Failure to assemble the alpha 3 beta 3 subcomplex of the ATP synthase leads to accumulation of the alpha and beta subunits within inclusion bodies and the loss of mitochondrial cristae in Saccharomyces cerevisiae

The F(1) component of mitochondrial ATP synthase is an oligomeric assembly of five different subunits, alpha, beta, gamma, delta, and epsilon. In terms of mass, the bulk of the structure ( approximately 90%) is provided by the alpha and beta subunits, which form an (alphabeta)(3) hexamer with adenine nucleotide binding sites at the alpha/beta interfaces. We report here ultrastructural and immunocytochemical analyses of yeast mutants that are unable to form the alpha(3)beta(3) oligomer, either because the alpha or the beta subunit is missing or because the cells are deficient for proteins that mediate F assembly (e.g. Atp11p, Atp12p, or Fmc1p). The F(1) alpha(1) and beta subunits of such mutant strains are detected within large electron-dense particles in the mitochondrial matrix. The composition of the aggregated species is principally full-length F(1) alpha and/or beta subunit protein that has been processed to remove the amino-terminal targeting peptide. To our knowledge this is the first demonstration of mitochondrial inclusion bodies that are formed largely of one particular protein species. We also show that yeast mutants lacking the alpha(3)beta(3) oligomer are devoid of mitochondrial cristae and are severely deficient for respiratory complexes III and IV. These observations are in accord with other studies in the literature that have pointed to a central role for the ATP synthase in biogenesis of the mitochondrial inner membrane.     

Biotin-phenyldiazomethane conjugates as labeling reagents at phosphate in mono and polynucleotides

Molecules 2-5 that include in their structure a biotin moiety as detectable unit and differently substituted phenyl diazo functions as reactive group were prepared as reagents for labeling the phosphate group in mono and polynucleotides. These molecules were shown to react selectively and quantitatively with the model nucleotide 3'-UMP. They were used successfully in the labeling step of DNA and RNA analysis using high-density DNA-chips (or microarrays) technology.     

Tumor-selective action of HDAC inhibitors involves TRAIL induction in acute myeloid leukemia cells

Chromatin is a dynamic macromolecular structure epigenetically modified to regulate specific gene expression. Altered chromatin function can lead to aberrant expression of growth regulators and may, ultimately, cause cancer. That many human diseases have epigenetic etiology has stimulated the development of 'epigenetic' therapies. Inhibitors of histone deacetylases (HDACIs) induce proliferation arrest, maturation and apoptosis of cancer cells, but not normal cells, in vitro and in vivo, and are currently being tested in clinical trials. We investigated the mechanism(s) underlying this tumor selectivity. We report that HDACIs induce, in addition to p21, expression of TRAIL (Apo2L, TNFSF10) by directly activating the TNFSF10 promoter, thereby triggering tumor-selective death signaling in acute myeloid leukemia (AML) cells and the blasts of individuals with AML. RNA interference revealed that the induction of p21, TRAIL and differentiation are separable activities of HDACIs. HDACIs induced proliferation arrest, TRAIL-mediated apoptosis and suppression of AML blast clonogenicity irrespective of French-American-British (FAB) classification status, karyotype and immunophenotype. No apoptosis was seen in normal CD34(+) progenitor cells. Our results identify TRAIL as a mediator of the anticancer action of HDACIs.     

Importance of UVA photoprotection as shown by genotoxic related endpoints: DNA damage and p53 status

In order to demonstrate the importance of photoprotection in the UVA range (320-400 nm), an in vitro approach where sun formulations are spread on a quartz slide, and placed over human keratinocytes in culture is proposed as a convenient test for photoprotection assessment at the DNA level. Using the comet assay, DNA strand breaks, oxidative DNA damage or drug-induced DNA breaks were assessed. Accumulation of p53 protein was also studied as a marker for UV-induced genotoxic stress. Such a method was used to compare two formulations with different photostability. Spectroradiometry showed that a photounstable formulation lost its effectiveness in UVA screening when pre-irradiated by simulated sunlight (UVB+UVA). As a consequence, it was also shown that this formulation was not as protective as the photostable one at the genomic level. These data demonstrate that the loss of absorbing efficiency within UVA wavelengths due to photounstability may have detrimental consequences leading to impairments implicated in genotoxic events.     

Roles of thioredoxin reductase during the aerobic life of Lactococcus lactis

Thiol-disulfide bond balance is generally maintained in bacteria by thioredoxin reductase-thioredoxin and/or glutathione-glutaredoxin systems. Some gram-positive bacteria, including Lactococcus lactis, do not produce glutathione, and the thioredoxin system is presumed to be essential. We constructed an L. lactis trxB1 mutant. The mutant was obtained under anaerobic conditions in the presence of dithiothreitol (DTT). Unexpectedly, the trxB1 mutant was viable without DTT and under aerated static conditions, thus disproving the essentiality of this system. Aerobic growth of the trxB1 mutant did not require glutathione, also ruling out the need for this redox maintenance system. Proteomic analyses showed that known oxidative stress defense proteins are induced in the trxB1 mutant. Two additional effects of trxB1 were not previously reported in other bacteria: (i) induction of proteins involved in fatty acid or menaquinone biosynthesis, indicating that membrane synthesis is part of the cellular response to a redox imbalance, and (ii) alteration of the isoforms of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GapB). We determined that the two GapB isoforms in L. lactis differed by the oxidation state of catalytic-site cysteine C152. Unexpectedly, a decrease specific to the oxidized, inactive form was observed in the trxB1 mutant, possibly because of proteolysis of oxidized GapB. This study showed that thioredoxin reductase is not essential in L. lactis and that its inactivation triggers induction of several mechanisms acting at the membrane and metabolic levels. The existence of a novel redox function that compensates for trxB1 deficiency is suggested.     

