Transporter-associated Protein Research Articles

Characterization Studies on the sugC Gene of Streptococcus suis Serotype 2 in Adhesion, Invasion, and Virulence in Mice.

The sugC gene of Streptococcus suis (S. suis) is a coding gene for the ATP-binding transporter-associated protein with strong pathogenicity. In order to reveal the effect of the sugC gene on the virulence of S. suis serotype 2, a wild-type strain of TJS75, isolated from fattening pigs' brain tissue samples, was used as a parent strain, and a knockout sugC gene (ΔsugC) and complementary strain (CΔsugC) were successfully constructed via homologous recombination technology. The biological characteristics of TJS75, ΔsugC and CΔsugC were compared and analyzed through growth curves, biochemical characteristics, hemolysis characteristics, cell infection tests and pathogenicity tests on BALB/c mice. The results of the growth characteristic experiments in vitro showed that the plateau stage growth period of ΔsugC was delayed compared to the TJS75 strain, but there was no difference in the total number of bacteria. The biochemical characteristics and hemolysis ability of ΔsugC in sheep blood had no difference compared with TJS75, but its adhesion and invasion abilities in PK-15 cells were decreased. Knockout of the sugC gene had no impact on the expression levels of adhesion-related genes in TJS75 in real-time PCR analysis. In addition, the LD50 of ΔsugC in BALB/c mice was 1.47 × 108 CFU, seven times higher than that of TJS75 (LD50 = 2.15 × 107 CFU). These results illustrate that the deletion of sugC reduced the virulence of TJS75 to BALB/c mice, but its role in the adhesion and invasion of PK-15 cells in this strain needs to be further explored. In summary, this study provides evidence that the sugC gene is a virulence-related gene in the S. suis serotype 2 strain and plays a crucial role in the adhesion and invasion of S. suis. This study lays a foundation for the further exploration of the potential virulence factors and pathogenesis of S. suis.

Erythroid Differentiation Regulator 1 as a Regulator of Neuronal GSH Synthesis.

Erythroid differentiation regulator 1 (Erdr1) is a cytokine known to play important roles in cell survival under stressful conditions, maintenance of cellular growth homeostasis, and activation of the immune system. However, the impact of Erdr1 on neurons remains undefined. In this study, we present novel evidence that Erdr1 plays a role in regulating glutathione (GSH) synthesis via glutamate transporter-associated protein 3-18 (GTRAP3-18), an anchor protein in the endoplasmic reticulum that holds excitatory amino acid carrier 1 (EAAC1) in neurons. Both DNA microarray and quantitative real-time PCR analyses revealed an approximately 2-fold increase in Erdr1 levels in the hippocampus of GTRAP3-18-deficient mice compared to those of wild-type mice. Knockdown of Erdr1 in vitro resulted in a decrease in GTRAP3-18 levels, leading to an increase in EAAC1 expression and intracellular GSH levels, and subsequently, cytoprotective effects against oxidative stress. Our findings shed light on the regulatory mechanisms involving Erdr1, GTRAP3-18, EAAC1, and GSH in the context of neuronal defense against oxidative stress. Understanding the intricate interplay among these molecules may pave the way for the development of promising therapeutic strategies for neurodegenerative disorders.

The Protective Role of Glutathione on Zinc-Induced Neuron Death after Brain Injuries.

Glutathione (GSH) is necessary for maintaining physiological antioxidant function, which is responsible for maintaining free radicals derived from reactive oxygen species at low levels and is associated with improved cognitive performance after brain injury. GSH is produced by the linkage of tripeptides that consist of glutamic acid, cysteine, and glycine. The adequate supplementation of GSH has neuroprotective effects in several brain injuries such as cerebral ischemia, hypoglycemia, and traumatic brain injury. Brain injuries produce an excess of reactive oxygen species through complex biochemical cascades, which exacerbates primary neuronal damage. GSH concentrations are known to be closely correlated with the activities of certain genes such as excitatory amino acid carrier 1 (EAAC1), glutamate transporter-associated protein 3-18 (Gtrap3-18), and zinc transporter 3 (ZnT3). Following brain-injury-induced oxidative stress, EAAC1 function is negatively impacted, which then reduces cysteine absorption and impairs neuronal GSH synthesis. In these circumstances, vesicular zinc is also released into the synaptic cleft and then translocated into postsynaptic neurons. The excessive influx of zinc inhibits glutathione reductase, which inhibits GSH's antioxidant functions in neurons, resulting in neuronal damage and ultimately in the impairment of cognitive function. Therefore, in this review, we explore the overall relationship between zinc and GSH in terms of oxidative stress and neuronal cell death. Furthermore, we seek to understand how the modulation of zinc can rescue brain-insult-induced neuronal death after ischemia, hypoglycemia, and traumatic brain injury.

