Amplification of ornithine decarboxylase gene in response to polyamine deprivation in Chinese hamster ovary cells

The effect of selenium, as selenomethionine, on genome stability and cytotoxicity in human lymphocytes measured using the cytokinesis-block micronucleus cytome assay

A supranutritional intake of selenium (Se) may be required for cancer prevention, but an excessively high dose could be toxic. Therefore, the effect on genome stability of seleno-L-methionine (Se-met), the most important dietary form of Se, was measured to determine its bioefficacy and safety limit. Peripheral blood lymphocytes were isolated from six volunteers and cultured with medium supplemented with Se-met in a series of Se concentrations (3, 31, 125, 430, 1880 and 3850 microg Se/litre) while keeping the total methionine (i.e. Se-met + L-methionine) concentration constant at 50 microM. Baseline genome stability of lymphocytes and the extent of DNA damage induced by 1.5-Gy gamma-ray were investigated using the cytokinesis-block micronucleus cytome assay after 9 days of culture in 96-microwell plates. High Se concentrations (>or=1880 microg Se/litre) caused strong inhibition of cell division and increased cell death (P < 0.0001). Baseline frequency of nucleoplasmic bridges and nuclear buds, however, declined significantly (P trend < 0.05) as Se concentration increased from 3 to 430 microg Se/litre. Se concentration (<or=430 microg Se/litre) had no significant effect on baseline frequency of micronuclei and had no protective effect against genome damage induced by exposure to 1.5-Gy gamma-ray irradiation. In conclusion, Se, as Se-met, may improve genome stability at concentrations up to 430 microg Se/litre, but higher doses may be cytotoxic. Therefore, a cautious approach to supplementation with Se-met is required to ensure that optimal genome health is achieved without cytotoxic effects.

Colorectal cancer prevention: is an ounce of prevention worth a pound of cure?

Colorectal cancer (CRC) is among the most common human malignancies and remains a leading cause of cancer-related morbidity and mortality. Colorectal carcinogenesis is a multistep process characterized by molecular and cellular alterations that result in an identifiable precursor lesion, ie, the adenomatous polyp. The transition from normal mucosa to adenoma and its subsequent progression to carcinoma are protracted events that offer opportunities for preventive interventions. Suppression or reversal of the carcinogenic process in the colorectum with nonpharmacologic or pharmacologic agents, ie, chemoprevention, is an area of considerable research interest and activity. Interest in this field derives from multiple epidemiologic studies showing that regular and continued use of nonsteroidal anti-inflammatory drugs (NSAIDs), predominantly aspirin, is associated with significant reductions in both colorectal adenoma and carcinoma incidence. NSAIDs were first shown to be effective in patients with familial adenomatous polyposis (FAP). Subsequent randomized trials in FAP demonstrated that sulindac and the selective cyclooxygenase-2 (COX-2) inhibitor, celecoxib, can significantly regress existing adenomas, and resulted in Food and Drug Administration (FDA) approval of celecoxib for adjunctive management of these patients. Based on the aforementioned data, aspirin and coxibs have been or are currently being evaluated for the prevention of sporadic adenoma recurrence in high-risk patient populations. Evidence indicates that aspirin can reduce adenoma recurrence rates in patients with prior colorectal neoplasia; however, questions remain, including the optimal dosage, timing of initiation and duration of treatment, and clinical benefit versus potential harm to patients. These same issues apply to the nonpharmacologic agents such as calcium, folic acid, and selenium given as dietary supplements. Apart from aspirin, calcium carbonate is the only other agent that has been shown to modestly reduce sporadic adenoma recurrence rates in a randomized trial. Folate and selenium are being actively studied based on provocative preclinical data. In addition to demonstrating efficacy, chemopreventive agents must also be safe for long-term use, be well accepted by patients, and be cost-effective. In this review, the current status of CRC chemoprevention will be discussed, including the available evidence for selected pharmacologic and nonpharmacologic agents, particularly among high-risk populations.

