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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The interaction between cell-cell contact and cyclic AMP-mediated control of the rat tyrosine hydroxylase (TH) gene was investigated in subclones of the PC12 rat pheochromocytoma cell line. Increasing cell culture density and elevation of intracellular cyclic AMP levels with forskolin both cause augmentation of TH RNA levels. However, the extent of increase in TH RNA following forskolin treatment is less in cultures grown at high density than those at low density, suggesting that there may be an interaction in the mechanism by which these two treatments modulate TH RNA levels. The role of cis-acting sequences in the TH gene in the induction of TH RNA by cyclic AMP and cell density was determined by the use of plasmid constructs containing the 5'-flanking sequences of the TH gene directing the transcription of the reporter gene, chloramphenicol acetyltransferase (CAT). Using transient transfection assays in PC12 cells, we have mapped the site of cyclic AMP regulation of the TH gene to a region between -60 and -41. Stable transformants of PC12 cells which express p5'TH CAT (-773/+27) were isolated and the activity of CAT following treatment of cells with forskolin and growth at different cell densities was evaluated. CAT activity does not differ between cells grown at low or high density. Forskolin induces CAT activity 2-4 fold, but the extent of induction does not vary with changes in cell culture density. We conclude from these experiments that the intracellular mechanism by which increased cell-cell contact modulates TH RNA levels is not through interaction with the same genomic elements as those which regulate gene expression by cyclic AMP.
Brain Res Mol Brain Res 1990 Jun
PMID:Interaction of cyclic AMP and cell-cell contact in the control of tyrosine hydroxylase RNA. 197 15

The 7-bromoacetyl-7-desacetyl (BrAcFsk) and 7-chloroacetyl-7-desacetyl (CIAcFsk) analogs of forskolin were synthesized as alkylating agents to study the high affinity binding sites for forskolin. BrAcFsk and CIAcFsk activated adenylate cyclase in human platelet membranes with EC50 values of about 20 and 12 microM, respectively. Both analogs increased cyclic AMP in human platelets; however, they were less potent that forskolin. Forskolin inhibited [3H]forskolin binding to human platelet membranes with an IC50 of 20 nM, whereas BrAcFsk and CIAcFsk inhibited [3H] forskolin binding with IC50 values of 0.1 microM. Pretreatment of intact platelets with 10 microM BrAcFsk caused a 90% irreversible loss in [3H]forskolin binding sites, whereas pretreatment with 10 microM CIAcFsk led to a loss of 55% of the binding sites. The loss of binding sites occurred within 5 min for BrAcFsk and within 30 min for CIAcFsk. The time required for the loss of binding sites produced by either alkylating agent was increased by the inclusion of 200 microM forskolin in the pretreatment buffer. The inactive bromoacetyl analog of forskolin 7-bromoacetyl-7-desacetyl-1.9-dideoxyforskolin (1,9-dideoxy-BrAcFsk) did not activate adenylate cyclase, inhibit [3H]forskolin binding, or cause an irreversible loss of [3H]forskolin binding sites. Adenylate cyclase was assayed in membranes from platelets treated with either 10 microM BrAcFsk or 10 microM 1,9-dideoxy-BrAcFsk. The stimulation of adenylate cyclase by prostaglandin E1, guanosine-5'-O-(3-thio)triphosphate, and AIF4 was inhibited by about 50% in membranes from platelets treated with BrAcFsk. However, the stimulation of adenylate cyclase by forskolin was unaffected by preincubation with BrAcFsk. Pretreatment of human platelets with 1,9-dideoxy-BrAcFsk had no effect on the stimulation of adenylate cyclase by prostaglandin E1, AIF4, or forskolin.
Mol Pharmacol 1990 Jan
PMID:Irreversible loss of [3H]forskolin binding sites in human platelets by alpha-haloacetyl analogs of forskolin. 215 11

