Loss of PTEN expression and AKT activation in HER2-positive breast carcinomas

PURPOSE: To examine the expression of AKT and PTEN in a series of HER2-positive primary invasive breast tumors using immunohistochemistry, and to associate these expression profiles with classic pathologic features such as tumor grade, hormone receptor expression, lymphatic vascular invasion, and proliferation.METHODS: A total of 104 HER2-positive breast carcinoma specimens were prepared in tissue microarrays blocks for immunohistochemical detection of PTEN and phosphorylated AKT (pAKT). Original histologic sections were reviewed to assess pathological features, including HER2 status and Ki-67 index values. The associations between categorical and numeric variables were identified using Pearson's chi-square test and the Mann-Whitney, respectively.RESULTS: Co-expression of pAKT and PTEN was presented in 59 (56.7%) cases. Reduced levels of PTEN expression were detected in 20 (19.2%) cases, and these 20 tumors had a lower Ki-67 index value. In contrast, tumors positive for pAKT expression [71 (68.3%)] were associated with a higher Ki-67 index value.CONCLUSION: A role for AKT in the proliferation of HER2-positive breast cancers was confirmed. However, immunohistochemical detection of PTEN expression did not correlate with an inhibition of cellular proliferation or control of AKT phosphorylation, suggesting other pathways in these mechanisms of control.

Ultimate capacity of stainless steel rectangular hollow section X- joints at low temperatures

Growing demand for stainless steel construction materials has increased the popularity of substitutive materials for austenitic stainless steels. The lean duplex grades have taken their place in building of structures exposed to corrosive environments. Since the duplex grades are relatively new materials, the current codes and norms do not fully cover the newest duplex grades. The joints tested in this thesis were designed and studied according to Eurocode 3, even though all the materials are not yet accepted to the standards. The main objective in this thesis was to determine the differences of the used materials in behaviour under loading at low temperatures. Tests in which the deformation and strength properties of the joints were determined were done at the temperature of -46°C, which is the requirement of temperature for structures designed according to Norsok standards. Results show that replacing the austenitic grade with the lean duplex grade is acceptable.

Optimized Fast-FISH with a-satellite probes: acceleration by microwave activation

It has been shown for several DNA probes that the recently introduced Fast-FISH (fluorescence in situ hybridization) technique is well suited for quantitative microscopy. For highly repetitive DNA probes the hybridization (renaturation) time and the number of subsequent washing steps were reduced considerably by omitting denaturing chemical agents (e.g., formamide). The appropriate hybridization temperature and time allow a clear discrimination between major and minor binding sites by quantitative fluorescence microscopy. The well-defined physical conditions for hybridization permit automatization of the procedure, e.g., by a programmable thermal cycler. Here, we present optimized conditions for a commercially available X-specific a-satellite probe. Highly fluorescent major binding sites were obtained for 74oC hybridization temperature and 60 min hybridization time. They were clearly discriminated from some low fluorescent minor binding sites on metaphase chromosomes as well as in interphase cell nuclei. On average, a total of 3.43 ± 1.59 binding sites were measured in metaphase spreads, and 2.69 ± 1.00 in interphase nuclei. Microwave activation for denaturation and hybridization was tested to accelerate the procedure. The slides with the target material and the hybridization buffer were placed in a standard microwave oven. After denaturation for 20 s at 900 W, hybridization was performed for 4 min at 90 W. The suitability of a microwave oven for Fast-FISH was confirmed by the application to a chromosome 1-specific a-satellite probe. In this case, denaturation was performed at 630 W for 60 s and hybridization at 90 W for 5 min. In all cases, the results were analyzed quantitatively and compared to the results obtained by Fast-FISH. The major binding sites were clearly discriminated by their brightness

Angiotensin II induces NF-κB, JNK and p38 MAPK activation in monocytic cells and increases matrix metalloproteinase-9 expression in a PKC- andRho kinase-dependent manner

