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PubMed1988

Cyclic AMP-cyclic AMP receptor protein as a repressor of transcription of the spf gene of Escherichia coli.

The spf gene of Escherichia coli encodes an unstable 109-nucleotide RNA, spot 42 RNA; the level of this RNA was reduced three- to fivefold when cells were grown in the presence of 3',5'-cyclic AMP (cAMP). We show that this regulation occurs through reduction in transcription and depends on both cAMP and the cAMP receptor protein (CRP) but is independent of the de novo protein synthesis. Through deletion analysis of the spf gene promoter, we have identified sequences that are important in the synthesis of spot 42 RNA. Deletion of sequences upstream of -77 completely eliminated the negative control of cAMP-CRP and resulted in high constitutive levels of transcription. This region contained a sequence that both conformed to the consensus binding site for cAMP-CRP in positively regulated promoters and acted as a cAMP-CRP binding site in a gel retardation assay. Deletion of sequences between positions -77 and -60 greatly reduced the level of transcription in the presence or absence of cAMP-CRP, indicating that at least part of this region is a binding site for a positive-acting transcription factor (or RNA polymerase itself). We propose that the proximity of the two sites defined here allows for the negative control of spf gene transcription by cAMP-CRP. In particular, if only one site at a time can be occupied, the binding of cAMP-CRP would interfere with the binding of a transcription factor.

Base Sequence↗

PubMed1989

Control mechanism of the Escherichia coli K-12 cell cycle is triggered by the cyclic AMP-cyclic AMP receptor protein complex.

The role of cyclic AMP (cAMP) in the cell cycle of Escherichia coli K-12 was studied in three mutant strains. One was KI1812, in which the cya promoter is replaced by the lacUV5 promoter. In KI1812, isopropyl-beta-D-thiogalactopyranoside induced the synthesis of cya mRNA, and at the same time cell division was inhibited and short filaments containing multiple nuclei were formed. The other strains were constructed as double mutants (NC6707 cya sulB [ftsZ(Ts)] and TR3318 crp sulB [ftsZ(Ts)]). In both double mutants, filamentation was repressed at 42 degrees C, but it was induced again by addition of cAMP in strain NC6707 and introduction of pHA7 containing wild-type crp in TR3318. These results indicate that lateral wall synthesis in the E. coli cell cycle is triggered by the cAMP-cAMP receptor protein complex.

Cell Cycle↗

PubMed1990

The CytR repressor antagonizes cyclic AMP-cyclic AMP receptor protein activation of the deoCp2 promoter of Escherichia coli K-12.

We have investigated the regulation of the Escherichia coli deoCp2 promoter by the CytR repressor and the cyclic AMP (cAMP) receptor protein (CRP) complexed to cAMP. Promoter regions controlled by these two proteins characteristically contain tandem cAMP-CRP binding sites. Here we show that (i) CytR selectively regulated cAMP-CRP-dependent initiations, although transcription started from the same site in deoCp2 in the absence or presence of cAMP-CRP; (ii) deletion of the uppermost cAMP-CRP target (CRP-2) resulted in loss of CytR regulation, but had only a minor effect on positive control by the cAMP-CRP complex; (iii) introduction of point mutations in either CRP target resulted in loss of CytR regulation; and (iv) regulation by CytR of deletion mutants lacking CRP-2 could be specifically reestablished by increasing the intracellular concentration of CytR. These findings indicate that both CRP targets are required for efficient CytR repression of deoCp2. Models for the action of CytR are discussed in light of these findings.

Base Sequence↗

PubMed1990

Activation of expression of the Escherichia coli cir gene by an iron-independent regulatory mechanism involving cyclic AMP-cyclic AMP receptor protein complex.

Synthesis of the colicin I receptor protein, encoded by the cir gene, was determined to be sensitive to control by the catabolite repression regulatory system. Under both high- and low-iron conditions for growth, mutants unable to produce cyclic AMP (cAMP) (cya) or functional cAMP receptor protein (crp) exhibited decreased membrane levels of the receptor relative to those of the wild-type strain. Exogenous addition of cAMP to the cya mutant restored maximal expression. cAMP-dependent changes in steady-state levels of cir mRNA suggested that the effect is mediated by control of transcript synthesis or stability. Potential mechanisms for regulation were examined by deletion and sequence analysis.

