京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20970号 / 医博第4316号 / 新制||医||1026(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 小川 修, 教授 戸井 雅和, 教授 万代 昌紀 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Researchers of <i>Clostridium perfringens</i>, a Gram-positive anaerobic pathogen, were lacking a tightlyregulated, inducible promoter system in their genetic toolbox. We constructed a lactose-inducible plasmid-based system utilizing the transcriptional regulator, BgaR. Using the <i>E. coli</i> reporter GusA, we characterized its induction in three different strains of <i>C. perfringens</i>. We then used a newly-developed mutation system to create in-frame deletion mutants in three genes with homology to Type IV pilins, and we used the promoter system described above to complement the mutants. We analyzed each pilin for localization and expression, as well as tested each of the mutants for various phenotypes frequently associated with type IV pili (TFP) and type II secretion systems. PilA2, PilA3, and PilA4 localized to the poles of the cells. PilA2 was expressed in the wildtype when <i>C. perfringens</i> was grown on agar plates, and the PilA3 mutant lacked a von Willebrand factor A domain-containing protein in its secretome. We used our promoter system to express GFP-tagged versions of the TFP ATPase homologues and view them in cells growing on surfaces. We saw that PilB1 and PilB2 co-localized nearly all of the time, while a portion of PilT was independent of the PilB proteins. PilT appeared necessary for the localization of PilB, and it localized independently of TFP proteins in <i>Bacillus subtilis</i>. PilT's typical localization in <i>Bacillus subtilis</i> was disrupted when the GTPase and polymerization activity of cell division protein FtsZ was blocked, suggesting that PilT associates with cell division proteins. / Master of Science

Lic.-avh. (sammanfattning) Stockholm : Karolinska institutet, 2010.

Areas of hypoxia caused by poor perfusion are a common occurrence in breast cancer. Hypoxia-inducible factors-1 and 2 (HIF1/2) drive the cellular response to hypoxia in such areas, resulting in the upregulation of genes which facilitate the survival of cancer cells and promote growth, invasion, metastasis and angiogenesis, generally leading to more aggressive tumour characteristics. Previous research has demonstrated that growth factor signalling, such as the ligand-mediated activation of HER receptors, can promote the action of HIFs in normoxia, and correlation between HER2 expression and HIFα proteins has been demonstrated in clinical samples of breast cancer. Despite this, little research has been conducted on how the growth factor-driven regulation of HIFα subunits might modify the cellular response to hypoxia. In this thesis, the role of HER2 overexpression in HIFα modulation was assessed in breast cancer cell lines and publically available clinical datasets for breast cancer with the aim of further understanding the implications of hypoxia and HIFα expression in the context of HER2-positive breast cancer. The upregulation of HIF1α and HIF2α by hypoxia was observed across breast cancer cell lines, and the role of HER2 in this process was assessed using an isogenic MCF7 cell line model overexpressing HER2. This demonstrated an increased hypoxic upregulation of HIF2α but not HIF1α when HER2 was overexpressed. The increased upregulation was shown to be facilitated by an increase in normoxic HIF2α, which is driven by a higher transcriptional rate of the EPAS1 (HIF2) gene as a direct result of HER2 overexpression. HER2 overexpression also resulted in the increased hypoxic upregulation of known hypoxia response genes in 2D and 3D culture models. This demonstrates a novel mechanism for growth-factor mediated HIFα regulation in the context of HER2 overexpression, with an important role for HIF2α. Microarray analysis of MCF7 and MCF7-HER2 cells was used to compare the global transcriptional response to acute (24 hrs) and chronic (>10 weeks) hypoxia (0.5% O2) and demonstrated a broadly increased upregulation of hypoxic response genes in the HER2 overexpressing cell line when compared to wild-type MCF7. This included an increase in previously described HIF1 and HIF2 target genes. MCF7-HER2 also illustrated an increased expression of hypoxia response genes in normoxia, and an analysis of the genes involved showed the promotion of a number of pathological processes including proliferation, invasion, angiogenesis and epithelial to mesenchymal transition. Large-scale, publically available expression datasets for breast cancer cell lines and clinical patient data were used to investigate the expression of HIF2α and hypoxia response genes in relation to HER2 expression. A set of pathologically important genes which were primed for hypoxia in MCF7-HER2 were also demonstrated to correlate with HER2 across breast cancer cell lines, suggesting that HER2 may more broadly promote a readiness to respond to hypoxia in breast cancer cells. Assessment of HIF2α in clinical samples has shown its increased expression in the HER2-positive subtype, and HIF2α was shown to be associated with worse disease-specific survival in the context of HER2-positive samples only. To investigate whether HIF2α is a potential target in HER2 overexpressing breast cancer, the effect of HIF2α inhibition through siRNA or HIF2-specific chemical inhibitors was assessed in cell lines with high or low HER2 expression, and this demonstrated an increased sensitivity of HER2 overexpressing cell lines to HIF2α inhibition. This work highlighted HER2 as an important modulator of the cellular response to hypoxia in breast cancer, demonstrating a previously overlooked role for HIF2α in this process. HIF2α expression can be directly driven by HER2 and this differs mechanistically from that previously reported for HIF1α. Finally, further work into the potential for HIF2α as a target for anti-cancer therapy is suggested, as an increased sensitivity of HER2-positive cell lines to anti-HIF2α agents was shown, as well as a HER2-specific relationship between HIF2α expression and worse prognosis. More generally, this work has shown an important interplay between growth factor receptor expression and the cellular response to hypoxia, suggesting that HER2 may promote a stronger response to hypoxia in breast cancer, which may contribute to the increased aggressiveness of HER2-positive tumours.

