Analysis of IE62 mutations found in Varicella-Zoster virus vaccine strains for transactivation activity

Abstract

Live attenuated vaccine strains have been developed for Varicella-Zoster virus (VZV). Compared to clinically isolated strains, the vaccine strains contain several non-synonymous mutations in open reading frames (ORFs) 0, 6, 31, 39, 55, 62, and 64. In particular, ORF62, encoding an immediate-early (IE) 62 protein that acts as a transactivator for viral gene expression, contains six non-synonymous mutations, but whether these mutations affect transactivation activity of IE62 is not understood. In this study, we investigated the role of non-synonymous vaccine-type mutations (M99T, S628G, R958G, V1197A, I1260V, and L1275S) of IE62 in Suduvax, a vaccine strain isolated in Korea, for transactivation activity. In reporter assays, Suduvax IE62 showed 2- to 4-fold lower transactivation activity toward ORF4, ORF28, ORF29, and ORF68 promoters than wild-type IE62. Introduction of individual M99T, S628G, R958G, or V1197A/I1260V/L1275S mutations into wild-type IE62 did not affect transactivation activity. However, the combination of M99T within the N-terminal Sp transcription factor binding region and V1197A/I1260V/L1275S within the C-terminal serine-enriched acidic domain (SEAD) significantly reduced the transactivation activity of IE62. The M99T/V1197A/I1260V/L1275S mutant IE62 did not show considerable alterations in intracellular distribution and Sp3 binding compared to wild-type IE62, suggesting that other alteration(s) may be responsible for the reduced transactivation activity. Collectively, our results suggest that acquisition of mutations in both Met 99 and the SEAD of IE62 is responsible for the reduced transactivation activity found in IE62 of the VZV vaccine strains and contributes to attenuation of the virus.

Whole Transcriptome Analyses Reveal Differential mRNA and microRNA Expression Profiles in Primary Human Dermal Fibroblasts Infected with Clinical or Vaccine Strains of Varicella Zoster Virus

“…To date, limited data has been published regarding the Korean vaccine strain SuduVax [10,11,31]. The comparative genome sequencing of clinical and vaccine strains of VZV revealed 24 vaccine-specific SNP sites that we previously detected in high passage clinical strains, such as Ellen, 32p72, YC01, and YC02 [20].…”

“…Given that ORF62 encodes for immediate early protein 62, which enables the activation of the majority of VZV promoters during lytic infection, ORF62 mutations may regulate the expression of many VZV genes. In fact, Ko et al previously reported that IE62 from SuduVax strains showed significantly reduced transactivation activity for the ORF4, ORF28, ORF29, and ORF68 promoters compared with wildtype IE62 from wildtype VZV strains [31]. Furthermore, IE62 suppresses innate immunity by inhibiting IRF expression as well as blocking the phosphorylation of IRF3 and inhibiting IFN production [32].…”

“…Furthermore, we conducted a comparative genomic analysis of VZV single nucleotide polymorphisms (SNPs) and identified 24 vaccine-specific sites that were commonly found in all vaccine strains, including SuduVax, VariVax, and VarilRix [12]. These nonsynonymous mutations were found in ORFs 0, 6,31,39,55,62, and 64 in all three vaccine strains. Over 40% (9 of 24) of the vaccine-type mutations were found in ORF62, which encodes the immediate early protein IE62, a known transactivator of VZV gene expression.…”

The Biology of Varicella-Zoster Virus Replication in the Skin

“…ORF62 is the gene that in the vOka strain contains the major number of SNPs compared to pOka, of which four are highly fixed, with two of them causing R958G and S628G substitutions in two highly conserved regions of the ORF62 gene [ 106 ]. It also appears that vOka IE62 induces a decreased level of gene transcription compared to pOka IE62 [ 107 ]. All in all, the current available evidence suggests that IE62 may play an important role in the skin attenuation of the VZV vaccine and studies aimed at elucidating these mechanisms are underway.…”