Control of ornithine decarboxylase in Chinese hamster ovary cells by polyamines. Translational inhibition of synthesis and acceleration of degradation of the enzyme by putrescine, spermidine, and spermine

Effect of ATP depletion and phenanthroline on the spermidine-mediated decay of ornithine decarboxylase in erythroleukemia cells

Addition of spermidine to Friend erythroleukemia cells caused a rapid decay of ornithine decarboxylase (ODC) activity and the accumulation of a ODC-antizyme complex. The induction of antizyme only partially accounted for the decrease of ODC activity by a direct inhibition of the enzyme. However, the antizyme induction was accompanied by a marked reduction of the half-life of ODC. Shift of the cells to an ATP-depleting medium prevented the spermidine-elicited decay of ODC activity as well as the accumulation of ODC-antizyme complex. However, ODC appeared to be stabilized even when ATP depletion was performed 40 min after spermidine addition, in the presence of high levels of antizyme. Similar results were obtained by treating the cells with phenanthroline, a heavy metal chelator and protease inhibitor. These findings indicate that ATP and some metalloprotease(s) may be involved in the degradation pathway of ODC, even in the presence of high levels of polyamines.

Spermine toxicity and glutathione depletion in BHK-21/C13 cells

Spermine, a polycationic amine, produced a dose-dependent inhibition of BHK-21/C13 cell growth. This response was not due to the extracellular metabolism of spermine by an amine oxidase found in bovine serum, as the toxicity was observed when the cells were grown in medium supplemented with horse serum. Three indices were used to monitor cell growth, cell number, protein content and [3H]thymidine incorporation into DNA. Spermine (2mM) caused significant reductions in all three measurements after a 6-8 hr exposure. The amine was rapidly taken up into the cells reaching levels 15-16-fold greater than in control cells within 2 hr. There was a rapid loss of intracellular reduced glutathione following exposure to toxic concentrations of spermine, which occurred before any effect on cell growth. Three methods for the determination of intracellular glutathione content were compared in this system. The effect on both cell growth and glutathione was reversible following removal of spermine from the extracellular medium. The possible mechanisms involved in this toxic response are discussed with particular reference to the depletion in intracellular reduced glutathione.

Cloning and functional analysis of the rat ornithine decarboxylase-encoding gene

We have isolated a functional gene (ODC) encoding rat ornithine decarboxylase (ODC; EC 4.1.1.17) from a partial rat liver genomic DNA bank. The entire gene is located on a 7776-bp BamHI fragment and was shown to comprise twelve exons, of which ten encode the ODC protein (exons III-XII). Introduction of the BamHI fragment into an ODC-deficient hamster cell line restores ODC activity, indicating that the gene is functional. Comparison of the structure and nucleotide (nt) sequence of the rat ODC gene with recently reported mouse ODC genes, reveals that the gene is highly conserved. Primer extension analysis and RNA sequencing demonstrates that the transcription start point of rat ODC mRNA is located 303 nt upstream from the A residue in the start codon. Compared with our previously published sequence of the rat ODC cDNA, this indicates that a short sequence at the extreme 5' end of our cDNA clone represents a cloning artefact. The correct 5' leader of ODC mRNA, which is very G + C rich (62%), can be folded into a highly stable secondary structure, which may play a role in the translational control of ODC activity. Like in mouse, the promoter region of rat ODC is also extremely rich in G + C, and contains a TATA box and several putative SP1-binding sites. Possible binding sites for other transcription factors, like AP-1, AP-2 and CREB, can also be observed in the promoter region and, moreover, in the first intron.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of the Na(+)-dependent and the Na(+)-independent polyamine transporters in renal epithelial cells (LLC-PK1)

