Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:4.6.1.1 (adenylate cyclase)
 19,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Choleragen and its A protomer catalyzed the hydrolysis of NAD to ADP-ribose and nicotinamide. NADase activity was inhibited by gangliosides GM1 (galactosyl-N-acetylgalactosaminyl-[N-acetylneuraminyl]-galactosylglucosylceramide), GM2 (N-acetylgalactosaminyl-[N-acetylneuraminyl]-galactosylglucosylceramide), GM3 (N-acetylneuraminyl-galactosylglucosylceramide), and GD1a (N-acetylneuraminylgalactosyl-N-acetylgalactosaminyl-E1N-acetylneuraminyl]-galactosylglucosylceramide). These gangliosides also increased the intensity of the tryptophanyl fluorescence of the isolated A protomer (lambda max = 328 nm). GM1 but not GM2, GM3, and GD1a caused a "blue shift" in the fluorescence spectrum of the B protomer. These results are consistent with other evidence that the specificity of GM1 as the choleragen receptor resides in its carbohydrate moiety. The NADase activity of choleragen was similar to that of diphtheria toxin previously described [J. Kandel, R. J. Collier & D. W. Chung (1974) J. Biol. Chem. 249, 2088-2097]. As with diphtheria toxin, analogues of NAD were inhibitory, adenine being the most effective. Significant inhibition was also noted with adenosine, AMP, ADP-ribose, nicotinamide, nicotinamide mononucleotide, and NADP. NADP was hydrolyzed only slowly by choleragen. In the NADase reaction catalyzed by diphtheria toxin, water serves as an acceptor for the ADP-ribose moiety of NAD in lieu of the natural acceptor molecule, which is elongation factor II (Kandel et al., 1974). It seems probable that the natural protein acceptor for ADP-ribose in the reaction catalyzed by choleragen is adenylate cyclase or a protein component of a cyclase complex that regulates enzymatic activity.
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PMID:Effect of gangliosides and substrate analogues on the hydrolysis of nicotinamide adenine dinucleotide by choleragen. 1 71

A monoclonal antibody against GM3 ganglioside (GM3Ab) was found to trigger differentiation of Neuro-2a cells in culture. The differentiation of Neuro-2a cells by GM3Ab was accompanied by increased levels of intracellular serotonin and amino acid neurotransmitters viz. aspartate, glutamate, glutamine, glycine and taurine. Further study indicated that the increase in the serotonin level was not due to a higher rate of serotonin synthesis but rather to a higher rate of active transport of serotonin from the medium. Studies on the cell surface gangliosides revealed that unlike the proliferating cells, the GM3Ab-mediated differentiated cells contained higher gangliosides in addition to GM3 and GM2 gangliosides. Analysis of total cellular proteins indicated the appearance of a 25 kDa protein, pI 5.4, in the GM3Ab-treated cells--a small amount of this protein was observed in dibutyryl cAMP (Bt2cAMP)-treated cells, however, the protein was totally absent in the 5-bromo-2'-deoxyuridine (BrdU)-treated cells. Investigation of the mode of action of GM3Ab indicated that the cellular differentiation was due to increased cAMP accumulation resulting from an increase in the adenylate cyclase activity. Further studies with different agents affecting protein kinase C (PKC) activity and direct assay of PKC ruled out the possibility that GM3Ab mediated its effect via PKC. This GM3Ab-induced differentiation could be inhibited by protein kinase A (PKA) inhibitor, H8, but could not be inhibited by sphingosine, an inhibitor of PKC. Pertussis toxin could mimic the effect of GM3Ab, suggesting that GM3Ab caused the elevation in the adenylate cyclase activity by reducing the Gi-protein inhibition of the adenylate cyclase. The data suggests that GM3Ab, after interaction with cell surface GM3, elevated intracellular cAMP level by withdrawing the inhibitory effect of some undefined factor(s) present in culture medium which normally keeps adenylate cyclase activity low through activation of Gi-protein.
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PMID:Differentiation of Neuro-2a neuroblastoma cells by an antibody to GM3 ganglioside. 132 94

Cultured A6 epithelial cells from toad kidney form confluent monolayers with tight junctions separating the apical and basolateral membranes. These two membrane domains have distinct compositions and functions. Thus, sodium is actively transported across the epithelia from the apical to basolateral surface via amiloride-inhibitable sodium channels located in the apical membrane. Sodium transport is stimulated by vasopressin, cholera toxin, and 8-bromo-cAMP applied to the basolateral surface where the receptors, adenylate cyclase, and Na+/K+-ATPase are located. In a previous study (Spiegel, S., Blumenthal, R., Fishman, P.H., and Handler, J.S. (1985) Biochim. Biophys. Acta 821, 310-318), we demonstrated that exogenous gangliosides inserted into the apical membrane of A6 epithelia do not redistribute to the basolateral membrane. With the ability to vary selectively the ganglioside composition of the apical membrane, we examined the effects of gangliosides on sodium transport in A6 epithelia. When the apical surface of A6 epithelia were exposed to exogenous gangliosides, sodium transport in response to vasopressin, cholera toxin, and 8-bromo-cAMP was enhanced compared to epithelia not exposed to gangliosides. The effect was observed with bovine brain gangliosides, NeuAc alpha 2----3Gal beta 1----3GalNAc beta 1----4[NeuAc alpha 2----3]Gal beta 1----4Glc beta 1----Cer (GD1a) and Gal beta-1----3GalNAc beta 1----4[NeuAc alpha 2----3]Gal beta 1----4Glc beta 1----Cer (GM1), but not with the less complex ganglioside, Neu-Ac alpha 2----3Gal beta 1----4Glc beta 1----Cer (GM3). We examined A6 cells for endogenous gangliosides and found that, whereas GM3 was a major ganglioside, only trace amounts of GM1 and GD1a were present. Based on cell surface and metabolic labeling studies, these gangliosides were synthesized by the cells and were present on the apical as well as the basolateral surface. Bacterial sialidase, which hydrolyzes more complex gangliosides to GM1, was used to modify the endogenous gangliosides on the apical surface; after sialidase treatment, the epithelia were more responsive to vasopressin, cholera toxin, and 8-bromo-cAMP. Thus, gangliosides may be modulators of sodium channels present in the apical membrane of epithelial cells.
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PMID:Gangliosides modulate sodium transport in cultured toad kidney epithelia. 378 88

