Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.1.3 (ATPase)
 65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We used lactoperoxidase-mediated iodination to investigate the lumenal polypeptide composition of rat hepatocyte endosomes. A chemical conjugate of asialoorosomucoid and lactoperoxidase that binds specifically to hepatocyte asialoglycoprotein receptors was perfused through isolated rat livers at 16 degrees C in the presence of mannan, resulting in the accumulation of ligand in early endosomes. Endosome containing low density vesicle fractions were subsequently isolated from sucrose gradients of microsomes, and the lactoperoxidase moiety was used to catalyze the iodination of lumenal-facing proteins. After gel electrophoresis, 125I-labeled early endosomes reproducibly showed a distinct 125I-polypeptide profile containing prominently labeled bands migrating at 43, 52, 58, 90, 110, 135, 230, and greater than 300 kDa. The asialoglycoprotein receptor (43-, 52-, and 58-kDa subunits) was by far the predominantly labeled protein even when iodinations were performed under conditions of receptor-ligand dissociation, and we conclude that it is the most abundant hepatocyte early endosomal protein. Furthermore, the iodination profile of the three asialoglycoprotein receptor subunits differed strikingly from their chemical amounts. Using immunoprecipitation, we directly identified the Na+,K(+)-ATPase; to our knowledge, this is the first biochemical evidence for the Na+,K(+)-ATPase in rat hepatocyte early endosomes. We also directly identified receptors for mannose 6-phosphate, epidermal growth factor, transferrin, and polymeric IgA in 125I-labeled early endosomes.
 ...
PMID:Lumenal labeling of rat hepatocyte early endosomes. Presence of multiple membrane receptors and the Na+,K(+)-ATPase. 131 20

The ionic environment of retinal photoreceptors is partially controlled by potassium transporters on retinal glial and retinal pigment epithelial cells (RPE). In this study, serum and epidermal growth factor (EGF) were examined as modulators of potassium transport in confluent cultures of human RPE and rabbit retinal glia. EGF is a known mitogen for confluent RPE cultures and was shown here to also stimulate [3H]thymidine incorporation in cultures of retinal glia. For potassium transport studies 86Rb was used as a tracer during a 17-min incubation. For both retinal cell types the mean total 86Rb uptake in 10% serum was approximately 60% above basal, serum-free controls. For EGF, tested in several experiments in a concentration range from 1 to 100 ng/ml, maximal total uptake was 33 and 24% above controls for RPE and glia, respectively. Inhibitor studies suggested that basal and serum-stimulated uptake for both cell types occurred by the ouabain-sensitive Na-K ATPase pump and by the furosemide- or bumetanide-sensitive Na-K-Cl cotransporter. EGF-stimulated uptake appeared to be due predominantly to the cotransporter. The data suggest that serum components and EGF, which may be available to retina-derived cells under pathologic conditions, may not only stimulate proliferation but may also act as short-term modulators of potassium ion movement and thus affect physiologic processes that are sensitive to ion homeostasis.
 ...
PMID:Modulation of potassium transport in cultured retinal pigment epithelium and retinal glial cells by serum and epidermal growth factor. 133 Jun 55

Preimplantation development encompasses the "free"-living period of mammalian embryogenesis, which culminates in the formation of a fluid-filled structure, the blastocyst. Cavitation (blastocyst formation) is accompanied by the expression of a novel set of gene products that contribute directly to the attainment of cell polarity with the trophectoderm, which is both the first epithelium of development and the outer cell layer encircling the inner cell mass of the blastocyst. Several of these gene products have been identified and include the tight junction (ZO-1), Na/K-ATPase (alpha and beta subunits), uvomorulin, gap junction (connexin43), and growth factors such as transforming growth factor-alpha (TGF-alpha) and epidermal growth factor (EGF). This review will examine the role(s) of each of these gene products during the onset and progression of blastocyst formation. The trophectodermal tight junctional permeability seal regulates the leakage of blastocoel fluid and also assists in the maintenance of a polarized Na/K-ATPase distribution to the basolateral plasma membrane domain of the mural trophectoderm. The polarized distribution of the Na/K-ATPase plays an integral role in the establishment of a trans-trophectoderm Na+ gradient, which drives the osmotic accumulation of water across the epithelium into the nascent blastocoelic cavity. The cell adhesion provided by uvomorulin is necessary for the establishment of the tight junctional seal, as well as the maintenance of the polarized Na/K-ATPase distribution. Growth factors such as TGF-alpha and EGF stimulate an increase in the rate of blastocoel expansion, which could, in part, be mediated by secondary messengers that result in an increase in Na/K-ATPase activity. Insight into the mechanism of cavitation has, therefore, directly linked blastocyst formation to trophectoderm cell differentiation, which arises through fundamental cell biological processes that are directly involved in the attainment of epithelial cell polarity.
 ...
PMID:The cell biology of blastocyst development. 133 76

