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PubMed1989

Stimulation of glucose transport in rat cardiac myocytes by guanosine 3',5'-monophosphate.

Glucose transport in isolated rat cardiomyocytes is stimulated by insulin, catecholamines, and anoxia approximately 2- to 3-fold over basal rates. The molecular mechanisms controlling these responses are unknown. In our search for possible cellular mediators of glucose transport stimulation, we examined the effects of a number of nucleotides on 3-O-methylglucose transport in heart cells. The nucleotides and/or permeable analogs (monosuccinyl, 8-bromo, and dibutyryl derivatives) included cUMP, cIMP, cCMP, cAMP, and cGMP at concentrations ranging from 10 nM to 1 mM. Of all the nucleotides tested only cGMP analogs induced a significant stimulation of transport at concentrations as low as 100 nM. This effect was observed in both the 8-bromo- and dibutyryl derivatives and with 1 mM cGMP itself. The effect was concentration dependent for both analogs and produced a maximal response equivalent to that of 100 nM insulin. This insulinomimetic effect of cGMP was examined in more detail in order to evaluate its role as a potential mediator of this response. Agents that are known to stimulate guanylate cyclase in the heart produced a clear stimulation of transport when added to cardiomyocytes. These include insulin, aminophylline, histamine, beta-estradiol, and biotin-nitrophenyl ester. Methylene blue, an inhibitor of guanylate cyclase, blocked the insulin response when added to cells before insulin, but was ineffective when added after insulin. In addition, agents that raise intracellular cGMP levels by inhibiting cyclic nucleotide phosphodiesterases were also examined for effects on glucose transport. Out of several phosphodiesterase inhibitors tested, only Zaprinast (which selectively increases cGMP in heart) stimulated transport in a concentration-dependent manner to within 80% of the maximal insulin effect. These results are consistent with the notion that cGMP may be involved in glucose transport stimulation.

Aminophylline↗
PubMed1984

Influence of cyclic nucleotides, norepinephrine and calcium on 3H-uridine incorporation into RNA in thyroid slices.

The role of cyclic nucleotides and Ca2+ on RNA synthesis was investigated in beef thyroid slices. Both cyclic AMP and cyclic GMP caused a significant stimulation of 3H-uridine incorporation into total RNA (around 500%). No additive effect was observed when slices were incubated with cAMP plus cGMP. Another cyclic nucleotide, cyclic 3'5' cytidine monophosphate (cCMP) was also studied. At 0.2 mM cCMP the stimulatory action of cGMP was no longer evident (control 2183 +/- 311 cpm/mg RNA; 0.5 mM cGMP 3849 +/- 316; 0.2 mM cCMP 1885 +/- 238; cGMP + cCMP 1750 +/- 178), extending our previous observation on the blocking effect of cCMP on cAMP stimulation of RNA synthesis. The distribution of uridine nucleotides, precursors of RNA, was studied by paper chromatography in slices labeled with 3H-uridine. Both cAMP and cGMP caused a significant increase in labeled UTP (% UTP in chromatogram: control 2.4 +/- 0.4; 1 mM cAMP 4.9 +/- 1.3 and 1 mM cGMP 5.3 +/- 0.5). The influence of Ca2+ on RNA labeling was studied by incubating the slices under mild Ca2+ depletion (KRB without Ca2+) and severe Ca2+ depletion (KRB without Ca2+ + 2 mM EGTA). Basal RNA labeling was significantly affected only by severe depletion (control 1312 +/- 50; severe Ca2+ depletion 912 +/- 190). Under this latter condition, RNA synthesis failed to respond to TSH, cAMP and cGMP stimulation, and EM showed severe alterations in structure (e.g., nuclear swelling, mitochondrial condensation, etc.).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

[Recent data on the mechanism of action of prolactin].

Prolactin is a hormone involved in the control of many functions, from osmoregulation in fishes to lactation in mammals. For that reason, the control of its secretion by hypophysis is particularly complex. Multiple factors of hypothalamic origin (dopamine, GABA, VIP, etc . . .) and hormones (oestrogens, TRH, thyroxine, . . .) are involved in this control. Prolactin molecule contains about 200 aminoacids. It has three disulfide bridges, of which one, at the center of the molecule, is required for the lactogenic activity. The expression of prolactin gene is dependent upon oestrogens, TRH, Ca++ ion and cAMP which favour its transcription. In contrast, dopaminergics such as CB 154 lower the expression rate of this gene. Prolactin receptor is located essentially on the plasma and intracellular membranes of target cells. Its essential binding part has a molecular weight of about 40,000. In mammary gland and liver prolactin receptor is up-regulated following a slow process. It is also down-regulated following a rapid and reversible process. In mammary gland, prolactin controls the expression of milk protein genes by enhancing their transcription rate and also by increasing the stability and the translation rate of the mRNAs. The transfer of the prolactin information to genes takes place through a relay which is released from plasma membrane when the receptor is occupied by the hormone or by anti-prolactin receptor antibodies. This relay which seems to be a small peptide (less than 1000 daltons and inactivated by trypsin) acts directly and specifically on isolated mammary nuclei via a dephosphorylation of nuclear proteins.

