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1
Chin, Jik, and Xiang Zou. "Catalytic hydrolysis of cAMP." Canadian Journal of Chemistry 65, no. 8 (August 1, 1987): 1882–84. http://dx.doi.org/10.1139/v87-315.
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[Co(trien)(OH2)(OH)]Cl2 is highly efficient in catalyzing the hydrolysis of cAMP to adenosine in neutral water (6 × 10−6 M−1 s−1 at 50 °C). The cobalt complex promoted hydrolysis of cAMP is estimated to be about a hundred million times faster than the uncatalyzed hydrolysis of cAMP. In the time that [Co(trien)(OH2)(OH)]Cl2 produces 50% cleavage of cAMP, [Co(en)2(NH3)(OH)]Cl2 or ZnCl2 has no observable effect on the hydrolysis of cAMP. A detailed mechanism is presented for the cobalt complex promoted hydrolysis of the phosphodiester.
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Witwicka, Hanna, Marcin Kobiałka, and Wojciech A. Gorczyca. "Hydrolysis of cyclic GMP in rat peritoneal macrophages." Acta Biochimica Polonica 49, no. 4 (December 31, 2002): 891–97. http://dx.doi.org/10.18388/abp.2002_3748.
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Intact rat peritoneal macrophages (rPM) treated with 3-isobutyl-1-methylxanthine (IBMX), an inhibitor of phosphodiesterases (PDEs), accumulated more cGMP than untreated cells. A PDE activity toward [(3)H]cGMP was detected in the soluble and particulate fractions of rPM. The hydrolysis of cGMP was Ca(2+)/calmodulin-independent but increased in the presence of cGMP excess. Similar results were obtained when [(3)H]cAMP was used as a substrate. The hydrolytic activity towards both nucleotides was inhibited in the presence of IBMX. Therefore, the PDEs of families 2, 5, 10 and 11 are potential candidates for cGMP hydrolysis in the rPM. They may not only regulate the cGMP level in a feedback-controlled way but also link cGMP-dependent pathways with those regulated by cAMP.
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Alava, M. A., K. E. DeBell, A. Conti, T. Hoffman, and E. Bonvini. "Increased intracellular cyclic AMP inhibits inositol phospholipid hydrolysis induced by perturbation of the T cell receptor/CD3 complex but not by G-protein stimulation. Association with protein kinase A-mediated phosphorylation of phospholipase C-γ 1." Biochemical Journal 284, no. 1 (May 15, 1992): 189–99. http://dx.doi.org/10.1042/bj2840189.
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Modulation of inositol phospholipid (InsPL) hydrolysis in response to increasing intracellular concentrations of cyclic AMP (cAMP) was studied in a murine T helper type II (Th2) lymphocyte clone, 8-5-5. Intact 8-5-5 cells produced maximal amounts of cAMP in response to prostaglandin E2 (PGE2), cholera toxin (CTx) or 7 beta-deacetyl-7 beta-(gamma-N-methylpiperazino)butyryl forskolin (dmpb-forskolin). cAMP generation reached a plateau after 5 min of treatment with dmpb-forskolin (300 microM) or PGE2 (1 microM), but required 60 min of treatment with CTx (1 microgram/ml). Preincubation of 8-5-5 cells with 1 microM-PGE2 or 300 microM-dmpb-forskolin (10 min at 37 degrees C) or with 1 microgram of CTx/ml (60 min at 37 degrees C) completely inhibited InsPL hydrolysis induced by perturbation of the T cell receptor (TCR)/CD3 complex with the monoclonal antibody 145.2C11. Preincubation with the cAMP analogue 8-bromo-cyclic AMP (8-Br-cAMP) also inhibited InsPL hydrolysis. Tetanolysin-permeabilized 8-5-5 cells produced cAMP in response to PGE2, dmpb-forskolin and guanosine 5′-[gamma-thio]triphosphate (GTP[S]), a non-cell-permeating, non-hydrolysable analogue of GTP that directly activates G-proteins. No inhibition of TCR/CD3-induced InsPL hydrolysis was observed under these conditions. InsPL hydrolysis was also unaffected when permeabilized cells were incubated with up to 10 mM-8-Br-cAMP, suggesting that permeabilized cells lost (a) soluble effector molecule(s) involved in mediating the inhibitory effect observed in intact cells. Treatment of 8-5-5 cells with dmpb-forskolin or CTx prior to permeabilization resulted in inhibition of TCR/CD3-induced InsPL hydrolysis, but did not affect InsPL hydrolysis induced via G-protein stimulation with GTP[S]. Treatment of permeabilized 8-5-5 cells with purified cAMP-dependent protein kinase (PKA) resulted in inhibition of TCR/CD3- but not GTP[S]-induced InsPL hydrolysis. This effect was associated with phosphorylation of phospholipase (PLC)-gamma 1 in the absence of phosphorylation of components of the TCR/CD3 complex. These results suggest that PKA-mediated phosphorylation of PLC may regulate TCR/CD3-induced InsPL hydrolysis.
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Mary TANG, K., Elliott K. JANG, and Richard J. HASLAM. "Expression and mutagenesis of the catalytic domain of cGMP-inhibited phosphodiesterase (PDE3) cloned from human platelets." Biochemical Journal 323, no. 1 (April 1, 1997): 217–24. http://dx.doi.org/10.1042/bj3230217.
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We have used reverse transcriptase PCR, platelet mRNA and degenerate primers based on platelet peptide sequences, to amplify a fragment of platelet cGMP-inhibited phosphodiesterase (cGI-PDE; PDE3). Sequence analysis of this clone established that both the platelet and the cardiac forms of PDE3 were derived from the same gene (PDE3A). A RT-PCR product representing the C-terminal half of platelet PDE3 cDNA and corresponding to amino acid residues 560-1141 of the cardiac enzyme, was cloned and expressed in Escherichia coli cGI-PDEΔ1. Further deletion mutants were constructed by removing either an additional 100 amino acids from the N-terminus (cGI-PDEΔ2) or the 44-amino-acid insert characteristic of the PDE3 family, from the catalytic domain (cGI-PDEΔ1Δi). In addition, site-directed mutagenesis was performed to explore the function of the 44-amino-acid insert. All mutants were evaluated for their ability to hydrolyse cAMP and cGMP, their ability to be photolabelled by [32P]cGMP and for the effects of PDE3 inhibitors. The Km values for hydrolysis of cAMP and cGMP by immunoprecipitates of cGI-PDEΔ1 (182±12 nM and 153±12 nM respectively) and cGI-PDEΔ2 (131±17 nM and 99±1 nM respectively) were significantly lower than those for immunoprecipitates of intact platelet PDE3 (398±50 nM and 252±16 nM respectively). Moreover, N-terminal truncations of platelet enzyme increased the ratio of Vmax for cGMP/Vmax for cAMP from 0.16±0.01 in intact platelet enzyme, to 0.37±0.05 in cGI-PDEΔ1 and to 0.49±0.04 in cGI-PDEΔ2. Thus deletion of the N-terminus enhanced hydrolysis of cGMP relative to cAMP, suggesting that N-terminal sequences may exert selective effects on enzyme activity. Removal of the 44-amino-acid insert generated a mutant with a catalytic domain closely resembling those of other PDE gene families but despite a limited ability to be photolabelled by [32P]cGMP, no cyclic nucleotide hydrolytic activities of the mutant were detectable. Mutation of amino acid residues in putative β-turns at the beginning and end of the 44-amino-acid insert to alanine residues markedly reduced the ability of the enzyme to hydrolyse cyclic nucleotides. The PDE3 inhibitor, lixazinone, retained the ability to inhibit cAMP hydrolysis and [32P]cGMP binding by the N-terminal deletion mutants and the site-directed mutants, suggesting that PDE3 inhibitors may interact exclusively with the catalytic domain of the enzyme.
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Takahashi, T., S. Kurosawa, and C. Owyang. "Regulation of PI hydrolysis and cAMP formation by muscarinic M3 receptor in guinea pig gallbladder." American Journal of Physiology-Gastrointestinal and Liver Physiology 267, no. 4 (October 1, 1994): G523—G528. http://dx.doi.org/10.1152/ajpgi.1994.267.4.g523.
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Carbachol (10(-8)-10(-3) M) produced two distinct biochemical responses in the guinea pig gallbladder smooth muscle: simulation of phosphoinositide (PI) hydrolysis and inhibition of forskolin-mediated adenosine 3',5'-cyclic monophosphate (cAMP) formation in a dose-dependent manner. The mean effective dose (ED50) concentration (1.6 x 10(-5) M) of carbachol-mediated stimulation of PI hydrolysis was 145 times greater than the ED50 concentration (1.1 x 10(-7) M) of carbachol mediated inhibition of cAMP formation. The inhibitory effect of carbachol on cAMP formation was antagonized by the pretreatment of pertussis toxin. To determine whether these two biochemical responses were mediated by the same or different subtypes of muscarinic receptors, the relative potencies of muscarinic receptor antagonists were calculated by Schild analysis. The M3 muscarinic antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) exhibited inhibitory constant (Ki) values at 0.3 and 1.2 nM in antagonizing the stimulation of PI hydrolysis and the inhibition of cAMP formation, respectively. The corresponding Ki values for pirenzepine, a muscarinic M1 antagonist, were 11 and 130 nM. The corresponding Ki values for AF-DX 116, a muscarinic M2 antagonist, were 34 and 450 nM. Thus 4-DAMP was 37x and 108x more potent than pirenzepine in antagonizing the stimulation of PI hydrolysis and the inhibition of cAMP formation, respectively. In addition, compared with AF-DX 116, 4-DAMP was 113x and 375x more potent in reducing stimulation of PI hydrolysis and inhibition of cAMP formation. Cholecystokinin (CCK) octapeptide (10(-10)-(10-6) M) caused a significant increase of PI hydrolysis but had no inhibitory effects on cAMP formation evoked by forskolin (10(-5) M).(ABSTRACT TRUNCATED AT 250 WORDS)
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Bosgraaf, Leonard, Henk Russcher, Helena Snippe, Sonya Bader, Joyce Wind, and Peter J. M. Van Haastert. "Identification and Characterization of Two Unusual cGMP-stimulated Phoshodiesterases in Dictyostelium." Molecular Biology of the Cell 13, no. 11 (November 2002): 3878–89. http://dx.doi.org/10.1091/mbc.e02-05-0302.
