The Amino Terminus of Herpes Simplex Virus Type 1 Glycoprotein K (gK) Modulates gB-Mediated Virus-Induced Cell Fusion and Virion Egress

Abstract

Herpes simplex virus type 1 (HSV-1)-induced cell fusion is mediated by viral glycoproteins and other membrane proteins expressed on infected cell surfaces. Certain mutations in the carboxyl terminus of HSV-1 glycoprotein B (gB) and in the amino terminus of gK cause extensive virus-induced cell fusion. Although gB is known to be a fusogenic glycoprotein, the mechanism by which gK is involved in virus-induced cell fusion remains elusive. To delineate the amino-terminal domains of gK involved in virus-induced cell fusion, the recombinant viruses gK⌬31-47, gK⌬31-68, and gK⌬31-117, expressing gK carrying in-frame deletions spanning the amino terminus of gK immediately after the gK signal sequence (amino acids [aa] 1 to 30), were constructed. Mutant viruses gK⌬31-47 and gK⌬31-117 exhibited a gK-null (⌬gK) phenotype characterized by the formation of very small viral plaques and up to a 2-log reduction in the production of infectious virus in comparison to that for the parental HSV-1(F) wild-type virus. The gK⌬31-68 mutant virus formed substantially larger plaques and produced 1-log-higher titers than the gK⌬31-47 and gK⌬31-117 mutant virions at low multiplicities of infection. Deletion of 28 aa from the carboxyl terminus of gB (gB⌬28syn) caused extensive virus-induced cell fusion. However, the gB⌬28syn mutation was unable to cause virus-induced cell fusion in the presence of the gK⌬31-68 mutation. Transient expression of a peptide composed of the amino-terminal 82 aa of gK (gKa) produced a glycosylated peptide that was efficiently expressed on cell surfaces only after infection with the HSV-1(F), gK⌬31-68, ⌬gK, or UL20-null virus. The gKa peptide complemented the gK⌬31-47 and gK⌬31-68 mutant viruses for infectious-virus production and for gK⌬31-68/gB⌬28syn-mediated cell fusion. These data show that the amino terminus of gK modulates gB-mediated virus-induced cell fusion and virion egress.Herpes simplex virus type 1 (HSV-1) specifies at least 11 virally encoded glycoproteins, as well as several nonglycosylated and lipid-anchored membrane-associated proteins, which serve important functions in virion infectivity and virus spread. Although cell-free enveloped virions can efficiently spread viral infection, virions can also spread by causing cell fusion of adjacent cellular membranes. Virus-induced cell fusion, which is caused by viral glycoproteins expressed on infected cell surfaces, enables transmission of virions from one cell to another, avoiding extracellular spaces and exposure of free virions to neutralizing antibodies (reviewed in reference 56). Most mutations that cause extensive virus-induced cell-to-cell fusion (syncytial or syn mutations) have been mapped to at least four regions of the viral genome: the UL20 gene (5,42,44); the UL24 gene (37, 58); the UL27 gene, encoding glycoprotein B (gB) (9, 51); and the UL53 gene, coding for gK (7,15,35,53,54,57).Increasing evidence suggests that virus-induced cell fusion is mediated by the concerted action of glycoproteins gD, gB, and gH/gL. Recent studies have shown tha...

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

“…African green monkey kidney (Vero) cells were obtained from the American Type Culture Collection (Rockville, MD) and were grown and propagated in growth medium consisting of Dulbecco's modified Eagle medium (DMEM) (Gibco-BRL, Grand Island, NY) supplemented with 10% fetal bovine serum (FBS) and antibiotics (22). VK302 cells permanently expressing gK were originally obtained from David Johnson (Oregon Health Sciences University, Portland, OR) and maintained in growth medium.…”

“…GFPtagged vesicular stomatitis virus (VSV-GFP) was a kind gift from John Rose (Yale University, New Haven, CT). The mutant viruses gK⌬31-68, gB⌬28syn (deletion of 28 aa from the carboxyl terminus of gB), and gK⌬31-68/gB⌬28syn were described earlier (22).…”

“…Viral plaques were visualized by immunohistochemistry as we have previously described (29)(30)(31)(32). Analysis of one-step growth kinetics was performed as described earlier (20,22,33). Confluent Vero cell monolayers were infected with each virus at 4°C for 1 h at a multiplicity of infection (MOI) of either 0.1 or 2.…”

“…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 virus (20,21).…”

p32 Is a Novel Target for Viral Protein ICP34.5 of Herpes Simplex Virus Type 1 and Facilitates Viral Nuclear Egress

“…Besides viral glycoproteins (such as gB, gK, gD, gE, and gM) (7)(8)(9)(10), several tegument proteins are reported to modulate the nuclear egress of HSV-1. For example, UL31 and UL34 are required for conformational changes of nuclear lamina in HSV-1-infected cells (11)(12)(13)(14).…”