No description available.

Mosquitoes affect human health worldwide as a result of their ability to vector multiple diseases. Mosquitocide resistance is a serious public health challenge that warrants the development of improved chemical control strategies for mosquitoes. Previous studies demonstrate the mosquito blood-brain barrier (BBB) to interfere with the target-site delivery and action of anticholinesterase chemistries. The ATP-binding cassette (ABC) transporters are efflux proteins that assist in maintaining the BBB interface and serve as a first line of defense to mosquitocide exposures. To date, there are three subfamilies (ABC -B, -C, -G) of ABC transporters; however, knowledge of these chemistries interacting with mosquito ABC transporter(s) is limited. Here, I report that tacrine and bis(7)-tacrine are relative non-toxic anticholinesterases at solubility limits; however, the addition of verapamil enhances toxicity of both tacrine and bis(7)-tacrine to mosquitoes. Verapamil significantly increases the mortality of mosquitoes exposed to tacrine and bis(7)-tacrine compared to the tacrine- and bis(7)- tacrine-only treatments. Tacrine and bis(7)-tacrine reduce acetylcholinesterase activity in mosquito head preparations compared to the untreated mosquitoes; however, the addition of verapamil significantly increases the anticholinesterase activity of tacrine and bis(7)-tacrine compared to the tacrine-and bis(7)-tacrine-only treatments. Tacrine and bis(7)-tacrine increase ATPase activity in Aedes aegypti at lower concentrations compared to that of verapamil (Fig. 3). The differential increase in ATPase activity suggests that tacrine and bis(7)-tacrine are more suitable substrates for ABC transporter(s) compared to verapamil and, thus, provides putative evidence that ABC transporter(s) is a pharmacological obstacle to the delivery of these anticholinesterases to their intended target site. / Master of Science in Life Sciences

Multidrug Resistenz (MDR), die simultane Resistenz gegenüber strukturell und funktionell nicht-verwandten Zytostatika, stellt eine wesentliche Ursache für unzureichende Behandlungserfolge maligner Erkrankungen dar. Die inherente Resistenz bzw. Resistenzentwicklung gegenüber chemotherapeutischen Substanzen ist vor allem die Folge der Präsens und Regulation unterschiedlicher Transportproteine wie MDR1, MRP1, BCRP und MVP. In der Konsequenz kommt es zu alteriertem Influx und/oder Efflux von Zytostatika, verminderter Akkumulation und Effektivität von Chemotherapeutika. Sowohl Zytostatika als auch Zytokine zeigten modulierende Einflüsse auf die Expression der MDR-Gene MDR1, MRP1 und MVP (Kapitel 2-9). Zytostatika wie Adriamycin resultierten vorwiegend in induzierten MDR1-Expressionen, dem hauptsächlichen Interventionstarget zur Überwindung des klassischen MDR-Phänotyps. Zytokine wie TNFa führten, extern appliziert als auch durch Gentransfer, zur Chemosensitivierung der Tumorzellen, verbunden mit Down-Regulationen von MDR1 und MVP. Die Zytokin-vermittelte Überwindung des klassischen MDR-Phänotyps weist auf die Inklusion definierter Zytokine in etablierte Chemotherapieprotokolle hin, wie bereits angewendet bei der hyperthermen isolierten Extremitätenperfusion mit TNFa (Kapitel 13). Die Verwendung BCRP-spezifischer Ribozyme demonstrierte deren Potential zur Überwindung des BCRP-bedingten, atypischen MDR-Phänotyps. Darüber hinaus wurde gezeigt, dass die Expression der ABC-Transporter als auch des MVP durch Hyperthermie temperatur- und zeitabhängig induzierbar ist (Kapitel 10-13). Diese Hyperthermie-Induktion wird für MDR1 und MRP1 über den Transkriptionsfaktor YB-1 zeitnah zum Stressereignis vermittelt. In der klinischen Situation konnte anhand verfügbarer Biopsien von Kolonkarzinomen, Sarkomen und Melanomen, jeweils mittels Hyperthermie im Kontext multimodaler Behandlungsregime behandelt, kein direktes, generelles