Gain-of-function mutations of c-kit in human gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors in the human digestive tract, but their molecular etiology and cellular origin are unknown. Sequencing of c-kit complementary DNA, which encodes a proto-oncogenic receptor tyrosine kinase (KIT), from five GISTs revealed mutations in the region between the transmembrane and tyrosine kinase domains. All of the corresponding mutant KIT proteins were constitutively activated without the KIT ligand, stem cell factor (SCF). Stable transfection of the mutant c-kit complementary DNAs induced malignant transformation of Ba/F3 murine lymphoid cells, suggesting that the mutations contribute to tumor development. GISTs may originate from the interstitial cells of Cajal (ICCs) because the development of ICCs is dependent on the SCF-KIT interaction and because, like GISTs, these cells express both KIT and CD34.

Molecular anatomy of a trafficking organelle

Membrane traffic in eukaryotic cells involves transport of vesicles that bud from a donor compartment and fuse with an acceptor compartment. Common principles of budding and fusion have emerged, and many of the proteins involved in these events are now known. However, a detailed picture of an entire trafficking organelle is not yet available. Using synaptic vesicles as a model, we have now determined the protein and lipid composition; measured vesicle size, density, and mass; calculated the average protein and lipid mass per vesicle; and determined the copy number of more than a dozen major constituents. A model has been constructed that integrates all quantitative data and includes structural models of abundant proteins. Synaptic vesicles are dominated by proteins, possess a surprising diversity of trafficking proteins, and, with the exception of the V-ATPase that is present in only one to two copies, contain numerous copies of proteins essential for membrane traffic and neurotransmitter uptake.

Bafilomycin A1 prevents maturation of autophagic vacuoles by inhibiting fusion between autophagosomes and lysosomes in rat hepatoma cell line, H-4-II-E cells

We studied the effects of bafilomycin A1, a potent and specific inhibitor of vacuolar H+ ATPase (V-ATPase), on the process of autophagy in rat hepatoma cell line, H-4-II-E cells. To induce autophagy, cells were transferred from Dulbecco's modified Eagle medium containing 12% fetal calf serum into Hanks' balanced salt solution. When bafilomycin A1 was added to Hanks' balanced salt solution, endogenous protein degradation was strongly inhibited and numerous autophagosomes accumulated in H-4-II-E cells, whereas autolysosomes decreased in number. Acid phosphatase activity was not detected in the autophagosomes which accumulated in the presence of bafilomycin A1, suggesting that fusion between autophagosomes and lysosomes was disturbed by this drug. Inhibition of the fusion was reversible, and the autophagosomes changed into autolysosomes after the removal of the inhibitor. Bafilomycin A1 also prevented the appearance of endocytosed HRP in autophagic vacuoles. These results suggested that acidification of the lumenal space of autophagosomes or lysosomes by V-ATPase is important for the fusion between autophagosomes and lysosomes.

A human transporter protein that mediates the final excretion step for toxic organic cations

In mammals, toxic electrolytes of endogenous and exogenous origin are excreted through the urine and bile. Before excretion, these compounds cross numerous cellular membranes in a transporter-mediated manner. However, the protein transporters involved in the final excretion step are poorly understood. Here, we show that MATE1, a human and mouse orthologue of the multidrug and toxin extrusion family conferring multidrug resistance on bacteria, is primarily expressed in the kidney and liver, where it is localized to the luminal membranes of the urinary tubules and bile canaliculi. When expressed in HEK293 cells, MATE1 mediates H(+)-coupled electroneutral exchange of tetraethylammonium and 1-methyl-4-phenylpyridinium. Its substrate specificity is similar to those of renal and hepatic H(+)-coupled organic cations (OCs) export. Thus, MATE1 appears to be the long searched for polyspecific OC exporter that directly transports toxic OCs into urine and bile.

The MATE proteins as fundamental transporters of metabolic and xenobiotic organic cations

Multidrug and toxic compound extrusion (MATE) proteins, comprising the most recently designated family of multidrug transporter proteins, are widely distributed in all kingdoms of living organisms, although their function is far from understood. The bacterial MATE-type transporters that have been characterized function as exporters of cationic drugs, such as norfloxacin and ethidium, through H(+) or Na(+) exchange. Plant MATE-type transporters are involved in the detoxification of secondary metabolites, including alkaloids. Mammalian MATE-type transporters are responsible for the final step in the excretion of metabolic waste and xenobiotic organic cations in the kidney and liver through electroneutral exchange of H(+). Thus, we propose that members of the MATE family are organic cation exporters that excrete metabolic or xenobiotic organic cations from the body.

