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

Abstract

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...

Herpes Simplex Virus Internalization into Epithelial Cells Requires Na + /H + Exchangers and p21-Activated Kinases but neither Clathrin- nor Caveolin-Mediated Endocytosis

“…These results are consistent with previous studies in Vero, HEp-2, CHO-PILR␣, BHK, J-nectin1, C10 murine melanoma, J-HVEM, or the neuroblastoma SK-N-SH cells (27,30,32,77,78) and the fact that low pH does not account for conformational changes in gB during fusion (79,80). Indeed, in HEp-2 and PtK 2 cells, HSV-1 infection was even more efficient when endosomal acidification, and thus presumably virion degradation, had been inhibited.…”

Contribution of N-linked glycans on HSV-2 gB to cell–cell fusion and viral entry

“…For instance, gC has been shown to share the same capability as gB in viral absorption (Laquerre et al, 1998). In addition, HSV-1 gK, UL20, gM, gH, gB and PILRα can assemble a complex to regulate virus-cell fusion (Chouljenko et al, 2009(Chouljenko et al, , 2010Chowdhury et al, 2013;Kim et al, 2013). The glycoproteins dispensable for membrane fusion might enhance fusion efficiency by strengthening or stabilizing the association of the fusion core machinery or by interacting with gB directly to modulate its fusion activity.…”

Herpes Simplex Virus 1 Glycoprotein M and the Membrane-Associated Protein UL11 Are Required for Virus-Induced Cell Fusion and Efficient Virus Entry

“…We have shown that gK and UL20 are expressed in virion envelopes and are involved in virus entry, since deletion of gK or a small segment of gK that interacts with gB causes virions to enter more slowly than their parental wild-type virus into cells and alter their ability to utilize HSV-1-specific receptors (29,52,57). Similarly, virions produced in the absence of either gM or UL11 exhibited slower kinetics of entry into Vero cells than did their parental virus.…”