Ornithine decarboxylase activity: control by cyclic nucleotides

Cytochemical Localization of Adenylate Cyclase in Broken Cell Preparations of the Cerebral Cortex

Broken cell preparations derived from rat cerebral cortical grey matter were studied cytochemically to localize adenylate cyclase (AC) activity in subcellular organelle membranes. AC activity was localized by visualizing reaction product in brain particulate fractions by electron microscopy. Activity was found in the endoplasmic reticulum, on the inside of the inner mitochondrial membrane and on both leaflets of the nuclear membrane. Reaction product was found in the postsynaptic density area of most synapses. The reaction product tended to be more prominent in the presence of flouride. A synaptosome-rich fraction was shown to have NE stimulated AC activity which was blocked in vitro by both a α-and an β-blocker and in vivo by propranolol.

Histamine H2-receptor mediated activation of neonatal rat brain ornithine decarboxylase in vivo

The effect of histamine (HA) administered via intracerebroventricular injection on ornithine decarboxylase (ODC) activity was studied in neonatal rat brain. The HA effect was dose and time dependent. Maximal increase in ODC activity was achieved 2 hr after administration of 10 micrograms HA (38% over control levels). Impromidine (HA H2-agonist) mimicked the effect of HA on ODC and ranitidine (HA H2-antagonist) inhibited the response to HA. Neither 2-thiazolylethylamine (HA H1-agonist) nor mepyramine (HA H1-antagonist) modified control ODC activity. The HA-releasers, compound 48/80 and polymixin B sulfate, elicited an increase in brain ODC activity of 35% and 32%, respectively, over the control value.

Increased activity of spermidine N1-acetyltransferase in the adrenal cortex of rats following administration of exogenous spermidine, carbamylcholine, 2-deoxyglucose and dopamine agonists

The activity of N1-acetyltransferase was increased in the dissected adrenal cortex of the rat following a single administration of spermidine. The activity was maximal 6-8 h after the onset of treatment. The increase in enzyme activity was abolished when the rats were given cycloheximide 2 h after spermidine; this suggests that increased activity results from an augmentation in the synthesis of the enzyme. Adrenocortical spermidine N1-acetyltransferase was also induced by carbamylcholine, 2-deoxyglucose, apomorphine and piribedil, drugs that are known to cause induction of ornithine decarboxylase in that organ. Hypophysectomized rats showed reduced activity of spermidine N1-acetyltransferase when compared to sham-operated controls, and carbamylcholine no longer elicited an increase in enzyme activity in such animals. Adrenocortical spermidine N1-acetyltransferase activity of hypophysectomized rats is induced by corticotropin (ACTH). These results suggest a hormonal control over the activity of the enzyme in the adrenal cortex with ACTH acting as a mediator.

Biochemical aspects of orthodontic tooth movement. I. Cyclic nucleotide and prostaglandin concentrations in tissues surrounding orthodontically treated teeth in vivo

The objective of this study was to extract and assay cyclic nucleotides and prostaglandins from tissues surrounding orthodontically treated canines in cats. Seven groups of three to five female cats were treated by 80 g tipping force to one maxillary canine for 0 to 28 days. Tissue samples were removed from sites of compression and tension around treated teeth, and from the corresponding control sites. Cyclic nucleotides and prostaglandins were simultaneously extracted by a solvent system at 0 to -5 degrees C. A portion of the aqueous fraction was used for cAMP assay by a binding protein method; cGMP was purified by column chromatography and measured by radioimmunoassay. The solvent fraction was dried, reconstituted with assay buffer, and each of the prostaglandins measured by radioimmunoassay. Analysis of variance showed no significant differences between summary control and treated sites at each of the time periods studied. However, when interactions at secondary and tertiary levels were considered (such as tension and compression, position [apical-gingival sites] of tissue sample, and jaws), significant differences were found in PGE, cAMP, and PGF2 alpha values. These results demonstrate that alterations in the levels of each of these substances in tissues surrounding teeth may be brought about by long-term applications of orthodontic force in vivo. The method of tissue sampling, however, does not permit measurement of the levels of these substances in target cells alone, thus diluting the acute response that may have occurred in these cells.

