Structural organization and chromosomal localization of the human Na,K-ATPase beta 3 subunit gene and pseudogene

Na,K-ATPase Expression Can Be Limited Post-Transcriptionally: A Test of the Role of the Beta Subunit, and a Review of Evidence

The Na,K-ATPase is an α-β heterodimer. It is well known that the Na,K-ATPase β subunit is required for the biosynthesis and trafficking of the α subunit to the plasma membrane. During investigation of properties of human ATP1A3 mutations in 293 cells, we observed a reciprocal loss of endogenous ATP1A1 when expressing ATP1A3. Scattered reports going back as far as 1991 have shown that experimental expression of one subunit can result in reduction in another, suggesting that the total amount is strictly limited. It seems logical that either α or β subunit should be rate-limiting for assembly and functional expression. Here, we present evidence that neither α nor β may be limiting and that there is another level of control that limits the amount of Na,K-ATPase to physiological levels. We propose that α subunits compete for something specific, like a private chaperone, required to finalize their biosynthesis or to prevent their degradation in the endoplasmic reticulum.

A century of exercise physiology: effects of muscle contraction and exercise on skeletal muscle Na+,K+-ATPase, Na+ and K+ ions, and on plasma K+ concentration-historical developments

This historical review traces key discoveries regarding K+ and Na+ ions in skeletal muscle at rest and with exercise, including contents and concentrations, Na+,K+-ATPase (NKA) and exercise effects on plasma [K+] in humans. Following initial measures in 1896 of muscle contents in various species, including humans, electrical stimulation of animal muscle showed K+ loss and gains in Na+, Cl- and H20, then subsequently bidirectional muscle K+ and Na+ fluxes. After NKA discovery in 1957, methods were developed to quantify muscle NKA activity via rates of ATP hydrolysis, Na+/K+ radioisotope fluxes, [3H]-ouabain binding and phosphatase activity. Since then, it became clear that NKA plays a central role in Na+/K+ homeostasis and that NKA content and activity are regulated by muscle contractions and numerous hormones. During intense exercise in humans, muscle intracellular [K+] falls by 21 mM (range - 13 to - 39 mM), interstitial [K+] increases to 12-13 mM, and plasma [K+] rises to 6-8 mM, whilst post-exercise plasma [K+] falls rapidly, reflecting increased muscle NKA activity. Contractions were shown to increase NKA activity in proportion to activation frequency in animal intact muscle preparations. In human muscle, [3H]-ouabain-binding content fully quantifies NKA content, whilst the method mainly detects α2 isoforms in rats. Acute or chronic exercise affects human muscle K+, NKA content, activity, isoforms and phospholemman (FXYD1). Numerous hormones, pharmacological and dietary interventions, altered acid-base or redox states, exercise training and physical inactivity modulate plasma [K+] during exercise. Finally, historical research approaches largely excluded female participants and typically used very small sample sizes.

ATP1B3 cooperates with BST-2 to promote hepatitis B virus restriction

Increasing evidence indicates ATP1B3, one of the regulatory subunits of Na⁺ /K⁺ -ATPase, is involved in numerous viral propagations, such as HIV and EV71. However, the function and mechanism of ATP1B3 on hepatitis B virus (HBV) propagation is unknown. Here, we demonstrated that ATP1B3 overexpression reduced the quantity of hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) in supernatants of HBV expression plasmids cotransfected HepG2 cells. Correspondingly, small interfering RNA and short hairpin RNA mediated ATP1B3 silencing promoted HBsAg and HBeAg expression in the supernatants of HBV expression plasmids transfected HepG2 cells. Mechanically, we reported that ATP1B3 expression could activate nuclear factor-κB (NF-κB) pathway by inducing the expression, phosphorylation, and nuclear import of P65 for the first time. And NF-κB inhibitor (Bay11) impaired the restraint of ATP1B3 on HBV replication. This counteraction effect of Bay11 proved that ATP1B3-induced NF-κB activation was crucial for HBV restriction. Accordingly, we observed that anti-HBV factors interferon-α (IFN-α) and interleukin-6 (IL-6) production were increased in HepG2 cells after the NF-κB activation. It suggested that ATP1B3 suppressed HBsAg and HBeAg by NF-κB/IFN-α and NF-κB/IL-6 axis. Further experiments proved that ATP1B3 overexpression induced anti-HBV factor BST-2 expression by NF-κB/IFN-α axis in HepG2 cells but not HEK293T cells, and ATP1B3 silencing downregulated BST-2 messenger RNA level in HepG2 cells. As an HBV restriction factor, BST-2 cooperated with ATP1B3 to antagonize HBsAg but not HBeAg in HepG2 cells. Our work identified ATP1B3 as a novel candidate of HBV restrictor with unrevealed mechanism and we highlighted it might serve as a potential therapeutic molecule for HBV infection.

