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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. The endocytic pathway of horseradish peroxidase (HRP) was investigated in the perikarya of cultured neurons by electron microscopy and enzyme cytochemistry. The tracer was observed in endocytic pits and vesicles, endosomes, multivesicular bodies, and lysosomes. It took approximate 15 min for the transfer of HRP from the exterior of the cell to the lysosomes. 2. Monensin induced distension of the Golgi apparatus and formation of intracellular vacuoles. When neurons were incubated with both monensin and HRP for 30 to 120 min, the number of HRP-labeled endosomes was greater than that in the monensin-free group, whereas the reverse was seen for HRP-positive lysosomes. The formation of HRP-positive lysosomes in monensin-treated cells was blocked by 47 to 79%. 3. These results indicate that the intracellular transport of the endocytosed macromolecule is pH dependent. It is also possible that the export of lysosomal enzymes is inhibited by monensin, resulting in an accumulation of the endosomes and a reduction of the lysosomes.
Cell Mol Neurobiol 1992 Aug
PMID:Effect of monensin on the neuronal ultrastructure and endocytic pathway of macromolecules in cultured brain neurons. 139 68

The ionophore monensin was found to markedly reduce the rate of return of vasopressin V2-receptors to the membrane following down-regulation with [Arg8]vasopressin (AVP), as well as hormone dissociation (unloading) from cells following ligand binding and internalization in LLC-PK1 renal epithelial cells. Monensin-resistant LLC-PK1 mutants were isolated and characterized for V2-receptor recycling. Whilst the MN-41 mutant appeared to be impaired in [3H]AVP internalization, the MN-11 and MN-21 mutants exhibited parental V2-receptor binding and internalization, but markedly impaired receptor recycling subsequent to ligand-dependent receptor down-regulation. Unloading subsequent to ligand binding and internalization at 37 degrees C was also much slower in the mutants either at 37 degrees C or 23 degrees C. In contrast, unloading subsequent to binding at 23 degrees C, or to binding at 37 degrees C in the presence of NH4Cl, was comparable in LLC-PK1 and mutant cells implying the active nature of the recycling process impaired in the mutants. The mutations conferring resistance to monesin thus concomitantly impaired V2-receptor recycling in the mutants. Results argue for a monensin-sensitive endosomal/lysosomal pathway for the renal V2-receptor, representing the first such report for an adenylate cyclase stimulating receptor.
Mol Cell Endocrinol 1991 Oct
PMID:Monensin-resistant LLC-PK1 cell mutants are affected in recycling of the adenylate cyclase-stimulating vasopressin V2-receptor. 179 84

Production and release of lymphotoxin (LT) was studied by metabolic labeling of human B- and T-cell lines with 14C-leucine and 35S-methionine. LT was immunoprecipitated with antiserum to LT and separated by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE) followed by fluorography. Two molecular weight forms of LT with different rates of release were found both in cell supernatants and cell extracts. Monensin, a sodium ionophore, inhibited the release of LT. LT still appeared in two molecular weight forms after deglycosylation with N-glycanase. Treatment of cells with swainsonine followed by digestion of released LT with endoglycosidase H (endo H) demonstrated that the oligosaccharides were of the complex type. Subcellular fractionation of cells on Percoll density gradients demonstrated that intracellular LT is located to intermediate density fractions. No LT was found in the high density fractions corresponding to lysosomes. Phorbol 12-myristate 13-acetate induced production of tumor necrosis factor (TNF) in the B-lymphoblastoid cell line RPMI-1788. In conclusion, we have demonstrated the presence of two distinct molecular weight forms of LT, which contain N-linked oligosaccharides of the complex type.
Mol Immunol
PMID:Lymphotoxin produced by human B- and T-cell lines appears in two distinct forms. 201 Nov 32

Maintenance of low coronary flow (1 ml/min) during 40 or 70 min of anoxia maintained function and prevented Ca2+ overload during reoxygenation in isolated rat hearts. In comparison, recovery from 40 min of global ischemia resulted in only 20% of preischemic function and an increase in end-diastolic pressure (LVEDP) to 39 mmHg. Reperfusion Ca2+ uptake rose from 0.6 to 10.2 mumol/g dry tissue. Intracellular Na+ (Nai+) increased from 13 to 61 mumol/g dry tissue after 40 min of global ischemia, but was unchanged in hearts with low flow anoxia. When glucose and pyruvate were omitted from buffer used for anoxic perfusion, recovery was only 15% of preanoxic values, LVEDP rose to 32 mmHg, and reperfusion Ca2+ uptake was 7.2 mumol/g dry. In addition, Nai+ increased (47.4 mumol/g dry tissue) and ATP was depleted (1.0 mumol/g dry tissue) in the absence of substrate. In anoxic hearts supplied substrate, Nai+ stayed low (12 mumol/g dry tissue) and ATP was preserved (11.6 mumol/g dry tissue). Addition of ouabain (100 or 200 microM) and provision of zero-K+ buffer increased Nai+ and resulted in impaired functional recovery, increased LVEDP, and greater reperfusion Ca2+ uptake. These interventions also decreased energy availability in anoxic hearts. To distinguish between effects of Na+ accumulation and ATP depletion, monensin, a Na+ ionophore, was added during low flow anoxia. Monensin increased Nai+, decreased functional recovery and increased reperfusion Ca2+ uptake in a dose-dependent manner (1-10 microM) without changing ATP content. These results suggested that reduction of Nai+ accumulation by maintenance of Na+, K+ pump activity was the major mechanism of the beneficial effects of low coronary flow on reperfusion injury.
J Mol Cell Cardiol 1990 Jan
PMID:Na+ accumulation increases Ca2+ overload and impairs function in anoxic rat heart. 215 54