The 44-amino-acid E5 oncoprotein is the major transforming protein of bovine papillomavirus type 1. It is a highly hydrophobic polypeptide which dimerizes and localizes to the Golgi apparatus and endoplasmic reticulum membranes. Recent evidence suggests that E5 modulates the phosphorylation and internalization of the epidermal growth factor and colony-stimulating factor 1 receptors and constitutively activates platelet-derived growth factor receptors in C127 and FR3T3 cells. Although no direct interaction with these growth factor receptors has yet been identified, the E5 oncoprotein has been shown recently to interact with the hydrophobic 16-kDa component of the vacuolar H(+)-ATPase (16K protein) [D. J. Goldstein, M. E. Finbow, T. Andresson, P. McLean, K. Smith, V. Bubb, and R. Schlegel, Nature (London) 352:347-349, 1991]. In the current study, we have further analyzed the E5-16K protein complex by fast protein liquid chromatography and shown that each E5 dimer appears to bind two 16K proteins. In order to define the specific amino acid residues of E5 which participate in this binding, mutated E5 epitope fusion proteins were analyzed for their ability to coprecipitate 16K protein. Transformation-defective mutants containing amino acid substitutions within the short hydrophilic carboxyl-terminal domain retained the ability to associate with the 16K protein. However, E5 mutants lacking the glutamine residue in the hydrophobic domain were markedly inhibited in 16K protein binding. Most interestingly, the placement of a glutamine in several random hydrophobic sequences facilitated 16K protein binding, defining this residue as a potential binding site for the 16K protein component of the proton pump and exemplifying the critical role of hydrophilic amino acids for mediating specific interactions between transmembrane proteins.
 ...
PMID:A glutamine residue in the membrane-associating domain of the bovine papillomavirus type 1 E5 oncoprotein mediates its binding to a transmembrane component of the vacuolar H(+)-ATPase. 137 89

Epoxygenase and omega- and omega-1-hydroxylases are the major cytochrome P-450-arachidonate (P-450-AA) metabolizing enzymes in renal tissues. We measured P-450-AA metabolism in single nephron segments and determined the tubular localization of this activity in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). Formation of 20-hydroxyeicosatetraenoic acid (20-HETE), the product of AA omega-hydroxylase was specifically localized in the entire proximal tubules (S1, S2, and S3 segments), whereas formation of 19-HETE, the product of omega-1-hydroxylase and epoxyeicosatrienoic acids (EETs), products of AA epoxygenase, was demonstrable throughout the tubule. Although distribution patterns were similar in SHR and WKY, formation of 19- and 20-HETE in the proximal tubules was higher in SHR, whereas the formation of EETs was not different between the two strains. In the proximal tubules, angiotensin II (ANG II) significantly stimulated epoxygenase activity (EETs formation), whereas parathyroid hormone (PTH) and epidermal growth factor (EGF) had no effect on epoxygenase but significantly stimulated omega-hydroxylase activity (20-HETE formation). Because P-450-AA metabolites have a wide and contrasting spectrum of biological and renal effects, from vasodilation to vasoconstriction and from inhibition to stimulation of Na(+)-K(+)-adenosinetriphosphatase, their localization to the specific nephron segments and differential stimulation of their formation by ANG II, PTH, and EGF may contribute not only to renal hemodynamics and blood pressure regulation but also to the regulation of renal sodium and water balance.
 ...
PMID:Renal cytochrome P-450-arachidonic acid metabolism: localization and hormonal regulation in SHR. 156 72