Metabolic control of vesicular glutamate transport and release

Fasting has been used to control epilepsy since antiquity, but the mechanism of coupling between metabolic state and excitatory neurotransmission remains unknown. Previous work has shown that the vesicular glutamate transporters (VGLUTs) required for exocytotic release of glutamate undergo an unusual form of regulation by Cl(-). Using functional reconstitution of the purified VGLUTs into proteoliposomes, we now show that Cl(-) acts as an allosteric activator, and the ketone bodies that increase with fasting inhibit glutamate release by competing with Cl(-) at the site of allosteric regulation. Consistent with these observations, acetoacetate reduced quantal size at hippocampal synapses and suppresses glutamate release and seizures evoked with 4-aminopyridine in the brain. The results indicate an unsuspected link between metabolic state and excitatory neurotransmission through anion-dependent regulation of VGLUT activity.

Identification and characterization of a proton pump on lysosomes by fluorescein-isothiocyanate-dextran fluorescence

Fluorescein isothiocyanate-conjugated dextran was introduced preferentially into hepatic lysosomes by intraperitoneal injection into rats. The pH in isolated lysosomes, measured by fluorescein fluorescence, was approximately 5 and gradually increased in KCl (to 7.0) at 25 degrees C. In the presence of Mg2+, ATP caused acidification of lysosomes that was reversed by the protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone. Mn2+, Co2+, and Fe2+ could replace Mg2+ but Ca2+ could not. Cu2+, Zn2+, and Cd2+ were inhibitory. A membrane-permeant anion, in practice chloride, was required for this acidification. ATP analogues, including 5'-adenylyl imidodiphosphate, could not be substituted for ATP. ATP-driven acidification was sensitive to N-ethylmaleimide and quercetin but insensitive to oligomycin, ouabain, and vanadate. There were some differences between "normal" lysosomes and tritosomes; the acidification was resistant to azide and N,N'-dicyclohexylcarbodiimide in normal lysosomes but sensitive to these reagents in tritosomes. These results provide evidence for the presence of an electrogenic proton pump driven by MgATP (H+-ATPase) on lysosomes.

cDNA sequence encoding the 16-kDa proteolipid of chromaffin granules implies gene duplication in the evolution of H+-ATPases

Vacuolar H+-ATPases function in generating protonmotive force across the membranes of organelles connected with the vacuolar system of eukaryotic cells. This family of H+-ATPases is distinct from the two other families of H+-ATPases, the plasma membrane-type and the eubacterial-type. One of the subunits of the vacuolar H+-ATPase binds N,N'-dicyclohexylcarbodiimide (DCCD) and has been implicated in the proton-conducting activity of these enzymes. We have cloned and sequenced the gene encoding the DCCD-binding protein (proteolipid) of the H+-ATPase of bovine chromaffin granules. The gene encodes a highly hydrophobic protein of 15,849 Da. Hydropathy plots revealed four transmembrane segments, one of which contains a glutamic residue that is the likely candidate for the DCCD binding site. Sequence homology with the vacuolar proteolipid and with the proteolipids of eubacterial-type H+-ATPases was detected. The proteolipids from Escherichia coli, spinach chloroplasts, and yeast mitochondria matched better to the NH2-terminal part of the vacuolar protein. The proteolipids of bovine mitochondria and Neurospora mitochondria matched better to the COOH-terminal end of the vacuolar proteolipid. These findings suggest that the proteolipids of the vacuolar H+-ATPases were evolved in parallel with the eubacterial proteolipid, from a common ancestral gene that underwent gene duplication.

Fluorescence behavior of tryptophan residues of bovine and human serum albumins in ionic surfactant solutions: a comparative study of the two and one tryptophan(s) of bovine and human albumins

The fluorescence behavior of two tryptophans (Trp-134, Trp-213) in bovine serum albumin (BSA) and a single tryptophan (Trp-214) in human serum albumin (HSA) was examined. The maximum emission wavelength (lambda max) was 340.0 nm for both proteins. In a solution of sodium dodecyl sulfate (SDS), the lambda max of BSA abruptly shifted to 332 nm at 1 mM SDS and then reversed to 334 nm at 3 mM SDS. The lambda max of HSA gradually shifted to 330 nm below 3 mM SDS, although it returned to 338 nm at 10 mM SDS. In contrast to this, in a solution of dodecltrimethylammonium bromide, the lambda max positions of BSA and HSA gradually shifted to 334.0 and 331.5 nm, respectively. Differences in the fluorescence behavior of the proteins are attributed to the fact that Trp-134 exists only in BSA, with the assumption that Trp-213 of BSA behaves the same as Trp-214 of HSA. The Trp-134 behavior appears to relate to the disruption of the helical structure in the SDS solution.

