Endosomes are now recognized as important sites for regulating signal transduction. Here we show that the lipid kinase phosphatidylinositol 4-kinase III beta (PI4KIIIβ) regulates both endocytic kinetics and receptor signaling in breast cancer cells. PI4KIIIβ generates phosphatidylinositol 4-phosphate from phosphatidylinositol and is highly expressed in a subset of breast cancers. However, the molecular mechanism by which PI4KIIIβ promotes breast cancer is unclear. We demonstrate that ectopic PI4KIIIβ expression increases the rates of both endocytic internalization and recycling. Furthermore, PI4KIIIβ deletion reduces endocytic kinetics. Regulation of endocytic function by PI4KIIIβ is independent of its kinase activity but requires interaction with the Rab11a GTPase. Additionally, we find that PI4KIIIβ activates IGF-IRβ signaling, dependent on endosome function. Finally, we observe that PI4KIIIβ deletion decreases the growth rate of mammary tumours in mice. Our work suggests a novel regulatory role for PI4KIIIβ in endosome function and plasma membrane receptor signaling, providing a mechanism by which increased PI4KIIIβ expression could promote breast cancer oncogenesis.

We recently reported that embryonic stem cells-conditioned medium (ES-CM) contains antiapoptotic factors that inhibit apoptosis in the cardiac myoblast H9c2 cells. However, the mechanisms of inhibited apoptosis remain elusive. In this report, we provide evidence for the novel mechanisms involved in the inhibition of apoptosis provided by ES-CM. ES-CM from mouse ES cells was generated. Apoptosis was induced after exposure with H2O2 (400 μm) in H9c2 cells followed by the replacement with ES-CM or culture medium. H9c2 cells treated with H2O2 were exposed to ES-CM, and ES-CM plus cell survival protein phosphatidylinositol 3-kinase/Akt inhibitor, LY-294002, or extracellular signal-regulated kinase (ERK1/2) inhibitor, PD-98050. After 24 h, H9c2 cells treated with ES-CM demonstrated a significant increase in cell survival. ES-CM significantly inhibited (P < 0.05) apoptosis determined by terminal deoxynucleotidyl transferase dUTP-mediated nickend labeling staining, apoptotic ELISA, and caspase-3 activity. Importantly, enhanced cell survival and inhibited apoptosis with ES-CM was abolished with LY-294002. In contrast, PD-98050 shows no effect on ES-CM-increased cell survival. Furthermore, H2O2-induced apoptosis is associated with decreased levels of phosphorylated (p)Akt activity. Following treatment with ES-CM, we observed a decrease in apoptosis with an increase in pAkt, and the increased activity was attenuated with the Akt inhibitor, suggesting that the Akt pathway is involved in the decreased apoptosis and cell survival provided by ES-CM. In contrast, we observed no change in ES-CM-decreased apoptosis or pERK with PD-98050. In conclusion, we suggest that ES-CM inhibited apoptosis and is mediated by Akt but not the ERK pathway.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第19552号 / 医博第4059号 / 新制||医||1012(附属図書館) / 32588 / 京都大学大学院医学研究科医学専攻 / (主査)教授 山田 泰広, 教授 藤田 潤, 教授 松田 道行 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(人間健康科学) / 甲第20293号 / 人健博第41号 / 新制||人健||4(附属図書館) / 京都大学大学院医学研究科人間健康科学系専攻 / (主査)教授 高桑 徹也, 教授 岩井 一宏, 教授 精山 明敏 / 学位規則第4条第1項該当 / Doctor of Human Health Sciences / Kyoto University / DFAM