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Recently, we recognized two genes, gbpA andgbpB, encoding putative cGMP-binding proteins with a Zn2+-hydrolase domain and two cyclic nucleotide binding domains. The Zn2+-hydrolase domains belong to the superfamily of β-lactamases, also harboring a small family of class II phosphodiesterases from bacteria and lower eukaryotes. Gene inactivation and overexpression studies demonstrate thatgbpA encodes the cGMP-stimulated cGMP-phosphodiesterase that was characterized biochemically previously and was shown to be involved in chemotaxis. cAMP neither activates nor is a substrate of GbpA. The gbpB gene is expressed mainly in the multicellular stage and seems to encode a dual specificity phosphodiesterase with preference for cAMP. The enzyme hydrolyses cAMP ∼9-fold faster than cGMP and is activated by cAMP and cGMP with aK A value of ∼0.7 and 2.3 μM, respectively. Cells with a deletion of the gbpB gene have increased basal and receptor stimulated cAMP levels and are sporogeneous. We propose that GbpA and GbpB hydrolyze the substrate in the Zn2+-hydrolase domain, whereas the cyclic nucleotide binding domains mediate activation. The human cGMP-stimulated cAMP/cGMP phosphodiesterase has similar biochemical properties, but a completely different topology: hydrolysis takes place by a class I catalytic domain and GAF domains mediate cGMP activation.
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Weijer, Cornelis J., and Antony J. Durston. "Influence of cyclic AMP and hydrolysis products on cell type regulation in Dictyostelium discoideum." Development 86, no. 1 (April 1, 1985): 19–37. http://dx.doi.org/10.1242/dev.86.1.19.
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We describe the effect of cyclic AMP on regulation of the proportion of prespore and prestalk cells in Dictyostelium discoideum. Prespore and prestalk cells from slugs were enriched on Percoll density gradients and allowed to regulate in suspension culture under 100% oxygen. The transition of prespore to prestalk cells is blocked by cAMP, while cAMP phosphodiesterase and caffeine cause a decrease in the number of prespore cells. This suggests that extracellular cAMP plays a role in cell type proportioning by inhibiting the conversion of prespore to prestalk cells. Low concentrations of cAMP prevent the conversion of prestalk to prespore cells; the same effect is seen with hydrolysis products of cAMP, 5 AMP, adenosine and also adenine. We suggest that, when low concentrations of cAMP are added to regulating cells, the cAMP itself is quickly broken down and the breakdown products thereafter inhibit the prestalk-to-prespore conversion. The relevance of these findings is discussed in the context of an non-positional double-negative feedback model for cell type homeostasis.
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Tulsian, Nikhil K., Abhijeet Ghode, and Ganesh S. Anand. "Adenylate control in cAMP signaling: implications for adaptation in signalosomes." Biochemical Journal 477, no. 16 (August 21, 2020): 2981–98. http://dx.doi.org/10.1042/bcj20200435.
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In cAMP-Protein Kinase A (PKA) signaling, A-kinase anchoring protein scaffolds assemble PKA in close proximity to phosphodiesterases (PDE), kinase-substrates to form signaling islands or ‘signalosomes’. In its basal state, inactive PKA holoenzyme (R2:C2) is activated by binding of cAMP to regulatory (R)-subunits leading to dissociation of active catalytic (C)-subunits. PDEs hydrolyze cAMP-bound to the R-subunits to generate 5′-AMP for termination and resetting the cAMP signaling. Mechanistic basis for cAMP signaling has been derived primarily by focusing on the proteins in isolation. Here, we set out to simulate cAMP signaling activation-termination cycles in a signalosome-like environment with PDEs and PKA subunits in close proximity to each other. Using a combination of fluorescence polarization and amide hydrogen exchange mass spectrometry with regulatory (RIα), C-subunit (Cα) and PDE8 catalytic domain, we have tracked movement of cAMP through activation-termination cycles. cAMP signaling operates as a continuum of four phases: (1) Activation and dissociation of PKA into R- and C-subunits by cAMP and facilitated by substrate (2) PDE recruitment to R-subunits (3) Hydrolysis of cAMP to 5′-AMP (4) Reassociation of C-subunit to 5′-AMP-bound-RIα in the presence of excess ATP to reset cAMP signaling to form the inactive PKA holoenzyme. Our results demonstrate that 5′-AMP is not merely a passive hydrolysis end-product of PDE action. A ‘ligand-free’ state R subunit does not exist in signalosomes as previously assumed. Instead the R-subunit toggles between cAMP- or 5′-AMP bound forms. This highlights, for the first time, the importance of 5′-AMP in promoting adaptation and uncovers adenylate control in cAMP signaling.
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Takasu, N., T. Yamada, and Y. Shimizu. "Thyrotrophin and prostaglandin E2 increase calmodulin levels and cyclic AMP phosphodiesterase activity in cultured porcine thyroid cells." Journal of Endocrinology 117, no. 1 (April 1988): 109–14. http://dx.doi.org/10.1677/joe.0.1170109.
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ABSTRACT Thyrotrophin (TSH) and prostaglandin E2 (PGE2) increased cellular cyclic AMP (cAMP), calmodulin levels and cAMP phosphodiesterase activity in cultured porcine thyroid cells. Dibutyryl cAMP (dbcAMP), a stable analogue of cAMP, increased calmodulin levels and cAMP phosphodiesterase activity. These results indicate that TSH- and PGE2-stimulated increases in calmodulin are mediated by cAMP. This increased concentration of calmodulin in turn stimulates cAMP phosphodiesterase. Double reciprocal plots of cAMP hydrolysis yielded two apparent Michaelis constants (Km); the lower in the 1 μmol/l and the higher in the 10 μmol/l range. Thyrotrophin, PGE2 and dbcAMP increased the values of maximal velocity without changing the Km values. J. Endocr. (1988) 117, 109–114
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Artman, M., P. A. Kithas, J. S. Wike, and S. J. Strada. "Inotropic responses change during postnatal maturation in rabbit." American Journal of Physiology-Heart and Circulatory Physiology 255, no. 2 (August 1, 1988): H335—H342. http://dx.doi.org/10.1152/ajpheart.1988.255.2.h335.
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Inotropic response to four different types of pharmacological stimuli were compared in isolated right ventricular papillary muscles from newborn (24–48 h of age), immature (14–16 days), and adult (6–7 mo) rabbits. Forskolin, a direct activator of adenylate cyclase, produced a 12.5-fold increase in the maximal rate of tension development in the newborn group. The maximum response to isoproterenol was only 45% of the maximum forskolin response, suggesting incomplete physiological coupling of myocardial beta-adrenergic receptors to adenylate cyclase at birth. In contrast to the substantial inotropic response to agents that stimulate adenosine 3',5'-cyclic monophosphate (cAMP) generation (forskolin and isoproterenol), a selective inhibitor of cAMP hydrolysis (milrinone) was relatively ineffective in the newborn group. Sulmazole, a drug that enhances calcium sensitivity of the contractile proteins, produced its greatest inotropic effect in immature myocardium. Cytosolic high-affinity cAMP phosphodiesterase activity was partially purified from ventricular homogenates by anion-exchange chromatography. The kinetics of cAMP hydrolysis (Km and Vmax) and inhibitory potency of milrinone were comparable in each age group. Thus the age-related differences in inotropic responsiveness may not be attributable to postnatal changes in myocardial cytosolic high-affinity cAMP phosphodiesterase activity.
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Haynes, J., P. A. Kithas, A. E. Taylor, and S. J. Strada. "Selective inhibition of cGMP-inhibitable cAMP phosphodiesterase decreases pulmonary vasoreactivity." American Journal of Physiology-Heart and Circulatory Physiology 261, no. 2 (August 1, 1991): H487—H492. http://dx.doi.org/10.1152/ajpheart.1991.261.2.h487.
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Guanosine 3',5'-cyclic monophosphate (cGMP) and adenosine 3',5'-cyclic monophosphate (cAMP) are mediators of smooth muscle relaxation. In this study, selective inhibitors of phosphodiesterase (PDE) isozymes were used to assess the role of cyclic nucleotide hydrolysis in angiotensin II (ANG II) and hypoxic pulmonary vasoconstriction. In isolated rat lungs, the hypoxic pressor response (HPR) was induced with a 95% N2-5% CO2 gas mixture. When administered during the plateau of the HPR, trequinsin (nonselective PDE inhibitor) and indolidan (cGMP-inhibitable cAMP PDE inhibitor) significantly (P = 0.01) decreased the pulmonary arterial pressure (Ppa) by 60 +/- 7 and 53 +/- 3%, respectively, compared with zaprinast (cGMP PDE inhibitor), rolipram (cGMP-insensitive cAMP PDE inhibitor), and the 0.1% dimethyl sulfoxide (DMSO) vehicle control, which decreased the Ppa by 6 +/- 3, 4 +/- 3, and 0%, respectively. In the trequinsin and indolidan groups, the subsequent ANG II pressor responses and HPRs were significantly (P = 0.01) decreased when compared with the zaprinast, rolipram, and DMSO groups. During normoxia, none of the PDE inhibitor (0.3-30 microM) had an effect on the baseline Ppa. These results suggest that cAMP hydrolysis by the cGMP-inhibitable cAMP PDE play a significant role in pulmonary vascular tone regulation.
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Delporte, C., P. Poloczek, and J. Winand. "Role of phosphodiesterase II in cross talk between cGMP and cAMP in human neuroblastoma NB-OK-1 cells." American Journal of Physiology-Cell Physiology 270, no. 1 (January 1, 1996): C286—C292. http://dx.doi.org/10.1152/ajpcell.1996.270.1.c286.
