The Interaction between Herpes Simplex Virus 1 Tegument Proteins UL51 and UL14 and Its Role in Virion Morphogenesis

Wang

et al. 2017

Although a varicella-zoster virus (VZV) vaccine has been used for many years, the neuropathy caused by VZV infection is still a major health concern. Open reading frame 7 (ORF7) of VZV has been recognized as a neurotropic gene in vivo, but its neurovirulent role remains unclear. In the present study, we investigated the effect of ORF7 deletion on VZV replication cycle at virus entry, genome replication, gene expression, capsid assembly and cytoplasmic envelopment, and transcellular transmission in differentiated neural progenitor cells (dNPCs) and neuroblastoma SH-SY5Y (dSY5Y) cells. Our results demonstrate that the ORF7 protein is a component of the tegument layer of VZV virions. Deleting ORF7 did not affect viral entry, viral genome replication, or the expression of typical viral genes but clearly impacted cytoplasmic envelopment of VZV capsids, resulting in a dramatic increase of envelopedefective particles and a decrease in intact virions. The defect was more severe in differentiated neuronal cells of dNPCs and dSY5Y. ORF7 deletion also impaired transmission of ORF7-deficient virus among the neuronal cells. These results indicate that ORF7 is required for cytoplasmic envelopment of VZV capsids, virus transmission among neuronal cells, and probably the neuropathy induced by VZV infection.IMPORTANCE The neurological damage caused by varicella-zoster virus (VZV) reactivation is commonly manifested as clinical problems. Thus, identifying viral neurovirulent genes and characterizing their functions are important for relieving VZV related neurological complications. ORF7 has been previously identified as a potential neurotropic gene, but its involvement in VZV replication is unclear. In this study, we found that ORF7 is required for VZV cytoplasmic envelopment in differentiated neuronal cells, and the envelopment deficiency caused by ORF7 deletion results in poor dissemination of VZV among neuronal cells. These findings imply that ORF7 plays a role in neuropathy, highlighting a potential strategy to develop a neurovirulenceattenuated vaccine against chickenpox and herpes zoster and providing a new target for intervention of neuropathy induced by VZV.

Section: Deletion Of Vzv-orf7 Affects Viral Envelopmentmentioning

confidence: 88%

ORF7 of Varicella-Zoster Virus Is Required for Viral Cytoplasmic Envelopment in Differentiated Neuronal Cells

Wang

et al. 2017

“…This suggests that the pUL7-pUL51 complex may be important for recruitment of the other tegument proteins to secondary envelopment sites and/or the coordinated assembly of tegument-envelope and tegument-capsid interactions necessary for efficient HSV-1 assembly. Interestingly, a recent report demonstrated that pUL14, another conserved tegument protein, interacts with pUL51 in HSV-1-infected cells, and inhibition of this interaction also caused defects in secondary envelopment (27). Furthermore, these studies demonstrated that deletion of pUL14 had similar effects on HSV-1 replication and assembly as the deletion of pUL51, suggesting that these two proteins may also function as a complex during virus assembly.…”

Section: Discussionmentioning

confidence: 99%

“…HSV-1 structural proteins are known to accumulate at juxtanuclear compartments, and virion assembly occurs at membranes that contain cellular trans -Golgi network and endosome marker proteins (5, 28). It therefore seems likely that pUL51 and pUL7 localized at these juxtanuclear compartments act in concert to aid virus assembly and secondary envelopment, perhaps in conjunction with pUL14 (27). …”

Section: Discussionmentioning

confidence: 99%

Dual Function of the pUL7-pUL51 Tegument Protein Complex in Herpes Simplex Virus 1 Infection

