RASA3 (Ras p21 GTPase Activating Protein 3) is required for D2SR (Dopamine D2 Short Receptor) induced ERK1/2 inhibition in pituitary lactotroph GH4ZR7 cells. We hypothesized that RASA3 may be important for D2SR signaling to inhibit ERK1/2 in dopamine neurons, and thus negatively regulate TH (Tyrosine Hydroxylase) expression and activity. We designed and made shRASA3 lentivirus and showed that it inhibits RASA3 expression. Lentivirus mediated RASA3 knockdown can partially reverse the D2SR mediated ERK1/2 inactivation in GH4ZR7 cells. We then showed that knockdown of RASA3 in dopamine-secreting PC12 cells increased NGF-stimulated ERK1/2 in cells expressing D2SR, but not in cells lacking D2SR, thus implicating RASA3 plays a role in D2SR-mediated inhibition of ERK1/2 signaling. We also found that knockdown of RASA3 increased TH protein levels in cells expressing D2R receptors but not those without D2SR, suggesting that D2SR tonically inhibits the synthesis of TH. We also found preliminary indication that mutant RASA3 mice show increased level of TH in SN compared to WT mice. RASA3 mutant mice showed no striking changes in basal locomotion, anxiety or depression phenotypes, but further studies are needed to specifically address dopamine-driven behaviors. In summary, our data support the role of RASA3 in mediating D2SR-induced inhibition of ERK1/2 in dopamine neurons to negatively regulate TH expression and activity.

Serotonin (5-HT) containing neuroepithelial cells (NECs) are O2 sensitive chemoreceptors found throughout the skin of larval zebrafish (Danio rerio). Zebrafish larvae are sensitive to changes in ambient PO2 as early as 2 days post fertilisation (dpf) and hyperventilate in response to hypoxia beginning at 3 dpf. Tryptophan hydroxylase (tph) is the rate-limiting enzyme in 5-HT synthesis; three tph paralogs are present in zebrafish (tph1a, tph1b and tph2). Although 5-HT has been implicated as a key neurotransmitter mediating hypoxic hyperventilation, it has not been possible to discern the role of 5-HT specifically contained within the NECs in promoting hypoxic hyperventilation. The purpose of this study was to determine the role of NEC 5-HT in regulating the hypoxic ventilatory response in larval zebrafish. It was hypothesised that 5-HT is a key neurotransmitter released from NECs which contributes to hypoxic hyperventilation. Immunohistochemistry was used to determine the distribution of tph paralogs and their role in 5-HT production in NECs. Tph1a was present in NECs and nerves innervating NECs. Exposure to the non-selective tph inhibitor, para-chlorophenylalanine (pCPA), or translational gene knockdown of tph1a, diminished 5-HT expression within NECs. Exposure to acute hypoxia (PO2 = 30 mmHg) revealed a blunted hypoxic ventilatory response (reduced breathing frequency) in fish exhibiting depleted 5-HT in NECs. The hypoxic hyperventilatory response was rescued with application of 5-HT. The results of these experiments demonstrate that tph1a is responsible for 5-HT production in NECs of larval zebrafish, and that 5-HT released from NECs is involved in establishing their hypoxic hyperventilatory response.

