Girolline interferes with cell-cycle progression, but not with translation

Girolline is a 2-aminoimidazole derivative with cytotoxic activity. It affects the survival of exponentially growing leukaemic cultured cells and has a significant antitumour activity on grafted murine tumours in vivo. In vitro studies showed that girolline affected protein synthesis by interfering with the translation termination process. Here, we investigate the effect of girolline on translation termination in human cultured cells. We show that girolline neither induces an increase in translational readthrough of stop codons nor affects the polysome profile in treated cells. This suggests that girolline does not act on translation in vivo. Then, we examine the effect of girolline on cell-cycle progression and we show that girolline induces an arrest of the cell cycle at the G2 stage

A multidecadal simulation of Atlantic tropical cyclones using a variable‐resolution global atmospheric general circulation model

Using a variable‐resolution option within the National Center for Atmospheric Research/Department of Energy Community Atmosphere Model (CAM) Spectral Element (SE) global model, a refined nest at 0.25° (∼28 km) horizontal resolution located over the North Atlantic is embedded within a global 1° (∼111 km) grid. The grid is designed such that fine grid cells are located where tropical cyclones (TCs) are observed to occur during the Atlantic TC season (June–November). Two simulations are compared, one with refinement and one control case with no refinement (globally uniform 1° grid). Both simulations are integrated for 23 years using Atmospheric Model Intercomparison Protocols. TCs are tracked using an objective detection algorithm. The variable‐resolution simulation produces significantly more TCs than the unrefined simulation. Storms that do form in the refined nest are much more intense, with multiple storms strengthening to Saffir‐Simpson category 3 intensity or higher. Both count and spatial distribution of TC genesis and tracks in the variable‐resolution simulation are well matched to observations and represent significant improvements over the unrefined simulation. Some degree of interannual skill is noted, with the variable‐resolution grid able to reproduce the observed connection between Atlantic TCs and the El Niño‐Southern Oscillation (ENSO). It is shown that Genesis Potential Index (GPI) is well matched between the refined and unrefined simulations, implying that the introduction of variable‐resolution does not affect the synoptic environment. Potential “upscale” effects are noted in the variable‐resolution simulation, suggesting stronger TCs in refined nests may play a role in meridional transport of momentum, heat, and moisture. Key Points Variable‐resolution models can improve the representation of tropical cyclones CAM produces realistic Atlantic TC climatology at 0.25° resolution Addition of local refinement in CAM does not impact synoptic scalesPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109331/1/jame20104.pd

Hurricanes and Climate: The U.S. CLIVAR Working Group on Hurricanes

While a quantitative climate theory of tropical cyclone formation remains elusive, considerable progress has been made recently in our ability to simulate tropical cyclone climatologies and to understand the relationship between climate and tropical cyclone formation. Climate models are now able to simulate a realistic rate of global tropical cyclone formation, although simulation of the Atlantic tropical cyclone climatology remains challenging unless horizontal resolutions finer than 50 km are employed. This article summarizes published research from the idealized experiments of the Hurricane Working Group of U.S. Climate and Ocean: Variability, Predictability and Change (CLIVAR). This work, combined with results from other model simulations, has strengthened relationships between tropical cyclone formation rates and climate variables such as midtropospheric vertical velocity, with decreased climatological vertical velocities leading to decreased tropical cyclone formation. Systematic differences are shown between experiments in which only sea surface temperature is increased compared with experiments where only atmospheric carbon dioxide is increased. Experiments where only carbon dioxide is increased are more likely to demonstrate a decrease in tropical cyclone numbers, similar to the decreases simulated by many climate models for a future, warmer climate. Experiments where the two effects are combined also show decreases in numbers, but these tend to be less for models that demonstrate a strong tropical cyclone response to increased sea surface temperatures. Further experiments are proposed that may improve our understanding of the relationship between climate and tropical cyclone formation, including experiments with two-way interaction between the ocean and the atmosphere and variations in atmospheric aerosols

L-Ilf3 and L-NF90 Traffic to the Nucleolus Granular Component: Alternatively-Spliced Exon 3 Encodes a Nucleolar Localization Motif

Ilf3 and NF90, two proteins containing double-stranded RNA-binding domains, are generated by alternative splicing and involved in several functions. Their heterogeneity results from posttranscriptional and posttranslational modifications. Alternative splicing of exon 3, coding for a 13 aa N-terminal motif, generates for each protein a long and short isoforms. Subcellular fractionation and localization of recombinant proteins showed that this motif acts as a nucleolar localization signal. Deletion and substitution mutants identified four arginines, essential for nucleolar targeting, and three histidines to stabilize the proteins within the nucleolus. The short isoforms are never found in the nucleoli, whereas the long isoforms are present in the nucleoplasm and the nucleoli. For Ilf3, only the posttranslationally-unmodified long isoform is nucleolar, suggesting that this nucleolar targeting is abrogated by posttranslational modifications. Confocal microscopy and FRAP experiments have shown that the long Ilf3 isoform localizes to the granular component of the nucleolus, and that L-Ilf3 and L-NF90 exchange rapidly between nucleoli. The presence of this 13 aminoacid motif, combined with posttranslational modifications, is responsible for the differences in Ilf3 and NF90 isoforms subcellular localizations. The protein polymorphism of Ilf3/NF90 and the various subcellular localizations of their isoforms may partially explain the various functions previously reported for these proteins