Hepcidin induces intestinal calcium uptake while suppressing iron uptake in Caco-2 cells.

Abnormal calcium absorption and iron overload from iron hyperabsorption can contribute to osteoporosis as found in several diseases, including hemochromatosis and thalassemia. Previous studies in thalassemic mice showed the positive effects of the iron uptake suppressor, hepcidin, on calcium transport. However, whether this effect could be replicated in other conditions is not known. Therefore, this study aimed to investigate the effects of hepcidin on iron and calcium uptake ability under physiological, iron uptake stimulation and calcium uptake suppression. To investigate the potential mechanism, effects of hepcidin on the expression of iron and calcium transporter and transport-associated protein in Caco-2 cells were also determined. Our results showed that intestinal cell iron uptake was significantly increased by ascorbic acid together with ferric ammonium citrate (FAC), but this phenomenon was suppressed by hepcidin. Interestingly, hepcidin significantly increased calcium uptake under physiological condition but not under iron uptake stimulation. While hepcidin significantly suppressed the expression of iron transporter, it had no effect on calcium transporter expression. This indicated that hepcidin-induced intestinal cell calcium uptake did not occur through the stimulation of calcium transporter expression. On the other hand, 1,25(OH)2D3 effectively induced intestinal cell calcium uptake, but it did not affect intestinal cell iron uptake or iron transporter expression. The 1,25(OH)2D3-induced intestinal cell calcium uptake was abolished by 12 mM CaCl2; however, hepcidin could not rescue intestinal cell calcium uptake suppression by CaCl2. Taken together, our results showed that hepcidin could effectively and concurrently induce intestinal cell calcium uptake while reducing intestinal cell iron uptake under physiological and iron uptake stimulation conditions, suggesting its therapeutic potential for inactive calcium absorption, particularly in thalassemic patients or patients who did not adequately respond to 1,25(OH)2D3.

Glutathione in the Brain.

Glutathione (GSH) is the most abundant non-protein thiol, and plays crucial roles in the antioxidant defense system and the maintenance of redox homeostasis in neurons. GSH depletion in the brain is a common finding in patients with neurodegenerative diseases, such as Alzheimer’s disease and Parkinson’s disease, and can cause neurodegeneration prior to disease onset. Excitatory amino acid carrier 1 (EAAC1), a sodium-dependent glutamate/cysteine transporter that is selectively present in neurons, plays a central role in the regulation of neuronal GSH production. The expression of EAAC1 is posttranslationally controlled by the glutamate transporter-associated protein 3–18 (GTRAP3-18) or miR-96-5p in neurons. The regulatory mechanism of neuronal GSH production mediated by EAAC1 may be a new target in therapeutic strategies for these neurodegenerative diseases. This review describes the regulatory mechanism of neuronal GSH production and its potential therapeutic application in the treatment of neurodegenerative diseases.

Integrated Proteomic and Transcriptomic Analyses Reveal the Roles of Brucella Homolog of BAX Inhibitor 1 in Cell Division and Membrane Homeostasis of Brucella suis S2.

