Ectromelia virus accumulates less double-stranded RNA compared to vaccinia virus in BS-C-1 cells

Abstract

Most orthopoxviruses, including vaccinia virus (VACV), contain genes in the E3L and K3L families. The protein products of these genes have been shown to combat PKR, a host defense pathway. Interestingly, ectromelia virus (ECTV) contains an E3L ortholog but does not possess an intact K3L gene. Here, we gained insight into how ECTV can still efficiently evade PKR despite lacking K3L. Relative to VACV, we found that ECTV-infected BS-C-1 cells accumulated considerably less double-stranded (ds) RNA, which was due to lower mRNA levels and less transcriptional read-through of some genes by ECTV. The abundance of dsRNA in VACV-infected cells, detected using a monoclonal antibody, was able to activate the RNase L pathway at late time points post-infection. Historically, the study of transcription by orthopoxviruses has largely focused on VACV as a model. Our data suggest that there could be more to learn by studying other members of this genus.

Ectromelia virus lacking the E3L ortholog is replication-defective and nonpathogenic but does induce protective immunity in a mouse strain susceptible to lethal mousepox

“…With respect to poxviruses, it has been known for some time that vaccinia virus (VACV) forms abundant amounts of dsRNA, especially during intermediate and late time points of the infection cycle (i.e., after DNA replication; “post-replicative”) (Boone et al, 1979; Colby and Duesberg, 1969; Colby et al, 1971; Duesberg and Colby, 1969). Other orthopoxviruses, such as cowpox virus, also form dsRNA albeit to a varying degree relative to VACV (Frey et al, 2017). The mechanism of dsRNA formation has been discussed elsewhere (Arndt et al, 2016; Frey et al, 2017).…”

“…Other orthopoxviruses, such as cowpox virus, also form dsRNA albeit to a varying degree relative to VACV (Frey et al, 2017). The mechanism of dsRNA formation has been discussed elsewhere (Arndt et al, 2016; Frey et al, 2017). Briefly, it has been demonstrated using VACV as a model that dsRNA forms as a result of several factors: minimal intergenic space, convergent transcription from opposite DNA strands, and inefficient termination of transcription, particularly during post-replicative time points (Xiang et al, 2000; 1998).…”

The herpes simplex virus host shutoff (vhs) RNase limits accumulation of double stranded RNA in infected cells: Evidence for accelerated decay of duplex RNA

“…Our procedure was modelled on previous reports [81–83]. HFF and HeLa cells were mock infected or infected with the indicated viruses at MOI 10 for 12 hours.…”

Myxoma Virus-Encoded Host Range Protein M029: A Multifunctional Antagonist Targeting Multiple Host Antiviral and Innate Immune Pathways

“…To counteract the host responses to viral dsRNA, viruses either sequester it, degrade it, or interfere with the host cell sensing machinery or effector pathways. Thus, the production of less dsRNA (presumably by minimizing late run-on transcription compared to VACV) can be a strategy for some poxviruses such as MPXV, ECTV, and MYXV to subvert host activation of innate immune responses [ 58 , 59 ]. As an additional measure, these viruses also encode E3-like dsRNA binding proteins ( Figure 2 ).…”