Mitogenic induction of ornithine decarboxylase in human mononuclear leukocytes: relationships with adenosine diphosphate ribosyltransferase

1. Relationships between ornithine decarboxylase (ODC) and adenosine diphosphate ribosyl transferase (ADPRT) in human mononuclear leukocytes (HML) were tested by statistical comparisons of their values in a group of 46 people, and by use of inhibitors of ADPRT. 2. ODC was assayed following exposure of HML, for 20 hr, to mitogens [phytohemagglutinin (PHA) and pokeweed mitogen]; ADPRT was measured following exposure of HML to H2O2 (100 microM) for 1 hr (activated ADPRT), and in parallel cultures without H2O2 (constitutive ADPRT). 3. Significant correlations were found between ODC and ADPRT values; the effects of smoking disturbed the correlations. PHA induction of ODC was negatively influenced by age (standardized beta coefficient = -2.95, P = 0.005), while age also influenced ADPRT values negatively in non-smokers (for H2O2 activated ADPRT, standardized beta coefficient = -2.74, P less than 0.008). 4. Inhibitors of ADPRT, nicotinamide, caffeine and benzamide inhibited the induction of ODC by PHA in a concentration-dependent manner, in the range (0.6-10 mM) known to inhibit ADPRT.     

Genetic evidence that a phorbol ester tumor promoter stimulates ornithine decarboxylase activity by a pathway that is independent of cyclic AMP-dependent protein kinases in CHO cells

Ornithine decarboxylase (ODC) inductions by cholera toxin and by the phorbol ester tumor promoter, TPA, were compared in wild-type Chinese hamster ovary (CHO) cells and in mutant cells having altered cyclic AMP-dependent protein kinase activity. The aim of these studies was to determine whether cyclic AMP-dependent protein kinase is involved in these inductions. The time course and the magnitude of ODC inductions by either 100 ng/ml cholera toxin or 100 ng/ml TPA were similar in wild-type cells with a maximum at 3-4 hours after treatment and a return to unstimulated levels by 8 hours. Induction of ODC by cholera toxin was suppressed more than 80% in the four protein kinase mutants studied (10215, 10248, 10260, and 10265), strongly implicating a cyclic AMP-dependent kinase step in the mechanism of induction. Similar results were found with the cyclic AMP analog 8-Br-cyclic AMP and the phosphodiesterase inhibitor, methyl-isobutylxanthine. The induction of ODC by TPA, on the other hand, was only partially inhibited (approximately 50%) in three of four mutants. Lower ODC activity in two mutants stimulated by cholera toxin or TPA whose kinetics were studied in more detail could not be ascribed to a reduced affinity (Km) of ornithine for the enzyme, but appeared to be due to reduced catalytic activity (Vmax) in the extracts. These results suggest that the induction of ODC by TPA proceeds by a mechanism which is only partially dependent on an intact cyclic AMP-dependent protein kinase activity.     

Trypanosoma brucei brucei: regulation of ornithine decarboxylase in procyclic forms and trypomastigotes

Ornithine decarboxylase (ODC) activity was measured in procyclic forms of Trypanosoma brucei brucei grown in semidefined medium. ODC activity rapidly increased in late log-phase cells which were resuspended in fresh medium. A biphasic induction curve similar to that observed in mammalian cells was observed over an 18-hr period. ODC activity increased 4.5- to 25-fold over control levels measured at zero time. Actinomycin D and cycloheximide inhibited induction by greater than 90%. Polyamines at a level not inhibitory to growth (10 microM) inhibited ODC induction, but only by 30-50%, late in the induction period. Putrescine inhibited the first peak of induction and suppressed activity at 14 hr by 75%. Polyamine analogs such as bis(ethyl)spermidine were not effective suppressors of ODC activity. The half-life of ODC in procyclic forms grown in the presence of cycloheximide was greater than 6 hr, while that of bloodstream trypomastigotes in mice treated with cycloheximide was 5 hr. A single dose of the ODC inhibitor DL-alpha-difluoromethylornithine given to infected rats or mice suppressed trypanosome ODC activity greater than 90% for more than 7 hr. These studies indicate that although trypanosome ODC increases rapidly under log growth conditions, it is less susceptible to fluctuation and external control than the enzyme from mammalian sources. The latter may be a factor in the clinical efficacy of ODC inhibitors.     

