The ubiquitin-proteasome system (UPS) controls the stability, activity and localisation of most of the proteome and regulates virtually all cellular processes through modification of proteins with ubiquitin. Ubiquitin conjugation is mediated by a conserved enzymatic cascade composed of E1, E2 and E3 enzymes, which cooperate to activate and transfer ubiquitin to substrate proteins. Dysfunction of the UPS is implicated in many disease states, including cancer, neurodegeneration, immune and cardiovascular disorders. Despite the central role of the UPS in cellular regulation, our understanding of the function, interactions and specificity of proteins that comprise the UPS is still limited. One approach to dissect and to study the UPS is to identify molecular probes, which can be used to specifically interrogate catalytic mechanisms and can be potentially considered as entry points for drug discovery. This work focuses on developing novel high-throughput screening methods for inhibitors of the ubiquitin-conjugating enzymes (E2s), using a unicellular organism Saccharomyces cerevisiae and in vitro technologies. S. cerevisiae is a model organism, commonly used in research as a valuable tool for genetic investigations and other high-throughput studies. In this work, we evaluated the toxicity of exogenously expressed human E2s on yeast cells and discovered that one of the E2s, Ube2U, significantly inhibited yeast growth. This inhibition was dependent on the Ube2U ubiquitin-conjugation activity, as demonstrated with a catalytically inactive Ube2U C89A control, which did not affect yeast growth. The growth defect induced by Ube2U allowed us to develop a screening setup for inhibitors of Ube2U, where the enzyme activity was coupled to cell growth readout. Potential Ube2U inhibitors would be identified as rescuers of the slow growing Ube2U-expressing yeast phenotype. Although screening methods in yeast are relatively straightforward to set up and run, the advantages of this system, namely simplicity of the detection signal and high-throughput, are limited by the fact that yeast is not a recognised large scale screening system in pharmaceutical industry, and that it is difficult to identify the target in a complex pathway such as the UPS. In vitro technologies are needed to provide the necessary structure-activity relationship for chemical optimisation. Therefore, we developed a novel, fluorescence-based, miniaturised assay technology, suitable for biochemical investigations and screening for inhibitors of a wide range of specific ubiquitination reactions within the UPS.

Peroxiredoxin 6 (PRDX6) is a bifunctional enzyme comprising a peroxidase and a Ca2+-independent phospholipase (iPLA2) activity. This renders the enzyme capable of detoxifying reactive oxygen species (ROS) and of catalyzing the liberation of arachidonic acid (AA) from cellular membranes. Released AA can be further metabolized to bioactive lipids including eicosanoids, which are involved in inflammation, cell growth, differentiation, invasion and proliferation. Human melanoma cells are often characterized by imbalances in both ROS and lipid levels, which can be generated by oncogenic signaling, altered metabolism or UV irradiation. In previous studies, a comparative proteome analysis of the Xiphophorus fish melanoma model revealed a strong upregulation of Prdx6 in benign and malignant lesions compared to healthy skin. As the Xiphophorus melanoma model displays in many respects molecular characteristics that are similar to human melanoma, I investigated the functional role of PRDX6 in human melanoma cells. The first part of the study deals with the regulation of PRDX6 in melanocytes and human melanoma cells. I could demonstrate that the protein level of PRDX6 was strongly enhanced by the induction of the EGFR orthologue Xmrk from the Xiphophorus fish as well as the human EGFR. The upregulation of PRDX6 was further shown to be mediated in a PI3K-dependent and ROS-independent manner. The main part of the thesis comprises the investigation of the functional role of PRDX6 in human melanoma cells as well as the analysis of the underlying mechanism. I could show that knockdown of PRDX6 enhanced the oxidative stress response and led to decreased proliferation of melanoma cells. This cell growth effect was mainly mediated by the iPLA2 activity of PRDX6. Under conditions of strongly enhanced oxidative stress, the