Akt regulates L-type Ca2+ channel activity by modulating Cavα1 protein stability

The insulin IGF-1–PI3K–Akt signaling pathway has been suggested to improve cardiac inotropism and increase Ca2+ handling through the effects of the protein kinase Akt. However, the underlying molecular mechanisms remain largely unknown. In this study, we provide evidence for an unanticipated regulatory function of Akt controlling L-type Ca2+ channel (LTCC) protein density. The pore-forming channel subunit Cavα1 contains highly conserved PEST sequences (signals for rapid protein degradation), and in-frame deletion of these PEST sequences results in increased Cavα1 protein levels. Our findings show that Akt-dependent phosphorylation of Cavβ2, the LTCC chaperone for Cavα1, antagonizes Cavα1 protein degradation by preventing Cavα1 PEST sequence recognition, leading to increased LTCC density and the consequent modulation of Ca2+ channel function. This novel mechanism by which Akt modulates LTCC stability could profoundly influence cardiac myocyte Ca2+ entry, Ca2+ handling, and contractility

Spadin, a Sortilin-Derived Peptide, Targeting Rodent TREK-1 Channels: A New Concept in the Antidepressant Drug Design

We found that spadin, a natural peptide derived from sortilin, blocks the mouse TREK-1 channel and might be an efficient and fast-acting antidepressant

Etude de la surveillance des ARNs aux locus des chaînes légères d'immunoglobulines (locus Igk)

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Etude de la surveillance des ARN d Immunoglobulines au cours du développement lymphocytaire B

L expression des immunoglobulines (Ig) par les lymphocytes B est assurée par des mécanismes particulièrement complexes et précisément régulés. Le processus aléatoire de recombinaisons V(D)J source de diversité du répertoire des lymphocytes B génère dans deux tiers des cas un décalage du cadre de lecture et à l apparition d un codon stop prématuré (PTC). Pour empêcher la traduction des transcrits contenant des PTC et, par conséquent la synthèse de protéines tronquées, la cellule utilise différents mécanismes de contrôle qualité des ARN. La thématique développée au cours de cette thèse a consisté à étudier ces mécanismes dits de surveillance des ARN au cours du développement lymphocytaire B, en utilisant les transcrits d Ig issus de réarrangements V(D)J hors phase comme modèles. Parmi les mécanismes de surveillance des ARN, l inhibition d épissage permet de limiter l apparition de transcrit matures (ARNm) contenant des PTC et provoque une accumulation de transcrits primaires (pré-ARNm) ; le NAS (nonsense-associated altered splicing) permet d éliminer l exon contenant un PTC lors de l épissage : phénomène de saut d exon ; et, le NMD (nonsense-mediated mRNA decay) permet de dégrader les ARNm contenant des PTC, Ces processus sont très actifs dans la lignée lymphoïde puisque l apparition de PTC y est fréquemment observée. Nous avons étudié la surveillance des ARN de chaînes légères d Ig et quantifié l efficacité de ces différents mécanismes : NMD, NAS et inhibition d épissage au cours de la maturation B (Chemin et al., 2010). Cette étude a permis de montrer que la coopération entre ces processus individuellement peu efficaces permettait de diminuer drastiquement le taux d ARNm Ig contenant des PTCs. L étude de la surveillance des ARNs de chaînes lourdes d Ig a révélé une transcription identique des allèles productifs (VDJ+) et non-productifs (VDJ-) et, le lien étroit entre l intensité de transcription, l épissage et la dégradation par NMD au cours de l activation B et de la différentiation plasmocytaire (Tinguely et al., 2011). Nous avons également analysé l influence des séquences introniques sur le processus de NAS et montré que la présence de sites donneurs d épissage au sein de l intron J -C semble diminuer l épissage alternatif de type L-C et favoriser la rétention de séquences introniques. Enfin, nous avons mis en évidence l existence d une contre-sélection des cellules contenant des allèles Ig non productifs, présentant un PTC au sein de l exon variable (classe VJPTC), au cours du développement B et de la différenciation plasmocytaire. Cette diminution semble corrélée à une faible dégradation par NMD et à un fort épissage alternatif des transcrits issus des allèles VJPTC (Chemin et al., en préparation). Dans les 2 cas, ces transcrits peuvent conduire à la production d Ig tronquées, potentiellement néfastes pour les cellules B et plasmocytaires. Bien que d autres travaux soient nécessaires pour identifier l impact physiologique des Ig tronquées, des approches thérapeutiques visant à induire la production d Ig tronquées à l aide d inhibiteurs du NMD, pourraient être envisagées dans le traitement du myélome ou d autres tumeurs lymphoïdes B.LIMOGES-BU Médecine pharmacie (870852108) / SudocSudocFranceF