Base Sequence↗

PubMed1999

Evidence that expression of the Vibrio vulnificus hemolysin gene is dependent on cyclic AMP and cyclic AMP receptor protein.

Glucose repressed hemolysin production in Vibrio vulnificus. Promoter activity of the hemolysin gene, vvh, assessed with a vvh-luxCDABE transcriptional fusion, required cyclic AMP (cAMP) and cAMP receptor protein (CRP) in Escherichia coli. Hemolysin production in V. vulnificus increased after the addition of cAMP and was undetectable in a putative crp mutant, suggesting that vvh is also regulated by cAMP-CRP in V. vulnificus.

Animals↗

PubMed2003

The cyclic AMP-cyclic AMP receptor protein complex regulates activity of the traJ promoter of the Escherichia coli conjugative plasmid pRK100.

The TraJ protein is a central activator of F-like plasmid conjugal transfer. In a search for regulators of traJ expression, we studied the possible regulatory role of the cyclic AMP (cAMP)-cAMP receptor protein (CRP) complex in traJ transcription using a traJ-lacZ reporter system. A comparison of the enzyme activities in the wild-type Escherichia coli strain MC4100 with those in cya and crp mutants indicated that disruption of the formation of the cAMP-CRP complex negatively influenced the activity of the traJ promoter of the F-like plasmid pRK100. The defect in the cya mutant was partially restored by addition of exogenous cAMP. Competitive reverse transcription-PCR performed with RNA isolated from the wild-type and mutant strains showed that the cAMP-CRP complex exerted its effect at the level of transcription. Electrophoretic mobility shift assays with purified CRP demonstrated that there was direct binding of CRP to the traJ promoter region. DNase I footprint experiments mapped the CRP binding site around position -67.5 upstream of the putative traJ promoter. Targeted mutagenesis of the traJ promoter region confirmed the location of the CRP binding site. Consistent with the demonstrated regulation of TraJ by the cAMP-CRP complex, mutants with defects in cya or crp exhibited reduced conjugal transfer from pRK100.

Bacterial Outer Membrane Proteins↗

PubMed1987

Cyclic AMP regulation of early gene expression in Dictyostelium discoideum: mediation via the cell surface cyclic AMP receptor.

We examined two sets of genes expressed early in the developmental cycle of Dictyostelium discoideum that appear to be regulated by cyclic AMP (cAMP). The transcripts of both sets of genes were not detectable in vegetative cells. During normal development on filter pads, RNA complementary to these genes could be detected at about 2 h, peaked around 6 to 8 h, and decreased gradually thereafter. Expression of these genes upon starvation in shaking culture was stimulated by pulsing the cells with nanomolar levels of cAMP, a condition that mimics the in vivo pulsing during normal aggregation. Expression was inhibited by caffeine or by continuous levels of cAMP, a condition found later in development when in vivo expression of these genes decreased. The inhibition of caffeine could be overcome by pulsing cells with cAMP. These results suggest that the expression is mediated via the cell surface cAMP receptor, but does not require a rise in intracellular cAMP. mRNA from a gene of the second class was induced upon starvation, peaked by 2.5 h of development, and then declined. In contrast to the other genes, its expression was maintained by continuous levels of cAMP and repressed by cAMP pulses. These and other results on a number of classes of developmentally regulated genes indicates that changing levels of cAMP, acting via the cell surface cAMP receptor, are involved in controlling these groups of genes. We also examined the structure and partial sequence of the cAMP pulse-induced genes. The two tandemly duplicated M3 genes were almost continuously homologous over the sequenced portion of the protein-coding region except for a region near the N-terminal end. The two M3 genes had regions of homology in the 5' flanking sequence and showed slight homology to the same regions in gene D2, another cAMP pulse-induced gene. D2 showed extremely significant homology over its entire sequenced length to an acetylcholinesterase. The results presented here and by others suggest that expression of many early genes in D. discoideum is regulated via the cell surface cAMP receptor. We expect that many of these genes may play essential roles in early Dictyostelium development and could code for elements of the cAMP signal transduction pathway involved in aggregation.

