Highbush blueberry (Vaccinium corymbosum L.) has one of the highest antioxidant capacities and flavonoid concentrations of any fruit or vegetable, and regular consumption of blueberries has been connected to a wide range of health benefits. A diversity of flavonoids (flavonols, anthocyanins, proanthocyanidins) are likely responsible for many of the health benefits, and these compounds also significantly contribute to the organoleptic properties of ripe blueberries. Despite the potential importance of these flavonoids in diet, there has been little investigation into the molecular genetics of blueberry flavonoid biosynthesis. Therefore, I developed a real-time quantitative PCR protocol to monitor expression of flavonoid genes throughout development and ripening. Following evaluation of five reference genes, expression profiling of biosynthetic genes revealed that flavonoid synthesis is tightly controlled at the transcriptional level in a biphasic developmental pattern. These results are discussed in relation to flavonoid metabolite accumulation profiles, which were produced as part of a collaboration. Finally, in conjunction with a second group of collaborating scientists, some promising preliminary evidence is provided suggesting that the hormone abscisic acid might have a role in regulating ripening initiation in blueberry. / Graduate

The enzymes CYP27A1 and CYP7B1 are widely expressed in various human tissues and perform catalytic reactions in cholesterol homeostasis and endocrine signaling. We have investigated the metabolism of a synthetic oxysterol. In this study, we show that CYP27A1 is the enzyme responsible for a 28-hydroxylation of this oxysterol and that the rate of CYP27A1-mediated metabolism is relatively slow. This may give an explanation for the prolonged inhibitory effects on cholesterol biosynthesis that have been shown for this oxysterol. The current study contributes to the knowledge of synthetically produced oxysterols and their potential use as cholesterol lowering drugs. In two studies we investigated CYP7B1-mediated metabolism of different sex hormones. Our data indicate that CYP7B1 may carry out a previously unknown catalytic reaction involving an androgen. Taken together the data suggest that varying steroid concentrations in cells and tissues may be important for CYP7B1-dependent metabolism of sex hormones and sex hormone precursors. CYP7B1-mediated hydroxylation of sex hormones may influence the cellular levels of these steroids and may be a potential pathway for elimination of the steroids from the cell. Some known CYP7B1 substrates are agonists for ERα and ERβ but the reported role(s) of CYP7B1 for ER action are not fully understood. In the last study we investigated the role(s) of CYP7B1-mediated metabolism for ER-mediated action. Our data indicate that CYP7B1-mediated conversion of steroids that affect ER-mediated response into their 7α-hydroxymetabolites will result in loss of action. This indicates that CYP7B1 may have an important role for regulation of ER-mediated processes in the body. In summary, results from this thesis contribute to the knowledge on the metabolism of synthetic oxysterols of potential use as cholesterol lowering drugs and the role(s) of CYP7B1-mediated metabolism for processes related to the functions of sex hormones. / Disputationsordförande;Professor Eva Brittebo, Inst. för Biovetenskap, Avd. för Toxikologi, Uppsala Universitet, UppsalaBetygsnämndens ledamöten; Docent Lena Ekström, Inst. för Laboratoriemedicin, Avd. för Klinisk Kemi, Karolinska Universitetssjukhuset, HuddingeDocent Ulf Diczfaluzy, Inst. för Laboratoriemedicin, Avd. för Klinisk Kemi, Karolinska Universitetssjukhuset, HuddingeProfessor Agneta Oskarsson, Inst. BVF, Avd. för farmakologi och toxikologi, SLU, Uppsala

Diss. (sammanfattning) Uppsala : Univ., 2002. / Härtill 5 uppsatser.

