京都大学 / 新制・課程博士 / 博士(医科学) / 甲第23424号 / 医科博第129号 / 新制||医科||9(附属図書館) / 京都大学大学院医学研究科医科学専攻 / (主査)教授 林 康紀, 教授 伊佐 正, 教授 高橋 淳 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Zinc is the second most abundant transition metal in biological systems. This cation is required for the catalytic activity of hundreds of enzymes which mediate protein synthesis, DNA replication and cell division. Despite the central importance of zinc in cellular homeostasis, the mechanism of zinc uptake, compartmentalization and efflux is unknown. Recently, a family of proteins, called ZIP, has been shown to control zinc uptake. Mutations in one of the genes coding for these proteins (ZIP4) can lead to potentially life-threatening diseases like Acrodermatitis Enteropathica and high levels of ZIP4 have been detected in patients suffering from pancreatic cancer. Therefore our goal is to investigate the mechanism of ZIP4 transport and regulation. It was previously shown that the intracellular loop between transmembrane III and IV (M3M4) of ZIP4 is ubiquitinated in the presence of high intracellular zinc which lead to protein degradation. Our initial hypothesis was that the large intracellular domain of ZIP4 (M3M4) is a sensor which detects the intracellular concentration of zinc and regulates the surface expression of ZIP4. In order to test this hypothesis we expressed and purified the M3M4 domain to examine the ability of M3M4 to bind zinc. Our results have demonstrated that M3M4 binds zinc with a 2:1 zinc:protein stoichiometry with nanomolar affinity. We have also shown that upon binding of zinc, M3M4 undergoes a large conformational change.

[Truncated abstract] Neuregulins (NRG’s) are pleiotropic growth factors that participate in a wide range of biological processes. The family of membrane-bound growth factors bind to and activate ErbB receptors on adjacent target cells, mediating multiple biological processes. NRG-1, NRG-2 and NRG-3 are all highly expressed in the nervous system, where it has been shown that NRG-1 is important for neuronal development, migration, synapse formation and glial cell proliferation. Little is known, however, on the specific roles of NRG-2 and NRG-3, although it is apparent that despite similar expression patterns and overlapping receptor specificity, NRG-2 and NRG-3 do not compensate for the loss of NRG-1 and mediate their own distinct activities. … Subcellular localisation experiments showed that this domain is important for trafficking of the fulllength protein to various intracellular compartments in an activity dependent manner. In addition, the ICD is required to elicit a cell death response in cultured cells and provoke an elevated α-amino-3-hydroxyl-5-methylisoxazole-4-propionate (AMPA) response in organotypic neuronal cultures following transient expression of NRG-3. A yeast two-hybrid screen identified 14-3-3ζ and PICK1 as two proteins that interacte with the human NRG-3 ICD. These interactions were confirmed both in vitro and in vivo, and were further characterised at a molecular level. This study demonstrates the ability of NRG-3 to mediate signal transduction through a biologically active ICD; a conclusion supported by identifying cytoplasmic proteins that interact with the ICD. These observations point to an additional layer of complexity where bi-directional signalling contributes to the full repertoire of NRG-3 functions.

