Cyclic AMP in metabolism

The nematode Caenorhabditis elegans and diverse potential invertebrate vectors predominantly interact opportunistically

Some small animals migrate with the help of other, more mobile animals (phoresy) to leave short-lived and resource-poor habitats. The nematode Caenorhabditis elegans lives in ephemeral habitats such as compost, but has also been found associated with various potential invertebrate vectors. Little research has been done to determine if C. elegans is directly attracted to these invertebrates. To determine whether C. elegans is attracted to compounds and volatile odorants of invertebrates, we conducted chemotaxis experiments with the isopods Porcellio scaber, Oniscus asellus, and Armadillidium sp. and with Lithobius sp. myriapods, Drosophila melanogaster fruit flies, and Arion sp. slugs as representatives of natural vectors. Because phoresy is an important escape strategy in nature, especially for dauer larvae of C. elegans, we examined the attraction of the natural C. elegans isolate MY2079 in addition to the laboratory-adapted strain N2 at the dauer and L4 stage. We found that DMSO washing solution of Lithobius sp. and the odor of live D. melanogaster attracted C. elegans N2 L4 larvae. Surprisingly, the natural isolate MY2079 was not attracted to any invertebrate during either the dauer or L4 life stages and both C. elegans strains were repelled by various compounds from O. asellus, P. scaber, Armadillidium sp., Lithobius sp., and Arion sp. feces. We hypothesize that this is due to defense chemicals released by the invertebrates. Although compounds from Lithobius sp. and D. melanogaster odorants were mildly attractive, the lack of attraction to most invertebrates suggests a predominantly opportunistic association between C. elegans and invertebrate vectors.

Regulation of a Ca2+-sensitive adenylyl cyclase in an excitable cell. Role of voltage-gated versus capacitative Ca2+ entry

In nonexcitable cells, we had previously established that Ca(2+)-sensitive adenylyl cyclases, whether expressed endogenously or heterologously, were regulated exclusively by capacitative Ca(2+) entry (Fagan, K. A., Mahey, R. and Cooper, D. M. F. (1996) J. Biol. Chem. 271, 12438-12444; Fagan, K. A., Mons, N., and Cooper, D. M. F. (1998) J. Biol. Chem. 273, 9297-9305). Relatively little is known about how these enzymes are regulated by Ca(2+) in excitable cells, where they predominate. Furthermore, no effort has been made to determine whether the prominent voltage-gated Ca(2+) entry, which typifies excitable cells, overwhelms the effect of any capacitative Ca(2+) entry that may occur. In the present study, we placed the Ca(2+)-stimulable, adenylyl cyclase type VIII in an adenovirus vector to optimize its expression in the pituitary-derived GH(4)C(1) cell line. In these cells, a modest degree of capacitative Ca(2+) entry could be discerned in the face of a dramatic voltage-gated Ca(2+) entry. Nevertheless, both modes of Ca(2+) entry were equally efficacious at stimulating adenylyl cyclase. A striking release of Ca(2+) from intracellular stores, triggered either by ionophore or thyrotrophin-releasing hormone, was incapable of stimulating the adenylyl cyclase. It thus appears as though the intimate colocalization of adenylyl cyclase with capacitative Ca(2+) entry channels is an intrinsic property of these molecules, regardless of whether they are expressed in excitable or nonexcitable cells.

Effects of triiodothyronine on rat-liver mitochondrial transcription process

1. In order to demonstrate that triiodothyronine affects mitochondrial RNA synthesis by acting on the enzyme component of the DNA. RNA polymerase complex, mitochondrial RNA polymerase from thyroidectomized and hormone-treated rats was purified up to a stage in which activity was dependent on the addition of exogenous template. In these conditions and using different DNAs as templates, the enzyme from hormone-treated animals displayed an activity about double that of the activity of thyroidectomized animals. 2. Measurements of stability of mitochondrial RNA synthesized in vitro suggest, however, that the hormone can act also at the template level in mitochondrial transcription: the RNA population synthesized in vitro from hormone-treated rats is indeed much more enriched in unstable, probably messenger, RNA species. 3. The turnover of mitochondrial messenger RNA is higher after hormone treatment. 4. Adenosine cyclic 3':5'-monophosphate (cAMP) and its dibutyryl derivative added in vitro to mitochondria from thyroidectomized animals do not affect the incorporation of labeled precursor into mitochondrial RNA, suggesting that the level of the cyclic nucleotide in mitochondria is probably not involved in the hormone action. 5. It is concluded from these and previous studies that the thyroid hormone affects more than one parameter in the mitochondrial transcription process. The interrelationship between these events at molecular level remains, however, to be clarified.

Mechanism of action of nerve growth factor and cyclic AMP on neurite outgrowth in embryonic chick sensory ganglia: demonstration of independent pathways of stimulation

The suggested role of adenosine 3':5'-cyclic monophosphate as the "second messenger" in the neurite outgrowth from chick embryonic sensory ganglia mediated by nerve growth factor was examined. Although N(6),O(2)-dibutyryl adenosine 3':5'-cyclic monophosphate induces fiber outgrowth at concentrations of 1-5 mM, this response is morphologically distinct from that produced by nerve growth factor, is pH dependent, is mimicked by sodium butyrate, and does not occur in sympathetic ganglia. In addition, nerve growth factor does not alter the amounts of intracellular cyclic AMP during incubations up to 24 hr and does not stimulate adenylate cyclase in broken-cell preparations. Addition of theophylline, an inhibitor of phosphodiesterase, causes increases in intracellular levels of cyclic AMP but does not affect fiber outgrowth. These observations indicate that the nerve growth factor response is not mediated through cyclic AMp and that stimulation of sensory ganglia by exogenous cyclic AMP derivatives is probably of limited physiological significance. These findings are also compatible with the developing hypothesis, based on structural similarities, that nerve growth factor and insulin exert their effects on their respective responsive tissues by related mechanisms.

