A Mutation in the UL24 Gene Abolishes Expression of the Newly Identified UL24.5 Protein of Herpes Simplex Virus 1 and Leads to an Increase in Pathogenicity in Mice

Abstract

Herpes simplex virus 1 (HSV-1) infects the host via epithelia and establishes latency in sensory neurons. The gene is conserved throughout the family, and the UL24 protein is important for efficient viral replication and pathogenesis. Multiple transcripts are expressed from the gene. The presence of a transcription initiation site inside the open reading frame of and an ATG start codon in the same open reading frame led us to suspect that another protein was expressed from the locus. To test our hypothesis, we constructed a recombinant virus that expresses a hemagglutinin tag at the C terminus of UL24. Western blot analysis revealed the expression of an 18-kDa protein that is not a degradation product of the full-length UL24, which we refer to as UL24.5. Ectopically expressed UL24.5 did not induce the dispersal of nucleolar proteins, as seen for UL24. In order to characterize the role of UL24.5, we constructed a mutant virus encoding a substitution of the predicted initiation methionine to a valine. This substitution eliminated the expression of the 18-kDa polypeptide. Unlike the UL24-null mutant (UL24X), which exhibits reduced viral yields, the-null mutant exhibited the same replication phenotype in cell culture as the parental strain. However, in a murine ocular infection model, we observed an increase in the incidence of neurological disorders with the mutant. Alignment of amino acid sequences for various herpesviruses revealed that the initiation site of UL24.5 is conserved among HSV-1 strains and is present in many herpesviruses. We discovered a new HSV-1 protein, UL24.5, which corresponds to the C-terminal portion of UL24. In contrast to the replication defects observed with HSV-1 strains that do not express full-length UL24, the absence of UL24.5 did not affect viral replication in cell culture. Moreover, in mice, the absence of UL24.5 did not affect viral titers in epithelia or trigeminal ganglia during acute infection; however, it was associated with a prolonged persistence of signs of inflammation. Strikingly, the absence of UL24.5 also led to an increase in the incidence of severe neurological impairment compared to results for wild-type control viruses. This increase in pathogenicity is in stark contrast to the reduction in clinical signs associated with the absence of full-length UL24. Bioinformatic analyses suggest that UL24.5 is conserved among all human alphaherpesviruses and in some nonhuman alphaherpesviruses. Thus, we have identified UL24.5 as a new HSV-1 determinant of pathogenesis.

Integrative functional genomics decodes herpes simplex virus 1

“…It thus remains unclear whether US3.5 is translated from an independent transcript or due to leaky scanning. Six of these NTTs (UL8.5, UL12.5, UL24.5, UL26.5, US1.5, and US3.5) had already been reported [33][34][35][36][37][38] . Only the NTT of the major DNA-binding protein pUL29 (ICP8; comprising aa 516-1212) had so far not been described.…”

Identification of a New Equid Herpesvirus 1 DNA Polymerase (ORF30) Genotype with the Isolation of a C2254/H752 Strain in French Horses Showing no Major Impact on the Strain Behaviour

“…HSV-1 UL24 has been shown to play a role in pathogenicity and to affect in vivo and in vitro replication and reactivation from latency [ 72 , 73 ]. This protein seems to carry numerous functions, such as viral gene expression regulation, dispersion of cellular proteins in the nucleus and glycoproteins distribution in the cytoplasm [ 74 , 75 ]. It was also shown to be required for EHV-1 pathogenicity in a mouse model [ 70 ].…”

Integrative functional genomics decodes herpes simplex virus 1

“…It thus remains unclear whether US3.5 is translated from an independent transcript or due to leaky scanning. Six of these NTTs (UL8.5, UL12.5, UL24.5, UL26.5, US1.5 and US3.5) had already been reported [31][32][33][34][35][36] . Only the NTT of the major DNA-binding protein pUL29 (ICP8;…”