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At least 397 records · Page 22Linked to original sources
PubMed1989

Iso stimulation of GH and cAMP: comparison of beta-adrenergic- to GRF-stimulated GH release and cAMP accumulation in monolayer cultures of anterior pituitary cells in vitro.

Growth hormone (GH) release and cAMP content were measured in monolayer cultures of anterior pituitary cells after beta-adrenergic and GH-releasing factor (GRF) receptor activation. Isoproterenol (Iso, ED50-20 nM) was less potent than GRF (ED50-20 pM) in stimulating GH release. Iso caused a rapid stimulation of GH release that was maximal after 15 min and declined thereafter, while GRF caused a more gradual increase in GH secretion that was maximal after 30 min and remained elevated after 3 h. Both Iso- and GRF-stimulated GH release were preceded by an increase in cAMP content in the pituitary cells. Further, the addition of 3-isobutyl-1-methylxanthine (IBMX) to the medium enhanced the GH-stimulatory and cAMP-accumulating effects of both secretagogues. Experiments performed with native catecholamines and synthetic catecholamine agonists and antagonists indicated that the GH-stimulatory effect of Iso was mediated by a mixed population of beta 1-adrenergic and beta 2-adrenergic receptors. Additionally, experiments performed with cultured GH3 tumor cells, found that incubation with GRF, Iso, vasoactive intestinal polypeptide, forskolin, or cholera toxin caused an increase in cAMP content in the cells. However, compared to the responses observed in primary pituitary cultures the GH secretory response to these agents was comparatively small. Together, these studies suggest that a mixed population of beta 1-adrenergic and beta 2-adrenergic receptors may act, at least in part, on somatotrophs in the anterior pituitary to stimulate GH release. Although both GRF and beta 2-adrenergic receptor agents affect GH release through a common second messenger system, their differing pharmacokinetic properties suggest distinct intracellular mechanisms.

1-Methyl-3-isobutylxanthine↗
PubMed1982

Adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase and the regulation of parathyroid hormone release by divalent cations and agents elevating cellular cAMP in dispersed bovine parathyroid cells.

Divalent cations and agents elevating cellular cAMP were tested for their effects on parathyroid hormone (PTH) secretion and protein kinase activity in dispersed bovine parathyroid cells. After incubation with secretagogue for 5-30 min, cells were sedimented, PTH in the supernatant was determined by RIA, and the pellet was disrupted by sonication for the measurement of protein kinase activity. Preliminary studies established conditions where the protein kinase activity ratio (AR = activity in the absence divided by that in the presence of 10(-6) M cAMP in the kinase assay) remained stable during the preparation and assay of cellular extracts. (-)Isoproterenol caused a rapid (within 5 min) increase in the AR from 0.28 to 0.63, which returned to 0.25-0.3 within 5 min after the addition of the potent beta-adrenergic blocker (-)propranolol. (-)Isoproterenol, dopamine, and the phosphodiesterase inhibitor methylisobutylxanthine caused parallel, dose-dependent increases in PTH release and the protein kinase AR of 2- to 2.5-fold. Calcium and magnesium, on the other hand, despite causing 2- to 4-fold inhibition of secretion at 2 and 5 mM, respectively, had no effect on the AR. Calcium (2.0 mM) likewise had only a modest (0-25%) inhibitory effect on the isoproterenol-stimulated increase in the AR in spite of a 3- to 4-fold inhibition of agonist-stimulated secretion. These results suggest that the stimulation of secretion associated with agents that elevate cAMP is mediated by cAMP. Changes in the degree of activation of protein kinase, on the other hand, cannot quantitatively for the effects of divalent cations on basal or agonist-stimulated secretion.

1-Methyl-3-isobutylxanthine↗
PubMed1997

Characterization of an intronic promoter of a cyclic adenosine 3',5'-monophosphate (cAMP)-specific phosphodiesterase gene that confers hormone and cAMP inducibility.