Den aktuellen Forschungsgegenstand dieser Arbeit bildet der in Glioblastomen häufig überaktivierte PI3K/AKT/mTOR-Signalweg. Eine entscheidende Rolle bei der Aktivierung des Signalwegs spielt das Tumorsuppressorprotein PTEN. Ein mutiertes PTEN sorgt für die zuvor genannte Überaktivierung des PI3K/AKT/mTOR-Signalwegs und korreliert mit einer Radioresistenz. In der vorliegenden Arbeit wurde die strahlensensibilisierende Wirkung des neuartigen dualen PI3K/mTOR-Inhibitors NVP-BEZ235 an zwei humanen Glioblastomzelllinien mit unterschiedlichem PTEN-Status (GaMG: PTEN wt und U373-MG: PTEN mut) analysiert. Vergleichend dazu erfolgten Untersuchungen mit dem mTOR-Inhibitor Rapamycin und dem PI3K-Inhibitor LY294002. Untersucht wurden die Auswirkungen auf die Zellproliferation, die Strahlensensibilität, das Proteinexpressionsmuster, die Zellzyklusverteilung, die Induktion und Reparaturfähigkeit des DNS-Schadens sowie die Einleitung des programmierten Zelltods. U373-MG stellte sich im Vergleich zu GaMG als die strahlensensiblere Zelllinie heraus. Des Weiteren konnte gezeigt werden, dass die mTOR-Inhibition durch NVP-BEZ235, unabhängig vom PTEN-Status, für die Einflussnahme auf Proliferation und Proteintranslation vordergründig ist. Es kam zu keinen radiosensibilisierenden Effekten durch Zugabe von NVP-BEZ235, Rapamycin und LY294002 24 Stunden vor Bestrahlung, was auf das Ausbleiben eines erhöhten DNA-Schadens und einer verzögerten DNA-Reparatur, einen G1-Arrest und der Aktivierung des PI3K-Signalwegs zum Zeitpunkt der Bestrahlung sowie der Unterdrückung der Apoptose zurückzuführen ist. Trotz Ausbleiben radiosensibilisierender Effekt, konnte durch die Testsubstanzen eine starke zytostatische Wirkung gezeigt werden. / The current research topic of this work is the PI3K/AKT/mTOR signaling pathway, which is often overactivated in glioblastomas. The tumor suppressor protein PTEN plays a decisive role in the activation of the signaling pathway. A mutated PTEN provides the overactivation of the PI3K/AKT/mTOR signaling pathway and correlates with radiation resistance. In the present paper, the radiosensitizing effect of the novel dual PI3K/mTOR inhibitor NVP-BEZ235 on two human glioblastoma cell lines with different PTEN status (GaMG: PTEN wt and U373-MG: PTEN mut) was analyzed. Comparative studies were carried out with the mTOR inhibitor rapamycin and the PI3K inhibitor LY294002. The effects on cell proliferation, radiation sensitivity, protein expression pattern, cell cycle distribution, induction, and repairability of DNA damage as well as the initiation of programmed cell death were investigated. U373-MG turned out to be more radiosensitive compared to GaMG. Furthermore, it has been shown that mTOR-Inhibition by NVP-BEZ235 is essential for the influence on proliferation and protein translation, regardless of the PTEN status. The addition of NVP-BEZ235, rapamycin and LY294002 24 hours prior to irradiation did not lead to any radiosensitizing effect. This is due to the absence of increased DNA damage and delayed DNA repair, a G1 arrest and the activation of the PI3K signaling pathway at the time of irradiation and the suppression of apoptosis. Despite the lack of radiosensitizing effects, the test substances showed strong cytostatic effects.

No description available.

The phosphatidylinositol signaling pathway utilizes inositol-containing second messengers to mediate signaling events. The enzymes that metabolize phosphoinositides can in some cases serve to terminate the signaling actions of phosphoinositides. The inositol polyphosphate 5-phosphatases (5PTases) comprise a large protein family that hydrolyzes 5-phosphates from a variety of inositol phosphate and phosphoinositide substrates. I have examined the substrate specificity of the At5PTase11 protein from the model plant, Arabidopsis thaliana. The At5PTase11 gene (At1g47510) encodes an active 5PTase enzyme that can dephosphorylate the phosphoinositide substrates phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2], phosphatidylinositol 3,5-bisphosphate [PtdIns(3,5)P2], and phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P3]. In addition, the At5PTase11 gene is regulated by abscisic acid, jasmonic acid, and auxin, suggesting a role for phosphoinositide action in these signal transduction pathways. To further delineate the function of At5PTase11 in Arabidopsis thaliana, two independent T-DNA insertion mutant lines were isolated (At5ptase11-1 and At5ptase11-2). Analysis of At5ptase11 mutant lines revealed that At5ptase11 mutant seeds germinate slower compared to wild-type seeds. Moreover, At5ptase11 mutant seedlings demonstrated less hypocotyl growth when grown in the dark. These results indicate that At5PTase11 is required for the early stages of seed germination and seedling growth. Since there are 15 predicted 5PTases in Arabidopsis thaliana, a group of 5PTases have been analyzed to identify the 5PTases with similar substrate selectivity. At5PTase1 (At1g34120), At5PTase2 (At4g18010) and At5PTase3 (At1g71710) have been found to hydrolyze all four potential substrates, inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4], PtdIns(4,5)P2, and PtdIns(3,4,5)P3. At5PTase7 (At2g32010) hydrolyzed PtdIns(4,5)P2, and PtdIns(3,4,5)P3 which is similar to the substrate selectivity of At5PTase11. In addition, At5PTase4 (At3g63240), and At5PTase9 (At2g01900) hydrolyzed only PtdIns(4,5)P2. These results indicate that there are different groups of Arabidopsis thaliana 5PTases based on the substrate selectivity. These results suggest that Arabidopsis thaliana 5PTases with similar substrate selectivity may have overlapping functions. In summary, the findings that At5PTase11 is a phospholipid-specific 5PTase and At5PTase11 functions in the early stages of seed germination and seedling growth indicate that 5PTases play important roles in plant growth and development. / Ph. D.