Angiotensin II (ANG II), the main effector of the renin-angiotensin system, is implicated in endothelial permeability, recruitment and activation of the immune cells, and also vascular remodeling through induction of inflammatory genes. Matrix metalloproteinases (MMPs) are considered to be important inflammatory factors. Elucidation of ANG II signaling pathways and of possible cross-talks between their components is essential for the development of efficient inhibitory medications. The current study investigates the inflammatory signaling pathways activated by ANG II in cultures of human monocytic U-937 cells, and the effects of specific pharmacological inhibitors of signaling intermediates on MMP-9 gene (MMP-9) expression and activity. MMP-9 expression was determined by real-time PCR and supernatants were analyzed for MMP-9 activity by ELISA and zymography methods. A multi-target ELISA kit was employed to evaluate IκB, NF-κB, JNK, p38, and STAT3 activation following treatments. Stimulation with ANG II (100 nM) significantly increased MMP-9 expression and activity, and also activated NF-κB, JNK, and p38 by 3.8-, 2.8- and 2.2-fold, respectively (P < 0.01). ANG II-induced MMP-9 expression was significantly reduced by 75 and 67%, respectively, by co-incubation of the cells with a selective inhibitor of protein kinase C (GF109203X, 5 µM) or of rho kinase (Y-27632, 15 µM), but not with inhibitors of phosphoinositide 3-kinase (wortmannin, 200 nM), tyrosine kinases (genistein, 100 µM) or of reactive oxygen species (α-tocopherol, 100 µM). Thus, protein kinase C and Rho kinase are important components of the inflammatory signaling pathways activated by ANG II to increase MMP-9 expression in monocytic cells. Both signaling molecules may constitute potential targets for effective management of inflammation.

Plasma cytokine response, lipid peroxidation and NF-κB activation in skeletal muscle following maximum progressive swimming

Our objective was to determine lipid peroxidation and nuclear factor-κB (NF-κB) activation in skeletal muscle and the plasma cytokine profile following maximum progressive swimming. Adult male Swiss mice (N = 15) adapted to the aquatic environment were randomly divided into three groups: immediately after exercise (EX1), 3 h after exercise (EX2) and control. Animals from the exercising groups swam until exhaustion, with an initial workload of 2% of body mass attached to the tail. Control mice did not perform any exercise but were kept immersed in water for 20 min. Maximum swimming led to reactive oxygen species (ROS) generation in skeletal muscle, as indicated by increased thiobarbituric acid reactive species (TBARS) levels (4062.67 ±1487.10 vs 19,072.48 ± 8738.16 nmol malondialdehyde (MDA)/mg protein, control vs EX1). Exercise also promoted NF-κB activation in soleus muscle. Cytokine secretion following exercise was marked by increased plasma interleukin-6 (IL-6) levels 3 h post-exercise (P < 0.05). Interleukin-10 (IL-10) levels were reduced following exercise and remained reduced 3 h post-exercise (P < 0.05). Plasma levels of other cytokines investigated, monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ) and interleukin-12 (IL-12), were not altered by exercise. The present findings showed that maximum swimming, as well as other exercise models, led to lipid peroxidation and NF-κB activation in skeletal muscle and increased plasma IL-6 levels. The plasma cytokine response was also marked by reduced IL-10 levels. These results were attributed to exercise type and intensity.

Kaurene diterpene induces apoptosis in U87 human malignant glioblastoma cells by suppression of anti-apoptotic signals and activation of cysteine proteases

Gliomas are the most common and malignant primary brain tumors in humans. Studies have shown that classes of kaurene diterpene have anti-tumor activity related to their ability to induce apoptosis. We investigated the response of the human glioblastoma cell line U87 to treatment with ent-kaur-16-en-19-oic acid (kaurenoic acid, KA). We analyzed cell survival and the induction of apoptosis using flow cytometry and annexin V staining. Additionally, the expression of anti-apoptotic (c-FLIP and miR-21) and apoptotic (Fas, caspase-3 and caspase-8) genes was analyzed by relative quantification (real-time PCR) of mRNA levels in U87 cells that were either untreated or treated with KA (30, 50, or 70 µM) for 24, 48, and 72 h. U87 cells treated with KA demonstrated reduced viability, and an increase in annexin V- and annexin V/PI-positive cells was observed. The percentage of apoptotic cells was 9% for control cells, 26% for cells submitted to 48 h of treatment with 50 µM KA, and 31% for cells submitted to 48 h of treatment with 70 µM KA. Similarly, in U87 cells treated with KA for 48 h, we observed an increase in the expression of apoptotic genes (caspase-8, -3) and a decrease in the expression of anti-apoptotic genes (miR-21 and c-FLIP). KA possesses several interesting properties and induces apoptosis through a unique mechanism. Further experiments will be necessary to determine if KA may be used as a lead compound for the development of new chemotherapeutic drugs for the treatment of primary brain tumors.