Nerve growth factor affects cyclic AMP metabolism, but not by directly stimulating adenylate cyclase activity

Published experiments both support and contradict the hypothesis that nerve growth factor (NGF) can regulate adenylate cyclase activity. Using a sensitive assay that measures the conversion of [2-3H]adenine to [3H]cyclic AMP, we have shown that NGF alone cannot measurably stimulate cyclic AMP production, whereas the adenosine analog phenylisopropyladenosine (PIA) stimulates adenylate cyclase 20-fold over basal activity. NGF potentiates the capacity of both PIA and cholera toxin to stimulate cyclic AMP accumulation at all concentrations tested. This potentiation occurs at the earliest measurable times and does not require RNA synthesis. Therefore, we conclude that cyclase activation alone does not account for the effect of NGF on cyclic AMP accumulation and we discuss possible mechanisms.

Opiates and cultured neuroblastoma x glioma cells. Effect on cyclic AMP and polyamine levels and on ornithine decarboxylase and protein kinase activities

In cultured NG 108-15 neuroblastoma x glioma cells, opiates decreased cellular cyclic AMP and polyamine levels. This decrease was related to the inhibition of ornithine decarboxylase and cyclic AMP-dependent protein kinase activities during the acute exposure of the cells to the drugs. Growing the cells in the presence of opiates for several days led to drug addiction. In the tolerant-addicted cells, polyamine and cyclic AMP levels were close to normal values as were the activities of ornithine decarboxylase and cyclic AMP-dependent protein kinase. Removal of the opiate from 'addicted' cells, by either washing or by adding the antagonist naloxone, resulted in an increase in cyclic AMP and polyamine levels and the activities of ornithine decarboxylase and cyclic AMP-dependent protein kinase. The effect of opiates was closely related to their biological activities. Inactive enantiomorphs did not affect cyclic AMP or polyamine levels; neither did they decrease ornithine decarboxylase and cyclic AMP-dependent protein kinase activities.

Effects of alpha-difluoromethylornithine on polyamine biosynthesis and tyrosine hydroxylase induction in the adrenal gland of the rat subjected to stress or apomorphine

Ornithine decarboxylase (ODC) and tyrosine hydroxylase (TH), the first enzymes in the polyamine and catecholamine biosynthetic pathways, respectively, are induced in the adrenal gland of the rat through the application of stressors or dopamine agonists. In the present work, following exposure of rats to cold, application of bodily restraint, or administration of apomorphine (APM), adrenal putrescine increased in proportion to the induction of ODC. Spermidine content increased by 60% after APM and about 30% after immobilization. Spermine was unaffected. To test whether the increases of ODC (and polyamines) are necessary to the slower and later induction of TH, induction of ODC in vivo was undertaken. alpha-Difluoromethylornithine (alpha-DFMO), an irreversible inhibitor of ODC, given orally or subcutaneously, almost completely abolished the induction of ODC by APM or immobilization, and inhibited the increase of putrescine in both cases, but did not affect spermidine after APM. Repeated administration of alpha-DFMO over several days did not affect the induction of adrenal TH. The results question whether increases of adrenal ODC activity and of putrescine are essential for the induction of TH in that gland.

Purine nucleotide synthesis in adrenal chromaffin cells

The synthesis of purine nucleotides from the salvage precursors adenine and adenosine, and from the de novo precursors formate and glycine, was studied in isolated adrenal chromaffin cells. Both [8-14C]adenine and [8-14C]adenosine from extracellular medium are effectively incorporated into intracellular nucleotides. [14C]Formate and [U-14C]glycine are also incorporated, but de novo synthesis is clearly lower than synthesis from salvage precursors, although similar to de novo synthesis in liver. The enzymes responsible for adenine and adenosine salvage, adenine phosphoribosyltransferase and adenosine kinase, were purified about 1,500-fold. Both enzymes are mainly cytosolic and exhibit a similar molecular weight of around 42,000. The results suggest that chromaffin cells can replenish their intracellular nucleotides lost during the secretory event by an active synthesis from salvage and de novo precursors.