Risiko einer MDR1- oder MRP1-vermittelten, Hyperthermie-bedingten Induktion/Verstärkung einer MDR beobachtet werden. Die Analyse der Promotoren MDR-assoziierter Gene wie MDR1 und MVP zeigte deren Induzierbarkeit durch unterschiedliche Therapie-relevante Faktoren wie Zytostatika und Hyperthermie in verschiedenen in vitro- und in vivo-Modellen (Kapitel 10,14-20). Spezifische Sequenzmotive sind für die Stressfaktor-induzierte Bindung von Transkriptionsfaktoren wie YB-1 verantwortlich; Mutationen in diesen Sequenzbereichen modulierten die Induzierbarkeit (Kapitel 14,15,20). Der Einsatz Therapie-induzierbarer Promotoren unterschiedlicher MDR-Gene wie MDR1 (Kapitel 14-18) und MVP (Kapitel 19,20) erlaubt somit generell die Anpassung an etablierte Behandlungsprotokolle verschiedener Tumorentitäten. In fortführenden Arbeiten bleibt die erfolgreiche Anwendung von Therapie-induzierbaren MDR-Promotorsequenzen zur Expression therapeutisch relevanter Gene im Kontext einer Gentherapie maligner Erkrankungen zu prüfen. / Multidrug resistance, the simultaneous resistance towards structurally and functionally unrelated cytostatic drugs, still represents a major cause of cancer treatment failure. Inherent or acquired resistance against a wide variety of chemotherapeutic drugs depends mainly on the presence and regulation of different transporter proteins, such as MDR1, MRP1, BCRP, and MVP. Thus, decreased uptake and/or increased efflux, lowered net accumulation, and in consequence, less efficiency of anti-cancer drugs is the clinical hurdle to struggle with. Cytostatics as well as cytokines showed modulating effects on the expression of the MDR-associated genes MDR1, MRP1, and MVP (chapter 2-9). Cytostatics such as adriamycin resulted mainly in increased expression of the MDR1 gene, the most prominent intervention target for the reversal of the classical MDR phenotype. Cytokines such as TNFa, externally applied or by gene transfer, led to chemosensitization of tumor cells, and to down regulation of MDR1 and MVP. This cytokine-mediated reversal of the classical MDR phenoype refer to the inclusion of defined cytokines into established chemotherapy protocols, as already realized by the hyperthermic isolated limb perfusion with TNFa (chapter 13). The employment of BCRP-specific ribozymes demonstrated their potential to reverse the BCRP-mediated atypical MDR phenotype. Furthermore it was shown, that the expression of the ABC transporters as well as of MVP was inducible by hyperthermia in a temperature and time-dependet manner (chapter 10-13). This hyperthermia-caused induction of MDR1 and MRP1 is mediated by the transcription factor YB-1 timely close to the stress event. However, no direct, general risk of a MDR1- or MRP1-mediated hyperthermia-caused induction/enhancement of the MDR phenotype was observed in clinical settings, analyzed by using biopsies available from colon carcinomas, sarcomas, and melanomas, which were treated with hyperthermia in the context of multimodal regimes. The analyses of promoters of the MDR-associated genes MDR1 and MVP revealed their inducibility by different therapy-related factors such as cytostatics and hyperthermia in several in vitro- and in vivo models (chapter 10,14-20). Specific sequence motifs were found to be responsible for the stress-induced binding of transcription factors; mutations within these sequence regions modulated their inducibility (chapter 14,15,20). Thus, the employment of therapy-inducible promoters of different MDR genes such as MDR1 (chapter 14-18) and MVP (chapter 19,20) allows the improvement of established treatment protocols for different tumor localizations. Based on this, the succesful use of therapy-inducible MDR promoter sequences for the expression of therapeutically relevant genes in the context of a gene therapy of cancer represents an ambitious goal for the future.

No description available.

