Re-evaluation of the genome sequence of guinea pig cytomegalovirus

Cytomegaloviruses are highly host restricted, resulting in cospeciation with their hosts. As a natural pathogen of rhesus macaques (RM), rhesus cytomegalovirus (RhCMV) has therefore emerged as a highly relevant experimental model for pathogenesis and vaccine development due to its close evolutionary relationship to human CMV (HCMV). Most in vivo experiments performed with RhCMV employed strain 68-1 cloned as a bacterial artificial chromosome (BAC). However, the complete genome sequence of the 68-1 BAC has not been determined. Furthermore, the gene content of the RhCMV genome is unknown, and previous open reading frame (ORF) predictions relied solely on uninterrupted ORFs with an arbitrary cutoff of 300 bp. To obtain a more precise picture of the actual proteins encoded by the most commonly used molecular clone of RhCMV, we reevaluated the RhCMV 68-1 BAC genome by whole-genome shotgun sequencing and determined the protein content of the resulting RhCMV virions by proteomics. By comparing the RhCMV genome to those of several related Old World monkey (OWM) CMVs, we were able to filter out many unlikely ORFs and obtain a simplified map of the RhCMV genome. This comparative genomics analysis suggests a high degree of ORF conservation among OWM CMVs, thus decreasing the likelihood that ORFs found only in RhCMV comprise true genes. Moreover, virion proteomics independently validated the revised ORF predictions, since only proteins that were conserved across OWM CMVs could be detected. Taken together, these data suggest a much higher conservation of genome and virion structure between CMVs of humans, apes, and OWMs than previously assumed.

Section: Resultsmentioning

confidence: 89%

Reevaluation of the Coding Potential and Proteomic Analysis of the BAC-Derived Rhesus Cytomegalovirus Strain 68-1

Malouli

Nakayasu

Viswanathan

et al. 2012

“…The UL116 gene is not conserved among alpha and gamma herpesviruses; thus, it does not belong to the core herpesvirus genes (61). Orthologous genes are present in cytomegaloviruses infecting nonhuman primates (62), mouse, rat, and guinea pig (63,64). The UL116 ORF from the HCMV TR strain is predicted to encode a 313-amino-acid glycoprotein comprising a signal peptide (amino acid positions 1 to 24) (Fig.…”

Section: Resultsmentioning

confidence: 99%

The Human Cytomegalovirus UL116 Gene Encodes an Envelope Glycoprotein Forming a Complex with gH Independently from gL

Caló

Cortese

Ciferri³

et al. 2016

Human cytomegalovirus (HCMV) is a major cause of morbidity and mortality in transplant patients and is the leading viral cause of birth defects after congenital infection. HCMV infection relies on the recognition of cell-specific receptors by one of the viral envelope glycoprotein complexes. Either the gH/gL/gO or the gH/gL/UL128/UL130/UL131A (Pentamer) complex has been found to fulfill this role, accounting for HCMV entry into almost all cell types. We have studied the UL116 gene product, a putative open reading frame identified by in silico analysis and predicted to code for a secreted protein. Virus infection experiments in mammalian cells demonstrated that UL116 is expressed late in the HCMV replication cycle and is a heavily glycosylated protein that first localizes to the cellular site of virus assembly and then inserts into the virion envelope. Transient-transfection studies revealed that UL116 is efficiently transported to the plasma membrane when coexpressed with gH and that gL competes with UL116 for gH binding. Further evidence for gH/UL116 complex formation was obtained by coimmunoprecipitation experiments on both transfected and infected cells and biochemical characterization of the purified complex. In summary, our results show that the product of the UL116 gene is an HCMV envelope glycoprotein that forms a novel gH-based complex alternative to gH/gL. Remarkably, the gH/UL116 complex is the first herpesvirus gH-based gL-less complex. IMPORTANCE HCMV infection can cause severe disease in immunocompromised adults and infants infected in utero.The dissection of the HCMV entry machinery is important to understand the mechanism of viral infection and to identify new vaccine antigens. The gH/gL/gO and gH/gL/UL128/UL130/UL131 (Pentamer) complexes play a key role in HCMV cell entry and tropism. Both complexes are formed by an invariant gH/gL scaffold on which the other subunits assemble. Here, we show that the UL116 gene product is expressed in infected cells and forms a heterodimer with gH. The gH/UL116 complex is carried on the infectious virions, although in smaller amounts than gH/gL complexes. No gH/UL116/gL ternary complex formed in transfected cells, suggesting that the gH/UL116 complex is independent from gL. This new gH-based gL-free complex represents a potential target for a protective HCMV vaccine and opens new perspectives on the comprehension of the HCMV cell entry mechanism and tropism. H uman cytomegalovirus (HCMV) is a ubiquitous betaherpesvirus infecting 40 to 60% of the human population (1).HCMV infection usually is mild or asymptomatic in immunocompetent individuals, while it can cause severe disease in immunocompromised adults. Infants infected in utero can suffer from disseminated HCMV disease and impaired neurological development (2). Transplant patients do not adequately control HCMV infection or reactivation, often resulting in graft rejection and death (3). Preventing primary HCMV infection could significantly decrease the frequency of organ rejection in seronegative recip...

