Seminar

Dynamic origin of loss-of-function mechanisms in cancer-associated NQO1: evolutionary and therapeutic implications

Angel Luis Pey, PhD

Human NADP(H):quinone oxidoreductase 1 (NQO1) is a dimeric flavoprotein involved in the detoxification of quinones, the antioxidant defense, the activation of cancer pro-drugs and the stabilization of tumor suppressors such as p53 and p73?. Two germline polymorphisms in hNQO1 (P187S and R139W) are associated with cancer susceptibility, and over 30 somatic mutations leading to single amino acid exchanges have been found in cancer cell lines. However, the molecular mechanisms by which cancer-associated single amino acid exchanges in NQO1 lead to loss-of-function have been largely unknown. We have recently shown that the common polymorphism P187S causes inactivation of NQO1 due to a decrease in binding affinity for FAD, while its low intracellular stability is linked to destabilization of the C-terminal domain and proteasomal degradation (1, 2). These two mechanisms are energetically and functionally coupled: P187S enhances conformational fluctuations in the FAD binding site and in the C-terminal domain through long-range allosteric effects (3). Intracellular destabilization of P187S is overcome upon ligand binding to the C-terminal domain, consequently restoring its proper folding and dynamics (2, 3). Evolutionary analyses identified two mammalian consensus mutations that fully protect NQO1 towards P187S mediated inactivation: i) H80R, that locally stabilizes the FAD binding site, and ii) E247Q, that stabilizes the C-terminal domain and transmits the stabilizing effect to the FAD binding site located at 25 Å (4, 5). These consensus analyses also suggest that small neutral networks of amino acids may have yielded human proteins more vulnerable towards disease-associated amino acid exchanges (4). Ongoing mutational screenings show that inactivating effects of P187S, as well as of those of the rare somatic mutation K240E, are not particularly restricted to these natural amino acid exchanges and support that mutational pathways determine to a large extent the identity of disease-causing amino acid exchanges. Overall, our work supports that the highly dynamic and malleable nature of NQO1 apo-state is key to understanding the mechanisms of disease-causing and suppressor mutations, with important implications to explain the dynamic relationships between human flavoproteome stability and function, flavin bioavailability and binding (4-6). 1. Pey AL, et al. (2014). BBA-Molecular Basis of Disease 1842:2163-2173. 2. Medina-Carmona E, et al. (2016) Scientific Reports 6:20331. 3. Medina-Carmona E, et al. (2017) Scientific Reports 7:44352. 4. Medina-Carmona E, et al. Human Molecular Genetics. in press. 5. Muñoz IG, et al. FEBS Lett. in press. 6. Martinez-Limon A, et al. (2016) Proc Natl Acad Sci U S A 113:12156-12161.