Resveratrol inhibits the intracellular calcium increase and angiotensin/endothelin system activation induced by soluble uric acid in mesangial cells

Resveratrol (Resv) is natural polyphenol found in grapes. This study evaluated the protective effect of Resv against the effects of uric acid (UA) in immortalized human mesangial cells (ihMCs). ihMCs were preincubated with Resv (12.5 µM) for 1 h and treated with UA (10 mg/dL) for 6 or 12 h. The intracellular calcium concentration [Ca2+]i was quantified by fluorescence using flow cytometry. Angiotensinogen (AGT) and pre-pro endothelin-1 (ppET-1) mRNA were assayed by quantitative real-time RT-PCR. Angiotensin II (AII) and endothelin-1 (ET-1) were assayed by ELISA. UA significantly increased [Ca2+]i. Pre-incubation with Resv significantly reduced the change in [Ca2+]i induced by UA. Incubation with UA for 6 or 12 h also increased AGT mRNA expression and AII protein synthesis. Resv blunted these increases in AGT mRNA expression and AII protein. Incubation with UA in the ihMCs increased ppET-1 expression and ET-1 protein synthesis at 6 and 12 h. When ihMCs were pre-incubated with Resv, UA had a significantly diminished effect on ppET-1 mRNA expression and ET-1 protein synthesis at 6 and 12 h, respectively. Our results suggested that UA triggers reactions including AII and ET-1 production in mesangial cells. The renin-angiotensin system may contribute to the pathogenesis of renal function and chronic kidney disease. Resv can minimize the impact of UA on AII, ET-1 and the increase of [Ca2+]i in mesangial cells, suggesting that, at least in part, Resv can prevent the effects of soluble UA in mesangial cells.

Activation of endogenous angiotensin converting enzyme 2 prevents early injuries induced by hyperglycemia in rat retina

Diabetic retinopathy (DR) is a serious complication of diabetes mellitus that may result in blindness. We evaluated the effects of activation of endogenous angiotensin converting enzyme (ACE) 2 on the early stages of DR. Rats were administered an intravenous injection of streptozotocin to induce hyperglycemia. The ACE2 activator 1-[[2-(dimethylamino) ethyl] amino]-4-(hydroxymethyl)-7-[[(4-methylphenyl) sulfonyl] oxy]-9H-xanthone 9 (XNT) was administered by daily gavage. The death of retinal ganglion cells (RGC) was evaluated in histological sections, and retinal ACE2, caspase-3, and vascular endothelial growth factor (VEGF) expressions were analyzed by immunohistochemistry. XNT treatment increased ACE2 expression in retinas of hyperglycemic (HG) rats (control: 13.81±2.71 area%; HG: 14.29±4.30 area%; HG+XNT: 26.87±1.86 area%; P<0.05). Importantly, ACE2 activation significantly increased the RCG number in comparison with HG animals (control: 553.5±14.29; HG: 530.8±10.3 cells; HG+XNT: 575.3±16.5 cells; P<0.05). This effect was accompanied by a reduction in the expression of caspase-3 in RGC of the HG+XNT group when compared with untreated HG rats (control: 18.74±1.59; HG: 38.39±3.39 area%; HG+XNT: 27.83±2.80 area%; P<0.05). Treatment with XNT did not alter the VEGF expression in HG animals (P>0.05). Altogether, these findings indicate that activation of ACE2 reduced the death of retinal ganglion cells by apoptosis in HG rats.

