High salt solution structure of a left-handed RNA double helix

Right-handed RNA duplexes of (CG)_n sequence undergo salt-induced helicity reversal, forming left-handed RNA double helices (Z-RNA). In contrast to the thoroughly studied Z-DNA, no Z-RNA structure of natural origin is known. Here we report the NMR structure of a half-turn, left-handed RNA helix (CGCGCG)₂ determined in 6 M NaClO₄. This is the first nucleic acid motif determined at such high salt. Sequential assignments of non-exchangeable proton resonances of the Z-form were based on the hitherto unreported NOE connectivity path [H6_(n)-H5′/H5″_(n)-H8_(n+1)-H1′_(n+1)-H6_(n+2)] found for left-handed helices. Z-RNA structure shows several conformational features significantly different from Z-DNA. Intra-strand but no inter-strand base stacking was observed for both CpG and GpC steps. Helical twist angles for CpG steps have small positive values (4–7°), whereas GpC steps have large negative values (−61°). In the full-turn model of Z-RNA (12.4 bp per turn), base pairs are much closer to the helix axis than in Z-DNA, thus both the very deep, narrow minor groove with buried cytidine 2′-OH groups, and the major groove are well defined. The 2′-OH group of cytidines plays a crucial role in the Z-RNA structure and its formation; 2′-O-methylation of cytidine, but not of guanosine residues prohibits A to Z helicity reversal.     

Drp-1-dependent division of the mitochondrial network blocks intraorganellar Ca2+ waves and protects against Ca2+-mediated apoptosis

By transiently or stably overexpressing the mitochondrial fission factor dynamin-related protein-1 (Drp-1), we evaluated the role of mitochondrial division in organelle Ca2+ homeostasis and apoptotic signaling. Quantitative 3D digital microscopy revealed a split mitochondrial network in Drp-1-overexpressing cells without changes in cell viability. High-speed mitochondrial [Ca2+] ([Ca2+]m) imaging revealed propagating intramitochondrial Ca2+ waves in intact cells, which were blocked in the Drp-1-fragmented network, leaving a fraction of individual mitochondria without substantial [Ca2+]m elevation. Consequently, in Drp-1-expressing cells the apoptotic efficacy of ceramide, which causes a Ca2+-dependent perturbation of mitochondrial structure and function, was drastically reduced. Conversely, the sensitivity to staurosporine-induced apoptosis, previously shown to be directly triggered by Drp-1-dependent recruitment of proapoptotic proteins to mitochondria, was enhanced. These results demonstrate that the regulated process of mitochondrial fusion and fission controls the spatiotemporal properties of mitochondrial Ca2+ responses and, thus, physiological and pathological consequences of cellular Ca2+ signals.     

An efficient route to novel 4,5-di- and 2,4,5-tri substituted imidazoles from imidazo[1,5-a]-1,3,5-triazine (5,8-diaza-7,9-dideazapurine) derivatives

Two new types of imidazole derivatives: N-(2-R1-5-R2-1H-imidazol-4-yl) thioureas 7a-g and N-(2-R1-5-R2-1H-imidazol-4-yl) formamides 8b,c,g were obtained in high yields by the hydrolytic degradation of 6-R1-8-R2-2-thioxo-2,3-dihydroimidazo[1,5-a]-1,3,5-triazin-4(1H)-ones 5a-g and 6-R1-8-R2-imidazo[1,5-a]-1,3,5-triazin-4(3H)-ones 6b,c,d, respectively. The tautomeric preferences of the new imidazoles were determined.     

Costs of immune response in cold-stressed laboratory mice selected for high and low basal metabolism rates

To study whether mounting an immune response is energetically costly, mice from two lines divergently selected for high (H-BMR) and low (L-BMR) basal metabolic rate (BMR) were immunized with sheep red blood cells. Their energy budgets were then additionally burdened by sudden transfer from an ambient temperature of 23 degrees C to 5 degrees C. We found that the immune response of H-BMR mice was lower than that of L-BMR mice. However, the interaction between line affiliation and ambient temperature was not significant and cold exposure did not result in immunosuppression in either line. At 23 degrees C the animals of both lines seemed to cover the costs of immune response by increasing food consumption and digestive efficiency. This was not observed at 5 degrees C, so these costs must have been covered at the expense of other components of the energy budget. Cold exposure itself elicited a considerable increase in food intake and the mass of internal organs, which were also heavier in H-BMR than in L-BMR mice. However, irrespective of the temperature or line affiliation, immunized mice had smaller intestines, while cold-exposed immunized mice had smaller hearts. Furthermore, the observed larger mass of the liver and kidneys in immunized mice of both lines kept at 23 degrees C was not observed at 5 degrees C. Hence, immunization compromised upregulation of the function of metabolically active internal organs, essential for meeting the energetic demands of cold. We conclude that the difficulties with a straightforward demonstration of the energetic costs of immune responses in these animals stem from the extreme flexibility of their energy budgets.     

