Identification and Structure of the Marek's Disease Virus Serotype 2 Glycoprotein M Gene: Comparison with Glycoprotein M Genes of Herpesviridae Family

The alphaherpesvirus UL51 protein is a tegument component that interacts with the viral glycoprotein E and functions at multiple steps in virus assembly and spread in epithelial cells. We show here that pUL51 forms a complex in infected cells with another conserved tegument protein, pUL7. This complex can form in the absence of other viral proteins and is largely responsible for recruitment of pUL7 to cytoplasmic membranes and into the virion tegument. Incomplete colocalization of pUL51 and pUL7 in infected cells, however, suggests that a significant fraction of the population of each protein is not complexed with the other and that they may accomplish independent functions. IMPORTANCEThe ability of herpesviruses to spread from cell to cell in the face of an immune response is critical for disease and shedding following reactivation from latency. Cell-to-cell spread is a conserved ability of herpesviruses, and the identification of conserved viral genes that mediate this process will aid in the design of attenuated vaccines and of novel therapeutics. The conserved UL51 gene of herpes simplex virus 1 plays important roles in cell-to-cell spread and in virus assembly in the cytoplasm, both of which likely depend on specific interactions with other viral and cellular proteins. Here we identify one of those interactions with the product of another conserved herpesvirus gene, UL7, and show that formation of this complex mediates recruitment of UL7 to membranes and to the virion. Human herpesviruses can reactivate from latency at internal anatomical sites and be shed from epithelial surfaces long after initial infection and establishment of an adaptive immune response (1-8). This suggests that the ability to spread from cell to cell in the presence of immune effectors is a conserved property of herpesviruses. Within the alphaherpesviruses, where this phenomenon has been the most extensively studied, the evidence suggests that cell-to-cell spread (CCS) between epithelial cells in vitro has two mechanistic components. The first of these is a virion trafficking component in which virions are targeted from the site of secondary envelopment to the junctional surfaces of cells, where they have access to adjacent cells in a compartment that is sterically protected from immune effectors in the medium (9-11). The second component is a specialized entry process that may involve gE binding to specific CCS receptors and that also may involve different patterns of receptor usage by the virus entry apparatus (12-15). In alphaherpesviruses, both mechanistic components involve the complex between the envelope glycoproteins gE and gI. However, since gE and gI are encoded only by alphaherpesvirus genomes, any mechanism for CCS that is conserved among all herpesviruses is likely to involve other, more widely conserved viral factors.Virus genome-encoded proteins that are specifically required for epithelial CCS fall into two categories: those required for virus entry into cells regardless of the mode of virus egress and those tha...

mentioning

confidence: 99%

The Herpes Simplex Virus 1 UL51 Protein Interacts with the UL7 Protein and Plays a Role in Its Recruitment into the Virion

Roller

Fetters

2015

“…Of the latter, those mediating viral entry, namely, gB, gD, and the gH/gL complex, are essential for the propagation of the virus (3). In contrast, the viral glycoprotein M (gM) is conserved throughout the family and typically critical for beta-and gammaherpesviruses but is not essential for most alphaherpesviruses, including HSV-1 (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16). Consequently, when gM is depleted from HSV-1 or the related alphaherpesvirus pseudorabies virus, viral yields are minimally reduced by 3-to 50-fold.…”

mentioning

confidence: 99%

Herpes Simplex Virus 1 gN Partners with gM To Modulate the Viral Fusion Machinery

