Presence of human cytomegalovirus (HCMV) immediate early mRNA but not ppUL83 (lower matrix protein pp65) mRNA in polymorphonuclear and mononuclear leukocytes during active HCMV infection

Endothelial cells (ECs) are a critical target of viruses, and infection of the endothelium represents a defining point in viral pathogenesis. Human cytomegalovirus (HCMV), the prototypical betaherpesvirus, encodes proteins specialized for entry into ECs and delivery of the genome to the nuclei of ECs. Virus strains competent to enter ECs replicate with differing efficiencies, suggesting that the virus encodes genes for postentry tropism in ECs. We previously reported a specific requirement for the UL133/8 locus of HCMV for replication in ECs. The UL133/8 locus harbors four genes: UL133, UL135, UL136, and UL138. In this study, we find that while UL133 and UL138 are dispensable for replication in ECs, both UL135 and UL136 are important. These genes are not required for virus entry or the expression of viral genes. The phenotypes associated with disruption of either gene reflect phenotypes observed for the UL133/8 NULL virus, which lacks the entire UL133/8 locus, but are largely distinct from one another. Viruses lacking UL135 fail to properly envelop capsids in the cytoplasm, produce fewer dense bodies (DB) than the wild-type (WT) virus, and are unable to incorporate viral products into multivesicular bodies (MVB). Viruses lacking UL136 also fail to properly envelop virions and produce larger dense bodies than the WT virus. Our results indicate roles for the UL135 and UL136 proteins in commandeering host membrane-trafficking pathways for virus maturation. UL135 and UL136 represent the first HCMV genes crucial for early-to late-stage tropism in ECs. H uman cytomegalovirus (HCMV) is a ubiquitous herpesvirus with 50 to 99% seroprevalence in the global population. Like all herpesviruses, HCMV persists for the lifetime of the host by way of latent infection (1-3). The persistence of HCMV is asymptomatic in immunocompetent individuals and is characterized by states of subclinical reactivation from latency and low-level virus shedding (1). However, in immunocompromised hosts, HCMV causes significant morbidity and mortality. Of particular concern are stem cell and solid-organ transplant patients, HIV/AIDS patients, and cancer patients undergoing chemotherapy or radiation regimens (4, 5). Additionally, HCMV is the leading cause of infectious disease-related birth defects in the United States, affecting 1 in 150 children born in the United States and most commonly resulting in mild to severe hearing loss (6). While CMV infection of seronegative women during pregnancy poses the most significant risk for severe sequelae in infants (microcephaly, cerebral palsy, and severe hearing loss or cognitive deficits), as many as 75% of congenital infections occur in infants whose mothers were seropositive at the time of conception, indicating that these infections result from reinfection or reactivation (7). Finally, the persistence of HCMV is increasingly associated with age-related pathologies, even when overt clinical symptoms are absent. Agerelated pathologies include vascular disease, immune dysfunction, and frailty (8-13)...

Section: Discussionmentioning

confidence: 99%

Human Cytomegalovirus UL135 and UL136 Genes Are Required for Postentry Tropism in Endothelial Cells

Bughio

Umashankar

Wilson

et al. 2015

“…In healthy hosts, infection of these organ systems allows for the establishment of the viral persistence needed for viral survival in the infected host and in the general population. In contrast, in immunocompromised hosts, because of the absence of a functional immune response, this same strategy of viral spread would lead to the overt organ disease seen in these individuals (83).The mechanisms of HCMV dissemination remain unclear; however, cells of the myeloid lineage, specifically monocytes, are thought to have a central role in this process for multiple reasons (4,22,30,34,43,44,55,79,83,89). First, monocytes containing viral DNA are found in patients with a cell-associated viremia (79,83).…”

mentioning

confidence: 99%

“…These results suggest that infected monocytes serve as a key cell type responsible for viral spread from the blood during a primary infection. A caveat to monocyte participation in viral dissemination are results suggesting that monocytes are only abortively infected (28,30,31,41,79,83,91). Nevertheless, monocytes appear to be the cell type that is "at the right place at the right time" for the hematogenous spread of HCMV following primary infection.…”

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confidence: 99%

Human Cytomegalovirus (HCMV) Infection of Endothelial Cells Promotes Naïve Monocyte Extravasation and Transfer of Productive Virus To Enhance Hematogenous Dissemination of HCMV