Tumor attenuation by combined heparan sulfate and polyamine depletion

Cells depend on polyamines for growth and their depletion represents a strategy for the treatment of cancer. Polyamines assemble de novo through a pathway sensitive to the inhibitor, alpha-difluoromethylornithine (DFMO). However, the presence of cell-surface heparan sulfate proteoglycans may provide a salvage pathway for uptake of circulating polyamines, thereby sparing cells from the cytostatic effect of DFMO. Here we show that genetic or pharmacologic manipulation of proteoglycan synthesis in the presence of DFMO inhibits cell proliferation in vitro and in vivo. In cell culture, mutant cells lacking heparan sulfate were more sensitive to the growth inhibitory effects of DFMO than wild-type cells or mutant cells transfected with the cDNA for the missing biosynthetic enzyme. Moreover, extracellular polyamines did not restore growth of mutant cells, but completely reversed the inhibitory effect of DFMO in wild-type cells. In a mouse model of experimental metastasis, DFMO provided in the water supply also dramatically diminished seeding and growth of tumor foci in the lungs by heparan sulfate-deficient mutant cells compared with the controls. Wild-type cells also formed tumors less efficiently in mice fed both DFMO and a xylose-based inhibitor of heparan sulfate proteoglycan assembly. The effect seemed to be specific for heparan sulfate, because a different xyloside known to affect only chondroitin sulfate did not inhibit tumor growth. Hence, combined inhibition of heparan sulfate assembly and polyamine synthesis may represent an additional strategy for cancer therapy.

Central administration of morphine inhibits brain and liver ornithine decarboxylase activity in neonatal rats: involvement of transcription- and non-transcription-dependent mechanisms

This study examined whether the developmental deficits usually observed in infants born to opiate addicted mothers could involve effects on ornithine decarboxylase, a growth-controlling enzyme. Intracerebroventricular (i.c.v.) injection of a single dose of morphine (2 microg) to 6-day-old rats markedly decreased basal brain and liver ornithine decarboxylase activity as well as the increases in hepatic ornithine decarboxylase activity produced by subcutaneously (s.c.) administered insulin, an important trophic hormone. Centrally applied morphine acts supraspinally to downregulate peripheral ornithine decarboxylase activity, since s.c. administration of the same dose as used i.c.v. decreased neither basal liver ornithine decarboxylase levels nor tissue responsiveness to insulin. This does not imply that the opiate is unable to affect ornithine decarboxylase when applied systemically. In fact, a robust inhibition of both basal and induced liver ornithine decarboxylase activity was obtained in rat pups given 20 microg of morphine s.c. This larger dose is able to trigger the hepatic ornithine decarboxylase effects presumably by stimulating opiate receptors located at central sites after crossing the blood-brain barrier and penetrating into the brain. Concomitant administration of naloxone plus morphine i.c.v. prevented morphine from downregulating ornithine decarboxylase activity, confirming the participation of supraspinal opioid receptors in morphine ornithine decarboxylase actions. Finally, as was the case for insulin induced stimulation of ornithine decarboxylase activity, i.c.v. injection of morphine markedly diminished insulin induced stimulation of hepatic ornithine decarboxylase mRNA accumulation. In turn, contrary to the inhibition of basal ornithine decarboxylase activity, morphine did not lower basal hepatic ornithine decarboxylase mRNA levels when given alone. Thus, CNS morphine can apparently suppress tissue ornithine decarboxylase expression through both transcriptional and posttranscriptional mechanisms. The evidence obtained suggest that postnatal exposure to opiate drugs might detrimentally affect development by altering normal tissue ornithine decarboxylase ontogeny.

Androgen induces ornithine decarboxylase gene expression in colonic cell line HT-29

Carcinoma of the colon is the second most common cancer among men and women combined in the United States.

