Dissertation
Characterization of the anti-inflammatory effects of the Molluscum Contagiosum MC159 protein
(2013)
Abstract
The Molluscum Contagiosum Virus (MCV) is a dermotropic poxvirus that strictly infects humans. MCV infections produce umbilicated lesions that can persist for six to nine months in children and young adults. Currently there is no cure for MCV infections. Recent evidence suggests that the pro-inflammatory Tumor Necrosis Factor-α (TNF-α) and anti-viral interferon- β (IFN-β) cytokines are highly expressed in MCV lesions and surrounding tissue. Despite the expression of pro-inflammatory factors, MCV infections cause little inflammation. Not surprisingly, MCV encodes immunomodulatory proteins such as the MC159 protein to combat the effects of TNF-α and IFN-β. The work presented here details MC159 mediated inhibition of these cytokines through the NF-κΒ and IRF-3 transcription factors. TNF-α is a critical initiator of the pro-inflammatory response during infection. Previous studies found that MC159 is a potent inhibitor of the TNF-α pathway by blocking activation of the NF-κB pro-inflammatory transcription factor. Mutational analysis revealed that the RxDL motif within the N-terminal DED of MC159 is required for inhibition of NF-κB. Additionally, my results show that MC159 inhibits TNF-α, PMA and MyD88 induced NF-κB activity, suggesting MC159 targets a step in the pathway shared by these inducers. I hypothesized that MC159 targeted the IκB kinase (IKK) complex to inhibit NF-κB activation. To this end, I found that MC159 co-immunoprecipitated with the IKKγ subunit of the IKK complex, suggesting that MC159 targets the IKK complex to inhibit NF-κB activation. Interferon beta (IFN-β) initiates the primary anti-viral response during infection. IFN-β synthesis is triggered by viral infection when host cellular sensors detect byproducts of viral propagation (e.g. dsRNA). Activation of these sensors initiates a signaling cascade that results in the phosphorylation and subsequent activation of the TBK-1 kinase that in turn phosphorylates the Interferon Regulatory Factor-3 (IRF-3) transcription factor. I hypothesized that MC159 inhibits IFN-β protein synthesis. In support of this hypothesis, I found that MC159 inhibits IFN- β production in an NF-κB-independent manner. In addition, my results show MC159 inhibits phosphorylation of TBK-1 and IRF-3. Taken together, these data suggest that MC159 inhibits IFN-β activation by acting on the TBK-1 kinase complex. Mutational analysis revealed that either Death Effector Domain (DED), a protein:protein interaction domain, of the MC159 protein was sufficient for inhibition. Finally, I show homologs of MC159 including MCV MC160 and cellular FLIPL, inhibit IFN-β expression, suggesting DEDs are important for regulation of IFN-β responses.
Keywords
- Poxviruses,
- Immune evasion
Disciplines
Publication Date
2013
Degree
Ph.D.
Field of study
Microbiology
Department
Microbiology
Advisors
Shisler, Joanna L.
Citation Information
Crystal Randall. "Characterization of the anti-inflammatory effects of the Molluscum Contagiosum MC159 protein" (2013) Available at: http://works.bepress.com/crystal-randall/8/