Entry of Herpes Simplex Virus 1 and Other Alphaherpesviruses via the Paired Immunoglobulin-Like Type 2 Receptor α

Herpes simplex virus (HSV) proteins specifically required for endocytic entry but not direct penetration have not been identified. HSVs deleted of gE, gG, gI, gJ, gM, UL45, or Us9 entered cells via either pH-dependent or pH-independent endocytosis and were inactivated by mildly acidic pH. Thus, the required HSV glycoproteins, gB, gD, and gH-gL, may be sufficient for entry regardless of entry route taken. This may be distinct from entry mechanisms employed by other human herpesviruses. Herpes simplex virus (HSV) has complex entry mechanisms and can utilize at least three distinct cellular pathways: pHindependent fusion at the plasma membrane or endocytosis, which can be either pH independent or pH dependent. For example, entry into Chinese hamster ovary (CHO) cells expressing nectin-1, human keratinocytes, and HeLa cells is through pH-dependent endocytosis (1, 2). HSV infects mouse melanoma cells expressing the nectin-1 receptor (B78C10) via pH-independent endocytosis (3). Infection of neurons and Vero cells occurs via pH-independent fusion at the plasma membrane (1, 2, 4-7).How HSV chooses its pathway remains an unanswered question. Both viral and cellular determinants contribute to the selection of the entry pathway. Different strains of HSV-1 can enter the same cell type via different pathways. In addition, different host receptors in the same cell type can direct HSV to different pathways (8). Studies in various cell backgrounds have indicated that cellular receptors such as nectin-1, nectin-2, paired immunoglobulin-like type 2 receptor alpha (PILR␣), and integrins can influence the entry route (3,(8)(9)(10)(11)(12)(13). This study tests the hypothesis that one or more envelope proteins direct HSV to an endocytic entry route. For HSV, gB, gD, and the heterodimer gH-gL are required via both the pH-independent and pH-dependent pathways (7,(14)(15)(16)(17)(18). Envelope proteins that are required for replication in Vero cells have been deemed "essential," and those that are dispensable are termed "nonessential" (19)(20)(21)(22). With the exception of gC and UL45p (17, 23), the contribution of the nonessential envelope proteins to the endocytic entry process has not been evaluated.The human herpesviruses Epstein-Barr virus (EBV) and human cytomegalovirus (HCMV) each use distinct but overlapping glycoprotein complexes to enter cells via endocytic or nonendocytic mechanisms (24-27). We explored the possibility that HSV might use a specific envelope protein together with the required complex of gB, gD, and gH-gL to selectively mediate entry via an endocytic pathway.To determine how HSV-1 infects cells via endocytic entry, equivalent inocula of a panel of membrane protein deletion viruses (Table 1) were added to B78C10 (B78 -nectin-1) cells (28). Infectivity in Vero cells as measured by plaque formation was set to 100%. Wild-type HSV-1 strains KOS and F had reduced plaquing efficiency on B78 receptor cells (Fig. 1) as reported previously (28). Compared to wild-type HSV F, each HSV mutant tested infected and formed pl...

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confidence: 81%

Contributions of Herpes Simplex Virus 1 Envelope Proteins to Entry by Endocytosis

Sari

Pritchard

Cunha

et al. 2013

“…Recently, it has been suggested that gBspecific receptors, such as PILR␣, or other cellular plasma membrane factors determine whether virions enter predominantly via fusion at the plasma membrane or via receptor-mediated endocytosis (pH dependent or pH independent), followed by fusion of the viral envelope with endosomal membranes (15).…”

mentioning

confidence: 99%

The Amino Terminus of Herpes Simplex Virus 1 Glycoprotein K Is Required for Virion Entry via the Paired Immunoglobulin-Like Type-2 Receptor Alpha