Made available in DSpace on 2015-05-14T13:21:34Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 8221472 bytes, checksum: cac315a193674c3a77482441306e409a (MD5) Previous issue date: 2013-11-03 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / An alternative route for the synthesis of the three isomers of Mn(III) N-metylpyridylporphyrins, MnTM-X-PyPCl5 (X = 2, 3, 4) was developed by the direct methylation of MnT-X-PyPCl (X = 2, 3, 4) with methyl tosylate; this methodology may be adapted for preparing the longer-alkyl-chain analogues. The investigation of the thermal stability of the potent redox modulator Mn(III) meso-tetrakis(N-ethylpyridinium-2- yl)porphyrin chloride (MnTE-2-PyPCl5) showed that the thermal decomposition of MnTE-2-PyPCl5∙11H2O under air occurs in three successive steps: dehydration, dealkylation (ethyl chloride loss) and combustion, to yield Mn oxide as final residue. Heating MnTE-2-PyPCl5∙11H2O up to ~100 ºC leads to dehydration, but with no effect onto the catalytic SOD activity after rehydration/dissolution. Heating the sample at temperatures above 100 ºC leads to dealkylation, which affects catalytic and biological properties. The immobilization of the neutral Mn porphyrins (MnPs) MnT-X-PyPCl (X = 2, 3, 4) covalently onto chloropropyl silica-gel (Sil-Cl) or the cationic MnPs MnTM-X-PyPCl5 (X = 2, 3, 4) electrostatically into sodium vermiculite (verm) yielded stable biomimetic models of cytochromes P450. The resulting materials, Sil-Cl/MnT-X-PyPCl e verm/MnTM-X-PyPCl5 (X = 2, 3, 4), were used as oxidation catalyst for hydroxylation of cyclohexane and adamantane by iodosylbenzene. The heterogeneous systems were more efficient, selective, and oxidatively stable than the homogeneous counterparts, and could be reused three times with no significant loss in efficiency. The use of more drastic conditions (i.e., large excess of PhIO), led to considerable decrease in efficiency, which was partial recovered upon catalyst reuse uner milder conditions, indicating that the support protects the supported MnP against oxidative degradation. The materials efficiently catalyzed the oxidation of cyclohexanol to cyclohexanone, suggesting that the ketone observed during cyclohexane hydroxylation may result, at least partially, from cyclohexanol oxidation. The covalent bond between Sil-Cl and MnPs via N-pyridyl moiety allowed the preparation of efficient and stable catalysts, even with first generation, simple MnPs, such as MnT-X-PyPCl (X = 2, 3, 4). Vermiculite was revealed as a simple and effective support for rapid and qualitative immobilization of cationic MnPs, MnTM-X-PyPCl5 (X = 2, 3, 4). Grinding of the vermiculite-based materials decreased the crystallinity of the systems, which was followed by an increase in the catalytic efficiency of the meta and para isomers verm/MnTM-X-PyPCl5 (X = 3 and 4), but did not affect of the high efficiency of the immobilized ortho isomer (verm/MnTM-2-PyPCl5), whose resistance to oxidative destruction and/or leaching was, additionally, higher than that of the other isomers. / Neste trabalho foi desenvolvida uma rota alternativa para obtenção dos três isômeros das N-metilpiridinioporfirinas de Mn(III), MnTM-X-PyPCl5 (X = 2, 3, 4), a partir da metilação direta dos complexos MnT-X-PyPCl (X = 2, 3, 4) com tosilato de metila; esta metodologia pode ser adaptada para obtenção de derivados alquilas de cadeias maiores. A investigação da estabilidade térmica do modulador redox potente cloreto de meso-tetraquis(N-etilpiridinio-2-il)porfirinatomanganês(III) (MnTE-2-PyPCl5) revelou que a decomposição térmica da MnTE-2-PyPCl5∙11H2O em ar ocorre em três etapas sucessivas, associadas à desidratação, desalquilação (perda dos grupos EtCl) e combustão, levando a óxidos de Mn como resíduo final. O aquecimento da MnTE-2- PyPCl5∙11H2O até ~100 °C leva à desidratação, mas não afeta a atividade catalítica SOD após a re-hidratação/dissolução. O aquecimento da amostra à temperatura elevada (>100 oC) leva à desalquilação e compromete as propriedades catalíticas e biológicas da amostra. O desenvolvimento de modelos biomiméticos dos citocromos P450 pela heterogeneização covalente das Mn-porfirinas (MnPs) neutras MnT-X-PyPCl (X = 2, 3, 4) na sílica cloropropil (Sil-Cl) e pela heterogeneização eletrostática das MnPs catiônicas MnTM-X-PyPCl5 (X = 2, 3, 4) na vermiculita de sódio (verm) foi estudado. Os materiais resultantes, Sil-Cl/MnT-X-PyPCl e verm/MnTM-X-PyPCl5 (X = 2, 3, 4), foram empregados como catalisadores em reações de hidroxilação de cicloexano e adamantano por iodosilbenzeno (PhIO). Os catalisadores heterogeneizados foram mais eficientes, seletivos e resistentes à destruição oxidativa do que os catalisadores em meio homogêneo, e foram reutilizados por três vezes sem perda significativa na eficiência catalítica. Sob condições mais drásticas, com o uso de grande excesso de PhIO, há diminuição considerável da eficiência, mas os catalisadores imobilizados puderam ser reutilizados com recuperação parcial da eficiência, o que indica que o suporte exerce proteção das MnPs contra degradação oxidativa. Os catalisadores heterogeneizados foram eficientes ao catalisar a oxidação do cicloexanol à cicloexanona, sugerindo que a cetona observada nas hidroxilações pode advir da oxidação seqüencial, cicloexano-cicloexanol-cicloexanona. A ligação covalente entre a Sil-Cl e as MnPs via grupo N-piridil possibilitou a obtenção de catalisadores eficientes e estáveis, mesmo utilizando MnPs simples de primeira geração, MnT-X-PyPCl (X = 2, 3, 4). Já a vermiculita mostrou-se um suporte simples e efetivo para imobilização rápida e quantitativa de MnPs catiônicas, MnTM-X-PyPCl5 (X = 2, 3, 4). A pulverização dos materiais à base de vermiculita diminuiu a cristalinidade dos sistemas, promoveu um aumento na eficiência dos isômeros meta e para (verm/MnTM-X-PyPCl5, X = 3 e 4), mas não modificou a alta eficiência do isômero orto imobilizado (verm/MnTM-2-PyPCl5), cuja resistência à destruição oxidativa e/ou lixiviação foi superior à dos outros isômeros.