Of the thousands of dividing progenitor cells (PCs) generated daily in the adult brain only a very small proportion survive to become mature neurons through the process of neurogenesis. Identification of the mechanisms that regulate cell death associated with neurogenesis would aid in harnessing the potential therapeutic value of PCs. Apoptosis, or programmed cell death, is suggested to regulate death of PCs in the adult brain as overexpression of B-cell lymphoma 2 (Bcl-2), an anti-apoptotic protein, enhances the survival of new neurons. To directly assess if Bcl-2 is a regulator of apoptosis in PCs, this study examined the outcome of removal of Bcl-2 from the developing PCs in the adult mouse brain. Retroviral mediated gene transfer of Cre into adult floxed Bcl-2 mice eliminated Bcl-2 from developing PCs and resulted in the complete absence of new neurons at 30 days post viral injection. Similarly, Bcl-2 removal through the use of nestin-induced conditional knockout mice resulted in reduced number of mature neurons. The function of Bcl-2 in the PCs was also dependent on Bcl-2-associated X (BAX) protein, as demonstrated by an increase in new neurons formed following viral-mediated removal of Bcl-2 in BAX knockout mice. Together these findings demonstrate that Bcl-2 is an essential regulator of neurogenesis in the adult hippocampus.

Hypoxia regulates many hundreds of genes with important roles in ischemic and neoplastic disorders. Central to this response are the hypoxia inducible transcription factors (HIF). This work aimed to better understand the direct transcriptional response to HIF by mapping HIF-binding sites across the genome using chromatin immunoprecipitation coupled to high-throughput sequencing (ChIP-seq). ChIP-seq for HIF in MCF-7 breast cancer cells under hypoxic conditions revealed more than 400 high-stringency HIF-binding sites genome-wide. Each member of the HIF heterodimer was present with near complete concordance. Binding of the two principle isoforms revealed a high degree of overlap with no differences in the DNA-binding motif. HIF-binding was associated with upregulation, but not downregulation of genes indicating that it functions as a transcriptional activator but not as a repressor. HIF-binding occurred preferentially at gene promoters, but was also present at promoter-distant sites, which were also associated with gene regulation, implicating long-range interactions in hypoxic gene activation. HIF-binding was associated with markers of open chromatin and active enhancers that were present in normoxia, indicating that HIF-binding sites are already “prepared” to bind HIF before the hypoxic stimulus. Analysis of normoxic and hypoxic RNA pol2 and H3K4me3 signals revealed distinctive hypoxia-inducible changes unique to HIF-binding genes. Comparable numbers of HIF-binding sites were observed in a second cell line (von Hippel-Lindau defective 786-O renal cancer cells) as in MCF-7 breast cancer cells, although approximately 65% were unique to 786-O cells. These unique sites were more frequently promoter-distant. Correlation with expression analyses from renal tumours indicated that many HIF-binding genes were upregulated in renal cancer. One such RCC unique promoter-distant HIF-binding site was identified at an intergenic locus on chromosome 11q13.3 that has been associated with renal cancer in Genome-Wide Association Studies. The HIF-binding site was in high linkage disequilibrium with the disease associated SNP and had the epigenetic hallmarks of an enhancer. Analysis of pan-genomic expression analyses identified the cell-cycle regulator cyclin D1 as highly HIF-regulated, and a physical association between the HIF-binding site and the CCND1 promoter could be determined. Furthermore, in a renal cancer cell line heterozygous at this locus, the RCC-protective allele disrupted HIF-binding leading to an allelic imbalance in cyclin D1 expression.