The solution structure of human mitochondria fission protein Fis1 reveals a novel TPR-like helix bundle

Fis1 in yeast localizes to the outer mitochondrial membrane and facilitates mitochondrial fission by forming protein complexes with Dnm1 and Mdv1. Fis1 orthologs exist in higher eukaryotes, suggesting that they are functionally conserved. In the present study, we cloned the human Fis1 ortholog that was predicted in a database, and determined the protein structure using NMR spectroscopy. Following a flexible N-terminal tail, six alpha-helices connected with short loops construct a single core domain. The C-terminal tail containing a transmembrane segment appears to be disordered. In the core domain, each of two sequentially adjacent helices forms a hairpin-like conformation, resulting in a six helix assembly forming a slightly twisted slab similar to that of a tandem array of tetratrico-peptide repeat (TPR) motif folds. Within this TPR-like core domain, no significant sequence similarity to the typical TPR motif is found. The structural analogy to the TPR-containing proteins suggests that Fis1 binds to other proteins at its concave hydrophobic surface. A simple composition of Fis1 comprised of a binding domain and a transmembrane segment indicates that the protein may function as a molecular adaptor on the mitochondrial outer membrane. In HeLa cells, however, increased levels in mitochondria-associated Fis1 did not result in mitochondrial translocation of Drp1, a potential binding partner of Fis1 implicated in the regulation of mitochondrial fission, suggesting that the interaction between Drp1 and Fis1 is regulated.     

Cytogenetic comparison of the sensitivity to mutagens in mice selected for high (HA) and low (LA) swim stress-induced analgesia

Sensitivity to mutagens was studied in mouse lines selectively bred for high analgesia (HA) and for low analgesia (LA) induced by 3-min swimming in 20 degrees C water. Apart from pain-related traits HA mice also manifest, as compared to the LA line, higher emotionality in various behavioural tests, and cope worse with the hypothermic challenge of swimming in cold water. In the present study HA mice appeared more susceptible to the mutagenic effect of whole-body gamma-radiation and mitomycin-C injection. Both treatments caused higher frequencies of chromosomal aberrations and micronucleus in bone marrow cells in the HA than in the LA line. The results are discussed in terms of a genetic correlation between animals' susceptibility to environmental stressors and the mechanism of mutagenesis. As shown by our recent molecular study, the selection for magnitude of swim analgesia has differentiated the parental outbred population into two distinct genotypes characterised by specific minisatellite and microsatellite sequences for each line, which may be genetic markers of particular traits. We conceive that the breeding strategy, along with the differentiation of stress-related phenomena, has altered the frequencies of genes controlling DNA repair in each line.     

Structure,function and DNA composition of Saccharomyces cerevisiae chromatin loops

Recent localization of cohesin association regions along the yeast chromatin fibre suggests that compositional variability of DNA in yeast is related to the function and organization of the chromosomal loops. The bases of the loops, where the chromatin fibre is attached to the chromosomal axis, are AT-rich, bind cohesin, and are flanked by genes transcribed convergently. The hotspots of meiotic recombination are mainly found in the GC-rich parts of the loops, ‘external’ with respect to the chromosomal axis, frequently in the vicinity of the promoters of divergently transcribed genes. There are two possible reasons why the regions of the hotspots of recombination were enriched in GC content during evolution. One is a biased repair of recombination intermediates, and the second is a selective advantage due to an increased chromatin accessibility, which may have the carriers of GC-enriched alleles over the carriers of AT-rich alleles.     

The influence of intracellular idarubicin and daunorubicin levels on drug cytotoxicity in childhood acute leukemia

Uptake and efflux of two anthracyclines, idarubicin (IDA) and daunorubicin (DNR), was studied in childhood acute leukemia samples. A comparison of IDA and DNR transport phenomena in relation to drug cytotoxicity and expression of P-glycoprotein (PGP) was made. Intracellular content of IDA/DNR was determined by flow cytometry using the fluorescent properties of the drugs. In vitro drug cytotoxicity was measured by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay. PGP expression was analysed by flow cytometry. The uptake and efflux rates were non-significantly higher for IDA than DNR. There were no differences between three types of leukemia with respect to drug content during accumulation and retention. After correction for the cell volume, intracellular concentration of both drugs in each moment of uptake and efflux was significantly lower in relapsed ALL and AML samples in comparison with initial ALL cells. Efflux, but not uptake, of both drugs was inversely correlated with PGP expression and IDA, but not DNR, cytotoxicity. The cytotoxicity was correlated with drug accumulation for both drugs and with drug retention for IDA. In conclusion, it seems that (1) intracellular content was related to the lipophilic properties of the drugs rather than to the type of leukemia, (2) decreased intracellular concentration of both drugs might have an impact on compromised therapy results in AML and relapsed ALL children, (3) IDA presents higher cytotoxicity, which possibly might be decreased by the presence of PGP. These results might have a practical impact on the rational design of new chemotherapy protocols.     

Diphosphonucleotide phosphatase/phosphodiesterase from yellow lupin (Lupinus luteus L.) belongs to a novel group of specific metallophosphatases

Butyric acid (BA) induces differentiation of human leukemia, including HL-60 cells. By using a fluorescent probe, we showed that reactive oxygen species (ROS) were generated in BA-treated cells. BA-induced differentiation was accompanied with an increased secretion of pro-matrix metalloproteinase (MMP)-9. Both phenomena were inhibited by antioxidants. Tissue inhibitors of MMP (TIMP)-1 and -2 secretion were increased by BA, but differently affected by antioxidants. By contrast, BA did not affect MMP-9 mRNA, and decreased TIMP-1 and TIMP-2 mRNA levels. In addition, migratory and invasive properties of HL-60 cells were enhanced by BA, but differently affected by antioxidants. Altogether, these results indicate that ROS are messengers of BA-induced differentiation and increased invasiveness.