Stimulation by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine of rat hepatic polyamine biosynthesis in vivo

Intraperitoneal injection of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX), resulted in a rapid and transient induction of rat hepatic ornithine decarboxylase (ODC) activity. Maximal activity was found about 5 hr after application. The levels of putrescine and spermidine increased accordingly, reaching a maximum at 7 and 12 hr following injection, respectively, while the concentration of spermine remained almost constant. The implications of these findings are discussed in relation to the mechanism of induction of ornithine decarboxylase and concomitant polyamine biosynthesis.

Comparison of the neuritogenic activity of cyclic nucleotides and skeletal muscle-conditioned medium on ciliary ganglia in vitro

The parasympathetic ciliary ganglion (CG) of the embryonic chick in vitro, is unresponsive to Nerve Growth Factor and has been reported to form neurites only in response to neurotrophic factors derived from striated muscle or optic tissues. We investigated a possible role of cyclic adenosine-3',5'-monophosphate (cAMP) in the neurotrophic activity of skeletal muscle-conditioned medium (SCM) on CG explants. We showed that treatment with cAMP or dibutyryl cAMP stimulated neuritogenesis of CG explants in a dose-dependent fashion. SCM and cyclic nucleotide stimulation produced distinctly different types of neuritic growth. The growth cones of SCM-stimulated neurites were observed consistently to contact other cells or processes whereas nucleotide-stimulated neurites were not associated with other cells. These observations suggested that the two neuritogenic agents do not act through identical mechanisms, a conclusion supported by experiments demonstrating that stimulation of the CG with dibutyryl cAMP enhanced ornithine decarboxylase (ODC) activity relative to controls, whereas stimulation with SCM had no effect on ODC activity. We conclude that although cAMP does exhibit neuritogenic activity on the CG in vitro, it does not appear to be involved directly in the neurite formation elicited by SCM. It is feasible that the two types of neuritic growth which we described are representative of the two populations of CG neurons. Because only one of these neuronal populations innervates striated muscle in vivo, SCM and cAMP might act on different neurons.

Diurnal variation in ornithine decarboxylase activity of different brain regions of the rat

The activity of ornithine decarboxylase (ODC) was studied in the brain of Sprague-Dawley male rats weighing 200-250 g. In this study, animals were maintained at a temperature of 21 +/- 1 degree C and a 12:12 h light--dark cycle for a minimum of 3 weeks prior to any experimentation. Animals were sacrificed at 06.00 h and 18.00 h and the brain cerebral cortex, hypothalamus, amygdala, hippocampus, midbrain, pons, medulla oblongata and cerebellum were isolated and assayed for ODC activity. The data show significant diurnal variations (P less than 0.05) in hypothalamus, midbrain, medulla oblongata and cerebellum, with peak values during the active phase of the animal. Other brain parts studied did not show any significant diurnal variations.

Butyrate-induced increase in neuron-specific enolase and ornithine decarboxylase in anaplastic glioma cells

Butyrate treatment results in the rapid formation of processes on F98 anaplastic glioma cells. The morphological differentiation occurs more rapidly and to a greater extent than that induced by nerve growth factor (NGF). The incorporation of [3H]thymidine is virtually stopped 1 day after treatment of F98 cells with sodium butyrate. Butyrate also caused a large increase in ornithine decarboxylase activity in F98 cells between 6 and 12 h after treatment. This was inhibited by both cycloheximide and actinomycin-D. NGF did not cause these effects. Butyrate also caused an increase in neuron-specific enolase (NSE) content in F98 cells. This effect appeared to be specific for butyrate. Since NSE induction is characteristic only of neurons and neuroendocrine cells, this finding indicates that butyrate is capable of inducing biochemical differentiation along neuronal lines in undifferentiated glioma cells.

