Master of Science
Shilton, Brian H.
Detoxification of quinone compounds is catalyzed by the NQO1 protein in humans. The related NQO2 is distinct from NQO1 as it uses NRH preferentially as a co-substrate to the exclusion of NAD(P)H. It is uncertain if NRH is available in cells for use by NQO2 and raises doubts that quinone detoxification is the adaptive role for NQO2. This study employed cell biology, protein structure and proteomics approaches to identify functions for NQO2 relevant to a cellular context. Several NQO2 interacting clinical drugs were found to have cytotoxic effects dependent upon NQO2 expression. Results from proteomic experiments identified novel roles for NQO2 in regulating lysosome and exosome proteins. Taken together the findings of this thesis are consistent with the hypothesis that NQO2 plays an alternative role in cells. NQO2 is proposed to function as a regulator of various cellular functions by acting as a redox switch rather than a quinone reductase.
Summary for Lay Audience
Quinone reductases are a class of proteins that perform detoxification roles in the cell. Specifically, they catalyze a two-electron reduction of quinone containing compounds. Quinones are prone to forming harmful byproducts that contribute to oxidative stress in cells thus, quinone reductase enzymes are required to detoxify such compounds. Humans have two quinone reductase enzymes; NQO1 and NQO2. NQO1 is well documented as functioning as a detoxification enzyme while the evidence regarding NQO2 function suggests that it is not able to perform its catalytic function with the co-substrates available in cells. The structural features of NQO2 make it unable to use NAD(P)H efficiently and it can only perform reductions of quinone compounds when provided with exogenous co-substrates. NQO2 is further notable for being a prominent target of a wide range of drugs used clinically. Many kinase inhibitors have been documented to bind to NQO2 but it is unclear why so many drugs would have such great affinity for the protein and what the cellular implications of the interactions are. The clinical drugs that bind to NQO2 are often used to treat various types of cancers or infections therefore, understanding how NQO2 contributes to the mechanisms of such drugs is important to optimizing their use clinically. This project focuses on investigating how NQO2 influences the cellular toxicity of a variety of drugs that have been documented to bind to the protein. It also reports novel structures of sunitinib, a recently identified NQO2 interacting drug, bound to the NQO2 protein that will further the understanding of NQO2 interactions with clinical drugs. Differences in the proteomes of cells that express NQO2 versus cells that have the gene for the protein knocked out were also identified and points towards novel roles for the protein in regulating the function of lysosomes and exosomes. This thesis is impactful as it will contribute towards identifying cellular functions for NQO2 and will inform the study and use of clinical drugs that interact with the protein.
Walker, Matthew D., "Quinone Reductase 2 Roles in Proteomic Regulation and Response to Treatment with Clinical Drugs" (2020). Electronic Thesis and Dissertation Repository. 7379.
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