Growth arrest and morphological change of human breast cancer cells by dibutyryl cyclic AMP and L-arginine

The growth in vitro of human breast cancer cells, line MCF-7, was inhibited by a daily supplement of L-arginine (1 milligram per milliliter). Arginine acted synergistically with dibutyryl adenosine 3',5'-monophosphate (cyclic AMP) (10(-6) molar) to enhance the growth inhibitory effect: the cell replication ceased completely within 2 days after treatment. The growth arrest accompanied a change in cell morphology and was preceded by increases in the cellular concentration of cyclic AMP, adenylate cyclase, and type II cyclic AMP-dependent protein kinase activities as well as a decrease of estrogen binding activity. The results suggest that growth of human breast cancer cells is subject to cyclic AMP-mediated regulation and that arginine may play a specific role in this process.     

Regulation of phosphodiesterase synthesis: requirement for cyclic adenosine monophosphate-dependent protein kinase

Endogenous cyclic adenosine monophosphate (AMP) and its dibutyryl derivative increase cyclic AMP phosphodiesterase activity in cultured lymphoma cells. This effect is prevented by cycloheximide. A variant population of cells deficient in cyclic AMP-dependent protein kinase contains lower basal phosphodiesterase activity, which cannot be induced by cyclic AMP.     

Oscillation of cyclic adenosine monophosphate concentration during the myocardial contraction cycle

The concentration of adenosine 3',5'-monophosphate (cyclic AMP) rises and falls during each myocardial contraction cycle. Peak concentrations of cyclic AMP precede peak development of systolic tension. Epinephrine alters the normal oscillation in myocardial cyclic AMP and increases both diastolic and systolic concentrations of the cyclic nucleotide. These transient changes in myocardial cyclic AMP indicate a potential role for cyclic AMP as a beat-to-beat regulator of myocardial contractility.     

Cyclic nucleotide phosphodiesterase: high activity in a mammalian photoreceptor

Purified outer segments of bovine rods exhibit phosphodiesterase activity against adenosine and guanosine cyclic 3',5'-monophosphates (cyclic AMP and cyclic GMP). The enzyme hydrolyzed cyclic GMP more rapidly than cyclic AMP at low substrate concentrations. The presence of high phosphodiesterase activity in this highly specialized organelle suggests that this enzyme may function in control of cyclic nucleotide concentration during visual excitation or adaptation.     

Histone phosphorylation: stimulation by adenosine 3',5'-monophosphate

Adenosine cyclic 3',5'-monophosphate at a concentration of 10-(7)M causes a four-to sixfold increase in the rate of histone phosphorylation catalyzed by a liver enzyme preparation. This observation suggests a mechanism for the induction of RNA synthesis by those hormones that cause increases in the concentration of cyclic AMP.     

Adenosine 3',5'-monophosphate waves in Dictyostelium discoideum: a demonstration by isotope dilution--fluorography

The distribution of adenosine 3',5'-monophosphate (cyclic AMP) in fields of aggregating amoebae of Dictyostelium discoideum was examined by a novel isotope dilution-fluorographic technique. Cellular cyclic AMP was visualized by its competition with exogenous 3H-labeled cyclic AMP for high-affinity binding sites on protein kinase immobilized on a Millipore filter used to blot the monolayer. The cyclic AMP was distributed in spiral or concentric circular wave patterns which centered on the foci of the aggregations. These patterns were correlated with those of cell shape change that propagate through the monolayers: cells in regions of high concentrations of cyclic AMP were elongated (presumably moving up a cyclic AMP gradient), whereas those in regions of low cyclic AMP concentrations were randomly directed. The highest cyclic AMP concentrations were about 10(-6)M. The widths of the regions of elevated cyclic AMP were about 0.3 to 1 millimeter which, assuming a wave velocity of 300 micrometers per minute, suggests that a cell signals for about 1 to 3 minutes. These observations support the hypothesis that the aggregation process in Dictyostelium is mediated by the periodic relay of cyclic AMP signals and suggest a simple scheme for the dynamics of the aggregation process.     

Growth inhibition by adenosine 3',5-monophosphate derivatives does not require 3',5' phosphodiester linkage

Analogs of adenosine 3',5'-monophosphate (cyclic AMP) inhibit the growth of cultured cell lines. The effects of 8-bromo- and N6-butyryl-substituted analogs of cyclic and noncyclic AMP on six cell lines were examined and were equally inhibitory. Variant cell lines with altered cyclic AMP-dependent protein kinase were more resistant to both cyclic and noncyclic nucleotides. We conclude that growth inhibition by analogs of cyclic AMP (i) does not require a 3',5' phosphodiester bond and (ii) may be mediated by a pathway involving endogenous cyclic AMP.     

