Date on Master's Thesis/Doctoral Dissertation

5-2023

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Microbiology and Immunology

Degree Program

Microbiology and Immunology, PhD

Committee Chair

Sokoloski, Kevin

Committee Co-Chair (if applicable)

Chung, Donghoon

Committee Member

Chung, Donghoon

Committee Member

Bagaitkar, Juhi

Committee Member

Mitchelle, Thomas

Committee Member

Lukashevich, Igor

Author's Keywords

Alphaviral; capsid; IRAK1; TLR

Abstract

Alphaviruses are positive-sense RNA viruses spread by mosquitos. They can cause a severe multi-joint febrile arthritis or encephalitis resulting in death or life-long cognitive impairments. To date there are no approved antiviral therapeutics or vaccine strategies for the treatment of alphaviruses creating a critical need to better understand the host pathogen interactions of alphaviruses that enable pathogenesis. It is known that alphaviruses evade innate immune responses by shutting down host transcription and translation, but these methods are dependent on viral gene expression and leave a critical time frame during early infection before viral gene expression has begun that the virus can be identified and responded to by host cells. In order to identify potential viral products that could serve to mask the virus during early infection Sindbis virus, a model alphavirus, was tested for the expression of proteins that could interfere with intracellular immune defenses. Through these efforts we discovered that the alphavirus capsid protein (CP) interacts with host Interleukin 1 Receptor Associated Kinase 1 (IRAK1) in order to block Toll-Like Receptor Signaling (TLR). IRAK1 is a key signaling kinase for several pro-inflammatory immune pathways and CP interacting with it provides a possible mechanism of inhibiting detection by host cells. Pursuing this interaction, we discovered that CP from several members of the Alphavirus family are capable of binding IRAK1 and inhibiting IRAK1-dependent TLR signaling. We were able to map the necessary interaction determinates on CP which, when mutated, ablated IRAK1 binding and restored IRAK1-depdent signaling. Host cells infected with this mutant virus increased their expression of IFN-β in vitro, relative to cells infected with wild-type Sindbis virus. The mutant virus was also impaired in an in vivo model of infection where it failed to cause symptoms of alphavirus infection. Collectively these data show a novel interaction between alphavirus CP and host IRAK1 that allows the virus to evade the immune detection during early infection a crucial time when the virus has yet not been able to shut down host transcription and translation. This interaction was also found to be crucial for viral pathogenesis and the absence of it leaves the virus attenuated. The data presented in this dissertation offer insight into a newly observed method Alphavirus uses to evade detection by the innate immune system which could be a potential target for therapeutic intervention as well as a mutant virus that could be a candidate for a live-attenuated vaccine.

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