Differential expression patterns of sodium potassium ATPase alpha and beta subunit isoforms in mouse brain during postnatal development

The sodium potassium ATPase (Na⁺/K⁺ ATPase) is essential for the maintenance of a low intracellular Na⁺ and a high intracellular K⁺ concentration. Loss of function of the Na⁺/K⁺ ATPase due to mutations in Na⁺/K⁺ ATPase genes, anoxic conditions, depletion of ATP or inhibition of the Na⁺/K⁺ ATPase function using cardiac glycosides such as digitalis, causes a depolarization of the resting membrane potential. While in non-excitable cells, the uptake of glucose and amino acids is decreased if the function of the Na⁺/K⁺ ATPase is compromised, in excitable cells the symptoms range from local hyper-excitability to inactivating depolarization. Although several studies have demonstrated the differential expression of the various Na⁺/K⁺ ATPase alpha and beta isoforms in the brain tissue of rodents, their expression profile during development has yet to be thoroughly investigated. An immunohistochemical analysis of postnatal day 19 mouse brain showed ubiquitous expression of Na⁺/K⁺ ATPase isoforms α1, β1 and β2 in both neurons and glial cells, whereas α2 was expressed mostly in glial cells and the α3 and β3 isoforms were expressed in neurons. Furthermore, we examined potential changes in the relative expression of the different Na⁺/K⁺ ATPase isoforms in different brain areas of postnatal day 6 and in adult 9 months old animals using immunoblot analysis. Our results show a significant up-regulation of the α1 isoform in cortex, hippocampus and cerebellum, whereas, the α2 isoform was significantly up-regulated in midbrain. The β3 isoform showed a significant up-regulation in all brain areas investigated. The up-regulation of the α3 isoform matched that of the β2 isoform which were both significantly up-regulated in cortex, hippocampus and midbrain, suggesting that the increased maturation of the neuronal network is accompanied by an increase in expression of α3/β2 complexes in these brain structures.

Substitutions in the cardenolide binding site and interaction of subunits affect kinetics besides cardenolide sensitivity of insect Na,K-ATPase

Substitutions within the cardenolide target site of several insects' Na,K-ATPase α-subunits may confer resistance against toxic cardenolides. However, to which extent these substitutions alter the Na,K-ATPase's kinetic properties and how they interact with different β-subunits is not clear. The cardenolide-adapted milkweed bug Oncopeltus fasciatus possesses three paralogs of the α-subunit (A, B, and C) that differ in number and identity of resistance-conferring substitutions. We introduced these substitutions into the α-subunit of Drosophila melanogaster and combined them with the β-subunits Nrv2.2 and Nrv3. The substitutions Q111T-N122H-F786N-T797A (A-copy mimic) and Q111T-N122H-F786N (B-copy mimic) mediated high insensitivity to ouabain, yet they drastically lowered ATPase activity. Remarkably, the identity of the β-subunit was decisive and all α-subunits were less active when combined with Nrv3 than when combined with Nrv2.2. Both the substitutions and the co-expressed β-subunit strongly affected the enyzme's affinity for Na⁺ and K⁺. Na⁺ affinity was considerably higher for all enzymes expressed with nrv3 while expression with nrv2.2 mostly increased K⁺ affinity. Our results provide the first evidence that resistance against cardenolides comes at the cost of significantly altered kinetic properties of the Na,K-ATPase. The β-subunit can strongly modulate these properties but cannot fully compensate for the effect of the substitutions.

Expression of the β3 subunit of Na+/K+-ATPase is increased in gastric cancer and regulates gastric cancer cell progression and prognosis via the PI3/AKT pathway

ATP1B3 encodes the β3 subunit of Na⁺/K⁺-ATPase and is located in the q22-23 region of chromosome 3. Na⁺/K⁺-ATPase participates in normal cellular activities but also plays a crucial role in carcinogenesis. In the present study, we found that expression of the β3 subunit of Na⁺/K⁺-ATPase was increased in human gastric cancer tissues compared with that in normal matched tissues and that this increased expression predicted a poor outcome. ATP1B3 expression was elevated at both the mRNA and protein levels in gastric cancer cell lines relative to those in a normal gastric epithelial cell line. Interestingly, ATP1B3 knockdown significantly inhibited cell proliferation, colony-formation ability, migration, and invasion and increased apoptosis in human gastric carcinoma cell lines. Additionally, knockdown induced cell cycle arrest at the G2/M phase. Furthermore, we demonstrated that ATP1B3 silencing decreased the expression of phosphatidylinositol 3-kinase (PI3K), protein kinase B (AKT) and phosphorylated AKT (p-AKT), indicating that ATP1B3 regulates gastric cancer cell progression via the PI3K/AKT signalling pathway. Hence, the β3 subunit of Na⁺/K⁺-ATPase plays an essential role in the tumourigenesis of gastric cancer and may be a potential prognostic and therapeutic target for the treatment of gastric cancer.