Unspecific peroxygenases (UPO, EC 1.11.2.1) secreted by fungi open an efficient way to selectively oxyfunctionalize diverse organic substrates, including less-activated hydrocarbons, by transferring peroxide-borne oxygen. We investigated a cell-free approach to incorporate epoxy and hydroxyl functionalities directly into the bulky molecule testosterone by a novel unspecific peroxygenase (UPO) that is produced by the ascomycetous fungus Chaetomium globosum in a complex medium rich in carbon and nitrogen. Purification by fast protein liquid chromatography revealed two enzyme fractions with the same molecular mass (36 kDa) and with specific activity of 4.4 to 12 U mg−1. Although the well-known UPOs of Agrocybe aegerita (AaeUPO) and Marasmius rotula (MroUPO) failed to convert testosterone in a comparative study, the UPO of C. globosum (CglUPO) accepted testosterone as substrate and converted it with total turnover number (TTN) of up to 7000 into two oxygenated products: the 4,5-epoxide of testosterone in β-configuration and 16α-hydroxytestosterone. The reaction performed on a 100 mg scale resulted in the formation of about 90 % of the epoxide and 10 % of the hydroxylation product, both of which could be isolated with purities above 96 %. Thus, CglUPO is a promising biocatalyst for the oxyfunctionalization of bulky steroids and it will be a useful tool for the synthesis of pharmaceutically relevant steroidal molecules.

Over the recent years, increasing scientific attention has been paid to pharmaceuticals, other drugs and their metabolites. These substances are of particular interest because of their physiological, toxicological and ecotoxicological effects in the human body and respectively in the environment. Cytochrome P450 enzymes (P450s) play a key role in the conversion and detoxification of bioactive compounds including many pharmaceuticals and drugs. Most of these enzymes belong to the monooxygenases; they are intracellular and rather unstable biocatalysts that are difficult to purify and require expensive, complex cofactors, which alltogether hampers their use in isolated form. The investigations carried out here with fungal peroxygenases have shown that this enzyme sub-subclass (EC 1.11.2.x) has a promising potential for oxyfunctionalizations and can catalyze a variety of reactions typical for P450s. Peroxygenases are extracellular, i.e. secreted fungal enzymes with high stability, which merely need peroxide for function. Results obtained with the unspecific/aromatic peroxygenases (APOs) of Agrocybe aegerita, Coprinellus radians and Marasmius rotula have demonstrated that APOs catalyze numerous H2O2-dependent monooxygenations of pharmaceuticals and psychoactive drugs. Among them are i) the monooxygenation of aromatic compounds, ii) the benzylic hydroxylation of toluene derivatives, iii) the O-dealkylation of different ether structures including the scission of benzodioxoles (O-demethylenation) and esters as well as iv) the N-dealkylation of secondary and tertiary amines. The peroxygenases studied considerably differ in their substrate spectrum and the preferred positions of oxidation. This finding opens the possibility to develop in the future an “enzymatic toolbox“ on the basis of fungal peroxygenases for the oxyfunctionalization of pharmaceutically relevant compounds. Mechanistic studies showed that (1) the monooxygenations always proceed via incorporation of one oxygen atom from the peroxide, (2) the demethylation of phenacetind1 established a deuterium isotope effect similar to P450s, (3) the catalytic efficiencies for the studied oxidations are in the same range as those of P450s (though the kcat- and Km values are noticeably higher), (4) the kinetic studies with nitro-1,3-benzodioxole gave parallel double reciprocal plots suggestive of a “ping pong” mechanism, (5) the substrate spectrum and the activity pattern of APOs follows in a wide range those of the human key P450s as well as that (6) the difference spectra obtained in bindings studies are of the