Calcium/calmodulin-dependent protein kinase II phosphorylates and regulates the Drosophila eag potassium channel

Modulation of neuronal excitability is believed to be an important mechanism of plasticity in the nervous system. Calcium/calmodulin-dependent protein kinase II (CaMKII) has been postulated to regulate the ether à go-go (eag) potassium channel in Drosophila. Inhibition of CaMKII and mutation of the eag gene both cause hyperexcitability at the larval neuromuscular junction (NMJ) and memory formation defects in the adult. In this study, we identify a single site, threonine 787, as the major CaMKII phosphorylation site in Eag. This site can be phosphorylated by CaMKII both in a heterologous cell system and in vivo at the larval NMJ. Expression of Eag in Xenopus oocytes was used to assess the function of phosphorylation. Injection of either a specific CaMKII inhibitor peptide or lavendustin C, another CaMKII inhibitor, reduced Eag current amplitude acutely. Mutation of threonine 787 to alanine also reduced amplitude. Moreover, both CaMKII inhibition and the alanine mutation accelerated inactivation. The reduction in current amplitudes and the accelerated inactivation of dephosphorylated Eag channels would result in decreased outward potassium currents and hyperexcitability at presynaptic terminals and, thus, are consistent with the NMJ phenotype observed when CaMKII is inhibited. These results show that Eag is a substrate of CaMKII and suggest that direct modulation of potassium channels may be an important function of this kinase.     

Synthesis of highly potent and selective hetaryl ureas as integrin alpha(V)beta3-receptor antagonists

Solid-phase synthesis and SAR of integrin alpha(V)beta3-receptor antagonists containing a urea moiety as non-basic guanidine mimetic are described. The most potent compounds exhibited IC(50) values towards alpha(V)beta3 in the nanomolar range and high selectivity versus related integrins like alpha(IIb)beta3. For selected examples efficacy in functional cellular assays is demonstrated.     

Take your vitamins with a pinch of RNA

RNA "aptamers" capable of binding and discriminating among structurally related small molecules can be concocted in the laboratory. Two groups have now discovered that conserved domains in the 5' ends of some mRNAs bind specific metabolites and respond by changing their shape in biologically useful ways, demonstrating that aptamers also are present in the natural world.     

Mice lacking the metalloprotease-disintegrin MDC9 (ADAM9) have no evident major abnormalities during development or adult life

MDC9 (ADAM9/meltrin gamma) is a widely expressed and catalytically active metalloprotease-disintegrin protein that has been implicated in the ectodomain cleavage of heparin-binding epidermal growth factor-like growth factor (HB-EGF) and as an alpha secretase for the amyloid precursor protein. In this study, we evaluated the expression of MDC9 during development and generated mice lacking MDC9 (mdc9(-/-) mice) to learn more about the function of this protein during development and in adults. During mouse development, MDC9 mRNA is ubiquitously expressed, with particularly high expression levels in the developing mesenchyme, heart and brain. Despite the ubiquitous expression of MDC9, mdc9(-/-) mice appear to develop normally, are viable and fertile, and do not have any major pathological phenotypes compared to wild-type mice. Constitutive and stimulated ectodomain shedding of HB-EGF is comparable in embryonic fibroblasts isolated from mdc9(-/-) and wild-type mice, arguing against an essential role of MDC9 in HB-EGF shedding in these cells. Furthermore, there were no differences in the production of the APP alpha and gamma secretase cleavage product (p3) and of beta- and gamma-secretase cleavage product (A beta) in cultured hippocampal neurons from mdc9(-/-) or wild-type mice, arguing against an essential major role of MDC9 as an alpha-secretase in mice. Further studies, including functional challenges and an evaluation of potential compensation by, or redundancy with, other members of the ADAM family or perhaps even with other molecules will be necessary to uncover physiologically relevant functions for MDC9 in mice.     