Na+, K+-ATPase β1 subunit associates with α1 subunit modulating a "higher-NKA-in-hyposmotic media" response in gills of euryhaline milkfish, Chanos chanos

The euryhaline milkfish (Chanos chanos) is a popular aquaculture species that can be cultured in fresh water, brackish water, or seawater in Southeast Asia. In gills of the milkfish, Na⁺, K⁺-ATPase (i.e., NKA; sodium pump) responds to salinity challenges including changes in mRNA abundance, protein amount, and activity. The functional pump is composed of a heterodimeric protein complex composed of α- and β-subunits. Among the NKA genes, α1-β1 isozyme comprises the major form of NKA subunits in mammalian osmoregulatory organs; however, most studies on fish gills have focused on the α1 subunit and did not verify the α1-β1 isozyme. Based on the sequenced milkfish transcriptome, an NKA β1 subunit gene was identified that had the highest amino acid homology to β233, a NKA β1 subunit paralog originally identified in the eel. Despite this high level of homology to β233, phylogenetic analysis and the fact that only a single NKA β1 subunit gene exists in the milkfish suggest that the milkfish gene should be referred to as the NKA β1 subunit gene. The results of accurate domain prediction of the β1 subunit, co-localization of α1 and β1 subunits in epithelial ionocytes, and co-immunoprecipitation of α1 and β1 subunits, indicated the formation of a α1-β1 complex in milkfish gills. Moreover, when transferred to hyposmotic media (fresh water) from seawater, parallel increases in branchial mRNA and protein expression of NKA α1 and β1 subunits suggested their roles in hypo-osmoregulation of euryhaline milkfish. This study molecularly characterized the NKA β1 subunit and provided the first evidence for an NKA α1-β1 association in gill ionocytes of euryhaline teleosts.

ATP1B3: a virus-induced host factor against EV71 replication by up-regulating the production of type-I interferons

Enterovirus 71 (EV71) infection can cause severe diseases, and is becoming increasingly common in children. In the current study, we carried out yeast two-hybrid assays to screen human proteins that could interact with 3A protein of EV71. Human β3 subunit of Na⁺/K⁺-ATPase (ATP1B3) protein was demonstrated to interact with the 3A protein of EV71. Although 3A protein had no effect on the expression of ATP1B3, EV71 infection resulted in elevated expression of ATP1B3 in RD cell line, both on messenger RNA (mRNA) and protein levels. Interestingly, knockdown of ATP1B3 could significantly increase the replication of EV71, whereas overexpression of ATP1B3 significantly suppressed the replication of EV71 in RD cells. Furthermore, we demonstrated that the expression of ATP1B3 could induce the production of type-I interferons. Our study demonstrated that ATP1B3 inhibit EV71 replication by enhancing the production of type-I interferons, which could act as a potential therapeutic target in EV71 infection.

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Human ATP1B3 protein was demonstrated to interact with EV71 3A protein.

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We found ATP1B3 can induce the production of type-I IFNs during EV71 infection.

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ATP1B3 can inhibit EV71 replication by up-regulating the production of type-I interferons.

Mammalian Actin-binding Protein-1/Hip-55 Interacts with FHL2 and Negatively Regulates Cell Invasion

Mammalian actin-binding protein-1 (mAbp1) is an adaptor protein that binds actin and modulates scission during endocytosis. Recent studies suggest that mAbp1 impairs cell invasion; however, the mechanism for the inhibitory effects of mAbp1 remain unclear. We performed a yeast two-hybrid screen and identified the adaptor protein, FHL2, as a novel binding partner that interacts with the N-terminal actin depolymerizing factor homology domain (ADFH) domain of mAbp1. Here we report that depletion of mAbp1 or ectopic expression of the ADFH domain of mAbp1 increased Rho GTPase signaling and breast cancer cell invasion. Moreover, cell invasion induced by the ADFH domain of mAbp1 required the expression of FHL2. Taken together, our findings show that mAbp1 and FHL2 are novel binding partners that differentially regulate Rho GTPase signaling and MTLn3 breast cancer cell invasion.

