Chemical tools to validate N-myristoyltransferase as a new target in cancer therapy

N-myristoylation is the irreversible attachment of myristate, a C14-lipid, to the N-terminal glycine of a protein. This modification is catalysed by myristoyl CoA: protein N-myristoyltransferase (NMT). N-myristoylation has been shown to be essential for the viability and survival of many organisms, including plants, parasites and humans. In humans, two isoforms of NMT, HsNMT1 and HsNMT2, were identified and it was suggested that they possess overlapping substrate specificities. NMT was identified as a potential chemotherapeutic target for cancer 18 years ago and subsequent studies showed that NMT was up-regulated in several cancers. However, no study demonstrated that NMT could be a therapeutic target in cancer therapy. In this study, chemically-tagged analogues of myristic acid were synthesised and applied to cancer cell lines to study protein N-myristoylation. The analogues can be incorporated on the N-terminal glycine of NMT substrates. The tag in this system enables a second extremely selective and high-yielding chemical ligation to any reporter of choice, for instance a dye label. Visualisation of the tagged proteins was carried out by in-gel fluorescence. Tagged-proteins could also be enriched and analysed by mass spectrometry-based proteomics. The combination of chemical proteomics with a potent NMT inhibitor is described in this thesis as a new method to identify with high confidence a large number of NMT substrates. In search for novel and potent human NMT inhibitors, various compounds were tested using an in vitro assay and a cell cytotoxicity assay. On-target inhibition of NMT in cells was assessed by in-gel fluorescence using analogues of myristic acid. The best inhibitors were employed as tools to study NMT inhibition in cancer cells. Western blot analysis and flow cytometry were used to assess the phenotype of NMT inhibition. Finally, the substrate specificity of the two isoforms was studied in cells using siRNAs against HsNMT1 or HsNMT2, and in vitro by screening for activity libraries of peptides against NMT1 or NMT2.Open Acces

Salt tectonics and crustal tectonics along the Eastern Sardinian margin,Western Tyrrhenian : New insights from the « METYSS » cruise (June 2009)

International audienceThe « METYSS » cruise was carried out in June 2009 onboard the R/V « Téthys II » along the eastern Sardinian and south-eastern Corsican margins, western Tyrrhenian Sea, in order to better constrain the potential links between deformation related to either crustal tectonics or salt tectonics and sediment accumulation, especially during the Messinian and Plio-Quaternary times. We acquired 15 high-resolution seismic reflection profiles (about 1200 km in cumulative length) along the south-eastern Corsican margin, immediately north of the Bonifacio Strait and along the upper and middle parts of the eastern Sardinian margin, from the continental slope to the Cornaglia Terrace. The Tyrrhenian Sea is considered as a Neogene back-arc basin that opened during continental rifting and oceanic spreading related to the eastward migration of the Apennine subduction system from Tortonian to Pliocene times (Jolivet et al., 2006). Rifting of the Tyrrhenian Sea started first along the Eastern Sardinian margin during the Tortonian-Messinian times and therefore the series of that age should be considered as syn-rift sediments (Sartori et al., 2004). The « METYSS » seismic profiles clearly illustrate that this part of the Tyrrhenian was highly segmented during the rifting stage by N-S trending normal faults delineating ridges (e.g., Baronie Ridge) and basins (e.g., Sardinian Basin and Cornaglia Terrace), as previously described for example by Thommeret (1999) and Sartori et al. (2004). The Messinian sedimentary units and especially the « Upper Unit » (UU, Lofi et al., this congress, corresponding to the « Upper Evaporites » in the previous literature) are, without any doubt, of syn-rift age, as they display a fan-shaped stratal geometry. The Mobile Unit (MU, Lofi et al., this congress), i.e. the Messinian halite, is clearly imaged in the study area and its spatial repartition can be outlined. The highly-variable thickness of the confined salt basins could be due to the initial basin geometry (i.e. before the Messinian salinity Crisis) or to the syn-rift character of the deposition. Southeastward of the study area, in the vicinity of the Cornaglia Seamount, salt tectonics appears surprisingly vigorous. More surprisingly, several normal faults seem to have remained active in recent times, if not even at present time. Fault slip has been recorded by bathymetric scarps and associated footwall debris flows interfingered within the Plio-Quaternary sequence, even though the eastern Sardinian margin is usually considered to be passive now. Moreover, some amount of tectonic inversion is visible on some normal faults that show contractional or transpressional components of late slip. In addition, this “post-rift” deformation can be illustrated within the Plio-Quaternary sequence by a regional unconformity. Consequently, numerous mass-transport deposits and channel-levees systems observed in the Plio-Quaternary cover could be partly controlled by tectonic activity. These very preliminary results require further investigations in order to better decipher the role of crustal tectonics and salt tectonics, salt-related structures being very efficient markers to discriminate between the respective contribution of gravity-driven, salt tectonics and deep-seated, crustal tectonics (Gaullier et al., 2010). Finally, we aim to precisely determine the relative vertical movements (tilting, subsidence, magmatism. . . ) and geodynamical history of the different segments of the area since 6 Ma

Quelques aspects floristiques et pédologiques de l’incidence écologique des reboisements du mont Ventoux

Work was carried out on the southern slopes of the mountain in four forest types ( Quercus ilex ; Q. pubescens ; Cedrus atlan- tica ; Pinus nigra ssp. austriaca) . Renewal of the forest cover reduces the Mediterranean nature of the environment, so that mesophytic species increase their range horizontally or down wards at the expense of previously established xerophytic species. This ultimately leads to a change in the vegetation series. The soils are all rendzinas, and show different responses to the four forest types. Q. pubescens is the most effective at improving the soil and increasing the humus content ; P. nigra on the other hand produces a humus rich in lignin which gives rise to a very acid mor humus and instigates degradation of the soil. The effects of Q. ilex and C. atlantica are intermediate between these two

La végétation du mont Ventoux au cours des derniers millénaires.