The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems. V. Do Self-consistent Atmospheric Models Represent JWST Spectra? A Showcase with VHS 1256–1257 b

The unprecedented medium-resolution (R λ ∼ 1500–3500) near- and mid-infrared (1–18 μm) spectrum provided by JWST for the young (140 ± 20 Myr) low-mass (12–20 MJup) L–T transition (L7) companion VHS 1256 b gives access to a catalog of molecular absorptions. In this study, we present a comprehensive analysis of this data set utilizing a forward-modeling approach applying our Bayesian framework, ForMoSA. We explore five distinct atmospheric models to assess their performance in estimating key atmospheric parameters: Teff, log(g), [M/H], C/O, γ, f sed, and R. Our findings reveal that each parameter’s estimate is significantly influenced by factors such as the wavelength range considered and the model chosen for the fit. This is attributed to systematic errors in the models and their challenges in accurately replicating the complex atmospheric structure of VHS 1256 b, notably the complexity of its clouds and dust distribution. To propagate the impact of these systematic uncertainties on our atmospheric property estimates, we introduce innovative fitting methodologies based on independent fits performed on different spectral windows. We finally derived a Teff consistent with the spectral type of the target, considering its young age, which is confirmed by our estimate of log(g). Despite the exceptional data quality, attaining robust estimates for chemical abundances [M/H] and C/O, often employed as indicators of formation history, remains challenging. Nevertheless, the pioneering case of JWST’s data for VHS 1256 b has paved the way for future acquisitions of substellar spectra that will be systematically analyzed to directly compare the properties of these objects and correct the systematics in the models

Cellular physiology and molecular events in hypoxia-induced apoptosis.

International audienceMalignant tumors contain a significant fraction of microregions that are chronically or transiently hypoxic. The experimental evidence showing that hypoxia may have a profound impact on malignant progression and on responsiveness to therapy is growing. In fact hypoxia, like other genotoxic and non-genotoxic stresses, has been shown to increase the p53 protein level, and subsequently activate target genes like p21/waf-1 which interact with cell cycle machinery or participate in apoptosis. Apoptosis is a genetically encoded program of cell death that can be activated under physiological conditions like hypoxia, and may be an important safeguard against tumour development. One of the first common manifestations of the apoptotic process, irrespective of the cell type, is the disruption of mitochondrial membrane function, including a dissipation of the delta psi m and/or a modification on the mitochondrial release of protease activators. These modifications are linked to specific patterns of bioenergetic parameters i.e. respiratory flux, mitochondrial redox potential and phosphate potential. We have studied gluconeogenesis and glycolysis pathways in intact hepatocytes isolated from fasted rats submitted to 24 h of hypoxic in vivo exposure. We have shown that hypoxia resulted in an inhibition of the gluconeogenesis pathway due to a decrease in phosphoenolpyruvate carboxykinase (PEPCK) activity and mRNA synthesis in rat hepatocytes. In conclusion, the disruption of mitochondrial membrane function in response to different oxygen content such as periarterial or perivenous PO2 led to the inhibition of gluconeogenesis and apoptosis in hypoxic cells

Cellular physiology and molecular events in hypoxia-induced apoptosis.

International audienceMalignant tumors contain a significant fraction of microregions that are chronically or transiently hypoxic. The experimental evidence showing that hypoxia may have a profound impact on malignant progression and on responsiveness to therapy is growing. In fact hypoxia, like other genotoxic and non-genotoxic stresses, has been shown to increase the p53 protein level, and subsequently activate target genes like p21/waf-1 which interact with cell cycle machinery or participate in apoptosis. Apoptosis is a genetically encoded program of cell death that can be activated under physiological conditions like hypoxia, and may be an important safeguard against tumour development. One of the first common manifestations of the apoptotic process, irrespective of the cell type, is the disruption of mitochondrial membrane function, including a dissipation of the delta psi m and/or a modification on the mitochondrial release of protease activators. These modifications are linked to specific patterns of bioenergetic parameters i.e. respiratory flux, mitochondrial redox potential and phosphate potential. We have studied gluconeogenesis and glycolysis pathways in intact hepatocytes isolated from fasted rats submitted to 24 h of hypoxic in vivo exposure. We have shown that hypoxia resulted in an inhibition of the gluconeogenesis pathway due to a decrease in phosphoenolpyruvate carboxykinase (PEPCK) activity and mRNA synthesis in rat hepatocytes. In conclusion, the disruption of mitochondrial membrane function in response to different oxygen content such as periarterial or perivenous PO2 led to the inhibition of gluconeogenesis and apoptosis in hypoxic cells

Mechanism of gluconeogenesis inhibition in rat hepatocytes isolated after in vivo hypoxia.