In the Sertoli cell, FSH stimulates transcription of a cAMP-phosphodiesterase (PDE) gene (PDE4D) and accumulation of corresponding mRNA and PDE protein. The regulation of this PDE gene is an important component of the desensitization state induced by this hormone. Given the ubiquitous nature of this regulation controlling cAMP levels, the molecular basis for the PDE4D induction was further investigated. FSH stimulation of the Sertoli cell causes the accumulation of only two of the four known PDE4D mRNAs (PDE4D1 and PDE4D2). The promoter controlling the expression of these two messages was identified and characterized. An EcoRI fragment containing a coding exon as well as 5'-upstream sequence of the PDE4D1/2 mRNA was isolated from rat genomic libraries and sequenced. No TATA box was identified, but GC-rich regions were present upstream of the putative translation start site. RNAse protection and PCR analysis indicated the presence of at least two distinct cap sites. This genomic region had promoter activity when transfected both in Sertoli and MA-10 cells. Deletion mutation indicated that basal promoter activity was contributed by regions upstream of both cap sites. Transcription from this promoter was activated by FSH and (Bu)2cAMP, and elements responsible for cAMP regulation were present upstream from the second cap site. These data demonstrate that an intronic promoter that is cAMP- and hormone-inducible directs the expression of these truncated PDE proteins.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1995

Activating transcription factor-1 is a specific antagonist of the cyclic adenosine 3'.5'-monophosphate (cAMP) response element-binding protein-1-mediated response to cAMP.

We have investigated the molecular basis of the variability of the somatostatin cAMP response element (CRE) function in different cell lines. All cells tested contain detectable levels of the CRE-binding protein CREB-1, which mediates transactivation in response to the cAMP-dependent protein kinase (protein kinase-A), in forms that can bind to a somatostatin CRE. Although both responsive and nonresponsive cells contain CREB-1 in heterodimers with activating transcription factor-1 (ATF-1), only cells that allow a cAMP response have a significant proportion of CREB-1 in a homodimeric form. Transfection experiments demonstrate that ATF-1 is capable of antagonizing CREB-1-dependent activation, suggesting that the ability of CREB-1 to mediate a cAMP response is down-regulated by heterodimer formation with ATF-1.

Activating Transcription Factor 1↗
PubMed2002

Expression of cAMP-responsive element binding protein and inducible cAMP early repressor in hyperfunctioning thyroid adenomas.

OBJECTIVE: The pathogenesis of thyroid hyperfunctioning adenomas is still only partially understood and controversy exists about the frequency of gain-of-function mutations of the TSH receptor or G(s)alpha gene, which activate the cAMP pathway. The nuclear transcription factors cAMP-responsive element binding protein (CREB) and inducible cAMP early repressor (ICER) are among the final targets of this signalling cascade. DESIGN: In our study we focused on the expression of CREB and ICER genes in the nodular as well as in the extranodular tissue of hyperfunctioning tumours of the thyroid. METHODS: RT-PCR and Western blot analysis were performed in a series of 14 patients. The presence of an activating mutation of the TSH receptor or of the G(s)alpha gene was ascertained by direct sequencing. RESULTS: The levels of CREB transcripts did not significantly differ in the adenomas and in the normal tissues (CREB/GAPDH, mean optical density+/-s.e.: 0.98+/-0.18 vs 0.88+/-0.27 respectively, P = not significant (N.S.)), although case-to-case variability was observed. The absence of a significant difference between the adenoma and the surrounding normal tissue was maintained after dividing the patients into two groups, according to TSH receptor status. Accordingly, no significant difference in the levels of CREB protein (total and Ser(133)-phosphorylated) was observed between the nodular and the extranodular tissue. In addition, no difference was found in the levels of ICER transcripts (ICER/GAPDH, mean optical density+/-s.e.: 0.52+/-0.11, nodule vs 0.36+/-0.11, normal thyroid, P=N.S.), independently of the TSH receptor gene status (i.e. wild-type or mutated). CONCLUSIONS: Our results support the recent hypothesis that the activation of the cAMP pathway in hyperfunctioning adenomas of the thyroid might be counteracted by opposite events and suggest that complex molecular mechanisms might take part in the pathogenesis of hyperfunctioning tumours.

Activating Transcription Factor 1↗
PubMed2000

Distinct signalling pathways mediate the cAMP response element (CRE)-dependent activation of the calcitonin gene-related peptide gene promoter by cAMP and nerve growth factor.

