ß subunit affects Na+ and K+ affinities of Na+/K+-ATPase: Na+ and K+ affinities of a hybrid Na+/K+-ATPase composed of insect α and mammalian ß subunits.

The affinity for K+ of silkworm Na+/K+-ATPase, which is composed of α and ß subunits, is remarkably lower than that of mammalian Na+/K+-ATPase, with a slightly higher affinity for Na+. Because the α subunit had more than 70% identity to the mammalian α subunit in the amino acid sequence, whereas the ß subunit, a glycosylated protein, had less than 30% identity to the mammalian ß subunit, it was suggested that the ß subunit was involved in the affinities for Na+ and K+ of Na+/K+-ATPase. To confirm this hypothesis, we examined whether replacing the silkworm ß subunit with the mammalian ß subunit affected the affinities for Na+ and K+ of Na+/K+-ATPase. Cloned silkworm α and cloned rat ß1 were co-expressed in BM-N cells, a cultured silkworm ovary-derived cell lacking endogenous Na+/K+-ATPase, to construct a hybrid Na+/K+-ATPase, in which the silkworm ß subunit was replaced with the rat ß1 subunit. The hybrid Na+/K+-ATPase increased the affinity for K+ by 4.1-fold and for Na+ by 0.65-fold compared to the wild-type one. Deglycosylation of the silkworm ß subunit did not affect the K+ affinity. These results support the involvement of the ß subunit in the Na+ and K+ affinities of Na+/K+-ATPase.

Helicobacter pylori induces somatic mutations in TP53 via overexpression of CHAC1 in infected gastric epithelial cells.

Infection with Helicobacter pylori is known to decrease the level of glutathione in gastric epithelial cells and increase the production of reactive oxygen species (ROS), which can lead to DNA damage and the development of gastric cancer. Cation transport regulator 1 (CHAC1) has γ-glutamylcyclotransferase activity that degrades glutathione. We found that cagA-positive H. pylori infection triggered CHAC1 overexpression in human gastric epithelial (AGS) cells leading to glutathione degradation and the accumulation of ROS. Nucleotide alterations in the TP53 tumour suppressor gene were induced in AGS cells overexpressing CHAC1, whereas no mutations were detected in cells overexpressing a catalytically inactive mutant of CHAC1. A high frequency of TP53 mutations occurred in H. pylori-infected AGS cells, but this was prevented in cells transfected with CHAC1 siRNA. These findings indicate that H. pylori-mediated CHAC1 overexpression degrades intracellular glutathione, allowing the accumulation of ROS which subsequently causes mutations that could contribute to the development of gastric cancer.

A possible mechanism for low affinity of silkworm Na+/K+-ATPase for K.

The affinity for K+ of silkworm nerve Na+/K+-ATPase is markedly lower than that of mammalian Na+/K+-ATPase (Homareda 2010). In order to obtain clues on the molecular basis of the difference in K+ affinities, we cloned cDNAs of silkworm (Bombyx mori) nerve Na+/K+-ATPase α and ß subunits, and analyzed the deduced amino acid sequences. The molecular masses of the α and ß subunits were presumed to be 111.5 kDa with ten transmembrane segments and 37.7 kDa with a single transmembrane segment, respectively. The α subunit showed 75% identity and 93% homology with the pig Na+/K+-ATPase α1 subunit. On the other hand, the amino acid identity of the ß subunit with mammalian counterparts was as low as 30%. Cloned α and ß cDNAs were co-expressed in cultured silkworm ovary-derived cells, BM-N cells, which lack endogenous Na+/K+-ATPase. Na+/K+-ATPase expressed in the cultured cells showed a low affinity for K+ and a high affinity for Na+, characteristic of the silkworm nerve Na+/K+-ATPase. These results suggest that the ß subunit is responsible for the affinity for K+ of Na+/K+-ATPase.

CARD8 is a negative regulator for NLRP3 inflammasome, but mutant NLRP3 in cryopyrin-associated periodic syndromes escapes the restriction.