Multiple RNA surveillance mechanisms cooperate to reduce the amount of nonfunctional Ig kappa transcripts.

International audienceRandom V(D)J junctions ensure that the diversity of the Ig primary repertoire is adapted to the vast heterogeneity of Ags. In two-thirds of cases, recombination between variable segments induces a frameshift in the open reading frame and generates a premature termination codon. In B cells harboring biallelic V(D)J rearrangement of Ig genes, transcription is known to occur on both the functional and nonfunctional alleles, generating considerable amounts of primary transcripts with out-of-frame V regions. In this study, we analyzed in cell lines and primary B cells the RNA surveillance of nonfunctional Igkappa transcripts arising from nonproductive rearrangement. We demonstrated that splicing inhibition, nonsense-mediated decay and nonsense-altered splicing each have an individual partial effect that together associate into an efficient surveillance machinery, downregulating nonfunctional Igkappa mRNA. Moreover, we provide evidence that the RNA surveillance efficiency increases throughout B cell development. Whereas splicing inhibition remains constant in most cell lines, differences in nonsense-mediated decay and nonsense-altered splicing are responsible for the higher RNA surveillance observed in plasma cells. Altogether, these data show that nonfunctionally rearranged alleles are subjected to active transcription but that multiple RNA surveillance mechanisms eradicate up to 90% of out-of-frame Igkappa mRNA

T-Type Calcium Channel Inhibition Underlies the Analgesic Effects of the Endogenous Lipoamino Acids

International audienceLipoamino acids are anandamide-related endogenous molecules that induce analgesia via unresolved mechanisms. Here, we provide evidence that the T-type/Cav3 calcium channels are important pharmacological targets underlying their physiological effects. Various lipoamino acids, including N-arachidonoyl glycine (NAGly), reversibly inhibited Cav3.1, Cav3.2, and Cav3.3 currents, with potent effects on Cav3.2 [EC 50 ϳ200 nM for N-arachidonoyl 3-OH-␥-aminobutyric acid (NAGABA-OH)]. This inhibition involved a large shift in the Cav3.2 steady-state inactivation and persisted during fatty acid amide hydrolase (FAAH) inhibition as well as in cell-free outside-out patch. In contrast, lipoamino acids had weak effects on high-voltage-activated (HVA) Cav1.2 and Cav2.2 calcium currents, on Nav1.7 and Nav1.8 sodium currents, and on anandamide-sensitive TRPV1 and TASK1 currents. Accordingly, lipoamino acids strongly inhibited native Cav3.2 currents in sensory neurons with small effects on sodium and HVA calcium currents. In addition, we demonstrate here that lipoamino acids NAGly and NAGABA-OH produced a strong thermal analgesia and that these effects (but not those of morphine) were abolished in Cav3.2 knockout mice. Collectively, our data revealed lipoamino acids as a family of endogenous T-type channel inhibitors, suggesting that these ligands can modulate multiple cell functions via this newly evidenced regulation

Simple power-law models to predict flow metrics for water resource and risk management along the Mekong tributaries. [Abstract only]