Energy-Coupling-Factor (ECF)-Transporter sind Aufnahmesysteme für Vitamine und Übergangsmetallkationen in Prokaryoten. Sie bestehen aus den zwei unverwandten Membranproteinen S und T sowie einem Paar ABC-ATPasen (A). Die S-Einheit vermittelt die Substratspezifität. Die Kombination aus der T- und den A-Einheiten wird als ECF bezeichnet. In dieser Arbeit wurden Fragen zur kontrovers diskutierten Stöchiometrie der Untereinheiten von ECF-Transportern sowie zur zuvor postulierten Substrattransport-Funktion einzelner S-Komponenten auch ohne ECF untersucht. Dazu wurden der ECF-Biotintransporter BioMNY, mehrere natürlicherweise in Organismen ohne ECF existierende biotinspezifische S Einheiten (BioY) sowie zwei Vertreter der metallspezifischen ECF-Systeme genutzt. Die S-Einheit BioY des dreiteiligen Biotinimporters lag in vitro als Monomer und Dimer vor. Oligomeres BioY wurde außerdem in lebenden Bakterienzellen beobachtet. „Pull-down“-Experimente zeigten, dass die T Komponente BioN im BioMNY-Komplex zum Teil als Dimer vorlag. Wachstumsuntersuchungen bestätigten die Transportfunktion von acht solitär vorkommenden BioY. Die in vitro auch für diese BioY-Proteine nachgewiesene Dimerisierung könnte die Transportfunktion von BioY ohne ECF erklären. Die metallspezifischen S Einheiten CbiM/NikM interagieren mit für die Transportfunktion essentiellen, zusätzlichen Transmembranproteinen (N) und zeichnen sich durch eine Topologie mit sieben Transmembranhelices und einem extrem konservierten, weit in das Proteininnere hineinragenden N-Terminus aus. Die Metallbindestelle besteht aus vier Stickstoffatomen von Met1, His2 und His67 und wird durch ein Netz aus Wasserstoffbrückenbindungen stabilisiert. Die Transport¬funktion von CbiMN bzw. Nik(MN) ohne ECF wurde in vivo mittels des nickelabhängigen Enzyms Urease als Indikator für die intrazelluläre Nickelkonzentration verifiziert. Zum gegenwärtigen Zeitpunkt ist die Funktion der für den Transport essentiellen N-Komponente jedoch noch unklar. / Energy-coupling factor (ECF) transporters are uptake systems for vitamins and transition metal cations in prokaryotes. They consist of the two unrelated membrane proteins S and T, and a pair of ABC ATPases (A). The S unit mediates substrate specificity. The combination of the T and the A units is called ECF. In this thesis the controversially discussed stoichiometry of the subunits of ECF transporters and the postulated substrate transport function of solitary S units without ECF were analysed. For this purpose, the biotin-specific ECF transporter BioMNY, several biotin-specific S units (BioY) encoded in organisms lacking any recognizable ECF and two metal-specific ECF transporters were used. The S unit BioY of the tripartite biotin importer existed in vitro as monomer and dimer. Furthermore, oligomeric BioY was observed in living bacterial cells. Oligomerisation of a part of the T unit BioN in the BioMNY complex was shown by “pull-down”- experiments. Growth analyses confirmed the transport function of eight solitary BioY proteins. The dimerisation, also proved for these solitary BioY proteins in vitro, could be an explanation for the transport function of BioY without ECF. The metal-specific S units CbiM/NikM interact with additional and for the transport function essential transmembrane proteins (N). The S units consist of seven transmembrane helices and an extremely conserved N-terminus, which extends deeply into the protein. The metal-binding site consists of four nitrogen atoms from Met1, His2 and His67 and is stabilised by a series of hydrogen bonds. The transport function of CbiMN and Nik(MN) without ECF was verified respectively in vivo using the nickel-depending enzyme urease as an indicator for intracellular nickel concentration, respectively. However, the role of the N component, which is essential for transport activity, is currently under investigation.