INTRODUCTION: NLRP3 plays a role in sensing various pathogen components or stresses in the innate immune system. Once activated, NLRP3 associates with apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) and procaspase-1 to form a large protein complex termed inflammasome. Although some investigators have proposed a model of NLRP3-inflammasome containing an adaptor protein caspase recruitment domain-containing protein 8 (CARD8), the role of this molecule remains obscure. This study aimed to clarify the interaction between CARD8 and wild-type NLRP3 as well as mutant forms of NLRP3 linked with cryopyrin-associated periodic syndromes (CAPS). METHODS: In here HEK293 expression system, cells were transfected with the cDNAs for inflammasome components. Also used were peripheral blood mononuclear cells (PBMCs) and human monocyte-derived macrophages (HMDMs) from healthy volunteers. The interaction of CARD8 and NLRP3 was studied by immunoprecipitation. The effect of CARD8 expression on IL-1ß secretion was assessed by ELISA. CARD8 knockdown experiments were carried out by transfection of the specific siRNA into HMDMs. RESULTS: In HEK293 cells, CARD8 interacted with wild-type NLRP3, but not with CAPS-associated mutant NLRP3. CARD8 significantly reduced IL-1ß secretion from cells transfected with wild-type NLRP3, but not if they were transfected with mutant NLRP3. In addition, association of endogenously expressed CARD8 with NLRP3 was confirmed in resting PBMCs, and CARD8 knockdown resulted in higher amount of IL-1ß secretion from HMDMs. CONCLUSIONS: Until specific stimuli activate NLRP3, CARD8 holds NLRP3, and is supposed to prevent activation by subtle stimuli. However, CAPS-associated mutant NLRP3 is unable to bind with CARD8, which might be relevant to the pathogenesis of CAPS.

Identification of placental leucine aminopeptidase and triton-slowed aminopeptidase N in serum of pregnant women.

BACKGROUND: Previously, we found characteristic triton-slowed bands of aminopeptidase N (APN) in cholestatic serum by triton-polyacrylamide gel electrophoresis (triton-PAGE) [Makoto Kawai, Yukichi Hara, Triton-polyacrylamide gel electrophoresis and leucine aminopeptidase activity staining detect Triton-slowed bands including high-molecular-mass aminopeptidase N (CD13) isoform in cholestatic patient sera. Clin Chim Acta 2006; 364:188-195]. METHODS: Sera from 14 normal pregnant women were electrophoresed on polyacrylamide gel containing 0.02 l/l triton (triton-PAGE) or a 0-0.02 l/l horizontal gradient of triton (gradient-triton-PAGE), and stained with leucine-beta-naphthylamide. Some samples were pretreated with a monoclonal APN antibody or rabbit anti-placental leucine aminopeptidase (PLAP) serum. The stained bands were eluted from the gel, treated with N- and O-glycosidase, and analyzed by Western blotting with rabbit anti-APN or anti-PLAP serum. RESULTS: Triton-PAGE clearly differentiated 5 LAP activity bands (1-5 from the front). Gradient-triton-PAGE revealed that bands 4-5 were slowed by triton (triton-slowed bands) much more than bands 1-3. Triton-PAGE of antibody-treated serum showed that bands 1, 2, 4, and 5 are mainly APN and that band 3 is PLAP. The molecular mass of PLAP was about 130-140 kDa before treatment with glycosidases but 100 kDa after. Triton-PAGE detected PLAP in 13 and triton-slowed APN in 4 of the 14 women. CONCLUSIONS: Triton-PAGE differentiates PLAP from APN. Triton-slowed APN as well as PLAP is present in the serum of pregnant women.

Functional consequences of various leucine mutations in the M3/M4 loop of the Na+,K +-ATPase alpha-Subunit.

Leucines were mutated within the sequence L311 ILGYTWLE319 of the extracellular loop flanking the third (M3) and fourth (M4) transmembrane segments (M3/M4 loop) of the Torpedo Na+,K+-ATPase alpha-subunit. Replacement of Leu311 with Glu resulted in a considerable loss of Na+,K+-ATPase activity. Replacement of Leu313 with Glu shifted the equilibrium of E1P and E2P toward E1P and reduced the rate of the E1P to E2P transition. The reduction of the transition rate and stronger inhibition of Na+,K+-ATPase activity by Na+ at higher concentrations together suggest that there is interference of Na+ release on the extracellular side in the Leu313 mutant. Thus, Leu313 could be in the pathway of Na+ exit. Replacement of Leu318 with Glu yielded an enzyme with significantly reduced apparent affinity for both vanadate and K+, with an equilibrium shifted toward E2P and no alteration in the transition rate. The reduced vanadate affinity is due to the lower rate of production of vanadate-reactive [K+ (2)]E2 caused by inhibition of dephosphorylation through reduction of the K+ affinity of E2P. Thus, Leu318 may be a critical position in guiding external K+ to its binding site.