Ornithine decarboxylase activity in foetal rat brain cells and in the mouse embryo fibroblasts C3H/10T1/2 CL8 cells: differences in response to medium change and to the tumor promoter TPA

12-O-tetradecanoyl-phorbol-13-acetate (TPA) induced ornithine decarboxylase (ODC, EC 4.1.1.17) in normal, preneoplastic and malignant rat brain cells in culture, but treatment with phorbol, acetate or medium shift resulted in a similar response. Medium shift induced ODC activity in C3H/10T1/2 CL8 cells 4 and 12 hr after treatment. TPA induced only the 12 hr peak. ODC induction in C3H/10T1/2 CL8 cells was completely inhibited by cycloheximide and actinomycin D. Addition of alpha-amanitin abolished the 12 hr peak, but the TPA induced ODC activity was only partly inhibited. ODC induction by TPA was lower in C3H/10T1/2 CL8 cells initiated with 3-methyl-cholanthrene (MCA). ODC increased with TPA up to 10(-7) M and decreased at higher concentrations of TPA.     

Quantification and localization of ornithine decarboxylase in the embryonic palate.

Ornithine decarboxylase (ODC; EC4.1.1.17), the key enzyme in polyamine biosynthesis, and intracellular polyamines increase rapidly and markedly in tissues and cells that are actively proliferating as well as differentiating and decrease as these processes cease. ODC activity has also been implicated as playing a role in the proliferation and differentiation of cells derived from the developing palate. Ornithine decarboxylase activity was thus quantified and ODC localized in the developing murine palate in vivo. Levels of ODC activity showed little variation during the ontogeny of the palate, averaging 126 pmol CO2/mg protein/hr. When difluoromethylornithine (DFMO), an irreversible inhibitor of ODC activity, was administered to pregnant mice throughout the period of palate development (days 11-14), palatal tissue ODC activity was reduced by 85%. No craniofacial malformations were observed, however. The lack of a teratogenic effect by DFMO treatment could be due to sufficient remaining ODC activity in craniofacial tissue and/or maintenance of intracellular polyamine levels by the activity of a polyamine transport system. The activity of this system was demonstrated by the ability of palatal tissue in vivo to take up radiolabeled putrescine. The presence of a polyamine transport system was previously suggested by the demonstration of such a system in palate mesenchymal cells in vitro. Dramatic temporal and spatial shifts in tissue patterns of immunolocalization for ODC in developing palatal tissue were also seen. Immunostaining for ODC was evenly distributed in oral, nasal, and medial edge palate epithelial cells on day 12 of gestation. The basal aspects of epithelial cells were, however, more intensely stained. Mesenchymal cells exhibited a peri-nuclear immunostaining pattern. On days 12 and 13 of gestation, the staining patterns for ODC in palate epithelial and mesenchymal cells were comparable. On day 14 of gestation, all regions of the palate epithelium, particularly the medial edge epithelia, were immunostained for ODC, whereas the intensity of staining in the mesenchymal cells was significantly reduced. This study represents essential initial observations toward understanding the role that ODC may play in normal craniofacial development.     