We have studied the regulation of the Na(+)-dependent and Na(+)-independent polyamine transport pathways in the renal LLC-PK1 cell line. Most of the experiments were performed in the presence of 5 mM DL-2-difluoromethylornithine (DFMO) in order to inhibit the cellular synthesis of polyamines. The activity of both transporters as measured by putrescine uptake was increased by growth-promoting stimuli and decreased by exogenous polyamines. The time course of the increase in uptake activity induced by fetal calf serum could be fitted by a single exponential, and the process was three times faster for the Na(+)-dependent than for the Na(+)-independent transporter. Maximum activity was reached after more than 24 h. This increase could be inhibited by actinomycin D and by cycloheximide. Other growth-promoting stimuli, such as subconfluent cell density, as well as growth factors also induced an increase in the transport activity. Particularly, there was a marked stimulation of the Na(+)-dependent pathway by epidermal growth factor in combination with insulin. On the other hand, the transport activity decayed very rapidly upon addition of exogenous polyamines (t1/2 less than 60 min). The diamine putrescine was much less effective in this respect than the polyamines spermidine and spermine. The non-metabolizable substrate methylglyoxal bis(guanylhydrazone) did not induce a decay of the transport activity, but it protected the Na(+)-dependent pathway against the polyamine-induced decay. Inhibition of the protein synthesis by cycloheximide did not induce a rapid decrease of the transport activity; neither did it affect the polyamine-induced decay. These observations suggest that this polyamine-induced decay is not owing to an inhibitory effect on the rate of synthesis of the transporters, but rather to a degradation or an inactivation of the transporters. The polyamine-induced decay slowed down at lower cell density. This effect was particularly pronounced for the Na(+)-dependent transporter. Since the uptake of polyamines was increased at low cell density, the decreased rate of decay in this condition pleads against a simple mechanism of transinhibition by the substrate. In conclusion, both transport pathways were similarly affected by the regulatory parameters, but the Na(+)-dependent transporter was more rapidly and more effectively regulated. The numerous interacting regulatory steps furthermore suggest a physiological role for these transporters, such as an involvement in urinary polyamine disposal.

Electrically stimulated rapid gene expression in the brain: ornithine decarboxylase and c-fos

A single electroconvulsive shock (ECS) resulted in a major induction of cerebral ornithine decarboxylase (ODC) mRNA and a rapid and transient elevation of ODC enzyme activity. The proto-oncogene c-fos was also transiently induced under the same conditions. Following a rapid rise in mRNA levels, the messages for these proteins take different courses. The c-fos mRNA fell to below control levels by 1 h, while the ODC mRNA remained elevated beyond 24 h. The ECS-induced elevation of ODC enzyme activity was not abolished by adrenalectomy but was attenuated significantly by the anti-convulsant MK-801. These results imply that the induction of cerebral ODC may be neuronal activity dependent, and suggest that the ODC/polyamine system may be linked to the proposed third messenger cascade, involving c-fos, which couples cell stimulation to gene expression, resulting in long-term adaptive responses.

Conformational changes in ornithine decarboxylase enable recognition by antizyme

Rapid, polyamine-induced degradation of mammalian ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) (ODC) is though to be controlled by the availability of a small, ODC-binding protein termed antizyme. In this study we have investigated the ability of antizyme to bind ODC protein in various altered physiological states. In particular, cold, NaCl, spermidine and deprivation of coenzyme and substrate enhance enzyme-antizyme complex formation and are all found to promote ODC homodimer dissociation. Conversely, conditions that maintain the active ODC homodimer state prevent antizyme binding and inactivation of ODC. Further, covalent modification of ODC near its active site by difluoromethylornithine or phosphate also increases its sensitivity to antizyme. These results suggest that the initial signal in ODC degradation may actually be a subtle conformational change in the enzyme that enables antizyme to bind to the enzyme and may subsequently facilitate its degradation.