BAX inhibitor 1 (BI-1) is an evolutionarily conserved transmembrane protein first identified in a screening process for human proteins that suppress BAX-induced apoptosis in yeast cells. Eukaryotic BI-1 is a cytoprotective protein that suppresses cell death induced by multiple stimuli in eukaryotes. Brucella, the causative agent of brucellosis that threatens public health and animal husbandry, contains a conserved gene that encodes BI-1-like protein. To explore the role of the Brucella homolog of BI-1, BrBI, in Brucella suis S2, we constructed the brbI deletion mutant strain and its complemented strain. brbI deletion altered the membrane properties of Brucella suis S2 and decreased its resistance to acidic pH, H2O2, polymyxin B, and lincomycin. Additionally, deleting brbI led to defective growth, cell division, and viability in Brucella suis S2. We then revealed the effect of brbI deletion on the physiological characteristics of Brucella suis S2 via integrated transcriptomic and proteomic analyses. The integrated analysis showed that brbI deletion significantly affected the expression of multiple genes at the mRNA and/or protein levels. Specifically, the affected divisome proteins, FtsB, FtsI, FtsL, and FtsQ, may be the molecular basis of the impaired cell division of the brbI mutant strain, and the extensively affected membrane proteins and transporter-associated proteins were consistent with the phenotype of the membrane properties’ alterations of the brbI mutant strain. In conclusion, our results revealed that BrBI is a bacterial cytoprotective protein involved in membrane homeostasis, cell division, and stress resistance in Brucella suis S2.

Decrease in Multidrug Resistance-associated Protein 2 Activities by Knockdown of Phosphatidylinositol 4-phosphate 5-kinase in Hepatocytes and Cancer Cells.

The plasma membrane localization and transport activity of multidrug resistance- associated protein 2 (MRP2/ABCC2) and P-glycoprotein (P-gp/ABCB1) efflux transporters are governed by transporter-associated proteins. Phosphatidylinositol 4,5-bisphosphate (PIP2) formed by phosphatidylinositol 4-phosphate 5-kinase type 1 (PIP5K1) activates the linker function of radixin for efflux transporters. Radixin is involved in the plasma membrane localization of efflux transporters. We examined whether PIP5K1 could be a target for the modulation of transporter activities in hepatocytes and cancer cells. The effects of PIP5K1 depletion by siRNA in mouse primary hepatocytes, PANC1 human pancreatic carcinoma cells, and HepG2 human hepatocellular carcinoma cells on the intracellular accumulation of MRP2 and P-gp substrates were examined. PIP5K1A depletion resulted in increased intracellular accumulation of carboxydichlorofluorescein, a MRP2 fluorescent substrate, in mouse primary hepatocytes, PANC1 cells, and HepG2 cells. In PANC1 and HepG2 cells, the transport activities of MRP2 were significantly decreased by PIP5K1C depletion. However, the transport activities of P-gp were unchanged by PIP5K1 depletion. PIP2 levels were unchanged between control and PIP5K1A- or PIP5K1C-depleted HepG2 cells. MRP2 mRNA levels showed few changes in HepG2 cells following PIP5K1A or PIP5K1C depletion. The expression of phosphorylated radixin was decreased by PIP5K1A and PIP5K1C depletion, although total radixin levels were unchanged. These data suggest that PIP5K1A and PIP5K1C could be target proteins for modulating MRP2 function, partly because of the resulting changes of the linker function of radixin.

GTRAP3‐18 regulates food intake and body weight by interacting with pro‐opiomelanocortin

Pro-opiomelanocortin (POMC)-expressing neurons provide α-melanocyte-stimulating hormone (α-MSH), which stimulates melanocortin 4 receptor to induce hypophagia by AMPK inhibition in the hypothalamus. α-MSH is produced by POMC cleavage in secretory granules and released. However, it is not known yet whether any posttranscriptional regulatory mechanism of POMC signaling exists upstream of the secretory granules in neurons. Here we show that glutamate transporter-associated protein 3-18 (GTRAP3-18), an anchor protein that retains interacting proteins in the endoplasmic reticulum, is a critical regulator of food intake and body weight by interacting with POMC. GTRAP3-18-deficient mice showed hypophagia, lean bodies, and lower blood glucose, insulin, and leptin levels with increased serum and brain α-MSH levels, leading to AMPK inhibition. Intraperitoneal glucose tolerance tests revealed significantly decreased blood glucose levels and areas under the curve in GTRAP3-18-deficient mice compared to wild-type mice. An intracerebroventricular infusion of a selective melanocortin 4 receptor antagonist to GTRAP3-18-deficient mice significantly increased their food intake and body weight. A fluorescence resonance energy transfer study showed an interaction between GTRAP3-18 and POMC in vitro These findings suggest that activation of the melanocortin pathway by modulating GTRAP3-18/POMC interaction could be an alternative strategy for obesity and/or type 2 diabetes.-Aoyama, K., Bhadhprasit, W., Watabe, M., Wang, F., Matsumura, N., Nakaki, T. GTRAP3-18 regulates food intake and body weight by interacting with pro-opiomelanocortin.

