RhoB is a component of the human cytomegalovirus assembly complex and is required for efficient viral production

Human Cytomegalovirus (HCMV), an ubiquitous β-herpesvirus, is a significant pathogen that causes medically severe diseases in immunocompromised individuals and in congenitally infected neonates. RhoB belongs to the family of Rho GTPases, which regulates diverse cellular processes. Rho proteins are implicated in the entry and egress from the host cell of mainly α- and γ-herpesviruses, whereas β-herpesviruses are the least studied in this regard. Here, we studied the role of RhoB GTPase during HCMV lytic infection. Microscopy analysis, both in fixed and live infected cells showed that RhoB was translocated to the assembly complex/compartment (AC) of HCMV, a cytoplasmic zone in infected cells where many viral structural proteins are known to accumulate and assembly of new virions takes place. Furthermore, RhoB was localized at the AC even when the expression of the late HCMV AC proteins was inhibited. At the very late stages of infection, cellular projections were formed containing RhoB and HCMV virions, potentially contributing to the successful viral spread. Interestingly, the knockdown of RhoB in HCMV-infected cells resulted in a significant reduction of the virus titer and could also affect the accumulation of AC viral proteins at this subcellular compartment. RhoB knockdown also affected actin fibers' structure. Actin reorganization was observed at late stages of infection originating from the viral AC and surrounding the cellular projections, implying a potential interplay between RhoB and actin during HCMV assembly and egress. In conclusion, our results demonstrate for the first time that RhoB is a constituent of the viral AC and is required for HCMV productive infection.人类巨细胞病毒（Human Cytomegalovirus, HCMV）是一种广泛传播的β疱疹病毒，是引发免疫功能低下人群及先天性感染新生儿罹患重症疾病的重要病原体。RhoB属于Rho GTP酶（Rho GTPases）家族，该家族调控多种细胞生理过程。Rho蛋白主要与α、γ疱疹病毒的宿主细胞入侵及逸出过程相关，而β疱疹病毒在该方面的研究最为匮乏。本研究探讨了RhoB GTP酶在HCMV裂解性感染过程中的作用。通过对固定及活的感染细胞开展显微镜分析，研究人员发现RhoB会被转运至HCMV的组装复合体/组装区室（AC）——这是感染细胞内的细胞质区域，已知多种病毒结构蛋白在此聚集并完成新病毒粒子的组装。进一步实验显示，即使抑制HCMV晚期组装区室蛋白的表达，RhoB仍可定位于组装区室。在感染极晚期，细胞会形成携带有RhoB与HCMV病毒粒子的细胞突起，这可能有助于病毒高效扩散。值得注意的是，在HCMV感染细胞中敲低RhoB的表达，会显著降低病毒滴度，同时还会影响组装区室病毒蛋白在该亚细胞区域的聚集。此外，RhoB敲低还会改变肌动蛋白纤维的结构。感染晚期可观察到源自病毒组装区室、环绕细胞突起的肌动蛋白重排现象，这提示RhoB与肌动蛋白可能在HCMV的组装及逸出过程中存在潜在相互作用。综上，本研究结果首次证实RhoB是病毒组装区室的组成成分，且对HCMV产毒性感染至关重要。