ATP1B3 Protein Modulates the Restriction of HIV-1 Production and Nuclear Factor κ Light Chain Enhancer of Activated B Cells (NF-κB) Activation by BST-2

Here, we identify ATP1B3 and fibrillin-1 as novel BST-2-binding proteins. ATP1B3 depletion in HeLa cells (BST-2-positive cells), but not 293T cells (BST-2-negative cells), induced the restriction of HIV-1 production in a BST-2-dependent manner. In contrast, fibrillin-1 knockdown reduced HIV-1 production in 293T and HeLa cells in a BST-2-independent manner. Moreover, NF-κB activation was enhanced by siATP1B3 treatment in HIV-1- and HIV-1ΔVpu-infected HeLa cells. In addition, ATP1B3 silencing induced high level BST-2 expression on the surface of HeLa cells. These results indicate that ATP1B3 is a co-factor that accelerates BST-2 degradation and reduces BST-2-mediated restriction of HIV-1 production and NF-κB activation.

Transcriptional regulators of Na,K-ATPase subunits

The Na,K-ATPase classically serves as an ion pump creating an electrochemical gradient across the plasma membrane that is essential for transepithelial transport, nutrient uptake and membrane potential. In addition, Na,K-ATPase also functions as a receptor, a signal transducer and a cell adhesion molecule. With such diverse roles, it is understandable that the Na,K-ATPase subunits, the catalytic α-subunit, the β-subunit and the FXYD proteins, are controlled extensively during development and to accommodate physiological needs. The spatial and temporal expression of Na,K-ATPase is partially regulated at the transcriptional level. Numerous transcription factors, hormones, growth factors, lipids, and extracellular stimuli modulate the transcription of the Na,K-ATPase subunits. Moreover, epigenetic mechanisms also contribute to the regulation of Na,K-ATPase expression. With the ever growing knowledge about diseases associated with the malfunction of Na,K-ATPase, this review aims at summarizing the best-characterized transcription regulators that modulate Na,K-ATPase subunit levels. As abnormal expression of Na,K-ATPase subunits has been observed in many carcinoma, we will also discuss transcription factors that are associated with epithelial-mesenchymal transition, a crucial step in the progression of many tumors to malignant disease.

Prostaglandin E2receptor subtype EP2- and EP4-regulated gene expression profiling in human ciliary smooth muscle cells

Prostanoids are an important class of intraocular pressure (IOP)-lowering antiglaucoma agents that act primarily via increased uveo-scleral aqueous humor outflow through the ciliary body. We have developed two novel PGE2analogs that are specific agonists for the PGE2receptor subtypes EP2 and EP4, respectively. To identify gene regulatory networks and key players that mediate the physiological effects observed in vivo, we performed genomewide expression studies using human ciliary smooth muscle cells. Quantitative real-time RT-PCR confirmed a largely overlapping gene expression profile subsequent to EP2 and EP4 agonist treatment, with 65 significantly regulated genes identified overall, 5 being specific for the EP2 agonist and 6 specific for the EP4 agonist. We found predicted functional cAMP-response elements in promoter regions of a large fraction of the predominantly upregulated genes, which suggests that the cAMP signaling pathway is the most important intracellular signaling pathway for these agonists in these cells. Several target genes were identified that, as part of complex regulatory networks, are implicated in tissue remodeling processes and osmoregulation (e.g., AREG, LOXL3, BMP2, AQP3) and thus may help elucidate the mechanism of action of these IOP-lowering drugs involving the uveo-scleral outflow path.

Eya4 regulation of Na+/K+-ATPase is required for sensory system development in zebrafish

To investigate the mechanisms by which mutations in the human transcriptional co-activator EYA4 gene cause sensorineural hearing loss that can occur in association with dilated cardiomyopathy, we studied eya4 expression during zebrafish development and characterized eya4 deficiency. eya4 morphant fish embryos had reduced numbers of hair cells in the otic vesicle and lateral line neuromasts with impaired sensory responses. Analyses of candidate genes that are known to be expressed in a temporal and spatial pattern comparable to eya4 focused our analyses on atp1b2b, which encodes the beta2b subunit of the zebrafish Na+/K+-ATPase. We demonstrate atp1b2b levels are reduced in eya4 morphant fish and that morpholino oligonucleotides targeting the atp1b2b gene recapitulated the eya4 deficiency phenotypes, including heart failure, decreased sensory hair cell numbers in the otic vesicle and neuromasts, and abnormal sensory responses. Furthermore, atp1b2b overexpression rescued these phenotypes in eya4 morphant fish. We conclude that eya4 regulation of Na+/K+-ATPase is crucial for the development of mechanosensory cells and the maintenance of cardiac function in zebrafish.

Further application of a two-step heparin affinity chromatography method using divalent cations as eluents: Purification and identification of membrane-bound heparin binding proteins from the mitochondrial fraction of HL-60 cells

Membrane proteins were obtained from the mitochondrial fraction of HL-60 cells by solubilization with octyl glucoside and bound to heparin-gels. Bound proteins were successively eluted with solutions containing increasing concentrations of Mg(2+) in the first and increasing concentrations of Ca(2+) in the second chromatography. After SDS-PAGE and subsequent N-terminal amino acid analysis of proteins on each band, 13 proteins were identified. Fifteen out of the 37 proteins analysed were modified at their N-termini. These results show that this two-step affinity chromatography method using divalent cations as eluents can be applied to a variety of membranes for the isolation of specific proteins.

