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A double mutation in glycoprotein gB compensates for ineffective gD-dependent initiation of herpes simplex virus type 1 infection.

ABSTRACT: Herpes simplex virus (HSV) entry into cells is triggered by the binding of envelope glycoprotein D (gD) to a specific receptor, such as nectin-1 or herpesvirus entry mediator (HVEM), resulting in activation of the fusion effectors gB and gH and virus penetration. Here we report the identification of a hyperactive gB allele, D285N/A549T, selected by repeat passage of a gD mutant virus defective for nectin-1 binding through cells that express a gD-binding-impaired mutant nectin-1. The gB allele in a wild-type virus background enabled the use of other nectins as virus entry receptors. In addition, combination of the mutant allele with an epidermal growth factor receptor (EGFR)-retargeted gD gene yielded dramatically increased EGFR-specific virus entry compared to retargeted virus carrying wild-type gB. Entry of the gB mutant virus into nectin-1-bearing cells was markedly accelerated compared to that of wild-type virus, suggesting that the gB mutations affect a rate-limiting step in entry. Our observations indicate that ineffective gD activation can be complemented by hypersensitization of a downstream component of the entry cascade to gD signaling.

SUBMITTER: Uchida H

PROVIDER: S-EPMC2976401 | biostudies-literature | 2010 Dec

REPOSITORIES: biostudies-literature

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A double mutation in glycoprotein gB compensates for ineffective gD-dependent initiation of herpes simplex virus type 1 infection.

Uchida Hiroaki H Chan Janet J Goins William F WF Grandi Paola P Kumagai Izumi I Cohen Justus B JB Glorioso Joseph C JC

Journal of virology 20100922 23

Herpes simplex virus (HSV) entry into cells is triggered by the binding of envelope glycoprotein D (gD) to a specific receptor, such as nectin-1 or herpesvirus entry mediator (HVEM), resulting in activation of the fusion effectors gB and gH and virus penetration. Here we report the identification of a hyperactive gB allele, D285N/A549T, selected by repeat passage of a gD mutant virus defective for nectin-1 binding through cells that express a gD-binding-impaired mutant nectin-1. The gB allele in ...[more]

PMID: 20861246

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Project description:Herpes simplex virus type 1 (HSV-1) glycoprotein K (gK) and the UL20 protein (UL20p) are strictly required for virus-induced cell fusion, and mutations within either the gK or UL20 gene cause extensive cell fusion (syncytium formation). We have shown that gK forms a functional protein complex with UL20p, which is required for all gK and UL20p-associated functions in the HSV-1 life cycle. Recently, we showed that the amino-terminal 82 amino acids (aa) of gK (gKa) were required for the expression of the syncytial phenotype of the mutant virus gBDelta28 lacking the carboxyl-terminal 28 amino acids of gB (V. N. Chouljenko, A. V. Iyer, S. Chowdhury, D. V. Chouljenko, and K. G. Kousoulas, J. Virol. 83:12301-12313, 2009). This work suggested that the amino terminus of gK may directly or indirectly interact with gB and/or other viral glycoproteins. Two-way coimmunoprecipitation experiments revealed that UL20p interacted with gB in infected cells. Furthermore, the gKa peptide was coimmunoprecipitated with gB but not gD. Three recombinant baculoviruses were constructed, expressing the amino-terminal 82 aa of gKa together with either the extracellular portion of gB (30 to 748 aa), gD (1 to 340 aa), or gH (1 to 792 aa), respectively. Coimmunoprecipitation experiments revealed that gKa physically interacted with the extracellular portions of gB and gH but not gD. Three additional recombinant baculoviruses expressing gKa and truncated gBs encompassing aa 30 to 154, 30 to 364, and 30 to 500 were constructed. Coimmunoprecipitation experiments showed that gKa physically interacted with all three truncated gBs. Computer-assisted prediction of possible gKa binding sites on gB suggested that gKa may interact predominantly with gB domain I (E. E. Heldwein, H. Lou, F. C. Bender, G. H. Cohen, R. J. Eisenberg, and S. C. Harrison, Science 313:217-220, 2006). These results imply that the gK/UL20p protein complex modulates the fusogenic properties of gB and gH via direct physical interactions.