Feedback regulation of ornithine decarboxylase expression. Studies using a polysomal run-off system

The rate-controlling enzyme in polyamine synthesis, ornithine decarboxylase (ODC), is subject to feedback regulation by the polyamines at the level of translation. In the present study we used a cell-free translation system to further investigate the mechanism by which this regulation occurs. Lysates of ODC-overproducing cells were capable of synthesizing large amounts of ODC. The degree of initiation was poor in the lysates and the synthesis of ODC was mainly a result of continued elongation of peptide chains on pre-initiated ribosomes. By determining the amount of ODC produced in the lysate, we obtained an estimate of the number of ribosomes that were actively translating ODC mRNA at the moment of lysis. Using this polysomal run-off assay we demonstrated that the polyamine-mediated regulation of ODC synthesis occurs without any change in the number of ribosomes associated with the message. This finding indicates that the polyamines exert a coordinate effect on initiation and elongation.

Different turnover of rat fetal and placental ornithine decarboxylases

The half-lives of ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC) have been studied in fetuses and placentas from 18-day-pregnant rats. While the turnover of fetal and placental SAMDC were slightly different (t1/2 = 38 and 75 min, respectively) the half-lives of fetal and placental ODC differed markedly. T1/2 of fetal ODC was 15 min, similar to other mammalian ODCs, but placental ODC showed a relatively high half-life, about 160 min. According to that, placental ODC was more resistant than the fetal enzyme to in vivo hyperthermic treatment (40 degrees C, 1 h). Our results suggest that the degradative mechanisms for ODC in rat placenta could be regulated differently to those in other mammalian tissues.

Control by hyperthermia of ornithine decarboxylase in Ehrlich ascites tumor cells

The effect of hyperthermia on the activity and the messenger RNA levels of ornithine decarboxylase (ODC), which has a rapid rate of turnover in cultured cells, was studied in Ehrlich ascites tumor cells. When the cells were incubated at 42 degrees C, elevation of ODC activity by a change of the medium was prevented. Total RNA was isolated from cells treated at 37 degrees C or 42 degrees C, and the relative abundance of the ODC mRNA was measured by Northern blot analysis. These levels in heat-treated cells were comparable to those in control cells. Inhibition by hyperthermia was reversible. The recovery was suppressed by cycloheximide but not by actinomycin D. In hyperthermic-treated cells, the biological half-life of ODC was 14 min, which was the same time as for cells cultured at 37 degrees C. These results suggest that hyperthermic treatment of Ehrlich ascites tumor cells suppressed ODC induction during translation, not during transcription or after translation.

Human ornithine decarboxylase(ODC)-encoding gene: cloning and expression in ODC-deficient CHO cells

We have cloned a full-length human ornithine decarboxylase (ODC)-encoding gene from a genomic library of human myeloma cells which overproduce ODC due to a selective gene amplification. Correct expression of the cloned gene was assessed by transfecting it into a Chinese hamster ovary (CHO) cell mutant devoid of ODC activity. Transfection with a 10-kb BamHI DNA fragment of the genomic clone, conferred ODC activity to the recipient cells and relieved them of dependence on exogenous polyamines for growth. A set of 40 transformants was isolated, eight of which were further characterized. The transfected ODC gene appeared to be hypomethylated at the cytosine residues in the sequence CpG. The transfectants were all responsive to serum stimulation, but showed different levels of ODC expression depending on both copy number and integration site of the transfected ODC gene. ODC serum induction in the transfectants was sensitive to cycloheximide and polyamine additions, and the half-life of the enzyme was very short, like that in normal CHO cells. These results suggest that the human ODC gene we transfected contains all the elements needed for normal control of ODC expression.

Degradation of ornithine decarboxylase in mammalian cells is ATP dependent but ubiquitin independent

Ornithine decarboxylase (ODC), a key enzyme in the biosynthesis of polyamines in mammalian cells is characterized by an extremely short half-life. In the present study, ODC degradation was investigated in 653-1 mouse myeloma cells that overproduce ODC and in ts85 cells that are thermosensitive for conjunction of ubiquitin to target proteins. Addition of 2-deoxyglucose and dinitrophenol (agents that efficiently deplete cellular ATP) to the growth medium of these cells inhibited ODC degradation. In contrast, chloroquine and leupeptin, inhibitors of intralysosomal proteolysis, did not affect ODC degradation. Shifting ts85 cells to 42 degrees C (a non-permissive temperature that inhibited conjugation of ubiquitin to target proteins) did not prevent ODC degradation. The ATP-dependent degradation of ODC in 653-1 cells was inhibited substantially by N alpha-tosyl-L-lysine chloromethane (TosPheMeCl), iodoacetamide and o-phenanthroline. These results suggest that ODC degradation occurs via a non-lysosomal. ATP-requiring and ubiquitin-independent cellular proteolytic mechanism, and that serine proteases and enzymes containing sulphydryl groups and metalloenzyme(s) may be involved in this process.