This research programme investigated the expression of prolyl hydroxylase (PHD) proteins in rodent tissues. The importance of PHD enzymes lies in their ability to render oxygen sensitivity to Hypoxia inducible factor (HIF), the principal mediator of intracellular oxygen homeostasis. The first part of this study focused on developing and validating anti-sera capable of detecting PHD proteins in rodent tissues. With these reagents, it was possible to assess the relative expression of each PHD protein in a number of different rat tissues. PHD2 was the most abundant isoform in all tissues studied. In contrast, an abundance of PHD1 was observed only in testis and skeletal muscle. A number of different tissue species of PHD3 were identified and their abundance was found to vary between different tissues. These observations provide further evidence of the principal role of PHD2 in regulating HIF in vivo, but also point towards additional roles for PHD1 and PHD3 in selected tissues. They highlight the potential for there being a complex interplay between different PHD enzymes which could, in the future, prove potential targets for therapeutic manipulation. This study also provides additional insights into the mechanisms underlying the phenotypes observed in PHD deletional mouse models which appear, in many cases, to be directly related to the abundance of a given PHD isoform. The emerging role of PHD3 as a promoter of sympathetic lineage apoptosis prompted further study of PHD3 expression in rat neuronal tissues. An abundance of PHD3 was demonstrated throughout the rat sympathetic nervous system, a finding which appeared at odds with its known role as a promoter of neuronal apoptosis and resulted in a series of collaborative studies which demonstrated a sympatho-adrenal phenotype in wild type compared to PHD3-/- mice. Further collaborative studies utilising wild type mice and those deleted of specific PHD isoforms, were carried out to assess the significance of the abundance of PHD3 and PHD1 noted here in rat hippocampus and testis respectively. While neither study demonstrated statistically significant phenotypes, these observations remain of interest and areas for future research.

<p>The growing complexity of scientific research demands further development of advanced gene regulation systems. For instance, the ultimate goal of tissue engineering is to develop constructs that functionally and morphologically resemble the native tissue they are expected to replace. This requires patterning of gene expression and control of cellular phenotype within the tissue engineered construct. In the field of synthetic biology, gene circuits are engineered to elucidate mechanisms of gene regulation and predict the behavior of more complex systems. Such systems require robust gene switches that can quickly turn gene expression on or off. Similarly, basic science requires precise genetic control to perturb genetic pathways or understand gene function. Additionally, gene therapy strives to replace or repair genes that are responsible for disease. The safety and efficacy of such therapies require control of when and where the delivered gene is expressed in vivo.</p><p>Unfortunately, these fields are limited by the lack of gene regulation systems that enable both robust and flexible cellular control. Most current gene regulation systems do not allow for the manipulation of gene expression that is spatially defined, temporally controlled, reversible, and repeatable. Rather, they provide incomplete control that forces the user to choose to control gene expression in either space or time, and whether the system will be reversible or irreversible.</p><p>The recent emergence of the field of optogenetics--the ability to control gene expression using light--has made it possible to regulate gene expression with spatial, temporal, and dynamic control. Light-inducible systems provide the tools necessary to overcome the limitations of other gene regulation systems, which can be slow, imprecise, or cumbersome to work with. However, emerging light-inducible systems require further optimization to increase their efficiency, reliability, and ease of use.</p><p>Initially, we engineered a light-inducible gene regulation system that combines zinc finger protein technology and the light-inducible interaction between Arabidopsis thaliana plant proteins GIGANTEA (GI) and the light oxygen voltage (LOV) domain of FKF1. Zinc finger proteins (ZFPs) can be engineered to target almost any DNA sequence through tandem assembly of individual zinc finger domains that recognize a specific three base-pair DNA sequence. Fusion of three different ZFPs to GI (GI-ZFP) successfully targeted the fusion protein to the specific DNA target sequence of the ZFP. Due to the interaction between GI and LOV, co-expression of GI-ZFP with a fusion protein consisting of LOV fused to three copies of the VP16 transactivation domain (LOV-VP16) enabled blue-light dependent recruitment of LOV-VP16 to the ZFP target sequence. We showed that placement of three to nine copies of a ZFP target sequence upstream of a luciferase or eGFP transgene enabled expression of the transgene in response to blue-light. Gene activation was both reversible and tunable based on duration of light exposure, illumination intensity, and the number of ZFP binding sites upstream of the transgene. Gene expression could also be spatially patterned by illuminating the cell culture through photomasks containing various patterns.