Effect of apomorphine, piribedil and haloperidol on adrenal ornithine decarboxylase activity of the rat

The administration of the dopaminergic drugs, apomorphine and piribedil to rats resulted in an increase in the activity of ornithine decarboxylase of the adrenal medulla and cortex. Pretreatment of the rats with the dopamine-receptor antagonist haloperidol caused a partial blockade of the apomorphine-induced effect at 4 hr in both medulla and cortex. At 6 hr, however, haloperidol did not block the effect of apomorphine and produced an increase in ornithine decarboxylase activity of both structures when administered alone. Hypophysectomy abolished the cortical ornithine decarboxylase response to apomorphine and haloperidol and the medullary response to haloperidol. The results suggest that the response of cortical ornithine decarboxylase activity to apomorphine and haloperidol is entirely mediated by the hypophysis and that the effect of apomorphine and the antagonistic action of haloperidol towards apomorphine in regard to the induction of adrenal medullary ornithine decarboxylase must be taking place at some central site independent of the hypothalamic-hypophyseal system.

Effect of 5'-deoxy-5'-isobutylthioadenosine on putrescine uptake and polyamine biosynthesis by chick embryo fibroblasts

The effect of 5'-deoxy-5'-S-isobutylthioadenosine (SIBA) on polyamine biosynthesis has been studied by using cultured chick embryo fibroblasts. It has been shown that the drug inhibits the uptake of [14C]putrescine and its conversion into labelled spermidine or spermine. The inhibitory effect is reversed by removing the inhibitor after exposing the cells to the drug for 24 h. SIBA also caused a significant decrease in cellular spermine levels and an accumulation of putrescine. These changes are reversed by removing the inhibitor. SIBA had the same effect on chick embryo fibroblasts transformed by Rous sarcoma virus; a decrease in cellular spermine levels in SIBA-treated cells was observed. In all the experiments SIBA caused a reduction in the spermine/putrescine and spermidine/putrescine ratios. It is suggested that SIBA is not only an inhibitor of transmethylation but also interferes with polyamine biosynthesis, probably by blocking aminopropyltransferase.

Adrenomedullary ornithine decarboxylase activity: its use in biochemical mapping of the origins of the splanchnic nerve in the rat

The activity of ornithine decarboxylase in the adrenal medulla of the rat can be induced transsynaptically by the repeated administration of apomorphine. Unilateral section of one to four ventral spinal cord roots from T4 to T12 partially prevents this effects. Interruption of the intercostal nerves (T7--T13), with preservation of the autonomic innervation of the adrenal medulla, does not produce any alteration in the response of the medullary ODC to APO in the operated side as compared to the intact side. Dorsal root section at T7--T10 leads to a small reduction, while section at T2--T4 has no effect at all. Thus, selective surgical interruption of spinal cord roots indicates that the bulk of splanchnic fibers mediating the transsynaptic induction of adrenomedullary ornithine decarboxylase course in the ventral roots between T7 and T10. Dorsal rhizotomy demonstrates a modulatory role in this induction of afferent information to sympathoadrenal preganglionic neurons involved in innervation of the chromaffin cells.

Stimulation of rat heart ornithine decarboxylase by isoproterenol evidence for post-translational control of enzyme activity?

The activity of rat heart ornithine decarboxylase (ODC), the enzyme involved in the initial step of polyamine biosynthesis, was markedly stimulated after isoproterenol treatment, reaching a maximum of about four times the basal value four hours after administration. At all times after isoproterenol, kinetic studies revealed only two forms of the enzyme with Km values for ornithine of 35-50 microM and 190 microM, compared to only one form (190 microM) in the controls. At no time was a form of ODC with an intermediate Kornm detected, nor did dialysis reverse stimulation of activity of enzyme from isoproterenol-treated rats, or increase activity in control preparations; it is therefore unlikely that small molecular activators or inhibitors participate in the stimulation. The time course of Vmax values for the high-affinity component of the enzyme coincided with that of net enzyme activity, indicating that increases of ODC activity in response to isoproterenol might result from a shift of enzyme from its low-affinity state to the high-affinity form, rather than from appearance of additional enzyme molecules. In support of this hypothesis, alpha-difluoromethylornithine, an irreversible ODC inhibitor, displayed identical ID50 values in control and isoproterenol-treated animals, a situation which would not occur if more enzyme were present. These data are consistent with the view that post-translational control mechanisms involving macromolecular factors could operate in regulating cardiac ODC activity.

