Department of Microbiology and Immunology, Center for Molecular and Tumor Virology, Louisiana State University Health Sciences Center, Shreveport, Louisiana, United States of America.
PLoS Pathog. 2013;9(7):e1003463. doi: 10.1371/journal.ppat.1003463. Epub 2013 Jul 11.
We have established that HCMV acts as a specific ligand engaging and activating cellular integrins on monocytes. As a result, integrin signaling via Src activation leads to the functional activation of paxillin required for efficient viral entry and for the biological changes in monocytes needed for viral dissemination. These biological/molecular changes allow HCMV to use monocytes as "vehicles" for systemic spread and the establishment of lifelong persistence. However, it remains unresolved how HCMV specifically induces this observed monocyte activation. It was previously demonstrated that the HCMV gH/gL/UL128-131 glycoprotein complex facilitates viral entry into biologically relevant cell types. Nevertheless, the mechanism by which the gH/gL/UL128-131 complex promotes this process is unknown. We now show that only HCMV virions possessing the gH/gL/UL128-131 complex are capable of activating integrin/Src/paxillin-signaling in monocytes. In fibroblasts, this signaling is reversed, such that virus lacking the gH/gL/UL128-131 complex is the only virus able to induce the paxillin activation cascade. The presence of the gH/gL/UL128-131 complex also may have an inhibitory effect on integrin-mediated signaling pathway in fibroblasts. Furthermore, we demonstrate that the presence of the gH/gL/UL128-131 complex on the viral envelope, through its activation of the integrin/Src/paxillin pathway, is necessary for efficient HCMV internalization into monocytes and that appropriate actin and dynamin regulation is critical for this entry process. Importantly, productive infection in monocyte-derived macrophages was seen only in cells exposed to HCMV expressing the gH/gL/UL128-131 complex. From our data, the HCMV gH/gL/U128-131 complex emerges as the specific ligand driving the activation of the receptor-mediated signaling required for the regulation of the actin cytoskeleton and, consequently, for efficient and productive internalization of HCMV into monocytes. To our knowledge, our studies demonstrate a possible molecular mechanism for why the gH/gL/UL128-131 complex dictates HCMV tropism and why the complex is lost as clinical isolates are passaged in the laboratory.
我们已经确定 HCMV 作为一种特定的配体，与单核细胞上的细胞整合素结合并激活它们。结果，整合素信号通过Src 激活导致病毒进入所需的功能性整联蛋白信号和病毒传播所需的单核细胞生物学变化所需的粘着斑激酶的激活。这些生物学/分子变化使 HCMV 能够利用单核细胞作为全身扩散和终生持续存在的“载体”。然而，HCMV 如何特异性诱导这种观察到的单核细胞激活仍然没有解决。先前已经证明，HCMV gH/gL/UL128-131 糖蛋白复合物促进病毒进入生物学相关细胞类型。然而，gH/gL/UL128-131 复合物促进这一过程的机制尚不清楚。我们现在表明，只有具有 gH/gL/UL128-131 复合物的 HCMV 病毒粒子才能激活单核细胞中的整合素/Src/粘着斑激酶信号。在成纤维细胞中，这种信号被逆转，使得缺乏 gH/gL/UL128-131 复合物的病毒是唯一能够诱导粘着斑激酶激活级联的病毒。gH/gL/UL128-131 复合物的存在也可能对成纤维细胞中整合素介导的信号通路具有抑制作用。此外，我们证明，病毒包膜上 gH/gL/UL128-131 复合物的存在通过激活整合素/Src/粘着斑激酶途径，对于 HCMV 有效进入单核细胞是必要的，并且适当的肌动蛋白和 dynamin 调节对于这种进入过程是关键的。重要的是，只有在暴露于表达 gH/gL/UL128-131 复合物的 HCMV 的单核细胞衍生的巨噬细胞中才观察到产生活性感染。根据我们的数据，HCMV gH/gL/U128-131 复合物作为特异性配体出现，驱动调节肌动蛋白细胞骨架所必需的受体介导信号的激活，并且因此对于 HCMV 有效和产生活性进入单核细胞是必需的。据我们所知，我们的研究证明了一种可能的分子机制，即为什么 gH/gL/UL128-131 复合物决定 HCMV 嗜性，以及为什么该复合物在实验室中作为临床分离物传代时丢失。