Amino Acid Sequence↗

PubMed1977

Cyclic AMP in action of antidiuretic hormone: effects of exogenous cyclic AMP and its new analogue.

Exogenous cyclic 3',5'-adenosine monophosphate (cAMP) stimulates the effect of the antidiuretic hormone, vasopressin (VP), only in pharmacologic quantities and results have often been inconsistent. The present study examined the ability of a new analogue, 8-[p-Cl-phenylthio]cyclic 3',5'-adenosine monophosphate (C1-PheS-cAMP) to mimic the effect of VP, both biochemically (protein kinase activation) and functionally (hydrosomatic response of perfused collecting tubules) in mammalian kidney tissue. C1PheS-cAMP was found to be about 100 times as effective as cAMP both biochemically and functionally. The increased effectiveness of C1PheS-cAMP is probably is probably due to a greater permeability across the cell membrane and to the resistance of C1PheS-cAMP to enzymatic degradation, Cyclic AMP phosphodiesterase inhibition was observed with C1PheS-cAMP, but its contribution to overall effect was minor. C1PheS-cAMP was found to be more effective than exogenous vasopressin, an effect probably due primarily to its resistance to catabolism. The results provide further new evidence that cAMP and protein kinase are involved in the cellular action of vasopressin. C1PheS-cAMP proved to be a useful tool in the study of hormone action, especially in steps subsequent to cAMP generation.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1999

Cyclic GMP and cyclic AMP induced changes in control and hypertrophic cardiac myocyte function interact through cyclic GMP affected cyclic-AMP phosphodiesterases.

We tested the hypothesis that the negative functional effects of cyclic GMP (cGMP) would be greater after increasing cyclic AMP (cAMP), because of the action of cGMP-affected cAMP phosphodiesterases in cardiac myocytes and that this effect would be altered in left ventricular hypertrophy (LVH) produced by aortic valve plication. Myocyte shortening data were collected using a video edge detector, and O2 consumption was measured by O2 electrodes during stimulation (5 ms, 1 Hz, in 2 mM Ca2+) from control (n = 7) and LVH (n = 7) dog ventricular myocytes. cAMP and cGMP were determined by a competitive binding assay. cAMP was increased by forskolin and milrinone (10(-6) M). cGMP was increased with zaprinast and decreased by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxilin-1-one (ODQ) both at 10(-6) and 10(-4) M, with and without forskolin or forskolin + milrinone. Zaprinast significantly decreased percent shortening in control (9 +/- 1 to 7 +/- 1%) and LVH (10 +/- 1 to 7 +/- 1%) myocytes. It increased cGMP in control (36 +/- 5 to 52 +/- 7 fmol/10(5) myocytes) and from the significantly higher baseline value in LVH (71 +/- 12 to 104 +/- 18 fmol/10(5) myocytes). ODQ increased myocyte function and decreased cGMP levels in control and LVH myocytes. Forskolin + milrinone increased cAMP levels in control (6 +/- 1 to 15 +/- 2 pmol/10(5) myocytes) and LVH (8 +/- 1 to 18 +/- 2 pmol/10(5) myocytes) myocytes, as did forskolin alone. They also significantly increased percent shortening. There were significant negative functional effects of zaprinast after forskolin + milrinone in control (15 +/- 2 to 9 +/- 1%), which were greater than zaprinast alone, and LVH (12 +/- 1 to 9 +/- 1%). This was associated with an increase in cGMP and a reduction in the increased cAMP induced by forskolin or milrinone. ODQ did not further increase function after forskolin or milrinone in control myocytes, despite lowering cGMP. However, it prevented the forskolin and milrinone induced increase in cAMP. In hypertrophy, ODQ lowered cGMP and increased function after forskolin. ODQ did not affect cAMP after forskolin and milrinone in LVH. Thus, the level of cGMP was inversely correlated with myocyte function. When cAMP levels were elevated, cGMP was still inversely correlated with myocyte function. This was, in part, related to alterations in cAMP. The interaction between cGMP and cAMP was altered in LVH myocytes.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed2000

Adrenal glucocorticoids modulate [3H]cyclic AMP binding to protein kinase A (PKA), cyclic AMP-dependent PKA activity, and protein levels of selective regulatory and catalytic subunit isoforms of PKA in rat brain.