Stabilization of ornithine decarboxylase in erythroleukemia cells depleted of ATP

Ornithine decarboxylase activity in Friend erythroleukemia cells decayed with a half-life of 50 minutes after addition of cycloheximide and at a faster rate after addition of spermidine. Incubation with a medium containing dinitrophenol and 2-deoxy-glucose in place of glucose caused ATP depletion and blocked the turnover of ornithine decarboxylase, even after addition of spermidine. Dinitrophenol in the presence of glucose was able to provoke only a slight increase of the half-life of the enzyme. These results suggest that degradation of ornithine decarboxylase in erythroleukemia cells is ATP-dependent.

Polyamine-mediated control of mammalian S-adenosyl-L-methionine decarboxylase expression: effects on the content and translational efficiency of the mRNA

The expression of mammalian AdoMet decarboxylase, a key enzyme in polyamine synthesis, was shown to be regulated by polyamines at two different levels. Polyamine depletion of Ehrlich ascites tumor cells induced a marked compensatory increase in the synthesis of the enzyme, as measured by 35S-methionine pulse-labeling and immuno-precipitation. This increase in synthesis rate was counteracted by provision of spermidine, which reduced the synthesis of AdoMet decarboxylase to an undetectable level. Northern analysis revealed a nearly 2-fold increase in the amount of AdoMet decarboxylase mRNA when the putrescine and spermidine content was depleted. This increase in AdoMet decarboxylase mRNA content cannot account for the more than 5-fold increase in synthesis rate, indicating a feedback regulation also at the level of mRNA translation.

Prevention of rapid intracellular degradation of ODC by a carboxyl-terminal truncation

Ornithine decarboxylase (ODC) was converted from a protein with a short intracellular half-life in mammalian cells to a stable protein by truncating 37 residues at its carboxyl terminus. Cells expressing wild-type protein lost ODC activity with a half-life of approximately 1 hour. Cells expressing the truncated protein, however, retained full activity for at least 4 hours. Pulse-chase experiments in which immunoprecipitation and gel electrophoresis were used confirmed the stabilizing effect of the truncation. Thus, a carboxyl-terminal domain is responsible for the rapid intracellular degradation of murine ODC.

Interleukin-2 regulates the activity of ornithine decarboxylase in a cloned murine T lymphocytic cell line: evidence for a protein kinase C-dependent pathway

The role of protein kinase C (PKC) in the regulation of ornithine decarboxylase (ODC) activity during interleukin-2 (IL-2)-dependent cell growth was investigated. A large biphasic increase in the activity of ODC was observed after treatment of IL-2-deprived CTLL-2 cells with recombinant human IL-2 (rec IL-2). The PKC activators phorbol 12-myristate 13-acetate (PMA) and 4 beta-phorbol 12,13-didecanoate (4 beta-PDD), but not the inactive analog 4 alpha-PDD, induced ODC activity in exponentially growing cultures. Unlike IL-2, however, phorbol esters were poor inducers of IL-2-depleted cultures. H-7, a potent inhibitor of PKC and cyclic nucleotide-dependent protein kinases (CN-PK), suppressed the IL-2-induced ODC activity, while HA1004, a more potent inhibitor of CN-PK than of PKC, had opposite effects depending on its concentration. The results suggest that activation of PKC is involved in but is not the sole mechanism for the induction of ODC by rec IL-2. At concentrations which suppressed the induction of ODC activity by IL-2, H-7 inhibited DNA synthesis and HA1004 did not.