Project description:A cascade of protein-protein interactions between four herpes simplex virus (HSV) glycoproteins (gD, gH/gL, and gB) drive fusion between the HSV envelope and host membrane, thereby allowing for virus entry and infection. Specifically, binding of gD to one of its receptors induces a conformational change that allows gD to bind to the regulatory complex gH/gL, which then activates the fusogen gB, resulting in membrane fusion. Using surface plasmon resonance and a panel of anti-gD monoclonal antibodies (MAbs) that sterically blocked the interaction, we previously showed that gH/gL binds directly to gD at sites distinct from the gD receptor binding site. Here, using an analogous strategy, we first evaluated the ability of a panel of uncharacterized anti-gH/gL MAbs to block binding to gD and/or inhibit fusion. We found that the epitopes of four gD-gH/gL-blocking MAbs were located within flexible regions of the gH N terminus and the gL C terminus, while the fifth was placed around gL residue 77. Taken together, our data localized the gD binding region on gH/gL to a group of gH and gL residues at the membrane distal region of the heterodimer. Surprisingly, a second set of MAbs did not block gD-gH/gL binding but instead stabilized the complex by altering the kinetic binding. However, despite this prolonged gD-gH/gL interaction, "stabilizing" MAbs also inhibited cell-cell fusion, suggesting a unique mechanism by which the fusion process is halted. Our findings support targeting the gD-gH/gL interaction to prevent fusion in both therapeutic and vaccine strategies against HSV.IMPORTANCE Key to developing a human HSV vaccine is an understanding of the virion glycoproteins involved in entry. HSV employs multiple glycoproteins for attachment, receptor interaction, and membrane fusion. Determining how these proteins function was resolved, in part, by structural biology coupled with immunological and biologic evidence. After binding, virion gD interacts with a receptor to activate the regulator gH/gL complex, triggering gB to drive fusion. Multiple questions remain, one being the physical location of each glycoprotein interaction site. Using protective antibodies with known epitopes, we documented the long-sought interaction between gD and gH/gL, detailing the region on gD important to create the gD-gH/gL triplex. Now, we have identified the corresponding gD contact sites on gH/gL. Concurrently we discovered a novel mechanism whereby gH/gL antibodies stabilize the complex and inhibit fusion progression. Our model for the gD-gH/gL triplex provides a new framework for studying fusion, which identifies targets for vaccine development.

Project description:Oncolytic viruses gain cancer specificity in several ways. Like the majority of viruses, they grow better in cancer cells that are defective in mounting the host response to viruses. Often, they are attenuated by deletion or mutation of virulence genes that counteract the host response or are naturally occurring oncolytic mutants. In contrast, retargeted viruses are not attenuated or deleted; their cancer specificity rests on a modified, specific tropism for cancer receptors. For herpes simplex virus (HSV)-based oncolytics, the detargeting-retargeting strategies employed so far were based on genetic modifications of gD. Recently, we showed that even gH or gB can serve as retargeting tools. To enable the growth of retargeted HSVs in cells that can be used for clinical-grade virus production, a double-retargeting strategy has been developed. Here we show that several sites in the N terminus of gB are suitable to harbor the 20-amino-acid (aa)-long GCN4 peptide, which readdresses HSV tropism to Vero cells expressing the artificial GCN4 receptor and thus enables virus cultivation in the producer noncancer Vero-GCN4R cell line. The gB modifications can be combined with a minimal detargeting modification in gD, consisting in the deletion of two residues, aa 30 and 38, and replacement of aa 38 with the scFv to human epidermal growth factor receptor 2 (HER2), for retargeting to the cancer receptor. The panel of recombinants was analyzed comparatively in terms of virus growth, cell-to-cell spread, cytotoxicity, and in vivo antitumor efficacy to define the best double-retargeting strategy.IMPORTANCE There is increasing interest in oncolytic viruses, following FDA and the European Medicines Agency (EMA) approval of HSV OncovexGM-CSF, and, mainly, because they greatly boost the immune response to the tumor and can be combined with immunotherapeutic agents, particularly checkpoint inhibitors. A strategy to gain cancer specificity and avoid virus attenuation is to retarget the virus tropism to cancer-specific receptors of choice. Cultivation of fully retargeted viruses is challenging, since they require cells that express the cancer receptor. We devised a strategy for their cultivation in producer noncancer Vero cell derivatives. Here, we developed a double-retargeting strategy, based on insertion of one ligand in gB for retargeting to a Vero cell derivative and of anti-HER2 ligand in gD for cancer retargeting. These modifications were combined with a minimally destructive detargeting strategy. This study and its companion paper explain the clinical-grade cultivation of retargeted oncolytic HSVs and promote their translation to the clinic.

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A double mutation in glycoprotein gB compensates for ineffective gD-dependent initiation of herpes simplex virus type 1 infection.

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A double mutation in glycoprotein gB compensates for ineffective gD-dependent initiation of herpes simplex virus type 1 infection.

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