Abstract
Enveloped animal viruses enter host cells either by direct fusion at neutral pH or by endocytosis. Herpes simplex virus (HSV) is believed to fuse with the plasma membrane of cells at neutral pH, and the glycoproteins gB and gD have been implicated in virus entry and cell fusion. Using cloned gB or gD genes, we show that cells expressing HSV-1 glycoproteins gB or gD can undergo fusion to form polykaryons by exposure only to acidic pH. The low pH-induced cell fusion was blocked in the presence of monoclonal antibodies specific to the glycoproteins. Infection of cells expressing gB or gD glycoproteins with HSV-1 inhibited the low pH-induced cell fusion. The results suggest that although the glycoproteins gB and gD possess fusogenic activity at acidic pH, other HSV proteins may regulate it such that in the virus-infected cell, this fusion activity is blocked.
Highlights
Enveloped animal viruses enter host cells either by direct fusion at neutral pH or by endocytosis
Infection of cells expressing gB or gD glycoproteins with Herpes simplex virus (HSV)-1, inhibited the low pH-induced cell fusion. These results suggest that endocytosis may play a role in HSV-1 entry; the low pH-induced cell fusion mediated by gB and gD glycoproteins may be regulated by the expression of other viral gene products
The resu1t.s presented in this paper show that HSV-1 glycoproteins gB and gD, when expressed in mammalian cells in the absence of any other HSV-1 gene products, can induce cell fusion under acidic conditions
Summary
Construction of Expression Plasmids-The construction of plasmid p9gB containing gB-1 gene inserted into the COS cell expression vector p91023 [27] has already been described [25]. The medium was washed off with phosphate-buffered saline, and the cells were incubated in the presence of regular medium for 2.5 h. COS cells transfected with p9gB or p9gD plasmids were treated with the antibodies as described by Noble et al [11]. Cells were incubated for 2.5 h with regular medium containing the antibody. Following exposure to the fusion medium, cells were further incubated for 4 h in the presence of regular medium containing the antibody. The cells were fixed, stained, and examined for polykaryon formation as described earlier. Cells were exposed to fusion medium at pH 5.7 for 60 s, incubated in regular medium for 2.5 h, treated again with pH. 5.7 fusion medium for 60 s, incubated in regular medium for 4 h, and fixed, stained, and photographed using a phase-contrast microscope equipped with a camera.
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