Kasmi

Lippé

2015

Herpes simplex virus 1 (HSV-1) capsids are assembled in the nucleus, where they incorporate the viral genome. They then transit through the two nuclear membranes and are wrapped by a host-derived envelope. In the process, several HSV-1 proteins are targeted to the nuclear membranes, but their roles in viral nuclear egress are unclear. Among them, glycoprotein M (gM), a known modulator of virus-induced membrane fusion, is distributed on both the inner and outer nuclear membranes at the early stages of the infection, when no other viral glycoproteins are yet present there. Later on, it is found on perinuclear virions and ultimately redirected to the trans-Golgi network (TGN), where it cycles with the cell surface. In contrast, transfected gM is found only at the TGN and cell surface, hinting at an interaction with other viral proteins. Interestingly, many herpesvirus gM analogs interact with their gN counterparts, which typically alters their intracellular localization. To better understand how HSV-1 gM localization is regulated, we evaluated its ability to bind gN and discovered it does so in both transfected and infected cells, an interaction strongly weakened by the deletion of the gM amino terminus. Functionally, while gN had no impact on gM localization, gM redirected gN from the endoplasmic reticulum (ER) to the TGN. Most interestingly, gN overexpression stimulated the formation of syncytia in the context of an infection by a nonsyncytial strain, indicating that gM and gN not only physically but also functionally interact and that gN modulates gM's activity on membrane fusion. H erpesviridae are among the most complex human viruses from the point of view of their large genomes and viral particle composition. Among them, herpes simplex virus 1 (HSV-1), the prototype of human alphaherpesviruses, incorporates its 152-kb genome into an icosahedral capsid surrounded by a multiprotein tegument layer and a cell-derived lipid layer containing over a dozen viral proteins (1, 2). Of the latter, those mediating viral entry, namely, gB, gD, and the gH/gL complex, are essential for the propagation of the virus (3). In contrast, the viral glycoprotein M (gM) is conserved throughout the family and typically critical for beta-and gammaherpesviruses but is not essential for most alphaherpesviruses, including HSV-1 (4-16). Consequently, when gM is depleted from HSV-1 or the related alphaherpesvirus pseudorabies virus, viral yields are minimally reduced by 3-to 50-fold. However, its impact is substantially increased when U L 11 and gE/gI are codepleted in combination with gM, likely due to overlapping functions between these viral proteins (5,(17)(18)(19). IMPORTANCE HSV-1 gM is an important modulator of virally induced cell-cell fusion and viral entry, a process that is likely finely modulatedDespite its nonessential status in tissue culture, gM of several alphaherpesviruses has been associated with a number of functions throughout the viral life cycle (7,10,(19)(20)(21)(22). The glycoprotein is thus known to downregu...

“…About half of the virusencoded proteins play critical roles in virus replication, but relatively few have been found to have specific functions in cell-to-cell spread of virus. The essential components of the virion entry apparatus, gB, gD, and gH/gL, are required for cell-to-cell spread (7,17,30,52). It is likely that this is because cell-to-cell spread requires interaction of the virus entry proteins with cellular receptors and subsequent fusion of the virion envelope with the plasma membrane of the naïve host cell.…”

mentioning

confidence: 99%

Herpes Simplex Virus 1 pUL34 Plays a Critical Role in Cell-to-Cell Spread of Virus in Addition to Its Role in Virus Replication

Haugo

Szpara

Parsons

et al. 2011

Herpes simplex virus (HSV) pUL34 plays a critical role in virus replication by mediating egress of nucleocapsids from the infected cell nucleus. We have identified a mutation in pUL34 (Y68A) that produces a major defect in virus replication and impaired nuclear egress but also profoundly inhibits cell-to-cell spread and trafficking of gE. Virion release to the extracellular medium is not affected by the Y68A mutation, indicating that the mutation specifically inhibits cell-to-cell spread. We isolated extragenic suppressors of the Y68A plaque formation defect and mapped them by a combination of high-throughput Illumina sequencing and PCR-based screening. We found that suppression is highly correlated with a nonsense mutation in the US9 gene, which plays a critical role in cell-to-cell spread of HSV-1 in neurons. The US9 mutation alone is not sufficient to suppress the Y68A spread phenotype, indicating a likely role for multiple viral factors.Dissemination of herpes simplex virus (HSV) during recurrent disease in the host is dependent upon efficient viral replication and on the ability of the virus to spread from cell to cell in the face of the host innate and adaptive immune defenses. Cytoplasmic envelopment of HSV-1 virions is followed by vesicular transport of virions to the cell surface and secretion by fusion of the vesicle membrane with the plasma membrane (8,23,44). Transport of virions to cell membranes in contact with the extracellular medium results in release of free virions. Transport to surfaces apposed to other cells results in cell-tocell spread of virus infection. The mechanism by which virions are sorted to junctional or basolateral surfaces in epithelial and fibroblast cells is poorly characterized. About half of the virusencoded proteins play critical roles in virus replication, but relatively few have been found to have specific functions in cell-to-cell spread of virus. The essential components of the virion entry apparatus, gB, gD, and gH/gL, are required for cell-to-cell spread (7,17,30,52). It is likely that this is because cell-to-cell spread requires interaction of the virus entry proteins with cellular receptors and subsequent fusion of the virion envelope with the plasma membrane of the naïve host cell. A few additional viral proteins have been shown to be required for efficient cell-to-cell spread at least in some cell types. HSV-1 gE and gI form a heterodimeric complex that is required for efficient cell-to-cell spread in the nervous system in vivo (10,11,21,22,36). The gE/gI complex is also required for spread in cultured neuronal cells and in epithelial and fibroblast cells that form well-defined cell junctions (1, 10, 12, 36). The gE spread phenotype in epithelial cells requires sequences in the cytoplasmic tail of gE and also requires sorting of gE to basolateral cell surfaces and adherens junctions, where it colocalizes with ␤-catenin (12, 16, 37, 64). Deletion of US9 in pseudorabies virus (PRV) is associated with failure of viral spread in neuronal cultures and in vivo (5, 33). ...