Ultra-low temperature structure determination of a Mn12 single-molecule magnet and the interplay between lattice solvent and structural disorder

We have determined the ultra-low temperature crystal structure of the archetypal single-molecule magnet (SMM) [Mn12O12(O2CMe)16(H2O)4]·4H2O·2MeCO2H (1) at 2 K, by using a combination of single-crystal X-ray and single-crystal neutron diffraction. This is the first structural study of any SMM in the same temperature regime where slow magnetic relaxation occurs. We reveal an additional hydrogen bonding interaction between the {Mn12} cluster and its solvent of crystallisation, which shows how the lattice solvent transmits disorder to the acetate ligands in the {Mn12} complex. Unusual quantum properties observed in 1 have long been attributed to disorder. Hence, we studied the desolvation products of 1, in order to understand precisely the influence of lattice solvent on the structure of the cluster. We present two new axially symmetric structures corresponding to different levels of desolvation of 1, [Mn12O12(O2CMe)16(H2O)4]·4H2O (2) and [Mn12O12(O2CMe)16(H2O)4] (3). In 2, removal of acetic acid of crystallisation largely resolves positional disorder in the affected acetate ligands, whereas removal of lattice water molecules further resolves the acetate ligand disorder in 3. Due to the absence of acetic acid of crystallisation, both 2 and 3 have true, unbroken S4 symmetry, showing for the first time that it is possible to prepare fully axial Mn12–acetate analogues from 1, via single-crystal to single-crystal transformations

Development of Resistance towards Artesunate in MDA-MB-231 Human Breast Cancer Cells

Breast cancer is the most common cancer and the second leading cause of cancer death in industrialized countries. Systemic treatment of breast cancer is effective at the beginning of therapy. However, after a variable period of time, progression occurs due to therapy resistance. Artesunate, clinically used as anti-malarial agent, has recently revealed remarkable anti-tumor activity offering a role as novel candidate for cancer chemotherapy. We analyzed the anti-tumor effects of artesunate in metastasizing breast carcinoma in vitro and in vivo. Unlike as expected, artesunate induced resistance in highly metastatic human breast cancer cells MDA-MB-231. Likewise acquired resistance led to abolishment of apoptosis and cytotoxicity in pre-treated MDA-MB-231 cells. In contrast, artesunate was more cytotoxic towards the less tumorigenic MDA-MB-468 cells without showing resistance. Unraveling the underlying molecular mechanisms, we found that resistance was induced due to activation of the tumor progression related transcription factors NFκB and AP-1. Thereby transcription, expression and activity of the matrix-degrading enzyme MMP-1, whose function is correlated with increased invasion and metastasis, was up-regulated upon acquisition of resistance. Additionally, activation of the apoptosis-related factor NFκB lead to increased expression of ant-apoptotic bcl2 and reduced expression of pro-apoptotic bax. Application of artesunate in vivo in a model of xenografted breast cancer showed, that tumors growth was not efficiently abolished as compared to the control drug doxorubicin. Taken together our in vitro and in vivo results correlate well showing for the first time that artesunate induces resistance in highly metastatic breast tumors