Anti-mouse GPI-PLD antisera highlight structural differences between murine and bovine GPI-PLDs

Despite its well characterised biochemistry, the physiological role of glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) is unknown. Most of the previous studies investigating the distribution of GPI-PLD have focused on the human and bovine forms of the enzyme. Studies on mouse GPI-PLD are rare, partly due to the lack of a specific anti-mouse GPI-PLD antibody, but also due to the apparent low reactivity of existing antibodies to rodent GPI-PLDs. Here we describe the isolation of a mouse liver cDNA, the construction and expression of a recombinant enzyme and the generation of an affinity-purified rabbit anti-mouse GPI-PLD antiserum. The antibody shows good reactivity to partially purified murine and purified bovine GPI-PLD. In contrast, a rat anti-bovine GPI-PLD antibody shows no reactivity with the mouse enzyme and the two antibodies recognise different proteolytic fragments of the bovine enzyme. Comparison between the rodent, bovine and human enzymes indicates that small changes in the amino acid sequence of a short peptide in the mouse and bovine GPI-PLDs may contribute to the different reactivities of the two antisera. We discuss the implications of these results and stress the importance of antibody selection while investigating GPI-PLD in the mouse.     

Clinical use of polyethylene glycols as marker substances and determination in urine by liquid chromatography

Adulteration of samples is a serious problem in the analysis of drugs of abuse. One of the most frequent methods is substitution of urines by "clean" urines to gain false-negative results in laboratory tests for drugs of abuse. One way to approach this problem may be to label the patient's urine with marker substances which are given orally prior to the delivery of urine. This concept is based on methods for determining malabsorption in pediatric medicine. We report a protocol for evaluating low-molecular-mass polyethylene glycols as enteral labelling marker substances. For monitoring renal excretion of the ingested polyethylene glycols we have developed and optimised an isocratic reversed-phase high-performance liquid chromatographic method with automatic sample cleanup by column switching in the back-flush technique and with RI detection. The chromatographic procedure is simple, reliable and rapid, allowing a high sample throughput for routine screening.     

Potential role for ADAM15 in pathological neovascularization in mice

ADAM15 (named for a disintegrin and metalloprotease 15, metargidin) is a membrane-anchored glycoprotein that has been implicated in cell-cell or cell-matrix interactions and in the proteolysis of molecules on the cell surface or extracellular matrix. To characterize the potential roles of ADAM15 during development and in adult mice, we analyzed its expression pattern by mRNA in situ hybridization and generated mice carrying a targeted deletion of ADAM15 (adam15(-/-) mice). A high level of expression of ADAM15 was found in vascular cells, the endocardium, hypertrophic cells in developing bone, and specific areas of the hippocampus and cerebellum. However, despite the pronounced expression of ADAM15 in these tissues, no major developmental defects or pathological phenotypes were evident in adam15(-/-) mice. The elevated levels of ADAM15 in endothelial cells prompted an evaluation of its role in neovascularization. In a mouse model for retinopathy of prematurity, adam15(-/-) mice had a major reduction in neovascularization compared to wild-type controls. Furthermore, the size of tumors resulting from implanted B16F0 mouse melanoma cells was significantly smaller in adam15(-/-) mice than in wild-type controls. Since ADAM15 does not appear to be required for developmental angiogenesis or for adult homeostasis, it may represent a novel target for the design of inhibitors of pathological neovascularization.     

Toxikologische Bewertung von Ochratoxin A: Offene Fragen und Forschungsbedarf

Ochratoxin A (OTA) is an important food and feed contaminant with potential adverse effects in humans and animals. In view of present discussions on limit values for OTA in foods, essential elements of a toxicological risk assessment are outlined. The exposure situation in Europe is now well documented. The data base, with respect to a characterization of hazard and dose-response relationships, allowed to calculate a provisional tolerable daily intake for OTA suited to protect the consumer against undesirable toxic effects. Nonetheless, further research on OTA is indicated in view of unresolved issues regarding the following points:

1. 1.
   mechanisms of action (mode of genotoxicity, role of bioactivation/metabolism, identification of DNA-adducts and dose-dependency);
    
2. 2.
   combinations of OTA and other mycotoxins (studies of relevant mixtures/conditions);
    
3. 3.
   individual susceptibility and/or situation-based vulnerability.
    

Better information on mechanistic aspects of mycotoxin-induced toxicities will further improve our knowledge on the “margin of safety” between a given exposure and a potential impairment of human health.