Previous studies have demonstrated that direct or indirect elevation of cAMP levels in cultured amphibian ovarian follicles simultaneously stimulated production of oocyte maturation-inducing steroid (progesterone) by the follicles and inhibited oocyte maturation induced by endogenous or exogenous hormone. The duration of cAMP stimulation influenced arrest and reinitiation of oocyte meiotic maturation in ovarian follicles of Rana dybowskii. Addition of forskolin (adenylate cyclase stimulator) to cultured follicles inhibited both progesterone- and frog pituitary homogenate (FPH)-induced oocyte maturation. Similar inhibitory results were obtained when hormone-treated follicles were cultured in the continual presence of cAMP. Oocyte maturation increasingly occurred in follicular oocytes when cAMP or forskolin addition was delayed following treatment with FPH or progesterone. Transient exposure (6-8 hr) of ovarian follicles to forskolin or cAMP markedly stimulated oocyte maturation as well as accumulation of progesterone as measured by radioimmunoassay within the ovarian follicles. Forskolin was more effective than cAMP, at the dose tested, in stimulating progesterone production and accumulation by the follicles. The data demonstrate that transient manipulation (elevation) of cAMP levels in cultured follicles, without added FPH or steroid, was sufficient to initiate oocyte maturation. Results suggest that, with transient exposure to forskolin or exogenous cAMP, there is a sequential increase and decrease in endogenous cAMP levels in the somatic cells and germ cell components of the ovarian follicle. These changes appear to mediate production of maturation-inducing steroid and secondarily allow its effects on the oocyte to be expressed.
Mol Reprod Dev 1990 Feb
PMID:Induction and inhibition of meiotic maturation of amphibian (Rana dybowskii) follicular oocytes by forskolin and cAMP in vitro. 215 27

The factors controlling the expression of the hypothalamic neuropeptide, corticotropin releasing hormone (CRH), are poorly understood. We have used a mouse anterior pituitary cell line, AtT-20, permanently transfected with the human CRH gene as a model for studying the regulation of the CRH gene by cyclic AMP. Previously, we demonstrated that in this system the CRH gene is correctly expressed and appropriately negatively regulated by glucocorticoids. Treatment of five CRH-producing cell lines with an activator of adenylate cyclase (forskolin, 0.1-50 microM for 24 h) caused a dose-dependent and specific increase in the amount of CRH mRNA and radioimmunoassay-detectable CRH peptide secreted into the medium. Ribonuclease protection analysis revealed that the CRH gene was transcribed from multiple transcriptional initiation sites located over several hundred nucleotides. Forskolin treatment resulted in a specific increase in the CRH mRNA transcripts initiating from one of these many transcriptional start sites.
Mol Cell Endocrinol 1990 Apr 17
PMID:Regulated expression of the human corticotropin releasing hormone gene by cyclic AMP. 216 64

Recent studies investigating the functional significance of gamma-aminobutyric acidA (GABAA) receptor complex phosphorylation have employed membrane-permeant compounds to manipulate second messenger systems. Although these compounds affect GABAA receptor function, the dependence of these effects on phosphorylation has not been established. Here we report that several second messenger system modulations can decrease GABAA receptor function independently of their effects on protein phosphorylation. Brain membrane vesicles were lysed and resealed in the presence of EDTA to chelate internal Mg2+. Under these conditions, phosphorylation of vesicle proteins was almost completely inhibited, as determined by incorporation of 32P into phosphoproteins. In these lysed/resealed vesicles, an inhibition of muscimol-stimulated 36Cl- uptake was observed with the cAMP analogs 8-(4-chlorophenylthio)-cAMP, N6,O2'-dibutyryl-cAMP, and 8-bromo-cAMP, the protein kinase inhibitor H7, and the adenylate cyclase activator forskolin. In both intact and EDTA-treated lysed/resealed microsacs, cAMP analogs and H7 inhibited binding of the GABAA receptor ligand [3H]SR 95531 at concentrations shown to inhibit muscimol-stimulated 36Cl- uptake. Forskolin was observed to inhibit the binding of t-butylbicyclophosphoro-[35S]thionate, a ligand that binds to a site on the chloride channel. These results demonstrate that compounds commonly used to alter second messenger systems affect the receptor sites and function of the GABAA receptor chloride channel by mechanisms that do not involve protein phosphorylation. In light of these findings, results obtained with these compounds should be interpreted with caution.
Mol Pharmacol 1990 Dec
PMID:Phosphorylation-independent effects of second messenger system modulators on gamma-aminobutyric acidA receptor complex function. 217 3

