Boris Bryk

Publications (4)13.84 Total impact

• Article: MAP4K3 regulates body size and metabolism in Drosophila.

  Boris Bryk, Katrin Hahn, Stephen M Cohen, Aurelio A Teleman
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  ABSTRACT: The TOR pathway mediates nutrient-responsive regulation of cell growth and metabolism in animals. TOR Complex 1 activity depends, amongst other things, on amino acid availability. MAP4K3 was recently implicated in amino-acid signaling in cell culture. We report here the physiological characterization of MAP4K3 mutant flies. Flies lacking MAP4K3 have reduced TORC1 activity detected by phosphorylation of S6K and 4EBP. Furthermore MAP4K3 mutants display phenotypes characteristic of low TORC1 activity and low nutrient availability, such as reduced growth rate, small body size, and low lipid reserves. The differences between control and MAP4K3 mutant animals diminish when animals are reared in low-nutrient conditions, suggesting that the ability of TOR to sense amino acids is most important when nutrients are abundant. Lastly, we show physical interaction between MAP4K3 and the Rag GTPases raising the possibility they might be acting in one signaling pathway.
  Developmental Biology 05/2010; 344(1):150-7. · 4.07 Impact Factor
• Article: Acetylcholinesterase/paraoxonase interactions increase the risk of insecticide-induced Parkinson's disease.

  Liat Benmoyal-Segal, Tatiana Vander, Sagiv Shifman, Boris Bryk, Richard P Ebstein, Esther-Lee Marcus, Jochanan Stessman, Ariel Darvasi, Yuval Herishanu, Alon Friedman, Hermona Soreq
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  ABSTRACT: Exposure to agricultural insecticides, together with yet incompletely understood predisposing genotype/phenotype elements, notably increase the risk of Parkinson's disease. Here, we report findings attributing the increased risk in an insecticide-exposed rural area in Israel to interacting debilitating polymorphisms in the ACHE/PON1 locus and corresponding expression variations. Polymorphisms that debilitate PON1 activity and cause impaired AChE overproduction under anticholinesterase exposure were strongly overrepresented in patients from agriculturally exposed areas, indicating that they confer risk of Parkinson's disease. Supporting this notion, serum AChE and PON1 activities were both selectively and significantly lower in patients than in healthy individuals and in carriers of the risky polymorphisms as compared with other Parkinsonian patients. Our findings suggest that inherited interactive weakness of AChE and PON1 expression increases the insecticide-induced occurrence of Parkinson's disease.
  The FASEB Journal 04/2005; 19(3):452-4. · 5.71 Impact Factor
• Article: Inherited and acquired interactions between ACHE and PON1 polymorphisms modulate plasma acetylcholinesterase and paraoxonase activities.

  Boris Bryk, Liat BenMoyal-Segal, Erez Podoly, Oded Livnah, Arik Eisenkraft, Shai Luria, Amir Cohen, Yoav Yehezkelli, Ariel Hourvitz, Hermona Soreq
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  ABSTRACT: The 5.5 Mb chromosome 7q21-22 ACHE/PON1 locus harbours the ACHE gene encoding the acetylcholine hydrolyzing, organophosphate (OP)-inhibitable acetylcholinesterase protein and the paraoxonase gene PON1, yielding the OP-hydrolyzing PON1 enzyme which also displays arylesterase activity. In search of inherited and acquired ACHE-PON1 interactions we genotyped seven polymorphic sites and determined the hydrolytic activities of the corresponding plasma enzymes and of the AChE-homologous butyrylcholinesetrase (BChE) in 157 healthy Israelis. AChE, arylesterase, BChE and paraoxonase activities in plasma displayed 5.4-, 6.5-, 7.2- and 15.5-fold variability, respectively, with genotype-specific differences between carriers of distinct compound polymorphisms. AChE, BChE and arylesterase but not paraoxonase activity increased with age, depending on leucine at PON1 position 55. In contrast, carriers of PON1 M55 displayed decreased arylesterase activity independent of the - 108 promoter polymorphism. Predicted structural consequences of the PON1 L55M substitution demonstrated spatial shifts in adjacent residues. Molecular modelling showed substrate interactions with the enzyme variants, explaining the changes in substrate specificity induced by the Q192R substitution. Intriguingly, PON1, but not BChE or arylesterase, activities displayed inverse association with AChE activity. Our findings demonstrate that polymorphism(s) in the adjacent PON1 and ACHE genes affect each other's expression, predicting for carriers of biochemically debilitating ACHE/PON1 polymorphisms adverse genome-environment interactions.
  Journal of Neurochemistry 04/2005; 92(5):1216-27. · 4.06 Impact Factor
• Article: TOR signaling : from FRET probes development to function of MAP4K3 in Drosophila