Le coenzyme Q est une molécule lipophile rédox rencontrée chez les eucaryotes et chez la plupart des procaryotes. La structure de Q correspond à une benzoquinone substituée par une chaîne polyisoprényle dont la longueur varie selon les organismes. Q joue le rôle de transporteur d'électrons dans les chaînes respiratoires d'où provient la plupart de l'énergie de la cellule. La biosynthèse de Q chez la bactérie Escherichia coli comporte huit étapes et implique au moins neuf protéines (UbiA-UbiH et UbiX). Trois réactions d'hydroxylation sont nécessaires pour la biosynthèse de Q8 en conditions aérobies. Alors que les protéines UbiH et UbiF présentent des homologies de séquence avec des monooxygénases à flavine connues pour catalyser des réactions d'hydroxylation, UbiB qui a été proposée comme étant la troisième hydroxylase, présente uniquement une homologie de séquence avec des kinases. Nous rapportons dans ce travail que la protéine VisC, renommée UbiI, catalyse la réaction d'hydroxylation auparavant attribuée à UbiB. Nous avons également identifié deux nouvelles protéines (YigP et YqiC, renommées respectivement UbiJ et UbiK) importantes pour le métabolisme de Q chez Escherichia coli puisque leur mutation diminue fortement le contenu en Q des souches mutantes. Ces protéines interagissent avec la plupart des protéines connues pour participer à la biosynthèse de Q ce qui implique l'existence d'un complexe de biosynthèse de Q. En utilisant des approches biochimiques et protéomiques, nous avons pu mettre en évidence un complexe impliquant plusieurs protéines Ubi et notamment UbiJ et UbiK. Ces deux protéines semblent avoir un rôle dans l'assemblage et/ou la stabilisation de ce complexe multiprotéique. Enfin, nous nous sommes intéressés à la biosynthèse de Q dans des conditions de cultures anaérobies. Nos résultats montrent l'existence « d'hydroxylases anaérobies », inconnues à ce jour, qui remplaçent les hydroxylases aérobies UbiH, UbiI et UbiF. Grâce à une approche phylogénétique, nous identifions un gène important pour la biosynthèse de Q uniquement en conditions anaérobies suggérant une réorganisation de la biosynthèse de Q entre ces deux environnements fréquemment rencontrés par E. coli. L'ensemble de nos résultats a permis d'améliorer notre connaissance de la voie de biosynthèse procaryote de Q grâce à la découverte de nouveaux gènes impliqués dans ce processus et grâce à l'identification de la fonction moléculaire de certaines protéines. / Ubiquinone (Q) is a lipophilic compound that plays an important role in electron and proton transport in the respiratory chains of Escherichia coli. Besides this important role in energy production, Q also functions as a membrane soluble antioxidant. The biosynthesis of Q8 requires eight reactions and involves at least nine proteins (UbiA-UbiH and UbiX) in Escherichia coli. Three of these reactions are hydroxylations resulting in the introduction of a hydroxyl group on carbon atoms at position 1, 5 and 6 of the aromatic ring. The C1 and C6 hydroxylation are well characterized whereas the C5 hydroxylation has been proposed to involve UbiB, a protein kinase without any sequence homology with monooxygenase. In this work, by genetic and biochemical methods we provide evidence that VisC which we renamed UbiI, displays sequence homology with monooxygenases and catalyzes the C5 hydroxylation, not UbiB. We have identified two new genes, yqiC and yigP (renammed UbiJ and UbiK) which are required only for Q8 biosynthesis in aerobic conditions. The exact role of the corresponding proteins, renamed UbiJ and UbiK, remains unknown. These proteins are able to interact with other Ubi proteins to be able to produce Q supporting the protein complex hypothesis. Our progress on the characterization of an Ubi-complex regrouping several Ubi proteins suggest that UbiJ and UbiK may fulfill functions related to the Ubi-complex stability. Mutants affected in hydroxylation steps are deficient for Q8 in aerobic conditions but recover a wild type Q8 content when grown in anaerobic conditions. This intriguing observation supports the existence of an alternative hydroxylation system independent from dioxygen which has not been characterized so far. By phylogenetic studies, we have identified a new gene in which the deletion affect the biosynthesis of Q only in anaerobic conditions suggesting a reorganization of Q biosynthesis in these two conditions. Our results has improved our knowledge of the prokaryotic Q biosynthetic pathway through the discovery of new genes involved in this process and through the identification of the molecular function of some proteins.