Acarbose hat als Inhibitor von Hydrolasen alpha-1,4-glykosidischer Bindungen medizinische Bedeutung. Das Acarbose-Biosynthese-Gencluster (acb) des grampositiven Produzenten Actinoplanes sp. wurde identifiziert und Genprodukte z. T. charakterisiert. Das Modell zum Acarbose-Metabolismus beschreibt einen Acarbosekreislauf, bei dem das Pseudotetrasaccharid als Carbophor fungiert. Das Molekül wird in das umgebende Medium abgegeben und durch das Zusammenwirken zweier extrazellulärer Enzyme nach Stärkehydrolyse mit einer unterschiedlichen Anzahl an Glukosemonomeren beladen. Nach dem vermuteten Re-Import über ein Bindeprotein-abhängiges ABC-Transportsystem AcbHFG stünde dem Organismus dann ein Gewinn an Glukosemolekülen zur Verfügung. Neben diesem Vorteil gegenüber Nahrungskonkurrenten im Habitat fungiert Acarbose ebenso als Hemmer der artfremden extrazellulären a-Amylasen. Die ökologische Funktion des Pseudotetrasaccharids wurde durch Untersuchungen zum Einfluss auf den Maltodextrin-Stoffwechsel von E. coli verifiziert und ausgeweitet. Es lässt sich ein ökonomisch sinnvolleres Konkurrenzverhalten von Actinoplanes sp. ableiten. Von den durch den Acarboseproduzenten selbst bereitgestellten Maltosacchariden aus Stärke profitieren artfremde Mikroorganismen nicht, da neben den Exoenzymen auch die Maltodextrin-Aufnahmesysteme in ihrer Funktion gehemmt sind. Außerdem wurde eine für Actinoplanes sp. geforderte Kapazität zur Aufnahme von Maltose und Maltodextrinen in vivo gefunden und in Transportexperimenten mit radioaktiv markierten Zuckern charakterisiert. Die Transportaktivität wird wahrscheinlich über zwei Bindeprotein-abhängige ABC-Importer mit multiplem Substratspektrum realisiert. Das ABC-Importsystem AcbHFG wurde heterolog in E. coli und S. lividans synthetisiert und z. T. erfolgreich gereinigt. In Substrat-Bindungsstudien konnte für das Bindeprotein AcbH eine Interaktion mit Acarbose und längerkettigen Derivaten, nicht jedoch mit Maltose/Maltodextrinen beobachtet werden. / Acarbose acts as an inhibitor of alpha-glucosidases and is therefore clinically used. The biosynthesis gene cluster (acb) was identified and partly characterized. The proposed model describes a pathway in which acarbose might function as a carbophor. The molecule is secreted into the medium where, after hydrolysis of starch, it is charged with additional glucose moieties. Re-uptake by a binding-protein dependent ABC importer AcbHFG would then result in a net gain of carbon and energy. Besides extracting glucose from the extracellular pool acarbose also acts as an inhibitor of alpha-amylases secreted by competitors in the natural environment. Prompted by the structural similarity between acarbose and maltotetraose, the effects of acarbose on the metabolism of maltose and maltodextrins in whole cells of E. coli and on individual components of the maltose / maltodextrin system were studied. The results demonstrate that acarbose is efficiently transported but not metabolized by E. coli due to its poor performance as a substrate of maltodextrin-degrading enzymes. Thus, besides acting as a carbophor acarbose also severely inhibits growth of competitors on maltodextrins. Actinoplanes using starch as carbon source should be able to import maltose and maltodextrins. Experiments with radioactive sugars indicate the action of two different binding-protein dependent ABC transport systems with a multiple substrate spectrum. Within the acb cluster a putative operon (acbHFG) encoding components of an ABC import system was found. To elucidate gene functions the products were overproduced in E. coli and S. lividans and some of the proteins were purified. Surface plasmon resonance analysis showed that the substrate binding protein AcbH binds acarbose and longer derivatives, but not maltose and maltodextrins.