Alterations in hypothalamic-pituitary-adrenal (HPA) function are associated with changes in mood and behavior. Protein kinase A (PKA), on activation, phosphorylates many important intracellular proteins and thereby plays a major role in mediating various physiological functions in brain. We systematically examined the relationship of altered HPA function with PKA modifications in rat brain after administering corticosterone to normal rats and by first adrenalectomizing rats and then simultaneously treating them with different doses of corticosterone. Rats were decapitated on day 1, 4, or 14. Subcutaneously implanted 50- or 100-mg corticosterone pellets in normal rats for 4 or 14 days significantly decreased PKA activity, B(max) of [3H]cyclic AMP binding, and protein levels of selective PKA regulatory (RIalpha, RIIbeta) and catalytic (Catbeta) subunit isoforms in cortex and hippocampus in a dose-dependent manner without any significant changes at day 1; these changes were more pronounced at day 14. However, adrenalectomy caused the opposite changes in these measures at day 4 or 14 in both cortex and hippocampus, and the magnitude of the changes was more pronounced at day 14. Simultaneous treatment with implanted corticosterone at 50- or 100-mg doses in adrenalectomized rats reversed the adrenalectomy-induced increases in PKA measures in a dose-dependent manner. These results suggest that endogenous glucocorticoid modifies the expression of RIalpha, RIIalpha, and Catbeta subunit isoforms of PKA, as well as the catalytic and regulatory activities of PKA, and that these alterations in PKA may in part explain HPA axis-mediated changes in mood and behavior.

Adrenalectomy↗

PubMed1985

Activation of cyclic GMP-binding and cyclic AMP-specific phosphodiesterases of rat platelets by a mechanism involving cyclic AMP-dependent phosphorylation.

We have previously reported that the cAMP-specific phosphodiesterase activity in washed rat platelets is increased by a short exposure of platelet suspension to PGE1 and 1-methyl-3-isobutyl-xanthine (MIX). We report here that the incubation of washed platelets with forskolin resulted in an increase in the binding of cGMP and the activity of cGMP-phosphodiesterase as well as that of cAMP-specific phosphodiesterase. As for PGE1, MIX potentiated the stimulatory effect of forskolin. The maximal activation of phosphodiesterases by forskolin and MIX occurred after 30 sec of incubation of platelets (with a slow decline thereafter). The activation of phosphodiesterases in intact platelets by forskolin occurred in parallel with the dissociation of a cAMP-dependent protein kinase. Prior incubation of a platelet supernatant with Mg-ATP and cAMP had only a slight effect on cAMP- or cGMP-phosphodiesterase activities, but the presence of MIX during the prior incubation, followed by appropriate dilution, greatly enhanced the activity of the two phosphodiesterases. The phosphodiesterase activation in vitro was inhibited by a non-hydrolysable analogue of ATP, AMP-PNP. Since the cGMP-binding phosphodiesterase activity is enhanced by the catalytic subunit of cAMP-dependent protein kinase in the presence of MIX and absence of cAMP, the effect of MIX cannot be explained in terms of the protection of cAMP from hydrolysis. It is possible that the xanthine increases the susceptibility of the cAMP-specific and cGMP-binding phosphodiesterases to phosphorylation.

1-Methyl-3-isobutylxanthine↗

PubMed1988

Inhibition of the low Km cyclic AMP phosphodiesterase and activation of the cyclic AMP system in vascular smooth muscle by milrinone.

