13 research outputs found
FYVE-Dependent Endosomal Targeting of an Arrestin-Related Protein in Amoeba
International audienceBACKGROUND: Visual and ÎČ-arrestins are scaffolding proteins involved in the regulation of receptor-dependent intracellular signaling and their trafficking. The arrestin superfamilly includes several arrestin domain-containing proteins and the structurally related protein Vps26. In Dictyostelium discoideum, the arrestin-domain containing proteins form a family of six members, namely AdcA to -F. In contrast to canonical arrestins, Dictyostelium Adc proteins show a more complex architecture, as they possess, in addition to the arrestin core, other domains, such as C2, FYVE, LIM, MIT and SAM, which potentially mediate selective interactions with either lipids or proteins. METHODOLOGY AND PRINCIPAL FINDINGS: A detailed analysis of AdcA has been performed. AdcA extends on both sides of the arrestin core, in particular by a FYVE domain which mediates selective interactions with PI(3)P, as disclosed by intrinsic fluorescence measurements and lipid overlay assays. Localization studies showed an enrichment of tagged- and endogenous AdcA on the rim of early macropinosomes and phagosomes. This vesicular distribution relies on a functional FYVE domain. Our data also show that the arrestin core binds the ADP-ribosylation factor ArfA, the unique amoebal Arf member, in its GDP-bound conformation. SIGNIFICANCE: This work describes one of the 6 arrestin domain-containing proteins of Dictyostelium, a novel and atypical member of the arrestin clan. It provides the basis for a better understanding of arrestin-related protein involvement in trafficking processes and for further studies on the expanding roles of arrestins in eukaryotes
Interaction of nitric oxide with the activity of cytosolic NADH/cytochrome c electron transport system
Nitric oxide (NO) generated by the dissociation of S-nitrosoglutathione or added as gaseous solution,
inhibits the oxidation of exogenous NADH supported by the activity of the cytosolic NADH/cyto-c electron
transport pathway. The inhibition is immediate, very strong, higher at lower oxygen concentration,
independent on the NO concentration and remains constant as long as NO is no more available and then
is spontaneously removed. The data obtained, not in contrast with those reported with isolated cytochrome
oxidase (Cox), strengthen a new concept: reduced cytochrome c (cyto-c) and NO behave as
two substrates of Cox, which promotes their oxidation with molecular oxygen as a co-substrate. In the
presence of NO, Cox exhibits the property of switching from cyto-c oxidase to NO oxidase activity. With
an ââall or nothingâ process Cox becomes an efficient NO scavenger. The persistence of membrane potential,
even in the presence of high inhibition of oxygen uptake, could be tentatively correlated to the protective
effect of NO on the ischaemicâreperfusion injury
Ceramide-induced activation of cytosolic NADH/cytochrome c electron transport pathway: An additional source of energy for apoptosis
We have investigated whether increase in the oxidation rate of exogenous cytochrome c (cyto-c), induced
by long-chain ceramides, might be due to an increased rate of cytosolic NADH/cyto-c electron transport
pathway. This process was identified in isolated liver mitochondria and has been studied in our laboratory
for many years. Data from highly specific test of sulfite oxidase prove that exogenous cyto-c both in
the absence and presence of ceramide cannot permeate through the mitochondrial outer membrane.
