Philosophiae Doctor - PhD / Global climate change has resulted in altered rainfall patterns, causing annual losses in maize crop yield due to water deficit stress. Therefore, it is important to produce maize cultivars which are more drought-tolerant. This not an easily accomplished task as plants have a plethora of physical and biochemical adaptation methods. One such mechanism is the drought-induced expression of enzymatic and non-enzymatic proteins which assist plants to resist the effects of water deficit stress. The RD22-like protein subfamily is expressed in response to water deficit stress. Members of the RD22-like subfamily include AtRD22, GmRd22 and BnBDC1 which have been identified in Arabidopsis thaliana, Glycine max and Brassica napus respectively. This study aims at characterising two putative maize RD22-like proteins (designated ZmRd22A and ZmRd22B) by identifying sequence/domain features shared with characterised RD22-like proteins. Semi-quantitative and quantitative PCR techniques were used to examine the spatial and temporal expression patterns of the two putative maize Rd22-like proteins in response to, water deficit stress and exogenously applied abscisic acid in the roots and 2nd youngest leaves of maize seedlings. Using an in silico approach, sequence homology of the two putative maize Rd22- like proteins with AtRD22, GmRD22 and BnBDC1 has been analysed. Online bioinformatic tools were used to compare the characteristics of these Rd22-like proteins with those of the two maize proteins. It was shown that the putative maize RD22-like proteins share domain organisation with the characterised proteins, these common features include a N-terminal hydrophobic signal peptide, followed by a region with a conserved amino acid sequence, a region containing several TxV (x is any amino acid) repeat units and a C-terminal BURP domain-containing the conserved X₅-CH-X₁₀-CH-X₂₃-₂₇-CH-X₂₃-₂₆-CH-X₈-W motif. The putative maize Rd22-like protein appears to be localized in the apoplast, similarly to AtRD22, GmRD22 and BnBDC1. Analysis of the gene's promotor regions reveals cis-acting elements suggestive of induction of gene expression by water deficit stress and abscisic acid (ABA). Semi-quantitative and quantitative real time PCR analysis of the putative maize RD22-like gene revealed that the genes are not expressed in the roots. Exposure to water deficit stress resulted in an increase of ZmRD22A transcript accumulation in the 2nd youngest leaves of maize seedlings. ZmRD22A was shown to be non-responsive to exogenous ABA application. ZmRD22B was highly responsive to exogenous ABA application and responded to water deficit stress to a lesser degree. Transcript accumulation studies in three regions of the 2nd youngest leaves in response to water deficit stress showed that ZmRd22A transcripts accumulate mainly at the base and tips of the leaves. A restricted increase in ZmRD22A transcript accumulation in the middle of the leaves was observed. ZmRD22B showed a similar, but weaker transcript accumulation pattern in response to water deficit stress. However, ZmRD22B showed increased transcript accumulation in the middle region of the leaves. In response to exogenous ABA application, ZmRd22B exhibited high transcript accumulation at the base of the 2nd youngest leaves, with the middle showing higher transcript accumulation than the tip of the leaves. It was concluded that ZmRD22A and ZmRD22B share the domain organisation of characterised RD22-like proteins as well as being responsive to water deficit stress, although only ZmRD22B was shown to be responsive to exogenous ABA application. / National Research Foundation (NRF)

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第18138号 / 医博第3858号 / 新制||医||1002(附属図書館) / 30996 / 京都大学大学院医学研究科医学専攻 / (主査)教授 木村 剛, 教授 坂田 隆造, 教授 羽賀 博典 / 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21459号 / 人健博第66号 / 新制||人健||5(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 青山 朋樹, 教授 岡 昌吾, 教授 髙橋 良輔 / 学位規則第4条第1項該当 / Doctor of Human Health Sciences / Kyoto University / DFAM