phenol type of P450s. Furthermore, APOs were found to be stable and active in long term experiments over two weeks and they oxidized pharmaceuticals at low, environmentally relevant concentration (ppb range). All the above properties strongly indicate that APOs respresent an interesting alternative for the enzymatic conversion of pharmaceuticals as well as for the preparation of human drug metabolites, for example, in medicinal and pharmacological research or the bioremediation sector (removal of pharmaceuticals from environmental media). / In den letzten Jahren sind Pharmazeutika und deren Metabolite mehr und mehr in den Fokus der Wissenschaft gerückt. Diese Substanzen sind aufgrund ihrer physiologischen und toxikologischen sowie ökotoxikologischen Wirkungen im menschlichen Körper bzw. in der Umwelt von besonderem Interesse. Cytochrom-P450-Enzyme (P450s) spielen eine Schlüsselrolle bei der Umsetzung und Detoxifizierung bioaktiver Substanzen, darunter vieler Pharmazeutika und Drogen. Es handelt sich bei diesen Enzymen in erster Linie um Monooxygenasen, die intrazellulär lokalisiert und relativ instabil sind; sie benötigen komplexe, teure Kofaktoren und sind nur unter hohem Aufwand zu reinigen, was ihre Anwendung in isolierter Form insgesamt erschwert. Die hier durchgeführten Untersuchungen zu pilzlichen Peroxygenasen haben gezeigt, dass diese Enzymsubklasse (EC 1.11.2.x) ein hohes Oxyfunktionalisierungspotenzial besitzt und eine Vielzahl P450-typischer Reaktionen zu katalysieren vermag. Peroxygenasen sind extrazelluläre, d.h. sekretierte Pilzenzyme, die eine hohe Stabilität aufweisen und lediglich ein Peroxid als Kosubstrat benötigen. Die unter Verwendung der unspezifischen/aromatischen Peroxygenasen (APOs) von Agrocybe aegerita, Coprinellus radians und Marasmius rotula gewonnenen Ergebnisse belegen, dass APOs verschiedene H2O2-abhängige Monooxygenierungen von Pharmazeutika und psychoaktiven Substanzen realisieren. Dazu gehören i) die Monooxygenierung von Aromaten, ii) die benzylische Hydroxylierung von Toluolderivaten, iii) die O-Dealkylierung verschiedener Etherstrukturen einschließlich der Spaltung von Benzodioxolen (O-Demethylenierung) und Estern sowie iv) die N-Dealkylierung von sekundären und tertiären Aminen. Die untersuchten Peroxygenasen wiesen teilweise deutliche Unterschiede im Substratspektrum und den präferierten Oxidationspositionen auf. Dieser Befund eröffnet die Möglichkeit, zukünftig einen „enzymatischen Werkzeugkasten“ auf Basis pilzlicher Peroxygenasen für die Oxyfunktionalisierung von pharmazeutisch relevanten Wirkstoffen zu entwickeln. Mechanistische Experimente zeigten, dass (1) die Monooxygenierungen stets unter Einbau eines aus dem Peroxid stammenden Sauerstoffatoms erfolgen, (2) die Deethylierung von Phenacetin-d1 einen Deuteriumisotopeneffekt ähnlich dem der P450s aufweist, (3) die katalytischen Effizienzen für die untersuchten Oxidationen im gleichen Bereich wie die der P450s liegen (wobei die kcat- und Km-Werte deutlich höher ausfallen), (4) die kinetischen Untersuchungen zur Oxidation von Nitro-1,3-Benzodioxol parallele Verläufe der ermittelten Ausgleichsgeraden in der doppelt reziproken Darstellung ergaben, was für einen “Ping-Pong-Mechanismus“ spricht, (5) sich das Substratspektrum und die Aktivitätsmuster der APOs in einem weiten Bereich mit denen der wichtigsten menschlichen P450s decken sowie dass (6) die in Bindungsstudien gewonnenen Differenzspektren denen des Phenoltyps der P450s entsprechen. Desweiteren erwiesen sich APOs in Langzeitexperimenten über zwei Wochen als stabil und aktiv und sie waren in der Lage, Pharmazeutika in umweltrelevanten Konzentrationen (ppb-Bereich) zu oxidieren. All die genannten Eigenschaften legen nahe, dass APOs eine interessante Alternative zur enzymatischen Umsetzung von Pharmazeutika sowie zur Herstellung von humanen Pharmazeutika-Metaboliten darstellen, die z.B. Einsatz in der medizinischpharmakologischen Forschung oder im Umweltbereich (Entfernung von Pharmazeutika aus Umweltmedien) finden könnten.