Functional Characterization of Human Cancer-Derived TRKB Mutations

Cancer originates from cells that have acquired mutations in genes critical for controlling cell proliferation, survival and differentiation. Often, tumors continue to depend on these so-called driver mutations, providing the rationale for targeted anticancer therapies. To date, large-scale sequencing analyses have revealed hundreds of mutations in human tumors. However, without their functional validation it remains unclear which mutations correspond to driver, or rather bystander, mutations and, therefore, whether the mutated gene represents a target for therapeutic intervention. In human colorectal tumors, the neurotrophic receptor TRKB has been found mutated on two different sites in its kinase domain (TRKBT695I and TRKBD751N). Another site, in the extracellular part of TRKB, is mutated in a human lung adenocarcinoma cell line (TRKBL138F). Lastly, our own analysis has identified one additional TRKB point mutation proximal to the kinase domain (TRKBP507L) in a human melanoma cell line. The functional consequences of all these point mutations, however, have so far remained elusive. Previously, we have shown that TRKB is a potent suppressor of anoikis and that TRKB-expressing cells form highly invasive and metastatic tumors in nude mice. To assess the functional consequences of these four TRKB mutations, we determined their potential to suppress anoikis and to form tumors in nude mice. Unexpectedly, both colon cancer-derived mutants, TRKBT695I and TRKBD751N, displayed reduced activity compared to that of wild-type TRKB. Consistently, upon stimulation with the TRKB ligand BDNF, these mutants were impaired in activating TRKB and its downstream effectors AKT and ERK. The two mutants derived from human tumor cell lines (TRKBL138F and TRKBP507L) were functionally indistinguishable from wild-type TRKB in both in-vitro and in-vivo assays. In conclusion, we fail to detect any gain-of-function of four cancer-derived TRKB point mutations

CD36-mediated activation of endothelial cell apoptosis by an N-terminal recombinant fragment of thrombospondin-2 inhibits breast cancer growth and metastasis in vivo

Thus far the clinical benefits seen in breast cancer patients treated with drugs targeting the vascular endothelial growth factor (VEGF) pathway are only modest. Consequently, additional antiangiogenic approaches for treatment of breast cancer need to be investigated. Thrombospondin-2 (TSP-2) has been shown to inhibit tumor growth and angiogenesis with a greater potency than the related molecule TSP-1. The systemic effects of TSP-2 on tumor metastasis and the underlying molecular mechanisms of the antiangiogenic activity of TSP-2 have remained poorly understood. We generated a recombinant fusion protein consisting of the N-terminal region of TSP-2 and the IgG-Fc1 fragment (N-TSP2-Fc) and could demonstrate that the antiangiogenic activity of N-TSP2-Fc is dependent on the CD36 receptor. We found that N-TSP2-Fc inhibited VEGF-induced tube formation of human dermal microvascular endothelial cells (HDMEC) on matrigel in vitro and that concurrent incubation of anti-CD36 antibody with N-TSP2-Fc resulted in tube formation that was comparable to untreated control. N-TSP2-Fc potently induced apoptosis of HDMEC in vitro in a CD36-dependent manner. Moreover, we could demonstrate a CD36 receptor-mediated loss of mitochondrial membrane potential and activation of caspase-3 in HDMEC in vitro. Daily intraperitoneal injections of N-TSP2-Fc resulted in a significant inhibition of the growth of human MDA-MB-435 and MDA-MB-231 tumor cells grown in the mammary gland of immunodeficient nude mice and in reduced tumor vascularization. Finally, increased serum concentrations of N-TSP2-Fc significantly inhibited regional metastasis to lymph nodes and distant metastasis to lung as shown by quantitative real-time alu PCR. These results identify N-TSP2-Fc as a potent systemic inhibitor of tumor metastasis and provide strong evidence for an important role of the CD36 receptor in mediating the antiangiogenic activity of TSP-2

GalNAc glycoprotein expression by breast cell lines, primary breast cancer and normal breast epithelial membrane

Over-expression of N-acetylgalactosamine glycoproteins as detected by binding of the lectin from Helix pomatia (HPA), is associated with metastatic competence and poor patient prognosis in a range of human adenocarcinomas. These glycoproteins remain poorly characterised, and their functional role has yet to be elucidated. This study describes characterisation of a range of human breast/breast cancer cell lines for the expression of the N-acetylgalactosaminylated glycoproteins of interest, and their comparison with normal breast epithelium and a range of clinical breast carcinoma samples. Confocal and light microscopy studies revealed cytochemical HPA-binding patterns consistent with a fundamental disruption in normal glycobiosynthetic pathways attending increasing metastatic potential. We report the most complete comparative analysis of HPA-binding ligands from cultured breast cells, clinical breast carcinoma samples and normal breast epithelium to date. Lectin blotting identified 11 major HPA-binding glycoprotein bands common to both clinical tumour samples and breast cell lines and 6 of these bands were also expressed by samples of normal breast epithelium, albeit at much lower levels. Moreover, very marked quantitative but not qualitative differences in levels of expression consistent with metastatic capability were noted. © 2001 Cancer Research Campaignhttp://www.bjcancer.co