PURPOSE

Ornithine decarboxylase (ODC) is the first and key regulatory enzyme in the polyamine biosynthesis pathway and is regulated by various factors. Polyamines are believed to participate in cellular proliferation and differentiation. High levels of polyamines and ODC activity are associated with rapid cell growth, particularly in tumor tissues. Regulation of this enzyme in vivo has important clinical implications. In the present study, we used Northern analysis and mobility shift assay to investigate whether ODC gene expression is regulated by androgens in the three human colonic cell lines, SW620, HT-29, and Caco-2.

METHODS

Cell lines were maintained in Dulbecco's Modified Eagle's medium/F12 supplemented with 5 percent fetal bovine serum. At 60 percent confluency, medium was replaced with steroid-depleted medium, and incubation continued for 24 hours. Following this period, medium was replaced with fresh steroid-free medium containing 1 nM dihydrotestosterone.

RESULTS

Dihydrotestosterone stimulated ODC messenger ribonucleic acid expression only in HT-29 colonic cell line. Studies using electrophoretic mobility shift assays of nuclear extracts also showed a binding pattern with SP1 and NF-kappaB regulatory sequences only in testosterone-treated HT-29 cells.

CONCLUSION

These results suggest that androgens may play an important role in the growth of HT-29 colonic cell lines.

Transcription-dependent and -independent regulation of hepatic ornithine decarboxylase activity by CNS beta-endorphin in rat pups

We have previously shown that intracerebroventricular administration of relatively low doses of beta-endorphin suppresses basal levels of hepatic ODC activity as well as tissue ODC responsiveness to administered insulin in developing rats. Using Northern blotting analysis, the current studies examine whether these effects of CNS beta-endorphin may be mediated by changes in ODC gene expression. Subcutaneous administration of insulin (20 IU/kg body weight) rapidly and profoundly increased liver ODC activity. The time course of the response was characterized by proportionally increased levels of ODC mRNA, suggesting that insulin-induced stimulation of ODC activity is due to an increased transcription of ODC mRNA. Pretreatment with actinomycin D (2 mg/kg body weight, intraperitoneally) completely prevented the insulin-induced increase in ODC activity, confirming the requirement for the de novo synthesis of ODC mRNA for the effect. More importantly, intracerebroventricular but not subcutaneous injection of beta-endorphin (1 microgram) markedly diminished the stimulatory effect of insulin on hepatic ODC mRNA accumulation. The time course and magnitude of the inhibition of mRNA accumulation essentially mirrored that of the peptide on ODC activity. On the other hand, contrary to the inhibitory effect of beta-endorphin on basal ODC activity, the peptide did not lower basal ODC mRNA levels when given alone. Taken together, the results from these studies provide evidence for the existence of at least two separate mechanisms through which CNS beta-endorphin might downregulate ODC activity in peripheral organs of rat pups. The peptide can suppress insulin-induced ODC activity in the liver tissue by decreasing the rate of transcription of the ODC gene, whereas the inhibition of basal ODC activity appears to involve posttranscriptional mechanisms.

Methylation status and chromatin structure of an early response gene (ornithine decarboxylase) in resting and stimulated NIH-3T3 fibroblasts

The early response gene ornithine decarboxylase (odc) is indispensable for normal and malignant cell growth. Although DNA methylation is generally associated with chromatin condensation and gene inactivation, the odc gene is heavily methylated at CCGG-sequences in animal cell lines. In this work we analyzed the chromatin structure and the DNA methylation status at the CpG-rich promoter sequences at the odc locus in mouse 3T3 fibroblasts. We show that the proximal promoter region of the odc locus is not hypermethylated, while the distal promoter sequences appear to have a few methylated CCGG-sites and display methylation polymorphism. Furthermore, it was found that the 5' promoter region of odc is constitutively more sensitive to micrococcal nuclease than the coding and 3' regions of the odc gene. Stimulation of the cells with serum resulted in an appearance of a DNase I sensitive site at the promoter region. The chromatin structure of the mid-coding and 3' regions of the odc gene also underwent structural changes that were accompanied by the rapid accumulation of odc mRNA. Such changes were not detected in the chromatin structure of glyceraldehyde-3-phosphate dehydrogenase (gadph) gene, whose expression remains invariant upon serum stimulation. These data suggest that the chromatin structure may play an important role in the rapid transcriptional activation of odc and other immediate early genes during serum stimulation.