The purposes of the present study were to quantitate the effects of the cardiotonic/vasodilator milrinone on phosphodiesterase (PDE) isozymes isolated from vascular (aortic) smooth muscle from several species, and to quantitate changes in cellular cyclic AMP (cAMP) content, activation of cAMP protein kinase (cAPK) and vasorelaxation by milrinone in isolated guinea pig aortic smooth muscle. With PDE isozymes isolated from rat (Wistar-Kyoto or spontaneously hypertensive rats), guinea pig, monkey or canine aortic smooth muscle, milrinone is a potent (IC50 = 0.16-0.90 microM) and selective (100 times peak III relative to peak I) peak III inhibitor. The potency of milrinone and other vascular peak III PDE inhibitors parallels their potency as vasorelaxants in isolated guinea pig aortic rings (r = 0.86; P less than .01). Vasorelaxation of phenylephrine-contracted (3 microM) guinea pig aortic rings is accompanied by significant increases in cAMP content or cAPK activation with concentrations of milrinone greater than or equal to 10 microM. Temporally, significant increases in cAMP content accompany significant vasorelaxation; however, activation of cAPK is not significantly increased until at least 1 to 2 min after addition of milrinone. Similar concentration and temporal relationships are seen with the cAMP-related vasorelaxants papaverine and forskolin. As with milrinone, a temporal dissociation between increases in cAMP content and increases in cAPK activity ratio is evident.(ABSTRACT TRUNCATED AT 250 WORDS)

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1997

Role of cyclic AMP response element-binding protein in cyclic AMP inhibition of NF-kappaB-mediated transcription.

The NF-kappaB family of transcription factors regulates the inducible expression of a variety of genes. Recently, we showed that elevation of intracellular cyclic AMP inhibits NF-kappaB-mediated transcription in human monocytes and endothelial cells without preventing nuclear translocation of NF-kappaB complexes. The present study examined the molecular mechanism of this inhibition. We hypothesized that activation of the protein kinase A signaling pathway may inhibit NF-kappaB-mediated transcription by phosphorylating proteins, such as cAMP response element-binding protein (CREB), which compete for limiting amounts of the coactivator CBP. Here, we show that the amino-terminal region (amino acids 1-450) of CBP specifically interacts with the carboxyl-terminal region (amino acids 286-551) of NF-kappaB p65 (RelA) both in vitro and in vivo. Functional studies using human endothelial cells demonstrated that overexpression of CBP rescued cAMP inhibition of NF-kappaB-mediated transcription and transcription mediated by a chimeric protein, GAL4-p65(286-551), which contained the GAL4 DNA binding domain fused to the carboxyl-terminal region of p65 (amino acids 286-551). In contrast, overexpression of CREB inhibited GAL4-p65(286-551)-mediated transcription. These results suggest that activation of the protein kinase A pathway inhibits NF-kappaB transcription by phosphorylating CREB, which competes with p65 for limiting amounts of CBP.

Calcium-Binding Proteins↗

PubMed1994

Characterisation of 5'-AMP-activated protein kinase in human liver using specific peptide substrates and the effects of 5'-AMP analogues on enzyme activity.

A specific peptide (SAMS peptide) phosphorylation assay has previously been used to measure and subsequently purify rat liver 5'-AMP-activated protein kinase (AMPK). In this report, we show that this peptide and a peptide based on the sequence surrounding the site phosphorylated on 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase by AMPK (HMG peptide) can be used to measure human liver AMPK. Our data demonstrate that both human and rat AMPKs have a higher affinity for the HMG peptide compared to the SAMS peptide. We have used these peptide phosphorylation assays to identify novel activators of AMPK.

AMP-Activated Protein Kinases↗

PubMed1987

Cyclic AMP-resistant mutants of S49 mouse lymphoma cells hemizygous for expression of regulatory subunit of type I cyclic AMP-dependent protein kinase.

For use in studies of the functional organization of regulatory (R) subunit of type I cAMP-dependent protein kinase, 84 independent cyclic AMP-resistant mutants were isolated from sublines of S49 mouse lymphoma cells that are hemizygous for expression of the R subunit. Mutants were characterized by two-dimensional gel analysis of the R subunits, assays of kinase activation, and assays of cAMP-binding. All but eight of the mutants had kinases with increased apparent Kas for cAMP-dependent activation, and studies with site-selective cAMP analogs revealed considerable phenotypic diversity among these mutants. Forty-nine of the mutants had "charge-shift" lesions that mapped to regions of the R subunit polypeptide implicated in cAMP-binding. Twenty-five of the "charge-shift mutants" expressed only mutant R subunits, and the lesions in most of these isolates inhibited binding of cAMP to mutated cAMP-binding sites. The remainder of the charge-shift mutants expressed both mutant R subunit and R subunit with wild-type gel mobilities. The origin of these "heterozygous" mutants from parental "hemizygous" cells remains a puzzle.

