Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:4.6.1.1 (adenylate cyclase)
19,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A novel clonal cell line derived from a human glioma (HOG) was found to express some oligodendrocyte-specific proteins including a 15-kDa form of myelin basic protein (MBP) and high 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) activity. Expression of the myelin lipids galactosylceramide and sulfogalactosylceramide (sulfatide) was low. HOG cells did not express the characteristic astrocyte markers glial fibrillary acidic protein (GFAP) or significant glutamine synthetase (GS) activity. After initial plating, HOG cells were flat and epitheloid and thus showed a limited oligodendrocyte-like morphology. However, after cells became more confluent, some cells were phase-bright and elaborated short processes. Receptor types expressed by HOG cells included A2-adenosine, prostaglandin E1 (PGE1), and beta 2-adrenergic receptors (beta-ARs) linked to stimulation of adenylate cyclase, and muscarinic cholinergic and H1-histamine coupled to phosphatidyinositol turnover (Post and Dawson, 1991). HOG cells should therefore provide a useful model for studying the extracellular regulation and phosphorylation of oligodendrocyte-specific proteins.
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PMID:Characterization of a cell line derived from a human oligodendroglioma. 132 95

The molecular mechanisms of myelin formation/reformation in the central nervous system are unknown. In previous work we have demonstrated that mature oligodendrocytes (OLG) respond to a signal(s), elicited by their adhesion to a substratum, by turning on a myelinogenic metabolism. Events occurring within 24 hr of adhesion include generation of diacylglycerol, activation of protein kinase C, phosphorylation of myelin basic protein, and enhanced synthesis of myelin lipids and proteins. To elucidate the mechanism(s) of signal transduction, we have investigated whether OLG-substratum interaction influences the level of basal cAMP and the expression of receptors coupled to adenylate cyclase. By using ovine brain OLG we have found that adhesion to a polylysine-coated surface for 24 hr increased the basal level of cAMP 2-fold and altered the expression (assessed by cAMP production) of receptors coupled to adenylate cyclase. Isoproterenol (beta-adrenergic agonist) augmented cAMP from 4 to 26 pmol/mg of protein in adhering OLG but had no such effect in nonattached OLG. Adhesion of OLG was accompanied by rapid synthesis of ethanolamine plasmalogen, a class of lipids believed to be associated with beta-adrenergic receptors. Nonattached OLG responded to prostaglandin E1 with only a 3-fold stimulation in their cAMP content; in attached OLG, 6-fold stimulation was observed. In contrast, vasoactive intestinal polypeptide elicited a 3-fold increase in cAMP in nonattached OLG but, following 24 hr of attachment, OLG did not respond to vasoactive intestinal polypeptide. The increase of cellular cAMP levels was accompanied by a 2.5-fold gain in protein kinase A. OLG-substratum adhesion resulted also in phosphorylation of the OLG/myelin protein, 2',3'-cyclic nucleotide 2'-phosphodiesterase, which proved to be a substrate for cAMP and phospholipid-, Ca2+-dependent protein kinases. These findings, in conjunction with our earlier work, implicate cAMP and diacylglycerol in signaling myelinogenesis; they suggest that phosphorylation/dephosphorylation of myelin basic protein and 2',3'-cyclic nucleotide 2'-phosphodiesterase may be key processes in the cascade of events that are initiated by adhesion of OLG to a polylysine surface (possibly acting as a surrogate for axons) and culminate in the reformation of myelin.
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PMID:Oligodendrocyte substratum adhesion modulates expression of adenylate cyclase-linked receptors. 244 85

The role of cAMP in lymphocyte proliferation was investigated in the response of a monoclonal T-cell population to a specific antigen and compared to the response to interleukin-2 (IL-2) and allogeneic cells. Myelin basic protein (MBP)-reactive and encephalitogenic T-cell clones were established from long-term lines derived from SJL/J (H-2s) mice. The clone 4b.14a recognizes the peptide sequence 89-101 of the MBP molecule in association with 1-As products of the major histocompatibility complex (MHC). Incubation of 4b.14a cells with syngeneic antigen-presenting cells, previously pulsed with the 89-101 synthetic peptide or with 80 U/ml of IL-2, or allogeneic H-2Ik cells, resulted in a significant increase in the accumulation of intracellular cAMP. This increase was preceded by a peak in membranal adenylate cyclase (AC) activity. Parallel time kinetics but significantly higher cAMP production and AC activity were observed when the cells were treated with pertussis toxin. At the same concentrations the toxin inhibits cellular proliferative responses, assayed by [3H]thymidine incorporation. Our results indicate the involvement of cAMP as a positive signal in the activation of the 4b.14a clone.
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PMID:Cyclic adenosine 3',5'-monophosphate metabolism in activated T-cell clones. 247 34