Serotonin Transporter Associated Protein Complexes Are Enriched in Synaptic Vesicle Proteins and Proteins Involved in Energy Metabolism and Ion Homeostasis.

The serotonin transporter (SERT) mediates Na+-dependent high-affinity serotonin uptake and plays a key role in regulating extracellular serotonin concentration in the brain and periphery. To gain novel insight into SERT regulation, we conducted a comprehensive proteomics screen to identify components of SERT-associated protein complexes in the brain by employing three independent approaches. In vivo SERT complexes were purified from rat brain using an immobilized high-affinity SERT ligand, amino-methyl citalopram. This approach was combined with GST pulldown and yeast two-hybrid screens using N- and C-terminal cytoplasmic transporter domains as bait. Potential SERT associated proteins detected by at least two of the interaction methods were subjected to gene ontology analysis resulting in the identification of functional protein clusters that are enriched in SERT complexes. Prominent clusters include synaptic vesicle proteins, as well as proteins involved in energy metabolism and ion homeostasis. Using subcellular fractionation and electron microscopy we provide further evidence that SERT is indeed associated with synaptic vesicle fractions, and colocalizes with small vesicular structures in axons and axon terminals. We also show that SERT is found in close proximity to mitochondrial membranes in both, hippocampal and neocortical regions. We propose a model of the SERT interactome, in which SERT is distributed between different subcellular compartments through dynamic interactions with site-specific protein complexes. Finally, our protein interaction data suggest novel hypotheses for the regulation of SERT activity and trafficking, which ultimately impact on serotonergic neurotransmission and serotonin dependent brain functions.

The copper transport-associated protein Ctr4 can form prion-like epigenetic determinants in Schizosaccharomyces pombe.

Prions are protein-based infectious entities associated with fatal brain diseases in animals, but also modify a range of host-cell phenotypes in the budding yeast, Saccharomyces cerevisiae. Many questions remain about the evolution and biology of prions. Although several functionally distinct prion-forming proteins exist in S. cerevisiae, [HET-s] of Podospora anserina is the only other known fungal prion. Here we investigated prion-like, protein-based epigenetic transmission in the fission yeast Schizosaccharomyces pombe. We show that S. pombe cells can support the formation and maintenance of the prion form of the S. cerevisiae Sup35 translation factor [PSI+], and that the formation and propagation of these Sup35 aggregates is inhibited by guanidine hydrochloride, indicating commonalities in prion propagation machineries in these evolutionary diverged yeasts. A proteome-wide screen identified the Ctr4 copper transporter subunit as a putative prion with a predicted prion-like domain. Overexpression of the ctr4 gene resulted in large Ctr4 protein aggregates that were both detergent and proteinase-K resistant. Cells carrying such [CTR+] aggregates showed increased sensitivity to oxidative stress, and this phenotype could be transmitted to aggregate-free [ctr-] cells by transformation with [CTR+] cell extracts. Moreover, this [CTR+] phenotype was inherited in a non-Mendelian manner following mating with naïve [ctr-] cells, but intriguingly the [CTR+] phenotype was not eliminated by guanidine-hydrochloride treatment. Thus, Ctr4 exhibits multiple features diagnostic of other fungal prions and is the first example of a prion in fission yeast. These findings suggest that transmissible protein-based determinants of traits may be more widespread among fungi.

Novel in silico tools for designing peptide-based subunit vaccines and immunotherapeutics.