<p>Alzheimer Disease (AD) is the most common neurodegenerative disorder in the world. One of the neuropathological hallmarks of AD is the senile plaques in the brain. The plaques are mainly composed of the amyloid β (Aβ) peptide. Aβ is generated from the amyloid precursor protein, APP, when it is first cleaved by the β-secretase and subsequently the γ-secretase complex. The γ-secretase complex cleaves at different sites, called γ and ε, where the γ-cleavage site generates Aβ peptides of different lengths and ε-cleavage generates the APP intracellular domain (AICD). The two major forms of Aβ is 40 and 42 amino acids long peptides, where the latter is more prone to aggregate and is the main component in senile plaques. The γ-secretase complex is composed of four proteins; Pen-2, Aph-1, nicastrin and presenilin (PS). The PS protein harbours the catalytic site of the complex, where two aspartate residues in position 257 and 385 (Presenilin 1 numbering) are situated. Most Familial AD (FAD) mutations in the PS gene cause a change in the γ-cleavage site, leading to a shift from producing Aβ40 to the longer more toxic variant Aβ42. Frequently, this often leads to impairments of the AICD production. Another substrate for the γ-secretase complex is Notch. It is important to maintain the Notch signaling since an intracellular domain (NICD) is formed after cleavage by the γ-secretase complex in the membrane (S3-site) and this domain is involved in transcription of genes important for cell fate decisions.</p><p>It has been reported that certain APP luminal juxtamembrane mutations could drastically alter Aβ secretion, however their effect on AICD production remains unknown. In this study we want to analyse wether the juxtamembrane region is important for the AICD production. To gain more insight into the luminal juxtamembrane function for γ-secretase-dependent proteolysis, we have made a juxtamembrane chimeric construct. A four-residue sequence preceding the transmembrane domain (TMD) of APP (GSNK), was replaced by its topological counterpart from the human Notch1 receptor (PPAQ). The resulting chimeric vector C99GVP-PPAQ and the wildtype counterpart were expressed in cells lacking PS1 and PS2 (BD8) together with PS1wt. We observed that the chimeric construct did not alter production of AICD when using a cell based luciferase reporter gene assay monitoring AICD production. We also introduced a PS1 variant lacking a big portion of the large hydrophilic loop, PS1∆exon10, since our group has previously observed that this region affect Aβ production¹⁴³. We found that the absence of the large hydrophilic loop in PS1 gave a 2-fold decrease in AICD-GVP formation from C99GVPwt compared to PS1wt.  The activity of PS1wt and PS1Δexon10 using C99GVP-PPAQ as a substrate gave similar result as the C99GVPwt substrate, i.e. a 2-fold decrease in AICD-GVP formation when comparing PS1Δexon10 with PS1wt. From this data we therefore suggest that the four residues in the juxtramembrane domain (JMD) (GSNK) is not altering ε-cleavage of APP when changed to Notch1 counterpart, PPAQ. Furthermore, we also show that the 2-fold decrease in AICD-production by the PS1Δexon10 molecule is not changed between the two substrates C99GVPwt and C99GVP-PPAQ. This indicates that the luminal region of APP is not directly involved in the ε-site processing. If the luminal region is affecting processing in the γ-cleavage sites, remains however to be investigated.</p>

Alzheimer Disease (AD) is the most common neurodegenerative disorder in the world. One of the neuropathological hallmarks of AD is the senile plaques in the brain. The plaques are mainly composed of the amyloid β (Aβ) peptide. Aβ is generated from the amyloid precursor protein, APP, when it is first cleaved by the β-secretase and subsequently the γ-secretase complex. The γ-secretase complex cleaves at different sites, called γ and ε, where the γ-cleavage site generates Aβ peptides of different lengths and ε-cleavage generates the APP intracellular domain (AICD). The two major forms of Aβ is 40 and 42 amino acids long peptides, where the latter is more prone to aggregate and is the main component in senile plaques. The γ-secretase complex is composed of four proteins; Pen-2, Aph-1, nicastrin and presenilin (PS). The PS protein harbours the catalytic site of the complex, where two aspartate residues in position 257 and 385 (Presenilin 1 numbering) are situated. Most Familial AD (FAD) mutations in the PS gene cause a change in the γ-cleavage site, leading to a shift from producing Aβ40 to the longer more toxic variant Aβ42. Frequently, this often leads to impairments of the AICD production. Another substrate for the γ-secretase complex is Notch. It is important to maintain the Notch signaling since an intracellular domain (NICD) is formed after cleavage by the γ-secretase complex in the membrane (S3-site) and this domain is involved in transcription of genes important for cell fate decisions. It has been reported that certain APP luminal juxtamembrane mutations could drastically alter Aβ secretion, however their effect on AICD production remains unknown. In this study we want to analyse wether the juxtamembrane region is important for the AICD production. To gain more insight into the luminal juxtamembrane function for γ-secretase-dependent proteolysis, we have made a juxtamembrane chimeric construct. A four-residue sequence preceding the transmembrane domain (TMD) of APP (GSNK), was replaced by its topological counterpart from the human Notch1 receptor (PPAQ). The resulting chimeric vector C99GVP-PPAQ and the wildtype counterpart were expressed in cells lacking PS1 and PS2 (BD8) together with PS1wt. We observed that the chimeric construct did not alter production of AICD when using a cell based luciferase reporter gene assay monitoring AICD production. We also introduced a PS1 variant lacking a big portion of the large hydrophilic loop, PS1∆exon10, since our group has previously observed that this region affect Aβ production143. We found that the absence of the large hydrophilic loop in PS1 gave a 2-fold decrease in AICD-GVP formation from C99GVPwt compared to PS1wt.  The activity of PS1wt and PS1Δexon10 using C99GVP-PPAQ as a substrate gave similar result as the C99GVPwt substrate, i.e. a 2-fold decrease in AICD-GVP formation when comparing PS1Δexon10 with PS1wt. From this data we therefore suggest that the four residues in the juxtramembrane domain (JMD) (GSNK) is not altering ε-cleavage of APP when changed to Notch1 counterpart, PPAQ. Furthermore, we also show that the 2-fold decrease in AICD-production by the PS1Δexon10 molecule is not changed between the two substrates C99GVPwt and C99GVP-PPAQ. This indicates that the luminal region of APP is not directly involved in the ε-site processing. If the luminal region is affecting processing in the γ-cleavage sites, remains however to be investigated.

<p>Liposarcoma (LPS) arises from adipocytes and is a rare malignancy among all cancer types, but represents the most common form of soft tissue sarcoma, with approximately 2,000 new cases reported annually. Clinically, liposarcomas are classified into four subtypes based on histological analysis: well-differentiated liposarcoma (WDLPS), dedifferentiated liposarcoma (DDLPS), myxoid/round cell liposarcoma, and pleomorphic liposarcoma. Although histological analysis provides useful information for identifying various liposarcoma subtypes, treatment options rely on a fundamental understanding of driver mutations and molecular mechanisms underlying tumorigenesis. This thesis focuses on elucidating important driver mutations and therapeutic targets to eradicate DDLPS. Notch signaling is an evolutionarily conserved signaling pathway essential for organ development and stem cell function. Aberrant Notch signaling underlies the tumorigenesis of many cancers including LPS. However, the specific role of Notch signaling in development of LPS remains elusive. In Chapter 2, I provide evidence demonstrating that Notch signaling plays a key role in cancer stem cells (CSCs), also referred to as tumor-initiating cells (TICs), that drive aggressive DDLPS. I used serial transplantation to enrich and generate a murine DDLPS cell line with constitutively activated Notch signaling (NICDOE). My analyses revealed that NICDOE DDLPS cells are heterogeneous and contain TICs that express cancer stem cell markers. Chapter 3 elucidates how Notch signaling regulates CSCs of LPS. I analyzed human LPS samples to establish a strong correlation between Notch signaling activation and tumor marker expression and prognosis. I further performed gene expression and metabolic analyses of NICDOE DDLPS cells. These assays revealed that NICDOE reduced mitochondrial respiration in DDLPS cells, which was associated with diminished expression of peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α), a master regulator of mitochondrial biogenesis. CRISPR/CAS9-mediated deletion of the NICDOE cassette rescued the expression of PGC-1α and mitochondrial respiration in DDLPS cells. Similarly, overexpression of PGC-1α was sufficient to rescue mitochondrial biogenesis in DDLPS cells. Together, these data demonstrate that Notch signaling regulates CSCs, at least partially by controlling PGC-1α mediated mitochondria biogenesis.</p>

