Abstract
Beta-herpesviruses develop a unique structure within the infected cell known as an assembly compartment (AC). This structure, as large as the nucleus, is composed of host-cell-derived membranous elements. The biogenesis of the AC and its contribution to the final stages of beta-herpesvirus assembly are still unclear. In this study, we performed a spatial and temporal analysis of the AC in cells infected with murine CMV (MCMV), a member of the beta-herpesvirus family, using a panel of markers that characterize membranous organelle system. Out of 64 markers that were analyzed, 52 were cytosolic proteins that are recruited to membranes as components of membrane-shaping regulatory cascades. The analysis demonstrates that MCMV infection extensively reorganizes interface between early endosomes (EE), endosomal recycling compartment (ERC), and the trans-Golgi network (TGN), resulting in expansion of various EE-ERC-TGN intermediates that fill the broad area of the inner AC. These intermediates are displayed as over-recruitment of host-cell factors that control membrane flow at the EE-ERC-TGN interface. Most of the reorganization is accomplished in the early (E) phase of infection, indicating that the AC biogenesis is controlled by MCMV early genes. Although it is known that CMV infection affects the expression of a large number of host-cell factors that control membranous system, analysis of the host-cell transcriptome and protein expression in the E phase of infection demonstrated no sufficiently significant alteration in expression levels of analyzed markers. Thus, our study demonstrates that MCMV-encoded early phase function targets recruitment cascades of host cell-factors that control membranous flow at the EE-ERC-TGN interface in order to initiate the development of the AC.
Highlights
Beta-herpesviruses infect almost all the human population, cause asymptomatic infections, and are associated with a wide range of pathologic conditions
We present spatio-temporal phenotyping of the assembly compartment (AC) of beta-herpesvirus infected cells and demonstrate that murine CMV (MCMV) infection reorganizes the interface between EEs, endosomal recycling compartment (ERC), and the transGolgi network (TGN)
The reorganization was initiated very early in the infection, indicating that MCMV encoded early genes drive the establishment of the new organelle structure (PrAC), which evolves into a sizeable cytoplasmic structure known as the AC
Summary
Beta-herpesviruses infect almost all the human population, cause asymptomatic infections, and are associated with a wide range of pathologic conditions (rev in. Britt and Prichard, 2018). The assembly of beta-herpesviruses occurs as a complex set of events in the nucleus and cytoplasm of the infected cell (rev in Tandon and Mocarski, 2012; Close et al, 2018a). Once the preparatory events in the membranous system are completed, pre-assembled nucleocapsids migrate from the nucleus, move through the cytoplasm, and acquire most of the tegument components and membranous envelope harboring viral glycoproteins by budding into the membranous organelle(s). All these cytoplasmic events take place within a sizeable cytoplasmic structure known as the assembly compartment (AC)
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