The conventional approach for designing vaccine against a particular disease involves stimulation of the immune system using the whole pathogen responsible for the disease. In the post-genomic era, a major challenge is to identify antigenic regions or epitopes that can stimulate different arms of the immune system. In the past two decades, numerous methods and databases have been developed for designing vaccine or immunotherapy against various pathogen-causing diseases. This review describes various computational resources important for designing subunit vaccines or epitope-based immunotherapy. First, different immunological databases are described that maintain epitopes, antigens and vaccine targets. This is followed by in silico tools used for predicting linear and conformational B-cell epitopes required for activating humoral immunity. Finally, information on T-cell epitope prediction methods is provided that includes indirect methods like prediction of Major Histocompatibility Complex and transporter-associated protein binders. Different studies for validating the predicted epitopes are also examined critically. This review enlists novel in silico resources and tools available for predicting humoral and cell-mediated immune potential. These predicted epitopes could be used for designing epitope-based vaccines or immunotherapy as they may activate the adaptive immunity. Authors emphasized the need to develop tools for the prediction of adjuvants to activate innate and adaptive immune system simultaneously. In addition, attention has also been given to novel prediction methods to predict general therapeutic properties of peptides like half-life, cytotoxicity and immune toxicity.

Immune Response in Acute Myeloid Leukemia with Mutated Nucleophosmin

In our recent work, we described changes in HLA class I frequencies in AML patients with nucleophosmin (NPM) mutations. Several allelic groups were found to be depleted in patients with C-terminal NPM mutations (NPMc+), but not in patients with wild-type NPM, and these differences corresponded well to in silico prediction of NPM-derived peptides binding to HLA class I. Moreover, patients with "favorable" HLA type (i.e., expressing HLA alleles suitable for presentation of NPM-derived peptides) were found to have significantly better overall survival than those without suitable HLA alleles. Altogether, our results suggested that spontaneous anti-NPM immune response may prevent AML development and helps achieve durable cure.In this contribution, an extended patient cohort (N = 71 patients with all available data) was divided into four groups according to HLA type (favorable/unfavorable) and Flt3-ITD status. Patients expressing suitable HLA alleles and not having internal tandem duplications in Flt3 gene (HLA+/Flt3-) had the best overall survival (Figure 1). The impact of unfavorable HLA type alone was comparable to that of Flt3-ITD positivity while the combination of both adverse factors was associated with particularly poor outcome (p = 0.0066 for trend).On the basis of these results, we believe that NPMc+ AML patients with favorable HLA type (about 65% of all NPMc+ AML patients) could benefit from an immunomodulatory therapy. Besides inhibitory receptors (such as PD-1, CTLA-4, TIM-3), regulatory T-cells or decreased HLA expression, reduced antigen presentation by leukemic cells belongs to possible mechanisms of immune escape. Insufficiency of molecular complexes such as the proteasome or the transport-associated protein (TAP) can result in increased presentation of Class II-associated invariant chain peptide (CLIP). Indeed, increased CLIP expression on residual leukemic blasts has recently been reported to correlate with increased relapse risk in AML. Interestingly, valproic acid used in combination with standard chemotherapy has been described to significantly decrease the relapse rate in elderly AML patients with mutated NPM (but not in other AML subgroups). This could be associated with restored antigen presentation following treatment with histonedeacetylase inhibitors. In our experiments, we observed marked reduction of CLIP expression on primary NPMc+ AML blasts following in vitro treatment with suberoylanilide hydroxamic acid (SAHA, Figure 2). Both the fraction of CLIP-positive cells (open circles) and CLIP surface density on positive cells (closed circles) were reduced. HLA class I expression was normal and was not affected by SAHA treatment. Importantly, the effect on CLIP expression occurred even at subtoxic (0.5 µM) drug concentration. [Display omitted] [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Dendritic cell maturation in HCV infection: Altered regulation of MHC class I antigen processing-presenting machinery

Modulation of dendritic cell (DC) function has been theorized as one of the mechanisms used by hepatitis C virus (HCV) to evade the host immune response and cause persistent infection. We used a range of cell and molecular biology techniques to study DC subsets from uninfected and HCV-infected individuals. We found that patients with persistent HCV infection have lower numbers of circulating myeloid DC and plasmacytoid DC than healthy controls or patients who spontaneously recovered from HCV infection. Nonetheless, DC from patients with persistent HCV infection display normal phagocytic activity, typical expression of the class I and II HLA and co-stimulatory molecules, and conventional cytokine production when stimulated to mature in vitro. In contrast, they do not display the strong switch from immunoproteasome to standard proteasome subunit expression and the upregulation of the transporter-associated proteins following stimulation, which were instead observed in DC from uninfected individuals. This different modulation of components of the HLA class I antigen processing-presenting machinery results in a differential ability to present a CD8(+) T cell epitope whose generation is dependent on the LMP7 immunoproteasome subunit. Overall, these findings establish that under conditions of persistent HCV antigenemia, HLA class I antigen processing and presentation are distinctively regulated during DC maturation.