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Cyclic nucleotides levels and cyclic nucleotide phosphodiesterase (PDE) activities were measured in human neuroblastoma NB-OK-1 cells possessing atrial natriuretic peptide (ANP) receptors of the A type and pituitary adenylate cyclase activating polypeptide (PACAP)-preferring receptors. Adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) degradation were interrelated since the increase in cGMP, induced by ANP-(99-126), stimulated the hydrolysis of cAMP by PDE isoenzyme II. In intact NB-OK-1 cells, the levels of cAMP and cGMP attained in the presence of, respectively, 1 nM PACAP-(1-27) and 10 nM ANP-(99-126), and in the absence or presence of PDE inhibitors, strongly suggested that cAMP hydrolysis was mainly achieved by isoenzyme IV, and to a lesser extent by isoenzymes I, II, and III, while cGMP was degraded by isoenzymes I, II, III, and V. More than one-half of total cAMP- and cGMP-hydrolyzing activities was present in the membrane-bound fraction. Cyclic nucleotide PDE activities separated by anion-exchange chromatography showed that isoenzymes III and IV were mainly present in the membrane fraction, while isoenzymes I, II, and V were in the cytosolic fraction.
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Zhang, Aihua, Kun Liu, Caixia Wang, Siyu Ma, and Zonghe Li. "Theoretical study on the ring-opening hydrolysis reaction of cAMP." Journal of Molecular Structure: THEOCHEM 719, no. 1-3 (April 2005): 149–52. http://dx.doi.org/10.1016/j.theochem.2004.12.034.
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Anderson, M. P., and M. J. Welsh. "Isoproterenol, cAMP, and bradykinin stimulate diacylglycerol production in airway epithelium." American Journal of Physiology-Lung Cellular and Molecular Physiology 258, no. 6 (June 1, 1990): L294—L300. http://dx.doi.org/10.1152/ajplung.1990.258.6.l294.
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Previous studies using phorbol esters and cell-free preparations suggest that protein kinase C (PKC) may regulate Cl- secretion and apical membrane Cl- channels in airway epithelium. To determine whether PKC may be involved in receptor-mediated control of secretion, we measured the mass of diacylglycerol (DAG) generated by two Cl- secretagogues, isoproterenol and bradykinin. Bradykinin increased cellular DAG at concentrations similar to those that increase inositol phosphates, suggesting that bradykinin stimulates phosphatidylinositol hydrolysis, as observed in other systems. Isoproterenol also increased cellular DAG at concentrations similar to those that stimulate adenosine 3',5'-cyclic monophosphate (cAMP) accumulation. The beta-adrenergic receptor antagonist, nadolol, blocked and cell-permanent analogues of cAMP mimicked the effect of isoproterenol. However, isoproterenol does not stimulate phosphatidylinositol turnover. Simultaneous addition of maximal concentrations of isoproterenol and bradykinin produced additive increases in DAG. To test the possibility that the isoproterenol-induced increase in DAG came from phosphatidylcholine turnover, we measured the release of water-soluble choline metabolites and the incorporation of choline into cellular lipids. Although phorbol ester and bradykinin stimulated phosphatidylcholine turnover, isoproterenol did not. These results suggest that isoproterenol and bradykinin generate DAG from the following different lipid sources: bradykinin stimulates phosphatidylinositol hydrolysis to produce DAG; isoproterenol stimulates an increase in DAG from unknown sources. The data suggest that simultaneous activation of cAMP-dependent protein kinase and PKC may occur during receptor-mediated stimulation of Cl- secretion.
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Tian, Ling, Rongsheng E. Wang, Ying Fei, and Yie-Hwa Chang. "A Homogeneous Fluorescent Assay for cAMP-Phosphodiesterase Enzyme Activity." Journal of Biomolecular Screening 17, no. 3 (November 7, 2011): 409–14. http://dx.doi.org/10.1177/1087057111426901.
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Cyclic adenosine monophosphate–phosphodiesterases (cAMP-PDEs) regulate the cellular level of cAMP by selectively catalyzing the hydrolysis of the phosphodiester bond in the cAMP molecule. They play important roles in modulating cellular and physiological functions. There is a growing interest in the study of cAMP-PDEs as therapeutic targets. We describe a novel method for measuring the enzyme activity of cAMP-PDEs that is based on a homogeneous fluorescence assay employing a cAMP-dependent DNA-binding protein (CAP). We demonstrate that the assay is quick and robust compared to traditional methods and is expected to be cost-effective for high-throughput screening of cAMP-PDE inhibitors. The usefulness of the assay is demonstrated by measuring IC50 values of three nonselective PDE inhibitors and by kinetic measurements of cAMP-PDEs from various rat tissues.
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Warburton, D., S. Buckley, and L. Cosico. "P1 and P2 purinergic receptor signal transduction in rat type II pneumocytes." Journal of Applied Physiology 66, no. 2 (February 1, 1989): 901–5. http://dx.doi.org/10.1152/jappl.1989.66.2.901.
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Extracellular ATP is a potent agonist of surfactant phosphatidylcholine (PC) exocytosis from type II pneumocytes in culture. We studied P1 and P2 receptor signal transduction in type II pneumocytes. The EC50 for ATP on PC exocytosis was 10(-6) M, whereas the EC50 for ADP, AMP, adenosine, and the nonmetabolizable ATP analogue alpha,beta-methylene ATP was 10(-4) M. The rank order of agonists for PC exocytosis was ATP greater than ADP greater than AMP greater than adenosine greater than alpha,beta-methylene ATP. The rank order of agonists for phosphatidylinositol (PI) hydrolysis was ATP greater than ADP, whereas AMP, adenosine, and alpha,beta-methylene ATP did not stimulate PI hydrolysis. ATP (10(-4) M) caused a 15-fold increase in adenosine 3′,5′-cyclic monophosphate (cAMP) production, and the nonmetabolizable adenosine analogue 5′-N-ethylcarboxyamidoadenosine (10(-6) M) increased cAMP production threefold. The effects of both these agonists on cAMP production were completely inhibited by the adenosine antagonist 8-phenyltheophylline (10(-5) M). The effects of ATP (10(-4) M) on PC exocytosis were inhibited 38% by 10(-5) M 8-phenyltheophylline. Thus, ATP regulates PC exocytosis by activating P2 receptors, which stimulate PI hydrolysis to inositol phosphate, as well as by activating P1 receptors, which stimulate cAMP production. Interactions between the P1 and P2 pathways may explain the high potency of extracellular ATP as an agonist of PC exocytosis.
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Rasmussen, H., G. Kelley, and J. S. Douglas. "Interactions between Ca2+ and cAMP messenger system in regulation of airway smooth muscle contraction." American Journal of Physiology-Lung Cellular and Molecular Physiology 258, no. 6 (June 1, 1990): L279—L288. http://dx.doi.org/10.1152/ajplung.1990.258.6.l279.
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Cholinergic stimuli acting via muscarinic receptors stimulate airway smooth muscle to contract and beta-adrenergic stimuli induce it to relax. Cholinergic agonists stimulate intracellular Ca2+ release and Ca2+ influx, and beta-adrenergic agonists stimulate adenosine 3',5'-cyclic monophosphate (cAMP) production. Since it was found that cAMP alters cholinergic agonist-induced changes in cellular Ca2+ metabolism, it was postulated that cAMP brought about a relaxation of this smooth muscle primarily by altering Ca2+ metabolism. More recently, it has become clear that when cholinergic agonists, as well as histamine and serotonin, act, the hydrolysis of polyphosphoinositols is stimulated, diacylglycerol production is increased, and coordinated changes in Ca2+ metabolism and protein kinase function occur. These agonists also act to inhibit adenylate cyclase activity. Conversely, it has been found that in the absence of agonist activation, cAMP increases Ca2+ influx without stimulating contraction and that in the presence of muscarinic agonists, it acts to inhibit polyphosphoinositide hydrolysis. In addition, cAMP has been shown to alter the state of phosphorylation of a number of cellular proteins, an effect that is independent of any effect on cellular Ca2+ metabolism. Based on these newer data, an expanded model of Ca2(+)-cAMP interactions in the regulation of airway smooth muscle tone is presented. A key feature of this model is the operation of dual, reciprocal inhibitory signals by which the Ca2+ and cAMP messenger systems modulate each other's expression.
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Anderson, K. L., G. Anderson, R. H. Michell, E. J. Jenkinson, and J. J. Owen. "Intracellular signaling pathways involved in the induction of apoptosis in immature thymic T lymphocytes." Journal of Immunology 156, no. 11 (June 1, 1996): 4083–91. http://dx.doi.org/10.4049/jimmunol.156.11.4083.
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Abstract We describe a novel technique for studying the signaling pathways that control thymocyte negative selection which maintains the essential interactions between thymocytes and thymic stromal cells. Bisected lobes from newborn mouse thymus are maintained in organ culture for up to 36 h, and the thymocytes analyzed by flow cytometry. Inclusion of [3H]inositol during culture allows measurements of phosphatidylinositol 4,5-biphosphate (PtdIns(4,5)P2) hydrolysis and inositol phosphate accumulation. Using this technique we have compared the thymocyte responses induced by anti-CD3, anti-Fas, Con A, and beta-adrenergic stimulation. We show that PtdIns(4,5)P2 hydrolysis precedes anti-CD3-induced thymocyte apoptosis, but not the apoptosis induced by anti-Fas. In contrast, Con A stimulates PtdIns(4,5)P2 hydrolysis, but does not induce thymocyte apoptosis. Anti-CD3, anti-Fas, and Con A all fail to change thymic cAMP levels, but beta-adrenergic stimulation causes a large increase in intracellular cAMP, and agents that elevate cAMP induce thymocyte apoptosis. Inhibition of protein synthesis (with cycloheximide or emetine) prevents the apoptosis induced by anti-CD3 and elevated cAMP, but not that induced by anti-Fas, whereas protease inhibition (with 3,4-dichloroisocoumarin or N(alpha)-tosyl-phenylalanine chloromethyl ketone) prevents the apoptosis caused by all of the effective stimuli. These results offer three important conclusions. First, activation of a variety of different signaling pathways can bring about thymocyte apoptosis. Second, ligation of the thymocyte TCR/CD3 complex provokes PtdIns(4,5)P2 hydrolysis, but signaling through this pathway alone does not necessarily lead to apoptosis. Third, by whichever signaling pathway the response is initiated, the activity of one or more protease enzymes appears to form an essential component in the final common pathway leading to apoptosis.