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Master of Science / Department of Biochemistry / Qize Wei / Proper regulation of mitosis and cytokinesis is fundamentally important for all living organisms. During anaphase, antiparallel microtubules are bundled between the separating chromosomes, forming the central spindle (also called the spindle midzone), and the myosin contractile ring is assembled at the equatorial cortex. Regulators of central spindle formation and myosin contractile ring assembly are mostly restricted to the interdigitated microtubules of central spindles and they can be collectively called midzone components. It is thought that characteristic microtubule configurations during mitosis and cytokinesis are dictated by the coordinated action of microtubule-stabilizing and -destabilizing factors. Although extensive investigations have focused on understanding the roles of microtubule-bundling/stabilizing factors in controlling central spindle formation, efforts have been lacking in aiming to understand how microtubule-destabilizing factors regulate the assembly of central spindles. This dissertation describes the role of a novel microtubule-destabilizing factor termed CCDC69 (coiled-coil domain-containing protein 69) in controlling the assembly of central spindles and the recruitment of midzone components. Endogenous CCDC69 was localized to the nucleus during interphase and to the central spindle during anaphase. Exogenous expression of CCDC69 in HeLa cells destabilized microtubules and disrupted the formation of bipolar mitotic spindles. RNA interference (RNAi)-mediated knockdown of CCDC69 led to the formation of aberrant central spindles and interfered with the localization of midzone components such as aurora B kinase, protein regulator of cytokinesis 1 (PRC1), MgcRacGAP/HsCYK-4, and pololike kinase 1 (Plk1) at the central spindle. CCDC69 knockdown also decreased equatorial RhoA staining, indicating that CCDC69 deficiency can impair equatorial RhoA activation and ultimately lead to cytokinesis defects. Four coiled-coil domains were found in CCDC69 and the C terminal coiled-coil domain was required for interaction with aurora B. Disruption of aurora B function in HeLa cells by treatment with a small chemical inhibitor led to the mislocalization of CCDC69 at the central spindle. Further, vitro kinase assay showed that Plk1 could phosphorylate CCDC69. Taken together, we propose that CCDC69 acts as a scaffold and a microtubule-destabilizing factor to control the recruitment of midzone components and the assembly of central spindles.

Sulfiredoxin (Srx) is an antioxidant enzyme that can be induced by oxidative stress. It promotes oncogenic phenotypes of cell proliferation, colony formation, migration, and metastasis in lung, skin and colon cancers. Srx reduces the overoxidation of 2-cysteine peroxiredoxins in cells, in addition to its role of removing glutathione modification from several proteins. In this study, I explored additional physiological functions of Srx in lung cancer through studying its interacting proteins. Protein disulfide isomerase (PDI) family members, thioredoxin domain containing protein 5 (TXNDC5) and protein disulfide isomerase family A member 6 (PDIA6), were detected to interact with Srx. Therefore, I proposed that TXNDC5 and PDIA6 are important for the oncogenic phenotypes of Srx in lung cancer. In chapter one, I presented background information about the role of Srx as an antioxidant enzyme in cancer. I also explained the functional significance of PDIs as oxidoreductase and chaperones in cells. In chapter two, I verified the Srx-TXNDC5/PDIA6 interaction in HEK293T and A549 cells by co-immunoprecipitation and other assays. In TXNDC5 and PDIA6, the N-terminal thioredoxin-like domain (D1) is determined to be the main platform for interaction with Srx. The Srx-TXNDC5 interaction was enhanced by H2O2 treatment in A549 cells. Srx was determined to localize in the endoplasmic reticulum (ER) of A549 cells along with TXNDC5 and PDIA6. This localization was confirmed by both subcellular fractionation and immunofluorescence imaging experiments. In chapter three I focused on studying the physiological function of Srx interacting proteins in the ER. A549 subcellular fractionation results showed that TXNDC5 facilitates Srx retention in the ER. Moreover, TXNDC5 and Srx were found to participate in chaperone activities in lung cancer. Both proteins contributed in the refolding of heat-shock induced protein aggregates. In addition, TXNDC5 and PDIA6 were found to enhance the protein refolding in response to H2O2 treatment. Conversely, Srx appeared to have an inhibitory effect on protein folding under same treatment conditions. Downregulation of Srx, TXNDC5, or PDIA6 significantly reduced cell viability in response to tunicamycin treatment. TXNDC5 knockdown decreased the time required for the splicing of X-box binding protein-1 (XBP-1). In either knockdown Srx or TXNDC5 cells, there was an observable decrease in the expression of GRP78 and the splicing of spliced XBP-1. These results suggest a possible role of Srx in unfolded protein response signaling. TXNDC5 and PDIA6, similar to Srx, contribute to the proliferation, anchorage independent colony formation and migration of lung cancer cells. In this dissertation I concluded that Srx TXNDC5, and PDIA6 proteins participate in oxidative protein folding in lung cancer. Srx and TXNDC5 can modulate unfolded protein response (UPR) sensor activation and growth inhibition. Furthermore, TXNDC5 and PDIA6 can promote tumorigenesis of lung cancer cells. Therefore, the molecular interaction of Srx with TXNDC5/PDIA6 has the potential to be used as novel therapeutic targets for lung cancer treatment.

