A mixed mirror-image DNA/RNA aptamer inhibits glucagon and acutely improves glucose tolerance in models of type 1 and type 2 diabetes.

Excessive secretion of glucagon, a functional insulin antagonist, significantly contributes to hyperglycemia in type 1 and type 2 diabetes. Accordingly, immunoneutralization of glucagon or genetic deletion of the glucagon receptor improved glucose homeostasis in animal models of diabetes. Despite this strong evidence, agents that selectively interfere with endogenous glucagon have not been implemented in clinical practice yet. We report the discovery of mirror-image DNA-aptamers (Spiegelmer®) that bind and inhibit glucagon. The affinity of the best binding DNA oligonucleotide was remarkably increased (>25-fold) by the introduction of oxygen atoms at selected 2'-positions through deoxyribo- to ribonucleotide exchanges resulting in a mixed DNA/RNA-Spiegelmer (NOX-G15) that binds glucagon with a Kd of 3 nm. NOX-G15 shows no cross-reactivity with related peptides such as glucagon-like peptide-1, glucagon-like peptide-2, gastric-inhibitory peptide, and prepro-vasoactive intestinal peptide. In vitro, NOX-G15 inhibits glucagon-stimulated cAMP production in CHO cells overexpressing the human glucagon receptor with an IC50 of 3.4 nm. A single injection of NOX-G15 ameliorated glucose excursions in intraperitoneal glucose tolerance tests in mice with streptozotocin-induced (type 1) diabetes and in a non-genetic mouse model of type 2 diabetes. In conclusion, the data suggest NOX-G15 as a therapeutic candidate with the potential to acutely attenuate hyperglycemia in type 1 and type 2 diabetes.

The effects of the anti-hepcidin Spiegelmer NOX-H94 on inflammation-induced anemia in cynomolgus monkeys.

Anemia of chronic inflammation is the most prevalent form of anemia in hospitalized patients. A hallmark of this disease is the intracellular sequestration of iron. This is a consequence of hepcidin-induced internalization and subsequent degradation of ferroportin, the hepcidin receptor and only known iron-export protein. This study describes the characterization of novel anti-hepcidin compound NOX-H94, a structured L-oligoribonucleotide that binds human hepcidin with high affinity (Kd = 0.65 ± 0.06 nmol/L). In J774A.1 macrophages, NOX-H94 blocked hepcidin-induced ferroportin degradation and ferritin expression (half maximal inhibitory concentration = 19.8 ± 4.6 nmol/L). In an acute cynomolgus monkey model of interleukin 6 (IL-6)-induced hypoferremia, NOX-H94 inhibited serum iron reduction completely. In a subchronic model of IL-6-induced anemia, NOX-H94 inhibited the decrease in hemoglobin concentration. We conclude that NOX-H94 protects ferroportin from hepcidin-induced degradation. Therefore, this pharmacologic approach may represent an interesting treatment option for patients suffering from anemia of chronic inflammation.

Redox regulation of the NPR1-TGA1 system of Arabidopsis thaliana by nitric oxide.

The role of reactive oxygen and nitrogen species in local and systemic defense reactions is well documented. NPR1 and TGA1 are key redox-controlled regulators of systemic acquired resistance in plants. NPR1 monomers interact with the reduced form of TGA1, which targets the activation sequence-1 (as-1) element of the promoter region of defense proteins. Here, we report the effect of the physiological nitric oxide donor S-nitrosoglutathione on the NPR1/TGA1 regulation system in Arabidopsis thaliana. Using the biotin switch method, we demonstrate that both NPR1 and TGA1 are S-nitrosylated after treatment with S-nitrosoglutathione. Mass spectrometry analyses revealed that the Cys residues 260 and 266 of TGA1 are S-nitrosylated and S-glutathionylated even at GSNO concentrations in the low micromolar range. Furthermore, we showed that S-nitrosoglutathione protects TGA1 from oxygen-mediated modifications and enhances the DNA binding activity of TGA1 to the as-1 element in the presence of NPR1. In addition, we observed that the translocation of NPR1 into the nucleus is promoted by nitric oxide. Taken together, our results suggest that nitric oxide is a redox regulator of the NPR1/TGA1 system and that they underline the importance of nitric oxide in the plant defense response.

Identification of S-nitrosylated proteins in plants.

Posttranslational protein modifications affect the function or the activity of proteins and exhibit important mechanisms in regulating cellular events. A broad spectrum of modifications is known, including redox-dependent alterations. During the last decade, covalent binding of nitric oxide (NO) to protein cysteines, termed S-nitrosylation, seems especially an evident process for redox-related signaling. To reveal potential target proteins for S-nitrosylation, the biotin switch method gains more and more in importance. This technique is a tool used for analyzing the nitrosylome as well as the examination of single candidates. It is based on substitution of the NO group by a biotin linker that simplifies the detection and the purification of recently S-nitrosylated proteins in a three-step procedure.

Nitric oxide-responsive genes and promoters in Arabidopsis thaliana: a bioinformatics approach.