Notch receptors and ligands are type I transmembrane proteins that regulate development and differentiation during cell-cell contact. There are four Notch receptor homologues and five notch ligands, identified in humans till date. Upon ligand activation, Notch1 intracellular domain (NIC-1) is released into the cytoplasm, which binds to several proteins as well as translocates into the nucleus to effect the Notch signaling. In the absence of the activated Notch signaling, the Notch target genes are kept repressed by the transcriptional repressor C protein binding factor 1 (CBF1) also known as RBPjk or CSL for CBF1/Su(H)/Lag1. RBPjk binds to the sequence “CGTGGGAA” and acts as a constitutive repressor. Upon ligand dependent activation, NIC-1 enters into the nucler and converts RBPjk from transcriptional repressor to an activator. Notch binding to CSL replaces the SMRT corepressor complex with a coactivator complex including SKIP, Mastermind like 1 (MAML1) (Mastermind in Drosophila), and histone acetyl transferases PCAF, GCN5 and p300 activating the transcription of target genes. Mastermind-like (MAML), a family of transcriptional activator proteins comprising of 3 members 1 to 3, has been shown to be required for Notch signaling. MAML forms a ternary complex with RBPjk-NIC by directly interacting with NIC. In turn, MAML recruits the histone acetyl transferase p300/CBP, which acetylates the histones, thereby altering the structure of chromatin amenable for transcription. Activation of Notch pathway induces oncogenesis, which can be divided into two categories including 1) Inhibition of Apoptosis and 2) Induction of proliferation. In T cells, activation of Notch1 protects cells from T cell receptor, dexamethasone and etoposide-mediated apoptosis, Fas receptor-mediated signaling by up regulating IAP (Inhibitor of Apoptosis) and Bcl-2 families, as well as FLIP (FLICE-like inhibitor protein). Notch signaling also promotes the survival of T cells through maintenance of cell size as well as through the promotion of glucose uptake and metabolism. Notch-1 has been shown to protect against anoikis (apoptosis induced by matrix withdrawal) or p53-mediated apoptosis in immortalized epithelial cells, T cell receptor-induced apoptosis in mature cells and dexamethasone-mediated apoptosis in thymocytes. This study was carried out to functionally characterize NIC-1 (human Notch1-intracellular domain) as an inhibitor of apoptosis and to evaluate the therapeutic potential of reversal of this apoptosis inhibition. The main objectives of this study are 1. Construction of recombinant adenovirus expressing human Notch1-intracellular domain (Ad-NIC-1) and characterization of NIC-1 as an inhibitor of chemotherapy and p53-induced cytotoxicity and apoptosis. 2. Role of PI3 kinase -Akt/PKB -mTOR pathway in NIC-1-mediated inhibition of p53-induced apoptosis. 3. Essential role of association between mTOR and NIC-1 and the dependent NIC-1 phosphorylation in Notch1-mediated transcription and survival signaling. 4. Identification of NIC-1 as an inhibitor of E1A-induced apoptosis and the role of mTOR in NIC-1-mediated inhibition of E1A-induced apoptosis. Activated Notch1 was first linked to tumorigenesis through identification of a recurrent t(7;9)(q34;q34.3) chromosomal translocation involving the human Notch1 gene that is found in a subset of human pre-T-cell acute lymphoblastic leukemia’s (T-ALL). Deregulated Notch signaling is oncogenic, inhibits apoptosis and promotes survival. In order to understand survival signaling induced by Notch1 and its possible role in chemoresistance, we have generated a replication deficient recombinant adenovirus expressing human Notch1-intracellular domain (Ad-NIC-1) and shown that it produces functional NIC-1 protein. Using this overexpression system, we characterized that activated Notch1-inhibits chemotherapy and in particular p53 induced apoptosis. Notch1-mediated inhibition of p53-induced apoptosis does not include coactivator squelching. p53 was inefficient in binding to its DNA in NIC-1 overexpressing cells. The levels of phosphorylation at Ser15, Ser20, and Ser392 of p53 expressed from Ad-p53 significantly reduced in NIC-1 preinfected cells. These results suggest that NIC-1-mediated inhibition of p53-mediated apoptosis involves reduced DNA binding, reduced nuclear localization and reduced post translational modifications and thus reduced transactivation of its target genes. Notch1-mediated inhibition of p53 was found to occur mainly through mammalian target of rapamycin (mTOR) using PI3 kinase-Akt/PKB pathway, as the mTOR inhibitor; rapamycin treatment was able to reverse Notch-1 mediated inhibition of p53 and chemoresistance. Consistent with this, rapamycin failed to reverse NIC-1 induced chemoresistance in cells expressing rapamycin resistant mTOR. Our results also suggest that the N-terminal HEAT repeat and the kinase function of mTOR are essential for Notch mediated inhibition of p53. Further, ectopic expression of eIF4E, a translational regulator that acts downstream of mTOR, inhibited p53-induced apoptosis and conferred protection against p53-mediated cytotoxicity to similar extent as that of NIC-1 overexpression, but was not reversed by rapamycin, which indicates that eIF4E is the major target of mTOR in Notch1-mediated