peroxidase activity became also important for cellular proliferation. Furthermore, the anti-proliferative effect in cells with lowered PRDX6 levels was the result of reduced cellular AA content and the decrease in the activation of SRC family proteins. Similarly, supplementation with AA led to regeneration of SRC family kinase activity and to an improvement in the reduced proliferation after knockdown of PRDX6. Since AA can be further processed into the prostaglandin PGE2, which has a pro-tumorigenic function in some cancer types, I further examined whether this eicosanoid is involved in the proliferative function of PRDX6. In contrast to AA, PGE2 was not consistently required for melanoma proliferation. In summary, I could demonstrate that PRDX6 plays a major role in AA-dependent lipid signaling in melanoma cells and thereby regulates proliferation. Interestingly, the proliferation relevant iPLA2 activity can be pharmacologically targeted, and melanoma cell growth was clearly blocked by the inhibitor BEL. Thus, I could identify the phospholipase activity of PRDX6 as a new therapeutically interesting target for melanoma treatment. / Peroxiredoxin 6 (PRDX6) ist ein bifunktionales Enzym, welches neben seiner Peroxidase-Aktivität auch eine Ca2+-unabhängige Phospholipase-Aktivität besitzt. Aufgrund dieser beiden Aktivitäten ist das Enzym in der Lage, sowohl oxidativen Stress zu bekämpfen als auch die Freisetzung von Arachidonsäure aus zellulären Membranen zu katalysieren. Freie Arachidonsäure (AA) dient der Generierung von bioaktiven Lipiden wie zum Beispiel Eicosanoiden, welche an Entzündungsreaktionen, Zellwachstum, Differenzierung, Invasion und Proliferation beteiligt sind. Humane Melanomzellen zeichnen sich oft durch ein gestörtes Gleichgewicht reaktiver Sauerstoffspezies und zellulärer Lipide aus. Dieses Ungleichgewicht kann durch onkogene Signalgebung, einen veränderten Metabolismus oder UV-Bestrahlung hervorgerufen werden. Eine vorangegangene Proteomanalyse des Xiphophorus-Fisch-Melanommodells zeigte, dass im Vergleich zur gesunden Haut die Menge an PRDX6 in benignen und malignen Läsionen stark erhöht ist. Da das Xiphophorus-Melanommodell in vielerlei Hinsicht die molekulare Situation des humanen Melanoms wiederspiegelt, habe ich die funktionale Rolle von PRDX6 in humanen Melanomzellen untersucht. Der erste Teil der Studie beschäftigt sich mit der Regulierung von PRDX6 in Melanozyten und humanen Melanomzellen. Ich konnte nachweisen, dass die Menge an PRDX6 Protein durch die Induktion des EGFR Orthologs Xmrk aus Xiphophorus Fischen, sowie des humanen EGFR stark erhöht wurde. Auch konnte ich zeigen, dass die Heraufregulierung von PRDX6 von der Signalgebung der PI3 Kinase, aber nicht von reaktiven Sauerstoffspezies abhängig war. Der Hauptteil der vorliegenden Forschungsarbeit befasst sich mit der Ermittlung der funktionalen Rolle von PRDX6 in humanen Melanomzellen und der Analyse des zugrundeliegenden Mechanismus. Ich konnte nachweisen, dass ein Knockdown von PRDX6 die oxidative Stress-Antwort verstärkte und die Proliferation von Melanomzellen reduzierte. Der Effekt auf das zelluläre Wachstum wurde hierbei hauptsächlich durch die iPLA2-Aktivität von PRDX6 verursacht. Bei stark erhöhtem oxidativem Stress konnte auch eine Relevanz der Peroxidase-Aktivität für die zelluläre Proliferation nachgewiesen werden. Auch ging der anti-proliferative Effekt mit einer Abnahme zellulärer AA und der Reduktion aktiver Kinasen der SRC-Familie einher. Die Zugabe von AA zu Zellen mit PRDX6-Knockdown führte zur Regeneration der SRC-Kinase-Aktivität und konnte die Proliferation wieder verbessern. Da AA zum Prostaglandin PGE2 prozessiert werden kann, welches in einigen Krebsarten pro-tumorigene Funktionen erfüllt, untersuchte ich, ob dieses Eicosanoid auch für die proliferative Funktion von PRDX6 relevant ist. Im Gegensatz zu AA wies PGE2 jedoch keine kontinuierliche pro-proliferative Funktion auf. Zusammenfassend konnte ich zeigen, dass PRDX6 eine entscheidende Rolle im AA- Stoffwechsel von Melanomzellen spielt und hierdurch die Proliferation reguliert. Interessanterweise ist die proliferationsrelevante iPLA2-Aktivität pharmakologisch hemmbar, und auch das Wachstum der Melanomzellen wurde durch den Inhibitor BEL deutlich inhibiert. Mit der Phospholipase-Aktivität von PRDX6 konnte ich somit einen neuen therapeutisch nutzbaren Angriffspunkt für das Melanom identifizieren.