Monooxygenase Diversity and Oxygen Activation within Polyketide Antibiotic Biosynthesis

Molecular oxygen (O2) is a key component in cellular respiration and aerobic life. Through the redox potential of O2, the amount of free energy available to organisms that utilize it is greatly increased. Yet, due to the nature of the O2 electron configuration, it is non-reactive to most organic molecules in the ground state. For O2 to react with most organic compounds it must be activated. By activating O2, oxygenases can catalyze reactions involving oxygen incorporation into organic compounds. The oxygen activation mechanisms employed by many oxygenases to have been studied, and they often include transition metals and selected organic compounds. Despite the diversity of mechanisms for O2 activation explored in this thesis, all of the monooxygenases studied in the experimental part activate O2 through a transient carbanion intermediate. One of these enzymes is the small cofactorless monooxygenase SnoaB. Cofactorless monooxygenases are unusual oxygenases that require neither transition metals nor cofactors to activate oxygen. Based on our biochemical characterization and the crystal structure of this enzyme, the mechanism most likely employed by SnoaB relies on a carbanion intermediate to activate oxygen, which is consistent with the proposed substrate-assisted mechanism for this family of enzymes. From the studies conducted on the two-component system AlnT and AlnH, both the functions of the NADH-dependent flavin reductase, AlnH, and the reduced flavin dependent monooxygenase, AlnT, were confirmed. The unusual regiochemistry proposed for AlnT was also confirmed on the basis of the structure of a reaction product. The mechanism of AlnT, as with other flavin-dependent monooxygenases, is likely to involve a caged radical pair consisting of a superoxide anion and a neutral flavin radical formed from an initial carbanion intermediate. In the studies concerning the engineering of the S-adenosyl-L-methionine (SAM) dependent 4-O-methylase DnrK and the homologous atypical 10-hydroxylase RdmB, our data suggest that an initial decarboxylation of the substrate is catalyzed by both of these enzymes, which results in the generation of a carbanion intermediate. This intermediate is not essential for the 4-O-methylation reaction, but it is important for the 10-hydroxylation reaction, since it enables substrate-assisted activation of molecular oxygen involving a single electron transfer to O2 from a carbanion intermediate. The only role for SAM in the hydroxylation reaction is likely to be stabilization of the carbanion through the positive charge of the cofactor. Based on the DnrK variant crystal structure and the characterizations of several DnrK variants, the insertion of a single amino acid in DnrK (S297) is sufficient for gaining a hydroxylation function, which is likely caused by carbanion stabilization through active site solvent restriction. Despite large differences in the three-dimensional structures of the oxygenases and the potential for multiple oxygen activation mechanisms, all the enzymes in my studies rely on carbanion intermediates to activate oxygen from either flavins or their substrates. This thesis provides interesting examples of divergent evolution and the prevalence of carbanion intermediates within polyketide biosynthesis. This mechanism appears to be recurrent in aromatic polyketide biosynthesis and may reflect the acidic nature of these compounds, propensity towards hydrogen bonding and their ability to delocalize π-electrons.

Surface effect ferromagnetism in pure and reduced strontium titanate

A room temperature ferromagnetic hysteresis is observed in single crystal strontium titanate substrates as purchased from several manufacturers. It was found that polishing all sides of the substrates removed this observed hysteresis, suggesting that the origin of the ferromagnetic behavior resides on the surface of the substrates. X-ray diffraction and energy dispersive x-ray spectra were measured however they were unable to detect any impurity phases. In similar semiconducting oxides it was previously suggested that ferromagnetism could originate in oxygen vacancies or from disorder within the single crystal. To this end substrates were annealed in both air and vacuum in a range of temperatures (600°C to 1100°G) to both create bulk oxygen vacancies and to heal surface damage. Annealing in vacuum was found to create a measureable number of oxygen vacancies however their creation could not be correlated to the ferromagnetic signal of the substrate. Annealing in air was found to effect the remnant moment of the substrate as well as the width of the x-ray diffraction peaks on the unpolished face, weakly suggesting a relation between surface based disorder and ferromagnetism. Argon ion bombardment was employed to create a layer of surface disorder in the polished crystal, however it was not found to induce ferromagnetism. It was found that acid etching was sufficient to remove the ferromagnetism from as purchased samples and similarly simulated handling with stainless steel tweezers was sufficient to re-create the ferromagnetism. It is suggested that the origin of this ferromagnetism in SrTi03 is surface contaminants (mainly iron).