Involvement of antizyme in stabilization of ornithine decarboxylase caused by inhibitors of polyamine synthesis

Contrary to previous findings, ornithine decarboxylase (ODC) was stabilized by treatment of cells with DL-alpha-difluoromethylornithine, an enzyme-activated irreversible inhibitor of ODC. Both this inhibitor and cyclohexylamine, a spermidine synthase inhibitor known to stabilize ODC, caused decreases in the antizyme/ODC ratio by increasing ODC content and conversely decreasing antizyme content. The relationship between cellular polyamine levels and antizyme content indicated that spermidine is the most important polyamine for antizyme induction. These results suggest that antizyme is involved in the mechanism underlying the stabilization of ODC by inhibitors of polyamine synthesis and support the hypothesis that cellular polyamines regulate ODC degradation via antizyme.

Interleukin-2 induces a rapid increase in ornithine decarboxylase mRNA in a cloned murine T lymphocytic cell line

We recently observed a 25-fold increase in the activity of ornithine decarboxylase (ODC) 6 h after treatment of G1-synchronized CTLL-2 cells with interleukin-2 (IL-2). Here we show that the ODC mRNA content increased in parallel with the ODC activity during the first hours of stimulation with IL-2, resulting in a 25-fold increase at 6 h. Between 6 and 24 h the ODC mRNA content continued to increase steadily up to 50-fold, even after the ODC activity had returned to low basal levels. In the case of density-arrested CTLL-2 cells deprived of IL-2 for 16 h, the IL-2-mediated increase in ODC mRNA was 2-fold at 1 h and 5-fold at 8 h, irrespective of the capability of the cells to resume their cycle. There was no marked increase in the rate of transcription of the ODC gene, at least during the first 2 h of stimulation with IL-2. These findings suggest that the regulation of the ODC activity by IL-2 is a primary event in IL-2-induced cell proliferation and occurs at the post-transcriptional level, possibly by stabilizing the ODC mRNA and affecting the efficiency of translation of the messenger.

Effect of 1 alpha,25-dihydroxyvitamin D3 on polyamine metabolism in human monocyte cell line-U937

1. Pretreatment with 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] caused an increase in ornithine decarboxylase (EC 4.1.1.17) (ODC) activity in lipopolysaccharide (LPS)-stimulated human monocyte cell line, U937. 2. The increase in ODC activity was dose-dependent and preincubation-time dependent. 3. 26,26,26,27,27,27-Hexafluoro-1,25-dihydroxyvitamin D3 was ca 7 times more potent than 1,25-(OH)2D3 in increasing ODC activity. 4. Pretreatment with 1,25-(OH)2D3 also potentiated the activity of spermidine/spermine-N1-acetyltransferase in LPS-stimulated U937 cells. 5. Putrescine levels in cells pretreated with 1,25-(OH)2D3 increased ca 2-fold 4-8 hr after LPS addition. 6. However, pretreatment with 1,25-(OH)2D3 did not cause any increase in ODC mRNA level, suggesting that 1,25-(OH)2D3 may modulate polyamine metabolism at the posttranscriptional level rather than the transcriptional step.

Feedback regulation of polyamine synthesis in Ehrlich ascites tumor cells. Analysis using nonmetabolizable derivatives of putrescine and spermine