Several adrenergic effectors and neurotransmitters were tested as potential regulators of myelin basic protein (MBP) and histone methyltransferase activities. Both enzymes were specifically activated by beta-adrenergic agonists in a stereospecific manner. Cyclic AMP (but not AMP) stimulated the enzymes to the same extent as did the beta-adrenergic agonist, (-) isoproterenol. The studies suggest that beta-adrenergic agonists stimulate adenylate cyclase thereby causing an increased production of cyclic AMP which stimulates the methyltransferases. Cycloheximide addition to the reaction mixture did not affect the stimulation due to cyclic AMP, indicating that new protein synthesis is not involved in the cyclic AMP stimulation of the methyltransferases. Thyroid hormone (T3) has been shown to stimulate MBP methyltransferase [Amur et al, 1984] and could exert its stimulatory effect through beta-adrenergic-dependent systems. But the beta-adrenergic antagonist, propranolol, did not block the stimulation by T3, suggesting that the effect of T3 is not mediated through beta-adrenergic-dependent systems. Thus, the methylation of MBP seems to be regulated both by T3 and by neurotransmitters and/or hormones mediating their effects through cyclic AMP production, whereas the methylation of histones seems to be regulated only by the latter.
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PMID:Beta-adrenergic stimulation of protein (arginine) methyltransferase activity in cultured cerebral cells from embryonic mice. 287 8

Cultured ovine oligodendrocytes (OLGs) express a number of voltage-dependent potassium currents after they attach to a substratum and as they begin to develop processes. At 24-48 hours following plating, an outward potassium current can be identified that represents a composite response of a rapidly inactivating component and a steady-state or noninactivating component. After 4-7 days in culture, OLGs also develop an inward rectifier current. We studied the effects of forskolin and phorbol 12-myristate 13-acetate (PMA) on OLG outward currents. These compounds are known to alter the myelinogenic metabolism of OLGs. PMA, an activator of protein kinase C (PK-C), has been shown to enhance myelin basic protein phosphorylation while forskolin acting on adenylate cyclase, and thereby increasing cAMP, inhibits it. Both forskolin and PMA increase the phosphorylation of 2'3'-cyclic nucleotide phosphodiesterase, an OLG/myelin protein. We found that forskolin decreased the steady-state outward current at 120 mV by 10% at 100 nM, and by 72% at 25 microM from a holding potential of -80 mV. The time course of inactivation of the peak currents was decreased, affecting both the fast and slow time constants. There was no significant change in the steady-state parameters of current activation and inactivation. The effect of forskolin was attenuated when the adenylate cyclase inhibitor adenosine (2 mM) was present in the intracellular/pipette filling solution. The results of PMA experiments were similar to those obtained with forskolin. Whereas the amplitude of the currents in the presence of PMA was reduced by 28% at 1.5 nM and 60% and 600 nM, the decay phase of the peak currents was less affected. The PMA effect could still be seen when the intracellular Ca2+ was reduced to less than or equal to 10 nM with 5 mM BAPTA, but was inhibited when the cells were pre-exposed to 50 microM psychosine, a PK-C inhibitor. It is postulated that the potassium currents in OLG can be physiologically modulated by two distinct second-messenger systems, perhaps converging at the level of a common phosphorylated enzyme or regulatory protein.
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PMID:Forskolin and phorbol esters decrease the same K+ conductance in cultured oligodendrocytes. 321 67