Feedback regulation of mammalian ornithine decarboxylase. Studies using a transient expression system

Ornithine decarboxylase catalyzes the first step in the biosynthesis of polyamines in mammalian cells. The enzyme is subject to various control mechanisms to maintain adequate intracellular levels of polyamines. Polyamines exert a strong feedback control on ornithine decarboxylase. In a recent study [van Daalen Wetters, T., Macrae, M., Brabant, M., Sittler, A. & Coffino, P. (1989) Mol. Cell. Biol. 9, 5484-5490], it was concluded that feedback control of ornithine decarboxylase is mainly, if not exclusively, a posttranslational phenomenon. The existence of a fast-acting polyamine-stimulated component of ornithine decarboxylase degradation that acts on newly synthesized monomeric forms of the enzyme was postulated. In the present study we have used a transient expression system to test this hypothesis. The expression of ornithine decarboxylase in mock-transfected COS cells varied depending on the cellular supply of polyamines as has been found in other mammalian cells. Thus, supplementing the cells with exogenous spermidine resulted in a marked decrease in ornithine decarboxylase activity, whereas depletion of intracellular polyamines, using an ornithine decarboxylase inhibitor, gave a large increase in the cellular content of the enzyme. COS cells expressing an ornithine decarboxylase mRNA devoid of its 5' non-translated region did not exhibit any feedback control of the enzyme, neither in the presence of exogenous spermidine nor when the intracellular polyamine levels were depleted to the same extent as in the mock-transfected COS cells. The results strongly suggest that the feedback control of ornithine decarboxylase is not merely a posttranslational phenomenon.

Ornithine decarboxylase from Crithidia fasciculata is metabolically unstable and resistant to polyamine down-regulation

Ornithine decarboxylase (ODC) of Crithidia fasciculata extracts shows maximal activity during exponential growth of the parasite and decreases markedly in the stationary phase. The inhibition of protein synthesis by cycloheximide evoked a rapid loss of enzyme activity with a half-life of about 30 min. Upon removal of DFMO from Crithidia cultures treated with the drug for 24 h, the ODC activity increased at the same rate as total protein synthesis. The addition of putrescine at high concentrations to parasites cultivated in a synthetic medium showed that Crithidia ODC levels were not reduced by polyamines.

Mapping of the mouse ornithine decarboxylase-related sequence family

A family of DNA sequences homologous to the mRNA encoding ornithine decarboxylase (ODC) and comprising approximately 12 members in the mouse genome has been analyzed genetically. The inheritance of variant DNA restriction fragments detected by ODC cDNA probes on Southern blots of DNA from inbred strain mice was determined in six sets of recombinant inbred (RI) mouse strains. The distributions of these variations among the RI strains were then compared with the RI strain distribution patterns (SDPs) of previously mapped loci. This allowed the identification of nine independent ODC-related loci, of which eight could be localized to specific regions of the mouse genome: Odc-rs1 near Lamb2 on Chromosome (Chr) 1; Odc-rs2 near Psp on Chr 2; Odc-rs5, a complex locus comprising at least 5-7 copies of the ODC sequence, associated with Igk on Chr 6; Odc-rs6 between Abpa and Tam-1 on proximal Chr 7; Odc-rs7 near Hbb on distal Chr 7; Odc-rs12 near Agt and Emv-2 on distal Chr 8; Odc-rs8 associated with the Igh complex on Chr 12; and Odc-rs9 near Otf-3f on Chr 14. The ODC-related sequence family thus comprises a set of genomically dispersed "marker" loci, and alleles for several of these loci can be analyzed simultaneously in DNA from mice or cell lines. DNA from mice of 70 inbred strains has been characterized for alleles at all nine Odc-rs loci.