Bentz

Jarquin-Pardo

Chan

et al. 2006

120

124

Human cytomegalovirus (HCMV) pathogenesis is dependent on the hematogenous spread of the virus to host tissue. While data suggest that infected monocytes are required for viral dissemination from the blood to the host organs, infected endothelial cells are also thought to contribute to this key step in viral pathogenesis. We show here that HCMV infection of endothelial cells increased the recruitment and transendothelial migration of monocytes. Infection of endothelial cells promoted the increased surface expression of cell adhesion molecules (intercellular cell adhesion molecule 1, vascular cell adhesion molecule 1, E-selectin, and platelet endothelial cell adhesion molecule 1), which were necessary for the recruitment of naïve monocytes to the apical surface of the endothelium and for the migration of these monocytes through the endothelial cell layer. As a mechanism to account for the increased monocyte migration, we showed that HCMV infection of endothelial cells increased the permeability of the endothelium. The cellular changes contributing to the increased permeability and increased naïve monocyte transendothelial migration include the disruption of actin stress fiber formation and the decreased expression of lateral junction proteins (occludin and vascular endothelial cadherin). Finally, we showed that the migrating monocytes were productively infected with the virus, documenting that the virus was transferred to the migrating monocyte during passage through the lateral junctions. Together, our results provide evidence for an active role of the infected endothelium in HCMV dissemination and pathogenesis.Human cytomegalovirus (HCMV) is a betaherpesvirus that establishes a life-long persistent infection (10). In immunocompromised individuals, such as AIDS patients, neonates, and transplant recipients, HCMV infection is associated with significant morbidity and mortality (13,38,56,87). In immunocompetent hosts, HCMV infection is generally asymptomatic, although it can cause mononucleosis (40) and is associated with chronic inflammatory diseases, such as the cardiovascular diseases atherosclerosis and coronary restenosis (1,19,35,46,51,57,59,86,90,107).HCMV pathogenesis is a direct result of viral spread to host organs and the subsequent infection of those organ systems (6,44,54,83). Systemic spread occurs during both asymptomatic and symptomatic infections (93) and is required for HCMV persistence in the host (83). During primary infection, the virus spreads from the initial site of infection to the peripheral blood and then to host organ tissue (6,54,83). In healthy hosts, infection of these organ systems allows for the establishment of the viral persistence needed for viral survival in the infected host and in the general population. In contrast, in immunocompromised hosts, because of the absence of a functional immune response, this same strategy of viral spread would lead to the overt organ disease seen in these individuals (83).The mechanisms of HCMV dissemination remain unclear; however, cells of the ...

“…Infected ECs contribute to virus dissemination and pathogenesis, in part through the infection of circulating leukocytes or polymorphonuclear cells (1,(22)(23)(24)(25)(26) and by promoting monocyte recruitment and extravasation, possibly increasing vascular permeability for dissemination of infected circulating cells into tissues (27). Further, infected ECs may detach and circulate (28,29). These modes of cell-cell-based dissemination likely define the contribution of ECs to viral spread in the host (30).…”

mentioning

confidence: 99%

An Endothelial Cell-Specific Requirement for the UL133-UL138 Locus of Human Cytomegalovirus for Efficient Virus Maturation

Bughio

Elliott

Goodrum

2013

Human cytomegalovirus (HCMV) infects a variety of cell types in humans, resulting in a varied pathogenesis in the immunocompromised host. Endothelial cells (ECs) are considered an important target of HCMV infection that may contribute to viral pathogenesis. Although the viral determinants important for entry into ECs are well defined, the molecular determinants regulating postentry tropism in ECs are not known. We previously identified the UL133-UL138 locus encoded within the clinical strain-specific ULb= region of the HCMV genome as important for the latent infection in CD34؉ hematopoietic progenitor cells (HPCs). Interestingly, this locus, while dispensable for replication in fibroblasts, was required for efficient replication in ECs infected with the TB40E or fusion-inducing factor X (FIX) HCMV strains. ECs infected with a virus lacking the entire locus (UL133-UL138 NULL virus) complete the immediate-early and early phases of infection but are defective for infectious progeny virus production. ECs infected with UL133-UL138 NULL virus exhibited striking differences in the organization of intracellular membranes and in the assembly of mature virions relative to ECs infected with wild-type (WT) virus. In UL133-UL138 NULL virus-infected ECs, Golgi stacks were disrupted, and the viral assembly compartment characteristic of HCMV infection failed to form. Further, progeny virions in UL133-UL138 NULL virus-infected ECs inefficiently acquired the virion tegument and secondary envelope. These defects were specific to infection in ECs and not observed in fibroblasts infected with UL133-UL138 NULL virus, suggesting an EC-specific requirement for the UL133-UL138 locus for late stages of replication. To our knowledge, the UL133-UL138 locus represents the first cell-type-dependent, postentry tropism determinant required for viral maturation.