Recently it has been reported that histone type H2A can inhibit gonadotrophin-stimulated cAMP formation and steroidogenesis by ovarian cells. In the present study we have investigated if similar antigonadotrophic effects of commercially available histones can also be demonstrated on testicular steroidogenic cells. Using percoll-purified mouse Leydig cells, we have demonstrated that several types of histones could almost completely inhibit hCG-stimulated testosterone production and cAMP formation. The inhibition was dose-dependent and could be reversed by the addition of excess of hCG. The most potent histone types were H2AS and H8S, both of which could inhibit hCG-stimulated cAMP formation half-maximally at concentrations of 4-5 micrograms/ml. Forskolin-stimulated cAMP formation was not affected by histones. When the cells were stimulated with either db-cAMP or rAP-II, histone H2AS and H8S failed to inhibit the testosterone production. In fact there was a marked increase in the amount of testosterone produced, the reason for which is not yet understood. The amount of cGMP accumulated in response to rAP-II was not affected by the presence of H2AS or H8S. In unstimulated cells, neither the cyclic nucleotide level nor the amount of steroid produced was affected by the histones. Based on the [125I]hCG binding data it is possible to conclude that histone H2AS inhibits the binding of hCG to its receptors on Leydig cells and thereby causes the inhibition of hCG-stimulated cAMP formation and steroidogenesis.
J Steroid Biochem Mol Biol 1990 Dec 10
PMID:Histones inhibit human chorionic gonadotrophin-stimulated but not atrial peptide-stimulated testosterone production and cyclic nucleotide formation by isolated mouse Leydig cells. 217 26

In addition to well known direct stimulatory and potentiatory actions of forskolin, we have previously reported that low doses of this diterpene (10(-9), 10(-12) M) markedly inhibit the production of cAMP and testosterone in rat Leydig cells through a pertussis toxin sensitive G-protein (A. Khanum and M. L. Dufau, J. Biol. Chem. 261, 1986). A different type of inhibitory effect of forskolin is described in this study. Forskolin (10(-5) M) markedly stimulates basal adenylate cyclase activity (about 200%) in rat Leydig cell membranes and potentiates the stimulatory effect of gonadotropin (10(-9), 10(-7) M) on adenylate cyclase in presence or in absence of GTP (10(-5) M). Similarly a time-dependent stimulation of forskolin (10(-5) M) alone is noted on all cAMP pools and testosterone production. Using a supramaximal steroidogenic dose of hCG (0.26 nM) or choleragen (0.1 microM), forskolin potentiates the gonadotrophin and toxin-induced responses of all cAMP pools significantly while inhibiting testosterone production. Moreover, forskolin also inhibits 8-Bromo-cAMP stimulated steroidogenesis. In contrast, pregnenolone synthesis was not altered by the diterpene. We have demonstrated in this study that the inhibitory effect of high doses of forskolin on steroidogenesis is distal to cAMP generation, and resulted from a steroidogenic block residing beyond pregnenolone synthesis.
J Steroid Biochem Mol Biol 1990 Dec 10
PMID:A cAMP independent inhibitory action of high doses of forskolin in rat Leydig cells. 217 27

We examined aspects of the mechanism of desensitization of adenylate cyclase activation by TSH in a cloned line of rat thyroid cells (FRTL). Increasing FRTL intracellular cAMP concentrations by preincubation for 6 h in either 1 mM dBcAMP or 100 microM forskolin did not induce TSH desensitization. Forskolin stimulation was unimpaired in TSH-desensitized cells, indicating 'uncoupling' of the adenylate cyclase catalytic unit from the TSH receptor. Stimulation by the Ni inhibitory pathway of the adenylate cyclase by epinephrine (10(-6) M-10(-4) M in the presence of 10(-4) M propranolol) was unaltered in cells previously desensitized to TSH. That is, Ni-mediated inhibition of adenylate cyclase was additive to TSH desensitization. Pre-exposure of FRTL cells for 18 h to 50 ng/ml pertussis toxin did not prevent the induction of TSH desensitization. TSH desensitization was prevented by cycloheximide or actinomycin D added during the last 3-4 h of a 6 h period of TSH stimulation. The rates of turnover of the putative desensitization protein and its mRNA therefore appear to be similar.
Mol Cell Endocrinol 1985 Aug
PMID:Studies on the mechanism of desensitization of the cyclic AMP response to TSH stimulation in a cloned rat thyroid cell line. 241 13