The gene encoding the calcitonin gene-related peptide (CGRP) is activated in neuronal cells by treatment with cAMP and nerve growth factor (NGF). Both stimuli induce the phosphorylation of the cAMP response element (CRE)-binding protein (CREB) transcription factor on Ser-133 and require the CRE in the CGRP promoter to stimulate transcription. However, whereas the CRE is necessary and sufficient for promoter activation by cAMP, it is necessary but not sufficient for activation by NGF. We show that this difference is paralleled by a difference in the signalling pathways which are required for each stimulus to activate the CGRP promoter. Thus whilst cAMP-mediated activation requires the protein kinase A pathway, NGF-mediated stimulation requires the Ras/Raf mitogen-activated protein kinase kinase-1 (MEK-1)/p42/p44 mitogen-activated protein kinase (MAPK) pathway. Although NGF can activate the protein kinase C, p38 MAPK and c-Jun N-terminal kinase (JNK) pathways, these pathways are not involved in its effect on the CGRP promoter. The effect of the p42/p44 MAPK pathway on CREB and associated transcription factors, and the manner in which this results in activation of the CGRP promoter is discussed.

Animals↗
PubMed2000

Induction of cAMP response element modulator (CREM) and inducible cAMP early repressor (ICER) expression in rat brain by uncompetitive N-methyl-D-aspartate receptor antagonists.

The N-methyl-D-aspartate (NMDA) subtype of glutamate receptor mediates fast excitatory neurotransmission, and agents that attenuate this function are neuroprotective, anesthetic, and psychotropic. To determine whether cAMP regulatable transcription factors play a role in the neurochemical actions of agents acting through NMDA receptors, the effects of the acute administration of uncompetitive and competitive antagonists on the expression of cAMP response element modulator (CREM) and inducible cAMP early repressor (ICER) transcription factors were examined. In situ hybridization to rat brain sections revealed that ICER mRNA expression was significantly increased by uncompetitive NMDA receptor antagonists (MK-801, phencyclidine, ketamine, memantine) but not by the competitive antagonist CPP [(+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid] or other psychotropic agents (clozapine, haloperidol, desipramine). Major brain regions where ICER transcripts were increased were the hippocampus, parietal cortex layers IV and VI, temporal cortex, cingulate cortex, thalamus, and granule cell layer of the olfactory bulb. Northern and Western blot analyses indicated that CREM mRNA and protein, respectively, were also increased after MK-801 treatment, but ICER isoforms predominate during both basal and induced conditions. MK-801 also transiently increased the binding of proteins to cAMP response element, which was supershifted by anti-CREM antibody, indicating that increased mRNA and protein levels have functional consequences on gene transcription. These results provide evidence for the involvement of CREM and ICER family transcription factors in the pharmacologic effects of uncompetitive NMDA receptor antagonists.

Animals↗
PubMed2003

CAMP activates Rap1 in differentiating mouse male germ cells: a new signaling pathway mediated by the cAMP-activated exchange factor Epac?

Rap1, a Ras-like G-protein, is implicated in the signaling of various cellular processes as morphogenesis, differentiation, cell adhesion and spreading, and maintenance of T cell anergy and B cell activation. The effectors that mediate Rap1 signaling have not yet been definitely identified, with the exception of B-Raf which, however, is restricted to neuronal tissues and a small subset of other cell types, including in particular male germ cells. We previously showed that in mouse spermatids Rap1 could interact with B-Raf giving rise to a signaling complex. Here we investigated about the possible molecules which "switch on" Rap1 finding that cAMP could in vivo activate endogenous Rap1. Spermatid-enriched cell cultures stimulated with 8-(4-chlorophenylthio)-cyclic AMP yielded higher levels of GTP-bound Rap1 than unstimulated cells. Since cAMP-induced Rap1 activation is actually retained to occur through Epac, we checked whether this recently discovered Rap1 exchange factor is expressed in male germ cells. Our findings indicate that Epac is present in spermatogenic cells and exhibits a preferential subplasmalemmal localization, although it shows also an intracellular location, more or less pronounced depending on the type of spermatogenic cell examined. Taken together, our data show that cAMP activates Rap1 in differentiating male germ cells which express the cAMP sensor Epac, thus suggesting that this activation might occur directly through Epac.