Polyamines inhibit the protein kinase 380--catalyzed phosphorylation of eukaryotic initiation factor 2 alpha

Polyamines putrescine, spermidine, and spermine specifically inhibit the PK 380--catalyzed phosphorylation of eukaryotic initiation factor 2 alpha (eIF-2 alpha). Since te PK 380--dependent phosphorylation of eIF-2 alpha inhibits the initiation or protein synthesis, the possibility exists that the polyamines enhance protein synthesis by inhibiting the phosphorylation of eIF-2 alpha by PK 380.

Altered activation of rat hepatic cyclic AMP-dependent protein kinases with increasing age

The activity ratio of hepatic cyclic AMP-dependent protein kinase has been found to change with increasing age in male, Long-Evans rats. In rats 35 days old (135 g), the activity ratio (cyclic AMP-dependent protein kinase activity measured in the absence and presence of exogenous cyclic AMP) was 0.76, it increased to 0.92 in rats 75 days old (315 g) and to 0.98 in rats 305 days old (646 g). This change in the activity ratio seems to correlate with the ability of aging animals to respond to a stimulus, and may be a primary mechanism in the biochemistry of aging.

Effects of acute and chronic protein deprivation on ornithine decarboxylase levels in rat liver and colon

The effects of protein intake on the levels of total and holo-ornithine decarboxylase (ODC) in colon and liver have been examined in male Sprague-Dawley rats fed varying amounts of casein in a defined purified diet. Pair-feeding was used to eliminate effects of food intake per se. In the colon, both total and holo-ODC activity increased in animals fed a low-protein diet (1% casein). In the liver, on the other hand, both total and holo-ODC activity decreased with protein deprivation. The observed changes in both colon and liver appeared to be maximal within several days after institution of the dietary regimen. Refeeding with a high-protein diet (20% casein) led to a dramatic rise in ODC activity in the liver in animals previously fed a low-protein diet. These results may be important in sorting out the effects of diet on the tumorigenic process.

Cyclic nucleotides in the denervated rat diaphragm and the effect of cyclic AMP on ornithine and adenosylmethionine decarboxylases

The concentrations of cyclic AMP and cyclic GMP were measured in the denervated rat diaphragm at various times following unilateral phrenicectomy. Cyclic AMP concentration was raised by the second day after operation, reached a peak by the third day, followed by another increase at around 10 days. By contrast, cyclic GMP concentration was decreased within a day after denervation and remained below control levels at all subsequent times studied. Epinephrine in vitro produced a comparable increase in the concentration of cyclic AMP in both normal and denervated tissue. The concentration of adenosine appeared unchanged in the denervated diaphragm by comparison with its innervated control. Activity of ornithine decarboxylase was elevated in the diaphragms of rats treated with dibutyryl cyclic AMP, but this effect could also be achieved with sodium butyrate alone. Adenosylmethionine decarboxylase activity, was unaffected after treatment with either compound. These observations and others discussed are taken to indicate a lack of direct relationship between cyclic AMP concentrations and the activity of the rate-limiting enzymes of polyamine biosynthesis in the rat diaphragm.

The action of adenosine analogs on PC12 cells

PC12 cells, a nerve growth factor-responsive clone of rat pheochromocytoma, contain a membrane-bound adenylate cyclase, which can be activated by adenosine analogs. The characteristics of the cyclase response indicate the presence of stimulatory adenosine receptors. Adenosine analogs also produce a marked increase in the ornithine decarboxylase levels of the cells, and the characteristics of this response suggest that it is linked to the adenylate cyclase-stimulatory adenosine receptors. The ornithine decarboxylase response elicited by 5'-N-ethylcarboxamideadenosine (NECA), a potent stimulatory adenosine analog, is synergistic with that produced by nerve growth factor. Differentiation of the cells with nerve growth factor, however, does not substantially alter either the response of cyclase to the adenosine analog or the magnitude of the adenosine-evoked ornithine decarboxylase response. Treatment of the cells with NECA produces an increase in the phosphorylation of a specific non-histone nuclear protein. While causing little or no morphological alteration by itself, NECA is synergistic with nerve growth factor in producing neurite outgrowth in PC12 cells. NECA does not cause an induction of acetylcholinesterase in the cells. NECA does not cause an induction of acetylcholinesterase in the cells, nor does it appear to affect the induction of this enzyme by nerve growth factor.

