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

Ornithine decarboxylase mRNA expression in curatively resected non-small-cell lung cancer

BACKGROUND

The effect of ornithine decarboxylase (ODC) on the pathogenesis of non-small-cell lung cancer (NSCLC) remains poorly investigated. Hence, the aim of this study was to explore the potential role of ODC mRNA expression as a prognostic biomarker in patients with curatively resected NSCLC.

PATIENTS AND METHODS

A total of 91 tumor and matching nontumorous lung tissue samples from patients with NSCLC were analyzed using a quantitative real-time reverse-transcriptase polymerase chain reaction method. The relative ODC mRNA expression was measured in tumorous and nontumorous lung tissue using beta-actin as a reference gene. Squamous cell carcinoma was found in 43 patients (47%), adenocarcinoma in 33 (36%), and large-cell carcinoma in 15 of the patients (17%). All patients' disease was R0 resected.

RESULTS

Ornithine decarboxylase was detected in all 91 tumor and nontumorous lung tissue samples. The median tumorous expression of 9.11 (range, 0.92-155.35) was significantly elevated compared with the median ODC expression of 7.89 (range, 0.0-45.8) in nontumorous lung tissue. Ornithine decarboxylase expression levels were not associated with any clinicopathologic parameters. Using an ODC/beta-actin ratio of 10 as a cutoff, tumorous ODC (tODC) expression is a significant prognostic factor in NSCLC. The ODC ratio between tumorous and nontumorous expression was even more prognostic. Moreover, Cox proportional hazards model analysis showed ODC expression to be an independent prognostic factor.

CONCLUSION

In this study, ODC is shown to have a prognostic potential in NSCLC. Low levels of tODC expression are associated with a more aggressive tumor biology. Also, an increase of ODC mRNA expression during carcinogenesis seems to have a favorable prognostic effect. Measuring the ODC expression in patients with NSCLC could aid in further chemotherapy decisions. Our results suggest that further investigation of ODC mRNA expression in NSCLC may be warranted.

Interaction of N1,N12-diacetylspermine with polyamine transport systems of polarized porcine renal cell line LLC-PK1

LLC-PK(1) cells grown on porous membrane filters were employed as a model system to explore the renal transport of polyamines. The polarity of LLC-PK(1) monolayers was confirmed by the exclusive appearance of a Na(+)-dependent alpha-methylglucoside transport system on the apical surface. The uptake of free polyamines from the basolateral side of monolayers was consistent with the existence of a single class of transport system, while the existence of two kinetically distinct polyamine transport systems with higher and lower affinities on apical membranes was suggested. The results of competition studies indicated that each of these transporters was able to interact with putrescine, spermidine and spermine. LLC-PK(1) cells incorporated monoacetylspermine from the apical surface of monolayers at about half the rate of spermine uptake. Monoacetylspermine inhibited spermidine uptake, indicating that free polyamine transport systems also recognized the monoacetylated derivative. In contrast, N(1),N(12)-diacetylspermine did not inhibit spermidine uptake, nor was it incorporated into the cells, indicating the absence of transport systems that recognize N(1),N(12)-diacetylspermine on the apical membranes of LLC-PK(1) cells. These results may be relevant as to our previous observation that the content of diacetylpolyamines in urine is relatively constant, and may explain the excellence of N(1),N(12)-diacetylspermine as a tumor marker.

Evaluation of the potential of cancer chemopreventive activity mediated by inhibition of 12-O-tetradecanoyl phorbol 13-acetate-induced ornithine decarboxylase activity

In order to discover new cancer chemopreventive agents from natural or synthetic products, a structurally diverse class of chemopreventive agents was evaluated using in vitro biomarker of inhibition of 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced ornithine decarboxylase (ODC) activity in cultured mouse epidermal 308 (ME 308) cells. As a result, apigenin, benzylisothiocyanate, curcumin, diallyl disulfide, N-(4-hydroxyphenyl)retinamide (4-HPR), menadione, miconazole, nordihydroguaiaretic acid (NDGA) and phenethyl isothiocyanate showed potent inhibitory effects in this process. A chemically diverse group of compounds was included in the evaluation, such as flavonoids, retinoids, isothiocyanates, sulfur-containing compounds and phenolic antioxidant compounds. These data are suggestive to understand the cancer chemopreventive potential mediated by these substances.