Hot cognition and activation of the medial prefrontal cortex: Self-regulating in contexts involving motivational pressures

The medial prefrontal cortex (mPFC) is involved in performance-monitoring and has been implicated in the generation of several electrocortical responses associated with self-regulation. The error-related negativity (ERN), the inhibitory Nogo N2 (N2), and the feedback-related negativity (FRN) are event-related potential (ERP) components which reflect mPFC activity associated with feedback to behavioural (ERN, N2) and environmental (FRN) consequences. Our main goal was to determine whether or not rnPFC activation varies as a function of motivational context (e.g., those involving performance-related incentives) or the use of internally versus externally generated feedback signals (i.e., errors). Additionally, we assessed medial prefrontal activity in relation to individual differences in personality and temperament. Participants completed a combination of tasks in which performance-related incentives were associated with task performance and feedback generated from internal versus external responses. MPFC activity was indexed using both ERP scalp voltage peaks and intracerebral current source density (CSD) of dorsal and ventral regions. Additionally, participants completed several questionnaires assessing personality and temperament styles. Given previous studies have shown that enhanced mPFC activity to loss (or negative) feedback, we expected that activity in the mPFC would generally be greater during the Loss condition relative to the Win condition for both the ERN and N2. Also, due to the evidence that the (vmPFC) is engaged in arousing contexts, we hypothesized that activity in the ventromedial prefrontal cortex (vmPFC) would be greater than activity in the dorsomedial prefrontal cortex (dmPFC), especially in the Loss condition of the GoNogo task (ERN). Similarly, loss feedback in the BART (FRN) was expected to engage the vmPFC more than the dmPFC. Finally, we predicted that persons rating themselves as more willing to engage in approach-related behaviours or to exhibit rigid cognitive styles would show reduced activity of the mPFC. Overall, our results emphasize the role of affective evaluations of behavioural and environmental consequences when self-regulating. Although there were no effects of context on brain activity, our data indicate that, during the time of the ERN and N2 on the MW Go-Nogo task and the FRN on the BART, the vrnPFC was more active compared to the dmPFC. Moreover, regional recruitment in the mPFC was similar across internally (ERN) and externally (FRN) generated errors signals associated with loss feedback, as reflected by relatively greater activity in the vmPFC than the dmPFC. Our data also suggest that greater activity in the mPFC is associated with better inhibitory control, as reflected by both scalp and CSD measures. Additionally, deactivation of the subgenual anterior cingulate cortex (sgACC) and lower levels of self-reported positive affect were both related to increased voluntary risk-taking on the BART. Finally, persons reporting higher levels of approach-related behaviour or cognitive rigidity showed reduced activity of the mPFC. These results are in line with previous research emphasizing that affect/motivation is central to the processes reflected by mediofrontal negativities (MFNs), that the vmPFC is involved in regulating demands on motivational/affective systems, and that the underlying mechanisms driving these functions vary across both individuals and contexts.

Étude du rôle de la MAP Kinase non-conventionnelle ERK3 dans le développement thymique et l'activation des lymphocytes T

Les voies de signalisation des MAP kinases (MAPK) conventionnelles jouent des rôles essentiels pendant le développement des lymphocytes T (LT) ainsi que lors de leur activation suite à la reconnaissance antigénique. En raison de ses différences structurelles ainsi que de son mode de régulation, ERK3 fait partie des MAPK dites non-conventionnelles. Encore aujourd’hui, les événements menant à l’activation de ERK3, ses substrats ou partenaires ainsi que sa fonction physiologique demeurent peu caractérisés. Nous avons entrepris dans cette thèse d’étudier le rôle de ERK3 lors du développement et de l’activation des LT en utilisant un modèle de souris déficient pour l’expression de ERK3. Nous avons premièrement établi que ERK3 est exprimée chez les thymocytes. Ensuite, nous avons évalué le développement thymique chez la souris ERK3-déficiente et nous avons observé une diminution significative de la cellularité aux étapes DN1, DP et SP CD4+ du développement des LT. La création de chimères hématopoïétiques ERK3-déficientes nous a permis de démontrer que la diminution du nombre de cellules observée aux étapes DN1 et DP est autonome aux thymocytes alors que le phénotype observé à l’étape SP CD4+ est dépendant de l’abolition simultanée de ERK3 dans l’épithélium thymique et dans les thymocytes. Une étude plus approfondie de l’étape DP nous a permis de démontrer qu’en absence de ERK3, les cellules DP meurent plus abondamment et accumulent des cassures doubles brins (DSB) dans leur ADN. De plus, nous avons démontré que ces cassures dans l’ADN sont réalisées par les enzymes RAG et qu’en absence de ces dernières, la cellularité thymique est presque rétablie chez la souris ERK3-déficiente. Ces résultats suggèrent que ERK3 est impliquée dans un mécanisme essentiel à la régulation des DSB pendant le réarrangement V(D)J de la chaîne  du récepteur des cellules T (RCT). Dans le deuxième article présenté dans cette thèse, nous avons montré que ERK3 est exprimé chez les LT périphériques, mais seulement suite à leur activation via le RCT. Une fois activés in vitro les LT ERK3-déficients présentent une diminution marquée de leur prolifération et dans la production de cytokines. De plus, les LT ERK3-déficients survivent de façon équivalente aux LT normaux, mais étonnamment, ils expriment des niveaux plus faibles de la molécule anti-apoptotique Bcl-2. Ces résultats suggèrent que la prolifération réduite des LT ERK3-déficients est la conséquence d’une altération majeure de leur activation. Ainsi, nos résultats établissent que ERK3 est une MAPK qui joue des rôles essentiels et uniques dans le développement thymique et dans l’activation des lymphocytes T périphériques. Grâce à ces travaux, nous attribuons pour la toute première fois une fonction in vivo pour ERK3 au cours de deux différentes étapes de la vie d’un LT.