Identification of tomoregulin-1 as a novel addicsin-associated factor

Addicsin is a novel factor encoding a 23-kDa hydrophobic protein that is highly upregulated in the amygdala nuclei of morphine-administered mice. It is a murine homolog of human JWA and rat glutamate transporter-associated protein 3-18 (GTRAP3-18), a negative modulator of the neural glutamate transporter excitatory amino acid carrier 1 (EAAC1). Recent findings demonstrated that addicsin participates in various physiological processes by forming hetero- or homomultimeric complexes. However, the binding targets and molecular functions of addicsin remain largely unknown. To identify potential factors that associate with mouse addicsin, we performed a yeast two-hybrid screen using a 17-day-old mouse whole embryo cDNA library. We identified tomoregulin-1 (TR1) as a novel addicsin-associated factor. TR1, a type I transmembrane protein containing two follistatin-like modules and an epidermal growth factor-like domain, participates in nodal and bone morphogenetic protein signaling. Immunoprecipitation assays demonstrated that TR1 bound to addicsin, and that amino acids 145–188 of addicsin and amino acids 228–266 of TR1 were important for the formation of the addicsin-TR1 heterocomplex. The double-fluorescent immunohistochemical analysis revealed that addicsin and TR1 were coexpressed in neurons in the mature mouse brain regions tested. Moreover, TR1 showed a punctuate pattern throughout the cell, with preferential expression on the cell surface when expressed alone. However, TR1 predominantly redistributed to the endoplasmic reticulum (ER) when coexpressed with addicsin. Furthermore, coexpression of an addicsin mutant that lacked TR1 binding ability had little effect on the distribution of TR1. Biotinylation assays showed that coexpression of addicsin with TR1 suppressed the cell surface expression of TR1. Wound-healing assays demonstrated that the interaction of addicsin with TR1 had a significant effect on cell migration. These findings demonstrate that addicsin in the ER controls intracellular TR1 trafficking from the ER to plasma membrane and regulates cell migration through its interaction with TR1.

Gene mutations in cardiac arrhythmias: a review of recent evidence in ion channelopathies

Over the past 15 years, molecular genetic studies have linked gene mutations to many inherited arrhythmogenic disorders, in particular, “ion channelopathies”, in which mutations in genes encode functional units of ion channels and/or their transporter-associated proteins in patients without primary cardiac structural abnormalities. These disorders are exemplified by congenital long QT syndrome (LQTS), short QT syndrome, Brugada syndrome (BrS) and catecholaminergic polymorphic ventricular tachycardia (CPVT). Functional and pathophysiological studies have led to better understanding of the clinical spectrum, ion channel structures and cellular electrophysiology involving dynamics of intracellular calcium cycling in many subtypes of these disorders and more importantly, development of potentially more effective pharmacological agents and even curative gene therapy. In this review, we have summarized (1) the significance of unveiling mutations in genes encoding transporter-associated proteins as the cause of congenital LQTS, (2) the technique of catheter ablation applied at the right ventricular outflow tract may be curative for severely symptomatic BrS, (3) mutations with channel function modulated by protein Kinase A-dependent phosphorylation can be the culprit of CPVT mimicry in Andersen-Tawil syndrome (LQT7), (4) ablation of the ion channel anchoring protein may prevent arrhythmogenesis in Timothy syndrome (LQT8), (5) altered intracellular Ca2+ cycling can be the basis of effective targeted pharmacotherapy in CPVT, and (6) the technology of induced pluripotent stem cells is a promising diagnostic and research tool as it has become a new paradigm for pathophysiological study of patient- and disease-specific cells aimed at screening new drugs and eventual clinical application of gene therapy. Lastly, we have discussed (7) genotype-phenotype correlation in relation to risk stratification of patients with congenital LQTS in clinical practice.