共著者あり。共著者名: Kuniaki Suzuki, Masatake Yoshikawa, Tohru Imai, Akira Matsumotob and Shinji Nakamura. Elsevier Science Ltd., Takashi Kajii, Kuniaki Suzuki, Masatake Yoshikawa, Tohru Imai, Akira Matsumotob and Shinji Nakamura, Long-term effects of prostaglandin E2 on the mineralization of a clonal osteoblastic cell line (MC3T3-E1), Archives of Oral Biology, 44(3), 1999 MAR, pp.233-241. doi:10.1016/S0003-9969(98)00120-4. Journal Website: http://intl.elsevierhealth.com/journals/arob/ / Prostaglandin (PG) E2 is thought to be a mediator of the effect of mechanical stress on bone formation, but its effects on osteoblasts have not yet been fully described. Here, the effects of the continuous application of PGE2 and indomethacin, an inhibitor of prostaglandin G/H synthase (cyclo-oxygenase), on the proliferation, differentiation and mineralization of a clonal osteoblastic cell line, MC3T3-E1, were investigated. The cells were cultured in media with either a high (1 μg/ml) or a low (1 ng/ml) concentration of PGE2, with indomethacin (1 μg/ml) and, as a control, with neither agent. The effects of PGE2 and indomethacin were assessed quantitatively. Indomethacin and a high concentration of PGE2 increased the total protein compared to the control and low-PGE2 cultures. 7 days after confluence, alkaline phosphatase (ALP) activity within the cells and extracellular matrices increased. This increase was highest with indomethacin and lowest with a high concentration of PGE2. ALP activity also increased in the medium, but only 21 days after confluence; the effects of the agents were similar to those on the cells and matrices. The accumulation of calcium, inorganic phosphate and hydroxyproline was highest with indomethacin. PGE2 production was at its maximum when the cells were at confluence and was inhibited by indomethacin. Specific [3H]PGE2 binding to the microsomal fraction of the cell was also measured to examine the expression of the PGE2 receptor. The amount of [3H]PGE2 binding per mg of protein was highest at confluence, then decreased and again increased in the mineralizing stage. These results suggest that indomethacin increases ALP activity and the accumulation of mineralized tissue in MC3T3-E1 cells, presumably by inhibiting the production of PGE2. PGE2 could signal the suppression of mineralization as early as confluence. / Hokkaido University (北海道大学) / 博士 / 歯学

Universiẗat, Diss.--Jena, 2008.

Konstanz, Univ., Diss., 2008.

abstract: Infections caused by the Hepatitis C Virus (HCV) are very common worldwide, affecting up to 3% of the population. Chronic infection of HCV may develop into liver cirrhosis and liver cancer which is among the top five of the most common cancers. Therefore, vaccines against HCV are under intense study in order to prevent HCV from harming people's health. The envelope protein 2 (E2) of HCV is thought to be a promising vaccine candidate because it can directly bind to a human cell receptor and plays a role in viral entry. However, the E2 protein production in cells is inefficient due to its complicated matured structure. Folding of E2 in the endoplasmic reticulum (ER) is often error-prone, resulting in production of aggregates and misfolded proteins. These incorrect forms of E2 are not functional because they are not able to bind to human cells and stimulate antibody response to inhibit this binding. This study is aimed to overcome the difficulties of HCV E2 production in plant system. Protein folding in the ER requires great assistance from molecular chaperones. Thus, in this study, two molecular chaperones in the ER, calreticulin and calnexin, were transiently overexpressed in plant leaves in order to facilitate E2 folding and production. Both of them showed benefits in increasing the yield of E2 and improving the quality of E2. In addition, poorly folded E2 accumulated in the ER may cause stress in the ER and trigger transcriptional activation of ER molecular chaperones. Therefore, a transcription factor involved in this pathway, named bZIP60, was also overexpressed in plant leaves, aiming at up-regulating a major family of molecular chaperones called BiP to assist protein folding. However, our results showed that BiP mRNA levels were not up-regulated by bZIP60, but they increased in response to E2 expression. The Western blot analysis also showed that overexpression of bZIP60 had a small effect on promoting E2 folding. Overall, this study suggested that increasing the level of specific ER molecular chaperones was an effective way to promote HCV E2 protein production and maturation. / Dissertation/Thesis / M.S. Biological Design 2011