survival signaling. Notch1-intracellular domain (NIC-1), following proteolytic cleavage, binds to RBPjk and regulates transcription. Active NIC-1 located in the nucleus is phosphorylated, which makes it more stable and bind better to RBPjk. NIC-1 was also shown to bind to Deltex1 in the cytoplasm. Next, we studied the requirement of components of Notch1 signaling pathway for this function. By using variety of approaches, we found that both RBPjk and Maml1 and hence transcription activation is required for NIC-1-mediated survival signaling and inhibition of p53 functions. Interestingly, while we found the other Notch1 effector, Deltex1 is also required for above functions, Notch1 failed to activate PI3 kinase -Akt/PKB -mTOR pathway in Deltex1, but not in RBPjk silenced cells. Our results suggest that Notch-Deltex1 pathway activates PI3 kinase. Previous studies show that NIC-1 interacts with Deltex1 and Grb2 interacts with PI3 kinase. Our data shows that Deltex1 interacts with SH3 domain of Grb2. Since Notch1-Deltex1 and PI3 kinase-Grb2 interactions are known, we conclude that Notch1 activation of PI3 kinase involves Deltex1 and Grb2. We found activated mTOR was able to binds to NIC-1 and regulates its phosphorylation. Inhibition of mTOR either by PI3 kinase inhibitors or mTOR inhibitor treatment or silencing of Akt/PKB or mTOR reduced the phosphorylation of NIC-1 with the concomitant reduction in NIC-1-mediated transcription. Further, endogenous Notch1 receptor activated by the DSL ligand failed to activate transcription efficiently in rapamycin treated cells, implying a positive role for mTOR in mammalian Notch signaling. These studies reveal that Notch1 activates PI3 kinase -Akt/PKB -mTOR signaling through Deltex1 and subsequently activated mTOR modulates Notch1 signaling by direct binding and possibly thorough phosphorylation of the intracellular domain of Notch. Adenoviral E1A, in the absence of cooperating oncogene, suppresses primary tumor growth and reverses the transformed phenotype of human tumor cells by inducing apoptosis. E1A requires p53 for efficient induction of apoptosis and was shown to induce apoptosis by down regulating Akt and the activation of pro apoptotic factor p38 MAP kinase. Since our results suggest Notch1 inhibits chemotherapy and p53-induced apoptosis, we analyzed the ability of Notch1 to protect cells from E1A-induced apoptosis. Here we show that NIC-1 suppresses the ability of E1A to induce apoptosis. NIC-1 requires mTOR-dependent signal to inhibit E1A-mediated apoptosis, as the rapamycin, an mTOR inhibitor was able to completely reverse the ability of Notch1 to protect cells against E1A-induced apoptosis. The role of mTOR in NIC-1-mediated survival signaling was further confirmed by using the cells stably expressing rapamycin resistant mTOR. Rapamycin was able to reverse Notch1-mediated protection in cells expressing wild type mTOR but not in rapamycin resistant mTOR expressing cells. We also found that E1A was able to induce apoptosis in cells silenced for the pro apoptotic factor p38 and NIC-1 continued to inhibit E1A-induced apoptosis in these cells. These results confirm that Notch1 requires the activation of mTOR signaling but not p38 MAP kinase for inhibition of E1A-induced apoptosis. These results also suggest that the combination therapy utilizing E1A-mediated gene delivery in combination with inhibition of mTOR pathway may prove successful in treating Notch overexpressing cancers. Chemotherapy remains a major treatment modality for human cancers. Chemoresistance is a clinical problem that severely limits treatment success. It can be divided into two forms: intrinsic and acquired. Intrinsic resistance is the essence of oncogenic transformation, resulting from activation of oncogenes and the loss of tumor suppressors, and manifests itself as alterations in cell cycle checkpoints and apoptotic pathways. It is now widely accepted that the apoptotic capacity of the cancer cell is crucial in determining the response to chemotherapeutic agents. Indeed, several gene products that regulate apoptosis, i.e., p53, Akt and PI3K are frequently altered in cancer cells. In this study, we identified that cells with aberrant Notch1 signaling are chemoresistant. Activated Notch1 overexpression makes cells resistant to chemotherapy in a wild type p53 dependent manner. Notch protected p53 wild type cells but not p53 mutated or p53 deleted cells against chemotherapy induced cytotoxicity. Further, inactivation of p53 by specific silencing abrogated the ability of NIC-1 to protect H460 cells against adriamycin induced cytotoxicity. Most importantly, NIC-1 mediated chemoresistance can be reversed by blocking PI3 kinase -Akt/PKB -mTOR pathway. Collectively, these results suggest that cancers with activated Notch1 signaling are chemoresistant and provide basis for the reversal of chemoresistance.