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Mendel, D. B., T. Cihlar, K. Moon, and M. S. Chen. "Conversion of 1-[((S)-2-hydroxy-2-oxo-1,4,2-dioxaphosphorinan-5-yl)methyl]cytosine to cidofovir by an intracellular cyclic CMP phosphodiesterase." Antimicrobial Agents and Chemotherapy 41, no. 3 (March 1997): 641–46. http://dx.doi.org/10.1128/aac.41.3.641.
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Cidofovir (HPMPC) [1-[(S)-3-hydroxy-2-(phosphonomethoxy)propyl]-cytosine] is an acyclic nucleotide analog with potent and selective activity against herpesviruses. The prodrug, cyclic HPMPC (cHPMPC) [1-[((S)-2-hydroxy-2-oxo-1,4,2-dioxaphosphorinan-5-yl) methyl]cytosine], has antiviral activity similar to that of the parent compound but exhibits reduced toxicity in animal models. cHPMPC is converted to cidofovir by a cellular cyclic CMP phosphodiesterase (EC 3.1.4.37) which hydrolyzes a variety of substrates, including adenosine 3',5'-cyclic monophosphate (cAMP) and cytidine 3',5'-cyclic monophosphate (cCMP). The K(m) and Vmax values for hydrolysis of cHPMPC by cCMP phosphodiesterase purified from human liver are 250 microM and 0.66 nmol.min-1.unit-1, respectively. These values are similar to the K(m) and Vmax values for cAMP (23 microM and 1.16 nmol.min-1.unit-1, respectively) and cCMP (75 microM and 2.32 nmol.min-1.unit of enzyme-1, respectively). The catalytic efficiency (Vmax/K(m) ratio) of this enzyme for the cHPMPC substrate is only 10- to 20-fold lower than those for the natural cyclic nucleotides, indicating that cHPMPC is a viable intracellular substrate for the human enzyme. Kinetic analysis indicates that cHPMPC, cAMP, and cCMP are competitive with respect to each other and that they are hydrolyzed by the same enzyme. cHPMPC is hydrolyzed to cidofovir in all primary human cell systems tested, including those derived from target organs that might be infected in patients with human cytomegalovirus (HCMV) disease. Importantly, hydrolysis of cHPMPC is not diminished in cells infected with HCMV.
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Carvalho, Thays Maria da Conceição Silva, Silvia Cardarelli, Mauro Giorgi, Andrea Lenzi, Andrea M. Isidori, and Fabio Naro. "Phosphodiesterases Expression during Murine Cardiac Development." International Journal of Molecular Sciences 22, no. 5 (March 5, 2021): 2593. http://dx.doi.org/10.3390/ijms22052593.
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3′-5′ cyclic nucleotide phosphodiesterases (PDEs) are a large family of enzymes playing a fundamental role in the control of intracellular levels of cAMP and cGMP. Emerging evidence suggested an important role of phosphodiesterases in heart formation, but little is known about the expression of phosphodiesterases during cardiac development. In the present study, the pattern of expression and enzymatic activity of phosphodiesterases was investigated at different stages of heart formation. C57BL/6 mice were mated and embryos were collected from 14.5 to 18.5 days of development. Data obtained by qRT-PCR and Western blot analysis showed that seven different isoforms are expressed during heart development, and PDE1C, PDE2A, PDE4D, PDE5A and PDE8A are modulated from E14.5 to E18.5. In heart homogenates, the total cAMP and cGMP hydrolytic activity is constant at the evaluated times, and PDE4 accounts for the majority of the cAMP hydrolyzing ability and PDE2A accounts for cGMP hydrolysis. This study showed that a subset of PDEs is expressed in developing mice heart and some of them are modulated to maintain constant nucleotide phosphodiesterase activity in embryonic and fetal heart.
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Nordgaard, Julie C., Lars S. Kruse, Morten Møller, and Christina Kruuse. "Phosphodiesterases 3 and 5 express activity in the trigeminal ganglion and co-localize with calcitonin gene-related peptide." Cephalalgia 34, no. 7 (December 9, 2013): 503–13. http://dx.doi.org/10.1177/0333102413515345.
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Background Understanding of the neuropathology leading to migraine pain has centered on either a vascular or neuronal origin. Sildenafil, a specific inhibitor of phosphodiesterase 5 (PDE5), induces migraine-like headache in a human headache model without concomitant artery dilation. The presence and activity of PDE3 and PDE5 is known in cerebral arteries. However, the presence in the neuronal part of the trigeminovascular pathway, i.e. the trigeminal ganglion and the possible co-localization with calcitonin gene-related peptide (CGRP), is not known. Methods Rat trigeminal ganglia were isolated and immunohistochemistry and in situ hybridization was applied. Evaluations of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) hydrolysis were performed using scintillation proximity assays. Results PDE3 and PDE5 were present and active in the trigeminal ganglia. A subset of PDE3- and PDE5-positive neurons contained CGRP. In contrast to cGMP, both sildenafil and cilostazol influenced cAMP hydrolysis. Interpretation Sildenafil may exert its effect on the neuronal part of the migraine pain pathway. In addition to the effects on cGMP signaling, sildenafil may indirectly affect cAMP signaling in the trigeminal ganglion. This result may suggest a common cAMP-related pathway for sildenafil, cilostazol, and CGRP in eliciting migraine pain.
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Rich, Thomas C., Tonia E. Tse, Joyce G. Rohan, Jerome Schaack, and Jeffrey W. Karpen. "In Vivo Assessment of Local Phosphodiesterase Activity Using Tailored Cyclic Nucleotide–Gated Channels as Camp Sensors." Journal of General Physiology 118, no. 1 (June 27, 2001): 63–78. http://dx.doi.org/10.1085/jgp.118.1.63.
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Phosphodiesterases (PDEs) catalyze the hydrolysis of the second messengers cAMP and cGMP. However, little is known about how PDE activity regulates cyclic nucleotide signals in vivo because, outside of specialized cells, there are few methods with the appropriate spatial and temporal resolution to measure cyclic nucleotide concentrations. We have previously demonstrated that adenovirus-expressed, olfactory cyclic nucleotide–gated channels provide real-time sensors for cAMP produced in subcellular compartments of restricted diffusion near the plasma membrane (Rich, T.C., K.A. Fagan, H. Nakata, J. Schaack, D.M.F. Cooper, and J.W. Karpen. 2000. J. Gen. Physiol. 116:147–161). To increase the utility of this method, we have modified the channel, increasing both its cAMP sensitivity and specificity, as well as removing regulation by Ca2+-calmodulin. We verified the increased sensitivity of these constructs in excised membrane patches, and in vivo by monitoring cAMP-induced Ca2+ influx through the channels in cell populations. The improved cAMP sensors were used to monitor changes in local cAMP concentration induced by adenylyl cyclase activators in the presence and absence of PDE inhibitors. This approach allowed us to identify localized PDE types in both nonexcitable HEK-293 and excitable GH4C1 cells. We have also developed a quantitative framework for estimating the KI of PDE inhibitors in vivo. The results indicate that PDE type IV regulates local cAMP levels in HEK-293 cells. In GH4C1 cells, inhibitors specific to PDE types I and IV increased local cAMP levels. The results suggest that in these cells PDE type IV has a high Km for cAMP, whereas PDE type I has a low Km for cAMP. Furthermore, in GH4C1 cells, basal adenylyl cyclase activity was readily observable after application of PDE type I inhibitors, indicating that there is a constant synthesis and hydrolysis of cAMP in subcellular compartments near the plasma membrane. Modulation of constitutively active adenylyl cyclase and PDE would allow for rapid control of cAMP-regulated processes such as cellular excitability.
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Wang, M., R. van Driel, and P. Schaap. "Cyclic AMP-phosphodiesterase induces dedifferentiation of prespore cells in Dictyostelium discoideum slugs: evidence that cyclic AMP is the morphogenetic signal for prespore differentiation." Development 103, no. 3 (July 1, 1988): 611–18. http://dx.doi.org/10.1242/dev.103.3.611.
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We investigated whether cyclic AMP is an essential extracellular stimulus for the differentiation of prespore cells in slugs of D. discoideum. A local reduction of the extracellular cAMP level inside the slug was induced by implantation of cAMP-phosphodiesterase (cAMP-PDE)-coated spheres in intact slugs. This treatment caused the disappearance of prespore antigen in the vicinity of the sphere. A general reduction of extracellular cAMP levels in slugs, induced by submerging slugs in 0.25i.u.ml-1 cAMP-PDE, reduced the proportion of prespore cells from 66% to 15%, without affecting slug morphology. The cAMP-PDE-induced dedifferentiation of prespore cells was counteracted by cAMP and was not due to the production of the hydrolysis product 5′AMP, but to the reduction of extracellular cAMP levels. We conclude that extracellular cAMP is the major morphogenetic signal for the differentiation of prespore cells in the multicellular stages of D. discoideum development and we present a working hypothesis for the generation of the prestalk/prespore pattern during multicellular development.
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Klausen, Christina, Fabian Kaiser, Birthe Stüven, Jan N. Hansen, and Dagmar Wachten. "Elucidating cyclic AMP signaling in subcellular domains with optogenetic tools and fluorescent biosensors." Biochemical Society Transactions 47, no. 6 (November 14, 2019): 1733–47. http://dx.doi.org/10.1042/bst20190246.
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The second messenger 3′,5′-cyclic nucleoside adenosine monophosphate (cAMP) plays a key role in signal transduction across prokaryotes and eukaryotes. Cyclic AMP signaling is compartmentalized into microdomains to fulfil specific functions. To define the function of cAMP within these microdomains, signaling needs to be analyzed with spatio-temporal precision. To this end, optogenetic approaches and genetically encoded fluorescent biosensors are particularly well suited. Synthesis and hydrolysis of cAMP can be directly manipulated by photoactivated adenylyl cyclases (PACs) and light-regulated phosphodiesterases (PDEs), respectively. In addition, many biosensors have been designed to spatially and temporarily resolve cAMP dynamics in the cell. This review provides an overview about optogenetic tools and biosensors to shed light on the subcellular organization of cAMP signaling.
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Fouchier, F., P. Bastiani, and J. Dang. "Intralysosomal hydrolysis of thyroglobulin: specific and cAMP-mediated activation by TSH." Molecular and Cellular Endocrinology 49, no. 1 (January 1987): 25–31. http://dx.doi.org/10.1016/0303-7207(87)90060-8.
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Bogoyevitch, M. A., S. J. Fuller, and P. H. Sugden. "cAMP and protein synthesis in isolated adult rat heart preparations." American Journal of Physiology-Cell Physiology 265, no. 5 (November 1, 1993): C1247—C1257. http://dx.doi.org/10.1152/ajpcell.1993.265.5.c1247.
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The involvement of adenosine 3',5'-cyclic monophosphate (cAMP) in the stimulation of ventricular protein synthesis by aortic hypertension or adrenergic agonists in the adult rat heart was investigated. In either the retrogradely or anterogradely perfused heart, aortic hypertension increased protein synthesis rates by up to 19%. However, no changes in cAMP concentrations or in cAMP-dependent protein kinase activity ratios could be detected either at early (< 5 min) or late (90 min) time points. Although isoproterenol, 3-isobutyl-1-methylxanthine, or forskolin raised cAMP concentrations (by up to 4.5-fold) and cAMP-dependent protein kinase ratios (by up to 4-fold), protein synthesis rates were not increased; however, under some perfusion conditions, glucagon did stimulate protein synthesis by 25%. Epinephrine stimulated protein synthesis by up to 32%, an effect that was not prevented by propranolol. Phenylephrine also stimulated protein synthesis, an effect that was prevented by prazosin but was unaffected by yohimbine. These findings implicate the alpha 1-adrenoceptor in the regulation of cardiac protein synthesis. Because changes in adenine nucleotide concentrations were similar in hearts perfused with epinephrine or with the agents that raised cAMP, it is unlikely that adenine nucleotide depletion is responsible for the failure to observe effects of the latter group of agents on protein synthesis. Although isoproterenol or forskolin raised cAMP concentrations in isolated ventricular cardiomyocytes where ATP depletion was minimal, neither stimulated protein synthesis. alpha 1-Adrenergic agonists stimulate phosphoinositide hydrolysis in the heart (Brown, J. H., I. L. Buxton, and L. L. Brunton. Circ. Res. 57:532-537, 1985). Aortic hypertension doubled the rate of phosphoinositide hydrolysis in the perfused heart. We suggest that the phosphoinositide-linked signal transduction pathway is more likely to be involved in stimulation of cardiac protein synthesis by hypertension or adrenergic agonism than the adenylyl cyclase/cAMP-linked pathway.
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Jackson, Edwin K., Zaichuan Mi, Keri Janesko-Feldman, Travis C. Jackson, and Patrick M. Kochanek. "2′,3′-cGMP exists in vivo and comprises a 2′,3′-cGMP-guanosine pathway." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 316, no. 6 (June 1, 2019): R783—R790. http://dx.doi.org/10.1152/ajpregu.00401.2018.
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The discovery in 2009 that 2′,3′-cAMP exists in biological systems was rapidly followed by identification of 2′,3′-cGMP in cell and tissue extracts. To determine whether 2′,3′-cGMP exists in mammals under physiological conditions, we used ultraperformance LC-MS/MS to measure 2′,3′-cAMP and 2′,3′-cGMP in timed urine collections (via direct bladder cannulation) from 25 anesthetized mice. Urinary excretion rates (means ± SE) of 2′,3′-cAMP (15.5 ± 1.8 ng/30 min) and 2′,3′-cGMP (17.9 ± 1.9 ng/30 min) were similar. Mice also excreted 2′-AMP (3.6 ± 1.1 ng/20 min) and 3′-AMP (9.5 ± 1.2 ng/min), hydrolysis products of 2′,3′-cAMP, and 2′-GMP (4.7 ± 1.7 ng/30 min) and 3′-GMP (12.5 ± 1.8 ng/30 min), hydrolysis products of 2′,3′-cGMP. To validate that the chromatographic signals were from these endogenous noncanonical nucleotides, we repeated these experiments in mice ( n = 18) lacking 2′,3′-cyclic nucleotide 3′-phosphodiesterase (CNPase), an enzyme known to convert 2′,3′-cyclic nucleotides to their corresponding 2′-nucleotides. In CNPase-knockout mice, urinary excretions of 2′,3′-cAMP, 3′-AMP, 2′,3′-cGMP, and 3′-GMP were increased, while urinary excretions of 2′-AMP and 2′-GMP were decreased. Infusions of exogenous 2′,3′-cAMP increased urinary excretion of 2′,3′-cAMP, 2′-AMP, 3′-AMP, and adenosine, whereas infusions of exogenous 2′,3′-cGMP increased excretion of 2′,3′-cGMP, 2′-GMP, 3′-GMP, and guanosine. Together, these data suggest the endogenous existence of not only a 2′,3′-cAMP-adenosine pathway (2′,3′-cAMP → 2′-AMP/3′-AMP → adenosine), which was previously identified, but also a 2′,3′-cGMP-guanosine pathway (2′,3′-cGMP → 2′-GMP/3′-GMP → guanosine), observed here for the first time. Because it is well known that adenosine and guanosine protect tissues from injury, our data support the concept that both pathways may work together to protect tissues from injury.
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Willoughby, D., and D. M. F. Cooper. "Use of single-cell imaging techniques to assess the regulation of cAMP dynamics." Biochemical Society Transactions 34, no. 4 (July 21, 2006): 468–71. http://dx.doi.org/10.1042/bst0340468.
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cAMP is a ubiquitous intracellular signalling molecule that can regulate a wide array of cellular processes. The diversity of action of this second messenger owes much to the localized generation, action and hydrolysis of cAMP within discrete subcellular regions. Further signalling specificity can be achieved by the ability of cells to modulate the frequency or incidence of such cAMP signals. Here, we discuss the use of two cAMP biosensors that measure real-time cAMP changes in the single cell, to address the mechanisms underlying the generation of dynamic cAMP signals. The first method monitors sub-plasmalemmal cAMP changes using mutant cyclic nucleotide-gated channels and identifies an AKAP (A-kinase-anchoring protein)–protein kinase A–PDE4 (phosphodiesterase-4) signalling complex that is central to the generation of dynamic cAMP transients in this region of the cell. The second study uses a fluorescence resonance energy transfer-based cAMP probe, based on Epac1 (exchange protein directly activated by cAMP 1), to examine interplay between Ca2+ and cAMP signals. This study demonstrates real-time oscillations in cAMP driven by a Ca2+-stimulated AC (adenylate cyclase) (AC8) and subsequent PDE4 activity. These studies, using two very different single-cell cAMP probes, broaden our understanding of the specific spatiotemporal characteristics of agonist-evoked cAMP signals in a model cell system.
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Tamir, A., and N. Isakov. "Cyclic AMP inhibits phosphatidylinositol-coupled and -uncoupled mitogenic signals in T lymphocytes. Evidence that cAMP alters PKC-induced transcription regulation of members of the jun and fos family of genes." Journal of Immunology 152, no. 7 (April 1, 1994): 3391–99. http://dx.doi.org/10.4049/jimmunol.152.7.3391.
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Abstract T lymphocyte stimulation via the Ag receptor results in activation of phospholipase C gamma 1 that catalyses the hydrolysis of phosphatidylinositol (PI). The hydrolysis generates inositol phosphate and diacylglycerol, which in turn, increase intracellular Ca2+ concentration and activates protein kinase C, respectively. Agonists operating via the adenylate cyclase pathway or cell permeable cAMP analogues inhibit T cell activation by interfering with the PI-turnover. We have shown that dbcAMP inhibits PI-independent mitogenic signals in T cells after stimulation with TPA plus ionomycin. dbcAMP inhibited the TPA plus ionomycin-induced transcription of IL-2 and IL-2R genes in EL4 cells, suggesting interference with biochemic events downstream to PI hydrolysis and upstream to transcription of early activation genes. Because many of the early genes operating in T cell mitogenesis possess a TPA-response element (TRE) in their promoter region, we tested the effect of cAMP on the TRE-binding protein, TPA-response element (TRE) in their promoter region, we tested the effect of cAMP on the TRE-binding protein, AP-1. dbcAMP increased the binding activity of nuclear proteins consisting of Fos:Jun heterodimers to a TRE-containing oligonucleotide, but altered the composition of Jun proteins in the AP-1. Furthermore, the TPA plus ionomycin-induced transcription program of members of the jun and fos family of genes was altered by dbcAMP, suggesting that inhibition of T cell proliferation by dbcAMP is a consequence of intervention in transcriptional regulation by TRE-binding proteins.
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Enyeart, J. J., B. Mlinar, and J. A. Enyeart. "Adrenocorticotropic hormone and cAMP inhibit noninactivating K+ current in adrenocortical cells by an A-kinase-independent mechanism requiring ATP hydrolysis." Journal of General Physiology 108, no. 4 (October 1, 1996): 251–64. http://dx.doi.org/10.1085/jgp.108.4.251.
