Pathogenesis of Herpes Simplex Virus Type 2 Virion Host Shutoff (vhs) Mutants

Abstract

During lytic infection, the virion host shutoff (vhs) protein mediates the rapid degradation of mRNA and the shutoff of host protein synthesis. In vivo, herpes simplex virus type 1 (HSV-1) mutants lacking vhs activity are profoundly attenuated. Homologs of vhs exist in all of the neurotropic herpesviruses, and the goal of this study was to determine the virulence of HSV-2 mutants lacking vhs. Two HSV-2 recombinants were used in this study: 333-vhsB, which has a lacZ cassette inserted into the N terminus of vhs, and 333d41, which has a 939-bp deletion in vhs. As expected, both 333-vhsB and 333d41 failed to induce the cellular RNA degradation characteristic of HSV. Corneal, vaginal, and intracerebral routes of infection were used to study pathogenesis. Both viruses grew to significantly lower titers in the corneas, trigeminal ganglia, vaginas, dorsal root ganglia, spinal cords, and brains of mice than wild-type and rescue viruses, with a correspondingly reduced induction of disease. Both viruses, however, reactivated efficiently from explanted trigeminal ganglia, showing that vhs is dispensable for reactivation. The lethality of 333d41 following peripheral infection of mice, however, was significantly higher than that of 333-vhsB, suggesting that some of the attenuation of 333-vhsB may be due to the presence of a lacZ cassette in the vhs locus. Taken together, these data show that vhs represents an important determinant of HSV-2 pathogenesis and have implications for the design of HSV-2 recombinants and vaccines.Herpes simplex virus (HSV) induces a rapid destabilization of mRNA due to the product of the viral UL41 gene, known as the virion host shutoff (vhs) protein. This 58-kDa phosphoprotein, packaged within the tegument of the virus, is released directly into the cytoplasm upon infection, where it immediately begins to degrade mRNA prior to any viral gene expression (7,23). Recent studies have demonstrated that vhs has endoribonucleolytic activity near the 5Ј end of target mRNA (3, 4, 15), which requires a cellular factor (18) but no other viral proteins (14,20). Viruses containing mutations within any of the four conserved domains in the UL41 gene do not cause RNA destabilization upon infection (8,22,23,25). Such mutants are viable in cell culture, and the effect of vhs deletion on viral replication in tissue culture is minimal (22).The genomes of HSV type 1 (HSV-1) and HSV-2, varicellazoster virus, equine herpesvirus, and pseudorabies virus all have homologs of vhs (1). The conservation of vhs in these and other neurotropic alphaherpesviruses and its apparent absence in beta-and gammaherpesviruses suggest that vhs plays a role in neuropathogenesis, although the role of vhs in this context has only been studied in HSV-1. The goal of this study was therefore to examine the contribution of vhs to the pathogenesis of HSV-2.The pathogenesis of HSV-1 and HSV-2 infections in humans and animal models has some general similarities and some important differences. HSV-1 is primarily associated with orolabial lesions, st...

Role of the UL41 Protein of Pseudorabies Virus in Host Shutoff, Pathogenesis and Induction of TNF-.ALPHA. Expression

“…In present study, the role of UL41 encoded vhs protein in pseudorabies virus (PRV, TNL strain) replication was characterized using a vhs loss of function mutant (41) in which the entire coding region of vhs was replaced by a GFP expression cassette under the control of a CMV promoter. Similar to previous observations recorded for HSV-1, the vhs mutant virus 41 shared similar growth kinetics with its wild type (wt) counterpart, and the yield of 41 progeny was only reduced by 3-to 5-fold compared to wt PRV at all infection times analyzed [25,26]. These results indicate that the function of vhs may be dispensable for PRV replication in cell culture systems.…”

Herpes Simplex Virus Type 2 Virion Host Shutoff Protein Regulates Alpha/Beta Interferon but Not Adaptive Immune Responses during Primary Infection In Vivo

“…333d41 has a targeted deletion within the UL41 gene between two XcmI sites, resulting in a 939-bp excision and complete lack of vhs activity. 333d41 R was constructed by cotransfecting full-length 333d41 DNA with p41SB5-B, a plasmid containing a BglII genomic fragment of HSV-2 333 that includes the UL41 gene (47). Briefly, 1 g of each DNA mixed with Lipofectamine (Invitrogen) was used to transfect Vero cells.…”

“…HSV-1 lacking vhs activity replicates to 1,000-fold-lower titers in the cornea, trigeminal ganglia, and brain of mice than wildtype virus and has impaired capacity to enter the central nervous system, establish latency, and undergo reactivation (48)(49)(50). vhs-deficient HSV-2 strains (333-vhsB or 333d41) also replicate much less efficiently than wild-type virus in the genital mucosa and nervous tissue of mice and cause less disease (47). vhs has been implicated in down-regulating major histocompatibility complex (MHC) class I (18,54) and class II (55) molecules.…”

“…Alternatively, the attenuation of HSV-1 and HSV-2 vhs null mutants within 24 to 48 h postinfection (47)(48)(49)(50) suggests a pivotal role for mediators of innate immunity in controlling acute infection. A key mediator of innate antiviral immunity to virus infection is the alpha/beta interferon (IFN-␣/␤) response.…”

The herpes simplex virus 1 U L 41 gene-dependent destabilization of cellular RNAs is selective and may be sequence-specific

“…The function of vhs appears to be twofold, to enable efficient transition from ␣ to ␤ and ␥ protein synthesis and to block host responses to infection. Indeed, ⌬U L 41 mutants are more sluggish in their replication and replicate poorly in immunocompetent experimental animal systems (7).…”