Ornithine decarboxylase (ODC) is subject to feedback regulation by the polyamines. Thus, addition of putrescine, spermidine or spermine to cells causes inhibition of ODC mRNA translation. Putrescine and spermine are readily converted into spermidine. Therefore, it is conceivable that the inhibition of ODC synthesis observed in putrescine- and spermine-supplemented cells is instead an effect of spermidine. To examine this possibility we have used two analogs of putrescine and spermine, namely 1,4-dimethylputrescine and 5,8-dimethylspermine, which cannot be converted into spermidine. Both analogs were found to inhibit the incorporation of [35S]methionine into ODC protein to approximately the same extent, suggesting that putrescine as well as spermine exert a negative feedback control of ODC mRNA translation in the cell. In addition to suppressing ODC synthesis, both analogs were found to increase the turnover rate of the enzyme. 5,8-Dimethylspermine caused a marked decrease in the activity of S-adenosylmethionine decarboxylase (AdoMetDC). This effect was not obtained with 1,4-dimethylputrescine, indicating that spermine, but not putrescine, exerts a negative control of AdoMetDC. Treatment with 1,4-dimethylputrescine caused extensive depletion of the cellular putrescine and spermidine content, but accumulation of spermine. 5,8-Dimethylspermine treatment, on the other hand, effectively depleted the spermine content and had less effect on the putrescine and spermidine content, at least initially. Nevertheless, the total polyamine content was more extensively reduced by treatment with 5,8-dimethylspermine than with 1,4-dimethylputrescine. Accordingly, only 5,8-dimethylspermine treatment exerted a significant inhibitory effect on Ehrlich ascites tumor cell growth.

Relationships between reversion of hydroxyurea resistance in hamster cells and the co-amplification of ribonucleotide reductase M2 component, ornithine decarboxylase and P5-8 genes

Hydroxyurea is a specific inhibitor of ribonucleotide reductase, which is a rate-limiting enzyme activity in DNA synthesis. Cells selected for resistance to hydroxyurea contain alterations in ribonucleotide reductase activity. An unstable hydroxyurea resistant population of hamster cells has been used to isolate a stable drug resistant cell line, and two stable revertant lines with different sensitivities to hydroxyurea cytotoxicity and different ribonucleotide reductase activity levels. We show for the first time that a decrease in hydroxyurea resistance is accompanied by a parallel decline in gene copies for the M2 component of ribonucleotide reductase, ornithine decarboxylase and a gene of unknown function called p5-8, indicating that the co-amplification of the three genes is associated with drug resistance, and supporting the concept that M2, ornithine decarboxylase and p5-8 are closely linked, and form part of a single amplicon in hamster cells.

Interrelation between the charge isoforms of mammalian ornithine decarboxylase

Ornithine decarboxylase (ODC) isolated from a variety of tissues has been separated, using DEAE ion-exchange chromatography, into multiple peaks of activity that appear to be related to control of this enzyme stability. Reports of these charge isoforms in current literature are generally unclear as to whether these represent a covalent posttranslational modification or merely an alteration in structural conformation or association. In this study we investigated the relationship of this form separation to the degree of enzyme polymerization, interaction with other proteins and buffer components, and the multiple isoelectric forms of this enzyme noted in denaturing concentrations of urea. High-performance chromatography techniques were used to demonstrate that two of the major enzyme forms, ODC I and II, are really monomers of the enzyme, while minor peaks of activity frequently observed to elute after ODC II contain various dimeric enzyme states. Pyridoxal 5'-phosphate (0.05 mM) added to isolated enzyme preparations composed of I and II monomers induced the formation of I and II dimers as well as a mixed I-II dimer. All three dimer forms were observed to be natural components of freshly isolated crude cell homogenates. The charge distinction between the monomer forms I and II was found to be maintained during ion-exchange chromatography in the presence of 8 M urea, and the enzyme isoforms demonstrated distinct bands on isoelectric focusing gels run in the presence of 9 M urea. Thus, although some of the multiple ornithine decarboxylase forms identified by ion-exchange chromatography of crude mammalian cell homogenates are related to enzyme conformation, the two major forms are distinctly charged protein states that can be visualized using two-dimensional gel electrophoresis of highly purified samples.