Monensin, an inhibitor of Golgi function, was used to investigate the role of this cell compartment in the glycosylation of Leishmania donovani promastigote secretory acid phosphatase (EC 3.1.3.2). Monensin-treated cells demonstrated morphological changes in the Golgi complex and secreted enzyme with an altered electrophoretic mobility: two discrete bands of approximately 95 and 110 kDa were found, as compared to the heterodisperse nature of the enzyme from untreated controls. Chemical deglycosylation by mild acid hydrolysis resulted in a similar effect on the electrophoretic mobility of purified extracellular enzyme. Acid phosphatase was also treated with N-glycosidase F (EC 3.5.1.52) to remove N-linked oligosaccharides. The altered lectin-binding properties of the enzyme after these two treatments demonstrated that an unusual type of galactose-containing acid-labile carbohydrate was present in secretory acid phosphatase in addition to the N-linked oligosaccharides. Further, experiments with 32P-labelled enzyme indicated that phosphodiester bonds were the structural component responsible for the sensitivity of this carbohydrate to mild acid hydrolysis. Cumulatively, these results demonstrated that a novel form of Golgi-mediated posttranslational modification had occurred to the secretory acid phosphatase presumably by the addition of an acid-labile phosphoglycan.
Mol Biochem Parasitol 1990 Mar
PMID:Golgi-mediated post-translational processing of secretory acid phosphatase by Leishmania donovani promastigotes. 232 58

New aspects of the distribution of highly phosphorylated proteins in cells infected with herpes simplex virus type 1 (HSV-1) were investigated at the ultrastructural level by the use of drugs which inhibit the glycosylation of viral proteins. The highly phosphorylated proteins were localized by the bismuth tartrate procedure applied on sections of glutaraldehyde-fixed cells embedded in Lowicryl. The drugs employed were tunicamycin, which alters the glycosylation activity of the rough endoplasmic reticulum (RER), and monensin, which blocks the migration of vesicles of the Golgi apparatus (GA) thereby impairing the glycosylation function of the GA. Tunicamycin induced proliferation of RER and the accumulation of highly phosphorylated proteins on its membranes and also impaired GA vesicle maturation and inhibited the usual accumulation of phosphorylated proteins within them. Monensin induced proliferation of the nuclear envelope, including both outer and inner membranes, with bismuth bound to staggered segments of the latter, and also affected the GA in that bismuth-binding proteins were accumulated on the external surface of the swollen vesicles instead of the lumen. These data suggest that an injury of one membrane system, RER or GA, engenders consequential effects on the other. This also supports evidence for an interrelationship between post-translational glycosylation and phosphorylation of proteins in HSV infection.
J Ultrastruct Mol Struct Res
PMID:Effects of tunicamycin and monensin on the distribution of highly phosphorylated proteins in cells infected with herpes simplex virus type 1. 247 42

When previous data suggested a growth hormone-releasing factor (GRF)-sensitive branch in intracellular hormone processing, the monensin-sensitive Golgi apparatus seemed a likely candidate. We examined monensin's effect on basal and GRF-stimulated release of newly synthesized and stored rat growth hormone (rGH) and rat prolactin (rPRL). 14C-Pre-labeled, perifused rat pituitary fragments were exposed to [3H]leucine in 0-10 microM monensin; a pulse of 3 nM GRF assessed subsequent secretory responsivity. Monensin dose-dependently reduced basal release of stored [14C]rGH and [14C]rPRL. GRF-stimulated release of stored [14C]hormone was doubled after 0.03 microM and 0.1 microM monensin; higher concentrations diminished stored hormone release. Low concentrations of monensin accelerated basal (0.03 microM and 0.1 microM) and GRF-stimulated (0.03 microM) [3H]rGH and [3H]rPRL release without altering recovery; higher monensin concentrations (greater than or equal to 1 microM) reduced basal, and abolished GRF-stimulated, new hormone release and reduced total [3H]rGH and [3H]rPRL recovery. These data are consistent with a GRF-sensitive and monensin-influenced branch in intracellular hormone processing that regulates the fraction of new hormone exiting the cell without prior immersion in storage compartments.
Mol Cell Endocrinol 1989 Apr
PMID:Monensin influences basal and human growth hormone-releasing hormone 44-induced release of stored and new rat growth hormone and prolactin. 250 Nov 24