Phosphoinositide-specific phospholipase C (PLC) is involved in Ca2+ mediated signalling events that lead to altered cellular status. PLC activation causes hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) and generates two second messengers, inositol 1,4,5-trisphosphate (IP3) and 1,2-diacylglycerol. Each has distinct role in depending on the cell type in mammalian cells, IP3 binds to intracellular receptors, stimulating the release of sequestered Ca2+. DAG remains in the membrane, where it can activate members of the protein kinase C (PKC) family. In plant absence of PKC keeps the question open as to what is the role of DAG in plants. The role of IP3 apart form triggering calcium release is not known, although the phosphorylated product of IP3 by groups of kinases has been implicated in certain nuclear signalling pathway. Using various sequence-analysis methods on plant PLC sequences, we identified two conserved motifs in known PLC sequences. The identified motifs are located in the C2 domain of plant PLCs and are not found in any other protein. These motifs are specifically found in the Ca2+ binding loops and form adjoining beta strands. Further, we identified certain conserved residues that are highly distinct from corresponding residues of animal PLCs. The motifs reported here could be used to annotate plant-specific phospholipase C sequences. Furthermore, we demonstrated that the C2 domain alone is capable of targeting PLC to the membrane in response to a Ca2+ signal. We also showed that the binding event results from a change in the hydrophobicity of the C2 domain upon Ca2+ binding. Bioinformatic analyses revealed that all PLCs from Arabidopsis and rice lack a transmembrane domain, myristoylation and GPI-anchor protein modifications. Our bioinformatic study indicates that plant PLCs are located in the cytoplasm, the nucleus and the mitochondria. Our results suggest that there are no distinct isoforms of plant PLCs, as have been proposed to exist in the soluble and membrane associated fractions. The same isoform could potentially be present in both subcellular fractions, depending on the calcium level of the cytosol. we have used Saccharomyces cerevisiae as a model system to investigate physiological function of PLC in regulation of lipid metabolism. S. cerevisiae synthesizes membrane phospholipids via a pathway which appears to be similar to that of higher eukaryotes. The synthesis of glycerolipid begins with the formation of phosphatidic acid which is quantitatively a minor lipid but is responsible for the repression of UNAINO-containing phospholipid biosynthetic gene by governing localization of Opi1. When the levels of phosphatidic acid are lowered which causes translocation of Opi1 from endoplasmic reticulum membrane to nucleus, where it binds to INO2 of the INO2-INO4 activator complex thereby attenuating transcriptional activation. The expression of phospholipid biosynthetic gene is affected by many conditions which include carbon source, nutrient availability, growth stage, pH and temperature. The well studied conditions which regulate phospholipid biosynthetic genes transcription are through exogenous supplementation of inositol, which is achieved by lowering of phosphatidic acid levels by its utilization for the synthesis of phosphatidylinositol. Since inositol was able to change regulates phospholipid biosynthetic gene we proposed to investigate inositol triphosphate role in such regulation. We overexpressed a plant phospholipase C in yeast to study its effect on lipid biosynthesis. The overexpressed yeast cells were subjected to microarray analysis and the result were confirmed by Q-PCR. The result obtained indicated that there was decrease in the expression of UNAINO-containing genes. To further validate our observation we carried out an in vivo assay to determined activity of enzyme involved in phospholipid biosynthesis. These results were in accordance with our expression analysis further supporting our hypothesis. Our study indicates that phospholipase c regulates phospholipid biosynthesis at transcription level in response to various stimuli. Overall, these data suggest that the C2 domain of plant PLC plays a vital role in calcium signalling. Further it can be inferred from this study that PI-PLC regulates lipid metabolism in S. cerevisiae.

In Saccharomyces cerevisiae, experiments with temperature-sensitive mutants of the PI4-kinase Pik1p revealed that the PI4P pool generated by this enzyme is essential for Golgi morphology and normal secretory function and that the PI4P pool at the Golgi represents a regulatory signal on its own. In order to function as a spatial and temporal regulator of membrane traffic, PI4P synthesis and turnover must be tightly regulated. It remains elusive which factors are involved in the targeting and regulation of Pik1p. Little is also known about PI4P binding proteins mediating the effects of this phosphoinositide on Golgi function. Since it has been shown that multiple pathways leave the Golgi towards the plasma membrane one can ask the question whether Pik1p and its product PI4P specifically control one pathway? Here we demonstrate an interaction of Pik1p with the 14-3-3 proteins Bmh1p and Bmh2p. Interestingly, overexpression of Bmh1p and Bmh2p results in multiple genetic interactions with genes involved in late steps of exocytosis and it affects the forward transport of the general amino acid permease Gap1p. The detected interaction depends on the phosphorylation state of Pik1p and Pik1p phosphorylation accompanies its shuttling out of the nucleus into the cytoplasm where presumably the binding to Bmh1/2p occurs. Therefore, we reason that these interactions might serve the sequestration of Pik1p away from the Golgi. This study reveals that Pik1p shows a strong effect on the delivery of Gap1p to the surface whereas the transport of exocytosis markers implicated in the direct Golgi-to-plasma membrane pathway are not significantly disturbed. Cells carrying a deletion of gga2 also show a strong defect in delivery of Gap1p to the surface. In addition, pik1-101 gga2[delta]double mutants display synthetic genetic and membrane transport phenotypes and recruitment of Gga2 to the TGN partially depends on functional Pik1p. Therefore, our results suggest a role of Pik1p in the TGN to endosome pathway.

Thesis (Ph. D.) -- University of Texas Southwestern Medical Center at Dallas, 2005. / Vita. Bibliography: 106-116.