The cellular retinol-binding protein genes are duplicated and differentially transcribed in the developing and adult zebrafish (Danio rerio)

There are single copies of the genes encoding the cellular retinol-binding protein type I and II (CRBPI and CRBPII) in the human and rodent genomes. We have identified duplicate genes for both CRBPI and CRBPII in the zebrafish (Danio rerio) genome (rbp1b and rbp2b). The zebrafish rbp1b and rbp2b have conserved gene structures, amino acid sequence similarities, gene phylogenies, and syntenic relationships with their mammalian orthologs and zebrafish paralogs, rbp1a and rbp2a. Like the mammalian genes for CRBPI and CRBPII, the zebrafish rbp1b and rbp2b genes are closely linked on a single linkage group. Comparative analysis suggests that the duplicate genes of rbp1 and rbp2 in the zebrafish genome may have arisen by chromosomal or whole-genome duplication. During embryonic development, rbp1b transcripts were detected in the gall bladder of 5-day postfertilization (5 dpf) larvae. The rbp2b mRNA was abundant in the developing liver through 48 hours postfertilization (48 hpf) to 5 dpf. Using reverse transcription-polymerase chain reaction (RT-PCR), rbp1b transcripts were detected in the ovary, and rbp2b mRNA was observed predominantly in the adult liver. Tissue section in situ hybridization and emulsion autoradiography localized rbp1b mRNA to primary oocytes within the zebrafish ovary. The differential mRNA distribution patterns of the rbp1a, rbp1b, rbp2a, and rbp2b genes in the developing and adult zebrafish suggest that shuffling of subfunctions among duplicate copies of paralogous genes may be a mechanism for the retention of duplicated genes in vertebrates.

Gene expression in mononuclear cells from patients with inflammatory bowel disease

OBJECTIVES

Discovery of Nod2 as the inflammatory bowel disease 1 (IBD1) susceptibility gene has brought to light the significance of mononuclear cells in inflammatory bowel disease pathogenesis. The purpose of this study was to examine changes in gene expression in peripheral blood mononuclear cells in patients with untreated Crohn's disease (CD) and ulcerative colitis (UC) as compared to patients with other inflammatory gastrointestinal disorders and to healthy controls.

METHODS

We used a 2400 gene cDNA glass slide array (MICROMAX) to examine gene expression in peripheral blood mononuclear cells from seven patients with Crohn's disease, five patients with ulcerative colitis, 10 patients with other inflammatory gastrointestinal disorders, and 22 age- and sex-matched controls. Results. Novel categories of genes differentially expressed in Crohn's disease and ulcerative colitis patients included genes regulating hematopoietic cell differentiation and leukemogenesis, lipid raft-associated signaling, the actin cytoskeleton, and vesicular trafficking.

CONCLUSIONS

Altered gene expression in mononuclear cells may contribute to inflammatory bowel disease pathogenesis.

Intense exercise up-regulates Na+,K+-ATPase isoform mRNA, but not protein expression in human skeletal muscle

Characterization of expression of, and consequently also the acute exercise effects on, Na(+),K(+)-ATPase isoforms in human skeletal muscle remains incomplete and was therefore investigated. Fifteen healthy subjects (eight males, seven females) performed fatiguing, knee extensor exercise at approximately 40% of their maximal work output per contraction. A vastus lateralis muscle biopsy was taken at rest, fatigue and 3 and 24 h postexercise, and analysed for Na(+),K(+)-ATPase alpha(1), alpha(2), alpha(3), beta(1), beta(2) and beta(3) mRNA and crude homogenate protein expression, using Real-Time RT-PCR and immunoblotting, respectively. Each individual expressed gene transcripts and protein bands for each Na(+),K(+)-ATPase isoform. Each isoform was also expressed in a primary human skeletal muscle cell culture. Intense exercise (352 +/- 69 s; mean +/-s.e.m.) immediately increased alpha(3) and beta(2) mRNA by 2.4- and 1.7-fold, respectively (P < 0.05), whilst alpha(1) and alpha(2) mRNA were increased by 2.5- and 3.5-fold at 24 h and 3 h postexercise, respectively (P < 0.05). No significant change occurred for beta(1) and beta(3) mRNA, reflecting variable time-dependent responses. When the average postexercise value was contrasted to rest, mRNA increased for alpha(1), alpha(2), alpha(3), beta(1), beta(2) and beta(3) isoforms, by 1.4-, 2.2-, 1.4-, 1.1-, 1.0- and 1.0-fold, respectively (P < 0.05). However, exercise did not alter the protein abundance of the alpha(1)-alpha(3) and beta(1)-beta(3) isoforms. Thus, human skeletal muscle expresses each of the Na(+),K(+)-ATPase alpha(1), alpha(2), alpha(3), beta(1), beta(2) and beta(3) isoforms, evidenced at both transcription and protein levels. Whilst brief exercise increased Na(+),K(+)-ATPase isoform mRNA expression, there was no effect on isoform protein expression, suggesting that the exercise challenge was insufficient for muscle Na(+),K(+)-ATPase up-regulation.