TELES, Patricia de Barros. Polimorfismo genético da apolipoproteína E e avaliação sociodemográfica em pacientes com periodontite crônica. 2013. 97 f. Dissertação (Mestrado em Farmacologia) - Universidade Federal do Ceará. Faculdade de Medicina, Fortaleza, 2013. / Submitted by denise santos (denise.santos@ufc.br) on 2014-03-17T12:41:40Z No. of bitstreams: 1 2013_dis_pbteles.pdf: 1461989 bytes, checksum: 2ec2d2a056edac264128a2ace887df84 (MD5) / Approved for entry into archive by denise santos(denise.santos@ufc.br) on 2014-03-17T12:42:25Z (GMT) No. of bitstreams: 1 2013_dis_pbteles.pdf: 1461989 bytes, checksum: 2ec2d2a056edac264128a2ace887df84 (MD5) / Made available in DSpace on 2014-03-17T12:42:25Z (GMT). No. of bitstreams: 1 2013_dis_pbteles.pdf: 1461989 bytes, checksum: 2ec2d2a056edac264128a2ace887df84 (MD5) Previous issue date: 2013 / Chronic periodontitis (CP) is characterized by an inflammation in the supporting tissues of the teeth. It is primarily caused by bacteria, but progression is associated with individual host response. CP is a complex and multifactorial disease. Genetic and environmental factors interacting can modify the clinical cause of the disease. Genetic polymorphisms have been studied to identify possible genetic markers and explain differences in the inflammatory cytokines expression. Apolipoprotein E (apoE) is an important protein in lipid metabolism and is also envolved in pathophysiological processes. The aim of this study was to investigate whether there is an association of the APOE polymorphisms with the CP´s susceptibility in subjects that sought periodontal treatment at Dental School of Federal University of Ceara and evaluate sociodemographic status related with the disease. A sample of 109 subjects between 30 and 70 years (mean age = 44,5 ± 9,64) were grouped into: 53 controls and 56 subjects with CP. DNA was obtained through a mouthwash and oral mucosa scraping and genotyped by PCR-RFLP method (Polimerase Chain Reaction – Restrict Fragment Length Polymorphism). Differences in the allele and genotype frequencies were assessed by Chi-squared test (p˂0.05). The risk associated with alleles and genotypes was calculated as odds ratio (OR) with 95% confidence intervals (CI). Logistic regression was used to associate sociodemographic status with CP and genotypes. No differences were observed in the apoE allelic distribution regarding control and periodontitis groups. Age and socio-economic status increase the risk for having CP, since individuals with lower socio-economic status was about 3-fold more likely to develop periodontitis (OR=3.1) and increase in age enhances the risk in 5.1% to develop disease in each year of age. Hypertension was a factor of clinic importance in development of CP, since subjects who self-reported hypertensive have 2,5-fold more likely to develop disease than individuals who not self-reported hypertension, although no statistic difference was reached. Similarly, CP was also associated with lower education level (OR=3.7). The polymorphism in the APOE gene was not associated with the susceptibility to CP in the studied population. / A periodontite crônica inflamatória (PC) caracteriza-se por um processo inflamatório nos tecidos de suporte dos dentes. É causada inicialmente por bactérias, mas sua progressão está relacionada à resposta individual do hospedeiro. É uma doença multifatorial e complexa, na qual fatores genéticos e ambientais interagem, promovendo e modificando a expressão clínica da doença. Polimorfismos de genes envolvidos no processo inflamatório têm sido estudados no intuito de identificar possíveis marcadores genéticos e elucidar diferenças na expressão de citocinas mediadoras da inflamação. Apolipoproteína E (apoE) é uma proteína de importância no metabolismo lipídico e está envolvida em processos fisiopatológicos. O objetivo deste estudo foi investigar se