Genetic cholesteryl ester transfer protein deficiency caused by two prevalent mutations as a major determinant of increased levels of high density lipoprotein cholesterol

Genetic determinants of HDL cholesterol (HDL-C) levels in the general population are poorly understood. We previously described plasma cholesteryl ester transfer protein (CETP) deficiency due to an intron 14 G(+1)-to-A mutation(Int14 A) in several families with very high HDL-C levels in Japan. Subjects with HDL-C > or = 100 mg/dl (n = 130) were screened by PCR single strand conformational polymorphism analysis of the CETP gene. Two other mutations were identified by DNA sequencing or primer-mediated restriction map modification of PCR products: a novel intron 14 splice donor site mutation caused by a T insertion at position +3 from the exon14/intron14 boundary (Int14 T) and a missense mutation (Asp442 to Gly) within exon 15 (D442G). The Int14 T mutation was only found in one family. However, the D442G and Int14 A mutations were highly prevalent in subjects with HDL-C > or = 60 mg/dl, with combined allele frequencies of 9%, 12%, 21% and 43% for HDL-C 60-79, 80-99, 100-119, and > or = 120 mg/dl, respectively. Furthermore, prevalences of the D442G and Int14 A mutations were extremely high in a general sample of Japanese men (n = 236), with heterozygote frequencies of 7% and 2%, respectively. These two mutations accounted for about 10% of the total variance of HDL-C in this population. The phenotype in a genetic compound heterozygote (Int14 T and Int14 A) was similar to that of Int14 A homozygotes (no detectable CETP and markedly increased HDL-C), indicating that the Int14 T produces a null allele. In four D442G homozygotes, mean HDL-C levels (86 +/- 26 mg/dl) were lower than in Int14 A homozygotes (158 +/- 35 mg/dl), reflecting residual CETP activity in plasma. In 47 D442G heterozygotes, mean HDL-C levels were 91 +/- 23 mg/dl, similar to the level in D442G homozygotes, and significantly greater than mean HDL-C levels in Int14 A heterozygotes (69 +/- 15 mg/dl). Thus, the D442G mutation acts differently to the null mutations with weaker effects on HDL in the homozygous state and stronger effects in the heterozygotes, suggesting dominant expression of a partially defective allele. CETP deficiency, reflecting two prevalent mutations (D442G and Int14 A), is the first example of a genetic deficiency state which is sufficiently common to explain a significant fraction of the variation in HDL-C in the general population.

Vacuolar transport of nicotine is mediated by a multidrug and toxic compound extrusion (MATE) transporter in Nicotiana tabacum

Alkaloids play a key role in plant defense mechanisms against pathogens and herbivores, but the plants themselves need to cope with their toxicity as well. The major alkaloid of the Nicotiana species, nicotine, is translocated via xylem transport from the root tissues where it is biosynthesized to the accumulation sites, the vacuoles of leaves. To unravel the molecular mechanisms behind this membrane transport, we characterized one transporter, the tobacco (Nicotiana tabacum) jasmonate-inducible alkaloid transporter 1 (Nt-JAT1), whose expression was coregulated with that of nicotine biosynthetic genes in methyl jasmonate-treated tobacco cells. Nt-JAT1, belonging to the family of multidrug and toxic compound extrusion transporters, was expressed in roots, stems, and leaves, and localized in the tonoplast of leaf cells. When produced in yeast cells, Nt-JAT1 occurred mainly in the plasma membrane and showed nicotine efflux activity. Biochemical analysis with proteoliposomes reconstituted with purified Nt-JAT1 and bacterial F(0)F(1)-ATPase revealed that Nt-JAT1 functioned as a proton antiporter and recognized endogenous tobacco alkaloids, such as nicotine and anabasine, and other alkaloids, such as hyoscyamine and berberine, but not flavonoids. These findings strongly suggest that Nt-JAT1 plays an important role in the nicotine translocation by acting as a secondary transporter responsible for unloading of alkaloids in the aerial parts and deposition in the vacuoles.