Increasing demographic pressure, economic development and resettlement policies in the Lower Mekong Basin induce greater population dependency on river flow to satisfy growing domestic and agricultural water demands. This dependency is particularly tight in upland areas where alternative water resources (groundwater) are scarce. As a result, communities tend to live closer to rivers, and so are more vulnerable to floods. This situation requires improved knowledge of flow variability for better management of water resources and risks. Unfortunately, stream flow measurements are scarce, especially in remote areas inhabited by the poorest and most vulnerable populations. Several water resource models have been developed to simulate and predict flows in the Lower Mekong Basin. However, most of these models have been designed to predict flow along the Mekong mainstream, precluding accurate assessments in headwater catchments. In most cases, their complexity and lack of transparency restricts potential users to modelling experts, and largely excludes those practitioners working closely with affected populations. The most integrated and informative way to characterize flow, at a specific location on a river, is to compute a flow duration curve which provides the percentage of time (duration) any particular flow is exceeded over a historical period. Using hydro-meteorological records from more than 60 gauged catchments in the Lower Mekong Basin, and a 90-meter digital elevation model, we used multiple linear regressions to develop power-law models predicting flow duration curves. These simple equations allow assessment of low, medium and high flow metrics, at any point on rivers in the Lower Mekong Basin, using easily determined geomorphological and climate characteristics. We believe that this parsimonious, transparent and highly predictive tool (89% <R2< 95%) can be used by a wide range of practitioners working in the fields of livelihood, water infrastructure engineering and agriculture

Multivariate power-law models for streamflow prediction in the Mekong Basin

Study region: Increasing demographic pressure and economic development in the Mekong Basin result in greater dependency on river water resources and increased vulnerability to streamflow variations. Study focus: Improved knowledge of flow variability is therefore paramount, especially in remote catchments, rarely gauged, and inhabited by vulnerable populations. We present simple multivariate power-law relationships for estimating streamflow metrics in ungauged areas, from easily obtained catchment characteristics. The relations were derived from weighted least square regression applied to streamflow, climate, soil, geographic, geomorphologic and land-cover characteristics of 65 gauged catchments in the Lower Mekong Basin. Step-wise and best subset regressions were used concurrently to maximize the prediction R-squared computed by leave-one-out cross-validations, thus ensuring parsimonious, yet accurate relationships. New hydrological insights for the region: A combination of 3–6 explanatory variables – chosen among annual rainfall, drainage area, perimeter, elevation, slope, drainage density and latitude – is sufficient to predict a range of flow metrics with a prediction R-squared ranging from 84 to 95%. The inclusion of forest or paddy percentage coverage as an additional explanatory variable led to slight improvements in the predictive power of some of the low-flow models (lowest prediction R-squared = 89%). A physical interpretation of the model structure was possible for most of the resulting relationships. Compared to regional regression models developed in other parts of the world, this new set of equations performs reasonably well

Simple power-law models to predict flow metrics for water resource and risk management along the Mekong tributaries. [Abstract only]

Increasing demographic pressure, economic development and resettlement policies in the Lower Mekong Basin induce greater population dependency on river flow to satisfy growing domestic and agricultural water demands. This dependency is particularly tight in upland areas where alternative water resources (groundwater) are scarce. As a result, communities tend to live closer to rivers, and so are more vulnerable to floods. This situation requires improved knowledge of flow variability for better management of water resources and risks. Unfortunately, stream flow measurements are scarce, especially in remote areas inhabited by the poorest and most vulnerable populations. Several water resource models have been developed to simulate and predict flows in the Lower Mekong Basin. However, most of these models have been designed to predict flow along the Mekong mainstream, precluding accurate assessments in headwater catchments. In most cases, their complexity and lack of transparency restricts potential users to modelling experts, and largely excludes those practitioners working closely with affected populations. The most integrated and informative way to characterize flow, at a specific location on a river, is to compute a flow duration curve which provides the percentage of time (duration) any particular flow is exceeded over a historical period. Using hydro-meteorological records from more than 60 gauged catchments in the Lower Mekong Basin, and a 90-meter digital elevation model, we used multiple linear regressions to develop power-law models predicting flow duration curves. These simple equations allow assessment of low, medium and high flow metrics, at any point on rivers in the Lower Mekong Basin, using easily determined geomorphological and climate characteristics. We believe that this parsimonious, transparent and highly predictive tool (89% <R2< 95%) can be used by a wide range of practitioners working in the fields of livelihood, water infrastructure engineering and agriculture