Adele M. Snowman

CAPON: a protein associated with neuronal nitric oxide synthase that regulates its interactions with PSD95.

Nitric oxide (NO) produced by neuronal nitric oxide synthase (nNOS) is important for N-methyl-D-aspartate (NMDA) receptor-dependent neurotransmitter release, neurotoxicity, and cyclic GMP elevations. The coupling of NMDA receptor-mediated calcium influx and nNOS activation is postulated to be due to a physical coupling of the receptor and the enzyme by an intermediary adaptor protein, PSD95, through a unique PDZ-PDZ domain interaction between PSD95 and nNOS. Here, we report the identification of a novel nNOS-associated protein, CAPON, which is highly enriched in brain and has numerous colocalizations with nNOS. CAPON interacts with the nNOS PDZ domain through its C terminus. CAPON competes with PSD95 for interaction with nNOS, and overexpression of CAPON results in a loss of PSD95/nNOS complexes in transfected cells. CAPON may influence nNOS by regulating its ability to associate with PSD95/NMDA receptor complexes.

Antipsychotic drug-induced weight gain mediated by histamine H1 receptor-linked activation of hypothalamic AMP-kinase

The atypical antipsychotic drugs (AAPDs) have markedly enhanced the treatment of schizophrenias but their use has been hindered by the major weight gain elicited by some AAPDs. We report that orexigenic AAPDs potently and selectively activate hypothalamic AMP-kinase, an action abolished in mice with deletion of histamine H1 receptors. These findings may afford a means of developing more effective therapeutic agents and provide insight into the hypothalamic regulation of food intake.

Synthesis of diphosphoinositol pentakisphosphate by a newly identified family of higher inositol polyphosphate kinases.

Inositol (1,4,5) trisphosphate (Ins(1,4,5)P(3)) is a well-known messenger molecule that releases calcium from intracellular stores. Homologues with up to six phosphates have been characterized and recently, homologues with seven or eight phosphate groups, including pyrophosphates, have been identified. These homologues are diphosphoinositol pentakisphosphate (PP-InsP(5)/InsP(7)) and bis(diphospho)inositol tetrakisphosphate (bis-PP-InsP(4)/InsP(8)) [1], the rapid turnover of which [2] is regulated by calcium [2] and adrenergic receptor activity [3]. It has been proposed that the high-energy pyrophosphates might participate in protein phosphorylation [4]. We have purified InsP(6) kinase [5] and PP-InsP(5) kinase [6], both of which display ATP synthase activity, transferring phosphate to ADP. Here, we report the cloning of two mammalian InsP(6) kinases and a yeast InsP(6) kinase. Furthermore, we show that the yeast protein, ArgRIII, is an inositol-polyphosphate kinase that can convert InsP(3) to InsP(4), InsP(5) and InsP(6). We have identified a new family of highly conserved inositol-polyphosphate kinases that contain a newly identified, unique consensus sequence.

GAPDH Mediates Nitrosylation of Nuclear Proteins

S-nitrosylation of proteins by nitric oxide is a major mode of signalling in cells. S-nitrosylation can mediate the regulation of a range of proteins, including prominent nuclear proteins, such as HDAC2 (ref. 2) and PARP1 (ref. 3). The high reactivity of the nitric oxide group with protein thiols, but the selective nature of nitrosylation within the cell, implies the existence of targeting mechanisms. Specificity of nitric oxide signalling is often achieved by the binding of nitric oxide synthase (NOS) to target proteins, either directly or through scaffolding proteins such as PSD-95 (ref. 5) and CAPON. As the three principal isoforms of NOS—neuronal NOS (nNOS), endothelial NOS (eNOS) and inducible NOS (iNOS) —are primarily non-nuclear, the mechanisms by which nuclear proteins are selectively nitrosylated have been elusive. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is physiologically nitrosylated at its Cys 150 residue. Nitrosylated GAPDH (SNO–GAPDH) binds to Siah1, which possesses a nuclear localization signal, and is transported to the nucleus. Here, we show that SNO–GAPDH physiologically transnitrosylates nuclear proteins, including the deacetylating enzyme sirtuin-1 (SIRT1), histone deacetylase-2 (HDAC2) and DNA-activated protein kinase (DNA-PK). Our findings reveal a novel mechanism for targeted nitrosylation of nuclear proteins and suggest that protein–protein transfer of nitric oxide groups may be a general mechanism in cellular signal transduction.