Animals↗
PubMed1990

Transcriptional regulation of the bovine CYP17 (P-450(17)alpha) gene. Identification of two cAMP regulatory regions lacking the consensus cAMP-responsive element (CRE).

Regions within the 5'-flanking sequence of the bovine CYP17 (P-450(17)alpha) gene which are required for cAMP-dependent regulation of transcription have been localized by transient transfection of chimeric reporter gene constructs into mouse adrenal tumor Y1 cells. Two sequences have been found which individually confer cAMP responsiveness to reporter genes; they are located at -243/-225 and -80/-40 base pairs (bp). Obvious sequence homology between these two regions is not apparent. Gel shift competition analysis indicates that nuclear protein(s) binding to the -243/-225-bp region can be competed for by the addition of a double-stranded oligonucleotide containing a consensus cAMP-responsive element (CRE) from the human chorionic gonadotropin alpha gene, whereas addition of this CRE does not abolish protein-DNA complexes formed with fragments containing the -80/-40-bp sequence. Gel shift and Southwestern analysis indicate that the -243/-225-bp region of the P-450(17)alpha gene and the CRE both bind a 47-kDa protein and that the CRE binds additional proteins (43 and 68 kDa) not apparently recognized by the -243/-225-bp sequence. Thus cAMP-dependent regulation of the bovine P-450(17)alpha gene appears to involve two independent cis-regulatory regions, neither of which contains a consensus CRE. Based on protein binding analysis, one of these regions (that including -80/-40 bp) is distinct from the consensus CRE while the other (that containing -243/-225 bp) may be related to the consensus CRE.

Adrenal Gland Neoplasms↗
PubMed1986

Pertussis toxin blocks the inhibitory effects of somatostatin on cAMP-dependent vasoactive intestinal peptide and cAMP-independent thyrotropin releasing hormone-stimulated prolactin secretion of GH3 cells.

It was shown that somatostatin (SRIF) inhibited cAMP-dependent vasoactive intestinal peptide (VIP)-stimulated prolactin (PRL) release by a GH3 clonal strain of rat pituitary tumor cells and decreased basal PRL secretion and inhibited PRL release in response to thyrotropin releasing hormone (TRH) whose action was independent of prior synthesis of cAMP. Pretreatment of these cells with pertussis toxin prevented SRIF's inhibitory effects on basal and TRH-stimulated hormone secretion as well as its VIP-stimulated responses. The blockade of SRIF's inhibitory effect on the actions of TRH or VIP was dependent on both the duration of preincubation and concentration of the toxin and was correlated with the ability of the toxin to catalyze the ADP-ribosylation of the 39,000-Da membrane protein. It is likely that this pertussis toxin substrate is involved in signal transduction of SRIF on cAMP-dependent actions of VIP and cAMP-independent action of TRH. However, the mechanism of SRIF's action on TRH is not clear, since SRIF did not affect the intracellular responses by TRH, neither intracellular Ca2+ mobilization nor the increase of 1,2-diacylglycerol formation following the breakdown of polyphosphoinositides.

Animals↗
PubMed1985

Transcription of the Escherichia coli adenylate cyclase gene is negatively regulated by cAMP-cAMP receptor protein.

The regulatory region of the Escherichia coli cya gene was analyzed by using S1 nuclease mapping and in vitro transcription experiments. The cya gene was transcribed, both in vivo and in vitro, from one major promoter (P2) and two weak promoters (P1 and P1') that are located about 200 base pairs upstream of P2. The transcription from P2 was specifically inhibited by cAMP-CRP (cAMP receptor protein) in vitro. This regulatory mechanism was shown to be physiologically relevant through quantitative analyses of the cya mRNA in intact cells by S1 and dot blot assays. DNase I protection experiments revealed that cAMP-CRP binds to the cya DNA region between +11 and -20, in which a consensus CRP binding sequence is present. Moreover, it was found that cAMP-CRP alters the binding of RNA polymerase to the promoter region, thus inhibiting the transcription of the cya gene.