A case of Muckle-Wells syndrome caused by a novel H312P mutation in NALP3 (cryopyrin).

Here, we report a case of Muckle-Wells syndrome (MWS) caused by a novel mutation in the CIAS1/NALP3 gene. A 23-year-old woman had recurrent self-limited inflammatory episodes from childhood, with headache, abdominal pain, arthritis, and urticarial rash, associated with profound sensorineural hearing loss. The diagnosis was established on the basis of a typical clinical picture together with a missense mutation, which replaced an amino acid adjacent to one in an earlier reported case of MWS resembling this one.

Generation of cell lines with tetracycline-regulated autophagy and a role for autophagy in controlling cell size.

Autophagy is an intracellular bulk degradation system. We established mouse fibroblast lines coupling the Tet-off system with an Atg5-/- mouse embryonic fibroblast line to artificially regulate autophagic ability. In the presence of doxycycline (Dox), Atg5 expression was completely suppressed and these cells were autophagy-defective. After removal of Dox, autophagic ability was restored within 6 h. Very low levels of Atg5 could induce an autophagy competent state. We applied this novel system to examine the contribution of autophagy to controlling cell size. Cell size reduction in response to starvation was significantly inhibited in cells unable to undergo autophagy. The generated cell lines will be useful reagents for future mechanistic studies into the regulation and physiologic significance of autophagy.

Molecular cloning and characterization of ouabain-insensitive Na(+)-ATPase in the parasitic protist, Trypanosoma cruzi.

Maintaining low intracellular sodium concentrations is vital for almost all organisms. Na(+) efflux is generally governed by P-type ATPases, Na(+)/K(+)-ATPase in animals and Na(+)-ATPase, called ENA, in fungi and plants. Trypanosoma cruzi, which parasitizes mammalian cells, must undergo drastic adaptations to high Na(+) concentrations outside and low Na(+) concentrations inside host cells. However, T. cruzi Na(+) efflux pumps have not been identified. We report here the cloning and characterization of the gene encoding Na(+)-ATPase in T cruzi, which resembled fungal and plant ENAs, termed TcENA. TcENA was a plasma membrane protein expressed throughout the parasite life cycle. The transcription level of TcENA was higher in insect stage epimastigotes and blood stream trypomastigotes than in intracellular amastigotes, probably reflecting the high Na(+) concentration outside the host cells. Biochemical analysis of TcENA expressed heterologously in mammalian cells demonstrated, for the fist time, that the ATPase activity of TcENA is stimulated by both Na(+) and K(+) and is insensitive to ouabain, a specific inhibitor of Na(+)/K(+)-ATPases. Furthermore, epimastigotes overproducing TcENA showed increased tolerance to high Na(+) stress. Our findings suggest that TcENA acts as a sodium pump and provide insights into the regulation of ion homeostasis in the parasitic protist.

Generation of cell lines with tetracycline-regulated autophagy and a role for autophagy in controlling cell size.

Autophagy is an intracellular bulk degradation system. We established mouse fibroblast lines coupling the Tet-off system with an Atg5(-/-) mouse embryonic fibroblast line to artificially regulate autophagic ability. In the presence of doxycycline (Dox), Atg5 expression was completely suppressed and these cells were autophagy-defective. After removal of Dox, autophagic ability was restored within 6h. Very low levels of Atg5 could induce an autophagy competent state. We applied this novel system to examine the contribution of autophagy to controlling cell size. Cell size reduction in response to starvation was significantly inhibited in cells unable to undergo autophagy. The generated cell lines will be useful reagents for future mechanistic studies into the regulation and physiologic significance of autophagy.

Triton-polyacrylamide gel electrophoresis and leucine aminopeptidase activity staining detect Triton-slowed bands including high-molecular-mass aminopeptidase N (CD13) isoform in cholestatic patient sera.