Effect of cyclic nucleotides on the induction of ornithine decarboxylase in BHK cells by serum and insulin

Quiescent baby hamster kidney cells in 0.5% serum synthesize little DNA and have low levels of ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine synthesis. After adding serum to 5%, ODC activity is increased 30 fold, reaching a maximum at 6 hr, whereas DNA synthesis is reinitiated at 12 hr. Five μg/ml insulin also increases ODC activity 3 fold by 4 hr. In quiescent 3T3 cells and mouse embryo fibroblasts, serum and insulin may trigger many metabolic events by causing a transient drop in intracellular cyclic AMP and a rise in cyclic GMP. To test this hypothesis in BHK cells, cAMP levels were raised by adding dibutyryl cAMP and/or theophylline, or by stimulating adenylate cyclase with Prostaglandin E₁. cAMP blocks the serum stimulation of DNA synthesis, but increases ODC activity, both in quiescent cells and in cells treated with serum and insulin. These results suggest that serum and insulin control ODC activity through a mechanism independent of a drop in cAMP.     

Epidermal growth factor potentiates the induction of ornithine decarboxylase activity by prostaglandins in embryonic palate mesenchymal cells: effects on cell proliferation and glycosaminoglycan synthesis

Epidermal growth factor (EGF) and prostaglandins (PGs) have been implicated in the regulation of a number of developmental processes in the mammalian embryonic palate. Normal palatal ontogenesis is dependent on the presence and quite possibly on the interaction of various hormones and growth factors. The interaction between EGF and PGs in regulation of murine embryonic palate mesenchymal (MEPM) cell growth and differentiation was therefore investigated by monitoring the activity of ornithine decarboxylase (ODC), the principle and rate limiting enzyme of polyamine biosynthesis. ODC activity is tightly coupled to the proliferative and differentiative state of eukaryotic cells and therefore serves as a reliable indicator of such cellular functions. Treatment of confluent cultures of MEPM cells with EGF (1-50 ng/ml) resulted in a dose-related increase in ODC activity, while similar treatment with either PGE2 or PGF2 alpha (at concentrations up to 1 microM) did not elicit a dose-dependent increase in enzyme activity. Concurrent treatment of MEPM cells with EGF (20 ng/ml) and either PGE2 or PGF2 alpha (0.1-10000 nM) resulted in a marked prostaglandin dose-dependent induction of ODC activity, suggesting a strong cooperative interaction between these factors. ODC activity was maximal by 4 to 8 hr and could be completely inhibited by preincubation of the cells with actinomycin D or cycloheximide, indicating that de novo synthesis of RNA and protein is necessary for enzyme induction. Stimulation of ODC activity by EGF and PGE2 in these cells was not positively correlated with the level of cellular DNA synthesis but did result in a ninefold increase in the synthesis of extracellular glycosaminoglycans (GAGs), a key macromolecular family implicated in palatal morphogenesis. Stimulation of GAG synthesis was significantly inhibited by the administration of 5 mM DFMO (an irreversible inhibitor of ODC), indicating that the marked increase in GAG production was dependent, in part, on the induction of ODC activity by EGF and PGE2. Qualitative analysis of the palatal GAGs indicated that synthesis of several major classes of GAGs was stimulated. Collectively these data demonstrate a cooperative interaction between EGF and PGs in the induction of ODC activity. Such activity may serve to regulate the synthesis of GAGs, which are instrumental in mammalian palatal ontogenesis.     

Ornithine decarboxylase induction and polyamine biosynthesis are required for the growth of interleukin-2- and interleukin-3-dependent cell lines