Variations in amplification and expression of the ornithine decarboxylase gene in human breast cancer cells

The polyamine biosynthetic pathway plays a critical role in the growth of human breast cancer cells. Ornithine decarboxylase (ODC) is a key enzyme in polyamine biosynthesis. To understand the regulation of ODC activity and polyamine accumulation in breast cancer cells, we studied amplification and expression of the ODC gene in four breast cancer cell lines. ODC gene dosage was analyzed by Southern blot hybridization and was 4- to 12-fold higher in T-47D, MDA-MB-231, and BT-20 cell lines than in the MCF-7 cell line. ODC mRNA level was 2- to 3-fold higher in BT-20 and MDA-MB-231 cell lines than in the other two lines. We also measured ODC activity and polyamine concentration in these cell lines, and determined their sensitivity to an ODC inhibitor, difluoromethylornithine (DFMO). BT-20 cells showed significantly higher ODC activity and polyamine concentrations than the other three cell lines. BT-20 cells were resistant to the growth inhibitory effect of DFMO even at 4 mM concentration, whereas the proliferation of MCF-7, T47D, and MDA-MB-231 cells was inhibited by this drug. These results suggest that different transcriptional and post-transcriptional mechanisms control the regulation of ODC gene expression in breast cancer cell lines.

Molecular genetics of polyamine synthesis in eukaryotic cells

The polyamines putrescine, spermidine and spermine are important cellular constituents involved in the regulation of cell growth and differentiation. Their intracellular levels are regulated by a multitude of mechanisms affecting their synthesis, degradation, uptake and excretion. As a result of the application of molecular biology techniques, some of these mechanisms are presently being unravelled, and are providing a basis for the rational development of novel agents effective against proliferative disorders and various parasitic diseases.

Chemical characterization of acylpolyamine toxins from venom of a trap-door spider and two tarantulas

Two acylpolyamines are identified from venom of the trap-door spider, Hebestatis theveniti. These toxins (paralytic to lepidopteran insect larvae) are amides containing 3-(3-indolyl)lactic acid joined to spermine or 1,13-diamino-4,10-diazatridecane (Het389 and Het403, respectively). Het389 is also abundant in venom from a tarantual from Mozambique (Harpactirella sp.). Two additional acylpolyamines (Apc600 and Apc728) are partially characterized from venom of another tarantula, Aphonopelma chalcodes.

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.

Epidermal growth factor: modulator of murine embryonic palate mesenchymal cell proliferation, polyamine biosynthesis, and polyamine transport