Modeling volcanic deformation in a regional stress field: Implications for the formation of graben structures on Alba Patera, Mars

Abundant grabens transect the volcano Alba Patera. Their complex geometry and formation mechanisms are still poorly understood. Tectonic processes and magmatic intrusions are responsible for these long surface features. Cross-cutting relationships of the grabens show radial fractures that were formed during early stages and were progressively overprinted by concentric fractures on the mid and upper flanks of the volcano. Two modeling methods are used to understand the formation of the observed structures and to evaluate their implications for hidden subvolcanic processes. Surface deformation and fault arrangements predicted in finite element models are compared to the graben systems observed in Viking images. The orientation and position of the concentric grabens are found to be best reproduced by local crustal subsidence, superimposed on a regional NW-SE oriented extension with decreasing magnitude from south to north. In analogue sandbox models we also simulate surface structures of arrangements that almost perfectly mimic the observed lineaments on Alba Patera. Formation of the grabens spans a period on the order of a billion years, suggesting long-term geodynamic processes to be responsible for the subsidence of the central Alba Patera area. The progressive change toward higher concentricity is likely resultant from an increase in density in the crust by accumulation of intrusive material and cooling, thus causing subsidence of the region above this volcanic root

Introducing a standard method for experimental determination of the solvent response in laser pump, x-ray probe time-resolved wide-angle x-ray scattering experiments on systems in solution

WOS:000323520600021International audienceIn time-resolved laser pump, X-ray probe wide-angle X-ray scattering experiments on systems in solution the structural response of the system is accompanied by a solvent response. The solvent response is caused by reorganization of the bulk solvent following the laser pump event, and in order to extract the structural information of the solute, the solvent response has to be treated. Methodologies capable of doing so include both theoretical modelling and experimental determination of the solvent response. In the work presented here, we have investigated how to obtain a reproducible solvent response-the solvent term-experimentally when applying laser pump, X-ray probe time-resolved wide-angle X-ray scattering. The solvent term describes difference scattering arising from the structural response of the solvent to changes in the hydrodynamic parameters: pressure, temperature and density. We present results based on NIR and dye mediated solvent heating, and demonstrate that the solvent response is independent of the heating method. The NIR heating is shown to be rendered unusable by higher order effects under certain experimental conditions, while the dye mediated solvent heating is demonstrated to exhibit first order behaviour with respect to the amount of energy deposited in the solution. We introduce a standardized method for recording solvent responses in laser pump, X-ray probe time-resolved X-ray wide-angle scattering experiments by using dye mediated solvent heating. Furthermore, we have generated a library of solvent terms, which can be used to describe the solvent term in any TRWAXS experiment, and made it available online

Type 1 diabetes: translating mechanistic observations into effective clinical outcomes

Type 1 diabetes remains an important health problem, particularly in Western countries where the incidence has been increasing in younger children(1). In 1986, Eisenbarth described Type 1 diabetes as a chronic autoimmune disease. Work over the past 3 ½ decades has identified many of the genetic, immunologic, and environmental factors that are involved in the disease and have led to hypotheses concerning its pathogenesis. Based on these findings, clinical trials have been conducted to test these hypotheses but have had mixed results. In this review, we discuss the findings that have led to current concepts of the disease mechanisms, how this understanding has prompted clinical studies, and the results of these studies. The findings from preclinical and clinical studies support the original proposed model for how type 1 diabetes develops, but have also suggested that this disease is more complex than originally thought and will require broader treatment approaches