Enzyme regulation as an approach to interference with polyamine biosynthesis--an alternative to enzyme inhibition

The progress reviewed here would seem to validate the regulatory approach to interference with polyamine biosynthesis as an antiproliferative strategy. To our knowledge, this is the first example, among anticancer drugs, of pharmacological intervention of a biochemical pathway based strictly on regulatory control. Several features of polyamine biology naturally favor this approach and may account for its relative success. These include (a) the nature of the regulatory mechanisms themselves, (b) the exquisite sensitivity of the pathway to regulatory control, (c) the rapid turnover of ODC and AdoMetDC, (d) the different structural specificity of ODC and AdoMetDC regulation versus growth-dependent functions, and (e) the direct dependence of growth on sustained polyamine biosynthesis. As such, the regulatory approach to interference with polyamine biosynthesis offers several advantages over the use of specific enzyme inhibitors (Table 10). Of these, perhaps, the more significant are the facts that more than one enzyme can be simultaneously and specifically suppressed and that compensatory mechanisms, which otherwise counter the effects of enzyme inhibitors (11), are not invoked. We are encouraged by the concurrence of in vitro mechanistic findings with the predictions of the hypothesis for the regulatory approach and by the in vitro and in vivo growth inhibitory effects of the analogs against murine leukemia. One disadvantage of the regulatory analogs, such as BESm, has been that, as with specific polyamine inhibitors such as DFMO, analog-induced polyamine depletion results in cytostatic growth inhibition. While this response may help to minimize host toxicities, it clearly compromises antitumor activity. An intriguing exception to this generality has recently been found among human lung carcinoma cell lines. Previously, Luk et al. (93, 94) and others (95) reported that, among a spectrum of human lung carcinoma lines, small cell carcinoma was exquisitely sensitive to the ODC inhibitor, DFMO. Not only did these cells display a cessation of growth but also an inability to survive during DFMO-induced polyamine depletion. Studies extending these findings to long term maintenance therapy in human small cell lung carcinoma implants in athymic mice revealed sustained growth inhibition of the tumor for longer than one year (96). Casero et al. (97) now find that human large cell carcinoma, which is otherwise refractory to chemotherapeutic intervention, displays a cytotoxic response in vitro to polyamine depletion induced by BES or BESm but not by DFMO.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of polyamine biosynthetic activity by spermidine and spermine analogs--a novel antiproliferative strategy

Interference with polyamine biosynthesis by analog-mediated regulatory mechanisms represents a viable alternative to the use of specific enzyme inhibitors as an antiproliferative strategy. The approach is unique among antimetabolite approaches and is made possible by unusual characteristics inherent to the polyamines and their biosynthetic pathway. Current antitumor data obtained with these analogs provides indication of their potential usefulness as antitumor agents but, at the same time, demonstrates the need for improvement. This latter might be attained by the rational design of analogs which (a) bind more tightly at enzyme regulatory sites, (b) which are less able to substitute for natural polyamines in growth related functions and (c) which are eliminated less rapidly from tumor-bearing animals. At the same time, the continued preclinical development of available analogs might proceed most productively by targeting large cell lung carcinoma and melanoma and by examining the generality of the relationship between oncogene expression and the accompanying sensitivity to regulatory analogs.

Polyamine administration reduces ornithine decarboxylase activity without affecting its mRNA content

Ornithine decarboxylase, the first enzyme in the polyamine biosynthetic pathway, is induced by androgens in the mouse kidney. Enzyme activity, as well as enzyme protein levels are increased 100-400 fold. Utilizing a specific cDNA probe to ODC, mRNA levels in these cells were found to increase 7-25 fold as measured by densitometric scanning. Treatment of the mice for 5 hours with 2 mmol/kg doses of putrescine or 1,3-diaminopropane after androgen stimulation reduced enzyme activity to control levels, while mRNA levels remained elevated 18-30 fold above control. In a different system, serum starved SV-3T3 cells showed low ODC activity and amounts of ODC mRNA. Serum stimulation increased the 2.2 kilobase mRNA levels 6 fold and enzyme activity 13 fold in a coordinate fashion within 5 hours. While the rise in activity was blocked by the simultaneous addition of serum and 1 mM putrescine, ODC mRNA levels appeared unchanged. The addition of 50 microM spermidine or 100 microM spermine also had no effect on ODC mRNA levels, while at the same time reducing enzyme activity amounts. These results suggest that the mechanism by which polyamines regulate ODC activity in the mouse is primarily translational.