Abstract HIF prolyl 4-hydroxylases (HIF-P4Hs) and HIF asparaginyl hydroxylase (FIH) are novel members of the 2-oxoglutarate dioxygenase family that play key roles in the regulation of the hypoxia-inducible transcription factor (HIF). They hydroxylate specific proline and asparagine residues in HIF-α, leading to its proteasomal degradation and inhibition of its transcriptional activity, respectively. These enzymes are inhibited in hypoxia, and as a consequence HIF-α becomes stabilized, forms a dimer with HIF-β, attains its maximal transcriptional activity and induces expression of many genes that are important for cell survival under hypoxic conditions. The three HIF-P4Hs and FIH were expressed here as recombinant proteins in insect cells and purified to near homogeneity. All these enzymes were found to require long peptide substrates. The three HIF-P4Hs and FIH acted differently on the various potential hydroxylation sites in the HIF-α isoforms. The HIF-P4Hs acted well on sequences with cores distinctly different from the core motif -Leu-X-X-Leu-Ala-Pro-, suggested based on sequence analysis studies, the alanine being the only relatively strict requirement in addition to the proline itself. Acidic residues around the hydroxylation site also played a distinct role. These results together with those of others provide evidence that there is no conserved core motif for the hydroxylation by HIF-P4Hs. The Km values of the HIF-P4Hs for O2 were slightly above its atmospheric concentration, while the Km of FIH was about one-third of these values but still 2.5 times that of the type I collagen P4H. The HIF-P4Hs are thus effective oxygen sensors, as even small decreases in the amount of O2 affect their activities, while a more severe decrease is required to inhibit FIH activity. Small molecule inhibitors of the collagen P4Hs also inhibited the HIF-P4Hs and FIH but with distinctly different Ki values, indicating that it should be possible to develop specific inhibitors for the HIF-P4Hs and FIH. The HIF-P4Hs were found to bind the iron cosubstrate more tightly than FIH and the collagen P4Hs, and the chelator desferrioxamine was an ineffective inhibitor of the HIF-P4Hs in vitro. Several metals were effective competitive inhibitors of FIH but they were ineffective inhibitors of the HIF-P4Hs. The well-known stabilization of HIF-1α by cobalt and nickel is thus not due to a simple competitive inhibition of the HIF-P4Hs, and is probably at least in part due to HIF-P4H-independent mechanisms. The effective inhibition of FIH by these metals nevertheless indicates that the stabilized HIF-1α is transcriptionally fully active.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第21816号 / 農博第2329号 / 新制||農||1066(附属図書館) / 学位論文||H31||N5188(農学部図書室) / 京都大学大学院農学研究科応用生命科学専攻 / (主査)教授 梅澤 俊明, 教授 矢﨑 一史, 教授 植田 充美 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

The present study investigated the effects of forced overexpression of Phox2a/2b, two transcription factors, in the locus coeruleus (LC) of aged rats on noradrenergic and dopaminergic phenotypes in brains. Results showed that a significant increase in Phox2a/2b mRNA levels in the LC region was paralleled by marked enhancement in expression of DBH and TH per se. Furthermore, similar increases in TH protein levels were observed in the substantial nigra and striatum, as well as in the hippocampus and frontal cortex. Overexpression of Phox2 genes also significantly increased BrdU-positive cells in the hippocampal dentate gyrus and NE levels in the striatum. Moreover, this manipulation significantly improved the cognition behavior. The in vitro experiments revealed that norepinephrine treatments may increase the transcription of TH gene through the epigenetic action on the TH promoter. The results indicate that Phox2 genes may play an important role in improving the function of the noradrenergic and dopaminergic neurons in aged animals, and regulation of Phox2 gene expression may have therapeutic utility in aging or disorders involving degeneration of noradrenergic neurons.

No description available.