Effect of haloperidol on adrenal ornithine decarboxylase activity of the rat

The administration of the dopamine antagonist haloperidol (HLP) to rats produced a temporary increase in adrenomedullary and cortical ornithine decarboxylase (ODC) activity. The time-course of stimulation of ODC activity by HLP showed different patterns in both structures. Medullary ODC activity was highest at 2.5 h, decreasing at later times; cortical ODC activity was not affected by the drug at 2.5 h, but then increased up to at least 6.5 h. The medullary increase observed at 2.5 h was dose-related and could be prevented by splanchnicotomy. Hypophysectomized rats, on the contrary, showed an enhanced response to HLP. The results suggest that haloperidol-induced increase of adrenomedullary ODC activity is caused by a reflex increase in preganglionic nerve activity, and that the pituitary gland can modulate this response. Cortical ODC response to HLP, as previously demonstrated, is mediated entirely by the hypophysis.

Effect of methionine deprivation on S-adenosylmethionine decarboxylase of tumour cells

Transference of Walker carcinoma and TLX5 lymphoma from normal L-methionine-containing medium to medium containing limiting amounts of L-methionine, or L-homocysteine only, caused a 2-fold increase of S-adenosylmethionine decarboxylase activity. Kinetic analysis showed an increase in the V value of the enzyme from 22 to 53 pmol/min per mg protein in media containing only 0.1 mM L-homocysteine, without any alteration in the Km value (0.1 mM). The increase in enzyme activity does not result from (a) a reduction of the intracellular level of S-adenosylmethionine, since cycloleucine, an inhibitor of methionine adenosyltransferase, had no effect on enzyme activity; (b) an increase in intracellular adenosine 3',5' monophosphate (cyclic AMP), since high extracellular concentrations of N6-monobutyryl cyclic AMP had no effect on enzyme activity; (c) an alteration of polyamine levels, since addition of micromolar concentrations of exogenous putrescine, spermidine and spermine did not prevent the induction of S-adenosylmethionine decarboxylase activity in methionine-free media containing 0.1 mM L-homocysteine. The increased enzyme activity appears to be mainly due to enhanced stabilization, since the half-life was increased from 2.45 to 5.0 h in media containing only 0.1 mM L-homocysteine. Induction of enzyme activity is specific to the removal of L-methionine, since no increase occurred in the absence of L-serine or L-glycine, or both, or by reduction of the serum concentrations in the medium.

Antiproliferative effects of retinoids related to the cell cycle-specific inhibition of ornithine decarboxylase

The induction of ornithine decarboxylase (ODC) during G1 phase of the cell cycle appears to be universal and essential for cell cycle progression. This induction has been demonstrated in at least 23 cell types in response to various growth stimuli. Further, specific inhibitors of ODC added to several of these cell lines resulted in inhibition of cell proliferation. The studies of the effects of retinoids to inhibit Chinese hamster ovary (CHO) cell growth indicate that the cells are blocked in G1 of cell cycle, and that there is a concentration-dependent inhibition of ODC induction. Retinoids only inhibit the induction of ODC activity when added in the first 2-3 hr of G1 progression. It is postulated that ODC induction is a requirement for G1 progression and that the antiproliferative properties of retinoids are related to the specific ability to inhibit this expression. Since retinoids do not dramatically alter the rate of protein synthesis, their ability to inhibit ODC may be related to their ability to inhibit messenger RNa synthesis for ODC.

Phosphorylation of nuclear and DNA-binding proteins in proliferating and quiescent mammalian cells