Adenylyl Cyclases↗
PubMed1983

[cAMP mediated cell growth regulation. II. Characterization of the biochemical change responsible for resistance to cAMP treatment].

In this paper we characterize the biochemical defect of a mutant (10248) of CHO cells, resistant to the cAMP treatment. Cells cultured on MEM were collected each three days, homogenized and centrifuged. The cell extract was assayed for protein kinases activity and the binding of 8-N3-(32P)cAMP. The same extract was also applied on to a DEAE cellulose column, eluted with a linear gradient and the fractions tested for the phosphotransferase activity and 8-N3-(32P)cAMP binding. Mutant 10248 shows a different profile of protein kinases activity as compared to 10001 control. Protein kinases II is absent whereas a normal RII binding activity is present. RI shows altered affinity for cAMP.

Animals↗
PubMed1980

The structural domains of cAMP-dependent protein kinase I. Characterization of two sites of proteolytic cleavage and homologies to cAMP-dependent protein kinase II.

The regulatory subunit of cAMP-dependent protein kinase I has been cleaved proteolytically into two structurally independent domains. The larger domain (35K with trypsin or thermolysin and 31K with chymotrypsin) corresponded to the COOH-terminal end of the polypeptide chain and retained the cAMP binding site(s). The smaller domain (11 to 12K with trypsin), corresponding to the NH2-terminal region of the regulatory subunit, contained the region of dimer interaction. In the absence of reducing reagent, the two protomers of the native regulatory subunit and of the smaller domain could be covalently cross-linked by a disulfide bond. In addition to the two major domains, a 15-residue peptide that links the two domains has been isolated and partially characterized. Two major sites on the type I regulatory subunit were susceptible to proteolytic degradation. Site 1, susceptible to cleavage by both trypsin and thermolysin, has the following sequence: LysArg-Arg-Gly-Ala-Ile-Ser-Ala-. Cleavage at this site generated a 35K cAMP-binding fragment. Site 2 contained a chymotryptic cleavage site as well as a secondary tryptic site. The sequence at Site 2 was Val-Arg-Arg-Val-Ile-Ala. Cleavage here generated a 31K cAMP-binding fragment. Both sites contained 2 consecutive basic amino acid residues similar to the corresponding sequence in the type II regulatory subunit; however, in the case of the type I regulatory subunit, the serine at Site 1 does not serve as a site of autophosphorylation. In contrast to the dissociated regulatory subunit, the holoenzyme is partially protected from proteolytic degradation.

Amino Acid Sequence↗
PubMed1994

1,25-dihydroxyvitamin D3 alters the effect of cAMP in thyroid cells by increasing the regulatory subunit type II beta of the cAMP-dependent protein kinase.

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) attenuates the stimulatory effects of cAMP on proliferation and iodide uptake in rat thyroid FRTL-5 cells. This study examines the effects of 1,25-(OH)2D3 on the cAMP-dependent protein kinase (PKA). Cytosol proteins separated by anion exchange chromatography showed increased [3H]cAMP binding activity as well as increased kinase activity in the fractions containing PKA type II in 1,25-(OH)2D3 (10 nM)-treated cells compared to the control cells. Western blot analysis of 1,25-(OH)2D3-treated cells revealed a 4-fold increase in the cytosolic amount of the PKA regulatory subunit RII beta, whereas no changes were detected in the regulatory subunits RI alpha and RII alpha or the catalytic (C) subunit. Northern blot analyses showed a similar increase in RII beta mRNA in cells treated for 12 h with 1,25-(OH)2D3 (10 nM), and RII beta mRNA increased further to 10-fold above control cell level after 96 h of incubation. Iodide uptake was synergistically stimulated with both PKAI- and PKAII-directed pairs of cAMP analogs. The PKAI synergism was, however, inhibited by 1,25-(OH)2D3 treatment of the cells, whereas the PKAII synergism was unaffected. In conclusion, 1,25-(OH)2D3 attenuates both PKAI formation and PKAI-stimulated iodide uptake in rat thyroid FRTL-5 cells by increasing the level of RII beta without altering the other PKA subunit levels.