há associação do polimorfismo do gene da apoE com a susceptibilidade à PC em indivíduos que procuraram o serviço odontológico da clínica de Periodontia da Universidade Federal do Ceará e avaliar achados sociodemográficos relacionados com essa doença. Foram selecionados 109 indivíduos entre 30 e 70 anos (média = 44,5 ± 9,64) de ambos os gêneros e agrupados da seguinte forma: grupo controle n=53 e grupo Periodontite Crônica n=56. Foi extraído DNA a partir de um bochecho e esfregaço da mucosa oral e o polimorfismo da apoE foi identificado pelo método de PCR-RFLP (reação de polimerase em cadeia – polimorfismo com restrição de fragmentos) e submetidos à eletroforese em gel de agarose a 5%. As distribuições da frequência alélica e dos genótipos foram avaliadas pelo teste qui-quadrado (p˂0,05). O risco associado com alelos e genótipos foi calculado como odds ratio (OR) com intervalo de confiança (IC) de 95%. Para relacionar os achados sociodemográficos com a PC em indivíduos com alelos específicos foi utilizada a análise de regressão logística. Os resultados da análise individual do polimorfismo da apoE não evidenciaram associação dos alelos e genótipos com a susceptibilidade à PC. Observou-se associação entre a doença e a renda familiar mensal, de maneira que a chance de adoecer aumenta 3 vezes quando a renda diminui de mais que 3 salários-mínimos para a renda de 1 a 3 salários-mínimos. Ainda, há um aumento significativo na chance de desenvolver a doença em 5,1% a cada ano de vida. Indivíduos que reportaram hipertensão arterial tiveram uma chance quase 2,5 vezes maior de ter a PC do que o grupo controle apesar de não ter dado significado estatístico. Da mesma forma, foi encontrada maior chance de desenvolver a doença em indivíduos com baixo nível de escolaridade (OR=3,7). O polimorfismo da apoE não está associado à PC na população estudada.

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / A periodontite crÃnica inflamatÃria (PC) caracteriza-se por um processo inflamatÃrio nos tecidos de suporte dos dentes. à causada inicialmente por bactÃrias, mas sua progressÃo està relacionada à resposta individual do hospedeiro. à uma doenÃa multifatorial e complexa, na qual fatores genÃticos e ambientais interagem, promovendo e modificando a expressÃo clÃnica da doenÃa. Polimorfismos de genes envolvidos no processo inflamatÃrio tÃm sido estudados no intuito de identificar possÃveis marcadores genÃticos e elucidar diferenÃas na expressÃo de citocinas mediadoras da inflamaÃÃo. ApolipoproteÃna E (apoE) à uma proteÃna de importÃncia no metabolismo lipÃdico e està envolvida em processos fisiopatolÃgicos. O objetivo deste estudo foi investigar se hà associaÃÃo do polimorfismo do gene da apoE com a susceptibilidade à PC em indivÃduos que procuraram o serviÃo odontolÃgico da clÃnica de Periodontia da Universidade Federal do Cearà e avaliar achados sociodemogrÃficos relacionados com essa doenÃa. Foram selecionados 109 indivÃduos entre 30 e 70 anos (mÃdia = 44,5  9,64) de ambos os gÃneros e agrupados da seguinte forma: grupo controle n=53 e grupo Periodontite CrÃnica n=56. Foi extraÃdo DNA a partir de um bochecho e esfregaÃo da mucosa oral e o polimorfismo da apoE foi identificado pelo mÃtodo de PCR-RFLP (reaÃÃo de polimerase em cadeia â polimorfismo com restriÃÃo de fragmentos) e submetidos à eletroforese em gel de agarose a 5%. As distribuiÃÃes da frequÃncia alÃlica e dos genÃtipos foram avaliadas pelo teste qui-quadrado (p˂0,05). O risco associado com alelos e genÃtipos foi calculado como odds ratio (OR) com intervalo de confianÃa (IC) de 95%. Para relacionar os achados sociodemogrÃficos com a PC em indivÃduos com alelos especÃficos foi utilizada a anÃlise de regressÃo logÃstica. Os resultados da anÃlise individual do polimorfismo da apoE nÃo evidenciaram associaÃÃo dos alelos e genÃtipos com a susceptibilidade à PC. Observou-se associaÃÃo entre a doenÃa e a renda familiar mensal, de maneira que a chance de adoecer aumenta 3 vezes quando a renda diminui de mais que 3 salÃrios-mÃnimos para a renda de 1 a 3 salÃrios-mÃnimos. Ainda, hà um aumento significativo na chance de desenvolver a doenÃa em 5,1% a cada ano de vida. IndivÃduos que reportaram hipertensÃo arterial tiveram uma chance quase 2,5 vezes maior de