Dibutyryl cyclic adenosine monophosphate stimulation of colcemid-inhibited axonal elongation

Adenosine 3',5'-monophosphate (cyclic AMP) and its dibutyryl derivative induce a variety of morphological changes, including those associated with in vitro axonal maturation. Established sensory ganglia treated with dibutyryl cyclic AMP show significant increases in average axonal length and number in comparison with controls; those treated with maintenance doses of Colcemid show no increases in either parameter; simultaneous treatment with both agents results in growth statistically similar to that produced by dibutyryl cyclic AMP alone. The data are consistent with our hypothesis that cyclic AMP promotes axonal elongation by stimulating microtubule assembly from a preexisting subunit pool.     

Compartmentalization of cyclic AMP during phagocytosis by human neutrophilic granulocytes

Immunocytochemistry shows that early during phagocytosis of zymosan, adenosine 3',5'-monophosphate (cyclic AMP) appears on the cell surface before the phagosome is internalized. The appearance of cyclic AMP on the cell surface is coincident with that of granule products and regulatory subunit of type I cyclic AMP-dependent protein kinase. Guanosine 3',5'-monophosphate is not associated with the initiation site of phagocytosis, but is observed throughout the granular cytoplasmic region. This sharply localized accumulation of cyclic AMP may serve as a signal for the initiation of phagocytosis.     

Adenosine 3',5'-monophosphate modulates thyrotropin receptor clustering and thyrotropin activity in culture

A biologically active rhodamine conjugate of thyrotropin binds at 4 degrees C to diffusely distributed membrane thyrotropin receptors which patch and become endocytosed into thyroid cells in a temperature-sensitive process. When the cells are first incubated with 8-bromo-cyclic adenosine monophosphate at 37 degrees C, the conjugate also binds to clustered receptors at 4 degrees C. Furthermore, 8-bromo-cyclic adenosine monophosphate reduces the amount of adenosine 3',5'-monophosphate (cyclic AMP) induced by thyrotropin. Hence, increased intracellular cyclic AMP induces receptor patching and reduces the concentration of cyclic AMP normally induced by thyrotropin. This suggests that cyclic AMP acts both as the second messenger of thyrotropin and also as the regulator of the level of thyrotropin receptors.     

Reversal of catecholamine refractoriness by inhibitors of RNA and protein synthesis

The generation of adenosine 3',5'-monophosphate (cyclic AMP) in response to catecholamines in the 2B subclone of RGC6 rat glioma cells previously exposed to norepinephrine and refractory to further norepinephrine addition is substantially increased by addition of inhibitors of RNA and protein synthesis. The time course of the effect of these inhibitors on cyclic AMP concentration suggests that rapid protein synthesis and turnover are involved in catecholamine refractoriness. Norepinephrine induction of cyclic nucleotide phosphodiesterase is demonstrable in RGC6 cells but not in the 2B subclone. Thus, catecholamine refractoriness cannot be attributed to induction of phosphodiesterase. This implies that induction of a protein or proteins, important in catecholamine refractoriness, affects the synthesis rather than the degradation of cyclic AMP.     

Catecholamine and dibutyryl cyclic AMP effects on myosin adenosine triphosphatase in cultured rat heart cells

Catecholamines and dibutyryl adenosine 3', 5'-monophosphate (dibutyryl cyclic AMP) increase the activity of myosin adenosine triphosphatase in cultured rat heart cells. Dichloroisoproterenol, an inhibitor of the beta receptor of the catecholamines, inhibits the action of the catecholamines but not of cyclic AMP.     

Norepinephrine-sensitive adenylate cyclases in rat brain: relation to behavior and tyrosine hydroxylase

Responses of norepiniephrine sensitive adeniosinie 3',5'-monophosphate (cyclic AMP)-generating systems in combined midbrain-striatal slices of four rat strains correlate positively with spontaneous behavioral activity and negatively with levels of midbrain and striatal tyrosine hydroxylase. Responses of cerebral cortical norepinephrine-sensitive cyclic AMP systems correlate negatively with spontaneous behavioral activity antd positively with midbrain and striatal tyrosine hydroxylase. Such correlations were not found with responses of the cyclic AMP- generatinlg systems to isoproterenol, adenosine. veratridine or of an adenosne and norepinephrine combination.     

