Abstract
Bovine herpesvirus-1 (BoHV-1) is a major cause of rhinotracheitis and vulvovaginitis in cattle. VP8, the major tegument protein of BoHV-1, is essential for viral replication in the host. VP8 is phosphorylated by the viral kinase US3, mediating its translocation to the cytoplasm. VP8 remains nuclear when not phosphorylated. Interestingly, VP8 has a significant presence in mature BoHV-1YmVP8, in which the VP8 phosphorylation sites are mutated. This suggests that VP8 might be packaged during primary envelopment of BoHV-1. This was investigated by mass spectrometry and Western blotting, which showed VP8, as well as VP22, to be constituents of the primary enveloped virions. VP8 and VP22 were shown to interact via co-immunoprecipitation experiments, in both BoHV-1-infected and VP8-transfected cells. VP8 and VP22 also co-localised with one another and with nuclear lamin-associated protein 2 in BoHV-1-infected cells, suggesting an interaction between VP8 and VP22 in the perinuclear region. In cells infected with VP22-deleted BoHV-1 (BoHV-1ΔUL49), VP8 was absent from the primary enveloped virions, implying that VP22 might be critical for the early packaging of VP8. In conclusion, a novel VP22-dependent mechanism for packaging of VP8 was identified, which may be responsible for a significant amount of VP8 in the viral particle.
Highlights
Bovine herpesvirus-1 (BoHV-1) belongs to the family Alphaherpesviridae and is a major cause of bovine rhinotracheitis and vulvovaginitis [1]; it causes reduced milk production as well as infertility in cows and, adversely affects the dairy industry [2]
We demonstrated that VP8 and VP22 interact and co-localize in the perinuclear region in cells infected with wild-type BoHV-1 or BoHV-1-YmVP8
In order to examine the possibility of VP8 being packaged at the early tegumentation stage, primary enveloped virions were isolated from the perinuclear region and tested for the presence of VP8 by mass spectrometry and Western blotting
Summary
Bovine herpesvirus-1 (BoHV-1) belongs to the family Alphaherpesviridae and is a major cause of bovine rhinotracheitis and vulvovaginitis [1]; it causes reduced milk production as well as infertility in cows and, adversely affects the dairy industry [2]. During entry into the host cell, HHV-1 and BoHV-1 lose the lipid envelope, and shed some of their tegument proteins. The capsid gains a primary envelope from the inner nuclear membrane, and buds into the perinuclear space [8,11]. It is known for HHV-1 that a few tegument proteins are packaged at this stage of primary envelopment [12]. The primary enveloped virus particle fuses with the outer nuclear membrane and loses the primary envelope, while retaining some of the tegument proteins, and buds out of the nucleus [13]. As the virus particle proceeds through the cytoplasm towards its site of maturation at the Golgi, the tegument undergoes changes in its composition due to loss and/or addition of proteins [12]
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