Active nuclear import and cytoplasmic retention of activation-induced deaminase

The enzyme activation-induced deaminase (AID) triggers antibody diversification in B cells by catalyzing deamination and consequently mutation of immunoglobulin genes. To minimize off-target deamination, AID is restrained by several regulatory mechanisms including nuclear exclusion, thought to be mediated exclusively by active nuclear export. Here we identify two other mechanisms involved in controlling AID subcellular localization. AID is unable to passively diffuse into the nucleus, despite its small size, and its nuclear entry requires active import mediated by a conformational nuclear localization signal. We also identify in its C terminus a determinant for AID cytoplasmic retention, which hampers diffusion to the nucleus, competes with nuclear import and is crucial for maintaining the predominantly cytoplasmic localization of AID in steady-state conditions. Blocking nuclear import alters the balance between these processes in favor of cytoplasmic retention, resulting in reduced isotype class switching.

Influence d’un rince-bouche fluoré sur la corrosion galvanique entre un fil NiTi ou un fil CuNiTi et différents boîtiers orthodontiques : incidence sur les propriétés mécaniques des fils

Objectif : il a été rapporté que l’utilisation d’agents prophylactiques fluorés pouvait favoriser la corrosion galvanique au sein des alliages de titane. L’objectif de la présente étude était d’évaluer l’effet d’un rince-bouche fluoré sur les propriétés mécaniques de fils en nickel-titane (NiTi) et de fils en cuivre-nickel-titane (CuNiTi) lorsque ces derniers sont couplés à des boîtiers de compositions différentes (boîtiers de marques Smartclip, Clarity, et Sprint). Matériels et Méthodes : 90 segments de fils en NiTi et 90 segments de fils en CuNiTi ont été chacun couplés à 2 boîtiers de chaque marque. Chaque assemblage fil-boîtiers a été par la suite incubé pendant 3 heures à 37°C, soit dans une solution de fluore neutre (Fluorinse™ 0,05% NaF), soit dans une solution de salive artificielle (solution contrôle). Suite à l’incubation, les échantillons étaient nettoyés avec de l’eau déshydrogénée, les fils séparés des boîtiers et montés sur un support pour subir un test de pliage en trois points en milieu humide (salive artificielle) à 37°C. Les modules d’élasticité ainsi que les limites conventionnelles d’élasticité en activation et en désactivation ont été mesurés et comparés. Des analyses de Variance (ANOVA) et des comparaisons post-hoc avec la correction de Bonferronni ont été utilisées pour comparer les groupes entre eux (α = 0,05). Résultats : L’utilisation d’un rince-bouche fluoré a produit une réduction du module d’élasticité et de la limite conventionnelle d’élasticité en activation et en désactivation pour les fils en NiTi ; cependant, cet effet a été modulé par le type de boîtier auquel le fil a été couplé. Les propriétés mécaniques de fils en CuNiTi n’ont pas été affectées par le fluor, ou par le type de boîtier utilisé. Conclusions : L’utilisation d’un rince-bouche fluoré modifie les propriétés mécaniques des fils en NiTi seulement. Cet effet est modulé par le boîtier auquel le fil en NiTi est couplé. A la différence des autres études publiées dans la littérature, nos résultats ne nous permettent pas de conclure que la modification des propriétés mécaniques des fils en NiTi entrainerait obligatoirement un allongement de la durée du traitement orthodontique. Mots clés : Fluor, fils nickel-titane, boîtiers orthodontiques, corrosion galvanique, propriétés mécaniques.

