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At least 1,621 records · Page 90Linked to original sources
PubMed1979

Effects of dibutyryl cyclic AMP and cytochalasin B on cultured human glioma cells.

Cultured human glioma cells (138 MG) exposed to dibutyryl cyclic AMP (dbc-AMP; 0.1--5 mM) attained an arborized shape with thin processes extending from a rounded cell body. Cytochalasin B (CB; 1--1 muM) induced similar morphological changes. The processes in both dbc-AMP and CB treated cells were formed by retraction of the cell margin. Colchicine (1muM) completely and liver treated phalloidin (0.1 mg/ml) partially inhibited the morphological alterations induced by dbc-AMP and CB. Dbc-AMP was found to arrest cell movement, cell division and uptake of 2-deoxy-D-glucose. CB has the same effects but was more potent. The effects of dbc-AMP and CB could be due to interference with a common cellular structure, e.g. microfilaments.

Bucladesine↗
PubMed1987

Retinoic acid-induced rapid loss of nuclear cyclic AMP-dependent protein kinase in teratocarcinoma cells.

To determine what effect retinoic acid might have in modulating cyclic AMP-mediated events at the nucleus of teratocarcinoma cells, we have investigated the effect of retinoic acid treatment of F9 and PC13 cells on cyclic AMP-dependent protein kinase activity and the amounts of the RI and RII cyclic AMP binding proteins present in the nuclear fraction. Exposure of F9 cells to retinoic acid (0.1 microM) induces differentiation to parietal endoderm, while retinoic acid treatment (3 microM) of PC13 cells induces differentiation to visceral endoderm. In both cell types retinoic acid treatment causes a rapid (within 4 h) and pronounced (by 2-fold) decrease in nuclear cyclic AMP-dependent protein kinase activity. Conversely, as measured by cyclic [8-azido-32P]AMP photoaffinity labeling a similar rapid and pronounced decrease in the RI and RII regulatory subunits is observed at the nucleus. This decrease in nuclear cyclic AMP-dependent protein kinases in at least two cell types may be an early event of retinoid action important in the initiation of differentiation.

Animals↗
PubMed1985

Fatty acyl-AMP as an intermediate in fatty acid reduction to aldehyde in luminescent bacteria.

The acyl protein synthetase component (50K) of the fatty acid reductase complex from the luminescent system of Photobacterium phosphoreum has been found to catalyze the activation of fatty acid via formation of an enzyme bound acyl-AMP (carboxyphosphate mixed anhydride) immediately prior to the acylation of the enzyme. PPi-ATP exchange and nucleotide binding experiments are dependent on fatty acid and indicate that the fatty acyl-AMP is directly formed and that an adenylated enzyme intermediate is not part of the mechanism. The formation of acyl-AMP from fatty acid and ATP is reversible with a standard free energy of -2 kcal/mol, and is dependent on Mg2+. The fatty acyl-AMP intermediate has been isolated and shown to be part of the pathway of fatty acid reduction. The 34K component of the complex, which strongly stimulates the acylation of the 50K protein by fatty acyl-AMP or fatty acid and ATP, is not required for the formation of acyl-AMP showing that it differentially affects the fatty acid activation and acylation steps catalyzed by the 50K protein.

Acyltransferases↗
PubMed1980

A novel reaction catalyzed by unadenylylated glutamine synthetase from Escherichia coli. AMP-dependent synthesis of pyrophosphate and L-Glutamate from orthophosphate and L-glutamine.

The unadenylylated, manganese form of glutamine synthetase (L-glutamate: ammonia ligase (ADP forming), EC 6.3.1.2 from Escherichia coli catalyzes a novel, AMP-dependent (reversible) synthesis of pyrophosphate and L-glutamate from orthophosphate and L-glutamine: Formula (See Text). The hydrolysis of the L-glutamine amide bond is coupled to the stoichiometric synthesis of pyrophosphate, although as PPi accumulates, additional hydrolysis of L-glutamine occurs in a secondary reaction catalyzed by the [manganese x enzyme x AMP x PPi] complex. The synthesis of PPi probably occurs at the subunit catalytic site in the positions normally occupied by the beta, gamma-phosphates of ATP. To promote PPi synthesis, AMP apparently binds to the subunit catalytic site rather than to the allosteric inhibitor site; equilibrium binding results suggest that Pi directs the binding of AMP to the active site. In this reaction, Mg2+ will not substitute for Mn2+, and adenylylated glutamine synthetase is inactive. Pyrophosphate is synthesized by the unadenylylated, manganese enzyme at approximately 2% of the rate of that of ATP in the reverse biosynthetic reaction. If P1 is replaced by arsenate, the enzymatic rate of the AMP-supported hydrolysis of L-glutamine is 100-fold faster than is PPi synthesis and is one-half the rate of the ADP-supported, irreversible arsenolysis of L-glutamine. This latter activity also is supported by GMP and IMP, suggesting that the catalytic site of glutamine synthetase has a rather broad specificity for the nucleotide base. The reactions supported by AMP directly relate to the mechanism of glutamine synthetase catalysis.