Polyamines (putrescine, spermidine, and spermine) are normal cellular constituents able to modulate cellular proliferation and differentiation in a number of tissues and cell types. This investigation explores the response of murine embryonic palate mesenchymal (MEPM) cells to epidermal growth factor (EGF) in terms of biosynthesis of putrescine and its transport across the plasma membrane and tests the hypothesis that polyamine transport can serve as an alternative mechanism (other than biosynthesis) for elevating intracellular polyamines during stimulation of MEPM cellular proliferation. MEPM cells treated with EGF were stimulated to proliferate and showed a dose- and time-dependent stimulation of ornithine decarboxylase (ODC) which was maximal at 4-6 hours. EGF also stimulated the initial rate of putrescine transport in a dose- and time-dependent manner. This stimulation was found to be maximal 3 hours after treatment and specific for the putrescine transport system. The kinetic parameters of putrescine transport shifted from 2.52 microM (Km) and 23.6 nmol/mg protein/15 minutes (Vmax) in nonstimulated cells to 4.48 microM (Km) and 39.8 nmol/mg protein/15 minutes (Vmax) in EGF-treated cells. This kinetic shift did not require de novo protein or RNA synthesis, as cycloheximide (10 micrograms/ml) and actinomycin D (50 micrograms/ml) had little effect on the ability of EGF to stimulate the initial rate of putrescine uptake. The rate of transport, however, was found to be inversely related to cell density. The addition of exogenous putrescine concomitantly with EGF blocked the induction of ODC, while in the presence of difluoromethylornithine (DFMO) (irreversible inhibitor of ODC) the initial rate of putrescine transport remained elevated throughout the time course studied. This stimulation of putrescine uptake caused by polyamine deprivation was reversed by exogenous putrescine and Ca++ while alpha-aminoisobutyric acid (AIB) further stimulated the rate of uptake. EGF's ability to stimulate cellular DNA synthesis was inhibited by DFMO. If DFMO-treated cells were stimulated with EGF in the presence of exogenous putrescine, this stimulatory effect was preserved. These studies indicate that the rate of polyamine transportation is highly responsive to a signal which initiates biosynthesis of polyamines. Further, this transportation system provides a compensatory mechanism allowing the cell to increase intracellular levels of polyamines when environmental conditions inhibit biosynthesis or when polyamines are abundant.

Rapid expression of ornithine decarboxylase mRNA in a macrophage-like cell line: cAMP repression of the requirement for prior protein synthesis

Ornithine decarboxylase (ODC) activity was rapidly induced in the RAW264 macrophage-like cell line after treatment with bacterial lipopolysaccharide (LPS). ODC mRNA levels were determined by isolating cellular RNA, followed by Northern blot and dot blot analysis using a 32P-labeled cDNA probe. ODC mRNA levels increased within 1 hour of stimulation of RAW264 cells with 1.0 microgram/ml LPS. Transcription rate analysis on isolated nuclei indicated that an increase in transcription rate contributed to this increase in ODC mRNA. ODC mRNA levels continued to rise for 4 hours, peaking at eight times the basal level. ODC mRNA appeared as a single 2.2-kb band prior to stimulation. After stimulation, the 2.2-kb band intensified, and a second (2.7 kb) band was seen by Northern gel analysis. Similar induction was demonstrated when 12-O-tetradecanoyl-phorbol-13-acetate (TPA) was used as the stimulus. The induction of ODC mRNA by either LPS or TPA was blocked by the addition of cycloheximide (25 micrograms/ml) or anisomycin (0.1 mM) to the cellular incubation mixture. This indicated that protein synthesis was required as a prerequisite to LPS or TPA induction of ODC mRNA. Experiments in which cycloheximide addition was delayed after LPS treatment indicated that some of the required protein synthesis occurred within the first 30 minutes and that complete expression of ODC mRNA was possible if protein synthesis continued for at least 2 hours before cycloheximide was added. Stimulation with 8-bromo-cAMP in addition to LPS has been shown to enhance the induction of ODC over that induced by LPS or TPA alone. It was not possible to block ODC mRNA induction with cycloheximide or anisomycin after treatment with the combined stimulus of LPS and cAMP or TPA and cAMP, indicating that protein synthesis was not required when cAMP was used as a coinducer. Thus, we have shown that in the same cell, ODC mRNA can be induced by two different pathways, one requiring protein synthesis and one not requiring protein synthesis.

Complete amino acid sequence of human ornithine decarboxylase deduced from complementary DNA