Comparison of gene expression between metastatic derivatives and their poorly metastatic parental cells implicates crucial tumor-environment interaction in metastasis of head and neck squamous cell carcinoma

Metastasis of human head and neck cancer is a multistep and highly heterogeneous process requiring activation and deactivation of multiple and specific genes. To identify these genes, we established highly metastatic head and neck squamous cell carcinoma (HNSCC) cell lines from poorly metastatic HNSCC cells through in vivo selection using a lymph node metastatic mouse model. The very close genetic relationship between these highly metastatic cell lines and the parental cell line provided an excellent model for differential gene expression analysis using cDNA microarrays. Comparison of 6 cell lines established individually from the lymph node metastases with their poorly metastatic parental cell line revealed 33 differentially expressed genes. Some of these genes are involved in cellular signal transduction and matrix modeling. Differences in expression of members of the tumor necrosis factor, interleukin, caspase, and matrix metalloproteinase families were also examined. We found that two upregulated genes participated in the NF-kappaB regulatory pathway. Furthermore, differences in gene expression between six cell lines derived from primary tumors and six cell lines derived from lymph node metastases in the mouse model were analyzed statistically. Tissue growth factor-beta and tumor necrosis factor-related genes showed significantly altered expression in cells derived from lymph node metastases as compared with cells derived from primary tumors, suggesting that the differential growth advantage of metastatic cells requires more aggressive responses to their environment, such as a lymph node tissue.

Two Na,K-ATPase beta 2 subunit isoforms are differentially expressed within the central nervous system and sensory organs during zebrafish embryogenesis

We have identified cDNAs encoding a second zebrafish ortholog of the human Na,K-ATPase beta 2 subunit. The beta 2b cDNA encodes a 292 amino acid-long polypeptide with 74% identity to the previously characterized zebrafish beta 2a subunit. By using a zebrafish meiotic mapping panel, we determined that the beta 2b gene (atp1b2b) was tightly linked to markers on linkage group 5, whereas the beta 2a gene was located on linkage group 23. In situ hybridization analysis shows that in developing zebrafish embryos, atp1b2a and atp1b2b are predominantly expressed in the nervous system. beta 2a transcripts were abundantly expressed throughout brain as well as spinal cord neurons and lateral line ganglia. In contrast, beta 2b mRNA expression was primarily detected in sensory organs, including retina, otic vesicles, and lateral line neuromast cells. These results suggest that the beta 2a and beta 2b genes play distinct roles in developing brain and sensory organs, and raise the possibility that the functions encoded by the single mammalian beta 2 gene may be partitioned between the two zebrafish beta 2 orthologs.

The betam protein, a member of the X,K-ATPase beta-subunits family, is located intracellularly in pig skeletal muscle

The sequence of the pig cDNA encoding the muscle-specific betam-protein, a member of the X,K-ATPase beta-subunits family, was determined. Two alternatively spliced transcripts encoding polypeptide chains of 355 and 351 residues were identified. The tissue specificity of expression of betam and other X,K-ATPase beta-subunit genes was studied by RT-PCR performed on 24 tissues from newborn pigs. The betam expression was shown to be highly tissue-specific, being detected at the highest level in skeletal muscle, at a lower level in heart, and at much lower level in skin. The betam transcripts are more abundant in the tissues from the newborn than adult. Immunoblotting and deglycosylation shift assay indicated that skeletal muscle membranes of newborn pigs contain betam protein with an electrophoretic mobility and carbohydrate content very similar to that of human betam. Fractionation of membranes from both newborn and adult pig skeletal muscles by isopycnic centrifugation revealed that the majority of the betam protein is concentrated in the sarcoplasmic reticulum-containing fractions. This intracellular location is a unique property that distinguishes the betam protein from other members of the X,K-ATPase beta-subunit family.