The dependence of cell proliferation on nuclear protein phosphorylation was studied with exponential-phase and stationary-phase cultures of Chinese-hamster ovary cells. Nuclear proteins were fractionated, according to their DNA-binding affinities, by using sequential extractions of isolated nuclei with increasing concentrations of NaCl. When viable whole cells were labelled with H332PO4, phosphorylation of nuclear proteins was found to be lower in quiescent cells than in proliferating cells. Phosphorylation of nuclear proteins soluble in 0.30M-NaCl (less than 50% of these proteins bind to DNA) was greater than for those proteins soluble in higher salt concentrations (80-100% of these proteins bind to DNA). Cyclic AMP enhanced the phosphorylation of nuclear proteins soluble in 0.3 m-NaCl by 40-50%, and this stimulation was independent of cell growth. Cyclic AMP also increased the phosphorylation of nuclear proteins soluble in 0.6M-NaCl and 2.0M-NaCl by 40-50% in exponential-phase cultures, but not in stationary-phase cultures. Several examples of specific phosphorylation in response to cyclic AMP were observed, including a 35000-mol.wt. protein in the 0.30 M-NaCl-soluble fraction and several proteins larger than 100000 molecular weight within this fraction. A major peptide of molecular weight approx. 31000 extracted with 0.6M-NaCl was also phosphorylated. Its phosphorylation was independent of cyclic AMP in exponential-phase cultures, and it was not phosphorylated in plateau-phase cells. These changes in cell-growth-dependent phosphorylation occurred in the absence of any apparent qualitative changes in the nuclear protein molecular-weight distributions. These data demonstrate that (1) phosphorylation of nuclear proteins is dependent on the culture's proliferative status, (2) both cyclic AMP-dependent and cyclic AMP-independent specific phosphorylation occurs, and (3) the cyclic AMP-dependent growth-independent phosphorylation that occurs does not appear to be a modification of DNA-binding proteins, whereas the cyclic AMP-dependent growth-dependent phosphorylation does involve modification of DNA binding proteins.

The role of cAMP in the induction of ornithine decarboxylase by nerve and epidermal growth factors

Nerve growth factor (NGF), epidermal growth factor (EGF), adenosine 3',5'-cyclic monophosphate (cAMP), and cholera toxin all increase the specific activity of ornithine decarboxylase (ODC) in the PC12 nerve-like cell line. A phosphodiesterase inhibitor augments the effect of NGF on the induction of ODC in these cells, while it is only additive with the EGF response. These data suggest that cAMP has an intermediary role in the induction of ODC by NGF and that cAMP is not involved in the EGF response.

Effects of cholera toxin on ornithine decarboxylase activity in mouse skin

The subcutaneous injection of cholera toxin into adult mice resulted in a sustained increase in cyclic AMP levels in mouse epidermis after a lag period of about 2 hr. An increase in ornithine decarboxylase activity occurred between 7 and 10 hr, which was maintained for at least 10 hr. The increase in decarboxylase activity was localized to the area of epidermis visually affected by cholera toxin and was unaffected by hypophysectomy, suggesting a direct effect of the toxin on the epidermal cells. The subcutaneous injection of cholera toxin also led to an increase in cyclic AMP levels in newborn mouse skin. In contrast to adult mice, newborn mouse skin contained high basal activities of ornithine decarboxylase in both the epidermal and dermal fractions. The activity in both fractions was markedly decreased following cholera toxin injection. The ability of cholera toxin to induce both epidermal and dermal ornithine decarboxylase activity developed between 10 and 21 days after birth.

Regulation of ornithine decarboxylase activity by amino acids, cyclic AMP and luteinizing hormone in cultured mammalian cells

Any one of five amino acis (alanine, asparagine, glutamine, glycine, and serine) is an essential requirement for the induction of ornithine decarboxylase (EC 4.1.1.17) in cultured chinese hamster ovary (CHO) cells maintained with a salts/glucose, medium. Each of these amino acids induced a striking activation of ornithine decarboxylase in the presence of dibutyryl cyclic AMP and luteinizing hormone. The effect of the other amino acids was considerably less or negligible. The active amino acids at optimal concentrations (10 mM) induced only a 10-20 fold enhancement of enzyme activity alone, while in the presence of dibutyryl cyclic AMP, ornithine decarboxylase activity was increased 40-50 fold within 7-8 h. Of the hormones and drugs tested, luteinizing hormone resulted in the highest (300-500 fold) induction of ornithine decarboxylase with optimal concentrations of dibutyryl cyclic AMP and asparagnine. Omission of dibutyryl cyclic AMP reduced this maximal activation to one half while optimal levels of luteinizing hormone alone caused no enhancement of ornithine decarboxylase activity. The induction of ornithine decarboxylase elicited by dibutyryl cyclic AMP, amino acid and luteinizing hormone was diminished about 50% with inhibitors of RNA and protein synthesis. The specific amino acid requirements for ornithine decarboxylase induction in chinese hamster ovary cells was similar to the requirements for induction in two other transformed cell lines. Understanding the mechanism of enzyme induction requires an identification of the essential components of the regulatory system. The essential requirement for enzyme induction is one of five amino acids. The induction of ornithine decarboxylase by dibutyryl cyclic AMP and luteinizing hormone was additive in the presence of an active amino acid.