“…A major drawback in GPCMV research has largely been overcome by the recent sequencing of the viral genome and the development of infectious bacterial artificial chromosome (BAC) clones of GPCMV (15,(26)(27)(28)(29). Manipulation of an infectious GPCMV BAC has allowed the preliminary study of some viral genes (1,(30)(31)(32)(33)(34)(35)(36).…”

mentioning

confidence: 99%

“…Manipulation of an infectious GPCMV BAC has allowed the preliminary study of some viral genes (1,(30)(31)(32)(33)(34)(35)(36). Analysis of the viral genome (15,29) indicated that GPCMV encodes homologs to the HCMV glycoproteins (gB, gH, gL, gM, gN, and gO) in genes colinear with the HCMV genome (designated GP55, GP75, GP115, GP100, GP73, and GP74, respectively). In HCMV, these six glycoproteins (gB, gH, gL, gM, gN, and gO) are required for fibroblast cell entry, and they form the glycoprotein complexes gCI (gB), gCII (gM/gN), and gcIII (gH/gL/gO) on the viral membrane (37)(38)(39).…”

mentioning

confidence: 99%

A Novel Non-Replication-Competent Cytomegalovirus Capsid Mutant Vaccine Strategy Is Effective in Reducing Congenital Infection

Choi

Root

McGregor

2016

Congenital cytomegalovirus (CMV) infection is a leading cause of mental retardation and deafness in newborns. The guinea pig is the only small animal model for congenital CMV infection. A novel CMV vaccine was investigated as an intervention strategy against congenital guinea pig cytomegalovirus (GPCMV) infection. In this disabled infectious single-cycle (DISC) vaccine strategy, a GPCMV mutant virus was used that lacked the ability to express an essential capsid gene (the UL85 homolog GP85) except when grown on a complementing cell line. In vaccinated animals, the GP85 mutant virus (GP85 DISC) induced an antibody response to important glycoprotein complexes considered neutralizing target antigens (gB, gH/gL/gO, and gM/gN). The vaccine also generated a T cell response to the pp65 homolog (GP83), determined via a newly established guinea pig gamma interferon enzyme-linked immunosorbent spot assay. In a congenital infection protection study, GP85 DISC-vaccinated animals and a nonvaccinated control group were challenged during pregnancy with wild-type GPCMV (10 5 PFU). The pregnant animals carried the pups to term, and viral loads in target organs of pups were analyzed. Based on live pup births in the vaccinated and control groups (94.1% versus 63.6%), the vaccine was successful in reducing mortality (P ‫؍‬ 0.0002). Additionally, pups from the vaccinated group had reduced CMV transmission, with 23.5% infected target organs versus 75.9% in the control group. Overall, these preliminary studies indicate that a DISC CMV vaccine strategy has the ability to induce an immune response similar to that of natural virus infection but has the increased safety of a non-replication-competent virus, which makes this approach attractive as a CMV vaccine strategy. IMPORTANCECongenital CMV infection is a leading cause of mental retardation and deafness in newborns. An effective vaccine against CMV remains an elusive goal despite over 50 years of CMV research. The guinea pig, with a placenta structure similar to that in humans, is the only small animal model for congenital CMV infection and recapitulates disease symptoms (e.g., deafness) in newborn pups. In this report, a novel vaccine strategy against congenital guinea pig cytomegalovirus (GPCMV) infection was developed, characterized, and tested for efficacy. This disabled infectious single-cycle (DISC) vaccine strategy induced a neutralizing antibody or a T cell response to important target antigens. In a congenital infection protection study, animals were protected against CMV in comparison to the nonvaccinated group (52% reduction of transmission). This novel vaccine was more effective than previously tested gB-based vaccines and most other strategies involving live virus vaccines. Overall, the DISC vaccine is a safe and promising approach against congenital CMV infection. H uman cytomegalovirus (HCMV), a betaherpesvirus, has evolved very closely with its human host. Virus infection in a healthy host is normally asymptomatic but leads to a lifelong infection. In contrast,...