Uptake by the multispecific bile acid transport system of [3H]taurocholate, [14C]cholate, and [3H]-bumetanide into primary cultures of rat hepatocytes was compared with their uptake into freshly isolated rat hepatocytes. The uptake maximum velocity (Vmax) of all compounds declined in primary culture, whereas the Michaelis constant (Km) values remained stable. Loss of uptake was not due to the reduction of driving forces as evaluated from the level of ATP and the activity of Na(+)-K(+)-ATPase. No alpha-fetoprotein was detectable in culture supernatants. Neither growth factors (glycylhistidyl-lysine, epidermal growth factor), peroxisome and cell proliferators (nafenopin, dimethyl sulfoxide), nor bile acids prevented the loss of transport in hepatocyte culture. However, addition of dibutyryl adenosine 3'5'-cyclic monophosphate protracted the transport activity significantly. When cultured rat hepatocytes with reduced transport were detached by trypsin, cells rounded up and showed the same uptake capacity for bumetanide, cholate, and taurocholate as seen in freshly isolated hepatocytes. "Cryptic" transport activity in the lower basolateral membrane facing the support was found using an incubation chamber for cultured hepatocytes, which allowed us to distinguish simultaneously between uptake via the upper and lower basolateral membrane of the cultured cells.
 ...
PMID:Alterations of bile acid and bumetanide uptake during culturing of rat hepatocytes. 169 84

Bafilomycin A1 is known as a strong inhibitor of the vacuolar type H(+)-ATPase in vitro, whereas other type ATPases, e.g. F1,F0-ATPase, are not affected by this antibiotic (Bowman, E.M., Siebers, A., and Altendorf, K. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 7972-7976). Effects of this inhibitor on lysosomes of living cultured cells were tested. The acidification of lysosomes revealed by the incubation with acridine orange was completely inhibited when BNL CL.2 and A431 cells were treated with 0.1-1 microM bafilomycin A1. The effect was revealed by washing the cells. Both studies using 3-(2,4-dinitroanilino)-3'-amino-N-methyldipropylamine and fluorescein isothiocyanate-dextran showed that the intralysomal pH of A431 cells increased from about 5.1-5.5 to about 6.3 in the presence of 1 microM bafilomycin A1. The pH increased gradually in about 50 min. In the presence of 1 microM bafilomycin A1, 125I-labeled epidermal growth factor (EGF) bound to the cell surface at 4 degrees C was internalized normally into the cells at 37 degrees C but was not degraded at all, in marked contrast to the rapid degradation of 125I-EGF in the control cells without the drug. Immunogold electron microscopy showed that EGF was transported into lysosomes irrespective of the addition of bafilomycin A1. These results suggest that the vacuolar type H(+)-ATPase plays a pivotal role in acidification and protein degradation in the lysosomes in vivo.
 ...
PMID:Bafilomycin A1, a specific inhibitor of vacuolar-type H(+)-ATPase, inhibits acidification and protein degradation in lysosomes of cultured cells. 183 76

The effects of epidermal growth factor on Ca2+ signaling in A431 cells were investigated. Epidermal growth factor induced a transient Ca2+ signal in the absence of external Ca2+ and a sustained response in the presence of extracellular Ca2+, indicating an ability to mobilize intracellular Ca2+ as well as the ability to increase Ca2+ entry from the extracellular space. The Ca(2+)-ATPase inhibitor thapsigargin also activated Ca2+ entry, and neither epidermal growth factor nor the guanine nucleotide-dependent protein-linked receptor agonist bradykinin activated additional Ca2+ entry over that due to thapsigargin. In nominally Ca(2+)-free medium, the addition of bradykinin to A431 cells rapidly but transiently increased inositol 1,4,5-trisphosphate and, in parallel fashion, transiently increased cytosolic Ca2+. Unexpectedly, under these experimental conditions, epidermal growth factor elicited a small but significant Ca2+ signal after the addition of bradykinin. Experiments were designed to determine whether the Ca2+ response to epidermal growth factor after bradykinin results from mobilization of Ca2+ by an inositol 1,4,5-trisphosphate-independent mechanism. Epidermal growth factor stimulated additional inositol 1,4,5-trisphosphate formation in bradykinin-treated cells. Furthermore, the Ca2+ signals elicited by both bradykinin and epidermal growth factor were blocked in cells microinjected with the inositol 1,4,5-trisphosphate receptor antagonist heparin, whereas the intracellular Ca(2+)-ATPase inhibitor thapsigargin still mobilized Ca2+. Finally, histamine, a less efficacious guanine nucleotide-dependent protein-linked receptor agonist, as well as photolyzed, microinjected, caged inositol 1,4,5-trisphosphate, also mobilized Ca2+ after bradykinin. The results of this study show (i) that epidermal growth factor activates intracellular Ca2+ release as well as Ca2+ entry, the latter most likely resulting from an indirect effect due to the depletion of intracellular Ca2+ pools, (ii) that the actions of epidermal growth factor on Ca2+ homeostasis can be fully accounted for by inositol 1,4,5-trisphosphate formation, and (iii) that the ability of A431 cells to produce Ca2+ signals when epidermal growth factor is applied after bradykinin can be explained by the rapid and complete desensitization of the bradykinin stimulated phospholipase C activity.
 ...
PMID:Role of inositol (1,4,5)trisphosphate in epidermal growth factor-induced Ca2+ signaling in A431 cells. 187 11