Adenosine Monophosphate↗
PubMed1984

Cooperation of fructose-2,6-bisphosphate and AMP in the activation of yeast phosphofructokinase.

Yeast phosphofructokinase is effectively activated by AMP and fructose-2,6-bisphosphate. Both effectors influence the sensitivity of the enzyme with respect to fructose-6-phosphate and increase the respective maximum activities. The dependence of phosphofructokinase activity on the concentration of fructose-2,6-bisphosphate was measured at different AMP concentrations and vice versa. By AMP the half activation constant for fructose-2,6-bisphosphate is decreased by one order of magnitude. The affinity to AMP is significantly increased by fructose-2,6-bisphosphate. AMP increases the maximum activity of the enzyme with respect to fructose-2,6-bisphosphate only slightly, while the maximum activity with respect to AMP is drastically increased by fructose-2,6-bisphosphate. The interaction of the two activators is most pronounced at low levels of fructose-6-phosphate and at high concentrations of ATP.

Adenosine Monophosphate↗
PubMed1980

Restoring effects of refeeding and dibutyril cyclic AMP on the increased glucagon secretion of rat pancreatic islets during starvation.

The glucagon release in the presence of glucose and the interaction of dibutyril cyclic AMP was studied in isolated pancreatic islets from fed and 96 h-fasted rats incubated for 30 min. In both states the increase of glucose concentration produced a similar inhibition of glucagon release and stimulation of cyclic AMP content. Higher glucagon secretion and lower cyclic AMP contents were observed in islets from fasted than in those from fed animals at both 2.75 and 16.7 mM glucose. Islets from rats starved for 96 h and refed for 48 h with normal diet or oral 20% glucose showed glucagon release patterns similar to those of controls. Addition of 2 mM dibutyril cyclic AMP to the incubation medium inhibited the fasting-induced increase of glucagon secretion at both glucose levels. These results show an inverse correlation between glucagon secretion and islet cyclic AMP content. However, the sensitivity of the islet to glucose-induced inhibition of glucagon secretion appears to be independent of the islet cyclic AMP levels.

Animals↗
PubMed1995

Inhaled lysine acetylsalicylate (L-ASA) attenuates the bronchoconstrictor response to adenosine 5'-monophosphate (AMP) in asthmatic subjects.

When administered by inhalation, adenosine 5'-monophosphate (AMP) provokes dose-related bronchoconstriction in asthmatic subjects by a mechanism believed to involve mast cell mediator release. However, little is known of the change in airway responsiveness to AMP after cyclo-oxygenase blockade. The aim of this study was to investigate the effect of the potent cyclo-oxygenase inhibitor, lysine acetylsalicylate (L-ASA) administered by inhalation, on AMP-induced bronchoconstriction in a group of nine asthmatic subjects. The subjects studied attended the laboratory on six separate occasions to receive nebulized L-ASA (solution of 90 mg.ml-1) or matched placebo (glycine solution, 30 mg.ml-1) 15 min prior to bronchoprovocation tests with AMP, histamine and methacholine in a randomized, double-blind order. Changes in airway calibre were followed as forced expiratory volume in one second (FEV1) and agonist responsiveness was expressed as the provocative concentration causing a 20% fall in FEV1 from baseline (PC20). Administration of both L-ASA and glycine solution caused a small but significant acute fall in FEV1 from baseline, which returned to normal within 15 min. When compared to placebo, inhaled L-ASA reduced the airway responsiveness to AMP in all the subjects studied, the geometric mean (range) values for PC20 AMP increasing significantly from 36.3 (7.9-250.5) to 101.8 (27.2-1300) mg.ml-1 after placebo and L-ASA, respectively. Moreover, nebulized L-ASA induced a small but significant reduction in airway responsiveness to histamine, the geometric mean (range) PC20 values for histamine increasing from 2.77 (1.05-5.49) to 4.36 (1.69-11.24) mg.ml-1 after placebo and L-ASA, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Monophosphate↗
PubMed1986

The relationship between intracellular cyclic AMP concentrations and the in vitro growth of macrophages.