L’attrait des compagnies pharmaceutiques pour des structures cycliques possédant des propriétés biologiques intéressantes par les compagnies pharmaceutiques a orienté les projets décrits dans ce mémoire. La synthèse rapide, efficace, verte et économique de ces structures suscite de plus en plus d’attention dans la littérature en raison des cibles biologiques visées qui deviennent de plus en plus complexes. Ce mémoire se divise en deux projets ciblant la synthèse de deux structures aromatiques importantes dans le monde de la chimie médicinale. Dans un premier temps, l’amélioration de la synthèse de dérivés phénoliques a été réalisée. L’apport de la chimie en flux continu dans le développement de voies synthétiques plus vertes et efficaces sera tout d’abord discuté. Ensuite, une revue des antécédents concernant l’hydroxylation d’halogénure d’aryle sera effectuée. Finalement, le développement d’une nouvelle approche rapide de synthèse des phénols utilisant la chimie en flux continu sera présenté, suivi d’un survol de ses avantages et ses limitations. Dans un deuxième temps, le développement d’une nouvelle méthodologie pour la formation de 3-aminoindazoles a été réalisé. Tout d’abord, un résumé de la littérature sur la synthèse de différents indazoles sera présenté. Ensuite, une présentation de deux méthodes efficaces d’activation de liens sera effectuée, soit l’activation d’amides par l’anhydride triflique et l’activation de liens C–H catalysée par des métaux de transition. Finalement, le développement d’une nouvelle méthodologie pour la synthèse de 3-aminoindazole utilisant ces deux approches sera discuté. / The continuous attraction towards accessing cyclic structures that possess interesting biological properties by pharmaceutical companies has guided the projects described in this M.Sc. thesis. Due to the increasing complexity of drug targets, methodologies encompassing efficient, rapid, economical and environmentally friendly syntheses are highly sought in the organic chemistry literature. The present work consists of two projects targeting the synthesis of two important aromatic structures in the field of medicinal chemistry. The first part of the thesis will present an improved synthesis of phenol derivatives. The recent chemical contributions in the continuous development of greener and efficient synthetic routes will be discussed, followed by a quick review of the literature on the hydroxylation of aryl halides. Then, the development of a new approach for rapid synthesis of phenol derivatives using continuous flow chemistry will be presented, including an overview of its benefits and limitations. The second part of the thesis will put forward the development of a novel methodology for the formation of 3-aminoindazoles. A summary of the literature on the synthesis of various indazoles will be presented, followed by an overview of two effective bond activation methods: the amide activation using triflic anhydride and transition metal catalyzed C–H activation. Finally, the evolution of a new method for the synthesis of 3-aminoindazole using the previously mentioned two approaches will be discussed.

Hypoxia-inducible factor (HIF) is the master regulator of genes involved in adaptation to hypoxia. The stability and transcriptional activity of HIF are regulated by post-translational hydroxylations: prolyl hydroxylation by the prolyl hydroxylase domain-containing enzymes PHD1 – 3 earmarks HIF for proteasomal degradation, whilst asparaginyl hydroxylation by factor inhibiting HIF (FIH) blocks the interaction of HIF with the transcriptional coactivators p300/CBP. The PHDs and FIH hydroxylate HIF directly from molecular oxygen and are therefore oxygen sensors. Recent literature shows that FIH also hydroxylates a number of proteins containing an ankyrin-repeat domain (ARD). Together with reports suggesting that the PHDs are involved in HIF-independent pathways, this suggests that the HIF hydroxylases may have a wide range of non-HIF targets. This thesis describes my investigations into novel substrates of the HIF hydroxylases. This work has characterized the FIH-dependent hydroxylation of the ARD-containing protein Notch1, and defined a consensus sequence for hydroxylation that corresponds to the ankyrin-repeat consensus. Using this consensus potential sites of hydroxylation in a novel ARD FIH substrate, myosin phosphatase targeting subunit 1 (MYPT1), were identified then subsequently confirmed and characterized. Notch1 competes with HIF for FIH hydroxylation. My experiments show that this occurs because Notch1 is a more efficient substrate than HIF, whilst studies on MYPT1 and other proteins indicate that competitive inhibition of FIH may be a general property of ARDs. There are more than 300 ARD proteins in the human genome, and this thesis demonstrates that FIH may hydroxylate a significant percentage of these. In addition to the analysis of ARD hydroxylation a proteomic investigation into novel PHD3 substrates has identified two candidate proteins, suggesting that the PHDs may also have multiple targets. These results have important implications for oxygen sensing, and indicate that post-translational hydroxylation is likely to be a widespread modification in cell biology.