The repertoire of Na,K-ATPase alpha and beta subunit genes expressed in the zebrafish, Danio rerio

We have identified a cohort of zebrafish expressed sequence tags encoding eight Na,K-ATPase alpha subunits and five beta subunits. Sequence comparisons and phylogenetic analysis indicate that five of the zebrafish alpha subunit genes comprise an alpha1-like gene subfamily and two are orthologs of the mammalian alpha3 subunit gene. The remaining alpha subunit clone is most similar to the mammalian alpha2 subunit. Among the five beta subunit genes, two are orthologs of the mammalian beta1 isoform, one represents a beta2 ortholog, and two are orthologous to the mammalian beta3 subunit. Using zebrafish radiation hybrid and meiotic mapping panels, we determined linkage assignments for each alpha and beta subunit gene. Na,K-ATPase genes are dispersed in the zebrafish genome with the exception of four of the alpha1-like genes, which are tightly clustered on linkage group 1. Comparative mapping studies indicate that most of the zebrafish Na,K-ATPase genes localize to regions of conserved synteny between zebrafish and humans. The expression patterns of Na,K-ATPase alpha and beta subunit genes in zebrafish are quite distinctive. No two alpha or beta subunit genes exhibit the same expression profile. Together, our data imply a very high degree of Na,K-ATPase isoenzyme heterogeneity in zebrafish, with the potential for 40 structurally distinct alpha/beta subunit combinations. Differences in expression patterns of alpha and beta subunits suggest that many of the isoenzymes are also likely to exhibit differences in functional properties within specific cell and tissue types. Our studies form a framework for analyzing structure function relationships for sodium pump isoforms using reverse genetic approaches.

Absence of a significant linkage between Na+,K+-ATPase subunit (ATP1A3 andATP1B3) genotypes and bipolar affective disorder in the old-order Amish

Previous studies provide evidence for a genetic component for susceptibility to bipolar affective disorder (BPAD) in the old-order Amish population. El-Mallakh and Wyatt [1995: Biol Psychiatry 37:235-244] have suggested that the Na(+),K(+)-ATPase may be a candidate gene for BPAD. This study examines the relationship between BPAD in the old-order Amish cohort and the Na(+),K(+)-ATPase alpha1 and beta3 subunit genes (ATP1A3, ATP1B3). A total of 166 sibling pairs were analyzed for linkage via nonparametric methods. Suggestive levels of statistical significance were not reached in any stratification model for affective illness. Overall, the results do not support linkage of bipolar disorder to the Na(+),K(+)-ATPase alpha subunit gene (ATP1A3) and beta subunit gene (ATP1B3) in these old-order Amish families and they show that these Na(+),K(+)-ATPase subunit genes are not major effect genes (>or=fourfold increased genetic risk of disease) for BPAD in the old-order Amish pedigrees. We cannot exclude other genetic variants of the Na(+),K(+)-ATPase hypothesis for BPAD, whereby other loci may modifying Na(+),K(+)-ATPase activity.

Carbachol inhibits Na(+)-K(+)-ATPase activity in choroid plexus via stimulation of the NO/cGMP pathway

Secretion of cerebrospinal fluid by the choroid plexus can be inhibited by its cholinergic innervation. We demonstrated that carbachol inhibits the Na(+)-K(+)-ATPase in bovine choroid tissue slices and investigated the mechanism. Many of the actions of cholinergic agents are mediated by nitric oxide (NO), which plays important roles in fluid homeostasis. The inhibition of Na(+)-K(+)-ATPase was blocked by the NO synthase inhibitor [N(omega)-nitro-L-arginine methyl ester] and was quantitatively mimicked by the NO agonists sodium nitroprusside (SNP) and diethylenetriamine NO. Inhibition by SNP correlated with an increase in tissue cGMP and was abolished by 1H-[1,2,4]oxadiazolo[4, 3-a]quinoxalin-1-one, an inhibitor of soluble guanylate cyclase. Inhibition was mimicked by the protein kinase G activator 8-bromo-cGMP and by okadaic acid, an inhibitor of protein phosphatases 1 and 2A. cGMP-dependent protein kinase inhibitors Rp-8-pCPT-cGMP (0.5-5 microM) and KT-5823 (2.0 microM) did not block the effects of SNP, but higher concentrations of the more selective inhibitor (Rp-8-pCPT-cGMP) had a pharmacological inhibitory effect on Na(+)-K(+)-ATPase. The data suggest that cholinergic regulation of the Na(+)-K(+)-ATPase is mediated by NO and involves activation of guanylate cyclase and elevation of cGMP.