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Bovine adrenal zona fasciculata (AZF) cells express a noninactivating K+ current (IAC) that is inhibited by adrenocorticotropic hormone (ACTH) at picomolar concentrations. Inhibition of IAC may be a critical step in depolarization-dependent Ca2+ entry leading to cortisol secretion. In whole-cell patch clamp recordings from AZF cells, we have characterized properties of IAC and the signalling pathway by which ACTH inhibits this current. IAC was identified as a voltage-gated, outwardly rectifying, K(+)-selective current whose inhibition by ACTH required activation of a pertussis toxin-insensitive GTP binding protein. IAC was selectively inhibited by the cAMP analogue 8-(4-chlorophenylthio)-adenosine 3':5'-cyclic monophosphate (8-pcpt-cAMP) with an IC50 of 160 microM. The adenylate cyclase activator forskolin (2.5 microM) also reduced IAC by 92 +/- 4.7%. Inhibition of IAC by ACTH, 8-pcpt-cAMP and forskolin was not prevented by the cAMP-dependent protein kinase inhibitors H-89 (5 microM), cAMP-dependent protein kinase inhibitor peptide (PKI[5-24]) (2 microM), (Rp)-cAMPS (500 microM), or by the nonspecific protein kinase inhibitor staurosporine (100 nM) applied externally or intracellularly through the patch pipette. At the same concentrations, these kinase inhibitors abolished 8-pcpt-cAMP-stimulated A-kinase activity in AZF cell extracts. In intact AZF cells, 8-pcpt-cAMP activated A-kinase with an EC50 of 77 nM, a concentration 2,000-fold lower than that inhibiting IAC half maximally. The active catalytic subunit of A-kinase applied intracellularly through the recording pipette failed to alter functional expression of IAC. The inhibition of IAC by ACTH and 8-pcpt-cAMP was eliminated by substituting the nonhydrolyzable ATP analogue AMP-PNP for ATP in the pipette solution. Penfluridol, an antagonist of T-type Ca2+ channels inhibited 8-pcpt-cAMP-induced cortisol secretion with an IC50 of 0.33 microM, a concentration that effectively blocks Ca2+ channel in these cells. These results demonstrate that IAC is a K(+)-selective current whose gating is controlled by an unusual combination of metabolic factors and membrane voltage. IAC may be the first example of an ionic current that is inhibited by cAMP through an A-kinase-independent mechanism. The A-kinase-independent inhibition of IAC by ACTH and cAMP through a mechanism requiring ATP hydrolysis appears to be a unique form of channel modulation. These findings suggest a model for cortisol secretion wherein cAMP combines with two separate effectors to activate parallel steroidogenic signalling pathways. These include the traditional A-kinase-dependent signalling cascade and a novel pathway wherein cAMP binding to IAC K+ channels leads to membrane depolarization and Ca2+ entry. The simultaneous activation of A-kinase- and Ca(2+)-dependent pathways produces the full steroidogenic response.
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LIEBMANN, Claus, Angela GRANESS, Beate LUDWIG, Antje ADOMEIT, Anette BOEHMER, Frank-D. BOEHMER, Bernd NÜRNBERG, and Reinhard WETZKER. "Dual bradykinin B2 receptor signalling in A431 human epidermoid carcinoma cells: activation of protein kinase C is counteracted by a GS-mediated stimulation of the cyclic AMP pathway." Biochemical Journal 313, no. 1 (January 1, 1996): 109–18. http://dx.doi.org/10.1042/bj3130109.
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Cell membranes of the human epidermoid cell line A431 express classical bradykinin (BK) B2 receptors, as assessed by [3H]BK binding studies. Furthermore, stimulation by BK induced a time-dependent modulation of protein kinase C (PKC) activity in A431 cells: a rapid activation (t½ ≈1 min) is followed by a slow inhibition (t½ ≈20 min) of PKC translocation measured by [3H]phorbol 12,13-dibutyrate binding. In addition, BK stimulated both adenylate cyclase activity in A431 membranes and accumulation of intracellular cyclic AMP (cAMP) in intact cells in a retarded manner. A possible BK-induced activation of the cAMP pathway mediated via PKC, phospholipase D, prostaglandins or Ca2+/calmodulin was excluded. A 35 kDa protein was found in A431 membranes to be specifically phosphorylated in the presence of both BK and protein kinase A (PKA). An anti-αs-antibody, AS 348, abolished stimulation of adenylate cyclase activity in response to BK, cholera toxin and isoprenaline, strongly suggesting the involvement of Gs proteins in the BK action. The BK-activated cAMP signalling system might be important for the observed inactivation of PKC slowly evoked by BK: the BK-induced rapid activation of PKC is decreased by dibutyryl cAMP, and the slow inhibition of PKC is prevented by an inhibitor of PKA, adenosine 3ʹ:5ʹ-monophosphothioate (cyclic, Rp isomer). The inhibition of PKC translocation might be exerted directly at the level of PKC activation, since stimulation of phosphoinositide hydrolysis by BK was affected by neither dibutyryl cAMP nor forskolin. Thus our results provide the first evidence that A431 cells BK is able to activate two independent signal-transduction pathways via a single class of B2 receptors but two different G proteins. The lagging stimulation of the cAMP signalling pathway via Gs might serve to switch off PKC, which is rapidly activated via Gq-mediated stimulation of phosphoinositide hydrolysis.
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Saltiel, A., J. Fox, P. Sherline, and P. Cuatrecasas. "Insulin-stimulated hydrolysis of a novel glycolipid generates modulators of cAMP phosphodiesterase." Science 233, no. 4767 (August 29, 1986): 967–72. http://dx.doi.org/10.1126/science.3016898.
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Van Genderen, Marcel H. P., Leo H. Koole, Raymond J. L. Van Kooyk, and Henk M. Buck. "The role of hydration and stereoelectronic effects in the hydrolysis of cAMP." Journal of Organic Chemistry 50, no. 13 (June 1985): 2380–83. http://dx.doi.org/10.1021/jo00213a038.
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Kyoi, Takashi, Michiko Oka, Kumiko Noda, and Yojiro Ukai. "Phosphodiesterase inhibition by a gastroprotective agent irsogladine: Preferential blockade of cAMP hydrolysis." Life Sciences 75, no. 15 (August 2004): 1833–42. http://dx.doi.org/10.1016/j.lfs.2004.03.022.
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Feng, Jane J., Tamara M. Frank, and Alan Fein. "Excitation of Limulus photoreceptors by hydrolysis-resistant analogs of cGMP and cAMP." Brain Research 552, no. 2 (June 1991): 291–94. http://dx.doi.org/10.1016/0006-8993(91)90094-c.
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Bagchi, Nandalal, Birdie Shivers, and Thomas R. Brown. "Studies on the mechanism of acute inhibition of thyroglobulin hydrolysis by iodine." Acta Endocrinologica 108, no. 4 (April 1985): 511–17. http://dx.doi.org/10.1530/acta.0.1080511.
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Abstract. Iodine in excess is known to acutely inhibit thyroidal secretion. In the present study we have characterized the time course of the iodine effect in vitro and investigated the underlying mechanisms. Labelled thyroid glands were cultured in vitro in medium containing mononitrotyrosine, an inhibitor of iodotyrosine deiodinase. The rate of hydrolysis of labelled thyroglobulin was measured as the proportion of labelled iodotyrosines and iodothyronines recovered at the end of culture and was used as an index of thyroidal secretion. Thyrotrophin (TSH) administered in vivo acutely stimulated the rate of thyroglobulin hydrolysis. Addition of Nal to the culture medium acutely inhibited both basal and TSH-stimulated thyroglobulin hydrolysis. The effect of iodide was demonstrable after 2 h, maximal after 6 h and was not reversible upon removal of iodide. Iodide abolished the dibutyryl cAMP induced stimulation of thyroglobulin hydrolysis. Iodide required organic binding of iodine for its effect but new protein or RNA synthesis was not necessary. The inhibitory effects of iodide and lysosomotrophic agents such as NH4C1 and chloroquin on thyroglobulin hydrolysis were additive suggesting different sites of action. Iodide added in vitro altered the distribution of label in prelabelled thyroglobulin in a way that suggested increased coupling in the thyroglobulin molecule. These data indicate that 1) the iodide effect occurs progressively over a 6 h period, 2) continued presence of iodide is not necessary once the inhibition is established, 3) iodide exerts its action primarily at a post cAMP, prelysosomal site and 4) the effect requires organic binding of iodine, but not new RNA or protein synthesis. Our data are consistent with the hypothesis that excess iodide acutely inhibits thyroglobulin hydrolysis by increasing the resistance of thyroglobulin to proteolytic degradation through increased iodination and coupling.
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Zhang, Wei, and Robert W. Colman. "Thrombin regulates intracellular cyclic AMP concentration in human platelets through phosphorylation/activation of phosphodiesterase 3A." Blood 110, no. 5 (September 1, 2007): 1475–82. http://dx.doi.org/10.1182/blood-2006-10-052522.
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Abstract Thrombin-induced cyclic AMP (cAMP) reduction potentates several steps in platelet activation, including Ca++ mobilization, cytoskeletal reorganization, and fibrinogen receptor conformation. We now reinvestigate the signaling pathways by which intracellular cAMP content is controlled after platelet activation by thrombin. When washed human platelets were stimulated with thrombin, cAMP-dependent phosphodiesterase (PDE3A) activity was significantly increased. A nonselective PDE inhibitor, 3-isobutyl-1-methylxanthine (IBMX), and the PDE3 selective inhibitors milrinone and cilostazol each suppressed thrombin-induced cAMP-dependent PDE responses, but not 2 different PDE2 inhibitors. Selective inhibition of PDE3A resulted in reversal of thrombin-induced cAMP reduction, indicating that thrombin activated PDE3A. In synergy with inhibition of adenylate cyclase by thrombin, activated PDE3A accelerates cAMP hydrolysis and maximally reduces the cAMP content. Thrombin-induced PDE3A activation was diminished concomitantly with dephosphorylation of PDE3A by protein phosphatase 1 (PP1). An Akt inhibitor blocked PDE3A activation and constrained thrombin-induced cAMP reduction. A P2Y12 inhibitor also reduced thrombin-induced cAMP reduction. The combination of both reversed cAMP decrease by thrombin. Thrombin-mediated phosphorylated PDE3A was isolated by liquid chromatography, detected by a monoclonal antibody against Akt-phosphorylated substrate, and verified by immunoprecipitation study. The predominant isoform phosphorylated by Akt was the 136-kDa species. We suggest that activation/phosphorylation of PDE3A via Akt signaling pathway participates in regulating cAMP during thrombin activation of platelets.
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Salari, H., V. Duronio, S. Howard, M. Demos, and S. L. Pelech. "Translocation-independent activation of protein kinase C by platelet-activating factor, thrombin and prostacyclin. Lack of correlation with polyphosphoinositide hydrolysis in rabbit platelets." Biochemical Journal 267, no. 3 (May 1, 1990): 689–96. http://dx.doi.org/10.1042/bj2670689.