Animals↗
PubMedDate not supplied

Cost analysis of eye camps and camp-based cataract surgery.

BACKGROUND: Although cataract accounts for half the blindness in the world, the resources available are not sufficient to meet the existing need for operations. The most effective low cost cataract surgery is probably performed in community camps. METHODS: We estimated the costs incurred in performing cataract operations in makeshift comprehensive eye care camps. Both the capital and recurrent inputs were costed at current market rates. RESULTS: Rupees 1,508,600 (US$ 47,100) was spent on conducting 17 camps during April 1992 to March 1993. Recurrent inputs were responsible for 83% of the total costs. Sixty per cent of the recurrent inputs were borne by non-governmental organizations. The total capital expenditure was borne by the mobile ophthalmic units. Food and drugs for patients (40%), and staff salaries and allowances (35%) were the major recurrent expenditure, while 60% of the capital expenditure was accounted for by vehicles. The unit cost of cataract surgery was Rs 772 (US$ 23). CONCLUSIONS: We suggest that comprehensive eye camps are cost-effective.

Cataract Extraction↗
PubMed1997

Inactivation of recombinant monocyte cAMP-specific phosphodiesterase by cAMP analog, 8-[(4-bromo-2,3-dioxobutyl)thio]adenosine 3',5'-cyclic monophosphate.

Two cAMP analogs, 8- and 2- [(4-bromo-2,3-dioxobutyl)thio]adenosine 3',5'-cyclic monophosphate (8- and 2-BDB-TcAMP) have been used in probing the catalytic site of recombinant monocyte cAMP-specific phosphodiesterase (PDE4a). 2-BDB-TcAMP is a reversible and competitive inhibitor (Ki = 5.5 mumol/L) of cAMP hydrolysis by PDE4a, 8-BDB-TcAMP irreversibly inactivates the enzyme in a time- and concentration-dependent manner with a second order rate constant of 0.022 mmol/L-1 min-1. The rate of inactivation of PDE4a is reduced by the presence of the substrate cAMP and specific inhibitors, rolipram and denbufylline, but not by cGMP or AMP. Reduction of the enzyme-inhibitor complex with sodium [3H]borohydride shows that 1.2 mol of the affinity label/mol of enzyme was incorporated. The radiolabeled peptide is composed of 10 amino acid residues (697 to 706) located near the carboxyl end of the proposed catalytic domain. The peptide (GPGHPPLPDK) has seven nonpolar and aliphatic residues, of which four are proline, giving the peptide a highly structured conformation. This peptide is the first to be identified in the putative catalytic domain involved in substrate recognition.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1983

Locus of control in juvenile diabetic campers: changes during camp, and relationship to camp staff assessments.

Locus of control was measured at the beginning and end of a three-week camp experience in 156 children with juvenile diabetes. The results were compared with those of 30 diabetic children who did not attend camp. Both the Nowicki Strickland Children's Locus of Control and the Parcel Health Locus of Control scales were used. In addition, subjective assessments of diabetes management skills were made in all campers by several staff members. Significant changes toward internal locus of control on the NSLC but not the CHLC were found. The changes in NSLC seem to have persisted for at least one year in a small subsample of 23 children who were retested. Initial scores on both scales correlated moderately with the diabetes management skills ratings made at the end of camp. In view of the apparent importance of the locus of control construct in the self-care expected of most children with juvenile diabetes, the results should stimulate further efforts to examine the usefulness of this measure in relationship to achievement of good control of diabetes.

Adolescent↗
PubMed1997

A residential summer camp for children with vertically transmitted HIV/AIDS: a six-year experience at the Hole in the Wall Gang Camp.

Residential camping sessions for children with vertically transmitted human immunodeficiency virus/acquired immunodeficiency syndrome have been offered at The Hole In The Wall Gang Camp for the past six summers. More than 600 children 6 to 12 years of age have attended. Such sessions are expensive and require extensive planning. Medical and nursing needs have increased greatly over the 6-year period, reflecting advances in treatment and especially an escalation of prescribed medications. We have found it possible for these children to have a fun-filled camping experience and participate in a wide variety of activities.

Acquired Immunodeficiency Syndrome↗