Circulating levels of secretory type II phospholipase A(2) predict coronary events in patients with coronary artery disease

Background-The circulating levels of secretory nonpancreatic type II phospholipase A(2) (sPLA(2)) are increased in various chronic inflammatory diseases and the increase in the levels correlates with the disease severity. sPLA(2) may possibly play a role in atherogenesis and is highly expressed in atherosclerotic arterial walls that are known to have inflammatory features. Thus, this study prospectively examined whether circulating levels of sPLA(2) may have a significant risk and prognostic values in patients with coronary artery disease (CAD). Methods and Results-Plasma levels of sPLA(2) were measured in 142 patients with CAD and in 93 control subjects by a radioimmunoassay. The sPLA(2) levels had a significant and positive relations with serum levels of C-reactive protein, a marker of systemic inflammation, and with the number of the traditional coronary risk factors associated with individuals. Multivariate logistic regression analysis showed that higher levels of sPLA(2) (>246 ng/dL; 75th percentile of sPLA(2) distribution in controls) were a significant and independent risk factor for the presence of CAD. In multivariate Cox hazard analysis, the higher levels of sPLA(2) were a significant predictor of developing coronary events (ie, coronary revascularization, myocardial infarction, coronary death) during a 2-year follow-up period in patients with CAD independent of other risk factors, including CRP levels, an established inflammatory predictor. Conclusions-The increase in circulating levels of sPLA(2) is a significant risk factor for the presence of CAD and predicts clinical coronary events independent of other risk factors in patients with CAD; these results may reflect possible relation of sPLA(2) levels with inflammatory activity in atherosclerotic arteries.

Effects of CYP2C19 genotypic differences in the metabolism of omeprazole and rabeprazole on intragastric pH

BACKGROUND

Omeprazole is mainly metabolized in the liver by CYP2C19, a genetically determined enzyme, whereas rabeprazole is mainly reduced non-enzymatically and partially metabolized by CYP2C19. The therapeutic effects of rabeprazole are therefore assumed to be less affected by an individual's CYP2C19 status.

AIM

To investigate the acid inhibitory effects and plasma levels of omeprazole and rabeprazole with reference to different CYP2C19 genotypes.

METHODS

Fifteen healthy volunteers took a daily dose of 20 mg of omeprazole or rabeprazole for 8 days. On post-dose days 1 and 8, 24-h profiles of intragastric pH were recorded and plasma concentrations of omeprazole, rabeprazole and their metabolites were determined.

RESULTS

After single and repeated doses of omeprazole, the intragastric pH values and plasma concentrations of omeprazole and its metabolites were significantly dependent on the CYP2C19 genotype. Significant differences in the same kinetic and dynamic parameters were also observed after single doses of rabeprazole. Although the plasma levels of rabeprazole differed among the different CYP2C19 genotype groups after repeated doses, no significant differences in intragastric pH values were observed.

CONCLUSIONS

The acid inhibitory effects of omeprazole and rabeprazole are significantly dependent on the CYP2C19 genotype status, as well as on their intrinsic pharmacokinetic and pharmacodynamic characteristics and dosing schemes.

A low prevalence of coronary heart disease among subjects with increased high-density lipoprotein cholesterol levels, including those with plasma cholesteryl ester transfer protein deficiency

BACKGROUND

Use of genetic analysis may improve the predictive value of risk factors for disease. A high plasma level of high-density lipoprotein (HDL) cholesterol is a strong negative risk factor for coronary heart disease (CHD). Cholesteryl ester transfer protein (CETP) deficiency causes increased levels of HDL cholesterol. However, recent studies suggest that CETP deficiency is a risk factor for CHD despite elevated HDL cholesterol levels.

METHODS

Plasma lipid levels, CHD prevalence, resting electrocardiograms, and common CETP gene mutations were analyzed cross-sectionally in a population of 19,044 male and 29,487 female Japanese subjects (ages 45-79 years).