Growth factor activation of ErbB2/ErbB3 signaling pathways regulate the activity of Estrogen Receptors (ER)

La signalisation par l’estrogène a longtemps été considérée comme jouant un rôle critique dans le développement et la progression des cancers hormono-dépendants tel que le cancer du sein. Deux tiers des cancers du sein expriment le récepteur des estrogènes (ER) qui constitue un élément indiscutable dans cette pathologie. L’acquisition d’une résistance endocrinienne est cependant un obstacle majeur au traitement de cette forme de cancer. L’émergence de cancers hormono-indépendants peut est produite par l’activation de ER en absence d’estrogène, l’hypersensibilité du récepteur aux faibles concentrations plasmique d’estrogène ainsi que l’activation de ER par des modulateurs sélectifs. L’activité du ER est fortement influencée par l’environnement cellulaire tel que l’activation de voie de signalisation des facteurs de croissances, la disponibilité de protéines co-régulatrices et des séquences promotrices ciblées. Présentement, les études ont principalement considérées le rôle de ERα, cependant avec la découverte de ERβ, notre compréhension de la diversité des mécanismes potentiels impliquant des réponses ER-dépendantes s’est améliorée. L’activation des voies des kinases par les facteurs de croissance entraîne le développement d’un phénotype tumoral résistant aux traitements actuels. Nos connaissances des voies impliquées dans l’activation de ER sont restreintes. ERα est considéré comme le sous-type dominant et corrèle avec la plupart des facteurs de pronostic dans le cancer du sein. Le rôle de ERβ reste imprécis. Les résultats présentés dans cette thèse ont pour objectif de mieux comprendre l’implication de ERβ dans la prolifération cellulaire par l’étude du comportement de ERβ et ERα suite à l’activation des voies de signalisation par les facteurs de croissance. Nous démontrons que l’activation des récepteurs de surfaces de la famille ErbB, spécifiquement ErbB2/ErbB3, inhibe l’activité transcriptionnelle de ERβ, malgré la présence du coactivateur CBP, tout en activant ERα. De plus, l’inhibition de ERβ est attribuée à un résidu sérine (Ser-255) situé dans la région charnière, absente dans ERα. Des études supplémentaires de ErbB2/ErbB3 ont révélé qu’ils activent la voie PI3K/Akt ciblant à son tour la Ser-255. En effet, cette phosphorylation de ERβ par PI3K/Akt induit une augmentation de l’ubiquitination du récepteur qui promeut sa dégradation par le système ubiquitine-protéasome. Cette dégradation est spécifique pour ERβ. De façon intéressante, la dégradation par le protéasome requiert la présence du coactivateur CBP normalement requis pour l’activité transcriptionnelle des récepteurs nucléaires. Malgré le fait que l’activation de la voie PI3K/Akt corrèle avec une diminution de l’expression des gènes sous le contrôle de ERβ, on observe une augmentation de la prolifération des cellules cancéreuses. L’inhibition de la dégradation de ERβ réduit cette prolifération excessive causée par le traitement avec Hrgβ1, un ligand de ErbB3. Un nombre croissant d’évidences indique que les voies de signalisations des facteurs de croissance peuvent sélectivement réguler l’activité transcriptionnelle de sous-types de ER. De plus, le ratio ERα/ERβ dans les cancers du sein devient un outil de diagnostique populaire afin de déterminer la sévérité d’une tumeur. En conclusion, la caractérisation moléculaire du couplage entre la signalisation des facteurs de croissance et la fonction des ERs permettra le développement de nouveaux traitements afin de limiter l’apparition de cellules tumorales résistantes aux thérapies endocriniennes actuelles.