The Lon protease is a mitochondrial matrix quality-control protease belonging to the family of AAA+ proteins (ATPases associated with many cellular activities). We had previously found Lon to be upregulated in lung tumours with a non-angiogenic phenotype in a microarray study comparing these to conventional angiogenic tumours. In this project I set out to investigate whether Lon had any role in modulating the hypoxic response of tumour cells. Using a novel monoclonal antibody against Lon, I found that upregulation of Lon was present in breast and lung tumours and that higher levels of Lon are correlated with shorter overall survival in breast cancer patients. Targeting Lon with siRNA and shRNA in tumour cell lines reduced the normoxic and hypoxic stabilisation of HIF-α subunits. This is mediated through a mechanism independent of the activity of HIF-prolyl hydroxylases and independent of any changes in mitochondrial transcription. I found that the pre-imported form of Lon could bind and chaperone VHL in the cytoplasm potentially modulating VHL activity. In cell lines and human tumours, I observed that the proline-hydroxylated form of HIF-1α is induced by hypoxia and the hydroxylated form of HIF-1α is associated with shorter overall survival in breast cancer patients. This observation supports the notion that higher levels of Lon is associated with poor survival by downregulating VHL leading to higher levels of hydroxylated HIF. Finally I show that targeting Lon in cell lines is able to inhibit growth in a cell-line dependent fashion and partially reverses the Warburg effect, increasing oxygen consumption and reducing lactate production. In conclusion, I have demonstrated the broad therapeutic potential of targeting the Lon protease in tumours and highlighted a mechanism of post-hydroxylation HIF-regulation that has not been previously recognised in VHL competent tumours.

Metazoans have evolved conserved mechanisms to promote cell survival under low oxygen tensions by initiating a transcriptional cascade centered on the action of Hypoxia Inducible transcription Factors (HIFs). In aerobic conditions, HIFs are inactivated by ubiquitin-proteasome-mediated degradation of their a subunit, which is dependent on prolyl hydroxylation by 2-oxoglutarate (2-OG) and Fe(II)-dependent prolyl hydroxylases (PHDs). In hypoxia, HIF-$\alpha$ is no longer hydroxylated and is therefore stabilised, activating a global transcriptional response to ensure cell survival. Interestingly, HIFs can also be activated in aerobic conditions, however the mechanisms of this oxygen-independent regulation are poorly understood. Here, I have explored the role of the vacuolar H+-ATPase (V-ATPase), the major proton pump for acidifying intracellular vesicles and facilitating lysosomal degradation, in regulating HIF-$\alpha$ turnover. Unbiased forward genetic screens in near-haploid human cells identified that disruption of the V-ATPase leads to activation of HIFs in aerobic conditions. Rather than preventing the lysosomal degradation of HIF-$\alpha$, I found that V-ATPase inhibition indirectly affects the canonical proteasome-mediated degradation of HIF-$\alpha$ isoforms by altering the intracellular iron pool and preventing HIF-$\alpha$ prolyl hydroxylation. In parallel, I characterised two putative mammalian V-ATPase assembly proteins, TMEM199 and CCDC115, identified by the forward genetic screen and subsequent mass spectrometry analysis. I confirmed that both TMEM199 and CCDC115 are required for V-ATPase function, and established assays to determine how TMEM199 and CCDC115 associate with components of the core V-ATPase complex. Lastly, to measure how V-ATPase activity leads to changes in the labile iron pool, I developed an endogenous iron reporter using CRISPR-Cas9 knock-in technology. This approach confirmed that iron homeostasis is impaired during V-ATPase inhibition, and demonstrated that exogenous ferric iron can restore the labile iron pool in a transferrin-independent manner. Together my studies highlight a crucial link between V-ATPase activity, iron homeostasis, and the hypoxic response pathway.