RESULTS

High HDL cholesterol levels (serum HDL cholesterol >/=80 mg/dl, >/=95th percentile) were found in 6 and 5% of Japanese men and women, respectively. In the group with HDL cholesterol >/=80 mg/dl, common CETP gene mutations were identified in 23-24% of men and 31-49% of women. The prevalence of CHD in the group with high HDL cholesterol (>/=80 mg/dl) was low among both men (1.0%) and women (1.3%). There was no difference in CHD prevalence between hyper-HDL-cholesterolemic subjects with and without CETP mutations.

CONCLUSIONS

Subjects with very high HDL levels (HDL cholesterol >/=80 mg/dl) as well as mild-to-moderate HDL elevations (60-79 mg/dl) appear to be protected against CHD, whether or not they have CETP deficiency, a genetic cause of elevated HDL.

Microglia release ATP by exocytosis

Microglia survey the brain environment by sensing several types of diffusible molecules, among which extracellular nucleotides released/leaked from damaged cells have central roles. Microglia sense ATP or other nucleotides by multiple P2 receptors, after which they change into several different phenotypes. However, so far, it is largely unknown whether microglia themselves release ATP and, if so, by what mechanism. Here we show that exocytosis is the mechanism by which microglia release ATP. When we stimulated microglia with ionomycin, they released ATP and the release was dependent on Ca²⁺, vesicular H⁺-ATPase, or SNAREs but independent of connexin/pannexin hemichannels. VNUT was found to be expressed in microglia and exhibited no colocalization with lysosome. We also visualized the exocytosis of ATP by a quinacrine-based fluorescent time-lapse imaging. Moreover, we found that lipopolysaccharide increased the ionomycin-induced release of ATP, which was dependent on the increase in VNUT. Taken together, our data suggested that exocytosis is the mechanism of ATP release from microglia. When activated, they would release ATP by increasing VNUT-dependent exocytotic mechanisms.

AtPHT4;4 is a chloroplast-localized ascorbate transporter in Arabidopsis

Ascorbate is an antioxidant and coenzyme for various metabolic reactions in vivo. In plant chloroplasts, high ascorbate levels are required to overcome photoinhibition caused by strong light. However, ascorbate is synthesized in the mitochondria and the molecular mechanisms underlying ascorbate transport into chloroplasts are unknown. Here we show that AtPHT4;4, a member of the phosphate transporter 4 family of Arabidopsis thaliana, functions as an ascorbate transporter. In vitro analysis shows that proteoliposomes containing the purified AtPHT4;4 protein exhibit membrane potential- and Cl⁻-dependent ascorbate uptake. The AtPHT4;4 protein is abundantly expressed in the chloroplast envelope membrane. Knockout of AtPHT4;4 results in decreased levels of the reduced form of ascorbate in the leaves and the heat dissipation process of excessive energy during photosynthesis is compromised. Taken together, these observations indicate that the AtPHT4;4 protein is an ascorbate transporter at the chloroplast envelope membrane, which may be required for tolerance to strong light stress.

In plants, ascorbate is synthesized in the mitochondria yet plays essential roles as an antioxidant in the chloroplast. Here, Miyaji et al. show that AtPHT4;4 is a chloroplast envelope ascorbate transporter and suggest it is required for dissipation of excess energy under light stress.

Vitamin E administration improves impairment of endothelium-dependent vasodilation in patients with coronary spastic angina

OBJECTIVES

We examined the effects of oral administration of vitamin E, an antioxidant, on endothelium-dependent vasodilation in patients with coronary spastic angina.

BACKGROUND

We have recently reported that endothelium-dependent vasodilation is impaired in patients with coronary spastic angina (CSA). Furthermore, it is known that oxidative stress may play an important role in the impairment of endothelium-dependent vasodilation in cardiovascular diseases.

METHODS

With the ultrasound technique, flow-dependent vasodilation of the brachial arteries during reactive hyperemia was examined before and after treatment for a month with either oral administration of vitamin E (alpha-tocopherol acetate, 300 mg/day) or placebo, which is randomly assigned, in patients with CSA (n=60).

RESULTS

Before treatment, patients with CSA had impaired flow-dependent vasodilation, lower plasma levels of alpha-tocopherol and higher plasma levels of thiobarbituric acid reactive substances (TBARS), as compared with age- and sex-matched control subjects (n=60) (flow-dependent vasodilation: 3.1+/-1.8 vs. 7.1+/-2.5%, p < 0.001; alpha-tocopherol levels: 8.9+/-1.8 vs. 10.8+/-1.8 microg/ml, p < 0.001). In patients with CSA, treatment with vitamin E restored flow-dependent vasodilation (3.1+/-1.7 vs. 8.3+/-2.0%, p < 0.001), and this improvement was associated with the decreases in plasma TBARS levels and anginal attacks.