The objective of this study was to evaluate induction of ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis, and subsequent polyamine accumulation in interleukin-2 (IL-2)- and interleukin-3 (IL-3)-dependent growth. The CTLL-20 and FDC-P1 cell lines, which have been shown to be absolutely dependent on IL-2 and IL-3, respectively, were used in these studies. The CTLL-20 and FDC-P1 cells each had different temporal patterns of ODC induction following lymphokine stimulation. ODC levels increased rapidly in the FDC-P1 cells, peaking 4 hr after stimulation with IL-3. In contrast, peak ODC activity in the CTLL-20 cells occurred 18 hr following stimulation with IL-2 and reached eightfold higher levels than those observed in the FDC-P1 cells. Treatment with D,L-alpha-difluoromethylornithine X HCl X H2O (DFMO), a specific irreversible inhibitor of ODC activity, completely abrogated lymphokine-dependent ODC induction in both the CTLL-20 and FDC-P1 cell lines. Similarly, intracellular levels of the polyamines putrescine and spermidine were reduced in both cell lines following DFMO treatment. DFMO treatment reduced both IL-2- and IL-3-dependent proliferation in a dose-dependent manner. However, this inhibition could be reversed by the addition of exogenous putrescine. DFMO treatment had no effect on cell viability. Polyamine-depleted CTLL-20 and FDC-P1 cells showed decreased absorption of IL-2 and IL-3 activity, respectively. However, the addition of exogenous putrescine restored the ability of the cells to absorb the appropriate lymphokine. These data are the first to demonstrate that ODC induction and polyamine biosynthesis are required in lymphokine dependent growth.     

Comparative effects of TGFβ on proliferation of 7- and 14-day-old chick embryo fibroblasts and lack of involvement of the ODC/PA system in the TGFβ signaling pathway

The growth regulatory activity of transforming growth factor β (TGFβ) on chick embryo skin fibroblasts was compared in two developmental ages, days 7 and 14. The time course of ³H-thymidine incorporation, an S-phase marker of replication, was determined during 36 hr of TGFβ treatment. Seven-day-old cells showed a prereplicative phase of 6 hr, and 14-day-old cells showed a prereplicative phase of 12 hr. DNA synthesis peaked at 24 hr in 7-day-old fibroblasts and was 10 times higher than that in 14-day-old fibroblasts. Ornithine decarboxylase (ODC) activity and content of the natural polyamines spermine (Spm), spermidine (Spd), and putrescine (Put) differed during cell cycle. ODC activity peaked at 12 hr in 7-day-old cells and at 6 hr in 14-day-old cells. Its level was two times higher at day 7 and was associated with a greater content of ODC mRNA. The maximum of polyamine (PA) concentration was determined after 12 hr of treatment in 7-day-old cells and after 36 hr in 14-day-old cells. These findings indicate that the TGFβ proliferative response of embryo fibroblasts changes during development and is associated with activation of the ODC/PA system. Cotreatment with α-difluoromethylornithine, an enzyme-activated irreversible inhibitor of ODC, did not reduced growth rate. Inhibition of ODC resulted in levels of Put and Spd comparable to that of quiescent fibroblasts, whereas Spm concentration remained higher. Because an altered ODC metabolism does not convey the effects of TGFβ on DNA synthesis, the ODC/PA system may not play a role in the pathway of TGFβ signaling. J. Cell. Physiol. 178:304–310, 1999. © 1999 Wiley-Liss, Inc.     

High concentration of L-arginine suppresses nitric oxide synthase activity and produces reactive oxygen species in NB9 human neuroblastoma cells.

Hereditary argininemia manifests as neurological disturbance and mental retardation, features not observed in other amino acidemias. The cytotoxic effect of a high concentration of L-arginine (L-Arg) was investigated using NB9 human neuroblastoma cells (NB9), which express neuronal nitric oxide synthase (nNOS). When the concentration of L-Arg in the medium increased from 50 microM to 2 mM after incubation for 48 hr, the intracellular concentration of L-Arg increased from 68.0 +/- 1 pmol/10(6) cells to 1310.0 +/- 5 pmol/10(6) cells and that of L-citrulline (L-Cit) from undetectable levels to 47.1 +/- 0.2 pmol/10(6) cells (mean +/- SD of three independent analyses). This increase in intracellular L-Arg levels caused a decrease in NOS activity by approximately 71%. Flow cytometric analysis showed that reactive oxygen species (ROS) are produced in NB9 exposed to 2 mM L-Arg. The production of ROS was abolished by a NOS inhibitor, NG-nitro-L arginine-methylester. Production of ROS was also observed when NB9 were treated with L-Cit for 48 hr. To investigate the effect of L-Cit on the activity of NOS, a kinetic study on nNOS was conducted using cellular extracts from NB9. The apparent Km value of nNOS for L-Arg was 8.4 microM, with a Vmax value of 8.2 pmol/min/mg protein. L-Cit competitively inhibited NOS activity, as indicated by an apparent Ki value of 65 nM. These results suggest that L-Cit formed by nNOS in L-Arg-loaded neuronal cells inhibits NOS activity and nNOS in these L-Arg-loaded cells functions as a NADPH oxidase to produce ROS, which may cause neurotoxicity in argininemia.     