Pleiotypic control by adenosine 3':5'-cyclic monophosphate: a model for growth control in animal cells

The effects of serum deprivation on several general cellular biochemical processes ("pleiotypic response") related to the growth of normal fibroblasts can be mimicked by treatment of these cells with prostaglandin E(1) in the presence of serum. N(6),O(2)'-Dibutyryl adenosine 3':5'-cyclic monophosphate and theophylline inhibit the membrane transport processes without much effect on other pleiotypic reactions such as overall protein and RNA synthesis and protein degradation. The amount of intracellular cyclic AMP increases during serum starvation and returns to the initial concentration in unstarved cells when growth is initiated again upon addition of serum. Fibroblasts transformed by simian virus 40 have a lower cyclic AMP content than their untransformed parents. Serum deprivation neither increases cyclic AMP content nor significantly affects the pleiotypic reactions in transformed cells. Cycloheximide causes a decrease in cyclic AMP content of normal fibroblasts coincidentally with the ability of this inhibitor to stimulate uridine transport and slow protein degradation in cells deprived of serum.

Identification of the cardiac beta-adrenergic receptor protein: solubilization and purification by affinity chromatography

A protein that binds catecholamines with a specificity parallel to that of their in vivo effects on cardiac contractility (isoproterenol > epinephrine or norepinephrine > dopamine > dihydroxyphenylalanine) was solubilized from a microsomal fraction of canine ventricular myocardium. The binding protein was purified 500 to 800-fold by solubilization and subsequent affinity chromatography with conjugates of norepinephrine linked to agarose beads. Purified beta-adrenergic binding protein exists in two forms, corresponding to molecular weights of 40,000 and 160,000. The purified material has a single association constant, 2.3 x 10(5) liters/mol (as compared to two association constants, 10(7) and 10(6) liters/mol, for the binding protein in particulate form) but retains the identical binding specificity for beta-adrenergic drugs and antagonists.

3',5'-cyclic adenosine monophosphate-requiring mutants of Escherichia coli

Mutants that require exogenous 3',5'-cyclic adenosine monophosphate (cAMP) for exponential growth were isolated from strains deficient in adenyl cyclase. Studies of one strain showed that cAMP is not incorporated into macromolecules; instead, it seems to have a regulatory function, i.e., in media lacking cAMP, cells form ribonucleic acid (RNA) and protein at linear rather than exponential rates. The exact lesion is not known; ribosomes, messenger RNA, and the beta and beta' subunits of RNA polymerase continue to be made in absence of added cAMP.

Protein kinase activity in equine herpesvirus

A protein kinase which is intimately associated with equine herpesvirus (equine abortion virus) was found by using adenosine triphosphate-gamma-(32)P as a phosphate donor and virus protein as an acceptor. Consistent demonstration of the activity requires prior removal of phosphohydrolase. The kinase activity requires Mg(2+), is not stimulated by cyclic adenosine monophosphate, but is enhanced by added protamine or arginine-rich histone. The labeled product is resistant to ribonuclease, deoxyribonuclease, and chloroform-methanol but is sensitive to Pronase. Other tests suggest that serine and threonine residues are the acceptor sites. In the in vitro reaction, the incorporation represents an average of approximately 4,500 phosphate residues per virion, and all 17 virus protein bands resolved by polyacrylamide gel electrophoresis appear to be labeled.

Regulation of adenosine 3',5'-cyclic monophosphate phosphodiesterase activity in fibroblasts by intracellular concentrations of cyclic adenosine monophosphate (3T3-dibutyryl cyclic AMP-SV40-transformed cells-michaelis constants-L cells-prostaglandin E 1 )

Cyclic AMP-phosphodiesterase is present in various mouse fibroblasts. Contact-inhibited 3T3 cells contain two forms of the enzyme, one with a K(m) of 2.5 muM and the second with a K(m) of 71 muM. As 3T3 cells grow to confluency and cAMP concentrations rise, the activity of the first enzyme increases, whereas that of the second is unchanged. A line of SV40-transformed 3T3 cells with low cAMP concentration also has low levels of the cAMP-phosphodiesterase with a K(m) of 2.5 muM. Treatment of 3T3 and SV40-transformed 3T3 cells with dibutyryl cAMP and theophylline increases cAMP-phosphodiesterase accumulation. This accumulation is blocked by cycloheximide and actinomycin D. The newly formed enzyme resembles the higher affinity enzyme present in unstimulated cells, since it has a K(m) of 1.2-2.0 muM, and is stimulated by snake venom. In L cells in which cAMP concentrations are elevated by treatment with prostaglandin E(1), cAMP phosphodiesterase also accumulates. We conclude that intracellular concentrations of cAMP regulate the synthesis of cAMP-phosphodiesterase, and that cAMP functions as an inducer of the enzyme.

Adenosine 3',5'-monophosphate levels in hemorrhagic shock

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