Increased neuronal glutathione and neuroprotection in GTRAP3-18-deficient mice

Glutathione (GSH) is an important neuroprotective molecule in the brain. The strategy to increase neuronal GSH level is a promising approach to the treatment of neurodegenerative diseases. However, the regulatory mechanism by which neuron-specific GSH synthesis is facilitated remains elusive. Glutamate transporter-associated protein 3-18 (GTRAP3-18) is an endoplasmic reticulum protein interacting with excitatory amino acid carrier 1 (EAAC1), which is a neuronal glutamate/cysteine transporter. To investigate the potential regulatory mechanism to increase neuronal GSH level in vivo, we generated GTRAP3-18-deficient (GTRAP3-18–/–) mice using a gene-targeting approach. Disruption of the GTRAP3-18 gene resulted in increased EAAC1 expression in the plasma membrane, increased neuronal GSH content and neuroprotection against oxidative stress. In addition, GTRAP3-18–/– mice performed better in motor/spatial learning and memory tests than wild-type mice. Therefore, the suppression of GTRAP3-18 increases neuronal resistance to oxidative stress by increasing GSH content and also facilitates cognitive function. The present results may provide a molecular basis for the development of treatments for neurodegenerative diseases.

Chronic Consumption of trans-Fat-Rich Diet Increases Hepatic Cholesterol Levels and Impairs Muscle Insulin Sensitivity without Leading to Hepatic Steatosis and Hypertriglyceridemia in Female Fischer Rats

Background: The impact of industrial trans fatty acids (TFAs) on lipid metabolism and health remains elusive. Methods: We compared the effect of long-term (52 weeks) ingestion of 10% partially hydrogenated vegetable oil, providing 4.2% of total energy from TFAs, on hepatic lipid metabolism and muscle insulin sensitivity in weanling female Fischer rats with that of palmolein (monounsaturated fatty acid, MUFA), sunflower (n–6 polyunsaturated fatty acid, PUFA), and a blend of sunflower and fish oil (n–3 PUFA). Results: The proportion of plasma high-density lipoprotein cholesterol in total cholesterol and reverse cholesterol transport-associated protein expressions were similar in all the groups. Despite higher lipogenic-pathway protein levels, steatosis or hypertriglyceridemia was not observed in TFA-fed rats. Though TFA ingestion had no effect on fasting plasma glucose, insulin levels or oral glucose tolerance, it significantly decreased muscle insulin-stimulated glucose uptake as compared to PUFAs. Further, TFA ingestion increased adipose tissue retinol-binding protein 4 mRNA as compared to PUFAs (n–6 or n–3). The effects of MUFA (oleic acid) on all these parameters were comparable to those observed for TFAs. Conclusions: Compared to PUFA-rich diets, chronic consumption of a TFA-rich diet did not lead to steatosis or hypertriglyceridemia; however, it significantly impaired muscle insulin sensitivity, while no changes were found in the oral glucose tolerance test.

Refining repolarization reserve

A body of cellular and molecular studies over the past 15 years has demonstrated that the fundamental molecular lesion in the drug-induced long QT syndrome (LQTS) is block of the repolarizing potassium current IKr, the “rapid” component of the repolarizing potassium current that was initially termed IK. 1 Hodgkin A.L. Huxley A.F. A quantitative description of membrane current and its application to conduction and excitation in nerve. J Physiol (Lond). 1952; 117: 500-544 Google Scholar , 2 Sanguinetti M.C. Jurkiewicz N.K. Two components of cardiac delayed rectifier K+ current: differential sensitivity to block by class III antiarrhythmic agents. J Gen Physiol. 1990; 96: 195-215 Crossref PubMed Scopus (1337) Google Scholar Further, decreased IKr due to KCNH2 mutations causes type 2 congenital LQTS, one of the commonest forms of this disease. 3 Ackerman M.J. Mohler P.J. Defining a new paradigm for human arrhythmia syndromes: phenotypic manifestations of gene mutations in ion channel- and transporter-associated proteins. Circ Res. 2010; 107: 457-465 Crossref PubMed Scopus (57) Google Scholar Both the congenital and drug-associated form of LQTS present with QT interval prolongation and torsades de pointes, and a striking clinical feature in both is the highly variable nature of the phenotype: not every patient exposed to IKr-blockers develops QT prolongation, let alone exaggerated QT prolongation and arrhythmias, and not every patient with a loss-of-function mutation in KCNH2 displays QT interval prolongation. It was this clinical disconnect and the increasing recognition that normal repolarization represents a complex interaction among multiple components that led in the late 1990s to the formulation of the idea of “repolarization reserve.” 4 Roden D.M. Taking the idio out of idiosyncratic—predicting torsades de pointes. PACE. 1998; 21: 1029-1034 Crossref Scopus (585) Google Scholar Recognizing that repolarization is accomplished not just by IK and ICa but by IKr, IKs, ICa-L, ICa-T, INa-L, INCX, and so on, the concept suggests that a reduction in IKr might generate a huge effect in cells, or in patients, in whom other efficient repolarization mechanisms were absent. By contrast, the same reduction in IKr might produce little change in repolarization time in settings in which other mechanisms could readily accomplish normal repolarization. The idea seems appealing, since a PubMed search identifies 209 references to “repolarization reserve” and a Google Scholar search identifies “about 5,480” hits. The term may have acquired some currency because the idea makes intuitive sense to basic and clinical electrophysiologists or perhaps because it has a nice alliterative ring. Quantification of repolarization reserve to understand interpatient variability in the response to proarrhythmic drugs: A computational analysisHeart RhythmVol. 8Issue 11Preview“Repolarization reserve” is frequently invoked to explain why potentially proarrhythmic drugs cause, across a population, a range of changes to cardiac action potentials (APs). However, the mechanisms underlying this interindividual variability are not understood quantitatively. Full-Text PDF