Tryosine kinase and ornithine decarboxylase activation in children with Helicobactor pylori gastritis.

H. pylori infection has been considered a risk factor for the development of gastric malignancy. Ornithine decarboxylase and tyrosine kinases activities are increased in patients with colon or esophageal cancer. In this study we compared the ODC and tyrosine kinases activities in the gastric mucosa of children with H. pylori infection and normal mucosa. Gastric biopsies were prospectively collected from children during routine upper endoscopic procedure. H. pylori infection was determined histologically. Biopsies were analyzed for ODC activity, total tyrosine kinases activities, and for the activity of protooncogene tyrosine kinase pp60(c-src). The mean ODC activity (pmol 14CO2/mg. protein/hr) and total tyrosine kinases activity (pmol 32P/mg. protein) were 186 and 5877 for H. pylori infected mucosa; and 229 and 4300, for normal mucosa, respectively (p> 0.05). Tyrosine kinase pp60(c-src) protein levels were similar between H. pylori infected mucosa and normal mucosa (3.12 and 2.15 pmol 32P/mg. protein, respectively; p>0.05). There was no correlation between gastric inflammation and the level of ODC or tyrosine kinase activities. ODC and tyrosine kinase activities in the gastric mucosa are similar in children with H. pylori infection compared to normal mucosa. The data suggest that these enzymes cannot be used as markers for future cancer development in children.     

Bacterial lipopolysaccharide induction of ornithine decarboxylase in the macrophage-like cell line RAW264: requirement of an inducible soluble factor

Ornithine decarboxylase (ODC, EC 4.1.1.17) activity is induced in the RAW264 macrophage-like cell line by bacterial lipopolysaccharide (LPS). As little as 0.1 ng/ml LPS promoted an increase in ODC activity, while maximal ODC activity (30-fold above control) was induced with 1.0 microgram/ml LPS. An increase in ODC activity was detectable within 90 min of LPS addition. The LPS-induced increase in ODC activity was prevented by inhibitors of protein and RNA synthesis. The induction of the enzyme by LPS was not dependent on prostaglandin production. However, PGE2 (1 microgram/ml) and 8-bromo-cyclic AMP (1 mM), neither of which had an effect on ODC activity when added alone, each acted synergistically to enhance the LPS induction of ODC activity. Enzyme induction was not associated with an alteration in Km for ornithine, which remained constant at 0.04 mM. The extent of the increase in ODC in response to LPS increased with increasing cellular density. This relationship was dependent not on absolute cell density of the monolayer but on the cell number in relation to medium volume, and this dependence could be extrapolated to the origin. Addition of conditioned media from LPS-stimulated but not unstimulated cultures enhanced the ODC increase in sparsely plated cultures in response to a maximal concentration of LPS. The addition of polymyxin B, a reagent that blocks the effects of LPS, including the increase in ODC activity, did not totally inhibit the conditioned medium stimulation. This data indicates that two signals, LPS and a LPS-induced mediator, are involved in the induction of ODC activity in RAW264 cells.     

