Herpes Simplex Virus 2 Latency-Associated Transcript (LAT) Region Mutations Do Not Identify a Role for LAT-Associated MicroRNAs in Viral Reactivation in Guinea Pig Genital Models.

Despite the long-standing observation that herpes simplex virus (HSV) latency-associated transcript (LAT) promoter deletion viruses show impaired recurrence phenotypes in relevant animal models, the mechanism by which these sequences exert this phenotypic effect is unknown. We constructed and evaluated four mutant HSV-2 isolates with targeted mutations in the LAT promoter and LAT-associated microRNAs (miRNAs) affecting (i) the LAT TATA box; (ii) the LAT ICP4-binding site; (iii) miRNA I (miR-I) and miR-II (miR-I/II), which both target ICP34.5; and (iv) miR-III, which targets ICP0. While the LAT TATA box mutant caused milder acute infections than wild-type (WT) virus, there was no difference in the recurrence phenotype between these viruses. LAT and miRNA expression during latency was not impaired by this mutation, suggesting that other promoter elements may be more important for latent HSV-2 LAT expression. Mutation of the LAT ICP4-binding site also did not cause an in vivo phenotypic difference between mutant and WT viruses. Acute infection and reactivation from latency of the miR-I/II mutant were similar to those of its rescuant, although the acute infection was slightly reduced in severity relative to that caused by the wild-type virus. The miR-III mutant also exhibited WT phenotypes in acute and recurrent phases of infection. While they do not rule out an effect of these elements in human latency or reactivation, these findings do not identify a specific role for LAT or LAT-associated miRNAs in the HSV-2 LAT promoter deletion phenotype in guinea pigs. Thus, other sequences in this region may play a more important role in the long-studied LAT-associated phenotype in animals. IMPORTANCE While it has been known for several decades that specific HSV-1 and HSV-2 sequences near the LAT promoter are required for efficient viral reactivation in animal models, the mechanism is still not known. We constructed four mutant viruses with the goal of identifying critical sequence elements and of specifically testing the hypothesis that microRNAs that are expressed during latency play a role. Determination that specific LAT promoter sequences and miRNA sequences do not influence viral reactivation of HSV-2 helps to narrow down the search for the mechanism by which the virus controls its latency and recurrence phenotype.
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