Regulation of acetylcholinesterase expression by calcium signaling during calcium ionophore A23187- and thapsigargin-induced apoptosis

We have recently reported that acetylcholinesterase expression was induced during apoptosis in various cell types. In the current study we provide evidence to suggest that the induction of acetylcholinesterase expression during apoptosis is regulated by the mobilization of intracellular Ca(2+). During apoptosis, treatment of HeLa and MDA-MB-435s cells with the calcium ionophore A23187 resulted in a significant increase in acetylcholinesterase mRNA and protein levels. Chelation of intracellular Ca(2+) by BAPTA-AM (1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester), an intracellular Ca(2+) chelator, inhibited acetylcholinesterase expression. A23187 also enhanced the stability of acetylcholinesterase mRNA and increased the activity of acetylcholinesterase promoter, effects that were blocked by BAPTA-AM. Perturbations of cellular Ca(2+) homeostasis by thapsigargin resulted in the increase of acetylcholinesterase expression as well as acetylcholinesterase promoter activity during thapsigargin induced apoptosis in HeLa and MDA-MB-435s cells, effects that were also inhibited by BAPTA-AM. We further demonstrated that the transactivation of the human acetylcholinesterase promoter by A23187 and thapsigargin was partially mediated by a CCAAT motif within the -1270 to -1248 fragment of the human acetylcholinesterase promoter. This motif was able to bind to CCAAT binding factor (CBF/NF-Y). These results strongly suggest that cytosolic Ca(2+) plays a key role in acetylcholinesterase regulation during apoptosis induced by A23187 and thapsigargin.     

The effects of calcium ionophore A23187 on interstitial cell steroidogenesis

The present study was performed to evaluate the effects of calcium ionophore A23187 on adenosine 3',5'-monophosphate (cyclic AMP) and testosterone production in rat interstitial cells. Interstitial cells were incubated in Krebs-Ringer solution with varying amounts of luteinizing hormone, pregnenolone, or A23187. Cyclic AMP and testosterone were measured in the incubation medium after 4 h incubation. A23187 (0.01--10 microgram/ml) caused progressive increases of cyclic AMP formation (from 0.18 +/- 0.02 (S.E.) pmol/10(6) cells for the control of 0.42 +/- 0.02 pmol/10(6) cells, P less than 0.025), while testosterone production remained unaltered. When varying amounts of A23187 were added concomitantly with luteinizing hormone (5 IU/l), A23187 inhibited luteinizing hormone-induced steroidogenesis in a dose-dependent manner, but it had no effect on luteinizing hormone-induced cyclic AMP formation. When pregnenolone (10(-6) M) was added to the cells, testosterone formation increased from 1.50 +/- 0.22 to 8.46 +/- 1.65 ng/10(6) cells. A23187 (1 microgram/ml) had no discernable effect on the conversion of pregnenolone to testosterone. The main effect of increased cytosol calcium on steroidogenesis seems to be at the steps beyond adenylate cyclase-cyclic AMP. These results suggest that calcium is important for the conversion of cholesterol to pregnenolone, while the steps beyond pregnenolone are relatively independent of Ca2+.     

Requirement for down-regulation of the CCAAT-binding activity of the NF-Y transcription factor during skeletal muscle differentiation

NF-Y is composed of three subunits, NF-YA, NF-YB, and NF-YC, all required for DNA binding. All subunits are expressed in proliferating skeletal muscle cells, whereas NF-YA alone is undetectable in terminally differentiated cells in vitro. By immunohistochemistry, we show that the NF-YA protein is not expressed in the nuclei of skeletal and cardiac muscle cells in vivo. By chromatin immunoprecipitation experiments, we demonstrate herein that NF-Y does not bind to the CCAAT boxes of target promoters in differentiated muscle cells. Consistent with this, the activity of these promoters is down-regulated in differentiated muscle cells. Finally, forced expression of the NF-YA protein in cells committed to differentiate leads to an impairment in the down-regulation of cyclin A, cyclin B1, and cdk1 expression and is accompanied by a delay in myogenin expression. Thus, our results indicate that the suppression of NF-Y function is of crucial importance for the inhibition of several cell cycle genes and the induction of the early muscle-specific program in postmitotic muscle cells.     