Beta-adrenergic receptor kinase: primary structure delineates a multigene family

The beta-adrenergic receptor kinase (beta-ARK), which specifically phosphorylates only the agonist-occupied form of the beta-adrenergic and closely related receptors, appears to be important in mediating rapid agonist-specific (homologous) desensitization. The structure of this enzyme was elucidated by isolating clones from a bovine brain complementary DNA library through the use of oligonucleotide probes derived from partial amino acid sequence. The beta-ARK cDNA codes for a protein of 689 amino acids (79.7 kilodaltons) with a protein kinase catalytic domain that bears greatest sequence similarity to protein kinase C and the cyclic adenosine monophosphate (cyclic AMP)--dependent protein kinase. When this clone was inserted into a mammalian expression vector and transfected into COS-7 cells, a protein that specifically phosphorylated the agonist-occupied form of the beta 2-adrenergic receptor and phosphorylated, much more weakly, the light-bleached form of rhodopsin was expressed. RNA blot analysis revealed a messenger RNA of four kilobases with highest amounts in brain and spleen. Genomic DNA blot analysis also suggests that beta-ARK may be the first sequenced member of a multigene family of receptor kinases.     

Adenosine 3'5'-monophosphate: inhibition of complement-mediated cell lysis

An increase in adenosine 3',5'-monophosphate (cyclic AMP) in rat mast cells, achieved by stimulating the cells with prostaglandin E(1), by preventing cyclic AMP breakdown with aminophylline, or by adding exogenous dibutyryl cyclic AMP, prevented complement-mediated cytolysis as assessed by both histamine release and vital dye exclusion. Dibutyryl cyclic AMP also suppressed water-induced osmotic lysis.     

A chemoattractant receptor controls development in Dictyostelium discoideum

During the early stages of its developmental program, Dictyostelium discoideum expresses cell surface cyclic adenosine monophosphate (cyclic AMP) receptors. It has been suggested that these receptors coordinate the aggregation of individual cells into a multicellular organism and regulate the expression of a large number of developmentally regulated genes. The complementary DNA (cDNA) for the cyclic AMP receptor has now been cloned from lambda gt-11 libraries by screening with specific antiserum. The 2-kilobase messenger RNA (mRNA) that encodes the receptor is undetectable in growing cells, rises to a maximum at 3 to 4 hours of development, and then declines. In vitro transcribed complementary RNA, when hybridized to cellular mRNA, specifically arrests in vitro translation of the receptor polypeptide. When the cDNA is expressed in Dictyostelium cells, the undifferentiated cells specifically bind cyclic AMP. Cell lines transformed with a vector that expresses complementary mRNA (antisense) do not express the cyclic AMP receptor protein. These cells fail to enter the aggregation stage of development during starvation, whereas control and wild-type cells aggregate and complete the developmental program within 24 hours. The phenotype of the antisense transformants suggests that the cyclic AMP receptor is essential for development. The deduced amino acid sequence of the receptor reveals a high percentage of hydrophobic residues grouped in seven domains, similar to the rhodopsins and other receptors believed to interact with G proteins. It shares amino acid sequence identity and is immunologically cross-reactive with bovine rhodopsin. A model is proposed in which the cyclic AMP receptor crosses the bilayer seven times with a serine-rich cytoplasmic carboxyl terminus, the proposed site of ligand-induced receptor phosphorylation.     

Selective reduction of forskolin-stimulated cyclic AMP accumulation by inhibitors of protein synthesis

Inhibiting protein synthesis by incubating C6-2B rat astrocytoma cells with cycloheximide or emetine for periods up to 24 hours caused a progressive decrease in the accumulation of adenosine 3',5'-monophosphate (cyclic AMP) when the cells were challenged for 30 minutes with 100 microM forskolin. In contrast, cholera toxin-stimulated (6 nM, 3 hours) cyclic AMP accumulation was not diminished in cycloheximide-treated cells, and cyclic AMP was only minimally diminished in response to a 30-minute challenge with 10 microM (-)-isoproterenol. These experiments suggest the presence of a previously unrecognized cyclase component, which is essential for forskolin-stimulated cyclic AMP accumulation and has a shorter half-life than the beta-adrenergic receptor, the guanine nucleotide regulatory proteins, or the cyclase catalytic component.     

AMPK is a direct adenylate charge-regulated protein kinase

The adenosine monophosphate (AMP)-activated protein kinase (AMPK) regulates whole-body and cellular energy balance in response to energy demand and supply. AMPK is an αβγ heterotrimer activated by decreasing concentrations of adenosine triphosphate (ATP) and increasing AMP concentrations. AMPK activation depends on phosphorylation of the α catalytic subunit on threonine-172 (Thr(172)) by kinases LKB1 or CaMKKβ, and this is promoted by AMP binding to the γ subunit. AMP sustains activity by inhibiting dephosphorylation of α-Thr(172), whereas ATP promotes dephosphorylation. Adenosine diphosphate (ADP), like AMP, bound to γ sites 1 and 3 and stimulated α-Thr(172) phosphorylation. However, in contrast to AMP, ADP did not directly activate phosphorylated AMPK. In this way, both ADP/ATP and AMP/ATP ratios contribute to AMPK regulation.