Due to its high reactivity and its ability to diffuse and permeate the cell membrane, nitric oxide (NO) and its exchangeable redox-activated species are unique biological messengers in animals and in plants. Although an increasing number of reports indicate that NO is an essential molecule in several physiological processes, there is not a clear picture of its method of action. Studies on the transcriptional changes induced by NO permitted identification of genes involved in different functional processes such as signal transduction, defence and cell death, transport, basic metabolism, and reactive oxygen species (ROS) production and degradation. The co-expression of these genes can be explained by the co-operation of a set of transcription factors that bind a common region in the promoter of the regulated genes. The present report describes the search for a common transcription factor-binding site (TFBS) in promoter regions of NO-regulated genes, based on microarray analyses. Using Genomatix Gene2Promotor and MatInspector, eight families of TFBSs were found to occur at least 15% more often in the promoter regions of the responsive genes in comparison with the promoter regions of 28,447 Arabidopsis control genes. Most of these TFBSs, such as ocs element-like sequences and WRKY, have already been reported to be involved in particular stress responses. Furthermore, the promoter regions of genes involved in jasmonic acid (JA) biosynthesis were analysed for a common TFBS module, since some genes responsible for JA biosynthesis are induced by NO, and an interaction between NO and JA signalling has already been described.

Generation and detection of S-nitrosothiols.

Nitric oxide (NO) plays a pivotal role in cellular signaling in many different organisms as the result of the modification of protein activities/functions by protein S-nitrosylation. This NO-dependent posttranslational modification is based on the attachment of NO to the sulfur moiety of cysteine residues. However, the instability of S-nitrosothiols makes it difficult to analyze this type of protein modification in vitro as well as in vivo. Jeffrey and colleagues developed a method--named the biotin switch method--that allows the detection and purification of S-nitrosylated proteins. The principle behind this technology is the substitution of the NO group by a biotin linker in a three-step procedure. First, the all free thiol groups are blocked with a thiol-reactive agent, followed by selective reduction of the S-nitrosylated cysteine residues using ascorbate. In the final step, the reduced thiol groups are labeled with a biotin linker, so that the previously S-nitrosylated cysteine residues are finally biotinylated. Afterwards, the biotinylated proteins can be detected with anti-biotin antibodies or can be purified by affinity chromatography on neutravidin agarose. In this chapter, we give a detailed description of the biotin switch method, which can be used for proteomics approach to identify candidates for protein S-nitrosylation as well as to analyse S-nitrosylation of selected proteins.

A fifth member of the tomato 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase gene family harbours a leucine zipper and is anaerobically induced.

Using the leucine zipper domain of a small anaerobically induced bZIP transcription factor in a yeast two hybrid screen, anaerobically induced genes were identified. One peptide corresponds to an anaerobically induced IDS4-like protein that maybe involved in G-protein signaling. Surprisingly, another interacting peptide corresponds to a novel anaerobically induced 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase, designated ACO5. ACO5 harbours a leucine zipper and transcription is mainly induced in fruits and to a lesser extend in leaves. The role of ACO5 in the low oxygen response of tomato is discussed.

Functional dissection of a small anaerobically induced bZIP transcription factor from tomato.

A small anaerobically induced tomato transcription factor was isolated from a subtractive library. This factor, designated ABZ1 (anaerobic basic leucine zipper), is anaerobically induced in fruits, leaves and roots and encodes a nuclear localized protein. ABZ1 shares close structural and sequence homology with the S-family of small basic leucine zipper (bZIP) transcription factors that are implicated in stress response. Nuclear localization of ABZ1 is mediated by the basic region and occurs under normoxic conditions. ABZ1 binds to G-box-like target sites as a dimer. Binding can be abolished by heterodimerization with a truncated protein retaining the leucine zipper but lacking the DNA binding domain. The protein binds in a sequence specific manner to the CaMV 35S promoter which is down regulated when ABZ1 is coexpressed. This correlates with the anaerobic down regulation of the 35S promoter in tomato and tobacco. These results may suggest that small bZIP proteins are involved in the negative regulation of gene expression under anaerobic conditions.

Heterologous expression of a bacterial homospermidine synthase gene in transgenic tobacco: effects on the polyamine pathway.

Homospermidine synthase (HSS) is a branch-point enzyme that links the secondary pathway (pyrrolizidine alkaloids) to primary metabolism (polyamines). Since the diamine putrescine is a precursor of homospermidine and nicotine in tobacco, we performed heterologous expression of a bacterial homospermidine synthase gene (hss)in Nicotiana tabacum and determined the effect on free and conjugated polyamine levels. The hss gene from Rhodopseudomonas viridis was placed under the control of the cauliflower mosaic virus (CaMV) 35S promoter in Agrobacterium tumefaciens Ti-plasmid in sense and antisense orientation and both hss constructs were transformed into tobacco plants. Expression of the hss gene was verified by "Northern" and "Southern Blot" analysis. 2 transgenic sense lines were generated from 1000 calli which showed weak expression of homospermidine synthase, i.e. 50 pktal/mg protein and 45 pktal/mg protein. These transgenic sense plants showed a significantly decreased content of free spermidine while the pool of conjugated spermidine was not affected. The 2 sense plants exhibited a range of abnormal phenotypes such as dwarfness and stunted growth. Homospermidine was sporadically detectable in wild type tobacco. To our knowledge, this is the first biotechnological approach to express a prokaryotic homospermidine synthase gene in tobacco plants.