High density lipoproteins facilitate hepatitis C virus entry through the scavenger receptor class B type I

The scavenger receptor class B type I (SR-BI) has recently been shown to interact with hepatitis C virus (HCV) envelope glycoprotein E2, suggesting that it might be involved at some step of HCV entry into host cells. However, due to the absence of a cell culture system to efficiently amplify HCV, it is not clear how SR-BI contributes to HCV entry. Here, we sought to determine how high density lipoproteins (HDLs), the natural ligand of SR-BI, affect HCV entry. By using the recently described infectious HCV pseudotyped particles (HCVpps) that display functional E1E2 glycoprotein complexes, we showed that HDLs are able to markedly enhance HCVpp entry. We did not find any evidence of HDL association with HCVpps, suggesting that HCVpps do not enter into target cells using HDL as a carrier to bind to its receptor. Interestingly, lipid-free apoA-I and apoA-II, the major HDL apolipoproteins, were unable to enhance HCVpp infectivity. In addition, drugs inhibiting HDL cholesteryl transfer (block lipid transport (BLT)-2 and BLT-4) reduced HDL enhancement of HCVpp entry, suggesting a role for lipid transfer in facilitating HCVpp entry. Importantly, silencing of SR-BI expression in target cells by RNA interference markedly reduced HDL-mediated enhancement of HCVpp entry. Finally, enhancement of HCVpp entry was also suppressed when the SR-BI binding region on HCV glycoprotein E2 was deleted. Altogether, these data indicate that HDL-mediated enhancement of HCVpp entry involves a complex interplay between SR-BI, HDL, and HCV envelope glycoproteins, and they highlight the active role of HDLs in HCV entry.     

NADP-malate dehydrogenase from unicellular green alga Chlamydomonas reinhardtii. A first step toward redox regulation?

The determinants of the thioredoxin (TRX)-dependent redox regulation of the chloroplastic NADP-malate dehydrogenase (NADP-MDH) from the eukaryotic green alga Chlamydomonas reinhardtii have been investigated using site-directed mutagenesis. The results indicate that a single C-terminal disulfide is responsible for this regulation. The redox midpoint potential of this disulfide is less negative than that of the higher plant enzyme. The regulation is of an all-or-nothing type, lacking the fine-tuning provided by the second N-terminal disulfide found only in NADP-MDH from higher plants. The decreased stability of specific cysteine/alanine mutants is consistent with the presence of a structural disulfide formed by two cysteine residues that are not involved in regulation of activity. Measurements of the ability of C. reinhardtii thioredoxin f (TRX f) to activate wild-type and site-directed mutants of sorghum (Sorghum vulgare) NADP-MDH suggest that the algal TRX f has a redox midpoint potential that is less negative than most those of higher plant TRXs f. These results are discussed from an evolutionary point of view.     

Galectin-4 and sulfatides in apical membrane trafficking in enterocyte-like cells

We have previously reported that 1-benzyl-2-acetamido-2-deoxy-alpha-D-galactopyranoside (GalNAc alpha-O-bn), an inhibitor of glycosylation, perturbed apical biosynthetic trafficking in polarized HT-29 cells suggesting an involvement of a lectin-based mechanism. Here, we have identified galectin-4 as one of the major components of detergent-resistant membranes (DRMs) isolated from HT-29 5M12 cells. Galectin-4 was also found in post-Golgi carrier vesicles. The functional role of galectin-4 in polarized trafficking in HT-29 5M12 cells was studied by using a retrovirus-mediated RNA interference. In galectin-4-depleted HT-29 5M12 cells apical membrane markers accumulated intracellularly. In contrast, basolateral membrane markers were not affected. Moreover, galectin-4 depletion altered the DRM association characteristics of apical proteins. Sulfatides with long chain-hydroxylated fatty acids, which were also enriched in DRMs, were identified as high-affinity ligands for galectin-4. Together, our data propose that interaction between galectin-4 and sulfatides plays a functional role in the clustering of lipid rafts for apical delivery.     

Proteomic analysis of grapevine (Vitis vinifera L.) tissues subjected to herbicide stress

Two-dimensional gel electrophoresis coupled to mass spectrometry analysis was used to examine for the first time the effect of a herbicide (flumioxazin) on a crop species (Vitis vinifera L.) at the proteome level. Examination of 2-D maps derived from chemically stressed tissues revealed the presence of 33 spots displaying a differential expression pattern. The presence of stress responsive proteins in the different plant organs analysed suggests that flumioxazin could act systemically. Among the responsive proteins, some photosynthesis-related proteins, including several fragments of the enzyme Rubisco, were identified. This effect suggests that photosynthesis could be impaired by the herbicide. The induction of several enzymatic antioxidant systems was also observed, probably as a result of an oxidative stress. Moreover, the photorespiration pathway was stimulated, as suggested by the induction of some key enzymes involved in this process. Changes in carbon metabolism-associated proteins presumably reflect altered patterns of carbon flux in response to impaired photosynthesis and an increased need for osmotic adjustment in affected tissues. Finally, plant defences were stimulated as revealed by the induction of a set of proteins belonging to the pathogenesis-related 10 class, suggesting that they could play an essential role in cell defence mechanisms against flumioxazin.