Novel antipsychotic drugs share high affinity for σ receptors

Evaluation de la fixation de 7 nouveaux neuroleptiques a 7 sites de liaison de recepteurs biologiques distincts. Leur unique trait commun est une forte affinite pour les recepteurs σ

Inositol Pyrophosphates Inhibit Akt Signaling, Thereby Regulating Insulin Sensitivity and Weight Gain

The inositol pyrophosphate IP7 (5-diphosphoinositolpentakisphosphate), formed by a family of three inositol hexakisphosphate kinases (IP6Ks), modulates diverse cellular activities. We now report that IP7 is a physiologic inhibitor of Akt, a serine/threonine kinase that regulates glucose homeostasis and protein translation, respectively, via the GSK3β and mTOR pathways. Thus, Akt and mTOR signaling are dramatically augmented and GSK3β signaling reduced in skeletal muscle, white adipose tissue, and liver of mice with targeted deletion of IP6K1. IP7 affects this pathway by potently inhibiting the PDK1 phosphorylation of Akt, preventing its activation and thereby affecting insulin signaling. IP6K1 knockout mice manifest insulin sensitivity and are resistant to obesity elicited by high-fat diet or aging. Inhibition of IP6K1 may afford a therapeutic approach to obesity and diabetes.

Protein pyrophosphorylation by inositol pyrophosphates is a posttranslational event

In a previous study, we showed that the inositol pyrophosphate diphosphoinositol pentakisphosphate (IP7) physiologically phosphorylates mammalian and yeast proteins. We now report that this phosphate transfer reflects pyrophosphorylation. Thus, proteins must be prephosphorylated by ATP to prime them for IP7 phosphorylation. IP7 phosphorylates synthetic phosphopeptides but not if their phosphates have been masked by methylation or pyrophosphorylation. Moreover, IP7 phosphorylated peptides are more acid-labile and more resistant to phosphatases than ATP phosphorylated peptides, indicating a different type of phosphate bond. Pyrophosphorylation may represent a novel mode of signaling to proteins.

Cystathionine γ-lyase deficiency mediates neurodegeneration in Huntington’s disease

Huntington’s disease is an autosomal dominant disease associated with a mutation in the gene encoding huntingtin (Htt) leading to expanded polyglutamine repeats of mutant Htt (mHtt) that elicit oxidative stress, neurotoxicity, and motor and behavioural changes. Huntington’s disease is characterized by highly selective and profound damage to the corpus striatum, which regulates motor function. Striatal selectivity of Huntington’s disease may reflect the striatally selective small G protein Rhes binding to mHtt and enhancing its neurotoxicity. Specific molecular mechanisms by which mHtt elicits neurodegeneration have been hard to determine. Here we show a major depletion of cystathionine γ-lyase (CSE), the biosynthetic enzyme for cysteine, in Huntington’s disease tissues, which may mediate Huntington’s disease pathophysiology. The defect occurs at the transcriptional level and seems to reflect influences of mHtt on specificity protein 1, a transcriptional activator for CSE. Consistent with the notion of loss of CSE as a pathogenic mechanism, supplementation with cysteine reverses abnormalities in cultures of Huntington’s disease tissues and in intact mouse models of Huntington’s disease, suggesting therapeutic potential.

Sulfhydration mediates neuroprotective actions of parkin

Increases in S-nitrosylation and inactivation of the neuroprotective ubiquitin E3 ligase, parkin, in the brains of patients with Parkinson’s Disease (PD) are thought to be pathogenic and suggest a possible mechanism linking parkin to sporadic PD. Here we demonstrate that physiologic modification of parkin by hydrogen sulfide (H2S), termed sulfhydration, enhances its catalytic activity. Sulfhydration sites are identified by mass spectrometry analysis and investigated by site directed mutagenesis. Parkin sulfhydration is markedly depleted in the brains of patients with PD, suggesting that this loss may be pathologic. This implies that H2S donors may be therapeutic.

Identification and characterization of a novel inositol hexakisphosphate kinase

The inositol pyrophosphate disphosphoinositol pentakisphosphate (PP-InsP3/InsP7) is formed in mammals by two recently cloned inositol hexakiphosphate kinases, InsP6K1 and InsP6K2 (Saiardi, A., Erdjument-Bromage, H., Snowman, A. M., Tempst, P., and Snyder, S. H. (1999) Curr. Biol. 9, 1323–1326). We now report the identification, cloning, and characterization of a third InsP7 forming enzyme designated InsP6K3. InsP6K3 displays 50 and 45% sequence identity to InsP6K1 and InsP6K2, respectively, with a smaller mass (46 kDa) and a more basic character than the other two enzymes. InsP6K3 is most enriched in the brain where its localization resembles InsP6K1 and InsP6K2. Intracellular disposition discriminates the three enzymes with InsP6K2 being exclusively nuclear, InsP6K3 predominating in the cytoplasm, and InsP6K1 displaying comparable nuclear and cytosolic densities.