CONCLUSIONS

The results indicate that vitamin E treatment improved endothelium-dependent vasodilation and decreased plasma TBARS levels in patients with CSA. Thus, increased oxidative stress may contribute to endothelial dysfunction and anginal attacks in patients with CSA.

Human sodium phosphate transporter 4 (hNPT4/SLC17A3) as a common renal secretory pathway for drugs and urate

The evolutionary loss of hepatic urate oxidase (uricase) has resulted in humans with elevated serum uric acid (urate). Uricase loss may have been beneficial to early primate survival. However, an elevated serum urate has predisposed man to hyperuricemia, a metabolic disturbance leading to gout, hypertension, and various cardiovascular diseases. Human serum urate levels are largely determined by urate reabsorption and secretion in the kidney. Renal urate reabsorption is controlled via two proximal tubular urate transporters: apical URAT1 (SLC22A12) and basolateral URATv1/GLUT9 (SLC2A9). In contrast, the molecular mechanism(s) for renal urate secretion remain unknown. In this report, we demonstrate that an orphan transporter hNPT4 (human sodium phosphate transporter 4; SLC17A3) was a multispecific organic anion efflux transporter expressed in the kidneys and liver. hNPT4 was localized at the apical side of renal tubules and functioned as a voltage-driven urate transporter. Furthermore, loop diuretics, such as furosemide and bumetanide, substantially interacted with hNPT4. Thus, this protein is likely to act as a common secretion route for both drugs and may play an important role in diuretics-induced hyperuricemia. The in vivo role of hNPT4 was suggested by two hyperuricemia patients with missense mutations in SLC17A3. These mutated versions of hNPT4 exhibited reduced urate efflux when they were expressed in Xenopus oocytes. Our findings will complete a model of urate secretion in the renal tubular cell, where intracellular urate taken up via OAT1 and/or OAT3 from the blood exits from the cell into the lumen via hNPT4.

Conformational change of bovine serum albumin by heat treatment

The thermal denaturation of bovine serum albumin (BSA) was studied at pH 2.8 and 7.0 in the range of 2-65 degrees C. The relative proportions of alpha-helix, beta-structure, and disordered structure in the protein conformation were determined as a function of temperature, by the curve-fitting method of circular dichroism spectra. With the rise of temperature at pH 7.0, the proportion of alpha-helix decreased above 30 degrees C and those of beta-structure and disordered structure increased in the same temperature range. The structural change was reversible in the temperature range below 45 degrees C. However, the structural change was partially reversible upon cooling to room temperature subsequent to heating at 65 degrees C. On the other hand, the structural change of BSA at pH 2.8 was completely reversible in the temperature range of 2-65 degrees C, probably because the interactions between domains and between subdomains might disappear due to the acid expansion. The secondary structure of disulfide bridges-cleaved BSA remained unchanged during the heat treatment up to 65 degrees C at pH 2.8 and 7.0.

Potent and specific inhibition of mMate1-mediated efflux of type I organic cations in the liver and kidney by pyrimethamine

This report describes a potent and selective inhibitor of multidrug and toxin extrusion (MATE) protein, pyrimethamine (PYR), and examines its effect on the urinary and biliary excretion of typical Mate1 substrates in mice. In vitro inhibition studies demonstrated that PYR is a potent inhibitor of mouse (m)Mate1 (K(i) = 145 nM) among renal organic cation transporters mOctn1 and mOctn2 (K(i) > 30 microM), mOct1 (K(i) = 3.6 microM), and mOct2 (K(i) = 6.0 microM). PYR inhibited the uptake of metformin by kidney brush-border membrane vesicles (BBMVs) (K(i) = 41 nM) and canalicular membrane vesicles in the presence of outward gradient of H+. PYR treatment significantly increased the kidney-to-plasma ratio of tetraethylammonium, and both the liver- and kidney-to-plasma ratios of metformin in mice, whereas it did not affect their plasma concentrations and urinary excretion rates. Furthermore, the plasma lactate concentration, a biomarker for inhibition of gluconeogenesis by metformin, was significantly higher in the PYR-treated group than in the control group. These results not only suggest the importance of mMate1 in the efflux of organic cations into the urine and bile in mice but also the importance of canalicular efflux mediated by MATE proteins for the therapeutic efficacy of metformin. PYR is a potent inhibitor of human (h)MATE1 and hMATE2-K (K(i) = 77 and 46 nM, respectively) and H+ and organic cation exchanger in human kidney BBMVs (K(i) = 31 nM) in the presence of outward gradient of H+. Taken together, PYR can be used as a potent probe inhibitor of human MATE transporters.