Induction of spermidine/spermine N1-acetyltransferase by interferon type I in cells of hematopoietic origin

A number of novel genes activated by type I interferons (IFNs) were identified by differential display. Of five induced genes examined, four were of unknown function. However, one gene sequence was identical to the human spermidine/spermine N1-acetyltransferase, the rate-limiting enzyme in polyamine catabolism. This enzyme was induced by type I IFNs in a series of hematopoietic cell lines, including Daudi, HL-60, HPBMa, and Wil-2. No induction above constitutive levels occurred in a cell line of epithelial (ME180) or liver (HepG2) origin following treatment with type I IFN. Spermidine/spermine N1-acetyltransferase was not induced by IFN-gamma in Daudi or ME180 cells. That induction occurred not only at the level of transcription but also at the enzyme level was confirmed by direct enzyme assays. As the levels of polyamines are related to cell viability, we propose that induction of this enzyme by IFN may be directly related to the anti-proliferative response to type I IFNs.

Analysis of ornithine decarboxylase messenger ribonucleic acid expression in colorectal carcinoma

PURPOSE

Ornithine decarboxylase (ODC) is a rate-limiting enzyme for polyamine synthesis. An elevated protein level of ODC was observed in the tumors. There has been, however, little information reported so far on the expression of ODC messenger ribonucleic acid (mRNA) in clinical colorectal carcinomas. In vitro studies disclosed that the transcriptions of the ODC gene is regulated by the c-myc gene.

METHODS

The expression of ODC and c-myc mRNA in biopsy specimens obtained from both tumor tissue and the corresponding normal tissue was examined by the reverse transcriptase polymerase chain reaction method in 40 cases of colorectal carcinoma.

RESULTS

The expression of ODC mRNA was observed in both tumor tissue and normal tissue. The tumor to normal ratio of ODC mRNA was higher in cases with deeply invasive tumors than in cases with shallow tumors, and it was also higher in Dukes B or C cases than in Dukes A cases. There was a significant correlation between the tumor to normal ratio of c-myc mRNA and that of ODC mRNA in each case.

CONCLUSIONS

These findings suggested that 1) the study of the expression of ODC mRNA may be useful for preoperatively predicting more advanced disease of colon carcinoma, and 2) there was a significant correlation between expression of ODC and c-myc mRNA in the clinical samples, which was similar to the findings of a previous in vitro study.

Ethanol inhibits human osteoblastic cell proliferation

The habitual consumption of alcoholic beverages is clearly associated with low bone mass and an increased prevalence of skeletal fractures. Microscopic analysis of skeletal tissue from alcoholic patients reveals reduced osteoblast number and suppressed bone formation activity with a relative sparing of resorptive indices. The decreased number of osteoblasts observed in alcoholic subjects results from either impaired proliferation or accelerated senescence. Polyamines and ornithine decarboxylase (ODC), the rate-limiting enzyme for polyamine synthesis, are essential for cell proliferation in a variety of cell types. To determine if the adverse effect of ethanol on osteoblast number involves modulation of polyamine biosynthesis, we examined the effect of ethanol on parameters of cell growth and ODC activity in a human osteoblast-like osteosarcoma cell line (TE-85). Ethanol markedly impaired DNA synthesis and cell proliferation in a dose-dependent fashion, but alkaline phosphatase activity (a marker of differentiated osteoblast function) remained intact, and accelerated apoptosis was not evident. Thus, the reduced osteoblastic cell number was a result of a direct effect on proliferative processes rather than a nonspecific toxic effect of ethanol to accelerate cell death. Induction of ODC activity was impaired in ethanol-exposed cell cultures in a dose-dependent fashion that paralleled the antiproliferative effects. Finally, supplemental polyamine administration substantially improved DNA synthesis in ethanol-exposed UMR 106-01 cell cultures. These data confirm a direct inhibitory effect of ethanol on osteoblast proliferation without overt cellular toxicity that may, in part, explain the reduced bone mass observed in those who consume excessive amounts of alcohol.

Phosphorylation of Okazaki-like DNA fragments in mammalian cells and role of polyamines in the processing of this DNA

In mammalian cells DNA synthesis is more complicated than in prokaryotes and less well understood. Here we incubated intact mammalian cells (polyamine auxotrophic Chinese hamster ovary cells and primary human fibroblasts) with [32P]orthophosphate and found that, besides high molecular weight DNA, a species of low molecular weight DNA, approximately 450 bp in size, became efficiently labeled. The short DNA was labeled first, and in pulse-chase experiments the labeling was transient. The isolated small DNA fragments (RNase A-treated) were phosphorylated by T4 polynucleotide kinase specific for polynucleotides with 5'-OH ends. A polynucleotide kinase phosphorylating these DNA pieces was also detected in nuclear extracts of the cells. Treatment with alkaline phosphatase removed most of the 32P label incorporated into the small DNA in vivo. Labeling with deoxyribonucleosides did not reveal these fragments. We hypothesize that the low molecular weight DNA represents Okazaki fragments and that the mammalian DNA replication machinery includes a polynucleotide kinase phosphorylating the 5'-termini of Okazaki fragments. This would imply a novel step in DNA synthesis. We also show that depriving cells of polyamines reversibly blocks synthesis of high molecular weight DNA and leads to accumulation of the short DNA pieces, suggesting a role for polyamines in joining the Okazaki fragments.

The ornithine decarboxylase gene of Caenorhabditis elegans: cloning, mapping and mutagenesis

The gene (odc-1) encoding ornithine decarboxylase, a key enzyme in polyamine biosynthesis, was cloned and characterized. Two introns interrupt the coding sequence of the gene. The deduced protein contains 422 amino acids and is homologous to ornithine decarboxylases of other eukaryotic species. In vitro translation of a transcript of the cDNA yielded an enzymatically active product. The mRNA is 1.5 kb in size and is formed by trans-splicing to SL1, a common 5' RNA segment. odc-1 maps to the middle of LG V, between dpy-11 and unc-42 and near a breakpoint of the nDf32 deficiency strain. Enzymatic activity is low in starved stage 1 (L1) larva and, after feeding, rises progressively as the worms develop. Targeted gene disruption was used to create a null allele. Homozygous mutants are normally viable and show no apparent defects, with the exception of a somewhat reduced brood size. In vitro assays for ornithine decarboxylase activity, however, show no detectable enzymatic activity, suggesting that ornithine decarboxylase is dispensible for nematode growth in the laboratory.

Flow cytometric analysis of the cell cycle in polyamine-depleted cells

Polyamines are found in all cells but their function is not fully understood. We have studied the effect of polyamines on the passage of cells through the cell cycle using a polyamine auxotrophic mutant, CHO-P22, which has no detectable ornithine decarboxylase activity. The ability of these cells to grow without serum allows efficient polyamine depletion. A flow cytometric analysis of DNA content and bromodeoxyuridine labeling showed that without added polyamines the cells accumulated in S-phase, the rate of DNA synthesis was retarded, and the entry into mitosis was blocked. Addition of polyamines to cultures deprived of polyamines induced cells in all phases of the cell cycle to reinitiate cycling. Earlier studies have shown that cells with damaged DNA are blocked from entering into mitosis but caffeine can partly overcome this block and induce premature chromosome condensation. Polyamine-depleted CHO-P22 cells responded to caffeine in the same way as cells with damaged DNA. These results show that polyamine depletion in CHO-P22 cells primarily affects DNA synthesis. The finding that polyamine-starved cells continuously take up bromodeoxyuridine without a corresponding increase in the amount of DNA is compatible with extensive repair of erroneous and/or damaged DNA. Polyamine auxotrophic Chinese hamster ovary (CHO) cells might be useful in studies on the regulation of mitosis in mammalian cells.

Prostaglandin E2/parathyroid hormone-induced suppression of alkaline phosphatase activity is mediated by protein kinase C

1. Bone resorptive factors, prostaglandin E2 and parathyroid hormone are shown to suppress alkaline phosphatase activity in a rat osteoblastic cell line. 2. Phorbol myristate acetate, but not dibutyryl cAMP or calcium ionophore can suppress alkaline phosphatase activity. 3. The protein kinase C inhibitors (H89, staurosporine) are able to block the suppression of alkaline phosphatase activity induced by prostaglandin E2 and parathyroid hormone. 4. These data suggest that protein kinase C is involved in the inhibition of alkaline phosphatase activity induced by prostaglandin E2 and parathyroid hormone.

Expression of high activity of ornithine decarboxylase and occurrence of unusual chromophobic cells in anterior pituitary gland of a novel growth-retarded strain of mice, grm/grm

Extremely high activity of ornithine decarboxylase (ODC) was detected in the pituitary gland of growth-retarded mice, grm/grm at 2 months after birth. The elevated enzyme activity gradually decreased to the control level in 14 months after birth. In the pituitary gland of the growth-retarded mice, unusual chromophobic cells were also present from the early stages after birth. The chromophobic cells showed conspicuous proliferations and resulted in a distinct hyperplasia of the tissue after 4 months after birth. These findings suggest that ODC is correlated to the progressive transformation of pituitary cells into the chromophobic cells.

Consequences of aberrant ornithine decarboxylase regulation in rat hepatoma cells

DH23A cells, an alpha-difluoromethylornithine (DFMO)-resistant variant of rat hepatoma tissue culture cells (HTC), contain high levels of very stable ornithine decarboxylase (ODC). In the absence of DFMO, the high ODC activity results in a large accumulation of endogenous putrescine. Concomitant with the putrescine increase is a period of cytostasis and a subsequent loss of viable cells. In contrast, HTC cells with a moderate polyamine content can be maintained in exponential growth. This suggests that a moderate polyamine concentration is necessary for both optimal cell growth and survival. The cytotoxicity observed in the DH23A cells is apparently not due to byproducts of polyamine oxidation or alterations in steady state intracellular pH or free [Ca2+]. It is possible to mimic the effects of high levels of stable ODC by treatment of cells with exogenous putrescine in the presence of DFMO. This suggests that overaccumulation of putrescine is the causative agent in the observed cytotoxicity, although the mechanism is unclear. These data support the hypothesis that downregulation of ODC may be necessary to prevent accumulation of cytotoxic concentrations of the polyamines.

Gly387 of murine ornithine decarboxylase is essential for the formation of stable homodimers

In its active form mammalian ornithine decarboxylase (ODC) is a homodimer composed of two 53-kDa subunits while the monomer retains no enzymic activity. In the present study we demonstrate that Gly387 of mouse ODC plays an important role in enabling dimer formation. Gly387 of mouse ODC, an evolutionary conserved residue, was converted to all possible 19 amino acids using site-directed mutagenesis. With the exception of alanine, all other substitutions of Gly387 completely abolished enzymic activity. Cross-linking analysis and fractionation through a Superose-12 sizing column have demonstrated that mutant subunits are detected only in their monomeric form. These results strongly suggest that the primary lesion of substitution at position 387 of mouse ODC is the inability of mutant subunits to associate with each other to form the active homodimers. In agreement with this conclusion, G387A, the only mutant that retained partial activity, displayed reduced dimerization. The degradation rate of ODC mutants in which Gly387 was substituted by aspartic acid or alanine was enhanced compared to the wild-type enzyme, suggesting that monomers may be more susceptible to degradation.

Isolation and characterization of the Drosophila ornithine decarboxylase locus: evidence for the presence of two transcribed ODC genes in the Drosophila genome

The polymerase chain reaction (PCR) was used to isolate two Drosophila ornithine decarboxylase (ODC) genes. Two mixtures of degenerate oligonucleotides corresponding to peptides that are fully conserved among ODCs from widely diverged species were used as opposing primers in the PCR with cDNA or genomic DNA as templates. Sequence analysis of the resulting DNA products confirmed their identity as ODC fragments. The genomic PCR product was then used as a probe for screening a Drosophila genomic library, resulting in the isolation of genomic clones representing two distinct ODC genes (dODC1 and dODC2). Sequence analysis of both genes demonstrated that although varying at their coding and noncoding regions, their overall structure is extremely similar containing 6 exons and 5 short introns. Southern blot and sequence analyses revealed that the two ODC genes are arranged in a tandem head-to-tail configuration. Both ODC genes were assigned by in situ hybridization analysis to position 44A on the right arm of the second chromosome. The isolation of cDNA clones corresponding to these two ODC genes demonstrated that both are transcribed in the adult fly. We hope that the isolation of genomic and cDNA clones of Drosophila ODC will permit the investigation of the expression of ODC during Drosophila development and the role of polyamines in this process.

Regulation of ovarian ornithine decarboxylase activity and its mRNA by gonadotropins in the immature rat

Previous studies have demonstrated that gonadotropin increases ornithine decarboxylase (ODC) activity in the rat ovary. The increase of ODC activity following gonadotropin stimulation is localized primarily to proliferating granulosa cells. The present studies were undertaken to characterize the mechanism of this hormone-induced increase of ODC. A single intraperitoneal injection of PMSG resulted in a 15-fold increase in ODC activity (p < 0.0001). Activity was maximal 1 day following PMSG administration, and thereafter declined with time. PMSG also induced an increase in ODC mRNA levels (p < 0.0001). However, ODC mRNA increased only 2-fold, as compared with a 15-fold increase in ODC activity. Actin mRNA levels were unaffected by PMSG. These results demonstrate that PMSG-induced increase in ODC activity cannot be fully explained by an increase in ODC mRNA, thus indicating that part of the regulation of ODC by PMSG is occurring at the translational and/or posttranslational level. Such regulation is likely a necessary dimension of the fine control of the levels/activity of this important enzyme which has a very short half-life.

Involvement of the 20S proteasome in the degradation of ornithine decarboxylase

Eukaryotic cells have been shown to contain two high-molecular-mass proteases of 700 kDa and 1400 kDa (20S and 26S proteases, respectively). It has been suggested that the 20S protease, also known as proteasome, may constitute the catalytic core of the 26S protease. While the role of the free 20S protease in intracellular protein degradation is unclear, the 26S protease is implicated in the degradation of ubiquinated proteins. We have recently demonstrated, that ornithine decarboxylase (ODC), one of the most labile proteins in mammalian cells, is degraded via an ATP-dependent but ubiquitin-independent proteolytic pathway. Here we extend these observations by demonstrating that in reticulocyte lysate ODC degradation is inhibited by antibodies raised against the C9 subunit of rat proteasome. Partial fractionation of the lysate demonstrated preferential degradation of ODC in the fraction of the lysate proteins that are precipitated by 38% ammonium sulfate. Since it was demonstrated that the 26S protease precipitates at this concentration of ammonium sulfate while the 20S proteasome remains soluble, our results suggest that the 26S protease is the one degrading ODC.

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.

Mouse ornithine decarboxylase is phosphorylated by casein kinase-II at a predominant single location (serine 303)

Ornithine decarboxylase (ODC), a key enzyme in the biosynthetic pathway of polyamines in mammalian cells is characterized by an extremely short half-life and by a rapid induction following stimulation with growth-promoting agents. Inspection of its deduced amino acid sequence revealed the presence of sequences that may serve as targets for phosphorylation by casein kinase II (CK-II). In the present study we demonstrate that ODC serves as a substrate for phosphorylation by CK-II in vitro and that it is phosphorylated in intact mammalian cells. One-dimensional phosphopeptide analysis demonstrated that all the phosphopeptides generated by V8 protease digestion of in vivo phosphorylated ODC correspond to the major phosphopeptides of ODC phosphorylated in vitro by CK-II. Phosphopeptide analysis of wild-type ODC and of a mutant in which serine 303 was converted to alanine demonstrated that the latter lacks the phosphopeptides that correspond to those detected in ODC phosphorylated in vivo. In addition, no incorporation of phosphate into the alanine 303 mutant was observed when it was expressed in transfected cos cells. Based on these observations, we conclude that in mammalian cells serine 303 is the major (if not the only) phosphorylated residue of ODC and that CK-II or another cellular kinase with very similar sequence specificity is responsible for manifestation of this modification. The unphosphorylated alanine 303 mutant retained enzymatic activity, which decayed at a similar rate to that of the wild-type enzyme. We therefore conclude that phosphorylation is not essential for maintaining enzymatic activity or regulating ODC turnover.