The effect of calcium ionophore A23187 on the ATP level of human erythrocytes

Incubation of red cells at 37° with the ionophore A23187 results in a loss of ATP that is dependent on the concentrations of A23187 and Ca²⁺ in the medium. ATP hydrolysis is greatest at micromolar concentrations of Ca²⁺ and decreases as Ca²⁺ in the medium is raised to millimolar levels. The ATP depletion is due to stimulation of calcium ATPase by A23187-mediated Ca²⁺ influx into the cell. The biphasic nature of Ca²⁺-stimulated ATP depletion in whole cells reflects the activity of Ca²⁺-ATPase in membrane preparations at varying Ca²⁺ concentrations. The ionophore can be removed by washing the cells with plasma or bovine serum albumin-containing medium and the ATP levels restored to normal by reincubating with 5 mM adenosine for 1 hr.     

Evidence for the activation of phospholipases during acrosome reaction of human sperm elicited by calcium ionophore A23187

Incubation of washed human sperm with [3H]- or [14C]arachidonic acid allowed a major incorporation of the label into phospholipids, provided that the final concentration of the fatty acid did not exceed 20 microM. A further challenge with calcium ionophore A23187 of spermatozoa suspended in a calcium-containing medium led to phospholipid hydrolysis, which could account for 10-12% of total cell radioactivity. Degradation products were identified as free, unconverted arachidonic acid, occurring with some diacylglycerol. Phospholipid hydrolysis was significant after 15 min of incubation and became maximal after 120 min. It was found to be calcium dependent, diacylglycerol and free arachidonate production occurring maximally at 2 mM and 5 mM CaCl2, respectively. Phosphatidylcholine and phosphatidylinositol were the most significantly degraded phospholipids after 60 min of incubation. Similar incubations conducted with 32P-labeled sperm confirmed the selective hydrolysis of phosphatidylcholine and revealed an increase production of phosphatidic acid probably due to a phosphorylation of diacylglycerol. Under the same conditions, one third of the cells remained motile and electron microscopy revealed that acrosome reaction was completed in 40% of the cells and displayed an intermediary state in 40-50% of the spermatozoa. Furthermore, a good parallelism was observed between the extent of the acrosome reaction and the extent of phospholipid hydrolysis promoted by increasing concentrations of A23187. It is concluded that calcium entry into the cells activates both a phospholipase A2 and a phospholipase C, leading to the production of substances, like lysophospholipid, diacylglycerol or phosphatidic acid, which may or may not be involved in acrosome reaction.     

Effect of changes in the rate of ionophore A23187-induced calcium influx on the pump-leak steady-state distribution of calcium in inosine-fed human red cells

We studied the effect of varying the rate of ionophore A23187-induced calcium influx on the mean calcium content of inosine-fed human red cells in pump-leak steady state. Slow calcium infusion caused only a marginal reduction in the mean calcium content of cells in the steady state relative to their content after sudden calcium addition.     

The calcium ionophore A23187 increases the tight-junctional permeability in rat liver.

The effect of an increase in intracellular Ca2+ concentration on tight-junctional permeability in rat liver was studied by using the calcium ionophore A23187. Infusion of 100 microliters of dimethyl sulphoxide containing various amounts of A23187 over 30 min into isolated perfused livers was followed by a pulse of horseradish peroxidase (HRP) under single-pass conditions. The first biliary HRP peak, a measure of junctional permeability, was increased 4-fold with 100 micrograms of A23187. There were, however, no significant effects on bile flow or on aspartate aminotransferase leakage as compared with the control at this dosage, and thus the increase in junctional permeability was occurring without evidence of appreciable cholestatic or hepatocellular damage. Higher dosages of A23187, however, caused not only an increase in HRP peak height but also changes in bile flow and increases in aminotransferase leakage, indicating more extensive effects at these higher dosages. A second peak of HRP secretion, occurring 20-25 min after the HRP pulse, was also elevated approx. 3.5-fold; this may indicate that pinocytosis and transcellular movement of HRP are also increased under these conditions.     

Effects of calpain inhibitor on the apoptosis of hepatic stellate cells induced by calcium ionophore A23187

We previously showed that changes in calcium concentrations were related to cell apoptosis in vitro. The endoplasmic reticulum (ER) is the main component of calcium storage and signal transduction, and disrupting the balance of intracellular Ca²⁺ can cause endoplasmic reticulum stress (ERS). In this process, the ER releases stored Ca ²⁺ into the cytoplasm and activates calpain-2. To further investigate the effect of calpain in hepatic stellate cells (HSCs), in the current study, we examine the effect of N-acetyl-leu-leu-norleucinal (ALLN) on apoptosis resulting from calcium ionophore A23187–induced ERS. Our findings indicate that calpain inhibition reduces calcium ionophore A23187–induced apoptosis of HSCs and decreases the expression of ER stress proteins that may be related to the calpain/caspase signaling pathway.     

