Targeting HIF-1α Function in Cancer through the Chaperone Action of NQO1

Abstract

HIF-1α is a master regulator of oxygen homeostasis involved in different stages of cancer development. Thus, HIF-1α inhibition represents an interesting target for anti-cancer therapy. It was recently shown that HIF-1α interaction with NQO1 inhibits its proteasomal degradation, thus suggesting that targeting the stability of NQO1 could led to destabilization of HIF-1α as a therapeutic approach. Since the molecular interactions of NQO1 with HIF-1α are beginning to be unraveled, we review here our current knowledge on the intracellular functions and stability of NQO1, its pharmacological modulation by small ligands, and the molecular determinants of its roles as a chaperone of many different proteins including cancer-associated factors such as p53 and p73α. This knowledge is then discussed in the context of potentially targeting the intracellular stability of HIF-1α by acting on its chaperone, NQO1. This could result in novel anti-cancer therapies.

The Catalytic Cycle of the Antioxidant and Cancer-Associated Human NQO1 Enzyme: Hydride Transfer, Conformational Dynamics and Functional Cooperativity

“…Although NQO1 can reduce a wide variety of substrates [ 4 ], most of them are not appropriate for enzymatic studies due to their low solubility in aqueous solutions, their characteristic spectral properties or, in some cases, their fast reduction that precludes pre-steady-state kinetic characterization using stopped-flow spectroscopy [ 34 , 44 ]. We have here used DCPIP, a suitable and artificial electron acceptor often used in activity measurements of human NQO1 [ 4 ], to study its oxidative half-reaction. Nonetheless, mixing NQO1 hq with DCPIP at equimolecular concentrations also resulted in the extremely fast re-oxidation of the protein, even at low temperatures, and with nearly 50% of the spectral changes occurring in the instrumental dead time ( Figure 8 A–C).…”

“…Our understanding of the roles of the multifunctional NQO1 protein in many physiological and pathological states, particularly in those associated with oxidative insults such as cancer and neurological disorders, is growing steadily [ 1 , 2 , 4 , 16 ]. In addition, NQO1 is an excellent example of an oligomeric human protein in which functional ligands exert remarkable cooperative effects with important implications for the understanding of how human genetic variability, divergent evolution and post-translational modifications shape the complex functional chemistry of multifunctional proteins [ 2 , 28 , 31 , 34 , 42 , 50 , 51 , 54 , 55 , 56 , 57 , 83 ].…”

“…In addition, the calculated isotope effect on the Arrhenius frequency factor (A H /A D ) strongly differed between both HT/DT events, with a value close to the unity for the faster one and about 10 for the slower one. As a consequence of the marginal differences between E aDT and E aHT and the small values for the apparent KIEs, the activation enthalpies and entropies for HT and DT are also small when these results are analyzed in the context of the Eyring equation (Equation (4), see Figure 9C and Table 3).…”

“…NAD(P)H quinone oxidoreductase 1 (NQO1; DT-diaphorase; EC 1.6.5.2) is a multi-functional and stress-inducible flavoprotein whose activity is associated with different pathologies, particularly with cancer [1,2]. NQO1 has a wide range of substrates and enzymatic functions associated with antioxidant defense and cancer development, including the NAD(P)H-dependent two-electron reduction of quinones to form hydroquinones, thus avoiding the formation of highly reactive and cytotoxic semiquinones [3,4], the maintenance of vitamin K 3 and ubiquinone in their reduced state [5][6][7][8] and scavenging of superoxide anions [9]. NQO1 activity is also required for the activation of cancer Importantly, most of our knowledge on the NQO1 kinetic mechanism has come from analysis of either ligand binding/release events from crystallographic analyses, or from single-wavelength kinetic analyses focused on the changes in FAD spectral properties associated with chemical steps (i.e., HT) [34,38,40,43,44].…”

“…NQO1 activity is also required for the activation of cancer prodrugs [ 10 , 11 , 12 , 13 , 14 ]. In addition, NQO1 is capable of interacting with over forty different proteins, such as p53, p73α and HIF-1α, and the general effect of these interactions is the protection of protein partners against proteasomal degradation [ 4 , 15 , 16 ].…”