Ces dernières années, de nombreuses études ont prouvé que la protéine précurseur de l'amyloïde (APP) joue un rôle clé dans le processus de formation de la mémoire, le développement des connexions synaptiques et la régulation de la force synaptique. L’importance d’APP naît du fait que son clivage protéolytique produit le peptide bêta-amyloïde (Aβ), considéré comme l'un des facteurs cruciaux dans le développement de la maladie d'Alzheimer. Les recherches se sont donc concentrées sur Aβ plutôt que sur le domaine intracellulaire APP (APP-ICD). Récemment, il a été démontré qu’APP-ICD affecte l'induction de la plasticité synaptique, et Aβ à haute concentration est connu pour induire une dépression synaptique. Ici, nous montrons qu’APP-ICD et Aβ fonctionnent ensemble et induisent une dépression synaptique en modifiant la transmission synaptique par effet additif. L’activation de la caspase-3 clivant APP-ICD est nécessaire pour la dépression à long terme. Nous constatons que l’activation de la caspase-3 et son site de clivage d’APP-ICD, ainsi que le clivage d’APP par la gamma-sécrétase sont nécessaires à la dépression synaptique dépendante d’Aβ. La microglie assure la clairance d’Aβ et certains effets de plasticité. Nous démontrons qu’elle médie partiellement la dépression synaptique dépendante d’Aβ. Les mécanismes par lesquels APP-ICD et Aβ médient la dépression synaptique ne sont pas connus. Ici, nous discutons de pistes possibles pour la recherche future, notamment des changements dans l'homéostasie du calcium en tant que cible thérapeutique potentielle. Comprendre comment APP-ICD et Aβ travaillent ensemble pour induire une dépression synaptique aiderait à développer de meilleurs traitements pour la maladie d'Alzheimer. / In recent years, more and more evidence has proven that the amyloid precursor protein (APP) plays a key role in the process of memory formation, the development of synaptic connections, and the regulation of synaptic strength. APP rose to prominence since its proteolytic cleavage produces the amyloid-beta (Aβ) peptide, which is believed to be one of the crucial factors in the development of Alzheimer disease. Therefore, most of the research focused on Aβ, while APP intracellular domain (APP-ICD) received much less attention. In a recent study, APP-ICD was shown to affect the induction of synaptic plasticity, and Aβ at high concentration is known to induce synaptic depression. Here we show that APP-ICD works together with Aβ to induce synaptic depression, meaning they have an additive effect that changes synaptic transmission. Caspase-3 cleaves APP-ICD, and its activation is required for long-term depression. We found that the caspase-3 cleavage site of APP-ICD and caspase-3 activation are needed for Aβ-dependent synaptic depression. We also show that cleavage of APP by gamma-secretase is needed for the effect. Microglia mediate clearance of Aβ as well as some plasticity effects. We demonstrate that microglia partially mediate Aβ-dependent synaptic depression. The mechanisms of how APP-ICD and Aβ mediate synaptic depression are not known, here, we discuss possible avenues for future research, specifically changes in calcium homeostasis as a potential therapeutic target. Hence, understanding how APP-ICD and Aβ work together to induce synaptic depression would aid in developing better treatments for Alzheimer disease.