Date of Award

5-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Program

Biomedical Sciences

Track

Microbial Pathogenesis, Immunology, and Inflammation

Research Advisor

Kui Li, Ph.D.

Committee

Santanu Bose, Ph.D Tony N. Marion, Ph.D Stacey L. Schultz-Cherry, Ph.D Michael A. Whitt, Ph.D

Abstract

The induction of Type I Interferons (IFNs) is a powerful and rapid innate defense mechanism against viral infection, and many viruses have developed elaborate strategies to overcome the antiviral effects of IFN, ensuring their survival and replication. Severe acute respiratory syndrome coronavirus (SARS-CoV) is a highly pathogenic virus that causes severe lung disease in humans and is associated with high mortality rates. SARS-CoV, like all other successful viruses, encode proteins that counteract the innate immune response. A number of reports have indicated the papain-like protease (PLpro) domain of SARS-CoV Non-Structural Protein 3 (NSP3) as a powerful interferon antagonist, by suppressing interferon regulatory factor 3 (IRF3) dependent innate antiviral defenses. IRF3 plays a key role in viral-induced type I IFN induction pathway. Thus, viruses are well-known to evade the establishment of an antiviral state by regulating the activation of IRF3. However, functional studies detailing the PLpro IFN antagonistic abilities, are not describe in the context of the full length nsp3 protein, in which it is contained in virus infected cells. Nsp3 is the largest replicase gene product in the coronavirus genome, which contains several functional domains that are required for coronavirus replication. Establishment of a stable and controllable CoV-nsp3 expression system will allow the physiological relevant study of the PLpro mediated function of this protein. Here, I described the development of tetracycline-inducible mammalian cell lines for stable expression of the full length nsp3 of HCoV-OC43, HCoV-NL63, MERS-CoV, and SARS-CoV, respectively. Although these cell lines exhibited stable and tight control of nsp3 expression in the presence of tetracycline, I observed a variation in CoV’s nsp3 protein expression levels. However, HeLa-Fit-SCoV-nsp3 and HeLa-Fit-SCoV-nsp3-delPLP stable cell lines expressed SARS-nsp3 and SARS-nsp3-delPLP robustly and at comparable levels. I found that expression of SARS-CoV nsp3 compromised virus-induced expression of IRF-3-dependent antiviral genes and that such ability depended on the PLpro domain. In agreement with our previous study examining the effects of the PLpro domain, the inhibitory effect was downstream of the IRF-3 kinases while upstream of IRF-3. Overall, my data demonstrates that SARS-CoV nsp3 is a bona fide interferon antagonist, which acts through PLpro-mediated suppression of IRF-3 activation.

ORCID

http://orcid.org/0000-0002-3829-365X

DOI

10.21007/etd.cghs.2016.0393

Available for download on Friday, June 22, 2018

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