Regulation of ornithine decarboxylase activity by corticotropin in adrenocortical tumor cell clones: roles of cyclic AMP and cyclic AMP-dependent protein kinase

In Y1 adrenocortical tumor cells, corticotropin (ACTH), cyclic AMP, and 8-bromoadenosine 3',5'-monophosphate (8BrcAMP) stimulated ornithine decarboxylase activity (L-ornithine carboxy-lyase, EC 4.1.1.17) and steroidogenesis. The concentrations required for half-maximal activation of ornithine decarboxylase were 60 pM for ACTH and 1 mM for 8BrcAMP; the concentrations required for half-maximal activation of steroidogenesis were 50 pM for ACTH and 0.2 mM for 8BrcAMP. Ornithine decarboxylase activity increased 1.5 hr after the addition of these agents, reached a maximum between 4 and 6 hr, and then declined. Mutant clones with impaired ACTH-responsive adenylate cyclase systems [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1]did not respond to ACTH with increased ornithine decarboxylase activity, but they responded normally to added cyclic AMP. These results indicate that adenylate cyclase and cyclic AMP are necessary for the stimulation of ornithine decarboxylase activity by ACTH. In a series of Y1(Kin) mutants with altered cyclic AMP-dependent protein kinase activities (ATP:protein phosphotransferase, EC 2.7.1.37), the effects of ACTH on ornithine decarboxylase also were attenuated. These findings suggest that cyclic AMP-dependent protein kinase also plays a necessary role in the stimulation of ornithine decarboxylase activity by ACTH. The effects of ACTH on ornithine decarboxylase in the Kin mutants, however, were quantitatively different from the effects on steroidogenesis and did not closely reflect the degree of defect in cyclic AMP-dependent protein kinase activity. These differences suggest that the pathways of ACTH action leading to stimulation of steroidogenesis and ornithine decarboxylase activity diverge subsequent to activation of the protein kinase.

Calcium and microtubule dependence for increased ornithine decarboxylase activity stimulated by beta-adrenergic agonists, dibutyryl cyclic AMP, or serum in a rat astrocytoma cell line

Ornithine decarboxylase (ODCase; L-ornithine carboxy-lyase; EC 4.1.1.17) activity was increased 5-20 fold above basal activity by N(6),O(2')-dibutyryl cyclic AMP, isoproterenol, epinephrine, or fetal calf serum in confluent C6-2B rat astrocytoma cells. Serum increased ODCase activity by a mechanism apparently independent of cyclic AMP because it decreased intracellular cyclic AMP. Calcium ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) buffers (pCa = 6.4) reduced basal ODCase activity and blocked the increase in activity by beta-adrenergic agonists, dibutyryl cyclic AMP, or serum. Readdition of calcium to pCa = 4.0 restored the ability of the cells to respond to these agents. The rise in ODCase activity stimulated by isoproterenol, dibutyryl cyclic AMP, or serum was also blocked by the microtubule disrupting agents, vinblastine and colchicine, and by the microfilament disrupting agent, cytochalasin B. Lumicolchicine, an analog of colchicine that does not disrupt microtubules, was ineffective. The microtubule and microfilament disrupting agents and EGTA had no effect on the intracellular accumulation of cyclic AMP. Cycloheximide inhibited protein synthesis >95% within 30 min, and caused an immediate decline of stimulated ODCase activity with a half-time of 20-30 min. The inhibition of ODCase activity by colchicine or EGTA was distinct from that seen with cycloheximide and could not be correlated to their effects on general protein synthesis. Colchicine or EGTA each caused identical rates of decline in ODCase activity with a half-time of 20-30 min after an initial lag period of about 60 min.