International audienceGluconeogenesis was studied in hepatocytes isolated from fasted rats submitted to 24 h of hypoxic exposure (inspired O2 fraction 0.1) or to room air. Hepatocytes from hypoxic rats compared with controls exhibited a lower gluconeogenic rate with lactate (5.1 +/- 0.3 vs. 7.2 +/- 0.3 mumol.min-1.g dry cells-1, P < 0.001) but not with dihydroxyacetone (9.1 +/- 0.3 vs. 9.4 +/- 0.4 mumol.min-1.g dry cells-1), suggesting involvement of the phosphoenolpyruvate-pyruvate cycle. Experiments with perifused hepatocytes from hypoxic and control rats showed a single relationship between phosphoenolpyruvate and glucose flux (JGlc) but two different curves when cytosolic oxalacetate was plotted against JGlc. The decreased phosphoenolpyruvate carboxykinase (PEPCK) activity in the hypoxic group (9.0 +/- 0.9 vs. 16.2 +/- 1.9 nmol.min-1.mg protein-1, P < 001) without change in the Michaelis constant further settled the involvement of this step. The significant decrease in PEPCK mRNA levels in livers from hypoxic rats led us to propose that in vivo hypoxic exposure inhibits gluconeogenesis at the PEPCK level by decreasing PEPCK gene transcription

The inhibition of phosphoenolpyruvate carboxykinase following in vivo chronic phenobarbital treatment in the rat is due to a post-translational event.

International audienceChronic treatment of rats with phenobarbital has been reported to decrease gluconeogenesis in rat hepatocytes by a 50% inhibition of phosphoenolpyruvate (P-pyruvate) carboxykinase activity [Argaud, D., Halimi, S., Catelloni, F. & Leverve, X. (1991) Biochem. J. 280, 663-669]. Contrary to the current knowledge of P-pyruvate carboxykinase regulation, we failed to find a diminution of either P-pyruvate carboxykinase protein (by using a polyclonal antibody) or P-pyruvate carboxykinase mRNA, in the liver of rats treated with phenobarbital for 2 weeks. Kinetic studies of P-pyruvate carboxykinase activity, measured by either carboxylation of P-pyruvate or decarboxylation of oxaloacetate, revealed a decrease in both V(max) and Km after phenobarbital treatment, whereas the nutritional state affected only the V(max), as expected. Assessment of P-pyruvate carboxykinase specificity was confirmed by the full inhibition of the enzyme with its specific inhibitor 3-mercaptopicolinate in the micromolar range. P-Pyruvate carboxykinase, purified either by ammonium sulfate fractionation or by immunoprecipitation, exhibited a similar decrease in affinity after phenobarbital treatment. Although the molecular mass does not appear to be altered, the pH sensitivity to 3-mercaptopicolinate inhibition and the enzyme recovery after immunoprecipitation both seemed to be affected. This leads us to propose that the effect of chronic phenobarbital treatment on P-pyruvate carboxykinase activity is not the result of transcriptional regulation but is exerted at the post-translational level

Effects of permeability transition inhibition and decrease in cytochrome c content on doxorubicin toxicity in K562 cells.

International audienceAs mitochondria play a key role in the commitment to cell death, we have investigated the mitochondrial consequences of resistance to doxorubicin (DOX) in K562 cells. We found that the permeability transition pore (PTP) inhibitor cyclosporine A (CsA) failed to inhibit PTP opening in the resistant clone. Moreover, the Ca2+ loading capacity in the resistant clone was identical to that observed in the parent cells in the presence of CsA, suggesting that the PTP was already inhibited in a CsA-like manner in the resistant cells. In agreement with this proposal, the mitochondrial target of CsA cyclophilin D (CyD) decreased by half in the resistant cells. The levels of adenine nucleotide translocator, voltage anion-dependent channel, Bax, Bcl-2, Bcl-xL, AIF and Smac/Diablo, were similar in both cell lines, whereas cytochrome c content was divided by three in the resistant cells. Since P-glycoprotein inhibition did not restore DOX toxicity in the resistant cells, while DOX-induced cell death in the parent cells was prevented by either PTP inhibition or siRNA-induced decrease in cytochrome c content, we conclude that the inhibition of PTP opening and the decrease in cytochrome c content participate in the mechanism that makes K562 cells resistant to DOX