Animals↗
PubMed1994

Absolute requirement of cyclic nucleotide in the activation of the G141Q mutant cAMP receptor protein from Escherichia coli.

cAMP receptor protein (CRP), when interacting with cAMP, controls the expression of a network of catabolite-sensitive genes in Escherichia coli. To understand the molecular events that lead to the activation of CRP, a combined approach of site-directed mutagenesis and thermodynamic analysis was employed to study a member of a specific class of CRP mutant, CRP, which activates the in vivo expression of CRP-dependent operons in cya- strains in the absence of exogenous cAMP. Results from in vitro studies show that the CRP mutant G141Q absolutely requires cAMP for interacting with specific DNA. A quantitative comparison of the thermodynamic parameters governing ligand binding and DNA-protein complex formation in the presence of different cyclic nucleotides leads to the conclusion that this CRP mutant is activated only in the presence of cyclic nucleotides. The specificity toward cyclic nucleotides exhibited by wild-type CRP is lost in this mutant. Furthermore, the binding affinity of the ligand for the first binding site of the mutant is essentially the same as that of wild-type CRP regardless of the identity of the cyclic nucleotide. Hence, the observed in vivo activation of CRP-dependent operons by G141Q in the absence of exogenous cAMP is most likely the consequence of the replacement of cAMP by other cyclic nucleotides to activate the mutant. It is also possible that trace levels of cAMP present in the cya- strain could account for the in vivo activation of the mutant. Furthermore, these results indicate that this CRP mutant does not assume the activated conformation in the absence of cyclic nucleotides, in contrast to the current model derived from results of in vivo studies.

Base Sequence↗
PubMed1990

Nerve growth factor acts through cAMP-dependent protein kinase to increase the number of sodium channels in PC12 cells.

cAMP-dependent protein kinase (PKA) and phospholipid-dependent protein kinase (PKC) play a role in nerve growth factor (NGF)-mediated differentiation. In PC12 cells, NGF causes neurite outgrowth and increases the number of voltage-gated Na+ channels. Neurite outgrowth involves in part activation of PKC. How NGF regulates Na+ channel number is unknown. Using patch-clamp techniques, we find that agents activating PKC, including phorbol esters and a ras oncogene product (p21) that induces neurites, caused little increase in channel number. In contrast, agents increasing intracellular cAMP were as effective as NGF. A specific protein inhibitor of the PKA catalytic subunit blocked increases by NGF or cAMP. Thus, NGF increases Na+ channel number in PC12 cells in part by activating PKA but apparently not PKC.

1-Methyl-3-isobutylxanthine↗
PubMed1987

Cyclic cytidine monophosphate stimulates DNA synthesis by bovine mammary tissue in vitro.

Mammary gland biopsies were taken from midpregnant heifers (n = 4), cut into pieces .5 mm thick and 3 - 5 mm2 and incubated for 48 hours in Eagle's Minimum Essential Medium containing 0, .1 or 1 micrograms/ml insulin and 0, 10(-8), 10(-7), 10(-6), 10(-5), or 10(-4) M dibutyryl cyclic 3', 5', cytidine monophosphate (dbcCMP). With 0 or .1 microgram/ml insulin, dbcCMP decreased incorporation of tritiated thymidine into DNA. Similar declines in DNA synthesis were observed with sodium butyrate, suggesting that the decline was due to the butyrate rather than to a cyclic CMP-specific effect. With 1 micrograms/ml insulin, dbcCMP increased DNA synthesis. Higher levels of dbcCMP reduced DNA synthesis relative to 10(-6)M dbcCMP, as did sodium butyrate. Thus cCMP is capable of stimulating mammary growth.

Animals↗
PubMed1983

Methylglyoxal-mediated growth inhibition in an Escherichia coli cAMP receptor protein mutant.

Under certain growth conditions, some strains of Escherichia coli accumulate toxic levels of methylglyoxal. This report characterizes a strain which synthesizes a mutant cAMP receptor protein in an adenylate cyclase deletion background. When cultured in glucose 6-phosphate minimal medium, this strain (222) was prematurely growth arrested due to methylglyoxal production; growth inhibition did not occur when the strain was grown in glucose minimal medium. A comparison of a variety of enzyme and cofactor levels in the related strains 222 (mutant) and 225 (wild-type) grown on either glucose or glucose 6-phosphate medium was carried out. The only difference found that might explain an increase in methylglyoxal accumulation was an elevated level of phosphofructokinase in strain 222 grown on glucose 6-phosphate. Since this enzyme activity probably limits hexose phosphate metabolism, it is suggested that growth inhibition in strain 222 may be due to increased production of triose phosphate, some of which is converted to methylglyoxal.