BACKGROUND: Western blotting of aminopeptidase N (APN) detects a high-molecular-mass isoform (260 kDa) [M. Kawai, Y. Otake, Y. Hara High-molecular-mass isoform of aminopeptidase N/CD13 in serum from cholestatic patients. Clin Chim Acta 330 (2003) 141-149] in cholestatic patient serum but is time-consuming. METHODS: Human sera were electrophoresed on polyacrylamide gel containing Triton-X100 (Triton-PAGE) and stained with leucine-B-naphthylamide (LAP-staining). The stained bands were eluted from the gel, treated with N- and O-glycosidase if necessary, and analyzed by Western blotting [M. Kawai, Y. Otake, Y. Hara High-molecular-mass isoform of aminopeptidase N/CD13 in serum from cholestatic patients. Clin Chim Acta 330 (2003) 141-149]. RESULTS: Triton-PAGE and LAP-staining clearly detected fast bands in all the sera examined. Almost parallel with leucine aminopeptidase activity, slow bands were strongly stained in all 11 cholestatic patients but clearly stained in 3 out of 14 patients with hepatobiliary diseases other than cholestasis. PAGE with various concentrations of Triton showed that Triton slows down slow bands but not fast bands. Western blotting showed that Triton-PAGE-slow bands of cholestasis contained 140 and 260-kDa APN and that fast bands were slightly smaller than monomer-size slow bands after glycosidase treatment. CONCLUSIONS: Less time-consuming than Western blotting, Triton-PAGE and LAP-staining detect novel APN bands slowed by Triton and partly composed of the high-molecular-mass isoform in cholestasis. The slow bands seem to be homodimers of APN with transmembrane anchors. The polypeptide of the fast band seems to be processed differently from that of the slow band.

Na+/K+ ATPase and its functional coupling with Na+/Ca2+ exchanger in mouse embryonic stem cells during differentiation into cardiomyocytes.

Cardiomyocytes derived from mouse embryonic stem (mES) cells have been demonstrated to exhibit a time-dependent expression of ion channels and signal transduction pathways in electrophysiological studies. However, ion transporters, such as Na+/K+ ATPase (Na+ pump) or Na+/Ca2+ exchanger, which play crucial roles for cardiac function, have not been well studied in this system. In this study, we investigated the functional expression of Na+/K+ ATPase and Na+/Ca2+ exchanger in mES cells during in vitro differentiation into cardiomyocytes, as well as the functional coupling between the two transporters. By measuring [Na+]i and Na+ pump current (Ip), it was shown that an ouabain-high sensitive Na+/K+ ATPase was expressed functionally in undifferentiated mES cells and these activities increased during a time course of differentiation. Using RT-PCR, the expression of mRNA for alpha1-subunit and alpha3-subunit of the Na+/K+ ATPase could be detected in both undifferentiated mES cells and derived cardiomyocytes. In contrast alpha2-subunit mRNA could be detected only in derived cardiomyocytes but not in undifferentiated mES cells. mRNA for the Na+/Ca2+ exchanger 1 isoform (NCX1) could be detected in undifferentiated mES cells and its expression levels seemed to gradually increase throughout the differentiation accompanied by increasing its Ca2+ extrusion function. At the middle stages of differentiation (after 10-day induction), more than 75% derived cardiomyocytes exhibited [Ca2+]i oscillations by blocking of Na+/K+ ATPase, suggesting the functional coupling with Na+/Ca2+ exchanger. From these results and RT-PCR analysis, we conclude that alpha2-subunit Na+/K+ ATPase mainly contributes to establish the functional coupling with NCX1 at the middle stages of differentiation of cardiomyocytes.

Target proteins of the cytosolic thioredoxins in Arabidopsis thaliana.

Possible target proteins of cytosolic thioredoxin in higher plants have been investigated in the cell lysate of dark-grown Arabidopsis thaliana whole tissues. We immobilized a mutant of cytosolic thioredoxin, in which an internal cysteine at the active site was substituted with serine, on CNBr activated resin, and used the resin for the thioredoxin-affinity chromatography. By using this resin, the target proteins for thioredoxin in the higher plant cytosol were efficiently acquired. The obtained proteins were separated by two-dimensional gel electrophoresis and analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Thus we have identified proteins of the anti-oxidative stress system proteins (ascorbate peroxidase, germin-like protein, and monomeric type II peroxiredoxin), proteins involved in protein biosynthesis (elongation factor-2 and eukaryotic translation initiation factor 4A), proteins involved in protein degradation (the regulatory subunit of 26S proteasome), and several metabolic enzymes (alcohol dehydrogenase, fructose 1,6-bis phosphate aldolase-like protein, cytosolic glyceraldehyde 3-phosphate dehydrogenase, cytosolic malate dehydrogenase, and vitamin B(12)-independent methionine synthase) together with some chloroplast proteins (chaperonin 60-alpha and 60-beta, heat shock protein 70, and glutamine synthase). The results in this study and recent proteomics studies on the target proteins of chloroplast thioredoxin indicate the versatility and the physiological significance of thioredoxin as reductant in plant cell.