Plasma membranes derived from a transplantable rat thyroid tumor (line 1-5G in Wollman's classification), which is unresponsive to thyrotropin (TSH) but is responsive to dibutyryl 3', 5' cAMP, have been evaluated to localize the defect. TSH binding in tumor plasma membrane is slightly lower than in normal rat thyroid membranes. No change in affinity, but simply a lower capacity was observed. The glycoprotein component of the TSH receptor exhibits similar binding and solubilization properties to the glycoprotein component derived from normal rat thyroid. Analogously to normal rat thyroid membranes, gangliosides more complex than N-acetylneuraminylgalactosylglucosyl-ceramide (GM3) are also present in tumor line 1-5G membranes. Phospholipid content of tumor line 1-5G is 50% lower than that of normal rat thyroid. At variance also with normal rat thyroid, 32P incorporation in tumor line 1-5G phospholipids such as phosphatidylserine and phosphatidylethanolamine is not modified after in vitro incubation with TSH. An even more pronounced effect by TSH on 32P incorporation into phosphatidylinositol is evident in tumor line 1-5G by comparison to normal. The 1-5G thyroid tumor membranes has a 12-fold higher basal adenylate cyclase activity than that of rat thyroid membranes. The high basal adenylate cyclase activity is associated with high ADP ribosylation activity. Both enzymes of tumor are only slightly responsive to TSH. These results suggest that the block in the transmission of TSH message to the cell machinery is localized to the regulatory domains between TSH receptor and adenylate cyclase catalytic subunit.
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PMID:Alteration in the transmission of TSH-message to thyroid target in a transplantable rat thyroid tumor. 379 81

A cloned line of normal rat thyroid cells, FRTL, contained a small number of high-affinity binding sites for thyrotropin (TSH) when measured under physiological conditions. The cells also bound small amounts of cholera toxin, and both hormone and toxin stimulated cyclic AMP production by the cells. The major ganglioside of FRTL cells was N-acetylneuraminylgalactosylglucosylceramide (GM3), with minor amounts of gangliosides corresponding to galactosyl-N-acetylgalactosaminyl-[N-acetyl-neuraminyl]-galactosylglucosylceramide (GM1) and N-acetylneuraminylgalactosyl-N-acetylgalactosaminyl-[N-acetylneuraminyl]-galactosylglucosylceramide (GD1a). Treatment of these cells with neuraminidase (acylneuraminyl hydrolase, EC 3.2.1.18) converted most of the GD1a to GM1. After neuraminidase treatment, the binding of cholera toxin, which binds to GM1, was increased, but there was no change in the binding of TSH. Preincubation of neuraminidase-treated FRTL cells with the B (binding) component of cholera toxin completely prevented cholera toxin binding but had no effect on the binding of TSH. Neuraminidase treatment also somewhat enhanced, rather than decreased, the cyclic AMP response to TSH. Pretreatment of FRTL cells with mixed brain gangliosides resulted in a 10-fold increase in cholera toxin binding. Again there was no enhancement of TSH binding or adenylate cyclase stimulation. Finally, prolonged exposure of FRTL cells to TSH induced down-regulation of TSH receptors but had no effect on gangliosides or cholera toxin receptors. The results indicate that more complex gangliosides do not serve as a component of the TSH receptor nor are they involved in the transmission of the hormone signal across the cell membrane of these cultured rat thyroid cells.
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PMID:Reevaluation of the role of gangliosides in the binding and action of thyrotropin. 627 78

When added to the culture medium, 3H-labeled GM1 (tritiated predominantly in the terminal galactose residue) was taken up by murine NCTC 2071 and rat glioma C6 cells, both of which are GM1-deficient. Upon incubating the labeled cells in fresh medium, the cell-associated GM1 was metabolized by the cells with a half-life of 1 to 2 days. Some of the GM1 was converted to GD1a but the bulk of the label appeared in the medium as degradation products. When GM1 labeled in the sialic acid or lipid portion of the molecule was utilized, GM2 also was detected with time in the cells and only a small fraction of the radioactivity was detected in the medium. The rat glioma C6 cells appeared unable to degrade the GM2 that they accumulated; this was demonstrated directly by incubating the cells with labeled GM2. The uptake and subsequent metabolism of GM1 was observed over a wide range of GM1 concentrations (10(-8) to 10(-4) M). The GM1-treated cells initially bound more iodinated choleragen than did untreated cells; but with time, binding capacity decreased. When GM1-treated cells were transferred to fresh medium in the presence of excess choleragen, the amount of cell-associated GM1 remained relatively constant for several days; the conversion of GM1 to GD1a also was blocked. Although labeled GM3 and GD1b also were taken up by the cells, choleragen had no effect on their subsequent metabolism. Choleragenoid, the binding subunit of choleragen, also inhibited GM1 metabolism without activating adenylate cyclase. These results indicate that exogenous gangliosides taken up by cultured cells are metabolized and that choleragen, which binds with high affinity to GM1, specifically prevents the metabolism of this ganglioside.
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PMID:Uptake and metabolism of exogenous gangliosides by cultured cells: effect of choleragen on the turnover of GM1. 663 Dec 29