A block of single-nucleotide polymorphisms within intron 1 of the FTO (fat mass and obesity associated) gene is associated with variation in body weight. Previous works suggest that increased expression of FTO, which encodes a 2-oxoglutaratedependent nucleic acid demethylase, leads to increased body weight, although the underlying mechanism has remained unclear. To elucidate the function of FTO, we examined the consequences of altered FTO levels in cultured cells and murine brain. Here we show that a knockdown of FTO in HEK293 cells affects the transcripts levels of genes involved in the response to starvation, whereas overexpression of FTO affects the transcript levels of genes related to RNA processing and metabolism. Subcellular localization of FTO further strengthens the latter notion. Using immunocytochemistry and confocal laser scanning microscopy, we detected FTO in nuclear speckles and -to a lesser and varying extent -in the nucleoplasm and nucleoli of HEK293, HeLa and MCF-7 cells. Moreover, RNA modification analyses revealed that loss of Fto affects the 3-methyluridine/ uridine and pseudouridine/uridine ratios in total brain RNA. We conclude that altered levels of FTO have multiple and diverse consequences on RNA modifications and the transcriptome. Keywords: FTO; RNA modifications; nuclear speckles; transcriptome INTRODUCTION Genome-wide association studies have revealed a strong association between a block of single-nucleotide polymorphisms (SNPs) in intron 1 of the fat mass and obesity-associated (FTO) gene, body mass index and other obesity-related traits in children and adults of different populations. 1-3 Stratigopoulos et al 4 have suggested that one of the SNPs (rs8050136) affects binding of the transcriptional regulator CUX1. By studying allelic expression levels in heterozygous individuals, we have found that the risk allele of the FTO gene makes more transcripts and have proposed that increased expression of the FTO gene leads to increased body weight. 5 This hypothesis is supported by the clinical findings in rare patients and in mouse models with an FTO/Fto mutation. Homozygous loss-of-function of FTO was reported to cause severe growth retardation and multiple malformations, 6 whereas a duplication of FTO was found to be associated with morbid obesity. 7 Fto-knockout mice 8 and mice with a missense mutation in exon 6 9 showed leanness, postnatal growth retardation and a higher metabolic rate. Mice with one or two additional copies of Fto had a gene-dosage-dependent increase in body weight. 10 FTO is a member of non-heme Fe(II)-and a-ketoglutaratedependent oxygenase superfamily and is found in vertebrates and green algea, but not in invertebrate animals, fungi and green plants. 11 By in vitro studies, FTO was shown to function as a demethylase with a strong preference for 3meU and 3meT in single-stranded RNA and DNA, respectively. 12,13 Han et al 14 have provided structural evidence for understanding the substrate specificity of FTO and have suggested
Oxaliplatin, [(1R,2R)-cyclohexane-1,2-diamine](ethanedioato-O,O')platinum(II) shows a great efficiency against colorectal cancer. Although the mode of action of oxaliplatin is not yet understood, it is commonly accepted that binding of oxaliplatin to DNA prevents DNA synthesis and alters protein to DNA binding. In order to elucidate the modified DNA-protein interaction and thus to understand the mechanisms leading to cellular misinterpretation of DNA information and apoptosis, we have identified the preferential binding sites and the dynamics of the oxaliplatin-DNA intrastrand and interstrand adducts at the oligomer level using high-performance liquid chromatography/electrospray ionization-tandem mass spectrometry (HPLC/ESI-MS/MS) and HPLC/inductively coupled plasma-MS for quantitative studies. We used a combination of benzonase, alkaline phosphatase and Nuclease S1 for digestion. This digestion procedure allows the study of platinated oligomeric nucleotides and more complex interstrand adducts. The digestion products were mostly chromatographically separated and characterized using HPLC/ESI-ion trap MS/MS experiments. We could show that the adducts to guanine and adenine are quite dynamic; that is, the ratios are changing for several days. In addition, the resulting adducts provide evidence for the action of the digesting enzymes and indicate that the adduct spectrum at the oligomeric level is different to that at the commonly studies dinucleotide level.
In this work we present a methodology to measure the complex adduct spectrum caused by the interaction of Cisplatin with DNA. By using an optimized DNA digestion procedure we were able to show that the adduct spectrum in in vivo duplex DNA is much more complex than described so far. For the first time a high abundance of interstrand adducts has been detected by using HPLC/ESI-MS. These adducts could play a key role in the DNA repair mechanisms and the development of cellular resistance to Cisplatin. By species-unspecific isotope dilution analysis HPLC/ICP-MS measurements, we were able to study the kinetics of adduct formation. With these experiments we proved that after the initial formation of adducts a rearrangement occurs on the DNA-strands leading to significant changes in adduct patterns over time. Furthermore, the parameters of the species-unspecific isotope dilution analysis were optimized to allow measurements of specific adducts in the DNA of Cisplatin exposed cells.
The use of peptide nucleic acids (PNAs) is steadily increasing in biochemistry and diagnostics. So far, PNAs have mostly been investigated using cationic conditions in mass spectrometry. Furthermore, the use of fragmentation techniques developed for peptides and proteins like infrared multiphoton dissociation (IRMPD) and electron capture dissociation (ECD) has barely been examined. However, especially the fragmentation behavior of PNA oligomers in negative ion mode is of high importance, due to the ability to interact with nucleic acids which are almost exclusively analyzed in the negatively charged state. In the current study PNA fragmentations under cationic and anionic conditions were investigated and different fragmentation techniques like collision-induced dissociation (CID), IRMPD and ECD were applied. Especially when using CID and IRMPD, amide bonds were broken, whereas ECD resulted in the elimination of nucleobases. Differences were also observed between positive and negative ionization, while the sequence coverage for the negative ions was superior to positive ions. The fragmentation behavior using IRMPD led to almost complete sequence coverage. Additionally, in anions the interesting effect of multiple eliminations of HNCO was found.
The use of carboxylates in the carbodiimide-mediated coupling to amines was investigated. The addition of pyridinium ptoluenesulfonate (PPTS) and a tertiary amine was found to significantly improve acylation yields by up to 70%.
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