Interactions of several divalent cations (Mn2+, Ca2+, Co2+, Sr2+, and Zn2+) with EGTA-inhibitable adenylate cyclase were investigated in washed membranes (particles) isolated from the gray matter of rat cerebral cortex. The EGTA-inhibitable (called sensitive) enzyme activity was assayed in the presence of Triton X-100 since this detergent caused a marked increase (up to 20-fold) in the enzyme activity. The effects of various divalent metals (all added as chloride salt) indicated the presence of two distinct sites called site I and site II. At low concentrations (less than micromolar) Mn2+, Co2+, and Ca2+ increased (up to 10-fold) the enzyme activity to the same extent and appeared to act via binding to site I (high affinity site). The rank order of affinity was Mn2+ greater than or equal to Co2+ greater than Ca2+. Zn2+ showed the highest affinity and Sr2+ the lowest towards binding to site I; both these metals increased the enzyme activity to lesser extents than Mn2+, Co2+, or Ca2+. GTP was not required for the stimulation of this enzyme by low concentrations of Ca2+. The interaction of Mn2+ with site II (low affinity site) caused further increase in the enzyme activity, whereas Co2+, Ca2+, and Sr2+ were inhibitory at concentrations greater than 10 microM. Isolated fraction contained loosely and tightly associated pools of calmodulin. Myelin basic protein, but not calcineurin, inhibited the EGTA-sensitive adenylate cyclase activity. The EGTA-insensitive enzyme activity was increased by norepinephrine by mechanisms that depended on GTP and was inhibited by Ca2+. The stimulation of the EGTA-insensitive enzyme modulated the Mg2+ requirement such that Mg2+ binding to the low affinity site (site II) apparently occurred with higher affinity. The likely significance of these results is discussed with regard to (i) the presence of two classes of adenylate cyclase in rat cerebral cortex gray matter and (ii) the regulation of their activities by calmodulin-requiring and GTP-requiring mechanisms.
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PMID:EGTA-sensitive and -insensitive forms of particulate adenylate cyclase in rat cerebral cortex: regulation by divalent cations and GTP. 393 3

Pax3 RNA is expressed in neural crest when Schwann cell (SC) precursors migrate to the PNS. Pax3 RNA and SC markers were monitored in sciatic nerves of mice during development and nerve repair. An inverse correlation was observed between expression of Pax3 RNA and myelin basic protein (MBP). Inverse correlation was also observed in SC primary cultures. Treating cultures with forskolin, an adenylate cyclase agonist, repressed Pax3 RNA, GFAP, NGFR, N-CAM, and L1 and elevated MBP. Subsequent microinjection with Pax3 expression vector elevated Pax3 RNA, GFAP, NGFR, N-CAM, and L1 and repressed MBP. Thus, Pax3 is likely involved in the differentiation pathway to myelinating SCs. Pax3 repressed a 1.3 kb MBP promoter fragment in cotransfection assays, suggesting that it represses MBP transcription.
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PMID:Pax3: a paired domain gene as a regulator in PNS myelination. 754 35

The repetitive passages of a Schwann cell culture results in the appearance of immortalized cells. In order to investigate the direct effects of cyclic AMP (cAMP) on Schwann cell proliferation, we used the immortalized Schwann cells because the responses of a short-term Schwann cell culture to agents increasing the intracellular cAMP are more complicated and it does not seem that all of them are due to the direct effects of cAMP. By adding up to 200 microM of forskolin, an adenylate cyclase activator, to the culture medium, Schwann cell proliferation was inhibited and the intracellular 1,2-diacylglycerol (DG) level was decreased in a dose-dependent manner to 44 and 53% of the control values, respectively. The protein phosphorylation activity in the cytosol from the cell treated with 100 microM forskolin, assayed with myelin basic protein as the acceptor, decreased to 78% and this inhibition was then reversed by the addition of 1-oleoyl-2-acetyl-sn-glycerol (OAG), a membrane-permeable DG, to the assay mixture. The cell proliferation inhibited by forskolin was also restored by the addition of OAG. These data suggest that cAMP inhibits both the activity of protein kinase C (PKC) and consequently cell proliferation through suppression of intracellular DG level, an activator of PKC. Since the inositol 1,4,5-triphosphate level and the hydrolysis of phosphatidylcholine to DG and phosphorylcholine were not affected, forskolin therefore appears to suppress the de novo synthesis of DG.
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PMID:Inhibition of the proliferation of cultured immortalized Schwann cells by forskolin with a decreased basal level of diacylglycerol. 806 31

