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Nathalie Griffon

Publications and source records attributed to Nathalie Griffon.

9 recordsLinked to original sources
PubMed2006

Substrate specificity of lipoprotein lipase and endothelial lipase: studies of lid chimeras.

The triglyceride (TG) lipase gene subfamily, consisting of LPL, HL, and endothelial lipase (EL), plays a central role in plasma lipoprotein metabolism. Compared with LPL and HL, EL is relatively more active as a phospholipase than as a TG lipase. The amino acid loop or "lid" covering the catalytic site has been implicated as the basis for the difference in substrate specificity between HL and LPL. To determine the role of the lid in the substrate specificity of EL, we studied EL in comparison with LPL by mutating specific residues of the EL lid and exchanging their lids. Mutation studies showed that amphipathic properties of the lid contribute to substrate specificity. Exchanging lids between LPL and EL only partially shifted the substrate specificity of the enzymes. Studies of a double chimera possessing both the lid and the C-terminal domain (C-domain) of EL in the LPL backbone showed that the role of the lid in determining substrate specificity does not depend on the nature of the C-domain of the lipase. Using a kinetic assay, we showed an additive effect of the EL lid on the apparent affinity for HDL(3) in the presence of the EL C-domain.

Amino Acid Sequence↗
PubMed2004

GIPC recruits GAIP (RGS19) to attenuate dopamine D2 receptor signaling.

Pleiotropic G proteins are essential for the action of hormones and neurotransmitters and are activated by stimulation of G protein-coupled receptors (GPCR), which initiates heterotrimer dissociation of the G protein, exchange of GDP for GTP on its Galpha subunit and activation of effector proteins. Regulator of G protein signaling (RGS) proteins regulate this cascade and can be recruited to the membrane upon GPCR activation. Direct functional interaction between RGS and GPCR has been hypothesized. We show that recruitment of GAIP (RGS19) by the dopamine D2 receptor (D2R), a GPCR, required the scaffold protein GIPC (GAIP-interacting protein, C terminus) and that all three were coexpressed in neurons and neuroendocrine cells. Dynamic translocation of GAIP to the plasma membrane and coassembly in a protein complex in which GIPC was a required component was dictated by D2R activation and physical interactions. In addition, two different D2R-mediated responses were regulated by the GTPase activity of GAIP at the level of the G protein coupling in a GIPC-dependent manner. Since GIPC exclusively interacted with GAIP and selectively with subsets of GPCR, this mechanism may serve to sort GPCR signaling in cells that usually express a large repertoire of GPCRs, G proteins, and RGS.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Glyceraldehyde-3-phosphate dehydrogenase is a GABAA receptor kinase linking glycolysis to neuronal inhibition.

Protein phosphorylation is crucial for regulating synaptic transmission. We describe a novel mechanism for the phosphorylation of the GABA(A) receptor, which mediates fast inhibition in the brain. A protein copurified and coimmunoprecipitated with the phosphorylated receptor alpha1 subunit; this receptor-associated protein was identified by purification and microsequencing as the key glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Molecular constructs demonstrated that GAPDH directly phosphorylates the long intracellular loop of GABA(A) receptor alpha1 subunit at identified serine and threonine residues. GAPDH and the alpha1 subunit were found to be colocalized at the neuronal plasma membrane. In keeping with the GAPDH/GABA(A) receptor molecular association, glycolytic ATP produced locally at plasma membranes was consumed for this alpha1 subunit phosphorylation, possibly within a single macrocomplex. The membrane-attached GAPDH is thus a dual-purpose enzyme, a glycolytic dehydrogenase, and a receptor-associated kinase. In acutely dissociated cortical neurons, the rundown of the GABA(A) responses was essentially attributable to a Mg(2+)-dependent phosphatase activity, which was sensitive to vanadate but insensitive to okadaic acid or fluoride. Rundown was significantly reduced by the addition of GAPDH or its reduced cofactor NADH and nearly abolished by the addition of its substrate glyceraldehyde-3-phosphate (G3P). The prevention of rundown by G3P was abolished by iodoacetamide, an inhibitor of the dehydrogenase activity of GAPDH, indicating that the GABA(A) responses are maintained by a glycolysis-dependent phosphorylation. Our results provide a molecular mechanism for the direct involvement of glycolysis in neurotransmission.

Adenosine Diphosphate↗
PubMed2003

Interactions of GIPC with dopamine D2, D3 but not D4 receptors define a novel mode of regulation of G protein-coupled receptors.

The C-terminus domain of G protein-coupled receptors confers a functional cytoplasmic interface involved in protein association. By screening a rat brain cDNA library using the yeast two-hybrid system with the C-terminus domain of the dopamine D(3) receptor (D(3)R) as bait, we characterized a new interaction with the PDZ domain-containing protein, GIPC (GAIP interacting protein, C terminus). This interaction was specific for the dopamine D(2) receptor (D(2)R) and D(3)R, but not for the dopamine D(4) receptor (D(4)R) subtype. Pull-down and affinity chromatography assays confirmed this interaction with recombinant and endogenous proteins. Both GIPC mRNA and protein are widely expressed in rat brain and together with the D(3)R in neurons of the islands of Calleja at plasma membranes and in vesicles. GIPC reduced D(3)R signaling, cointernalized with D(2)R and D(3)R, and sequestered receptors in sorting vesicles to prevent their lysosomal degradation. Through its dimerization, GIPC acts as a selective scaffold protein to assist receptor functions. Our results suggest a novel function for GIPC in the maintenance, trafficking, and signaling of GPCRs.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Brain-derived neurotrophic factor controls dopamine D3 receptor expression: therapeutic implications in Parkinson's disease.

