Thrombocytopenia induced by the histone deacetylase inhibitor abexinostat involves p53-dependent and -independent mechanisms

Abexinostat is a pan histone deacetylase inhibitor (HDACi) that demonstrates efficacy in malignancy treatment. Like other HDACi, this drug induces a profound thrombocytopenia whose mechanism is only partially understood. We have analyzed its effect at doses reached in patient plasma on in vitro megakaryopoiesis derived from human CD34⁺ cells. When added at day 0 in culture, abexinostat inhibited CFU-MK growth, megakaryocyte (MK) proliferation and differentiation. These effects required only a short incubation period. Decreased proliferation was due to induction of apoptosis and was not related to a defect in TPO/MPL/JAK2/STAT signaling. When added later (day 8), the compound induced a dose-dependent decrease (up to 10-fold) in proplatelet (PPT) formation. Gene profiling from MK revealed a silencing in the expression of DNA repair genes with a marked RAD51 decrease at protein level. DNA double-strand breaks were increased as attested by elevated γH2AX phosphorylation level. Moreover, ATM was phosphorylated leading to p53 stabilization and increased BAX and p21 expression. The use of a p53 shRNA rescued apoptosis, and only partially the defect in PPT formation. These results suggest that HDACi induces a thrombocytopenia by a p53-dependent mechanism along MK differentiation and a p53-dependent and -independent mechanism for PPT formation.     

Light controls shoot meristem organogenic activity and leaf primordia growth during bud burst in Rosa sp

Light controls bud burst in many plants, which subsequently affects their architecture. Nevertheless, very little is known about this photomorphogenic process. This study ascertains the effects of light on bud burst and on two of its components, i.e. growth of preformed leaves and meristem organogenesis in six cultivars from three Rosa species (R. hybrida L., R. chinensis L., R. wichurana L.). Defoliated plants were severed above the third basal bud and exposed, either to darkness or to different intensities of white light, to blue, red or to FR, at constant temperature. Bud bursting was inhibited in darkness in the six cultivars of Rosa, but not in Arabidopsis, tomato and poplar plants under the same condition. In all Rosa cultivars, bud burst, growth of preformed leaves and meristem organogenesis were triggered by blue and red lights, and extended by increasing light intensities. FR was inhibitory of bud burst. Partial shading experiments demonstrated that bud and not stem was the active site for light perception in bud burst.     

Drought survival in Dactylis glomerata and Festuca arundinacea under similar rooting conditions in tubes

Drought survival in perennial forage plants involves different adaptative responses such as delay of dehydration through water uptake, limitation of water loss and tolerance of tissues to dessication. To compare the importance of these responses in contrasting cultivars of forage grasses at the whole plant level, we carried out two experiments under glasshouse conditions. Plants of cocksfoot (Dactylis glomerata L.) cultivars, cvs. Currie, Medly (both of Mediterranean origin) and Lutetia (of continental origin), and of tall fescue (Festuca arundinacea L.) cv. Centurion (Mediterranean) were grown in 60 cm-deep cylinders to eliminate the effect of differences of root depth on water availability whilst allowing severe drought to be imposed at a realistic rate. In both experiments, the cvs. were ranked similarly for plant survival, with high mortality for Centurion, low for the Mediterranean cocksfoots Currie and Medly, and intermediate for Lutetia. These differences could not be ascribed to water use during most of the drought period since water uptake and decrease in leaf extension were not significantly different between species and cultivars. However, resistant cvs. of cocksfoot were able to extract water for a longer period and at a lower soil water potential (s) than other cvs. The critical s at plant death was –3.8 and –3.6 MPa for Medly and Currie and –3.0-,–2.6 MPa for Lutetia and Centurion. Moreover, at a low soil water reserve (15–2%), membrane stability and water content were maintained for longer in enclosed immature leaf bases of cocksfoots cultivars, whereas the fescue Centurion exhibited accelerated lamina senescence and steady increase of membrane damage in surviving tissues. Therefore, it is proposed that the drought resistance of tall fescue in the field can mainly be ascribed to its ability to develop a deep root system. In cocksfoot, dehydration tolerance in surviving tissues and the ability of roots to extract water at low soil water potentials may, in addition to root depth, contribute significantly to plant survival under severe drought.     