Intracellular cAMP levels can be elevated by activation of cAMP-generating adenylate cyclase (AC) or inhibition of cAMP-cleavage by phosphodiesterases. Elevation of intracellular cAMP levels in immune cells inhibits production of some Th1-cytokines, particularly TNF-alpha, and results mainly in downregulation of the immune response. Experimental autoimmune encephalomyelitis (EAE) of Lewis rats is a disease mediated by type 1 T helper lymphocytes and macrophages and serves as a model of multiple sclerosis. In EAE we therefore tested the immunomodulatory potency of an AC-activating, stable prostacyclin analogue, iloprost, and of a potent and non-selective inhibitor of phosphodiesterases, propentofylline, which also has neuroprotective properties. Preventive treatment of Lewis rats with propentofylline (2 x 10 or 12.5 mg/ kg/d), iloprost (2 x 10 or 12.5 micrograms/kg/d), or both did not significantly ameliorate clinical or histological signs of EAE actively induced by immunization with myelin basic protein (MBP) in complete Freund's adjuvant. Furthermore, adoptive transfer EAE (AT-EAE), passively induced by injection of encephalitogenic MBP-specific Th1 lymphocytes, was not altered in its course by the combined application of iloprost (2 x 10 micrograms/kg/d) and propentofylline (2 x 20 mg/kg/d) starting on the day of cell transfer. In vitro assays demonstrated that iloprost strongly and propentofylline moderately inhibited the production of TNF-alpha by macrophages and that iloprost in vivo similarly suppressed TNF-alpha secretion, although this effect was limited to a few hours after a single injection. In contrast to macrophages, TNF-alpha production by antigen-activated encephalitogenic T helper line cells in vitro was completely resistant to modulation by these agents. In addition, the presence of iloprost, propentofylline, or both drugs during activation of the line cells in vitro did not impair their encephalitogenicity in vivo. The findings delineate immunomodulatory effects of both substances, particularly of iloprost, but fail to support a possible therapeutic role of these agents in autoimmune inflammation of the central nervous system.
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PMID:Propentofylline and iloprost suppress the production of TNF-alpha by macrophages but fail to ameliorate experimental autoimmune encephalomyelitis in Lewis rats. 945 91

Culture of an H-2(s)-restricted, bovine myelin basic protein (BMBP)-specific murine Th1 clone with the adenyl cyclase agonist forskolin (FSK) or isobutylmethylxanthine (IBMX), an inhibitor of cAMP catabolism, before culture with anti-CD3 or BMBP and antigen-presenting cells (APC) suppressed antigen or anti-CD3-induced proliferation and production of interferon-gamma (IFN-gamma). Other H-2(s)-derived or H-2(b)-derived clones specific for BMBP or keyhole limpet hemocyanin (KLH) were similarly affected. FSK did not affect the expression of CD4 or the T cell receptor (TCR) but did diminish levels of the phosphorylated (activated) mitogen-activated protein (MAP) kinases early response kinase-1 (ERK-1) and ERK-2. Immunoblotting of lysates from an FSK-treated Th1 clone with antibodies to a carboxy-terminal epitope of p56(lck), a signal transduction enzyme upstream from ERK-1 and ERK2, did not detect p56(lck) unless the lysates were reduced prior to electrophoresis. Immunoblotting of nonreduced lysates with antibodies to an amino-terminal epitope demonstrated p56(lck) with a lower apparent molecular weight, characteristic of oxidized proteins. Reduction restored the detection of p56(lck) by anticarboxy-terminal p56(lck) and to mobilities indistinguishable from controls detected by the antiamino-terminal p56(lck). N-acetylcysteine or catalase prevented FSK-induced suppression of antigen-induced proliferation and the loss of carboxy-terminal epitopes of p56(lck). An inhibitor of cAMP-dependent protein kinase A (PKA) or nitric oxide synthase (NOS) did not affect FSK-induced inhibition of antigen-induced proliferation. In contrast, inhibitors of PKA or NOS, but not catalase, prevented FSK-induced suppression of IFN-gamma production. Moreover, immunoblots of lysates precipitated with anti-p56(lck), phosphotyrosine, or CD4 demonstrated that in FSK-treated, anti-CD3-stimulated cells, p56(lck) is not associated with CD4 zeta chain, nor is p56(lck) or zeta chain phosphorylated. In vitro kinase assays demonstrated that p56(lck) from FSK-treated cells does not have kinase activity. Taken together, the results suggest that an elevation of intracellular cAMP (in the absence of antigen) creates an oxidative environment that oxidizes and inactivates p56(lck) by an H(2)O(2)-dependent, PKA-independent mechanism and inhibits the production of IFN-gamma by an NO, PKA-dependent mechanism. Thus, antigen-induced proliferation and IFN-gamma production in a Th1 clone are controlled separately by different cAMP-dependent, redox-based mechanisms.
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PMID:Differential regulation of T cell receptor-mediated Th1 cell IFN-gamma production and proliferation by divergent cAMP-mediated redox pathways. 1171 Sep 91


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