Monocarboxylate transporters 1 and 4 are involved in the invasion activity of human lung cancer cells

Cancer cells show constitutive upregulation of glycolysis, and the concentration of lactate thus produced correlates with prognosis. Here, we examined whether lactate concentration and lactate transporter expression are related to migration and invasion activity. We found that the expression of the monocarboxylate transporters MCT1 and MCT4, but not MCT5, in human lung cancer cell lines was significantly correlated with invasiveness. To clarify the effects of MCT1 and MCT4 expression on invasion, we performed migration and invasion assays after transfection with siRNA specific for MCT1 or MCT4. Knockdown of MCT1 or MCT4 did not influence cell migration but reduced invasion; this was also observed for knockdown of the lactate transporter-associated protein basigin. We also demonstrated that both expression and activity of MMP9 and MMP2 were not correlated with invasion activity and not regulated by MCT1, MCT4 and basigin. Furthermore, the addition of lactate did not increase migration and invasion activity, but low concentration of 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS), a general anion channel blocker, as well as other MCT inhibitors quercetin and simvastatin, inhibited cell invasion without influencing migration activity and the cellular expression of MCT1 and MCT4. This is the first report suggesting that lactate transporters are involved in human cancer cell invasiveness. As such, these proteins may be promising targets for the prevention of cancer invasion and metastasis.

Modulation of neuronal glutathione synthesis by EAAC1 and its interacting protein GTRAP3-18

Glutathione (GSH) plays essential roles in different processes such as antioxidant defenses, cell signaling, cell proliferation, and apoptosis in the central nervous system. GSH is a tripeptide composed of glutamate, cysteine, and glycine. The concentration of cysteine in neurons is much lower than that of glutamate or glycine, so that cysteine is the rate-limiting substrate for neuronal GSH synthesis. Most neuronal cysteine uptake is mediated through the neuronal sodium-dependent glutamate transporter, known as excitatory amino acid carrier 1 (EAAC1). Glutamate transporters are vulnerable to oxidative stress and EAAC1 dysfunction impairs neuronal GSH synthesis by reducing cysteine uptake. This may start a vicious circle leading to neurodegeneration. Intracellular signaling molecules functionally regulate EAAC1. Glutamate transporter-associated protein 3-18 (GTRAP3-18) activation down-regulates EAAC1 function. Here, we focused on the interaction between EAAC1 and GTRAP3-18 at the plasma membrane to investigate their effects on neuronal GSH synthesis. Increased level of GTRAP3-18 protein induced a decrease in GSH level and, thereby, increased the vulnerability to oxidative stress, while decreased level of GTRAP3-18 protein induced an increase in GSH level in vitro. We also confirmed these results in vivo. Our studies demonstrate that GTRAP3-18 regulates neuronal GSH level by controlling the EAAC1-mediated uptake of cysteine.