A complementary DNA (cDNA) encoding ornithine decarboxylase was isolated from a human liver cDNA library, and the nucleotide sequence coding for the entire enzyme was determined. The 1825-nucleotide-long cDNA contained an open reading frame of 1383 nucleotides, 87 nucleotides 5' from the first methionine codon, 346 nucleotides in the 3'-noncoding region, and a poly(A) tail of nine bases. Primer extension studies indicated that the 5'-noncoding region of the human ornithine decarboxylase mRNA was 335 nucleotides long. The amino acid sequence deduced from the open reading frame for a 461-residue polypeptide predicts a molecular weight of 51.156 for the human enzyme and has about 90% homology with the amino acid sequence of the murine ornithine decarboxylase (44 differences among the 461 amino acids). The nucleotide sequences of the human and murine ornithine decarboxylase mRNAs share an 85% homology, even in their 3'-noncoding regions. In contrast to rodent tissues with two ornithine decarboxylase mRNAs, normal human tissues appear to express only a single mRNA species with a molecular size of 2.25 kb. Southern blotting of human leukocyte DNA from 20 individuals indicated that the ornithine decarboxylase gene belongs to a multigene family in man and showed restriction fragment length polymorphism when cleaved with Pst I, but not when cleaved with Pvu II, Msp I, Hinc II, or Bam HI.

Cloning and nucleotide sequence of rat ornithine decarboxylase cDNA

The enzyme ornithine decarboxylase (ODC; EC 4.1.1.17) catalyses the first and rate-limiting step in polyamine biosynthesis. Its activity is markedly increased in rapidly growing or regenerating tissue and is subject to regulation by a variety of trophic and mitogenic stimuli. ODC is therefore believed to play an essential role in the onset of cellular proliferation. In a molecular-biological approach to investigate ODC regulation upon induction by tumor promoters in rat liver we isolated an almost full-length rat ODC cDNA clone of 2.4 kb (designated pODC.E10) from a cDNA library of testosterone-induced rat kidney poly(A)+ RNA. Characterization by restriction-endonuclease mapping and sequence analysis showed strong homology to mouse ODC cDNA sequences previously published [Gupta and Coffino, J. Biol. Chem. 260 (1985) 2941-2944; Kahana and Nathans, Proc. Natl. Acad. Sci. USA 82 (1985) 1673-1677; Hickok et al., Proc. Natl. Acad. Sci. USA 83 (1986) 594-598]. This homology is most pronounced in the 461-aa-spanning coding region, amounting to 94% and 97% at the DNA and protein levels, respectively. In the 423-nt 5' leader the rat-mouse homology (approx. 75%) is most pronounced in a region of about 175 nt directly upstream from the translational start site. The leader sequence also contains a perfect inverted repeat of 54 nt and ten additional upstream ATG triplets, which are all followed by nonsense codons before the initiating ATG. In the 633-nt 3' trailer region of pODC.E10 an additional polyadenylation signal is observed more than 300 nt upstream from the 3' end. Rat-mouse homology is about 80% up to this first polyadenylation signal and is considerably less thereafter. The presence of two alternate polyadenylation sites most likely accounts for the 3' size heterogeneity observed in the two ODC mRNAs of 2.1 and 2.6 kb, respectively. In rat liver both mRNAs are coordinately induced by different tumor promoters. Finally, Southern blot analysis of normal rat liver and rat hepatoma DNA revealed that rat ODC, as in other rodents, belongs to a multigene family.

Human lung tumor sensitivity to difluoromethylornithine as related to ornithine decarboxylase messenger RNA levels

The differential response to polyamine depletion has been studied in two types of human lung tumor cells. Small cell lung carcinoma cells die following polyamine depletion by difluoromethylornithine treatment while non-small cell lines demonstrate a typical cytostatic response. We now report that a small cell line, NCI H82, has a lower apparent capacity for polyamine biosynthesis than does a representative non-small cell, NCI H157. In subconfluent cultures, the ornithine decarboxylase activity is 25 times lower in the small cell than the non-small cell and by comparison, the polyamines in the small cell line are markedly reduced. Most significantly, levels of mRNA coding for ornithine decarboxylase are approximately 100-fold lower in the small cell than the non-small cell line, and this difference does not appear to be a result of gene rearrangement. These results suggest that differential sensitivity to polyamine depletion is related to different steady-state levels of ornithine decarboxylase mRNA.