</p><p>Although this system was useful for controlling the expression of a transgene, for many applications it is useful to control the expression of a gene in its natural chromosomal position. Therefore we capitalized on recent advances in programmed gene activation to engineer an optogenetic tool that could easily be targeted to new, endogenous DNA sequences without re-engineering the light inducible proteins. This approach took advantage of CRISPR/Cas9 technology, which uses a gene-specific guide RNA (gRNA) to facilitate Cas9 targeting and binding to a desired sequence, and the light-inducible heterodimerizers CRY2 and CIB1 from Arabidopsis thaliana to engineer a light-activated CRISPR/Cas9 effector (LACE) system. We fused the full-length (FL) CRY2 to the transcriptional activator VP64 (CRY2FL-VP64) and the N-terminal fragment of CIB1 to the N-, C-, or N- and C- terminus of a catalytically inactive Cas9. When CRY2-VP64 and one of the CIBN/dCas9 fusion proteins are expressed with a gRNA, the CIBN/dCas9 fusion protein localizes to the gRNA target. In the presence of blue light, CRY2FL binds to CIBN, which translocates CRY2FL-VP64 to the gene target and activates transcription. Unlike other optogenetic systems, the LACE system can be targeted to new endogenous loci by solely manipulating the specificity of the gRNA without having to re-engineer the light-inducible proteins. We achieved light-dependent activation of the IL1RN, HBG1/2, or ASCL1 genes by delivery of the LACE system and four gene-specific gRNAs per promoter region. For some gene targets, we achieved equivalent activation levels to cells that were transfected with the same gRNAs and the synthetic transcription factor dCas9-VP64. Gene activation was also shown to be reversible and repeatable through modulation of the duration of blue light exposure, and spatial patterning of gene expression was achieved using an eGFP reporter and a photomask. </p><p>Finally, we engineered a light-activated genetic "on" switch (LAGOS) that provides permanent gene expression in response to an initial dose of blue light illumination. LAGOS is a lentiviral vector that expresses a transgene only upon Cre recombinase-mediated DNA recombination. We showed that this vector, when used in conjunction with a light-inducible Cre recombinase system,1 could be used to express MyoD or the synthetic transcription factor VP64-MyoD2 in response to light in multiple mammalian cell lines, including primary mouse embryonic fibroblasts. We achieved light-mediated upregulation of downstream myogenic markers myogenin, desmin, troponin T, and myosin heavy chains I and II as well as fusion of C3H10T½ cells into myotubes that resembled a skeletal muscle cell phenotype. We also demonstrated LAGOS functionality in vivo by engineering the vector to express human VEGF165 and human ANG1 in response to light. HEK 293T cells stably expressing the LAGOS vector and transiently expressing the light-inducible Cre recombinase proteins were implanted into mouse dorsal window chambers. Mice that were illuminated with blue light had increased microvessel density compared to mice that were not illuminated. Analysis of human VEGF and human ANG1 levels by enzyme-linked immunosorbent assay (ELISA) revealed statistically higher levels of VEGF and ANG1 in illuminated mice compared to non-illuminated mice.</p><p>In summary, the objective of this work was to engineer robust light-inducible gene regulation systems that can control genes and cellular fate in a spatial and temporal manner. These studies combine the rapid advances in gene targeting and activation technology with natural light-inducible plant protein interactions. Collectively, this thesis presents several optogenetic systems that are expected to facilitate the development of multicellular cell and tissue constructs for use in tissue engineering, synthetic biology, gene therapy, and basic science both in vitro and in vivo.</p> / Dissertation