Evolution de la composition génétique du tissu nourricier de la graine (Double fécondation, polysporie et empreinte parentale)

Chez les plantes à graine, l'albumen est un tissu nourricier surprenant, puisqu'il résulte de la double fécondation, qui est la fécondation concomitante de l'oosphère d'une part, et de la cellule mère de l'albumen, la cellule centrale, d'autre part. Dans cette thèse, nous étudions les pressions de sélection qui déterminent l'évolution de l'albumen et pourraient expliquer l'évolution (1) de la double fécondation, (2) d'un doublement des contributions maternelles dans la cellule centrale, (3) de la polysporie, qui consiste en la participation de plusieurs produits de méiose à la formation du gamétophyte, et (4) de l'empreinte parentale, l'expression différentielle des allèles maternels et paternels.Ces innovations modifient l'hétérozygotie dans le tissu nourricier et par conséquent, ont le potentiel de changer l'hétérosis de la graine. Dans cette thèse, nous commençons par étudier comment les changements génétiques qui découlent de la double fécondation, du doublement des contributions maternelles, de la polysporie et de l'empreinte parentale modifient l'hétérosis, ce qui peut jouer en faveur ou en défaveur de leurs évolutions. Puis, nous faisons une revue des données disponibles dans la littérature pour tester si ces traits sont le résultat d'un conflit mâle-femelle sur l'allocation des ressources. Enfin, nous étudions de manière expérimentale les patrons de l'allocation des ressources chez le maïs, pour tester si les embryons sont en compétition pour les ressources, ce qui est une des conditions nécessaires pour qu'un conflit sur l'allocation des ressources ait lieu.Nos modèles théoriques nous permettent de décrire un conflit mâle-femelle sur l'exposition des allèles délétères dans les tissus pour lesquels l'expression des gènes est asymétrique. Ce conflit n'avait jamais été décrit auparavant, et ouvre de nouvelles perspectives pour la compréhension de l'évolution de l'expression génétique. L'analyse des données indique que les théories alternatives à la théorie du conflit sur l'allocation des ressources ont parfois un bon pouvoir explicatif, et méritent par conséquent d'être d'avantage explorées. Enfin, notre étude expérimentale sur le maïs montre que la compétition entre embryons est prédominante lors de l'allocation des ressources chez cette espèce, ce qui est concordant avec les prédictions de la théorie du conflit sur l'allocation.In seed plants, the endosperm is a surprising nutritive tissue, because it results from double fertilization, an eccentricity which results from the parallel fertilization of the egg cell on the one hand, and of the mother cell of the endosperm, the central cell, on the other hand. In this thesis, we study the selective pressures which drive the evolution of the endosperm and may explain the evolution of (1) double fertilization, (2) a doubling of maternal contributions in the central cell, (3) polyspory, the participation of several meiotic products to the gametophyte and (4) imprinting, the differential expression of maternal and paternal alleles. These innovations modify heterozygosity in the endosperm and as a consequence, have the potential to change heterosis in the seed. In this thesis, we first investigate how genetic changes that result from double fertilization, doubling of maternal contribution, polyspory and imprinting modify heterosis, which may play in favour or against the evolution of these traits. Second, we review the available data to test whether these traits are the result of a male-female conflict over resource allocation. Finally, we study experimentally patterns of resource allocation in maize to assess whether embryos compete for resources, which is a necessary condition for the conflict over resource allocation to occur. Our theoretical models allow us to describe a male-female conflict over the exposition of deleterious alleles in tissues with asymmetrical gene expression. This conflict had never been described before and opens perspectives for understanding the evolution of gene expression. We conclude from our analysis of data that theories which are alternative to the conflict theory over resource allocation may have a better explanatory power and therefore deserve to be further explored. Finally, our experimental study in maize shows that competition between embryos drives resource allocation in this species, which is consistent with predictions of the conflict over resource allocation theory.MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF