Ornithine decarboxylase mRNA in mouse kidney: a low abundancy gene product regulated by androgens with rapid kinetics

Role of ornithine decarboxylase antizyme inhibitor in vivo

Ornithine decarboxylase (ODC) antizyme inhibitor (AZI) has been shown to regulate ODC activity in cell cultures. However, its biological functions in an organism remain unknown. An embryonic stem (ES) cell clone was established, in which the Azin1 gene was disrupted by the gene trap technique. To identify the function of Azin1 gene in vivo, a mutant mouse line was generated using these trapped ES cells. Homozygous mutant mice died at P0 with abnormal liver morphology. Further analysis indicated that the deletion of Azin1 in homozygous mice resulted in the degradation of ODC, and reduced the biosynthesis of putrescine and spermidine. Our results thus show that AZI plays an important role in regulating the levels of ODC, putrescine and spermidine in mice, and is essential for the survival of mice.

Influence of testosterone on regulation of ODC, antizyme, and N1-SSAT gene expression in mouse kidney

Polyamines are involved in the control of the cell cycle and cell growth. In murine kidney, testosterone enhances gene expression of ornithine decarboxylase (ODC), the first enzyme in polyamine biosynthesis. In this study, we document the time course effect of testosterone on 1) gene expression of ODC, antizyme 1 (AZ1), and spermidine/spermine-N1-acetyltransferase (N1-SSAT); 2) ODC activity in proximal convoluted tubules (PCT) and cortical proximal straight tubules (CPST); and 3) renal polyamine levels. Female mice were treated with testosterone for a period of 1, 2, 3, and 5 consecutive days. ODC gene expression was extremely low in kidneys of untreated female mice compared with that of males. Consequently, the renal putrescine level was sevenfold lower in females than in males, whereas spermidine and spermine levels did not differ between sexes. In female kidneys, testosterone treatment sharply increased ODC mRNA and protein levels as well as ODC activity. Testosterone increased the expression of ODC in PCT and CPST over different time courses, which suggests that ODC activity is differentially regulated in distinct tubules. The expression of AZ1 and N1-SSAT mRNA was similar in male and female mouse kidneys. Testosterone treatment enhanced AZ1 and N1-SSAT mRNA levels in a time-dependent manner by unknown molecular mechanisms. Putrescine and spermidine levels increased after testosterone treatment in female kidneys. Surprisingly, although ODC protein and activity were undetectable in female kidneys, the levels of AZ1 mRNA and protein were similar to those in males. Therefore, one may propose that ODC protein could be continuously degraded by AZ1 in female kidneys.

[Nitric oxide, L-arginine and the kidney. Experimental studies of new therapy approaches]

BACKGROUND

Nitric oxide (NO) is a small gaseous molecule with multiple biological effects. NO is produced from the semi-essential amino acid L-arginine by NO synthases (NOS). In the kidney, neuronal NOS (bNOS), which is localized in the macula densa, and endothelial NOS (ecNOS) are involved in the regulation of glomerular hemodynamics. Dysfunction of these enzymes may cause glomerular hypertension and increased intraglomerular platelet aggregation. NO production in high tissue concentrations can be achieved by activation of an inducible NOS isoform (iNOS) and may act as a potent mediator of inflammation in immune-mediated renal diseases. Selective inhibition of iNOS may, therefore, become a novel anti-inflammatory approach in the treatment of glomerulonephritis. Based on experimental data, the potential importance of NO and other metabolites of L-arginine in the pathophysiology and therapy of renal diseases is summarized in this article.

CONCLUSION

Modulation of the renal L-arginine/NO-system represents a promising therapeutic target in the treatment of acute an chronic kidney diseases.

Co-operation of the 5' and 3' untranslated regions of ornithine decarboxylase mRNA and inhibitory role of its 3' untranslated region in regulating the translational efficiency of hybrid RNA species via cellular factor

The 5' untranslated region (UTR) has an inhibitory role in the translatability of ornithine decarboxylase (ODC) mRNA and of hybrid mRNA species, whereas the ODC 3' UTR causes a partial release of this inhibition. We designed experiments to explore whether the co-operation between ODC 5' UTR and 3' UTR in the translational regulation is due to a direct interaction of those sequences or whether it is mediated by their interaction with cellular factor(s). We stably transfected Chinese hamster ovary (CHO)-K1 cells and transiently transfected COS-1 cells with expression vectors carrying different chimaeric DNAs having the luciferase (LUC) coding sequence as reporter gene, the ODC 5' UTR or the ODC 3' UTR, or both, in the appropriate positions. We compared the results obtained by assaying the LUC activities of both transfected cell lines with each chimaeric DNA with those observed by translating the hybrid RNAs in a translation system in vitro. When the ODC 3' UTR was present, we observed a partial release of the translation inhibition owing to the ODC 5' UTR only in vivo. The releasing effect was restored in vitro by the addition of cytoplasmic extracts from wild-type CHO-K1 or COS-1 cells, prepared 2 and 8 h after their release from serum starvation. We also observed a partial inhibition of the translatability of the hybrid RNA owing to the presence of the ODC 3' UTR itself; the translational efficiency could be rescued by cell extract from 8 h serum-stimulated cells. The co-operation between the ODC-UTRs might be mediated by factors expressed by cells during particular phases of the cell cycle. Excess copies of the ODC-UTRs, expressed in trans, could compete in binding limited amounts of such regulatory factors and remove them from interaction with the endogenous ODC mRNA. This phenomenon should be reflected by modifications of the kinetics of ODC and/or LUC activities during serum stimulation. The overexpression of the ODC 3' UTR determined an increase in both endogenous ODC activity and LUC activity. Moreover, in the transfectants expressing the hybrid RNA species bearing the ODC 3' UTR the basal ODC activity is higher than that observed in control cells. We suggest that excess copies of the ODC 3' UTR mis-regulate the endogenous ODC translatability, probably by tying up regulatory molecules expressed by cells in limited amounts and sequestering them from the ODC mRNA species they should interact with.

Antiandrogenic effect of RU-486 in the mouse kidney

RU-486 (mifepristone) is a synthetic steroid with potent antiprogesterone and antiglucocorticoid activity, that is currently used as a contraceptive agent. In the present work we have evaluated the antiandrogenic effect of this compound on mouse kidney, a very well known extragenital model of androgen action by studying the effect of RU-486 on renal parameters that depend on androgens, such as renal ornithine decarboxylase (ODC) activity and kidney hypertrophy, as well as the inhibitory action of mifepristone on the induction of renal ODC and kidney hypertrophy elicited by testosterone treatment in female mice and in castrated male. The results showed that: (1) 48 hr after treatment of male mice with of RU-486 (50 mg/kg, four injections) renal ODC activity decreased from 3.381 +/- 490 nmol CO2/h.g to 605 +/- 163 (SD, n = 5); (2) in female mice or orchidectomized male mice, RU-486 also inhibited the renal ODC induction elicited by exogenous administration of testosterone propionate (TP), the magnitude of the inhibition was dependent on the doses of TP and RU-486 used. While RU-486 at a dose of 25 mg/kg inhibited more than 80% ODC induction produced by treatment with 5 mg/kg TP, the same dose did not significantly affect ODC when the dose of TP was increased up to 100 mg/kg. Higher concentration of RU-486 (200 mg/kg) clearly inhibited the increase in ODC produced by treatment with TP 100 mg/kg; (3) RU-486 was more effective in blocking the anabolic effects produced by stanozolol, a steroidal anabolizing agent, than those produced by testosterone; and (4) RU-486 was less effective than the nonsteroidal antiandrogen flutamide in inhibiting renal ODC activity in male mice. Our results clearly indicate that RU-486 possesses moderate antiandrogenic activity in mouse kidney. The possibility that RU-486 may have similar effects in man should be considered when using this drug.

Ornithine decarboxylase activity is critical for cell transformation

The enzyme ornithine decarboxylase is the key regulator of the synthesis of polyamines which are essential for cell proliferation. Expression of this enzyme is transiently increased upon stimulation by growth factors, but becomes constitutively activated during cell transformation induced by carcinogens, viruses or oncogenes. To test whether ornithine decarboxylase could be a common mediator of transformation and oncogenic itself, we transfected NIH3T3 cells with expression vectors carrying the complementary DNA encoding human ornithine decarboxylase in sense and antisense orientations. The increased expression of the enzyme (50-100-times endogenous levels) induced not only cell transformation, but also anchorage-independent growth in soft agar and increased tyrosine phosphorylation of a protein of M(r) 130K. Expression of ornithine decarboxylase antisense RNA was associated with an epithelioid morphology and reduced cell proliferation. Moreover, blocking the endogenous enzyme using specific inhibitor or synthesizing antisense RNA prevented transformation of rat fibroblasts by temperature-sensitive v-src oncogene. Our results imply that the gene encoding ornithine decarboxylase is a proto-oncogene central for regulation of cell growth and transformation.

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.

Fine-structure mapping of the complex locus Odc-rs5 relative to Igk and distal loci

Odc-rs5 was previously identified as a complex locus closely linked to the Igk complex on mouse Chromosome (Chr) 6 and comprising at least five copies of a sequence related to the mRNA encoding ornithine decarboxylase (ODC) in the genomes of mice of some inbred strains and at least seven copies in others (Richards-Smith and Elliott, Mammalian Genome 2: 215, 1992). In the present study, Odc-rs5 was shown to be composed of at least seven copies of the ODC sequence in both the Odc-rs5a and Odc-rs5b haplotypes. Based upon the distribution of DNA restriction fragments (RFs) that had previously been associated with Odc-rs5a or Odc-rs5b among 42 mice of inbred laboratory strains having various haplotypes at Igk and in mice of two congenic strains [B6.PL-Ly-2a, Ly-3a(75NS)/Cy and B6.PL-Ly-2a,Ly-3a(85NS)/Cy] and a backcross-derived stock (NAK) known to be recombinant within Igk, a fine structure map of Odc-rs5 was deduced relative to Igk and more distal loci. Odc-rs5-derived RFs were located to three distinct regions within and/or distal to Igk and to a fourth site between (Ly-3, Ly-2) and Raf-1. Additionally, DNAs from 19 mice of inbred strains and random-bred stocks derived from wild progenitors trapped at various locations were analyzed and found to exhibit an unexpected variety of combinations of RFs associated with the two Odc-rs5 haplotypes most frequently observed among inbred laboratory strains of mice.

Androgen-regulation of ornithine decarboxylase and S-adenosylmethionine decarboxylase genes

Ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (AdoMetDC) are two key enzymes in polyamine biosynthesis. Both the ODC and the AdoMetDC gene is regulated by androgens in accessory sex organs of mice and rats, whereas only the ODC gene is androgen-responsive in rodent kidney. Androgenic responses in murine and rat kidneys are, however, dissimilar in that the induction of ODC activity and ODC mRNA accumulation is transient in the rat but sustained in the murine renal cells. In addition, in situ hybridization experiments with single-stranded cRNA probes revealed that ODC gene expression occurs in different subpopulations of epithelial cells of the proximal tubules in mice and rats. ODC and AdoMetDC genes are androgen-regulated in the same cell types of the accessory sex organs, as judged by hybridization histochemistry. Sequencing of the promotor region of the murine ODC gene has indicated the presence of several DNA elements for binding of transcription factors/regulatory proteins, including a putative androgen-response element at about 900 nucleotides upstream of the transcription start site.

Deprivation of a single amino acid induces protein synthesis-dependent increases in c-jun, c-myc, and ornithine decarboxylase mRNAs in Chinese hamster ovary cells

Genes of higher eucaryotic cells are considered to show only a limited response to nutritional stress. Here we show, however, that omission of a single essential amino acid from the medium caused a marked rise in the mRNA levels of c-myc, c-jun, junB and c-fos oncogenes and ornithine decarboxylase (ODC) in CHO cells. There was no general accumulation of mRNAs in amino acid-starved cells, since the gamma-actin, beta-tubulin, protein kinase C, RNA polymerase II, and glyceraldehyde-3-phosphate dehydrogenase mRNAs and the total poly(A)+ mRNA were not increased. The levels of c-myc, ODC, and c-jun mRNAs were elevated more by amino acid starvation than by inhibition of protein synthesis with cycloheximide, which is known to increase the levels of these mRNAs. Importantly, however, cycloheximide present during amino acid starvation reduced the rise in the levels of the mRNAs down to the level obtained with cycloheximide alone. This implies that protein synthesis is required for the accumulation of c-myc, ODC, and c-jun mRNAs in amino acid-deprived cells. The junB and c-fos mRNAs, instead, were increased to the same extent or less by amino acid starvation than by cycloheximide treatment. The accumulation of the c-myc mRNA in amino acid-starved cells was due to both stabilization of the mRNA and increase of its transcription. The rise in the c-jun mRNA level seemed to be caused merely by stabilization of the mRNA. Further, despite the inhibition of general protein synthesis, amino acid starvation led to an increase in the synthesis of c-myc polypeptide. The results suggest that mammalian cells have a specific mechanism for registering shortages of amino acids in order to make adjustments compatible with cellular growth.

Deprivation of a single amino acid induces protein synthesis-dependent increases in c-jun, c-myc, and ornithine decarboxylase mRNAs in Chinese hamster ovary cells

Genes of higher eucaryotic cells are considered to show only a limited response to nutritional stress. Here we show, however, that omission of a single essential amino acid from the medium caused a marked rise in the mRNA levels of c-myc, c-jun, junB and c-fos oncogenes and ornithine decarboxylase (ODC) in CHO cells. There was no general accumulation of mRNAs in amino acid-starved cells, since the gamma-actin, beta-tubulin, protein kinase C, RNA polymerase II, and glyceraldehyde-3-phosphate dehydrogenase mRNAs and the total poly(A)+ mRNA were not increased. The levels of c-myc, ODC, and c-jun mRNAs were elevated more by amino acid starvation than by inhibition of protein synthesis with cycloheximide, which is known to increase the levels of these mRNAs. Importantly, however, cycloheximide present during amino acid starvation reduced the rise in the levels of the mRNAs down to the level obtained with cycloheximide alone. This implies that protein synthesis is required for the accumulation of c-myc, ODC, and c-jun mRNAs in amino acid-deprived cells. The junB and c-fos mRNAs, instead, were increased to the same extent or less by amino acid starvation than by cycloheximide treatment. The accumulation of the c-myc mRNA in amino acid-starved cells was due to both stabilization of the mRNA and increase of its transcription. The rise in the c-jun mRNA level seemed to be caused merely by stabilization of the mRNA. Further, despite the inhibition of general protein synthesis, amino acid starvation led to an increase in the synthesis of c-myc polypeptide. The results suggest that mammalian cells have a specific mechanism for registering shortages of amino acids in order to make adjustments compatible with cellular growth.

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.

Early events in the antiproliferative action of tumor necrosis factor are similar to the early events in epidermal growth factor growth stimulation

The process of TNF-induced cytotoxicity is complex but appears to be mediated through a TNF-specific cell surface receptor. Recent evidence suggests that TNF action on tumor cells may be antagonized by epidermal growth factor (EGF) and other EGF-receptor modulatory peptides implicating a role for EGF-R in the process of TNF-induced cytotoxicity. In the present report, we investigated the biochemical actions of TNF on several biochemical events known to occur in the process of EGF signal transduction in intact cells. The actions of TNF were compared directly to those of EGF in both TNF-sensitive and -resistant tumor cell lines. In TNF-sensitive ME-180 cervical carcinoma cells, TNF (20 ng/ml) stimulated the tyrosine protein kinase activity of the EGF-receptor (EGF-R) fivefold when measured by receptor autophosphorylation in an immune complex kinase assay. TNF activation of EGF-R kinase activity in ME-180 was measurable 10 min after TNF incubation and enzymatic activity remained elevated 20 min after TNF addition. Activation of the receptor by TNF correlated with increased 32P incorporation into EGF-R protein when receptor was immunoprecipitated from 32P-equilibrated cells following a 20 min incubation with TNF. Acid hydrolysis of EGF-R protein isolated from TNF-treated ME-180 cells demonstrates an increase in the phosphotyrosine content of EGF-R when compared to receptor isolated from untreated cells. The results suggest that TNF increased EGF-R tyrosine protein kinase activity and the state of EGF-receptor tyrosine phosphorylation in a manner similar to that reported for EGF. However, TNF does not appear to be structurally related to EGF since TNF was unable to directly activate EGF-R when incubated with extensively washed immunoprecipitates of EGF-R. In TNF-resistant T24 bladder carcinoma cells, TNF failed to alter EGF-R tyrosine protein kinase activity although both EGF and phorbol ester were shown to modulate the enzymatic activity of the receptor in these cells. These results indicate that the ability of TNF to modulate EGF-R kinase in target cells may correlate with its cytotoxic actions on TNF-sensitive tumor cells. Other biochemical activities associated with the induction or regulation of cellular growth were examined in TNF- or EGF-treated tumor cells. EGF stimulated a rapid 8-16-fold increase in the expression of the proto-oncogene c-myc when analyzed by dot-blot analysis of total cellular RNA or Northern blot hybridization of polyadenylated RNA. TNF treatment failed to alter c-myc expression in ME-180 cells when analyzed by either technique.(ABSTRACT TRUNCATED AT 400 WORDS)

Activation of the neu tyrosine kinase induces the fos/jun transcription factor complex, the glucose transporter and ornithine decarboxylase

We have studied the ability of the neu tyrosine kinase to induce a signal for the activation of cell growth-regulated genes. Serum-starved NIH 3T3 cells expressing an epidermal growth factor receptor (EGF-R)/neu construct encoding a hybrid receptor protein were stimulated with EGF and the activation of the neu tyrosine kinase and stimulation of growth factor inducible genes were followed at the mRNA, protein, and activity levels, and compared to the corresponding responses in the neu proto-oncogene and oncogene expressing cells. Induction of the expression of jun mRNAs was an immediate early effect of EGF stimulation, followed by a marked increase in the biosynthesis of the fos/jun transcription factor complex and an increased transcription factor activity as measured by a recombinant transcription unit using chloramphenicol acetyltransferase assays. In distinction, elevated AP-1/PEA-1 activity in the absence of a significant increase in jun and fos expression was characteristic of the neu oncogene-expressing cells. The glucose transporter mRNA increased at 2 h of EGF stimulation and was associated with enhanced glucose transport of the EGF-treated cells. An increase of ornithine decarboxylase (ODC) mRNA and activity followed these changes. In contrast, serum-starved, EGF-treated neu proto-oncogene- and oncogene-expressing cells showed constitutively low and high glucose transporter and ODC activities, respectively. These findings demonstrate that the chimeric EGF-R/neu receptor is capable of activating the expression of both immediate early genes and biochemical activities associated with cell growth stimulation.

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.

Ornithine decarboxylase activity and the accumulation of its mRNA during early stages of liver regeneration

The marked and well documented stimulation of hepatic ornithine decarboxylase (ODC; EC 4.1.1.17) in response to partial hepatectomy is at least to some extent attributable to an enhanced accumulation of the enzyme's mRNA. The stimulation of ODC activity was associated with an increased accumulation of two ODC-related mRNA species (2.1 and 2.6 kilobases; kb) as revealed by Northern blot hybridization analyses. The levels of the above-mentioned messages remained elevated for 6 h after partial hepatectomy, at which time the enzyme activity had returned to almost control levels. Furthermore, ODC protein levels remained relatively stable after the first peak of ODC activity, suggesting that posttranslational activity was responsible for the changes in ODC activity after the initial burst. In addition to the two mRNA species typical of mouse cells, rat tissues contained a third hybridizable message (1.6 kb). This smaller poly(A)+ RNA was never seen in samples obtained from mouse or human cells, but was always present in samples obtained from rat tissues. Interestingly this rat-specific message appeared to be expressed in somewhat opposite manner to the other two mRNA species.

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.

Cadaverine supplementation during a chronic exposure to difluoromethylornithine allows an overexpression, but prevents gene amplification, of ornithine decarboxylase in L1210 mouse leukaemia cells

We recently selected a variant mouse L1210 leukaemia-cell line overproducing ornithine decarboxylase (ODC) (EC 4.1.1.17) as a result of chronic exposure to 2-difluoromethylornithine (DFMO) in the presence of micromolar concentrations of cadaverine. These cells, now grown for more than 2 years in the presence of DFMO and cadaverine, continued to accumulate ODC-specific mRNA in an amount 30-50 times higher than that in the parental cells, yet showing practically no changes in the gene dosage for the enzyme. However, analysis of the genomic DNA with the isoschizomeric restriction enzymes HpaII and MspI revealed that the ODC sequences in the overproducer cells were hypomethylated in comparison with the parental cells. The natural polyamines (putrescine, spermidine and spermine) were almost totally replaced by cadaverine and aminopropylcadaverine. Omission of cadaverine from the culture medium, but leaving 10 mM-DFMO, resulted in an about 10-fold ODC gene amplification within a few weeks. The accumulation of ODC mRNA was enhanced by the same factor. Concomitantly, the content of the natural polyamines was almost normalized, representing about 65% of that found in the parental cells. The present results suggest that, under a given selection pressure, an overproduction of the target gene product may be primarily based on an enhanced transcriptional activity, possibly associated with hypomethylation and, if not sufficient, a secondary amplification of the active gene occurs.

Mouse and human ornithine decarboxylase genes. Methylation polymorphism and amplification

With the use of the isoschizomeric restriction endonucleases HpaII and MspI, we found that mouse tumour ornithine decarboxylase (ODC; EC 4.1.1.17) genes are extensively methylated. ODC genes in L1210 mouse leukaemia cells were apparently more methylated than in Ehrlich ascites carcinoma, as revealed by the use of HpaII endonuclease, yet the digestion of genomic DNA isolated from these two murine tumour cell lines with MspI, which cleaves at a CCGG sequence, also with internally methylated cytosine, resulted in an apparently identical restriction pattern. It is possible that the amplification of ODC genes in Ehrlich ascites-carcinoma cells in response to 2-difluoromethylornithine (DFMO) was associated with hypomethylation, or that less-methylated genes were amplified. A human myeloma (Sultan) cell line only revealed three separate hybridization signals when cleaved with HpaII. One of these signals was amplified under the pressure of DFMO. When cleaved with MspI, these three HpaII fragments disappeared and were replaced by a double signal of 2.3-2.4 kilobase-pairs (kbp) in size. The amplified ODC sequences in the Sultan myeloma cell line apparently originated from chromosome 2, as indicated by a unique hybridization signal in a 5.8 kbp HindIII fragment specific for the human ODC locus on chromosome 2. A comparison of different human cells, the Sultan myeloma, a lymphocytic B-cell leukaemia (Ball), normal mononuclear leucocytes and leucocytes obtained from leukaemia patients, revealed interesting differences in the methylation of ODC genes. The use of two restriction endonucleases (HpaII and CfoI), the cleavage site for both of which contains a CG sequence and which only cleave when cytosine is unmethylated, indicated that ODC genes in the lymphocytic leukaemia cells were much less methylated than those in the normal leucocytes or in the Sultan cells.

Human myeloma cells acquire resistance to difluoromethylornithine by amplification of ornithine decarboxylase gene

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.

Posttranscriptional regulation of ornithine decarboxylase activity

We have used a Chinese hamster ovary cell line (DF3) that overproduces ornithine decarboxylase (ODC) to examine various parameters in the cell cycle-dependent regulation of this enzyme. Under a variety of conditions, alterations in the activity of ODC were accompanied by parallel changes in the levels of the protein, as measured by immunologically cross-reactive material (CRM). While putrescine has been known to suppress the induction of ODC, we have found that in DF3 cells 10(-4)M ornithine completely suppresses ODC activity. We also show that the levels of ODC mRNA are not modulated when the levels of ODC activity and CRM change drastically. The data can be interpreted in terms of models involving either an effect of putrescine on the translation of ODC mRNA, or on the activity of a relatively specific protease with ODC as its target.

Two ornithine decarboxylase mRNA species in mouse kidney arise from size heterogeneity at their 3' termini

Ornithine decarboxylase (OrnDCase; L-ornithine carboxy-lyase, EC 4.1.1.17) mRNA present in mouse kidney comprises two species with molecular sizes of approximately 2.2 and approximately 2.7 kilobases (kb). cDNA clones prepared from murine kidney OrnDCase mRNA were used to determine the reason for the size heterogeneity of these mRNAs. Two of the cDNA clones (pODC16 and pODC74) that differed at the 3' termini were isolated and sequenced. DNA sequencing indicated that each cDNA had a poly(A) tail; however, pODC74 was 429 nucleotides longer than pODC16 at the 3' end and contained two AATAAA signals for poly(A) addition. That the longer cDNA corresponded to the larger mRNA was confirmed by hybridization of a unique Pst I/Pst I fragment from the 3' terminus of pODC74 only to the 2.7-kb OrnDCase mRNA. The two cDNAs did not represent full-length copies of OrnDCase mRNAs and were 1199 (pODC16) and 1204 base pairs (bp) (pODC74) long. There were five mismatches in their 759-bp-long overlapping nucleotide sequence, suggesting that the 2.2- and 2.7-kb OrnDCase mRNAs may be products of two separate, yet very similar, OrnDCase genes. Androgen regulation of the accumulation of these two OrnDCase mRNAs appeared to occur coordinately, as testosterone administration brought about comparable increases in their concentrations in mouse kidney.

Gene expression of ornithine decarboxylase in L1210 leukaemia cells exposed to DL-2-difluoromethylornithine in the presence of cadaverine

Cultured mouse L1210 leukaemia cells treated with DL-2-difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase (EC 4.1.1.17), in the presence of micromolar concentrations of cadaverine, started to overproduce ornithine decarboxylase after an exposure of several weeks. The more than 60-fold excess of the enzyme protein in the drug-treated cells apparently resulted from a strikingly enhanced accumulation of mRNA for the enzyme associated with only a modest (about 2-fold) gene amplification.

Effects of bis(guanylhydrazones) on the activity and expression of ornithine decarboxylase

Derivatives of glyoxal bis(guanylhydrazone) (GBG), such as methylglyoxal bis(guanylhydrazone) and ethylglyoxal bis(guanylhydrazone), are potent inhibitors of S-adenosylmethionine decarboxylase (EC 4.1.1.50), the key enzyme required for the synthesis of spermidine and spermine. These compounds, but not the parent compound, induce a massive accumulation of putrescine, partly by blocking the conversion of putrescine into spermidine, but also by strikingly stimulating ornithine decarboxylase (ODC; EC 4.1.1.17) activity. The mechanism of the stimulation of ODC activity and enhanced accumulation of the enzyme protein apparently involved a distinct stabilization of the enzyme against intracellular degradation. However, although the parent compound GBG also stabilized ODC, it powerfully inhibited the enzyme activity and the accumulation of immunoreactive protein in cultured L1210 leukaemia cells. Kinetic considerations indicated that, in addition to the stabilization, all three compounds, GBG in particular, inhibited the expression of ODC. It is unlikely that the decreased rate of synthesis of ODC was attributable to almost unaltered amounts of mRNA in drug-treated cells, thus supporting the view that especially GBG apparently depressed the expression of ODC at some post-transcriptional level.

Mutant strain of Chinese hamster ovary cells with no detectable ornithine decarboxylase activity

We previously described an arginase-deficient, polyamine-dependent Chinese hamster ovary cell line which grows in serum-free medium. From this strain we isolated a new mutant strain that has no detectable catalytic ornithine decarboxylase activity. The mutant cells contain, however, immunoreactive ornithine decarboxylase-like protein roughly in the same quantity as the parent strain. The mutant and the parent cell line strains also contain similar amounts of ornithine decarboxylase-mRNA hybridizable to a specific cDNA. If polyamines are omitted from the medium, proliferation of the mutant cells is considerably retarded and ceases in 6 to 10 days. Addition of ornithine or alpha-difluoromethylornithine, a specific inhibitor of ornithine decarboxylase, has no effect on these cells. Putrescine and spermidine decreased in the mutant cells to undetectable levels during polyamine starvation, whereas spermine was reduced to 1/5th of that found in the control cultures. Polyamines appear to be indispensable for the mutant strain, but this was obvious only after the amount of polyamines, found as impurities in bovine serum albumin used in the medium, was reduced by dialysis to 10(-12) M. Because sera contain polyamines, the ability of the mutant strain to grow in serum-free medium is a great advantage in elucidation of the mechanisms of polyamine function.

Tumourigenicity, cell-surface glycoprotein changes and ornithine decarboxylase gene pattern in Ehrlich ascites-carcinoma cells

We selected a 2-difluoromethylornithine-resistant Ehrlich ascites-carcinoma cell line that grows in the presence of 20 mM-difluoromethylornithine. These cells contain 10-20 times the normal amount of hybridizable sequences for ornithine decarboxylase (EC 4.1.1.17) in their genomic DNA. We used these gene-amplified cells, their revertant counterparts (grown in the absence of the drug after an established gene amplification) and tumour cells grown in the presence of putrescine to investigate the changes of ornithine decarboxylase gene pattern and simultaneously occurring phenotypic changes, such as tumourigenicity and the expression of cell-surface glycoproteins. In the tumour cells reverted back to the normal gene frequency, not only did the amplified sequences disappear, but there were also signs of gene re-arrangements seen as a "gene jump', when a signal evidently moved to a heavier restriction fragment. Similar gene re-arrangement likewise occurred in cells exposed to putrescine. Although the wild-type tumour cells and the gene-amplified cells readily grew in the peritoneal cavity of mice, the revertant cells and the putrescine-treated cells had lost their tumourigenicity in mice. Gene-amplified tumour cells and the revertant cells showed distinct changes in their surface glycoprotein pattern in comparison with the parental cell line. These findings indicate that alterations of ornithine decarboxylase gene pattern/dosage may be associated with phenotypic changes possibly related to the tumourigenicity of these carcinoma cells.

Mutant strain of Chinese hamster ovary cells with no detectable ornithine decarboxylase activity

We previously described an arginase-deficient, polyamine-dependent Chinese hamster ovary cell line which grows in serum-free medium. From this strain we isolated a new mutant strain that has no detectable catalytic ornithine decarboxylase activity. The mutant cells contain, however, immunoreactive ornithine decarboxylase-like protein roughly in the same quantity as the parent strain. The mutant and the parent cell line strains also contain similar amounts of ornithine decarboxylase-mRNA hybridizable to a specific cDNA. If polyamines are omitted from the medium, proliferation of the mutant cells is considerably retarded and ceases in 6 to 10 days. Addition of ornithine or alpha-difluoromethylornithine, a specific inhibitor of ornithine decarboxylase, has no effect on these cells. Putrescine and spermidine decreased in the mutant cells to undetectable levels during polyamine starvation, whereas spermine was reduced to 1/5th of that found in the control cultures. Polyamines appear to be indispensable for the mutant strain, but this was obvious only after the amount of polyamines, found as impurities in bovine serum albumin used in the medium, was reduced by dialysis to 10(-12) M. Because sera contain polyamines, the ability of the mutant strain to grow in serum-free medium is a great advantage in elucidation of the mechanisms of polyamine function.