However, the oxidation of added NADH, mediated by exogenous cyto-c and coupled to the generation
of a membrane potential supporting the ATP synthesis, can also be stimulated by ceramide. The results
obtained suggest that ceramide molecules, by increasing mitochondrial permeability, with the generation
of either raft-like platforms or channels, may have a dual function. They can promote the release of
endogenous cyto-c and activate, with an energy conserving process, the oxidation of cytosolic NADH
either inducing the formation of new respiratory contact sites or increasing the frequency of the preexisting
porin contact sites. In agreement with the data in the literature, an increase of mitochondrial ceramide
molecules level may represent an efficient strategy to activate and support the correct execution of
apoptotic program
Valinomycin induced energy-dependent mitochondrial swelling, cytochrome c release, cytosolic NADH/cytochrome c oxidation and apoptosis
In valinomycin induced stimulation of mitochondrial
energy dependent reversible swelling, supported
by succinate oxidation, cytochrome c (cyto-c) and sulfite
oxidase (Sox) [both present in the mitochondrial intermembrane
space (MIS)] are released outside. This effect
can be observed at a valinomycin concentration as low as
1 nM. The rate of cytosolic NADH/cyto-c electron transport
pathway is also greatly stimulated. The test on the
permeability of mitochondrial outer membrane to exogenous
cyto-c rules out the possibility that the increased rate
of exogenous NADH oxidation could be ascribed either to
extensively damaged or broken mitochondria. Accumulation
of potassium inside the mitochondria, mediated by
the highly specific ionophore valinomycin, promotes an
increase in the volume of matrix (evidenced by swelling)
and the interaction points between the two mitochondrial
membranes are expected to increase. The data reported and
those previously published are consistent with the view that
âârespiratory contact sitesââ are involved in the transfer of
reducing equivalents from cytosol to inside the mitochondria
both in the absence and the presence of valinomycin.
Magnesium ions prevent at least in part the valinomycin effects. Rather than to the dissipation of membrane
potential, the pro-apoptotic property of valinomycin can be
ascribed to both the release of cyto-c from mitochondria to
cytosol and the increased rate of cytosolic NADH coupled
with an increased availability of energy in the form of
glycolytic ATP, useful for the correct execution of apoptotic
program
Helicobacter pylori-induced inflammation masks the underlying presence of low-grade dysplasia on gastric lesions
BACKGROUND Helicobacter pylori (H. pylori) infection has been associated with a long-term risk of precancerous gastric conditions (PGC) even after H. pylori eradication. AIM To investigate the efficacy of High-Resolution White-Light Endoscopy with Narrow-Band Imaging in detecting PGC, before/after H. pylori eradication. METHODS We studied 85 consecutive patients with H. pylori-related gastritis with/without PGC before and 6 mo after proven H. pylori eradication. Kimura-Takemoto modified and endoscopic grading of gastric intestinal metaplasia classifications, were applied to assess the endoscopic extension of atrophy and intestinal metaplasia. The histological result was considered to be the gold standard. The Sydney System, the Operative-Link on Gastritis-Assessment, and the Operative-Link on Gastric-Intestinal Metaplasia were used for defining histological gastritis, atrophy and intestinal metaplasia, whereas dysplasia was graded according to World Health Organization classification. Serum anti-parietal cell antibody and anti-intrinsic factor were measured when autoimmune atrophic gastritis was suspected. RESULTS After H. pylori eradication histological signs of mononuclear/polymorphonuclear cell infiltration and Mucosal Associated Lymphoid Tissue-hyperplasia, disappeared or decreased in 100% and 96.5% of patients respectively, whereas the Operative-Link on Gastritis-Assessment and Operative-Link on Gastric-Intestinal Metaplasia stages did not change. Low-Grade Dysplasia prevalence was similar on random biopsies before and after H. pylori eradication (17.6% vs 10.6%, P = 0.19), but increased in patients with visible lesions (0% vs 22.4%, P < 0.0001). At a multivariate analysis, the probability for detecting dysplasia after resolution of H. pylori-related active inflammation was higher in patients with regression or reduction of Mucosal Associated Lymphoid Tissue hyperplasia, greater alcohol consumption, and anti-parietal cell antibody and/or anti-intrinsic factor positivity [odds ratio (OR) = 3.88, 95% confidence interval (CI): 1.31-11.49, P = 0.01; OR = 3.10, 95%CI: 1.05-9.12, P = 0.04 and OR = 5.47, 95%CI: 1.33-22.39, P < 0.04, respectively]. CONCLUSION High-Resolution White-Light Endoscopy with Narrow-Band Imaging allows an accurate diagnosis of Low-Grade Dysplasia on visible lesions after regression of H. pylori-induced chronic gastritis. Patients with an overlap between autoimmune/H. pylori-induced gastritis may require more extensive gastric mapping