Phase III study comparing tacrolimus (FK506) with cyclosporine for graft-versus-host disease prophylaxis after allogeneic bone marrow transplantation

We report the results of a phase III trial comparing tacrolimus (FK506) with cyclosporine for GVHD prophylaxis after allogeneic BMT. From February 1995 to July 1996, 136 patients were enrolled and followed up to September 1997. During the first 100 days post-transplant the incidence of grade II-IV acute GVHD (the primary end-point) was lower in the tacrolimus group (17.5%) compared with the cyclosporine group (48.0%, P < 0.0001). A significant difference was observed between the tacrolimus and cyclosporine groups when subset analyses were performed based on recipients from HLA-matched siblings (13.3% vs 41.3%, P = 0.015) or donors other than HLA-matched siblings (21.4% vs 53.8%, P= 0.0029). The incidence of chronic GVHD (47.3% and 47.8%) and Kaplan-Meier estimate of overall survival (62.9% and 65.2%) were similar between the tacrolimus and cyclosporine groups, respectively. The overall leukemia relapse rate was not significantly different between the tacrolimus and cyclosporine groups (19.6% and 11.4%, respectively). However, the relapse rate among recipients from HLA-matched siblings was significantly higher in the tacrolimus group (30.9%) compared with the cyclosporine group (3.6%, P = 0.013). These results suggest the merit of tacrolimus for the prophylaxis of acute GVHD, but a lack of merit for a graft-versus-leukemia effect among recipients from HLA-matched sibling donors.

Luminal acidification of diverse organelles by V-ATPase in animal cells

Eukaryotic cells contain organelles bounded by a single membrane in the cytoplasm. These organelles have differentiated to carry out various functions in the pathways of endocytosis and exocytosis. Their lumina are acidic, with pH ranging from 4.5 to 6.5. This article describes recent studies on these animal cell organelles focusing on (1) the primary proton pump (vacuolar-type H(+)-ATPase) and (2) the functions of the organelle luminal acidity. We also discuss similarities and differences between vacuolar-type H(+)-ATPase and F-type ATPase. Our own studies and interests are emphasized.

Secretory granule-mediated co-secretion of L-glutamate and glucagon triggers glutamatergic signal transmission in islets of Langerhans

L-Glutamate is believed to function as an intercellular transmitter in the islets of Langerhans. However, critical issues, i.e. where, when and how L-glutamate appears, and what happens upon stimulation of glutamate receptors in the islets, remain unresolved. Vesicular glutamate transporter 2 (VGLUT2), an isoform of the vesicular glutamate transporter essential for neuronal storage of L-glutamate, is expressed in alpha cells (Hayashi, M., Otsuka, M., Morimoto, R., Hirota, S., Yatsushiro, S., Takeda, J., Yamamoto, A., and Moriyama, Y. (2001) J. Biol. Chem. 276, 43400-43406). Here we show that VGLUT2 is specifically localized in glucagon-containing secretory granules but not in synaptic-like microvesicles in alpha TC6 cells, clonal alpha cells, and islet alpha cells. VGLUT1, another VGLUT isoform, is also expressed and localized in secretory granules in alpha cells. Low glucose conditions triggered co-secretion of stoichiometric amounts of L-glutamate and glucagon from alpha TC6 cells and isolated islets, which is dependent on temperature and Ca(2+) and inhibited by phentolamine. Similar co-secretion of L-glutamate and glucagon from islets was observed upon stimulation of beta-adrenergic receptors with isoproterenol. Under low glucose conditions, stimulation of glutamate receptors facilitates secretion of gamma-aminobutyric acid from MIN6 m9, clonal beta cells, and isolated islets. These results indicate that co-secretion of L-glutamate and glucagon from alpha cells under low glucose conditions triggers GABA secretion from beta cells and defines the mode of action of L-glutamate as a regulatory molecule for the endocrine function. To our knowledge, this is the first example of secretory granule-mediated glutamatergic signal transmission.