Animals↗

PubMed2006

Immunohistochemical analysis of human skeletal muscle AMP deaminase deficiency. Evidence of a correlation between the muscle HPRG content and the level of the residual AMP deaminase activity.

We have previously described that, in healthy human skeletal muscle, an anti-histidine-proline-rich-glycoprotein (HPRG) antibody selectively binds to type IIB fibers that are well known to contain the highest level of AMP deaminase (AMPD) activity, suggesting an association of the HPRG-like protein to the enzyme isoform M. The present paper reports an immunohistochemical study performed on human skeletal muscle biopsies from patients with AMPD deficiency and carried out utilizing both the anti-HPRG antibody and an anti-AMPD antibody specific for the isoform M. A correlation between the muscle content of the HPRG-like protein and the level of AMPD activity was demonstrated. In the specimens from patients with Acquired AMPD deficiency the HPRG-immunoreactivity was less intense than that shown by the control subjects and was related to the residual AMPD activity. The patients affected by Primary and Coincidental AMPD deficiency, which were characterized by an absence of enzyme activity and AMPD immunoreactivity, showed the lowest HPRG immunoreactivity that was clearly detectable by Western blot analysis, but not by immunohistochemistry. The interpretation of the significance of these observations suggests a physiological mutual dependence between skeletal muscle HPRG and AMPD polypeptides with regard to their stability.

AMP Deaminase↗

PubMed1977

Influence of dibutyryl cyclic AMP on thymidine uptake by herpes simplex virus infected cells and the intracellular level of cyclic AMP.

Dibutyryl cyclic AMP inhibits the increase of dThd and BrdUrd transport normally observed after infection with Herpesvirus hominis, type I and II. Incorporation is also reduced. Inhibition of uptake is non-competitive as analysed by the Lineweaver-Burk plot. Addition of this drug to infected cells also reduces the activity of the thymidine kinase (EC 2.7.1.75). Transport of dUrd, dCyd and dAdo is not reduced. 4--8 h after infection with thymidine kinase (+) herpes strains the level of cAMP increases. On infection with a thymidine kinase (-) virus, only a small elevation of cAMP can be shown. It was also found that early addition of actinomycin D or of cycloheximide prevents the increase of the cAMP level. This increase seems to depend on the activity of the herpes genome, because ultraviolet irradiation of infective particles destroys this ability.

Biological Transport↗

PubMed1989

Evidence for the existence of a GTP-dependent factor in hepatic cytosol that stimulates cyclic AMP binding: possible role in the modulation of cyclic AMP action.

GTP, in physiologic concentration (10(-4) mol/L), enhances cAMP binding to an Mr 57,000 binding protein (BP) in hepatic cytosol, which probably is the phosphorylated receptor subunit of protein kinase II (PK II). When we attempted to separate PK II from other hepatic cytosol proteins by DEAE-cellulose chromatography, we observed that GTP caused little stimulation of [3H]cAMP binding in an eluate fraction (110 to 170 mmol/L KCI), which was rich in PK II but did stimulate cAMP binding to the 210 to 325 mmol/L KCI fraction, which also contains PK II. This suggested that the latter fraction might contain a cofactor necessary for GTP stimulation of cAMP binding, which was lacking in the 110 to 170 mmol/L KCI fraction. Cyclic AMP BP in the 210 to 325 mmol/L fraction was removed by absorption onto cAMP agarose in the presence of 325 mmol/L KCI. When an aliquot of the BP-poor fraction, containing the putative cofactor, was added to the 110 to 170 mmol/L fraction containing PK II, the addition of 10(-4) mol/L GTP to the mixture increased [3H]cAMP binding by more than 80%. Cofactor activity could be extracted from the 210 to 325 mmol/L eluate by adsorption onto cAMP agarose in the presence of 10 mmol/L K phosphate, and eluted with 100 mmol/L KCI, suggesting that the cofactor may bind to the cAMP BP under appropriate circumstances. Addition of this eluted cofactor fraction to the 110 to 170 mmol/L fraction in the presence of 10(-4) mol/L GTP, increased the specific binding of [3H] cAMP more than twofold. Pretreatment of the cofactor fraction with trypsin eliminated this effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