Glucose elevates ornithine decarboxylase expression in Vero cells

The addition of Earle's balanced salt solution (EBSS) of amino acids that are transported by a Na+-dependent cotransport system was not required by Vero cells for ornithine decarboxylase (ODC:EC 4.1.1.17) amplification. Vero cell ODC activity was elevated tenfold above basal levels when confluent cells were incubated for 5 hr in EBSS alone. ODC activity increased as a function of the incubation time in EBSS and was not elevated above basal enzyme levels when cells were incubated in EBSS minus glucose. ODC expression increased as a function of the glucose concentration in EBSS, with 20 mM glucose producing a 90-fold increase in ODC activity. ODC expression is more responsive to glucose in high-density quiescent cultures than in low-density growing cultures. Enhanced ODC expression by glucose depended on Na+ and K+ concentrations. The specific activity of ODC was also elevated above basal levels when mannose or fructose replaced glucose in EBSS. The addition of alanine or asparagine to EBSS enhanced ODC activity above levels obtained with EBSS containing standard (5.5 mM) glucose concentrations. In the absence of glucose, alanine was more effective than asparagine in enhancing ODC expression. These results suggest that the transport of amino acids is not an absolute requirement for Vero cell ODC expression and that ODC expression is linked to changes in cellular energetics and/or ion fluxes.     

Induction of ornithine decarboxylase in cultured mouse L cells. I. Effects of cellular growth, hormones, and actinomycin D.

The activity of ornithine decarboxylase [EC 4.1.1.17] (ODC) in mouse L cells in the confluent state was induced within 4 hr by cyclic AMP (cAMP) or by insulin. During growth of L cells the concentration of cAMP increased first, then induction of ODC occurred and finally the cell number increased: the levels of cAMP and ODC increased only transitorily and returned to the basal levels when the cells become confluent. In growing cultures, however, the presence of cAMP reduced induction of ODC and cell growth. These results suggest that cAMP is involved in induction of ODC and that its concentration may be important for enzyme induction as well as for cell growth. Actinomycin D with or without these inducers stimulated induction of ODC in L cells, whereas cycloheximide inhibited it, suggesting that these hormones affect the translational level of ODC synthesis. The effect of actinomycin D on induction of ODC was much greater in non-growing cells than in growing cells. It was also found that the half life of ODC was 81 min in non-growing cells and 112 min in growing cells. This suggests that turnover of the enzyme is more rapid in the non-growing than in the growing state and that there may be an RNA fraction which controls its turnover and which also has a very short half life.     

Interaction of Zn2+ and Eu3+ with bovine liver glutamate dehydrogenase.

Stepwise increments of the concentration of 2-difluoromethylornithine (DFMO), a mechanism-based irreversible inhibitor of mammalian ornithine decarboxylase (ODC), resulted in a selection of cultured human IgG-myeloma cells (Sultan cell line) capable of growing in the presence of up to 3 mM-DFMO. This capacity was associated with 10-fold increase in ODC activity in the dialysed extracts of drug-resistant myeloma cells, markedly enhanced synthesis rate for ODC enzyme molecules, as revealed by a 20 min [35S]methionine labelling of cellular proteins, followed by specific immunoprecipitation and SDS/polyacrylamide-gel electrophoresis, dose-dependently increased expression of ODC mRNA in resistant cells (effective dose causing 50% inhibition), dose-dependent amplification of ODC gene sequences in a 9-kilobase-pairs EcoRI genomic DNA fragment, and (v) a 10-fold increase in the ED50 (effective dose causing 50% inhibition) for the anti-proliferative action of DFMO in these myeloma cells. These results represent one of the few gene amplifications described in cultured human cells.     

Stimulation of phosphorylcholine turnover and diacylglycerol production in human polymorphonuclear leukocytes. Novel assay for phosphorylcholine.