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The relationship between polyphosphoinositide hydrolysis and protein kinase C (PKC) activation was explored in rabbit platelets treated with the agonists platelet-activating factor (PAF), thrombin and 12-O-tetradecanoylphorbol 13-acetate (TPA), and with the anti-aggregant prostacyclin (PGI2). Measurement of the hydrolysis of radiolabelled inositol-containing phospholipids relied upon the separation of the products [3H]inositol mono-, bis- and tris-phosphates by Dowex-1 chromatography. PKC activity, measured in platelet cytosolic and Nonidet-P40-solubilized particulate extracts that were fractionated by MonoQ chromatography, was based upon the ability of the enzyme to phosphorylate either histone H1 in the presence of the activators Ca2+, diacylglycerol and phosphatidylserine, or protamine in the absence of Ca2+ and lipid. Treatment of platelets for 1 min with PAF (2 nM) or thrombin (2 units/ml) led to the rapid hydrolysis of inositol-containing phospholipids, a 2-3-fold stimulation of both cytosolic and particulate-derived PKC activity, and platelet aggregation. Exposure to TPA (200 nM) for 5 min did not stimulate formation of phosphoinositides, but translocated more than 95% of cytosolic PKC into the particulate fraction, and induced a slower rate of aggregation. PGI2 (1 microgram/ml) did not enhance phosphoinositide production, and at higher concentrations (50 micrograms/ml) it antagonized the ability of PAF, but not that of thrombin, to induce inositol phospholipid turnover, even though platelet aggregation in response to both agonists was blocked by PGI2. On the other hand, PGI2 alone also appeared to activate (by 3-5-fold) cytosolic and particulate PKC by a translocation-independent mechanism. The activation of PKC by PGI2 was probably mediated via cyclic AMP (cAMP), as this effect was mimicked by the cAMP analogue 8-chlorophenylthio-cAMP. It is concluded that this novel mechanism of PKC regulation by platelet agonists may operate independently of polyphosphoinositide turnover, and that activation of cAMP-dependent protein kinase represents another route leading to PKC activation.
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Hilal-Dandan, R., and L. L. Brunton. "Transmembrane mechanochemical coupling in cardiac myocytes: novel activation of Gi by hyposmotic swelling." American Journal of Physiology-Heart and Circulatory Physiology 269, no. 3 (September 1, 1995): H798—H804. http://dx.doi.org/10.1152/ajpheart.1995.269.3.h798.
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We have studied the effect of hyposmotic swelling on adenosin 3',5'-cyclic monophosphate (cAMP) metabolism in isolated cardiac myocytes. Decreasing extracellular osmolarity by 12.5-50% results in graded inhibition (10-40%) of isoproterenol-stimulated and forskolin-stimulated cAMP accumulation but does not affect basal and hormone-stimulated phosphoinositide hydrolysis or cellular ATP content. Treatment with pertussis toxin does not alter the swelling response but abolishes the inhibitory effect of swelling on cAMP accumulation. The response to swelling seems not to involve the release of effectors known to couple to inhibitory G protein (Gi) in myocytes: BQ-123, atropine, and adenosine deaminase do not alter the inhibitory effect of swelling on isoproterenol-stimulated cAMP accumulation; conditioned medium from swollen cells, with restored osmolarity, has no effect on cAMP accumulation when added to control myocytes. In distinction to these effects on myocytes, swelling enhances hormone-stimulated cAMP accumulation in cultured S49 lymphoma cells. We conclude that swelling of cardiac myocytes inhibits cAMP accumulation through a mechanism that involves activation of a pertussis toxin-sensitive Gi protein. Activation of Gi by this means may contribute to adrenergic hyporesponsiveness in hypoxic and ischemic myocardium.
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Huang, R. C., and R. Gillette. "Kinetic analysis of cAMP-activated Na+ current in the molluscan neuron. A diffusion-reaction model." Journal of General Physiology 98, no. 4 (October 1, 1991): 835–48. http://dx.doi.org/10.1085/jgp.98.4.835.
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cAMP-activated Na+ current (INa,cAMP) was studied in voltage-clamped neurons of the seaslug Pleurobranchaea californica. The current response to injected cAMP varied in both time course and amplitude as the tip of an intracellular injection electrode was moved from the periphery to the center of the neuron soma. The latency from injection to peak response was dependent on the amount of cAMP injected unless the electrode was centered within the cell. Decay of the INa,cAMP response was slowed by phosphodiesterase inhibition. These observations suggest that the kinetics of the INa,cAMP response are governed by cAMP diffusion and degradation. Phosphodiesterase inhibition induced a persistent inward current. At lower concentrations of inhibitor, INa,cAMP response amplitude increased as expected for decreased hydrolysis rate of injected cAMP. Higher inhibitor concentrations decreased INa,cAMP response amplitude, suggesting that inhibitor-induced increase in native cAMP increased basal INa,cAMP and thus caused partial saturation of the current. The Hill coefficient estimated from the plot of injected cAMP to INa,cAMP response amplitude was close to 1.0. An equation modeling INa,cAMP incorporated terms for diffusion and degradation. In it, the first-order rate constant of phosphodiesterase activity was taken as the rate constant of the exponential decay of the INa,cAMP response. The stoichiometry of INa,cAMP activation was inferred from the Hill coefficient as 1 cAMP/channel. The equation closely fitted the INa,cAMP response and simulated changes in the waveform of the response induced by phosphodiesterase inhibition. With modifications to accommodate asymmetric INa,cAMP activation, the equation also simulated effects of eccentric electrode position. The simple reaction-diffusion model of the kinetics of INa,cAMP may provide a useful conceptual framework within which to investigate the modulation of INa,cAMP by neuromodulators, intracellular regulatory factors, and pharmacological agents.
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Lerner, A., B. Jacobson, and R. A. Miller. "Cyclic AMP concentrations modulate both calcium flux and hydrolysis of phosphatidylinositol phosphates in mouse T lymphocytes." Journal of Immunology 140, no. 3 (February 1, 1988): 936–40. http://dx.doi.org/10.4049/jimmunol.140.3.936.
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Abstract Activation of T cells by lectins or mAb directed at components of the Ag-specific TCR results in hydrolysis of phosphorylated derivatives of phosphatidylinositol and an increase in intracellular free calcium concentration (Cai). We report that cholera toxin, which activates adenylate cyclase by ADP ribosylation of a G protein, also reduces both inositol phosphate (IP) production and the rise in Cai in Con A-stimulated murine T cells. We find that similar dose-dependent inhibitory effects can be induced by each of four other agents that raise cAMP levels in such cells: forskolin, PGE2, 2-chloroadenosine, and isoproterenol. The effects of these agents on IP production are reversible and therefore do not simply reflect cytotoxicity. Activation by PHA and by antibody to the T3-epsilon-chain of the TCR complex are also inhibited by agents that increase intracellular cAMP. Thus, changes in cAMP concentration seem to regulate both IP production and the Ca2+ response, two early components of the mitogen-induced activation process.
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Redmon, J. B., T. W. Gettys, V. S. Sheorain, J. D. Corbin, and I. L. Taylor. "Failure of insulin to antagonize cAMP-mediated glycogenolysis in rat ventricular cardiomyocytes." American Journal of Physiology-Endocrinology and Metabolism 258, no. 5 (May 1, 1990): E871—E877. http://dx.doi.org/10.1152/ajpendo.1990.258.5.e871.
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Isolated rat ventricular cardiomyocytes were used to study the effects of insulin on glycogen metabolism in cells treated with various agents that activate adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase. Incubation of myocytes with isoproterenol produced a rapid concentration-dependent increase in cAMP concentration, cAMP-dependent protein kinase activity, and phosphorylase activity and a simultaneous decrease in the glycogen synthase activity ratio. Various cAMP analogues also produced a concentration-dependent increase in phosphorylase activity and a decline in the glycogen synthase activity ratio. Incubation of cells with insulin produced no change in basal phosphorylase activity but produced a rapid 40% increase in the glycogen synthase activity ratio. Inclusion of insulin in cell incubations containing increasing concentrations of isoproterenol did not modify the increases in cAMP concentration, protein kinase activity, or phosphorylase activity. Insulin also did not antagonize the ability of any of the cAMP analogues tested to activate phosphorylase, irrespective of the suitability of the particular cAMP analogue as a substrate for cAMP phosphodiesterases. The failure of insulin to antagonize the glycogenolytic effects of isoproterenol or cAMP analogues was paralleled by its failure to activate low-Km phosphodiesterase activity, but the cAMP analogue, 8-parachlorophenylthio-cAMP produced a small reproducible activation of the low-Km enzyme. In contrast to hepatocytes and adipocytes, where some effects of insulin appear to be due to activation of the phosphodiesterase and hydrolysis of cAMP, the effects in cardiomyocytes appear to be independent of an insulin-sensitive phosphodiesterase or of the effects on other components of the cAMP cascade.
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Jung, Won Hee, and Lubomira I. Stateva. "The cAMP phosphodiesterase encoded by CaPDE2 is required for hyphal development in Candida albicans." Microbiology 149, no. 10 (October 1, 2003): 2961–76. http://dx.doi.org/10.1099/mic.0.26517-0.
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The cAMP-dependent pathway, which regulates yeast-to-hypha morphogenesis in Candida albicans, is controlled by changes in cAMP levels determined by the processes of synthesis and hydrolysis. Both low- and high-affinity cAMP phosphodiesterases are encoded in the C. albicans genome. CaPDE2, encoding the high-affinity cAMP phosphodiesterase, has been cloned and shown to be toxic in Saccharomyces cerevisiae upon overexpression under pGAL1, but functional under the moderate pMET3. Deletion of CaPDE2 causes elevated cAMP levels and responsiveness to exogenous cAMP, higher sensitivity to heat shock, severe growth defects at 42 °C and highly reduced levels of EFG1 transcription. In vitro in hypha-inducing liquid medium CaPDE2, deletion prohibits normal hyphal, but not pseudohyphal growth. On solid medium capde2 mutants form aberrant hyphae, with fewer branches and almost no lateral buds, which are deficient in hypha-to-yeast reversion. The phenotypic defects of capde2 mutants show that the cAMP-dependent pathway plays specific roles in hyphal and pseudohyphal development, its regulatory role however, being greater in liquid than on solid medium in vitro. The increased expression of CaPDE2 after serum addition correlates well with a drop in cAMP levels following the initial rise in response to the hyphal inducer. These results suggest that Capde2p mediates a desensitization mechanism by lowering basal cAMP levels in response to environmental stimuli in C. albicans.