Albecka

Owen

Ivanova

et al. 2017

The tegument of herpesviruses is a highly complex structural layer between the nucleocapsid and the envelope of virions. Tegument proteins play both structural and regulatory functions during replication and spread, but the interactions and functions of many of these proteins are poorly understood. Here we focus on two tegument proteins from herpes simplex virus 1 (HSV-1), pUL7 and pUL51, which have homologues in all other herpesviruses. We have now identified that HSV-1 pUL7 and pUL51 form a stable and direct protein-protein interaction, their expression levels rely on the presence of each other, and they function as a complex in infected cells. We demonstrate that expression of the pUL7-pUL51 complex is important for efficient HSV-1 assembly and plaque formation. Furthermore, we also discovered that the pUL7-pUL51 complex localizes to focal adhesions at the plasma membrane in both infected cells and in the absence of other viral proteins. The expression of pUL7-pUL51 is important to stabilize focal adhesions and maintain cell morphology in infected cells and cells infected with viruses lacking pUL7 and/or pUL51 round up more rapidly than cells infected with wild-type HSV-1. Our data suggest that, in addition to the previously reported functions in virus assembly and spread for pUL51, the pUL7-pUL51 complex is important for maintaining the attachment of infected cells to their surroundings through modulating the activity of focal adhesion complexes.IMPORTANCE Herpesviridae is a large family of highly successful human and animal pathogens. Virions of these viruses are composed of many different proteins, most of which are contained within the tegument, a complex structural layer between the nucleocapsid and the envelope within virus particles. Tegument proteins have important roles in assembling virus particles as well as modifying host cells to promote virus replication and spread. However, little is known about the function of many tegument proteins during virus replication. Our study focuses on two tegument proteins from herpes simplex virus 1 that are conserved in all herpesviruses: pUL7 and pUL51. We demonstrate that these proteins directly interact and form a functional complex that is important for both virus assembly and modulation of host cell morphology. Further, we identify for the first time that these conserved herpesvirus tegument proteins localize to focal adhesions in addition to cytoplasmic juxtanuclear membranes within infected cells.

“…Roles in envelopment for the viral protein UL71 and its interacting protein UL103 have recently become well established (7)(8)(9)(10). Furthermore, the alphaherpesvirus homologues UL7 and UL51 also play roles in virus assembly and spread (11)(12)(13). Thus, UL71 may function by recruiting the ESCRT-III complex, which subsequently recruits VPS4.…”

mentioning

confidence: 99%

Nonenvelopment Role for the ESCRT-III Complex during Human Cytomegalovirus Infection

Streck

Carmichael

Buchkovich

2018

Secondary envelopment of human cytomegalovirus (HCMV) occurs through a mechanism that is poorly understood. Many enveloped viruses utilize the endosomal sorting complexes required for transport (ESCRTs) for viral budding and envelopment. Although there are conflicting reports on the role of the ESCRT AAA-ATPase protein VPS4 in an HCMV infection, VPS4 may act in an envelopment role similar to its function during other viral infections. Because VPS4 is normally recruited by the ESCRT-III complex, we hypothesized that ESCRT-III subunits would also be required for HCMV infection. We investigated the role of ESCRT-III, the core ESCRT scission complex, during the late stages of infection. We show that inducible expression of dominant-negative ESCRT-III subunits during infection blocks endogenous ESCRT function, but does not inhibit virus production. We also show that HCMV forms enveloped intracellular and extracellular virions in the presence of dominant-negative ESCRT-III subunits, suggesting that ESCRT-III is not involved in the envelopment of HCMV. We also found that similar to ESCRT-III, inducible expression of a dominant-negative form of VPS4A did not inhibit the envelopment of virions or reduce virus titers. Thus, HCMV does not require the ESCRTs for secondary envelopment. However, we found that ESCRT-III subunits are required for efficient virus spread. This suggests a role for ESCRT-III during the spread of HCMV that is independent of viral envelopment. Human cytomegalovirus (HCMV) is a prevalent opportunistic pathogen in the human population. HCMV infection in neonatal and immunocompromised patients can cause severe and possibly life-threatening complications in these at-risk patients. It is important to define mechanisms of the viral replication cycle to identify potential targets for new therapies. Secondary envelopment, or acquisition of the membrane envelope, of HCMV is a mechanism that needs further study. Using an inducible fibroblast system to carefully control for the toxicity associated with blocking ESCRT-III function, this study determines that the ESCRT proteins are not required for viral envelopment. However, the study does discover a non-envelopment role for the ESCRT-III complex in the efficient spread of the virus. Thus, this study advances our understanding of an important process essential for the replication of HCMV.