ter a PC do que o grupo controle apesar de nÃo ter dado significado estatÃstico. Da mesma forma, foi encontrada maior chance de desenvolver a doenÃa em indivÃduos com baixo nÃvel de escolaridade (OR=3,7). O polimorfismo da apoE nÃo està associado à PC na populaÃÃo estudada. / Chronic periodontitis (CP) is characterized by an inflammation in the supporting tissues of the teeth. It is primarily caused by bacteria, but progression is associated with individual host response. CP is a complex and multifactorial disease. Genetic and environmental factors interacting can modify the clinical cause of the disease. Genetic polymorphisms have been studied to identify possible genetic markers and explain differences in the inflammatory cytokines expression. Apolipoprotein E (apoE) is an important protein in lipid metabolism and is also envolved in pathophysiological processes. The aim of this study was to investigate whether there is an association of the APOE polymorphisms with the CPÂs susceptibility in subjects that sought periodontal treatment at Dental School of Federal University of Ceara and evaluate sociodemographic status related with the disease. A sample of 109 subjects between 30 and 70 years (mean age = 44,5  9,64) were grouped into: 53 controls and 56 subjects with CP. DNA was obtained through a mouthwash and oral mucosa scraping and genotyped by PCR-RFLP method (Polimerase Chain Reaction â Restrict Fragment Length Polymorphism). Differences in the allele and genotype frequencies were assessed by Chi-squared test (p˂0.05). The risk associated with alleles and genotypes was calculated as odds ratio (OR) with 95% confidence intervals (CI). Logistic regression was used to associate sociodemographic status with CP and genotypes. No differences were observed in the apoE allelic distribution regarding control and periodontitis groups. Age and socio-economic status increase the risk for having CP, since individuals with lower socio-economic status was about 3-fold more likely to develop periodontitis (OR=3.1) and increase in age enhances the risk in 5.1% to develop disease in each year of age. Hypertension was a factor of clinic importance in development of CP, since subjects who self-reported hypertensive have 2,5-fold more likely to develop disease than individuals who not self-reported hypertension, although no statistic difference was reached. Similarly, CP was also associated with lower education level (OR=3.7). The polymorphism in the APOE gene was not associated with the susceptibility to CP in the studied population.

The ubiquitination of proteins serves as molecular signal to control an enormous number of physiological processes and its dysregulation is connected to human diseases like cancer. The versatility of this signal stems from the diverse ways by which ubiquitin can be attached to its targets. Thus, specificity and tight regulation of the ubiquitination are pivotal requirements of ubiquitin signaling. Ubiquitin-conjugating enzymes (E2s) act at the heart of the ubiquitination cascade, transferring ubiquitin from a ubiquitin-activating enzyme (E1) to a ubiquitin ligase (E3) or substrate. When cooperating with a RING-type E3, ubiquitin-conjugating enzymes can determine linkage specificity in ubiquitin chain formation. Our understanding of the regulation of E2 activities is still limited at a structural level. The work described here identifies two regulation mechanisms in UBE2S, a cognate E2 of the human RING-type E3 anaphase-promoting complex/cyclosome (APC/C). UBE2S elongates ubiquitin chains on APC/C substrates in a Lys11 linkage-specific manner, thereby targeting these substrates for degradation and driving mitotic progression. In addition, UBE2S was found to have a role in DNA repair by enhancing non-homologous end-joining (NHEJ) and causing transcriptional arrest at DNA damage sites in homologous recombination (HR). Furthermore, UBE2S overexpression is a characteristic feature of many cancer types and is connected to poor prognosis and diminished response to therapy. The first regulatory mechanism uncovered in this thesis involves the intramolecular auto-ubiquitination of a particular lysine residue (Lys+5) close to the active site cysteine, presumably through conformational