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Cell type-specific biogenesis of novel vesicles containing viral products in human cytomegalovirus infection.

ABSTRACT: Human cytomegalovirus (HCMV), while highly restricted for the human species, infects an diverse array of cell types in the host. Patterns of infection are dictated by the cell type infected, but cell type-specific factors and how they impact tropism for specific cell types is poorly understood. Previous studies in primary endothelial cells showed that HCMV infection induces large multivesicular-like bodies (MVBs) that incorporate viral products, including dense bodies (DBs) and virions. Here we define the nature of these large vesicles using a recombinant virus where UL32, encoding the pp150 tegument protein, is fused in frame with green fluorescent protein (GFP, TB40/E-UL32-GFP). In fibroblasts, UL32-GFP-positive vesicles were marked with classical markers of MVBs, including CD63 and lysobisphosphatidic acid (LBPA), both classical MVB markers, as well as the clathrin and LAMP1. Unexpectedly, UL32-GFP-positive vesicles in primary human microvascular endothelial cells (HMVECs) were not labeled by CD63, and LBPA was completely lost from infected cells. We defined these UL32-positive vesicles in endothelial cells using markers for the cis-Golgi (GM130), lysosome (LAMP1), and autophagy (LC3B). These findings suggest that UL32-GFP containing MVBs in fibroblasts are derived from the canonical endocytic pathway and takeover classical exosomal release pathway. However, UL32-GFP containing MVBs in HMVECs are derived from the early biosynthetic pathway and exploit a less characterized early Golgi-LAMP1-associated non- canonical secretory autophagy pathway. These results reveal striking cell-type specific membrane trafficking differences in host pathways that are exploited by HCMV, which may reflect distinct pathways for virus egress.ImportanceHuman cytomegalovirus (HCMV) is a herpesvirus that, like all herpesvirus, that establishes a life-long infection. HCMV remains a significant cause of morbidity and mortality in the immunocompromised and HCMV seropositivity is associated with age-related pathology. HCMV infects many cells in the human host and the biology underlying the different patterns of infection in different cell types is poorly understood. Endothelial cells are important target of infection that contribute to hematogenous spread of the virus to tissues. Here we define striking differences in the biogenesis of large vesicles that incorporate virions in fibroblasts and endothelial cells. In fibroblasts, HCMV is incorporated into canonical MVBs derived from an endocytic pathway, whereas HCMV matures through vesicles derived from the biosynthetic pathway in endothelial cells. This work defines basic biological differences between these cell types that may impact how progeny virus is trafficked out of infected cells.

SUBMITTER: Momtaz S

PROVIDER: S-EPMC8139684 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Clinical strains of HCMV encode 20 putative ORFs within a region of the genome termed ULb' that are postulated to encode functions related to persistence or immune evasion. We have previously identified ULb'-encoded pUL138 as necessary, but not sufficient, for HCMV latency in CD34+ hematopoietic progenitor cells (HPCs) infected in vitro. pUL138 is encoded on polycistronic transcripts that also encode 3 additional proteins, pUL133, pUL135, and pUL136, collectively comprising the UL133-UL138 locus. This work represents the first characterization of these proteins and identifies a role for this locus in infection. Similar to pUL138, pUL133, pUL135, and pUL136 are integral membrane proteins that partially co-localized with pUL138 in the Golgi during productive infection in fibroblasts. As expected of ULb' sequences, the UL133-UL138 locus was dispensable for replication in cultured fibroblasts. In CD34+ HPCs, this locus suppressed viral replication in HPCs, an activity attributable to both pUL133 and pUL138. Strikingly, the UL133-UL138 locus was required for efficient replication in endothelial cells. The association of this locus with three context-dependent phenotypes suggests an exciting role for the UL133-UL138 locus in modulating the outcome of viral infection in different contexts of infection. Differential profiles of protein expression from the UL133-UL138 locus correlated with the cell-type dependent phenotypes associated with this locus. We extended our in vitro findings to analyze viral replication and dissemination in a NOD-scid IL2R?(c) (null)-humanized mouse model. The UL133-UL138(NULL) virus exhibited an increased capacity for replication and/or dissemination following stem cell mobilization relative to the wild-type virus, suggesting an important role in viral persistence and spread in the host. As pUL133, pUL135, pUL136, and pUL138 are conserved in virus strains infecting higher order primates, but not lower order mammals, the functions encoded likely represent host-specific viral adaptations.

Project description:Human cytomegalovirus (HCMV) is a common cause of morbidity and mortality in immunocompromised and immunosuppressed individuals. During infection, HCMV is known to employ host transcription factors to facilitate viral gene expression. To further understand the previously observed delayed viral replication and protein expression in p53 knockout cells, we conducted microarray analyses on p53+/+ and p53-/- immortalized fibroblast cell lines. At 12 hpi, applying the significance criteria defined above, no genes showed a significant difference in any of the comparisons. At 24 hpi, we found 19 genes to be significantly different in the THF versus p53-/- comparison and 14 genes to be significantly different in the HFF versus p53-/- comparison. Eleven genes were shared between HFF and THF cells when compared to p53-/- cells (UL30, UL54, UL63, UL65, UL69, UL75, UL110, UL122, IRL4, IRS1, TRS1, shown in bold in Table 1). Eight genes were unique in the THF versus p53-/- comparison (UL48, UL68, UL84, UL100, UL106, UL109, UL111, RL5A), and three genes in the HFF versus p53-/- cell comparison (UL14, UL16, US2). When comparing HFF and THF cells, only US2 showed a significant difference. The ratio (HFF versus p53-/- divided by THF versus p53-/-) of the expression levels of the eleven shared genes from the HFF versus p53-/- and THF versus p53-/- comparisons was an averaged 1.2, indicating that, with the exception of US2, these two cell lines behaved similarly with respect to p53-driven viral gene expression. Keywords: time course, virus, cytomegalo, hhv5, infection, p53 Each slide consisted of 4 arrays. Each array consisted of 305 control features, 1265 cellular gene features and 670 viral gene features. The study was performed on 6 slides (HFF-THF, HFF-p53-/-, THF-p53-/- at 12 and 24 hpi). 3 arrays per slide were hybridized with 3 biological replicates of labelled RNA, the 4th array was hybridized with an equimolar mixture of the 3 biological replicate samples. This array was used for control purposes only, and the results were not used for downstream calculations. Each slide was stripped and reprobed two times to provide 3 technical replicates of each sample. As our experiments concentrated on viral genes and their expression, cellular genes were not further analyzed in this study.

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Cell type-specific biogenesis of novel vesicles containing viral products in human cytomegalovirus infection.

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