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Riley, B. B., and S. L. Barclay. "Ammonia promotes accumulation of intracellular cAMP in differentiating amoebae of Dictyostelium discoideum." Development 109, no. 3 (July 1, 1990): 715–22. http://dx.doi.org/10.1242/dev.109.3.715.
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We used sporogenous mutants of Dictyostelium discoideum to investigate the mechanism(s) by which exogenous NH4Cl and high ambient pH promote spore formation during in vitro differentiation. The level of NH4Cl required to optimize spore formation is correlated inversely with pH, indicating that NH3 rather than NH4+ is the active species. The spore-promoting activity of high ambient pH (without exogenous NH4Cl) was eliminated by the addition of an NH3-scavenging cocktail, suggesting that high pH promotes spore differentiation by increasing the ratio of NH3:NH4+ secreted into the medium by developing cells. High ammonia levels and high pH stimulated precocious accumulation of intracellular cAMP in both sporogenous and wild-type cells. In both treatments, peak cAMP levels equaled or exceeded control levels and were maintained for longer periods than in control cells. In contrast, ammonia strongly inhibited accumulation of extracellular cAMP without increasing the rate of extracellular cAMP hydrolysis, indicating that ammonia promotes accumulation of intracellular cAMP by inhibiting cAMP secretion. These results are consistent with previous observations that factors that raise intracellular cAMP levels increase spore formation. Lowering intracellular cAMP levels with caffeine or progesterone inhibited spore formation, but simultaneous exposure to these drugs and optimal concentrations of NH4Cl restored both cAMP accumulation and spore formation to normal levels. These data suggest that ammonia, which is a natural Dictyostelium morphogen, favors spore formation by promoting accumulation or maintenance of high intracellular cAMP levels.
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Jenkins, L. A., and T. K. Bashkin. "Mechanistic studies of RNA strand cleavage: Hydrolysis of cAMP with copper(II)terpyridine." Journal of Inorganic Biochemistry 51, no. 1-2 (July 1993): 536. http://dx.doi.org/10.1016/0162-0134(93)85562-m.
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Gerstin, Edward H., and Frederick J. Ehlert. "Inhibition of muscarinic stimulated phosphoinositide hydrolysis in the rat parotid gland by cAMP." Life Sciences 58, no. 2 (December 1995): 145–53. http://dx.doi.org/10.1016/0024-3205(95)02267-8.
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Brown, L. A., and M. Chen. "Vasopressin signal transduction in rat type II pneumocytes." American Journal of Physiology-Lung Cellular and Molecular Physiology 258, no. 6 (June 1, 1990): L301—L307. http://dx.doi.org/10.1152/ajplung.1990.258.6.l301.
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Previous studies demonstrate that in cultured type II pneumocytes, [Arg8]-vasopressin (AVP) stimulates surfactant secretion independent of adenosine 3',5'-cyclic monophosphate (cAMP). In the current study AVP stimulated a 50% loss of radioactive phosphatidylinositol 4,5-bisphosphate (PIP2) within 15 s. Consistent with AVP-induced PIP2 hydrolysis was an increased appearance of the two breakdown products 1,2-diacylglycerol (1,2-DAG) and inositol 1,4,5-trisphosphate (IP3). Also, AVP stimulated the appearance of radiolabel in phosphatidic acid (PA) suggesting that the conversion of 1,2-DAG to PA could be used for PIP2 resynthesis. The effects of AVP on PIP2 and IP3 were mimicked by the bioactive AVP fragment and inhibited by the specific AVP1 antagonist. The EC50 for AVP on IP3 production was 6 nM. AVP stimulated protein kinase C (PK-C) activity twofold over the basal activity of 0.74 +/- 0.07 nmol P.min-1.mg protein-1 but did not activate cAMP-dependent protein kinase activity. The AVP1 antagonist inhibited AVP activation of PK-C. Therefore, activation of the AVP1 receptor resulted in PIP2 hydrolysis for signal transduction, PK-C activation, and surfactant secretion.
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Rajkumar, K., P. J. Chedrese, H. Ly, and B. D. Murphy. "Protein kinase C, an endogenous regulator of hormone-induced cyclic AMP induction in porcine luteal cells." Journal of Endocrinology 130, no. 2 (August 1991): 273–80. http://dx.doi.org/10.1677/joe.0.1300273.
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ABSTRACT LH, in addition to increasing cyclic AMP (cAMP) in ovarian cells, stimulates phosphoinositide hydrolysis producing inositol trisphosphate and diacylglycerol (DG). DG activates phospholipid- and calcium-dependent protein kinase (PKC). In the present study, we have used both PKC activators and inhibitors to examine the interactions of the PKC pathway on hormone-induced cAMP production in porcine luteal cells. Phorbol 12-myristate 13-acetate (PMA) enhanced LH- and forskolin-induced cAMP production. A time-course study indicated that the facilitatory effect of PMA was greater when added to incubation tubes following addition LH or forskolin. The non-tumour-promoting phorbol ester 4α-phorbol 12,13-didecanoate, which does not stimulate PKC activation, did not facilitate hormone-induced cAMP induction. PKC inhibitors polymyxin B, sphingosine and 1-(5-isoquinolinesulphonyl)-2-methylpiperazine (H7) antagonized the facilitatory effect of PMA on LH-induced cAMP production. The cAMP induction by both LH and forskolin was inhibited in the presence of PKC inhibitors. Polymyxin E, which differs from polymyxin B by a single amino acid and does not inhibit PKC activation, did not inhibit LH- or forskolin-induced cAMP induction. The results of this study provide evidence for a facilitative action of the PKC effector system on hormonally stimulated cAMP production. Furthermore, PKC may be an important endogenous regulator of adenylate cyclase activity in porcine luteal cells. Journal of Endocrinology (1991) 130, 273–280
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Xu, Hao-Liang, Hailemariam M. Wolde, Vitaliy Gavrilyuk, Verna L. Baughman, and Dale A. Pelligrino. "cAMP modulates cGMP-mediated cerebral arteriolar relaxation in vivo." American Journal of Physiology-Heart and Circulatory Physiology 287, no. 6 (December 2004): H2501—H2509. http://dx.doi.org/10.1152/ajpheart.00319.2004.
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No studies have specifically addressed whether cAMP can influence nitric oxide (NO)/cGMP-induced cerebral vasodilation. In this study, we examined whether cAMP can enhance or reduce NO-induced cerebral vasodilation in vivo via interfering with cGMP efflux or through potentiating phosphodiesterase 5 (PDE5)-mediated cGMP breakdown, respectively, in cerebral vascular smooth muscle cells (CVSMCs). To that end, we evaluated, in male rats, the effects of knockdown [via antisense oligodeoxynucleotide (ODN) applications] of the cGMP efflux protein multidrug resistance protein 5 (MRP5) and PDE5 inhibition on pial arteriolar NO donor [ S-nitroso- N-acetyl penicillamine (SNAP)]-induced dilations in the absence and presence of cAMP elevations via forskolin. Pial arteriolar diameter changes were measured using well-established protocols in anesthetized rats. In control (missense ODN treated) rats, forskolin elicited a leftward shift in the SNAP dose-response curves (∼50% reduction in SNAP EC50). However, in MRP5 knockdown rats, cAMP increases were associated with a substantial reduction in SNAP-induced vasodilations (reflected as a significant 35–50% lower maximal response). In the presence of the PDE5 inhibitor MY-5445, the repression of the NO donor response accompanying forskolin was prevented. These findings suggest that cAMP has opposing effects on NO-stimulated cGMP increases. On the one hand, cAMP limits CVSMC cGMP loss by restricting cGMP efflux. On the other, cAMP appears to enhance PDE5-mediated cGMP breakdown. However, because increased endogenous cAMP seems to potentiate NO/cGMP-induced arteriolar relaxation when MRP5 expression is normal, the effect of cAMP to reduce cGMP efflux appears to predominate over cAMP stimulation of cGMP hydrolysis.
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Vettel, C., S. Lämmle, S. Ewens, C. Cervirgen, J. Emons, A. Ongherth, M. Dewenter, et al. "PDE2-mediated cAMP hydrolysis accelerates cardiac fibroblast to myofibroblast conversion and is antagonized by exogenous activation of cGMP signaling pathways." American Journal of Physiology-Heart and Circulatory Physiology 306, no. 8 (April 15, 2014): H1246—H1252. http://dx.doi.org/10.1152/ajpheart.00852.2013.
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Recent studies suggest that the signal molecules cAMP and cGMP have antifibrotic effects by negatively regulating pathways associated with fibroblast to myofibroblast (MyoCF) conversion. The phosphodiesterase 2 (PDE2) has the unique property to be stimulated by cGMP, which leads to a remarkable increase in cAMP hydrolysis and thus mediates a negative cross-talk between both pathways. PDE2 has been recently investigated in cardiomyocytes; here we specifically addressed its role in fibroblast conversion and cardiac fibrosis. PDE2 is abundantly expressed in both neonatal rat cardiac fibroblasts (CFs) and cardiomyocytes. The overexpression of PDE2 in CFs strongly reduced basal and isoprenaline-induced cAMP synthesis, and this decrease was sufficient to induce MyoCF conversion even in the absence of exogenous profibrotic stimuli. Functional stress-strain experiments with fibroblast-derived engineered connective tissue (ECT) demonstrated higher stiffness in ECTs overexpressing PDE2. In regard to cGMP, neither basal nor atrial natriuretic peptide-induced cGMP levels were affected by PDE2, whereas the response to nitric oxide donor sodium nitroprusside was slightly but significantly reduced. Interestingly, despite persistently depressed cAMP levels, both cGMP-elevating stimuli were able to completely prevent the PDE2-induced MyoCF phenotype, arguing for a double-tracked mechanism. In conclusion, PDE2 accelerates CF to MyoCF conversion, which leads to greater stiffness in ECTs. Atrial natriuretic peptide- and sodium nitroprusside-mediated cGMP synthesis completely reverses PDE2-induced fibroblast conversion. Thus PDE2 may augment cardiac remodeling, but this effect can also be overcome by enhanced cGMP. The redundant role of cAMP and cGMP as antifibrotic meditators may be viewed as a protective mechanism in heart failure.