The isolation and characterization of 60 nm vesicles (''nanovesicles'') produced during ionophore A23187-induced budding of human erythrocytes.

1. Penicillin N was synthesized by coupling alpha-amino-alpha-p-nitrobenzyl-N-p-nitro-benzyloxycarbonyl-D-adipate with 6-aminopenicillanic acid benzyl ester, followed by removal of the protecting groups through hydrogenolysis. 2. alpha-Amino-alpha-p-nitrobenzyl-N-p-nitrobenzyloxycarbonyl-D-[5-14C]adipate was prepared by treating alpha-p-nitrobenzyl-N-p-nitrobenzyloxycarbonyl-D-glutamic acid with [14C]diazomethane followed by rearrangement with silver trifluoromethanesulphonate. 3. Coupling of alpha-amino-alpha-p-nitrobenzyl-N-p-nitrobenzyloxycarbonyl-D-[5-14C]adipate with 6-aminopenicillanic acid benzyl ester gave triprotected [10-14C]penicillin N. 4. 3H was introduced at C-6 of the Schiff's base derivative (10) by oxidation followed by reduction with NaB3H4. 5. The so-derived (6 alpha-3H)-labelled Schiff's base was hydrolysed to give 6-amino [6 alpha-3H]penicillanic acid benzyl ester p-toluenesulphonic acid salt, which after coupling as the free amine with alpha-amino-alpha-p-nitrobenzyl-N-pnitrobenzyloxycarbonyl-D-adipate and then hydrogenolysis, yielded [6alpha-3H]penicillin N. 6. Triprotected [10-14C]penicillin N and triprotected [6alpha-3H]penicillin N in admixture were hydrogenolysed to give [10-14C,6alpha-3H]penicillin N.     

The role of calcium in eicosanoid production induced by ricinoleic acid or the calcium ionophore A23187

Rat isolated intestine incubated in Krebs solution converted exogenous [¹⁴C]-arachidonic acid into products that chromatographed with prostaglandins, leukotriene B₄ and 5-hydroxy-eicosatetraenoic acid. Accumulation of these products was increased by the laxative ricinoleic acid (0.34 mM) or the calcium ionophore A23187 (7.6μM). In the presence of the calcium antagonists TMB-8 (0.43μM). or verapamil (0.2μM) the mean effects of ricinoleic acid or the calcium ionophore were smaller. Stimulation of arachidonic acid metabolism by ricinoleic acid therefore seems likely to involve a calcium-dependent mechanism.     

The role of calcium in eicosanoid production induced by ricinoleic acid or the calcium ionophore A23187

Rat isolated intestine incubated in Krebs solution converted exogenous [14C]-arachidonic acid into products that chromatographed with prostaglandins, leukotriene B4 and 5-hydroxy-eicosatetraenoic acid. Accumulation of these products was increased by the laxative ricinoleic acid (0.34 mM) or the calcium ionophore A23187 (7.6 microM). In the presence of the calcium antagonists TMB-8 (0.43 microM) or verapamil (0.2 microM) the mean effects of ricinoleic acid or the calcium ionophore were smaller. Stimulation of arachidonic acid metabolism by ricinoleic acid therefore seems likely to involve a calcium-dependent mechanism.     

Effect of the calcium ionophore A23187 on superoxide generation in phorbol ester stimulated human neutrophils

The calcium ionophore, A23187, and the tumor-promoting phorbol ester, phorbol 12-myristate 13-acetate (PMA), interacted synergistically to elicit an accelerated superoxide production response in human neutrophils. The lag period preceding PMA-induced superoxide generation was decreased in a dose-dependent manner by A23187 at a concentration range from 1.0 X 10(-8) to 1.0 X 10(-5) M. Superoxide production rate, however, was subject to biphasic effects. While the rate was potentiated in a dose-dependent manner at A23187 concentrations below 1.0 X 10(-6) M, inhibitory influences became manifest at higher concentrations. Total superoxide production was subject to inhibitory effects, characterized by a mean inhibitory dose of 1.3 X 10(-6) M. The synergistic interaction of A23187 with PMA is consistent with a role for protein kinase C in neutrophil activation. Inhibition at high A23187 concentrations appeared to result from the effects of elevated intracellular Ca2+ levels on either NADPH oxidase itself, or some step in the transduction process linking protein kinase C to the oxidase complex.