Distinctions between Bovine Herpesvirus 1 and Herpes Simplex Virus Type 1 VP22 Tegument Protein Subcellular Associations

Abstract

The alphaherpesvirus tegument protein VP22 has been characterized with multiple traits including microtubule reorganization, nuclear localization, and nonclassical intercellular trafficking. However, all these data were derived from studies using herpes simplex virus type 1 (HSV-1) and may not apply to VP22 homologs of other alphaherpesviruses. We compared subcellular attributes of HSV-1 VP22 (HVP22) with bovine herpesvirus 1 (BHV-1) VP22 (BVP22) using green fluorescent protein (GFP)-fused VP22 expression vectors. Fluorescence microscopy of cell lines transfected with these constructs revealed differences as well as similarities between the two VP22 homologs. Compared to that of HVP22, the BVP22 microtubule interaction was much less pronounced. The VP22 nuclear interaction varied, with a marbled or halo appearance for BVP22 and a speckled or nucleolus-bound appearance for HVP22. Both VP22 homologs associated with chromatin at various stages of mitosis and could traffic from expressing cells to the nuclei of nonexpressing cells. However, distinct qualitative differences in microtubule, nuclear, and chromatin association as well as trafficking were observed. The differences in VP22 homolog characteristics revealed in this study will help define VP22 function within HSV-1 and BHV-1 infection.As with those of other alphaherpesviruses, the bovine herpesvirus 1 (BHV-1) virion contains a complex structure called the tegument located between the nucleocapsid and the virus envelope (21). Limited data elucidating the functions of the various BHV-1 tegument proteins exist. In fact, practically all information about this crucial alphaherpesvirus virion structure has been obtained from studies with herpes simplex virus type 1 (HSV-1). Tegument proteins are first to encounter the intracellular environment and provide essential functions to subjugate the host cell (20). The tegument can assemble into a stable structure without capsid interaction, and its assembly or dissociation depends on the phosphorylation state of its structural proteins (15,21). However, the site and mechanisms of tegument assembly and the functions of its protein components are largely unknown.Homologs of the major HSV-1 tegument proteins VP13/14, VP16, and VP22 are found in BHV-1. Available information suggests similar as well as distinct roles for each BHV-1 and HSV-1 tegument homolog. The BHV-1 homolog to HSV-1 VP13/14 (HVP13/14) is BHV-1 VP8 (BVP8), the most abundant BHV-1 protein (14). Like HVP13/14, BVP8 contains Olinked carbohydrates acquired during transport of tegumented nucleocapsids through the Golgi (27). Compared to HVP13/ 14, BVP8 has less affinity for the nucleocapsid (19). Whether BVP8 can modulate alpha gene expression as does HVP13/14 is not known (30). HVP16 and BVP16 are both transcription activators that can recruit host homeodomain proteins Oct-1 and HCF into a transcriptional regulatory complex. However, they differ in DNA recognition, binding to HSV-1-or BHV-1-specific response element sequences (13). BVP22, like HVP22, is a phosp...

Enhanced suicide gene effect by adenoviral transduction of a VP22-cytosine deaminase (CD) fusion gene

“…39 Others concluded that methanol fixation is merely mimicking VP22-mediated protein transport. 40 This is contradicted by a report only investigating the fixation procedures of VP22 chimaeric proteins 31 together with our present analysis on quantitating a significant enhancement of the suicide gene effect. Additionally, many studies are dealing with the GFP-VP22 fusion being the only transgene tested.…”

“…23,25 However, the yellow fluorescent protein (YFP) mutant is described to be more sensitive than GFP, so that detection of VP22 transport in live cells has been reported. 40 Moreover, the same study indicated that the transport property of the bovine herpes virus homologue of VP22 may be more effective than the HSV-1 protein.…”

Mapping of herpes simplex virus-1 VP22 functional domains for inter- and subcellular protein targeting

“…In previous studies it has been shown that a GFP-VP22 fusion protein retains the properties of the native VP22 in a recombinant HSV-1 virus, 5 and allowed the characterisation in detail of the subcellular localisation of VP22 1 and its intercellular transfer. [6][7][8][9] GFP-VP22 fusion protein has been found to retain the intercellular trafficking properties of VP22 in all the cell lines studied.…”

Direct evidence for the absence of intercellular trafficking of VP22 fused to GFP or to the herpes simplex virus thymidine kinase

“…Since two groups claimed that they could detect the transport of GFP/VP22 in live cells by direct fluorescence, 44,45 this possibility was carefully investigated using tagged recipient cells. MCF-7 cells expressing GFP/VP22 were incubated for 24 h with an equal number of MCF-7 cells tagged with DsRed2, and the cell mixture was analyzed by double color fluorescence.…”