Abstract Collagens are subject to extensive post-translational modifications, including the formation of 4-hydroxyproline, 3-hydroxyproline and hydroxylysine. These reactions are catalyzed by collagen prolyl 4-hydroxylases (C-P4Hs), prolyl 3-hydroxylases (P3Hs) and lysine hydroxylases (LHs), which belong to the 2-oxoglutarate-dependent dioxygenase family and require oxygen for their reaction. 4-Hydroxyproline residues have for a long time been known to be required for the stability of the collagen triple helix, but the role of prolyl 3-hydroxylation was revealed only a few years ago when mutations in P3H1 and the consequent loss of a single 3-hydroxyproline in collagen I was shown to cause recessive osteogenesis imperfecta. In this thesis the human P3H isoenzymes were expressed as recombinant enzymes, and analyses of their tissue expression and kinetic properties revealed that P3H2 is located in tissues rich in basement membranes and that it hydroxylates collagen IV, the major basement membrane collagen. The roles of the collagen hydroxylases and collagen IV in basement membrane formation were further studied using Madin-Darby canine kidney (MDCK) epithelial cells as an in vitro model for cell polarization. 4-Hydroxyproline also has a pivotal role in the system of cellular response to reduced oxygen levels (hypoxia). At a normal oxygen concentration, two proline residues in the α subunit of the hypoxia-inducible factor (HIF) are 4-hydroxylated by the HIF-P4Hs, which target HIF-α for proteasomal degradation. In hypoxia, the HIF-P4Hs are inactive, and the α subunit thus escapes degradation, dimerizes with a β subunit and after recruiting transcriptional coactivators induces the transcription of hypoxia-responsive genes in order to adapt the cell to hypoxia. Three human HIF-α subunits have been characterized to date, of which the third is known to be subject to extensive alternative splicing, with one of the splicing variants acting as a negative regulator of the hypoxia responsive system. Four novel splicing variants generated from the human HIF-3α locus are characterized here, and the expression of HIF-3α variants has been shown to be upregulated by hypoxia in a HIF-1 dependent manner. Further studies on the binding partners and transcriptional activity of HIF-3α revealed that this subunit has a more complex role in the adaptation of cells to hypoxia than had been expected. / Tiivistelmä Kollageenit ovat valkuaisaineita, joihin kohdistuu useita synteesin jälkeisiä muokkauksia kuten 4-hydroksiproliinin, 3-hydroksiproliinin ja hydroksilysiinin muodostuminen. Näitä reaktioita katalysoivat kollageeniprolyyli-4-hydroksylaasit (C-P4H:t), prolyyli-3-hydroksylaasit (P3H:t) ja lysyylihydroksylaasit (LH:t), jotka kuuluvat 2-oksoglutaraattidioksygenaasien entsyymiperheeseen ja tarvitsevat happea reaktioonsa. 4-hydroksiproliinitähteiden on kauan tiedetty stabiloivan kollageeninrakenteen, kun taas 3-hydroksiproliinitähteiden merkitys on selvinnyt vasta viime vuosina. Mutaatiot P3H1-isoentsyymiä koodittavassa geenissä ja sen seurauksena yhden ainoan 3-hydroksiproliinitähteen puuttuminen kollageenissa I johtavat vaikeaan luustosairauteen, osteogenesis imperfectaan. Tässä väitöskirjassa ihmisen P3H:t tuotettiin rekombinanttiproteiineina. Tulokset paljastivat, että P3H2 ilmentyy erityisesti kudoksissa, joissa on paljon tyvikalvorakenteita ja että P3H2 hydroksyloi tehokkaasti kollageeni IV:n kaltaisia synteettisiä peptidejä. Lisäksi koiran munuaisten epiteelisoluihin pohjautuvaa in vitro-mallia käytettiin apuna tutkiessamme kollageeneja hydroksyloivien entsyymien ja kollageenin IV roolia tyvikalvon muodostumisessa sekä solujen polarisaatiossa. Kollageenia stabiloivan tehtävänsä lisäksi 4-hydroksiproliinilla on myös merkittävä rooli solujen vasteessa vähähappisille olosuhteille (hypoksia). Normaalissa happiosapaineessa (normoksia), hypoksiaindusoituvan tekijän (HIF) α-alayksikköön muodostuu HIF-P4H entsyymien katalysoimana kaksi 4-hydroksiproliinitähdettä, jotka kohdistavat α-alayksikön proteasomaaliseen hajotukseen. Hypoksiassa HIF-P4H:t eivät kykene toimimaan, jolloin α-alayksikkö säästyy hajotukselta, muodostaa kompleksin β-alayksikön kanssa ja sitoo transkriptiokofaktoreita. HIF-kompleksi kykenee tällöin lisäämään hypoksiassa tarvittavien geenien luentaa. Tänä päivänä tunnetaan kolme HIF α-alayksikköä, joista HIF-3α:sta tiedetään esiintyvän useita erilaisia silmukointimuotoja ja yhden näistä muodoista tiedetään toimivan negatiivisena säätelijänä hypoksiavasteessa. Tässä väitöskirjatyössä on tunnistettu neljä uutta HIF-3α:n silmukointimuotoa ja osoitettu että HIF-3α:n määrä kasvaa hypoksiassa HIF-1:n säätelemänä. Lisäksi sitoutumis- ja transkriptiokokeet paljastivat, että HIF-3α:n rooli hypoksiavasteessa on monimutkaisempi kuin aikaisemmin kuviteltiin.