Brain-derived neurotrophic factor (BDNF) belongs to a family of proteins related to nerve growth factor, which are responsible for neuron proliferation, survival and differentiation. A more diverse role for BDNF as a neuronal extracellular transmitter has, nevertheless, been proposed. Here we show that BDNF synthesized by dopamine neurons is responsible for the appearance of the dopamine D3 receptor during development and maintains its expression in adults. Moreover, BDNF triggers behavioral sensitization to levodopa in hemiparkinsonian rats. In monkeys rendered parkinsonian with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, which develop levodopa-induced dyskinesia, we show an overexpression of this receptor. Administration of a dopamine D3 receptor-selective partial agonist strongly attenuated levodopa-induced dyskinesia, while leaving unaffected the therapeutic effect of levodopa. These results suggest that the dopamine D3 receptor participates in both dyskinesia and the therapeutic action of levodopa and that partial agonists may normalize dopamine D3 receptor function and correct side-effects of levodopa therapy in PD patients.

Animals↗
PubMed2003

CLIC6, a member of the intracellular chloride channel family, interacts with dopamine D(2)-like receptors.

To identify proteins interacting with the C-terminal cytoplasmic tail of the dopamine D(3) receptor (D(3)R), we used the two-hybrid system to screen a rat brain cDNA library. We isolated three partial cDNAs encoding, respectively, for the MUPP1 multi-PDZ protein, for the N-terminal region of radixin, for GIPC and for a 160-amino acid open reading frame sharing high homology with the human CLIC6, also identified as parchorin in rabbit. In the two-hybrid system, CLIC6 was also able to interact with the D(2)R and D(4)R. The interaction between D(3)R and CLIC6 was confirmed by the use of a GST-D(3)R C-terminus fusion protein and COS cell extracts transiently expressing epitope-tagged CLIC6. In adult rat brain, CLIC6 mRNA expression was restricted to the choroid plexus, the striatal proliferative subventricular zone and the cerebellum where it is co-expressed with the D(3)R in the Purkinje cells of the lobules IX and X. CLIC6 mRNA was also detected in the pituitary in the posterior lobe and in cells co-expressing the D(2)R at the border between the intermediate and anterior lobes. In transfected HEK293 cells, D(3)R and CLIC6 co-localized at the plasma-membrane. No effect of CLIC6 transfection was observed on either intracellular chloride concentration or D(3)R/D(2)R-mediated response. In two-hybrid system, CLIC6 also interacted with MUPP1 and radixin but not GIPC, suggesting it could take part in a complex with D(2)-like receptors, not only by direct interaction with their C-termini, but also through interactions with scaffolding proteins.

Amino Acid Sequence↗
PubMed2002

Control of the allosteric equilibrium of hemoglobin by cross-linking agents.

The kinetics of ligand rebinding have been studied for modified or cross-linked hemoglobins (Hbs). Several compounds were tested that interact with alpha Val 1 or involve a cross-link between alpha Val 1 and alpha Lys 99 of the opposite dimer. By varying the length of certain cross-linking molecules, a wide range in the allosteric equilibrium could be obtained. Several of the mono-aldehyde modified Hbs show a shift toward the high affinity conformation of Hb. At the other extreme, for certain di-aldehyde cross-linked Hbs, the CO kinetics are typical of binding to deoxy Hb, even at low photodissociation levels, with which the dominant photoproduct is the triply liganded species; in these cases the hemoglobin does not switch from the low to high affinity state until after the fourth ligand is bound. Although each modified Hb shows only two distinct rates, the kinetic data as a function of dissociation level cannot be simulated with a simple two-state model. A critical length is observed for the maximum shift toward the low affinity T-state. Longer or shorter lengths of the cross-linker yielded more high affinity R-state. Unlike native Hb, which is in equilibrium with free dimers, the cross-linked Hbs maintain the fraction slow kinetics, which is unique to Hb tetramers, even at 0.5 microM (total heme). Addition of HbCN to unmodified HbCO solutions results in dimer exchange, which decreases the relative fraction of slow bimolecular kinetics; the cross-linked Hbs did not show such an effect, indicating that they do not participate in dimer exchange.

Aldehydes↗
PubMedDate not supplied

Brain-derived neurotrophic factor controls dopamine D3 receptor expression: implications for neurodevelopmental psychiatric disorders.

Brain-derived neurotrophic factor (BDNF) belongs to a family of proteins related to nerve growth factor, which are responsible for neuron proliferation, survival and differentiation. A more diverse role for BDNF as a neuronal extracellular transmitter has, nevertheless, been proposed. The dopamine D(3) receptor has been implicated in neuropsychiatric disorders including schizophrenia, drug addiction, depression and Parkinson's disease. Its expression during development and in adulthood is highly dependent on dopaminergic innervation. Here we show that BDNF synthesized by dopamine neurons is responsible for the appearance of the D(3) receptor during development and maintains D(3) receptor expression in adults. Moreover, BDNF triggers D(3) receptor overexpression and behavioral sensitization to levodopa in denervated animals. These results suggest that BDNF, by controlling the expression of specific genes such as the D(3) receptor gene, may be an important factor in neurodevelopmental psychiatric diseases.

Journal Article↗