ABC (ATP-binding-cassette)-Transporter katalysieren den ATP-abhängigen Transport diverser niedermolekularer Substanzen durch die biologische Zellmembran. Ihr Vorkommen erstreckt sich auf alle drei Domänen des Lebens. Der Maltose Transporter von E.coli gehört zu dieser Superfamilie der ABC-Transporter. Die Kristallstrukturen des Transporters MalFGK2 wurden kürzlich gelöst für dessen inaktiven Zustand als auch für dessen katalytischen Zwischenzustand. Um den Transportmechanismus besser verstehen zu können, müssen die Kristallstrukturen des Transporters und seiner Komponenten unter physiologischen Bedingungen genau geprüft werden, um den daraus katalytischen Mechanismus zu bewerten. Im rahmen der Dissertation konnte mittels Lösungs-NMR kann gezeigt werden, dass die periplasmatische Schleife P2 von MalF eine unabhängige Faltung aufweist und eine wohl definierte Tertiärstruktur einnimmt, die vergleichbar ist mit der im Kristall vorliegenden Konformation. MalF-P2 interagiert unabhängig von der Transmembranregion von MalF und MalG mit dem Maltose-Bindeprotein in An- und Abwesenheit des Substrats mit einem KD im mikromolaren Bereich. NMR Untersuchungen zu den an der Interaktion beteiligten Aminosäuren stehen in Einklang mit den Kristallstrukturdaten. Die Analyse residualer dipolarer Kopplungen (RDC) zeigt, dass die Konformation der zwei individuellen Domänen von MalF-P2 in Abwesenheit von MalE erhalten bleibt und der im Kristall ähnelt. Die Zugabe von MalE induziert eine Änderung der relativen Orientierung der zwei Domänen von MalF-P2 um so dem räumlichen Anspruch des Liganden gerecht zu werden. Besonders betroffen hiervon ist die Domäne 2 von MalF-P2, deren Konformation abweicht von der in der Kristallstruktur. Die Struktur der Domäne 1 dagegen bleibt konserviert, während sich lediglich ihre relative Orientierung zu Domäne 2 ändert. MD Simulationen des MalF-P2-MalE-Komplexes deuten auf eine stark dynamische Interaktion von MalF-P2 mit der MalE Bindungsregion hin. NMR CPMG Kinetikstudien weisen auf die Bildung eines ungewöhnlichen Knicks in alhpa-Helix alpha2 während der Assoziation hin. Diese konformelle Änderung der alpha-Helix findet auf einer Zeitskala von Millisekunden statt, was im Einklang mit der Austauschrate der Komplexbildung ist. / ABC (ATP-binding-cassette)-transporters catalyze the ATP-dependent transport of diverse solutes across the cellular membrane. They are present in all three kingdoms of life. The E.coli maltose transporter belongs to the ATP binding cassette (ABC) transporter superfamily. Recently, the crystal structures of the full transporter MalFGK2 in its resting and a catalytic intermediate state was solved. At the present state of research, it is of particular interest to scrutinize the X-ray structures of the transporter and its components under physiological conditions as well as to evaluate their implications for the catalytic mechanism. In the context of the PhD thesis, it could be shown using solution-state NMR that the periplasmic loop P2 of MalF folds independently in solution and adopts a well-defined tertiary structure, which is similar to the one found in the crystal structure. MalF-P2 interacts with the maltose binding protein, independent of the transmembrane region of MalF and MalG, with a KD in the µM range, in the presence and absence of substrate. NMR studies showed good agreement of the residues interacting in solution to those identified in the X-ray structure. Analysis of residual dipolar coupling (RDC) experiments shows that the conformation of the two individual domains of MalF-P2 is preserved in the absence of MalE, and resembles the conformation in the X-ray structure. Upon titration of MalE to MalF-P2, the two domains of MalF-P2 change their relative orientation in order to accommodate the ligand. In particular, a conformational change of domain 2 of MalF-P2 is induced, which is distinct to the conformation found in the X-ray structure. Domain 1 retains its structure but changes its relative orientation to domain 2. MD simulations of the MalF-P2 – MalE complex show a highly dynamic interaction of MalF-P2 to the MalE interface. From NMR CPMG kinetic studies, a peculiar kink of alpha-helix alpha2 can be seen introduced upon association. The transition time of this conformational change of the alpha-helix is on the ms timescale, which is matching the exchange rate of the complex formation.