  Boris Bryk
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  ABSTRACT: Cells in a multicellular organism need to monitor their environment for nutritional cues, growth and stress signals in order to adapt their metabolism and growth to the changing conditions. The Target of Rapamycin (TOR) signaling pathway is an evolutionary conserved cellular protein network that controls responses to these signals. TOR signaling is a major research topic because of its role in several prevalent human disorders, including cancer and diabetes, but our understanding of TOR pathway is still far from complete. This work is aimed at improving our understanding of TOR signaling in two ways: by developing new research tools to dissect the dynamics of TOR signaling in cells and by characterizing the function of a novel component in the TOR pathway. The first chapter presents the project to develop a probe, based on the Fluorescence Resonance Energy Transfer (FRET) method, for measuring TOR activity in cell culture. I used several approaches to design a FRET probe, based on a substrate of TOR kinase called 4EBP1. These probes did not prove to be useful because fusions to fluorophore domains abolished biological regulation of 4EBP1. An alternative strategy whereby a small tag was introduced into 4EBP1 and then used for in vivo labeling, could solve this problem. Unfortunately, when this probe was expressed in the cells, its interaction with a corresponding partner did not produce a reliable FRET signal, as determined by three different methods. Nevertheless, the obtained results can be used as a basis for future attempts to develop probes for TOR kinase. The second chapter describes the genetic analysis of the MAP4K3 function in Drosophila. MAP4K3 is a new component of the TOR pathway proposed to mediate nutrient sensing by TOR. I identified a strong hypomorphic MAP4K3 mutant and investigated the phenotypes caused by absence of this protein. MAP4K3 mutant flies were viable but weak. Mutant animals demonstrated delayed growth, reduced cell and organ size. Furthermore, they were lean, displaying reduced fat, which could be rescued by genetically increasing TOR activity. This suggests that the observed metabolic defect is due to low TOR activity. The mechanism of MAP4K3 action may involve the MAP kinase pathway and/or modifying activity of Rag GTPases, which can interact with MAP4K3 in cell culture. These results establish MAP4K3 as a regulator of metabolism and growth and open up new possibilities for manipulating TOR signaling. Die Zellen eines vielzelligen Organismus müssen ihre Umbegung auf Nahrungs-, Wachstums- und Stresssignale überwachen, um ihren Stoffwechsel und ihr Wachstum den sich wandelnden Bedingungen anzupassen. Der Rapamycin (TOR) Signalweg stellt ein evolutionär konserviertes zelluläres Proteinnetzwerk dar, welches die spezifischen Reaktionen der Zelle auf obige Reize kontrolliert. Die Signalübertragung durch TOR ist wegen seiner Rolle in mehreren weit verbreiteten menschlichen Krankheiten, darunter Krebs und Diabetis, ein wichtiges Forschungsgebiet, aber unser Verständnis des TOR Signalweges ist immer noch lückenhaft. In der vorliegenden Arbeit werden zwei Ansätze verfolgt, um unser Verständnis des TOR Signalweges zu erweitern: die Entwicklung neuer Werkzeuge zur Untersuchung des dynamischen Verhaltens des TOR Signalweges in Zellen und die funktionelle Charakterisierung einer neuen Komponente des TOR Signalweges. Das erste Kapitel stellt ein Projekt vor, im Rahmen dessen eine neue Sonde entwickelt wurde, die auf dem Prinzip des Flourescence Resonance Energy Transfer (FRET) beruht und mit deren Hilfe die TOR Aktivität von Zellen in Kultur gemessen werden sollte. Ich habe mehrere unterschiedliche Versuche unternommen, die Sonde auf dem TOR Kinase Substrat 4EBP1 basierend zu entwickeln. Diese Sonden konnten jedoch nicht für die Messungen verwendet werden, da die Fluorophordomäne die biologische Regulation des 4EBP1 beeinträchtigte. Durch eine andere Strategie, bei der ein kleinerer Affinitäts “tag“ in 4EBP1 eingeführt und für die in vivo Markierung verwendet wurde, konnte dieses Problem jedoch behoben werden. Leider zeigte diese FRET-Sonde, wenn sie in Zellen exprimiert wurde, aber das Problem, bei Interaktion mit ihrem entsprechenden Bindungspartner kein zuverlässiges FRET Signal zu liefern, was durch drei unterschiedliche Methoden nachgewiesen wurde. Die gewonnenen Ergebnisse können jedoch als Ausgangspunkt für zukünftige Versuche genutzt werden, Sonden für die TOR Kinase zu entwickeln. Das zweite Kapitel beschreibt die genetische Untersuchung der Funktion von MAP4K3 in Drosophila. MAP4K3 ist eine neue Komponente des TOR Signalweges, der die Funktion zugeschrieben wird, das Aufspüren von Nährstoffen durch TOR zu vermitteln. Ich habe eine starke hypomorphe Mutation in MAP4K3 identifiziert und den Phänotyp untersucht, den das Fehlen dieses Proteins verursacht. Fliegen mit der MAP4K3 Mutation waren lebensfähig, aber schwach. Sie wiesen ein verzögertes Wachstum und eine geringere Zell- nud Organgröße auf. Weiterhin waren sie übermäßig dünn und besaßen einen verminderten Körperfettanteil, was durch genetische Erhöhung der TOR Aktivität aufgehoben werden konnte. Dies legt nahe, dass der beobachtete Stoffwechseldefekt auf zu geringer TOR Aktivität beruht. Es ist möglich, dass für den Wirkmechanismus von MAP4K3 der MAP Kinase Signalweg eine Rolle spielt oder die Modulierung der Aktivität von Rag GTPasen, welche mit MAP4K3 in Zellkultur interagieren können. Die vorliegenden Ergebnisse etablieren MAP4K3 als einen Stoffwechsel- und Wachstumsregulator und eröffnen neue Möglichkeiten, den TOR Signalweg zu manipulieren.