Receptor-bypassing stimulants of human polymorphonuclear leukocytes (PMNLs), such as ionomycin or phorbol 12-myristate 13-acetate (PMA), generate an increase in diacylglycerol (DAG) which is independent of a phospholipase C specific for phosphatidylinositol 4,5,-bisphosphate (PIP2). Activation of a phospholipase C specific for phosphatidylcholine (PC) has been implicated as a source of DAG in other cells by measuring the release of radiolabelled phosphorylcholine. However, since PMNLs could not be labelled sufficiently with [3H]choline, we developed an h.p.l.c. assay to quantify mass levels of phosphorylcholine after enzymic conversion to [32P]CDP-choline with CTP-phosphorylcholine (choline phosphate) cytidylyltransferase (EC 2.7.7.15). This assay was linear to at least 20 nmol, and was sensitive to 10 pmol of phosphorylcholine. Baseline phosphorylcholine levels in unstimulated PMNLs were 2300 +/- 510 pmol/10(7) cells and were decreased by pretreatment with PMA (166 nM) or ionomycin (1 microM) for 10 min by 360 +/- 130 and 600 +/- 290 pmol/10(7) cells respectively (P less than 0.05). In contrast, baseline DAG levels were 147.6 +/- 11.7 pmol/10(7) cells in unstimulated PMNLs, and were increased by PMA or ionomycin by 1320 +/- 222 and 1891 +/- 264 pmol/10(7) cells respectively (P less than 0.05). Similarly, the chemoattractant fMet-Leu-Phe raised DAG levels by 731 +/- 111 pmol/10(7) cells and decreased phosphorylcholine levels by 180 +/- 60 pmol/10(7) cells. Activation of PMNLs by PMA, ionophore or fMet-Leu-Phe thus leads to the sustained production of DAG accompanied by the disappearance of phosphorylcholine. This suggests that these stimulants enhance PC turnover via a hydrolytic mechanism which is independent of phospholipase C, with activation of a PC-specific phospholipase D being a plausible mechanism.     

Immunocytochemical localization of ornithine decarboxylase in cultured murine cells

Summary Antiserum elicited to ornithine decarboxylase (ODC) purified from murine RAW 264 macrophage-like cells has been employed to localize ODC in cultured murine cells. The antiserum immunoprecipitated 100% of the ODC activity from the cultured cells. The specificity of the antiserum was demonstrated by the immunoprecipitation from ³⁵S-methionine metabolically-labeled cell extracts of a single protein which migrated upon SDS-gel electrophoresis coincident with authentic ODC. Indirect immunofluorescence experiments were performed on paraformaldehyde-fixed RAW 264 cells and JB6 epidermal cells using the rabbit anti-ODC antiserum and FITC-conjugated goat anti-rabbit IgG. Little immunofluorescence was apparent in non-stimulated cells. Intense immunofluorescence was detectable in stimulated cells at times of peak cellular ODC activity. Antigenically-reactive ODC was localized diffusely in the cytoplasm and was absent in the nuclei of RAW 264 cells, whereas in the JB6 cells the immunodetectable enzyme protein was localized in a punctate pattern in both the cytoplasm and nucleoplasm and was absent in the nucleolus. The appearance and disappearance of immunoreactive ODC in both cell types after stimulation was consistent with the alterations in ODC activity.     

Cell cycle phase-dependent induction of ornithine decarboxylase-antizyme

The activities of ornithine decarboxylase (ODC) and ODC inhibitory protein (ODC-antizyme) were studied in Ehrlich ascites tumor cells, separated according to their position in the cell cycle by centrifugal elutriation. Release and/or synthesis of ODC-antizyme was induced by putrescine treatment. Each mouse received an intraperitoneal injection of 25 mumoles of putrescine at 0, 1, 2, and 3 hr after tumor transplantation. Tumor cells obtained from putrescine-treated and control mice at 4 hr after transplantation were separated into fractions representing all phases of the cell cycle. The cell cycle distribution of the tumor cells in each fraction was determined by flow cytometry. In control tumor cells the ODC activity exhibited two maxima; in late-G1/early-S and in late-S/G2. A marked decrease in ODC activity was observed in mid-S phase. This decrease coincided with maximum ODC-antizyme activity (revealed by putrescine treatment), suggesting that ODC-antizyme is involved in the regulation of ODC activity during the cell cycle.