ATP-binding cassette (ABC) transporters are transmembrane proteins that transport a wide variety of substrates across intra and extra-cellular membranes. A few examples of endo and xenobiotic substrates are metabolic products, lipids, sterols, and drugs. An important function of ABC transporters involved in export is to prevent intracellular the buildup of toxic products. Several ABC transporters have also been associated with drug resistance upon treatment with chemotherapeutic agents. P-glycoprotein (P-GP) and the multidrug resistant (MRP) transporters of the ABC C family are examples of transporters that confer chemo-resistance. We have studied two unique roles of ABC transporters in the liver and the heart. In the liver, maintenance of bile secretion is important during lactation to ensure proper absorption of nutrients for the offspring. Three main ABC transporters are involved in this process: ABCB11 (transports bile acids), ABCB4 (transporters phospholipids), and ABCG5/ABCG8 (transports cholesterol). In the rat, expression of ABCB11 remains the same as the size of the bile acid pool increases. However, the expression of ABCG5/ABCG8 is abolished, preventing excessive export and loss of cholesterol from the liver. The regulation of these transporters during lactation maintains the production of bile acids from cholesterol by decreasing export while preventing toxicity from bile acids by maintaining bile flow. Another protective role of ABC transporters is seen in oxidative stress-induced toxicity of cardiac tissue following treatment with Doxorubicin (DOX), a drug used in cancer treatment. Multidrug resistance protein 1 (Mrp1) can transport toxic products by conjugation with sulfate, glutathione (GSH) or glucuronide. In Mrp1-/- mice, DOX causes advanced cell damage through intracellular edema and increased apoptotic nuclei. However, P-glycoprotein expression increases upon DOX treatment, potentially compensating for the loss of Mrp1. Mrp1 can also transport GSH, GSH disulfide (GSSG), and products of oxidation, like GSH conjugates. In the absence of Mrp1, GSH levels are increased in the heart, providing protection against oxidative stress. Both of these examples in liver and heart show the diversity of ABC transporters and the role they play in preventing cell toxicity. These studies also provide insight into ways to prevent cell toxicity through manipulation of ABC transport proteins.

Breast cancer is a leading cause of death among women in many countries. In the treatment of the breast cancer cytotoxic drugs (chemotherapy) are often used. Interindividual differences of drug response are an important cause of treatment failures. Bioavailability also depends on a major extent from the expression and activity of drug transport across biomembranes. In particular efflux transporters of the ATP-binding cassette family such as ABCB1, ABCC1 and ABCC2 have been identified as major determinants of chemoresistance in tumor cells. It was hypothesized that variance in the gene expression of membrane transporters and their genetic variance could explain at least in part interindividual differences of pharmacokinetics and clinical outcome of a variety of drugs. This thesis focuses on the functional significance of gene expression of ABCB1, ABCC1 and ABCC2 and single nucleotide polymorphisms in ABCC1 gene.

Benznidazol (BZ), fármaco utilizado para o tratamento da doença de Chagas, apresenta eficácia limitada na fase crônica da doença. Falhas terapêuticas foram atribuídas majoritariamente a diferenças na suscetibilidade a BZ entre as cepas do T. cruzi. Resultados prévios de nosso grupo indicam que o gene de um transportador ABC da subfamília G, TcABCG1, encontra-se super-expresso em cepas resistentes a BZ. Transportadores ABCG foram associados a resistência a drogas em vários organismos. O objetivo central do presente estudo foi caracterizar o gene TcABCG1 em cepas de diferentes linhagens e cuja suscetibilidade a BZ foi definida. A sequência do gene TcABCG1 (1.998 pb) de 14 cepas foi determinada. Observamos algumas variações de aminoácidos na proteína ABC entre as cepas. Análises genealógicas de TcABCG1 definiram quatro clados (TcI, TcII, TcIII e Tcbat). Os dois haplótipos das cepas híbridas TcV e TcVI agruparam com os clados TcII e TcIII. Dados de imunofluorescência indireta em epimastigotas indicam que TcABCG1 está localizado em vesículas intracelulares. / Benznidazole (BZ), drug employed for Chagas disease treatment, has limited efficacy in the chronic phase of the disease. Treatment failures have been attributed mostly to differences in BZ susceptibility among T. cruzi strains. Previous data from our group indicate that one ABC transporter gene of the G subfamily, named TcABCG1, is overexpressed in BZ-resistant strains. ABCG transporters have been associated to drug resistance in several organisms. The central goal of the present study was to characterize TcABCG1 gene in strains belonging to different lineages and of defined BZ susceptibility. TcABCG1 gene sequence (1,998 bp) of 14 strains was determined. Few amino acid substitutions were detected in the ABC transporter protein among the strains. Genealogic analyses of TcABCG1 showed four distinct clades (TcI, TcII, TcIII and Tcbat). The two haplotypes of TcV and TcVI hybrid strains clustered with TcII and TcIII clades. Indirect immunofluorescence analysis in epimastigote forms indicated that TcABCG1 is localized to intracellular vesicles.