Expression, activity and distribution of Na,K-ATPase subunits during in vitro neuronal induction

The expression pattern of the alpha and beta isoforms and the gamma subunit of the Na,K-ATPase was investigated during in vitro induction of pluripotent murine embryonic stem (ES) cells into neuronal cells. alpha1 protein was expressed in undifferentiated ES (UES) cells and throughout all stages studied. In contrast, alpha3 protein was prominent only when neuronal cells have reached full differentiation. In this model, neuron-depleted cultures did not express the alpha3 isoform, indicating its specificity for mature neuronal cells. UES possessed Na,K-ATPase activity consistent with a single isoform (alpha1), whereas in fully mature neuronal cells a ouabain-sensitive isoform (alpha3) accounted for 27+/-4% of the activity, and a ouabain-resistant isoform (alpha1) 66+/-3%. Immunocytochemistry of mature neuronal cells for alpha1 and alpha3 proteins showed a similar distribution, including cell soma and processes, without evidence of polarization. beta1 protein was expressed in uninduced ES, embryonic bodies (EB) and neuronal cells. While proteins of the beta2 and beta3 isoforms were not detected by immunoblots (except for beta2 in UES), their mRNAs were detected in UES and EB (beta2 and beta3), and in immature and fully differentiated neuronal cells (beta3). Message for the beta2 isoform, however, was not present in neuronal cells. gamma subunit mRNA and protein were undetectable at any stage. These results provide further characterization of neuron-like cells obtained by induction of ES cells in vitro, and establish a model for the expression of isoforms of the Na,K-ATPase during neuronal differentiation. The relation to other aspects of neuronal cell development and relevance to a specialised function for the alpha3 subunit in neurons are discussed.

Oligodendrocytes in brain and optic nerve express the beta3 subunit isoform of Na,K-ATPase

The Na,K-ATPase, which catalyzes the active transport of Na(+) and K(+), has two principal subunits (alpha and beta) that have several genetically distinct isoforms. Most of these isoforms are expressed in the nervous system, but certain ones are preferentially expressed in glia and others in neurons. Of the beta isoforms, beta1 predominates in neurons and beta2 in astrocytes, although there are some exceptions. Here we demonstrate that beta3 is expressed in rat and mouse white matter oligodendrocytes. Immunofluorescence microscopy identified beta3 in oligodendrocytes of rat brain white matter in typical linear arrays of cell bodies between fascicles of axons. The intensity of stain peaked at 20 postnatal days. beta3 was identified in cortical oligodendrocytes grown in culture, where it was expressed in processes and colocalized with antibody to galactocerebroside. In the mouse and rat optic nerve, beta3 stain was seen in oligodendrocytes, where it colocalized with carbonic anhydrase II. For comparison, optic nerve was stained for the beta1 and beta2 subunits, showing distinct patterns of labelling of axons (beta1) and astrocytes (beta2). The C6 glioma cell line was also found to express the beta3 isoform preferentially. Since beta3 was not found at detectable levels in astrocytes, this suggests that C6 is closer to oligodendrocytes than astrocytes in the glial cell lineage.

The molecular basis of hypertension

More than 50 million Americans display blood pressures outside the safe physiological range. Unfortunately for most individuals, the molecular basis of hypertension is unknown, in part because pathological elevations of blood pressure are the result of abnormal expression of multiple genes. This review identifies a number of important blood pressure regulatory genes including their loci in the human, mouse, and rat genome. Phenotypes of gene deletions and overexpression in mice are summarized. More detailed discussion of selected gene products follows, beginning with proteins involved in ion transport, specifically the epithelial sodium channel and sodium proton exchangers. Next, proteins involved in vasodilation/natriuresis are discussed with emphasis on natriuretic peptides, guanylin/uroguanylin, and nitric oxide. The renin angiotensin aldosterone system has an important role antagonizing the vasodilatory cyclic GMP system.

Organization and transcriptional regulation of Drosophila Na(+), K(+)-ATPase beta subunit genes: Nrv1 and Nrv2

Drosophila melanogaster has two Na(+),K(+)-ATPase beta subunit genes (Nervana 1 and 2; Nrv), with tissue-specific expression patterns. Nrv1 produces a single beta subunit isoform expressed primarily in muscle tissue, whereas Nrv2 codes for two different isoforms (2.1 and 2.2) expressed in the nervous system. We have determined the complete molecular genomic organization for both Nrv genes. Only 3kb of DNA separate the 3' end of Nrv2 from Nrv1. The cDNAs from all three forms of Nrv have been mapped onto the genomic structure and all intron-exon junctions have been confirmed by direct sequencing. The genomic DNA positioned in the 5' flanking region of each Nrv gene has also been tested for tissue-specific transcriptional regulatory activity. P-element transformation vectors were constructed, which contained either 7.7kb of Nrv2 or 3.5kb Nrv1 5' flanking DNA driving expression of a lacZ reporter gene. Multiple transgenic Drosophila lines were established for each construct and analyzed for their beta-galactosidase expression pattern. The tissue-specific expression of each Nrv gene is independently regulated by the cis-element(s) present in the 5' flanking region. The Nrv2 5' flanking DNA directs expression exclusively to the nervous system, whereas Nrv1 5' flanking DNA directs expression primarily in muscle tissue.