The addition of cholera toxin, prostaglandins, or one of a series of xanthine phosphodiesterase inhibitors to bone marrow-derived macrophages maintained in liquid culture caused a dose-dependent decrease in colony formation measured 7-10 days following seeding. The growth inhibitory effects of xanthines were in the same order of potency (caffeine less than theophylline less than isobutylmethylxanthine) as their reported ability to inhibit cyclic AMP phosphodiesterase. The relationship between the magnitude of the increases in intracellular concentrations of cyclic AMP observed following the addition of the drugs and the degree of growth inhibition was complex. Combinations of cholera toxin and phosphodiesterase inhibitors caused synergistic elevations in cyclic AMP levels after a lag of approximately 3 days. However, the growth rate was decreased immediately following the addition of the combination of drugs, and thus seemed to be independent of the nucleotide levels. A cyclic AMP-resistant variant of a cloned nontransformed macrophage cell line was found to be also resistant to the growth inhibitory actions of both cholera toxin and prostaglandins. However, resistance to the inhibitory effects of cyclic AMP did not render the cells resistant to a xanthine-induced growth inhibition.

1-Methyl-3-isobutylxanthine↗
PubMed1996

Cyclic AMP stimulates the phosphorylation and activation of p42 and p44 mitogen-activated protein kinases in 3T3-F442A preadipocytes.

The effects of cyclic AMP on mitogen-activated protein (MAP) kinase activation were investigated in 3T3-F442A preadipocytes. Several agents, which raise intracellular cyclic AMP levels by distinct mechanisms, induced a transient activation of the p42 and p44 isoforms of MAP kinase and of a MAP kinase kinase. Activation of MAP kinase by cyclic AMP was prevented by two distinct inhibitors of cyclic AMP-dependent protein kinase and by PD 098059, a specific inhibitor of the activation of the MAP kinase kinase MEK 1. Therefore, in contrast to most cell types studied, cyclic AMP exerts a positive influence on the MAP kinase pathway in 3T3-F442A preadipocytes at a level upstream of the activation of MAP kinase kinase.

3T3 Cells↗
PubMed1998

Cyclic AMP mediates endothelial protection by nitric oxide.

Incubation with TNF-alpha (50 ng/ml) for 72 hours markedly reduced viability of endothelial cells. A 6-hour preincubation with S-nitroso-N-acetyl-D,L-penicillamine (SNAP, 3-100 microM) protected cells in a concentration-dependent manner and decreased TNF-alpha-mediated toxicity by up to 70%. Cytoprotection by SNAP was completely abolished by the adenylyl cyclase inhibitor 2', 5'-dideoxyadenosine and mimicked by 8-bromo cyclic AMP or forskolin. SNAP produced significant increases in cyclic GMP and cyclic AMP, both being abrogated in the presence of the NO scavenger 2-phenyl-4, 4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide (PTIO). Moreover, no endothelial protection by SNAP was detected in the presence of the protein kinase A inhibitor KT5720, whereas the protein kinase G inhibitor KT5823 left cytoprotection virtually unaltered. Our results demonstrate a crucial role for cyclic AMP in mediating NO-induced endothelial protection against TNF-alpha, possibly through cyclic GMP-dependent inhibition of cyclic AMP breakdown. NO-dependent endothelial protection may ultimately result from cyclic AMP-induced up-regulation of antioxidant proteins or down-regulation of cytotoxic processes.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1997

Induction of human thioredoxin in cultured human retinal pigment epithelial cells through cyclic AMP-dependent pathway; involvement in the cytoprotective activity of prostaglandin E1.