Glucose utilization in isolated islets of Langerhans of the rat was determined by measuring the conversion of [5-3H]glucose (10 mM) to 3H2O. The alpha 2-adrenoceptor agonists clonidine, epinephrine, and norepinephrine in the presence of the alpha 1-adrenoceptor antagonist prazosin and the beta-adrenoceptor antagonist propranolol inhibited glucose utilization by as much as 50%. Yohimbine, an alpha 2-adrenoceptor antagonist, reversed the reduction in glucose utilization evoked by alpha 2 receptor agonists. The cholinomimetics carbachol and muscarine, and 8-bromo-cyclic GMP, but not other cyclic nucleotides, reversed the clonidine-induced suppression of glucose utilization. 3-Isobutyl-1-methylxanthine potentiated the stimulation of glucose utilization by carbachol with clonidine. In contrast, the beta-adrenoceptor agonist isoproterenol did not affect glucose utilization. Forskolin, which activates adenylate cyclase, reduced glucose utilization and did not affect the inhibitory response to clonidine. The ester phorbol 12,13-dibutyrate induced a latent reversal of the effects of clonidine. Insulin release paralleled changes in glucose utilization with alpha 2-adrenoceptor agonists. Carbachol and 8-bromo-cyclic GMP antagonized the alpha 2-adrenoceptor-induced inhibition of insulin release. During sustained insulin release (60 min), 8-bromo-cyclic AMP became a more potent modulator of secretion than 8-bromo-cyclic GMP in the presence of clonidine, although glucose utilization was not enhanced by 8-bromo-cyclic AMP.
Mol Pharmacol 1987 Aug
PMID:Alpha 2-adrenoceptor stimulation affects total glucose utilization in isolated islets of Langerhans. 244 Dec 40

The mechanism by which tripeptide aldehyde proteinase inhibitors decrease prolactin (PRL) and growth hormone (GH) secretion was studied. Agents known to modify the intracellular levels of cyclic adenosine monophosphate (cAMP) or cytosolic free calcium were used in monolayer cultures of the rat anterior pituitary gland. The phosphodiesterase inhibitor isobutyl-methylxanthine (IBMX), 8-bromo-cAMP and forskolin all stimulated PRL release. Boc-D-Phe-Pro-arginal (Boc-DPPA) at 1 mmol/l concentration was a potent inhibitor of basal PRL release and significantly decreased the effect of 8-Br-cAMP, forskolin or IBMX (0.5 mmol/l). Forskolin (1 mumol/l) stimulated ACTH, PRL and GH release and all these effects were decreased by 100 mumol/l of Boc-D-Phe-Phe-lysinal (Boc-DPPL). Neither tripeptide aldehyde affected the forskolin-induced rise in intracellular cAMP. Growth hormone releasing factor (hpGRF, 1 nmol/l) stimulated both GH release and intracellular cAMP generation; Boc-DPPL (100 mumol/l) significantly decreased stimulated GH release without affecting cAMP accumulation. Increasing medium K+ to 10 times normal level stimulated PRL release presumably by enhancing Ca2+ entry into the cells and 1 mmol/l Boc-DPPA decreased high potassium-stimulated PRL release. The ionophore A-23187 stimulated PRL release at 10 mumol/l but not at 1 mumol/l. At 1 mumol/l A-23187 prevented the Boc-DPPA-induced inhibition of PRL release. These findings suggest that the tripeptide aldehyde proteinase inhibitors inhibit PRL and GH release at a site beyond cAMP formation.
Mol Cell Endocrinol 1987 Jul
PMID:Is calcium or cyclic AMP involved in the inhibitory effect on pituitary hormone secretion of the tripeptide aldehyde proteinase inhibitors? 244 48


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