Chowdhury

Chouljenko

Naderi

et al. 2013

The herpes simplex virus 1 (HSV-1) glycoprotein K (gK)/UL20 protein complex is incorporated into virion envelopes and cellular membranes and functions during virus entry and cell-to-cell spread. To investigate the role of gK/UL20 in the context of a highly neurovirulent virus strain, the HSV-1(McKrae) genome was cloned into a bacterial artificial chromosome plasmid T he herpes simplex virus 1 (HSV-1) entry mechanism is both complex and unique among enveloped viruses, involving multiple glycoproteins for attachment, binding, and membrane fusion (1). Viral glycoproteins interact with different cellular receptors to facilitate virus entry. Initial attachment of the virus to cellular membranes is mediated by interaction of glycoproteins gB and gC with glycosaminoglycan (GAG) moieties of cell surface proteoglycans (2, 3). Attachment of virions to cellular membranes facilitates subsequent binding of gD to cellular receptors, including the herpesvirus entry mediator (HVEM, also called HveA), nectin-1 (HveC), and 3-O-sulfated heparan sulfate (4-6). Apparently, gB can also bind to additional cellular receptors, including paired immunoglobulin-like type 2 receptor alpha (PILR␣), nonmuscle myosin heavy chain IIA (NMHC-IIA), and myelin-associated glycoprotein (MAG) (7-9). Sequential binding of gD and then gB to their respective cellular receptors during virus entry and virus-induced cell-to-cell fusion is thought to alter gB's conformation, resulting in gB-mediated membrane fusion (1, 10-12).HSV-1 can enter into cells by utilizing different cell-dependent pathways: (i) virus entry into Vero and HEp-2 cells is predominantly mediated via pH-independent fusion of the viral envelope with the host cell membrane (13); (ii) virus entry into HeLa and Chinese hamster ovary (CHO) cells expressing the nectin-1 gD receptor is predominantly achieved via receptor-mediated endocytosis, followed by pH-dependent fusion of the viral envelope with endocytic membranes (14); and (iii) virus entry into C10 murine melanoma cells predominantly occurs via pH-independent endocytosis (13). Recently, it has been suggested that gBspecific receptors, such as PILR␣, or other cellular plasma membrane factors determine whether virions enter predominantly via fusion at the plasma membrane or via receptor-mediated endocytosis (pH dependent or pH independent), followed by fusion of the viral envelope with endosomal membranes (15).HSV-1 gK has been shown to be involved in neurovirulence and immunomodulation (16,17). We have shown that HSV-1 gK and UL20 functionally and physically interact, and this interaction is mandatory for their coordinated intracellular transport, cell surface expression, and functions in virion egress, virus-induced cell fusion, and virus entry (18)(19)(20)(21). Recently, we showed that the amino terminus of gK interacts with gB and gH and can complement gB-mediated cell fusion (22,23). Virions lacking the entire gK or the amino terminus of gK (amino acids [aa] 31 to 68) enter susceptible cells substantially slower than the wild-type vi...

“…It was recently shown that HSV-1 gB and PRV gB engage the paired immunoglobulin-like type 2 receptor ␣ (PILR␣) and that the process is required for viral entry into cells transduced with this receptor (1,40). PILRs are expressed in a variety of tissues, including the nervous system (40).…”

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confidence: 99%

Virion-Incorporated Glycoprotein B Mediates Transneuronal Spread of Pseudorabies Virus

Curanovic

Enquist

2009

Transneuronal spread of pseudorabies virus (PRV) is a multistep process that requires several virally encoded proteins. Previous studies have shown that PRV glycoprotein B (gB), a component of the viral fusion machinery, is required for the transmission of infection to postsynaptic, second-order neurons. We sought to identify the gB-mediated step in viral transmission. We determined that gB is not required for the sorting of virions into axons of infected neurons, anterograde transport, or the release of virions from the axon. trans or cis expression of gB on the cell surface was not sufficient for transneuronal spread of the virus; instead, efficient incorporation of gB into virions was required. Additionally, neuron-to-cell spread of PRV most likely does not proceed through syncytial connections. We conclude that, upon gB-independent release of virions at the site of neuron-cell contacts, the virion-incorporated gB/gH/gL fusion complex mediates entry into the axonally contacted cell by fusion of the closely apposed membranes.Alphaherpesviruses, which constitute a subfamily of the family Herpesviridae, include the human pathogens herpes simplex virus (HSV) and varicella-zoster virus and the swine pathogen pseudorabies virus (PRV). These closely related pantropic, neuroinvasive viruses establish latency in the peripheral nervous systems of their natural hosts. During the normal course of infection, periodic viral reactivation leads to recurrent epithelial lesions (38). Although rare in the natural host, transneuronal spread of the virus from the peripheral to the central nervous system (CNS) results in death or debilitating disease, such as encephalitis or keratitis (50). Nonnatural hosts infected with PRV almost invariably experience viral spread to the CNS and succumb to infection (36).Transneuronal spread of alphaherpesviruses is an incompletely understood multistep process that requires the concerted action of viral and cellular proteins. Following replication in the soma of an infected neuron, viral progeny may spread in the retrograde direction to the presynaptic cell or anterogradely to the postsynaptic cell. During anterograde spread of PRV, virus particles are sorted from the neuronal soma into the cognate axon. Upon entering the axonal compartment, virions are transported in a microtubule-dependent manner toward the synaptically connected cell (41). Recent in vitro evidence suggests that boutons en passant and axon termini serve as sites for PRV spread from the axon (13). Additionally, in vivo experiments demonstrate that the transneuronal spread of alphaherpesviruses is remarkably specific, occurring only between synaptically connected cells (15). This property has made alphaherpesviruses invaluable as neural circuit tracers in studies that aim to map the synaptic architecture of the CNS (14). However, the mechanisms that confer such specificity on the spread of infection are not well understood.The study of mechanisms underlying PRV trafficking revealed that the virally encoded membrane proteins Us9,...