Human thioredoxin is one of the oxidative stress-inducible proteins and has a protective function against oxidant-induced injury. To evaluate the possible involvement of thioredoxin in the cytoprotective function of prostaglandin E1, we analysed the effect of prostaglandin E1 on cellular injury by hydrogen peroxide and intracellular thioredoxin induction. Cellular survival of human retinal pigment epithelial cell line, established from normal retinal pigment epithelial cells, following exposure to hydrogen peroxide was markedly improved by pretreatment of 1 microm prostaglandin E1. Thioredoxin expression was augmented in a dose-dependent manner when retinal pigment epithelial cells were pretreated with 10 nm-1 microm prostaglandin E1 1 hr before the exposure to hydrogen peroxide. Intracellular cyclic AMP level was elevated by Prostaglandin E1 when the cells were simultaneously exposed to hydrogen peroxide. Forskolin, an activator of adenylate cyclase, and dibutylyl cAMP, a cyclic AMP analog, could also induce thioredoxin and extend survival of retinal pigment epithelial cells. On the other hand, thioredoxin induction and cellular protection by prostaglandin E1 was blocked by Rp diastereoisomer of cyclic adenosine 3', 5', monophosphorothioate, a competitive inhibitor of cyclic AMP dependent protein kinase. Thioredoxin induction was augmented significantly by pretreatment with prostaglandin I2, a stimulator of cyclic AMP dependent signal pathway, while treatment with prostaglandin F2alpha, a stimulator of inositol phosphate-dependent signal pathway, failed to enhance thioredoxin. These findings indicate that prostaglandin E1 has a cytoprotective activity against oxidative injury, partly through thioredoxin induction via cyclic AMP dependent pathway.

Adenylyl Cyclases↗
PubMed1979

Metabolism of cyclic AMP in non-pathogenic Mycobacterium smegmatis.

The intracellular concentration of cyclic AMP reached a maximum in 3.5-day old cultures of Mycobacterium smegmatis grown in the presence of glycerol as the main source of carbon. Glucose-grown cells exhibited decreased cyclic AMP levels at all stages of growth. When M. smegmatis cells were incubated with various metabolites, pyruvate increased whereas glucose, ctric acid, succinic acid and lactic acid decreased intracellular cyclic AMP levels. No cyclic AMP was detected in the incubation medium. The presence of a cyclic AMP-binding protein was demonstrated in cell-free extracts of M. smegmatis.

Cyclic AMP↗
PubMed1992

Effect of nucleosides and nucleotides and the relationship between cellular adenosine 3':5'-cyclic monophosphate (cyclic AMP) and germ tube formation in Candida albicans.

A yeast-mycelium (Y-M) transition in Candida albicans was induced by exogenous yeast extract, adenosine, adenosine 5'-monophosphate (AMP), adenosine 5'-diphosphate (ADP), adenosine 3':5' cyclic monophosphate (cAMP) and its analogue N6, O2'-dibutyryl adenosine 3':5'-cyclic monophosphate (dbcAMP) in defined liquid medium at 25 degrees C. Adenosine 5'-triphosphate (ATP) was found to delay germ tube formation in yeast cells, whereas the cAMP phosphodiesterase inhibitors, theophylline and caffeine, induced a Y-M transition. Intracellular and extracellular cyclic AMP levels increased during the yeast-mycelium transition and maximum levels of intracellular cyclic AMP coincided with maximum germ tube formation. Of the many inducers and inhibitors of germ tube and mycelium formation in C. albicans tested, including incubation at 37 degrees C or in the presence of 1.5 mM CaCl2, the calmodulin inhibitor calmidazolium (R24571) added together with CaCl2 induced the highest intra- and extracellular cyclic AMP levels. These results confirm the involvement of cyclic AMP in the yeast-mycelium transition of C. albicans.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1985

Selective adsorption of 2'-O-anthraniloyl-AMP on DEAE-Sephadex: the basis of a direct, fluorescent assay for cyclic nucleotide phosphodiesterase.

The fluorescent, 2'-O-anthraniloyl derivative of AMP was selectively absorbed onto DEAE-Sephadex in the presence of zirconyl chloride in citrate buffer. Under these conditions 2'-O-anthraniloyl-cAMP was eluted from the column. The selective adsorption of the AMP derivative onto DEAE-Sephadex, in the presence of zirconyl chloride, was adapted to the direct discontinuous assay of cyclic nucleotide phosphodiesterase. In this assay the enzyme is incubated for 4 min with 2'-O-anthraniloyl-cAMP; after quenching of the reaction by boiling, zirconyl chloride is added and the product (2'-O-anthraniloyl-AMP) is separated from the substrate on a column (0.6 ml) of DEAE-Sephadex. 2'-O-Anthraniloyl-AMP is then eluted with NaCl (2 M) and quantitated spectrofluorometrically. Under the conditions employed, 2'-O-anthraniloyl-AMP concentrations as low as 0.1 nmol can be detected. In the present study, this assay has been used to estimate Km and Vmax values for 2'-O-anthraniloyl-cAMP hydrolysis catalyzed by highly purified, as well as crude, preparations of cyclic nucleotide phosphodiesterase from bovine brain.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1989

Purification and properties of the cyclic 3',5'-AMP-binding protein from the muscle of the Nematode Ascaris suum.