Cultured human lymphocytes may be assayed for aryl hydrocarbon hydroxylase (AHH) in whole cell preparations. The optimum assay conditions are pH 8.5, and 1.5 mM Mg++. The reaction is linear with time and cell number, and is inhibited by CO. Estradiol may inhibit induction of AHH by 3-methylcholanthrene, but is a poor competitor for the enzyme. A Caucasian population was assayed for AHH activity. The distribution was lognormal; no difference was found in cultured cells from males and females or smokers and nonsmokers. Cells from relatives of lung cancer patients showed higher activity. An American Indian population showed no difference from the Caucasian population in enzyme level. No linkage was found between AHH and 16a-hydroxylase.

This thesis sought to investigate novel methods for protecting the liver from ischaemia reperfusion injury in the context of liver transplantation. Research in the heart, brain and kidneys has suggested that hypoxia inducible factor (HIF) may play a key role in the delayed phase of ischaemic preconditioning and can protect organs for up to 3 days. However, although there is good evidence for the potential of HIF to protect organs from ischaemia, the HIF pathway still presents some what of a paradox because it targets both pro-death (e.g. BNIP3,NIX) as well as pro-survival genes (e.g. HO-I, EPO). HIF is primarily controlled by 3 oxygen dependent prolyl hydroxylases (PHD 1 , PHD2, PHD3), and inhibition of these prolyl hydroxylases leads to HIF activation. It was hypothesised that differential inhibition of PHD 1,2 or 3 may result in selective gene regulation and may confer greater or less protection against ischaemia reperfusion injury. To investigate this hypothesis mouse embryonic fibroblasts (MEFs) were isolated from PHDl, 2, and 3 knock-out (KO) embryos and compared to MEFs derived from WT littermate controls. In these MEFs, cell growth and proliferation, as well as cell survival following exposure to anoxia and inducers of apoptosis was studied. The principal findings were that PHD2 is the dominant regulator of HIF in normoxia. PHD2 knock-out MEFs exhibited glycolytic metabolism and had a lower oxygen consumption compared to wild-type MEFs. Gene array studies confirmed the dominant role of PHD2 but also demonstrated that PHD 1 upregulates a number of HIF target genes, albeit to a lesser extent than PHD2. There were no differences, however, in susceptibility to hypoxic injury in the PHDl, 2, and 3 knock-out MEFs compared to wild-type controls. A further aim of the study was to investigate whether prolyl hydroxylase inhibition using dimethyloxalyglycerine (DMOG) may protect the liver in a rodent model of ischaemia reperfusion injury. DMOG effectively upregulated HIF and IllF target genes. Serum transaminases (AST and AL T) were significantly lower in the DMOG treated animals compared to the normal saline treated controls 24 hours following ischaemia. This protection was similar to the protection conferred by surgically induced ischaemic preconditioning. This thesis provides important insights into the individual function of the prolyl hydroxylases and provides preliminary evidence that prolyl hydroxylase inhibitors may be useful in the treatment of ischaemia reperfusion injury in liver transplantation.