The role of vacuolar-type H(+)-ATPase (V-ATPase) in the cytotoxic action of diphtheria toxin (DT) was studied by using bafilomycin A1, a specific inhibitor of V-ATPase. Studies with acridine orange showed that the acidification of intracellular acidic compartments was inhibited strongly when Vero cells were treated with 500 nM bafilomycin A1, indicating that bafilomycin effectively inhibits V-ATPase when it is added to the culture medium. The toxicity of DT to Vero cells, which was determined by the inhibition of protein synthesis by DT, was inhibited partially by bafilomycin at 10 nM and inhibited completely at 500 nM. Therefore, V-ATPase is involved in the expression of the toxicity of DT. Studies using 125I-labeled DT showed that bafilomycin inhibited the degradation of internalized DT, indicating that V-ATPase is also involved in this step. Subcellular fractionation revealed that 125I-DT accumulated mainly in the endosome fraction, and not in the lysosome fraction, when the cells were incubated with 125I-DT in the presence of bafilomycin. Under the cell fractionation conditions similar to those used for the DT-treated cells, we determined the location of 125I-labeled epidermal growth factor in the degradation pathway. The result suggests that bafilomycin A1 does not inhibit the transport of epidermal growth factor to lysosome.
 ...
PMID:The cytotoxic action of diphtheria toxin and its degradation in intact Vero cells are inhibited by bafilomycin A1, a specific inhibitor of vacuolar-type H(+)-ATPase. 214 89

The human hepatoma cell line (Li-7A) possesses a high concentration of epidermal growth factor (EGF) receptors and exhibits ectoATPase activity in the presence of either MgATP or CaATP (Knowles: J. Cell. Physiol., 134:109-116, 1988). Growth for 96 hours in the presence of both EGF and cholera toxin or another cyclic AMP elevating agent induced an ectoATPase activity which was more active with CaATP and resistant to inhibition by the sulfydryl reagent, p-chloromercuriphenylsulfonate (pCMPS) (Knowles: Arch. Biochem. Biophys., 263: 264-271, 1988). In contrast, treatment of cells with butyrate, a short chain organic acid which can be derived from the analogue, dibutyryl cyclic AMP, resulted in a 4-7-fold increase of an ectoATPase which was more active with MgATP and highly sensitive to pCMPS inhibition. Maximal induction by butyrate required 48 hours and was dependent on butyrate concentration, but was independent of EGF and cyclic AMP elevating agents. Of six organic acids tested, butyrate was most effective in the induction of the ectoMg2(+)-ATPase. The increase in the ectoMg2(+)-ATPase activity could be prevented with actinomycin D and cycloheximide, indicating that both transcription and translation were necessary for induction. In addition to the induction of the ectoMg2(+)-ATPase, butyrate induced alkaline phosphatase activity, but had no effect on a third ectoenzyme 5'-nucleotidase. These data further support our proposal that two distinct ectoATPases exist in the plasma membrane of Li-7A hepatoma cells.
 ...
PMID:Butyrate induces an ectoMg2(+)-ATPase activity in Li-7A human hepatoma cells. 216 33


1 2 3 4 5 6 7 8 9 10 Next >>