T47D cells possess specific calcitonin (CT) receptors and a CT-responsive adenylate cyclase. Internalization of part of their CT receptors has been suggested. At 37 degrees C, bound 125I-labelled salmon CT (sCT) becomes increasingly resistant to acid washing, which can remove surface-bound hormone, thus indicating internalization. Monensin and chloroquine, which raise the pH of the lysosomes and thereby inhibit cellular processing of endosomes, inhibit the decrease of total bound activity seen in the controls. Acid-resistant (internalized) activity increases to the levels of total binding. Preincubation with sCT leads to a loss of specific binding. Recovery of CT binding is prevented by monensin, which also inhibits transport of cellular proteins to the cell membrane. Recovery is not influenced by chloroquine. As chloroquine prevents recycling, we conclude that after binding of CT the receptors are internalized, transferred to a lysosomal compartment, and degraded intracellularly without recycling. All receptors seem to undergo internalization. Desensitization to CT in T47D cells is at least partly mediated by intracellular metabolism of CT receptors.
Mol Cell Endocrinol 1988 Jul
PMID:Down-regulation of calcitonin receptors in T47D cells by internalization of calcitonin-receptor complexes. 285 Feb 44

The existence and importance of the Na+/H+ exchanger in intracellular pH (pHi) regulation in ovarian cells was studied in acid-loaded avian granulosa cells by monitoring the recovery of normal pHi using a trapped fluorescein derivative as an indicator. The resting pHi of freshly isolated granulosa cells from preovulatory follicles was 6.80 +/- 0.08 when the extracellular pH (pHo) and sodium concentration (Na+o) were 7.3 and 144 mmol/l respectively. While exposure of granulosa cells to high pHo (pHo greater than 7.45) medium shifted the pHi upward with time, incubation of the cells in low pHo (pH less than 6.80) buffer resulted in a significant decrease in pHi. In contrast, pHi remained constant when pHo was varied between the broad range of 6.8-7.4. When the cytoplasm was acidified by treatment with nigericin in choline+ buffer, both the magnitude and rate of recovery of normal pHi was suppressed significantly with decreasing pHo, but increased in high pHo medium. The recovery of pHi was dependent upon the concentration of extracellular sodium, in that the recovery rate and magnitude increased concomitantly with increases in Na+o concentrations, while the recovery was abolished when Na+o was completely replaced with choline+. In addition, the sodium ionophore monensin enhanced the recovery rate of normal pHi in a concentration-dependent manner. This action of monensin was observed only when sodium was present in the incubation medium, indicating that Na+o entry is important for the recovery of normal pHi. Monensin also evoked further cytoplasmic alkalinization in fully recovered cells, with a relative net effect dependent upon the level of Na+o present.(ABSTRACT TRUNCATED AT 250 WORDS)
J Mol Endocrinol 1988 Sep
PMID:Sodium-dependent intracellular pH regulation in granulosa cells of the domestic hen (Gallus domesticus). 285 92

The molecular mechanism of desensitization of antidiuretic hormone receptors is not well understood. Preincubation of LLC-PK1 cells with lysine vasopressin (LVP) (10(-6) M, 5 h) decreased subsequent LVP-stimulated cAMP accumulation in cells by 83% and reduced the Vmax of LVP-stimulated adenylate cyclase by 81%. Such preincubation also reduced by 90% the binding of [3H]LVP to both intact cells and isolated plasma membranes, suggesting a loss of vasopressin receptors. Both the reduction in cAMP response and the apparent loss of receptors showed similar dose and time dependence. Monensin (33 microM) did not alter [3H]LVP binding or stimulation of cAMP by LVP, nor did it prevent desensitization. However, membranes prepared from cells preincubated with LVP in the presence of monensin did not show a decrease in [3H]LVP binding. Forskolin preincubation, at 0.1, 1, 10 and 100 microM, did not alter [3H]LVP binding or accumulation of cellular cAMP by LVP, nor did it induce desensitization to LVP. Cells desensitized with varying LVP concentrations in the presence of 10 microM forskolin displayed the same loss of [3H]LVP binding and LVP responsiveness as observed in the absence of forskolin. LVP-desensitized cells, upon removal from LVP-containing medium, recovered cAMP responsiveness to LVP and specific binding of [3H]LVP at the same rate, achieving control levels after 50 h. Recovery was prevented by cycloheximide (25 micrograms/ml). These findings are consistent with a desensitization process involving LVP-mediated receptor internalization, and a recovery process requiring protein synthesis.
Mol Cell Endocrinol 1985 May
PMID:Desensitization of LLC-PK1 cells by vasopressin results in receptor down-regulation. 298 32


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