Effects of Orf Virus on the Inflammation Signalling Pathways of the Toll-like, Interleukin-1 and Tumor Necrosis Factor Receptor Families
Poxviruses are complex, large double stranded DNA viruses that replicate in the cytoplasm of infected cells. The early phase of infection involves a two step uncoating process, firstly releasing viral core structures, then later viral DNA into the host cell before completion of their replicative lifecycle. Orf virus is the type species of the parapoxvirus genus, which infects primarily sheep and goats in addition to humans by zoonosis transmission. Resulting symptoms are characterised by rapidly developing acute pustular lesions. Orf virus is known to encode several immuno-modulatory factors to permit its replication in the presence of strong host innate and inflammatory responses. Genomic sequencing and bioinformatics analysis have identified an orf virus gene (057) encoding a structural protein containing a phosphatase motif, with close homology to vaccinia virus VH1. As structural proteins, both 057 and VH1 are predicted to become immediately available in the host cytoplasm soon after virion uncoating, where targeted dephosphorylation of intracellular signalling pathways can ensue. This study set out to investigate the potential effect of an orf viral phosphatase on cell signalling pathways through central transcription factor NFĸB, a key upregulator of pro-inflammatory cytokine and chemokine genes. Several classes of receptors, notably, toll-like receptor 4, interleukin-1 and tumor necrosis factor receptor families strongly induce NFĸB by virtue of adapter proteins which transduce signals mediated via phosphorylation and ubiquitylation events. These pathways converge on the IKK complex, which in turn phosphorylates IĸB-α, an inhibitory protein that sequesters NFĸB-p65, resulting in ubiquityn-proteasomal targeted degradation of IĸB-α effectively liberating NFĸB-p65 to undergo nuclear translocation. Assays were performed in HeLa cells to establish stimulatory dynamics and kinetics of NFĸB-p65 activation through induction with respective ligands, LPS, IL-1β, and TNF-α of the aforementioned receptors. Lysates were prepared, resolved by SDS-page and western blot analysis to determine endogenous levels of IĸB-α, and in addition to phosphorylated levels of NFĸB-p65. Initial results from preliminary assays showed rapid phosphorylation kinetics of NFĸB-p65 observable within 10 minutes following induction. The effects upon infection of cells with orf virus were then examined. The most notable result revealed an apparent temporal delay in the maximal levels of phosphorylated NFĸB-p65 induced by LPS and TNF-α when comparing mock and orf virus infected cells with a shift in the accumulation time of maximal levels of phosphorylated NFĸB-p65. Although definitive results of the involvement of orf structural protein 057 in this observation remain inconclusive at this stage, this effect could potentially be attributed to an orf virion-associated phosphatase due to the occurrence preceding viral de novo protein synthesis which is known to begin approximately 4 hours post infection.
Advisor: Fleming, Stephen
Degree Name: Bachelor of Biomedical Sciences with Honours
Degree Discipline: Microbiology & Immunology
Publisher: University of Otago
Keywords: Orf virus; Toll-like receptor; parapoxvirus; innate immunity
Research Type: Thesis