Hypoxia inducible factor-1&alpha; (HIF-1&alpha;) plays a critical role in the oxygen homeostasis of all metazoans. HIF-1&alpha; is a master transcriptional regulator which coordinates the adaptive response to low oxygen tension. Through activation of a plethora of downstream target genes, HIF-1&alpha; facilitates oxygenation by promoting angiogenesis and blood vessel dilation, in addition to modulating metabolic pathways to inhibit oxidative phosphorylation and promote glycolytic energy production. Given the critical roles of hypoxia, insufficient blood supply and perturbed energetics in the pathogenesis of cardiovascular disorders, notably ischaemic heart disease, therapeutic modulation of HIF-1&alpha; is of significant clinical interest. Previous studies have demonstrated an acute cardioprotective role for both endogenous and supraphysiological HIF-1&alpha; signalling in the context of myocardial ischaemia. In contrast, chronic supraphysiological HIF-1&alpha; activation in the unstressed heart has been shown to induce cardiac dysfunction. To address the effect of chronic endogenous HIF-1&alpha; activation post-myocardial infarction (MI), the present work employed a murine coronary artery ligation (CAL) model in conjunction with temporally-inducible, cardiac-specific deletion of Hif-1&alpha;. While CAL surgery successfully modelled myocardial infarction – eliciting substantial adverse cardiac remodelling and contractile dysfunction – there was no evidence of chronic HIF-1&alpha; activation by CAL in HIF knockout or control left ventricular samples. In keeping with this, chronic ablation of Hif-1&alpha; (from 2 weeks post-CAL) had no discernible additional effect upon cardiac function. Overall, these findings do not support a potential therapeutic role for inhibition of HIF-1&alpha; signalling in the chronic phase post-MI. The fundamental tricarboxylic acid (TCA) cycle enzyme fumarate hydratase (FH) converts fumarate to malate. FH deficiency is associated with smooth muscle and kidney tumours which exhibit normoxic HIF signalling due to fumarate accumulation. To investigate the potential for fumarate accumulation to elicit protective HIF signalling, a cardiac-specific Fh1 null mouse was developed through Cre-loxP recombination. Strikingly, despite interruption of the TCA cycle in a highly metabolically demanding organ, cardiac Fh1 null mice were viable, fertile and survived into adulthood, demonstrating the remarkable metabolic plasticity of the heart. However, by 3-4 months Fh1 null mice develop a lethal cardiomyopathy characterised by cardiac hypertrophy, ventricular dilatation and contractile dysfunction. Despite lack of a pseudohypoxic response, Fh1 null hearts did exhibit another phenomenon observed in FH-deficient cancers and also attributed to fumarate accumulation – activation of the nuclear factor (erythroid-derived 2)-like 2 (NRF2) antioxidant pathway. Heterozygous, but not homozygous, somatic deletion of Nrf2 extended the life expectancy of cardiac Fh1 null mice. Exploration of redox status revealed a more reductive environment in Fh1 null hearts than controls. As a corollary, inhibition of the rate limiting enzyme of the pentose phosphate pathway – a major source of cellular reducing equivalents – with dehydroepiandrosterone conferred striking amelioration of the Fh1 null cardiomyopathy, suggesting a possible pathogenic role for reductive stress. While loss of mitochondrial Fh1 activity and subsequent TCA cycle dysfunction likely contribute to the Fh1 null phenotype, the importance of cytosolic FH was unclear. To clarify this, FH was expressed specifically in the cytosol in vivo. This was sufficient to substantially rescue the Fh1 null cardiomyopathy, supporting a role for cytosolic FH disruption in its pathogenesis. Taken together, these findings highlight the potential for reductive stress to contribute to cardiac dysfunction and suggest a function for cytosolic FH in cardiac metabolic homeostasis.

Dipeptidyl peptidase IV (DPP-IV) is a serine protease, which executes its proteolytic activity by cleaving X-Pro dipeptides from the N-termini of its substrates. Furthermore, DPP-IV exhibits many biological functions independent of its enzymatic aktivity. Previous studies in our laboratory proved increased expression of DPP-IV in high-grade astrocytic tumours. To evaluate the enzymatic and non-enzymatic functions of DPP-IV in a glioma model, clones of asctrocytic cell line U373MG transfected by enzymatically inactive, mutated DPP-IV (mutDPP-IV) and enzymatically active, wild type DPP-IV (wtDPP-IV), were prepared. Enzymatically inactive mutDPP-IV was prepared using point mutation the active site serine residue. Cells U373MG were transfected using a doxycycline inducible Tet-On® system. For further analysis of the transgenic forms of DPP-IV, methods were used for verification of protein expression, enzymatic activity and subcellular localization. Doxycycline induced U373MG mutDPP-IV and U373MG wtDPP-IV cells, expressing mutated and wild type DPP-IV, respectivelly, exhibited increased expression of transgenic DPP-IV in a concentration and time dependent manner. Doxycycline induced U373MG wtDPP-IV cells exhibited both increased expression and enzymatic activity of DPP-IV. In contrast, DPP-IV enzymatic...