High-molecular-mass isoform of aminopeptidase N/CD13 in serum from cholestatic patients.

BACKGROUND: Because non-denaturing electrophoresis and aminopeptidase activity staining often detect noncovalent multi-enzyme complexes, we adopted procedures to specifically detect the aminopeptidase N (APN) molecule itself in liver disease serum. METHODS: Sera or their immunoprecipitate with anti-APN monoclonal antibody were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) or two-dimensional electrophoresis and subsequent Western blotting with rabbit anti-APN serum. RESULTS: In all the patient sera examined, the 140-kDa APN isoform was predominant. In all the sera from 10 patients with cholestatic diseases (8 with extra-hepatic cholestasis and 2 with primary biliary cirrhosis), we observed the 260-kDa isoform that was immunoprecipitated with monoclonal APN antibodies and had a similar isoelectric point to the 140-kDa isoform. However, the 260-kDa isoform was observed faintly in 2 out of 12 patients with other liver diseases, including chronic hepatitis and cirrhosis. CONCLUSIONS: We found a novel high-molecular-mass APN isoform (260-kDa) in serum, which is highly likely to be a homodimer of APNs bound covalently and a promising marker of cholestasis. This suggests increased cross-linking reaction between two APN molecules in cholestatic patients.

A new on-line dual enzymatic method for simultaneous quantification of cholesterol and triglycerides in lipoproteins by HPLC.

We describe an on-line dual detection method using HPLC for lipoprotein analysis that allows simultaneous determination of cholesterol and triglyceride profiles from a single injection of sample. Two different gel permeation columns, TSKgel LipopropakXL and Superose 6HR, were applied to the dual detection system, evaluating analytical performance of the proposed method and the columns by analyzing serum samples from human and nonhuman subjects. Both TSK and Superose columns produced good within-day imprecision values less than 4.7% for cholesterol and 4.2% for triglyceride determination. Linear regression analysis showed the results from the Superose column (y) correlated well with those from the TSK column (x): y = 0.969x + 5.44 (r = 0.990) for total cholesterol (mg/dl), y = 1.08x - 11.14 (r = 0.985) for total triglycerides (mg/dl), and y = 1.093x - 0.06 (r = 0.978) for the ratios of triglycerides to cholesterol (mg/mg). Furthermore, the cholesterol and triglyceride profiles elucidated the differences in the resolution ability of the columns, which have not been apparent from a single lipid profile. We conclude that the dual detection concept with proper choice of column and enzymic reagents specific to the objectives of the particular study can facilitate studies of lipoprotein metabolism.

Estrogen treatment of prostate cancer increases triglycerides in lipoproteins as demonstrated by HPLC and immunoseparation techniques.

BACKGROUND: Estrogen administration is known to increase serum triglyceride concentrations. This study measured changes in lipoproteins of patients with prostate cancer treated with estrogen to determine whether the increased triglyceride concentrations are associated with atherogenic lipoprotein patterns. METHODS: Fifteen patients (52-87 years) with histologically diagnosed prostate cancer received diethylstilbestrol diphosphate (250 mg/day). Serum samples were collected before and after 1 and 2 weeks of treatment. Cholesterol and triglyceride profiles of major lipoproteins were determined by HPLC, remnant-like particle cholesterol and triglyceride concentrations by an immunoseparation technique, and apolipoproteins by immunologic methods. RESULTS: Estrogen treatment induced a 63.3% increase in total triglyceride concentrations, which occurred in all major lipoprotein classes with significant increases in HDL-triglycerides (130.4%), LDL-triglycerides (60.7%) and VLDL-triglycerides (56.2%). HDL-cholesterol increased significantly by 26.8%, while LDL-cholesterol decreased (15.6%). Remnant-like particle triglyceride concentrations also increased significantly by 77%, whereas remnant-like particle cholesterol concentrations remained unchanged. Apolipoproteins A-I and A-II increased; apolipoprotein E and Lp(a) decreased. CONCLUSIONS: The techniques used here conveniently demonstrated that short-term estrogen treatment in prostate cancer patients resulted in triglyceride enrichment of all major lipoprotein classes but did not induce changes in the lipoprotein profiles generally recognized as increasing risk for cardiovascular disease, except for the elevation of plasma triglyceride and remnant-like particle triglyceride.