flexibility of the active site region. The Lys+5-linked ubiquitin molecule adopts a donor-like, ‘closed’ orientation towards UBE2S, thereby conferring auto-inhibition. Notably, Lys+5 is a major physiological ubiquitination site in ~25% of the human E2 enzymes, thus providing regulatory opportunities beyond UBE2S. Besides the active, monomeric state and the auto-inhibited state caused by auto-ubiquitination, I discovered that UBE2S can adopt a dimeric state. The latter also provides an auto-inhibited state, in which ubiquitin transfer is blocked via the obstruction of donor binding. UBE2S dimerization is promoted by its unique C-terminal extension, suppresses auto-ubiquitination and thereby the proteasomal degradation of UBE2S. Taken together, the data provided in this thesis illustrate the intricate ways by which UBE2S activity is fine-tuned and the notion that structurally diverse mechanisms have evolved to restrict the first step in the catalytic cycle of E2 enzymes. / Die Ubiquitinierung von Proteinen fungiert als molekulares Signal zur Kontrolle einer Vielzahl physiologischer Prozesse, wobei eine gestörte Regulation der Ubiquitinierung eng mit zahlreichen Erkrankungen, wie beispielsweise Krebs, verbunden ist. Aufgrund der verschiedenen Verknüpfungsmöglichkeiten von Ubiquitin, die das zelluläre Schicksal des Zielproteins bestimmen, sind Spezifität und stringente Regulation unabkömmliche Voraussetzungen im Ubiquitinierungsprozess. Ubiquitin-konjugierende Enzyme (E2s) fungieren in der Mitte der Ubiquitinierungskaskade. Sie übernehmen ein Ubiquitinmolekül vom Ubiquitin-aktivierenden Enzym (E1) und übertragen es auf eine Ubiquitin-Ligase (E3) oder direkt auf das Zielprotein. Arbeiten Ubiquitin-konjugierende Enzyme mit E3s des RING-Typus zusammen, so bestimmen E2s die Art der Verknüpfung. Die Regulation der Aktivität Ubiquitin-konjugierender Enzyme auf struktureller Ebene ist jedoch bisher nur bedingt verstanden. Die hier dargelegte Arbeit umfasst die Identifizierung zweier Regulationsmechanismen des Ubiquitin-konjugierenden Enzyms UBE2S. UBE2S arbeitet mit einem humanen E3 des RING-Typus‚ dem ‚Anaphase Promoting Complex/Cyclosome‘ (APC/C) zusammen und bildet Lys11-spezifische Ubiquitinketten auf Substraten des APC/Cs. Hierdurch werden die Substrate für den Abbau durch das Proteasom markiert, was das Fortschreiten der Mitose bedingt. Zusätzlich wird UBE2S eine Rolle in der DNS-Reparatur zugeschrieben. Hierbei verstärkt UBE2S die nicht-homologe Rekombination (NHEJ) und verhindert außerdem die Transkription an DNS-Bruchstellen, die durch Homologe Rekombination (HR) repariert werden. Die Überexpression von UBE2S ist ein Charakteristikum verschiedenster Krebsarten, vermindert den Erfolg herkömmlicher Krebstherapien, und führt somit zu schlechten Prognosen für betroffenen Patienten. Der erste hier beschriebene Regulationsmechanismus beinhaltet die intramolekulare Ubiquitinierung eines Lysins (Lys+5) nahe des katalytischen Cysteins, mutmaßlich durch strukturelle Flexibilität der Region des aktiven Zentrums. Das Lys+5-verknüpfte Ubiquitin nimmt eine Donorubiquitin-ähnliche Position auf UBE2S ein, wodurch UBE2S gehemmt wird. Da ein Lysin an der Position +5 in ~25% der humanen E2-Enzyme vorhanden und eine physiologische Ubiquitinierungsstelle ist, birgt dieser Mechanismus Regulationsmöglichkeiten über UBE2S hinaus. Zusätzlich zum aktiven monomeren Zustand und dem durch Autoubiquitinierung ausgelösten inhibierten Zustand, kann UBE2S auch als Dimer vorliegen. In diesem Zustand ist es ebenfalls inaktiv, da die Donorubiquitin-Bindestelle auf UBE2S durch ein zweites Molekül des E2s blockiert wird. Begünstigt wird die Dimerisierung durch die C-terminale Verlängerung von UBE2S und verhindert so deren Autoubiquitinierung, und folglich den proteasomalen Abbau von UBE2S. Es handelt sich hierbei somit um einen zweiten Regulationsmechanismus von UBE2S. Zusammenfassend veranschaulichen die in dieser Arbeit dargelegten Daten die komplexen Möglichkeiten, durch die die Aktivität von UBE2S reguliert werden kann, sowie die Erkenntnis, dass strukturell unterschiedliche Mechanismen existieren, um den ersten Schritt der von Ubiquitin-konjugierenden Enzymen katalysierten Reaktion zu hemmen.

No description available.