Adenylyl Cyclases↗
PubMed1982

In vitro effect of LH-releasing factor on the content of cyclic cytidine 3' 5' monophosphate (c-CMP) in the rat anterior pituitary.

The effect of LH-RF on pituitary content of cyclic cytidine 3' 5' monophosphate (c-CMP), one of the newly detected cyclic nucleotides, was examined by the RIA procedure. In results showed that the pituitary content of c-CMP was lower than in various other organs of the rat. When incubated in vitro in the presence of 0.5 ng LH-RF/ml incubation medium, c-CMP content of the anterior pituitaries was reduced slightly, but the difference was not statistically significant when compared with the controls. No difference in c-CMP content was observed between the controls and the 5 ng LH-RF/ml group. C-CMP content in the rat anterior pituitary tissue did not change significantly during an in vitro time-course study (5, 15, and 30 min.) in the presence of 5 ng LH-RF/ml. In contrast, c-AMP content of the pituitary was significantly (P less than 0.05) elevated by the stimulation of 5 ng of LH-RF/ml at a 15 minutes of incubation. These data suggest that c-CMP content, unlike c-AMP, might not be changed significantly by hypothalamic gonadotropin releasing hormone.

Animals↗
PubMed1986

5'-Nucleotidase activity in adult and fetal rabbit lungs.

5'-Nucleotidase was assayed in the membrane fractions isolated from rabbit lung homogenate. The enzyme activity was measured from the rate of hydrolysis of [U-14C]cytidine 5'-monophosphate (CMP). The optimal pH of the rate of hydrolysis is around 8.0 and the enzyme activity is stimulated by Mg2+. The apparent Km and Vmax of the enzyme in the microsomal fraction for CMP were 3.33 mM and 1.43 mumol/min/mg protein, respectively. During lung development the enzyme activity increased moderately at late gestational ages and reached its maximum level in adults (p less than 0.001). The developing profile of 5'-nucleotidase activity is similar to the developing pattern of the CMP content in rabbit lungs.

5'-Nucleotidase↗
PubMed2005

A comparison of the diagnostic accuracy and prognostic value of the first and second anti-cyclic citrullinated peptides (CCP1 and CCP2) autoantibody tests for rheumatoid arthritis.

OBJECTIVES: To compare the diagnostic performance and prognostic value of the anti-cyclic citrullinated peptide (CCP1) and anti-CCP2 autoantibody tests in a clinical setting. METHODS: Anti-CCP1 and anti-CCP2 antibody tests were performed on the same serum samples obtained from 467 patients with early arthritis from the Leiden Arthritis Cohort. The sensitivity, specificity, positive predictive value, and negative predictive value for discriminating between rheumatoid arthritis (RA) and non-RA at 1 year's follow up were calculated for both tests. Results were graphically presented using receiver operating characteristic curves. Progression of radiological joint damage was assessed over 4 years in patients with RA and used to assess the prognostics values of the CCP tests. RESULTS: At a similar specificity the CCP2 test had a higher sensitivity than the CCP1 test. Both tests identified a subgroup of patients with RA with an increased rate of joint damage progression. The anti-CCP2 test identified more patients with an increased rate of joint damage progression than the anti-CCP1 test, and in multiple regression analysis CCP2 was the better predictor of joint damage. CONCLUSIONS: The CCP2 test had better diagnostic and prognostic ability than the CCP1 test.

Adolescent↗
PubMed1997

Estimation of cytidylyl cyclase activity and monitoring of side-product formation by fast-atom bombardment mass spectrometry.

The enzyme cytidylyl cyclase catalyses the conversion of cytidine 5'-triphosphate into cytidine 3',5'-cyclic monophosphate, a third naturally occurring cyclic nucleotide currently under investigation to assign a biochemical function. Quantitation of the activity of this enzyme has been carried out by the positive-ion fast-atom bombardment mass spectrometric analysis of the enzyme incubation mixture after the reaction has been terminated. The data obtained are in good agreement with those obtained from the conventional radiometric and radioimmunoassays of the same enzyme preparations. The advantage of the mass spectrometer-based assay is the facility for multiple component monitoring. Thus, the production of the cytidine diphosphates and monophosphates, and the production of four cytidine 3',5'-cyclic monophosphate analogues as side-products, were simultaneously estimated. The identities of two of the side-products, 2'-O-glutamyl- and 2'-O-aspartyl-cytidine-3',5'-cyclic monophosphate, and of the cytidine 3',5'-cyclic monophosphate product, were confirmed by mass-analysed ion kinetic energy spectra from the collision-induced dissociation of the protonated molecules.

Animals↗