京都大学 / 新制・課程博士 / 博士(生命科学) / 甲第24983号 / 生博第512号 / 新制||生||68(附属図書館) / 京都大学大学院生命科学研究科統合生命科学専攻 / (主査)教授 荒木 崇, 教授 鈴木 淳, 教授 谷口 雄一 / 学位規則第4条第1項該当 / Doctor of Philosophy in Life Sciences / Kyoto University / DFAM

Because it can expand the range of a protein’s interactions or modulate its activity, post-translational methylation of arginine residues in proteins must be duly coordinated and ‘decoded’ to ensure appropriate cellular interpretation of this biological cue. This can be achieved through modulation of the enzymatic activity/specificity of the protein arginine methyltransferases (PRMTs) and proper recognition of the methylation ‘mark’ by a subset of proteins containing ‘methyl-sensing’ protein modules known as ‘Tudor’ domains. In order to gain a better understanding of these regulatory mechanisms, we undertook a detailed biochemical characterization of the predominant member of the PRMT family, PRMT1, and of the novel Tudor domain-containing protein 3 (TDRD3). First, we found that PRMT1 function can be modulated by 1) the expression of up to seven PRMT1 isoforms (v1-7), each with a unique N-terminal region that confers distinct substrate specificity, and by 2) differential subcellular localization, as revealed by the presence of a nuclear export sequence unique to PRMT1v2. Second, our findings suggest that TDRD3 is recruited to cytoplasmic stress granules (SGs) in response to environmental stress potentially by engaging in methyl-dependent protein-protein interactions with proteins involved in the control of gene expression. We also found that arginine methylation may serve as a general regulator of overall SG dynamics. Finally, we uncovered that alteration of PRMT1, TDRD3, and global arginine methylation levels in breast cancer cells may be closely associated with disease progression and poor prognosis. Therefore, further studies into the pathophysiological consequences ensuing from misregulation of arginine methylation will likely lead to the development of novel strategies for the prevention and treatment of breast cancer.

Because it can expand the range of a protein’s interactions or modulate its activity, post-translational methylation of arginine residues in proteins must be duly coordinated and ‘decoded’ to ensure appropriate cellular interpretation of this biological cue. This can be achieved through modulation of the enzymatic activity/specificity of the protein arginine methyltransferases (PRMTs) and proper recognition of the methylation ‘mark’ by a subset of proteins containing ‘methyl-sensing’ protein modules known as ‘Tudor’ domains. In order to gain a better understanding of these regulatory mechanisms, we undertook a detailed biochemical characterization of the predominant member of the PRMT family, PRMT1, and of the novel Tudor domain-containing protein 3 (TDRD3). First, we found that PRMT1 function can be modulated by 1) the expression of up to seven PRMT1 isoforms (v1-7), each with a unique N-terminal region that confers distinct substrate specificity, and by 2) differential subcellular localization, as revealed by the presence of a nuclear export sequence unique to PRMT1v2. Second, our findings suggest that TDRD3 is recruited to cytoplasmic stress granules (SGs) in response to environmental stress potentially by engaging in methyl-dependent protein-protein interactions with proteins involved in the control of gene expression. We also found that arginine methylation may serve as a general regulator of overall SG dynamics. Finally, we uncovered that alteration of PRMT1, TDRD3, and global arginine methylation levels in breast cancer cells may be closely associated with disease progression and poor prognosis. Therefore, further studies into the pathophysiological consequences ensuing from misregulation of arginine methylation will likely lead to the development of novel strategies for the prevention and treatment of breast cancer.