AtNRAMP3, a multispecific vacuolar metal transporter involved in plant responses to iron deficiency

Metal homeostasis is critical for the survival of living organisms, and metal transporters play central roles in maintaining metal homeostasis in the living cells. We have investigated the function of a metal transporter of the NRAMP family, AtNRAMP3, in Arabidopsis thaliana. A previous study showed that AtNRAMP3 expression is upregulated by iron (Fe) starvation and that AtNRAMP3 protein can transport Fe. In the present study, we used AtNRAMP3 promoter beta-glucoronidase (GUS) fusions to show that AtNRAMP3 is expressed in the vascular bundles of roots, stems, and leaves under Fe-sufficient conditions. This suggests a function in long-distance metal transport within the plant. Under Fe-starvation conditions, the GUS activity driven by the AtNRAMP3 promoter is upregulated without any change in the expression pattern. We analyze the impact of AtNRAMP3 disruption and overexpression on metal accumulation in plants. Under Fe-sufficient conditions, AtNRAMP3 overexpression or disruption does not lead to any change in the plant metal content. Upon Fe starvation, AtNRAMP3 disruption leads to increased accumulation of manganese (Mn) and zinc (Zn) in the roots, whereas AtNRAMP3 overexpression downregulates Mn accumulation. In addition, overexpression of AtNRAMP3 downregulates the expression of the primary Fe uptake transporter IRT1 and of the root ferric chelate reductase FRO2. Expression of AtNRAMP3::GFP fusion protein in onion cells or Arabidopsis protoplasts shows that AtNRAMP3 protein localizes to the vacuolar membrane. To account for the results presented, we propose that AtNRAMP3 influences metal accumulation and IRT1 and FRO2 gene expression by mobilizing vacuolar metal pools to the cytosol.     

High resolution proteome analysis of cryoglobulins using Fourier transform-ion cyclotron resonance mass spectrometry

Cryoglobulins are cold-precipitable serum immunoglobulins associated with a number of infectious, autoimmune and neoplastic disorders such as hepatitis C, Waldenstr?m's macroglobulinemia, multiple myeloma, chronic lymphocytic leukemia, and rheumatoid arthritis. The mechanism(s) of cryoprecipitation has remained obscure hitherto, which has prompted recent intensive efforts on the identification of cryoglobulin components. In the present study, two-dimensional gel electrophoresis (2-DE) combined with high resolution Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry has been applied as a powerful approach for the analysis of cryoglobulins. While FT-ICR mass spectrometry has been shown to enable the high resolution identification and structure analysis of biopolymers using both electrospray (ESI) and matrix-assisted laser desorption ionization (MALDI), the recently developed MALDI-FT-ICR source is shown here to provide high (sub-ppm) mass determination accuracy and isotopic fine structure as particular advantages in the identification of proteins. The main protein components in a serum cryoprecipitate from a patient with hepatitis C virus (HCV) infection and presenting type II cryogobulinemia are immunoglobulin (Ig)M and IgG which were identified by MALDI-FT-ICR MS analysis after separation by 2-DE as mu- and gamma-heavy chains, kappa- and lambda-light chains, and J-chains. Furthermore, complementarity determining regions CDR1 and CDR2 from monoclonal IgM-RF variable region (V)L were directly identified using accurate mass determinations by FT-ICR-MS. The presence of Spalpha was ascertained as an IgM-associated protein in the serum cryoprecipitate from a patient with HCV infection.     

Molecular and genetic characterization of a non-climacteric phenotype in melon reveals two loci conferring altered ethylene response in fruit

Fruit ripening and abscission are associated with an ethylene burst in several melon (Cucumis melo) genotypes. In cantaloupe as in other climacteric fruit, exogenous ethylene can prematurely induce abscission, ethylene production, and ripening. Melon genotypes without fruit abscission or without ethylene burst also exist and are, therefore, non-climacteric. In the nonabscising melon fruit PI 161375, exogenous ethylene failed to stimulate abscission, loss of firmness, ethylene production, and expression of all target genes tested. However, the PI 161375 etiolated seedlings displayed the usual ethylene-induced triple response. Genetic analysis on a population of recombinant cantaloupe Charentais x PI 161375 inbred lines in segregation for fruit abscission and ethylene production indicated that both characters are controlled by two independent loci, abscission layer (Al)-3 and Al-4. The non-climacteric phenotype in fruit tissues is attributable to ethylene insensitivity conferred by the recessive allelic forms from PI 161375. Five candidate genes (two ACO, two ACS, and ERS) that were localized on the melon genetic map did not exhibit colocalization with Al-3 or Al-4.     

Renal sclerosis: a public health problem

In France, 45,000 patients are treated by hemodialysis and/or transplantation for chronic renal failure. Every year 7,000 new patients need such a therapeutic approach. The estimated cost of this pathology is about 1% of the total amount of the budget of social security, even though the number of patients is limited. Some treatments were shown to be effective in improving the progression of chronic renal failure, as for example the anti-hypertensive therapy and the adequate treatment of diabetes mellitus. Collagen deposition in each segment of the kidney, mainly in the interstitium, plays a pivotal role in the progression of renal deficiency in chronic renal failure. In order to ameliorate the progression renal failure it would be essential to know: 1) the different types of collagen deposit; 2) the proteinase/antiproteinase systems involved in the remodelling of the extracellular matrix (serine-protease, metallo-protease and their inhibitors); 3) the autocrine/paracrine effects of proteases and of growth factors on collagen synthesis. The more precise the knowledge of these factors, the more useful will be new pharmacological-, gene- or cellular therapies for limiting the progression of chronic renal failure.