不依赖于配体的结构性信号活性，US28也被证明是细胞趋化因子反应的信号。相比之下，还没有确定US27的配体或信号结果，它仍然是一个孤立的受体。为了筛选US27可能的趋化因子配体，先前建立了稳定表达US27的细胞系。虽然没有确定任何配体，但我们意外地观察到，US27显著增强了人趋化因子受体CXCR4的信号，以响应其天然配体CXCL12/SDF-1？CXCR4的许多重要生理作用之一涉及将免疫细胞引导到骨髓，这是HCMV潜伏期的主要部位。US27对CXCR4信号的增强可能代表了一种策略，通过这种策略，HCMV将病毒感染的细胞靶向骨髓，以启动新一轮感染，并扩大潜伏感染细胞库。具体的 正在测试的假设是，US27与CXCR4形成异构体，刺激感染细胞向趋化因子CXCL12/SDF-1？移动增加。这一假设得到了强有力的初步数据的支持，这些数据表明，同时表达US27和CXCR4的细胞在CXCL12/SDF-1？而不是控制。此外，免疫荧光染色和共聚焦显微镜发现US27和CXCR4共定位于细胞中的不同位置。这项建议的具体目标是确定在US27存在的情况下CXCR4信号增加的机制，并确定病毒感染细胞中是否发生增强的CXCR4反应。该项目的总体目标是阐明US27在病毒致病机制中的作用，结果有望揭示一种新的孤儿受体调节功能，可能对维持HCMV潜伏期有影响。

DESCRIPTION (provided by applicant): Human cytomegalovirus (HCMV) is a member of the Herpesviridae family that manipulates the host immune system and establishes life-long latent infection. This successful co-existence with the host is mediated by the production of viral proteins that mimic normal immune modulators like cytokines, chemokines, and chemokine receptors. HCMV encodes four proteins with similarity to human chemokine receptors, US27, US28, UL33, and UL78. US28 and UL33 both exhibit ligand-independent constitutive signaling activity, and US28 has also been shown to signal in response to cellular chemokines. In contrast, no ligands or signaling outcomes have been identified for US27, and it remains an orphan receptor. A stable cell line expressing US27 was developed previously in order to screen for possible chemokine ligands for US27. While no ligands were identified, we made the unexpected observation that US27 significantly enhanced the signaling of a human chemokine receptor, CXCR4, in response to its natural ligand, CXCL12/SDF-1?. One of the many important physiological roles of CXCR4 involves directing immune cells to the bone marrow, which is the primary site of HCMV latency. Potentiation of CXCR4 signaling by US27 could represent a strategy by which HCMV targets virus-infected cells to the bone marrow in order to initiate a new round of infection and expand the reservoir of latently infected cells. The specific hypothesis being tested is that US27 forms heteromers with CXCR4 that stimulate increased movement of infected cells toward the chemokine CXCL12/SDF-1?. This hypothesis is supported by strong preliminary data demonstrating that cells expressing both US27 and CXCR4 exhibit greater calcium mobilization and enhanced chemotaxis in response to CXCL12/SDF-1? than controls. In addition, US27 and CXCR4 were found to co-localize to discrete locations in the cell by immunofluorescence staining and confocal microscopy. The specific goals of this proposal are to identify the mechanism for increased CXCR4 signaling in the presence of US27 and to determine whether enhanced CXCR4 responses occur in virus-infected cells. The overall goal of the project is to clarify the role of US27 in viral pathogenesi, and the results are expected to reveal a novel regulatory function for an orphan receptor with possible implications for the maintenance of HCMV latency.