Grâce à l'analyse des charbons de bois récoltés dans des avens du versant nord ou extraits des sols du mont Ventoux, il est possible d'avoir un aperçu de la végétation qu'abritait ce massif depuis environ 4000 ans. Ainsi, la calotte sommitale était colonisée par des peuplements mixtes de sapin, d'érable à feuille d'obier et de pins. La chênaie caducifoliée occupait les régions de plus basse altitude. Ces peuplements ont progressivement été détruits par, entre autre, les activités pastorales à partir du Néolithique, pour aboutir au déboisement presque total du XIXe siècle

Crustal structure of Guadeloupe Islands and the Lesser Antilles Arc from a new gravity and magnetic synthesis

Guadeloupe Island (West French Indies) is one of the twenty islands that compose the Lesser Antilles Arc, which results from the subduction of the Atlantic Ocean plate beneath the Caribbean one. The island lies in a complex volcano-tectonic system and the need to understand its geological context has led to numerous on- and offshore geophysical investigations. This work presents the compilation and processing of available, on-land, airborne and marine, gravity and magnetic data acquired during the last 40 years on Guadeloupe Islands and at the scale of the Lesser Antilles Arc. The overall dataset provides new Bouguer and reduced to the pole magnetic anomaly maps at the highest achievable resolution. Regionally, the main central negative gravity trend of the arc allows defining two subsident areas. The first one is parallel to the arc direction (~N160°E) to the north, whereas the second unexpected southern one is oriented parallel to oceanic ridges (N130°E). Along the Outer Arc, the long wavelength positive anomaly is interpreted, at least along the Karukera Spur, as an up-rise of the volcanic basement in agreement with the seismic studies. To the NE of Guadeloupe, the detailed analysis of the geophysical anomalies outlines a series of structural discontinuities consistent with the main bathymetric morphologies, and in continuity of the main fault systems already reported in this area. Based on geophysical evidences, this large scale deformation and faulting of the Outer Arc presumably primarily affects the Atlantic subducting plate and secondarily deforms the upper Caribbean plate and the accretion prism. At the scale of Guadeloupe Island, joined gravity and magnetic modeling has been initiated based on existing interpretation of old seismic refraction profiles, with a general structure in three main layers. According to our geophysical anomalies, additional local structures are also modeled in agreement with geological observations: i) the gravity and magnetic signals confirm an up-rise of the volcanic basement below the limestone platforms outcropping on Grande-Terre Island ; ii) the ancient volcanic complexes of Basse-Terre Island are modeled with high density and reverse magnetized formations; iii) the recent volcanic centre is associated with formations consistent with the low measured density and the underlying hydrothermal system. The EW models coherently image a NNW-SSE depression structure in half-graben beneath Basse-Terre Island, its western scarp following the arc direction in agreement with bathymetric and seismic studies to the north of the island. The so-defined depressed area, and particularly its opening in half-graben toward the SW, is interpreted as the present-day front of deformation of the upper plate associated with the recent volcanic activity on and around Guadeloupe. Based on this regional deformation model, perspectives are given for further integrated investigation of key targets to address the internal structure and evolution of the Lesser Antilles Arc and Guadeloupe volcanic system

Deep structure of the Armorican Basin (Bay of Biscay): a review of Norgasis seismic reflection and refraction data

International audienceThe Bay of Biscay is bounded to the North by the North Biscay margin, which comprises the Western Approaches and Armorican segments. In the 1970s and 1980s, most researchers considered this margin typical of a non-volcanic passive margin: It is characterized by a striking succession of tilted blocks beneath which occurs the S reflector and the continent/ocean boundary is abrupt. This paper examines the Armorican segment and is based on a study of all early seismic profiles together with new multichannel reflection and refraction seismic data (NORGASIS cruise). An important result is the discovery of a 80-km wide Ocean-Continent Transition zone that coincides with the Armorican Basin (a deep sedimentary basin). It is characterized by a High-Velocity Layer-Crust (7.4-7.5 km/s) overlain by sediments. The other results are: i) the main crustal thinning occurs exclusively under the narrow continental slope. ii) The tilted blocks and the S-reflector are observed only at the base of the continental slope in the narrow domain called "neck area". iii) the North Biscay Ridge is a large oceanic plateau present only off the NW Armorican margin rather than a long ridge elongated off the whole North Biscay Margin

Multifunctional Reagents for Quantitative Proteome-Wide Analysis of Protein Modification in Human Cells and Dynamic Profiling of Protein Lipidation During Vertebrate Development

Novel multifunctional reagents were applied in combination with a lipid probe for affinity enrichment of myristoylated proteins and direct detection of lipid-modified tryptic peptides by mass spectrometry. This method enables high-confidence identification of the myristoylated proteome on an unprecedented scale in cell culture, and allowed the first quantitative analysis of dynamic changes in protein lipidation during vertebrate embryonic development