[Show abstract][Hide abstract] ABSTRACT: The alphaherpesvirus envelope protein Us9 is a type II viral membrane protein that is required for anterograde spread of bovine herpesvirus 5 (BHV-5) infection from the olfactory receptor neurons to the brain. In a rabbit seizure model, Us9-deleted BHV-5 failed to invade the central nervous system (CNS) following intranasal infection. However, when injected directly into the olfactory bulb, retrograde-spread infection from the olfactory bulb (OB) to the piriform cortex and other areas connected to the OB was not affected. In contrast to BHV-5, wild-type BHV-1 failed to invade the CNS following intranasal infection. In this study, we show that mature BHV-1 Us9 is a 30- to 32-kDa protein, whereas mature BHV-5 Us9 is an 18- to 20-kDa protein. In vitro, BHV-1 Us9 is expressed at 3 h postinfection (hpi), whereas BHV-5 Us9 is expressed at 6 hpi. Despite these differences, BHV-1 Us9 not only complemented for BHV-5 Us9 and rescued the anterograde-spread defect of the BHV-5 Us9-deleted virus but conferred increased neurovirulence and neuroinvasiveness in our rabbit seizure model. Rabbits infected with BHV-5 expressing BHV-1 Us9 showed severe neurological signs at 5 days postinfection, which was 1 to 2 days earlier than BHV-5 wild-type or Us9-reverted BHV-5 virus. The data underscore the importance of both Us9 genes for virion anterograde transport and neuroinvasiveness. However, Us9 is not the determinant of the differential neuropathogenesis of BHV-1 and BHV-5.
Full-text · Article · Jun 2006 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: The bovine herpesvirus 5 (BHV-5) gE ectodomain contains a glycine-rich epitope coding region (gE5 epitope), residues 204 to 218, that is significantly different from the corresponding gE region of BHV-1. Deletion of the gE epitope significantly reduced the neurovirulence of BHV-5 in rabbits. Pulse-chase analyses revealed that the epitope-deleted and wild-type gE were synthesized as N-glycosylated endoglycosidase H-sensitive precursors with approximate molecular masses of 85 kDa and 86 kDa, respectively. Like the wild-type gE, epitope-deleted gE complexed with gI and was readily transported from the endoplasmic reticulum. Concomitantly, the epitope-deleted and wild-type gE acquired posttranslational modifications in the Golgi leading to an increased apparent molecular mass of 93-kDa (epitope-deleted gE) and 94-kDa (wild-type gE). The kinetics of mutant and wild-type gE processing were similar, and both mature proteins were resistant to endoglycosidase H but sensitive to glycopeptidase F. The gE epitope-deleted BHV-5 formed wild-type-sized plaques in MDBK cells, and the epitope-deleted gE was expressed on the cell surface. However, rabbits infected intranasally with gE epitope-deleted BHV-5 did not develop seizures, and only 20% of the infected rabbits showed mild neurological signs. The epitope-deleted virus replicated efficiently in the olfactory epithelium. However, within the brains of these rabbits there was a 10- to 20-fold reduction in infected neurons compared with the number of infected neurons within the brains of rabbits infected with the gE5 epitope-reverted and wild-type BHV-5. In comparison, 70 to 80% of the rabbits exhibited severe neurological signs when infected with the gE5 epitope-reverted and wild-type BHV-5. These results indicated that anterograde transport of the gE epitope-deleted virus from the olfactory receptor neurons to the olfactory bulb is defective and that, within the central nervous system, the gE5 epitope-coding region was required for expression of the full virulence potential of BHV-5.
Preview · Article · Jun 2004 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: Bovine herpesvirus 5 (BHV-5) is a neurovirulent alphaherpesvirus that causes fatal encephalitis in calves. In a rabbit model, the virus invades the central nervous system (CNS) anterogradely from the olfactory mucosa following intranasal infection. In addition to glycoproteins E and I (gE and gI, respectively), Us9 and its homologue in alphaherpesviruses are necessary for the viral anterograde spread from the presynaptic to postsynaptic neurons. The BHV-5 Us9 gene sequence was determined, and the predicted amino acid sequence of BHV-5 Us9 was compared with the corresponding Us9 sequences of BHV-1.1. Alignment results showed that they share 77% identity and 83% similarity. BHV-5 Us9 peptide-specific antibody recognized a doublet of 17- and 19-kDa protein bands in BHV-5-infected cell lysates and in purified virions. To determine the role of the BHV-5 Us9 gene in BHV-5 neuropathogenesis, a BHV-5 Us9 deletion recombinant was generated and its neurovirulence and neuroinvasive properties were compared with those of a Us9 rescue mutant of BHV-5 in a rabbit model. Following intranasal infection, the Us9 rescue mutant of BHV-5 displayed a wild-type level of neurovirulence and neural spread in the olfactory pathway, but the Us9 deletion mutant of BHV-5 was virtually avirulent and failed to invade the CNS. In the olfactory mucosa containing the olfactory receptor neurons, the Us9 deletion mutant virus replicated with an efficiency similar to that of the Us9 rescue mutant of BHV-5. However, the Us9 deletion mutant virus was not transported to the bulb. Confocal microscopy of the olfactory epithelium detected similar amounts of virus-specific antigens in the cell bodies of olfactory receptor neuron for both the viruses, but only the Us9 rescue mutant viral proteins were detected in the processes of the olfactory receptor neurons. When injected directly into the bulb, both viruses were equally neurovirulent, and they were transported retrogradely to areas connected to the bulb. Taken together, these results indicate that Us9 is essential for the anterograde spread of the virus from the olfactory mucosa to the bulb.
Preview · Article · May 2002 · Journal of Virology