Date of Award

5-4-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Christopher F Basler

Second Advisor

Margo Brinton

Third Advisor

Donald Hamelberg

Fourth Advisor

Ming Luo

Abstract

Filoviruses belong to a family of RNA viruses that includes deadly emerging zoonotic pathogens such as Ebola and Marburg viruses. A concern of public health is whether recently discovered filoviruses have the potential to infect humans and cause disease. Filoviruses encode proteins that suppress innate immune signaling and this is postulated as a contributing determinant of virulence in animals. Měnglà virus (MLAV), a recently discovered bat filovirus, can infect human cells using a vesicular stomatitis virus (VSV)-MLAV GP pseudotype system. In Chapter 2, we characterize MLAV’s VP35, VP40 and VP24 proteins on their ability to regulate both human and bat type I IFN responses. Our assessment also includes MARV and EBOV protein homologs for points of comparison. Analogous to its filovirus equivalents, MLAV VP35 and VP40 proteins inhibited type I IFN responses. MLAV VP40 suppressed the IFNβ production pathway, and this is independent of its inhibition on the type I IFN signaling pathway. MLAV VP24 did not behave like either EBOV VP24, an inhibitor of type I IFN, or MARV VP24, an activator of the antioxidant response pathway.

Another critical concern is the lack of approved pan-filovirus therapeutics. Broad-spectrum nucleoside analogs have demonstrated antiviral activity against filoviruses. 3-deazaneplanocin (DzNep) and its brominated derivates (CL123, CL4033 and CL4053) are adenosine analogs and exhibit inhibition of non-segmented negative sense (NNS) RNA viruses. The antiviral effect is through inhibition of the enzyme, S-adenosylhomocysteine hydrolase (SAHase), resulting in obstruction of viral methyltransferase activity and consequently impaired translation of viral mRNA. The D-like-CL4033 and L-like-CL4053 exert antiviral activity against NNS RNA viruses, however the L-isomer, CL4053, has approximately a 1000 fold higher 50 percent inhibitory concentration (IC50) relative to the D-isomer, CL4033, suggesting an alternative antiviral mechanism. In chapter 3 we have elucidated, using VSV as a model NNS RNA virus, mechanisms of how DzNep, CL123, CL4033 and CL4053 exert their antiviral activity in cell culture. Our data indicates that DzNep, CL123 and CL4033 inhibit VSV by preventing viral mRNA cap methylation. A virus selected for CL123-resistance demonstrates cross-resistance against all derivatives, suggesting L-like-CL4053 may function through a similar mechanism of inhibition as the D-like-CL4033.

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