The cyclic 3',5'-AMP-binding protein was isolated from the muscle of Ascaris suum and purified to apparent homogeneity. It migrated as a protein with a relative Mr 54,000 on electrophoresis under denaturing conditions. On gel filtration columns it was eluted at a volume corresponding to a protein of Mr greater than 200,000 under conditions which kept the cyclic 3',5'-AMP-binding property intact. The purified catalytic subunit of protein kinase from Ascaris and the C subunit of cyclic 3',5'-AMP-dependent protein kinase from bovine heart were inhibited by the cyclic 3',5'-AMP-binding protein. Gel filtration studies indicated the formation of a stable protein complex between the protein kinase and the cyclic 3',5'-AMP-binding protein from Ascaris.

Animals↗
PubMed1984

Subcellular distribution and partial characterization of the cyclic AMP-binding proteins of Trypanosoma brucei.

We assayed the cyclic AMP-binding activity of Trypanosoma brucei by two well established methods, such as the one of Gilman (Proc. Natl. Acad. Sci. U.S.A. 67, 305-312, 1970) and Ueland & Doskeland (Biochem. J., 157, 117-126, 1976). The results indicate that the former technique underestimated the total amount of cyclic AMP bound by T. brucei homogenates by up to 7.5 fold. Similar results were obtained with other Trypanosomatidae such as Leishmania tropica, and Crithidia luciliae. The bulk of the cyclic AMP-binding proteins of T. brucei appeared soluble after centrifugation of post-large-granule extracts in isopycnic sucrose-gradients. Upon fractionation by DEAE-Sephacel column chromatography, two peaks of activity eluted which were responsible for all the specific cyclic AMP-binding activity present in the cytosol of T. brucei. These two activities, which we denominated as Peak 'a' and Peak 'b' respectively, differed in a number of properties such as sensitivity to proteases, stability to storage at -20 degrees C, displacement of cyclic AMP bound by adenine analogues, and coefficients of sedimentation.

Animals↗
PubMed1985

A unique type of cyclic AMP-binding protein of Trypanosoma cruzi.

On centrifugation on sucrose density gradients, the cyclic AMP-receptor protein of Trypanosoma cruzi was clearly resolved from the type II regulatory subunit of protein kinase from bovine heart (S20,W = 8.25 and 4.1, respectively). The binding of cyclic [3H]AMP to these two proteins was affected to different extents by several cyclic AMP analogues. Such differences between the cyclic AMP-receptor protein of T. cruzi and cyclic AMP-binding proteins of other eukaryotes might be exploitable by chemotherapy.

Animals↗
PubMed1983

Decreased glucagon-stimulated cyclic AMP production by isolated liver cells of rats with type 2 diabetes.

This study was undertaken to investigate the effect of experimental type 2 diabetes in the rat on the insulin and glucagon receptors and on the early steps of glucagon action. The binding of insulin and glucagon and the glucagon-stimulated cyclic AMP accumulation in the presence of a phosphodiesterase inhibitor (IBMX, 0.1 mmoles/l) were studied in liver cells isolated from 7-9-month-old rats with chronic type 2 diabetes and from control rats. No significant change was observed in [125I] insulin binding and [125I]glucagon binding of diabetic liver cells as compared to controls. Scatchard analysis of the competition experiments indicated that affinity and number of insulin and glucagon receptors were not significantly changed in the liver cells of diabetic rats. The basal cyclic AMP level was significantly lower in the diabetic hepatocytes (2.3 +/- 0.9 pmoles/10(6) cells) than in the controls (4.0 +/- 0.6 pmoles/10(6) cells). Cyclic AMP response to physiological concentrations of glucagon (0.1-1 nmoles/l) was about 2 times lower in the diabetic hepatocytes than in the controls. Furthermore, the basal liver membrane adenylate cyclase activity and the fluoride-activatable adenylate cyclase activity were about 2 times lower in the diabetics as compared to control rats, while the liver cyclic AMP and cyclic GMP phosphodiesterase activities were unchanged. The ability of glucagon to stimulate liver membrane adenylate cyclase over a 10(-12)-10(-6) M concentration range was decreased in diabetic rats. Taken together, these data are consistent with the thesis that the impairment of the liver cyclic AMP response to glucagon in rats with type 2 diabetes is caused by a decrease in the amount of adenylate cyclase in the liver plasma membranes.

3',5'-Cyclic-AMP Phosphodiesterases↗