The regulation of G0-S transition in mouse T lymphocytes by polyamines

While the role of polyamines in DNA synthesis during the S phase of the cell cycle has been repeatedly postulated, recent studies point also to polyamine involvement in the early phase of the G0-S transition. In order to determine polyamine-dependent steps in the cell cycle we have studied the effects of inhibitors of polyamine biosynthesis and exogenous polyamines on the proliferation of T lymphocytes as well as on the expression of some growth-regulated genes. The ability of Con A-stimulated mouse T lymphocytes to enter DNA synthesis was markedly inhibited by methylglyoxal bis(guanylhydrazone) in a dose-dependent manner. This inhibitory effect was stronger in the presence of fetal calf serum containing a high level of activities of polyamine oxidases than in the presence of horse serum. Putrescine and spermine added to T splenocyte culture instead of mitogen-Con A stimulated [3H]thymidine incorporation with kinetics similar to that observed with Con A. The growth-stimulating effects of polyamines were concentration-dependent. Polyamines at optimal growth-stimulating concentrations (10 microM spermine and 80 microM putrescine) induced the expression of genes encoding the cytoskeletal proteins beta-actin, vimentin, and alpha-tubulin to an extent and with kinetics similar to those of Con A. The results presented herein suggest that polyamines are capable of stimulating the transition of G0 cells to the S phase and that this effect may be mediated by their influence on the gene expression.

Mammalian drug resistant mutants with multiple gene amplifications: genes encoding the M1 component of ribonucleotide reductase, the M2 component of ribonucleotide reductase, ornithine decarboxylase, p5-8, the H-subunit of ferritin and the L-subunit of ferritin

Hydroxyurea was used to select two very highly drug resistant cell lines, designated HR-15 and HR-30. Both drug resistant lines contained elevated levels of ribonucleotide reductase activity. Northern and Southern blot analysis indicated that the two drug resistant lines contained increased levels of mRNA for the two components, M1 and M2, of ribonucleotide reductase, and M1 and M2 gene amplifications. Alterations in M1 and M2 protein levels were also evident in Western blot analysis. Further studies of HR-15 and HR-30 cells by Northern and Southern blot analysis showed that the drug resistant cell lines had elevated levels of ornithine decarboxylase mRNA and p5-8 mRNA, as well as increased ornithine decarboxylase and p5-8 gene copy numbers, respectively. Furthermore, characterization of HR-15 and HR-30 drug-resistant cell lines revealed increased mRNA levels for both H- and L-ferritin. Both cell lines exhibited by Southern blot analysis, amplification of the H- and L-ferritin genes. Increases in the cellular levels of H- and L-ferritin subunit proteins were also observed in both HR-15 and HR-30 cells, by Western blot analysis. This is the first description of mutant cell lines containing this complex combination of modified gene expressions and gene amplifications. The alterations exhibited by these lines confirm and extend present models of hydroxyurea resistance, are in agreement with and help substantiate models of ribonucleotide reductase regulation and provide interesting links between the expressions of several cellular activities important in proliferation.

Human ornithine decarboxylase-encoding loci: nucleotide sequence of the expressed gene and characterization of a pseudogene

Previous studies have shown that human ornithine decarboxylase (ODC)-encoding sequences map to two chromosome regions: 2pter-p23 and 7cen-qter. In the present work we have cloned the expressed human ODC gene from a genomic library of myeloma cells that overproduce ODC protein due to selective gene amplification and determined its entire nucleotide sequence. The gene comprises 12 exons and 11 introns and spans about 8 kb of chromosome 2 DNA. The organization of the human gene is very similar to that of the mouse and rat, with the major difference being the presence of longer intronic sequences in the human gene. Some of these differences can be accounted for by the insertion of four Alu sequences in the human gene. Several potential regulatory elements are present in the promoter region and in 5'-proximal introns, including a TATA box; GC boses; AP-1-, AP-2- and NF-1-binding sites; and a cAMP-responsive element. The 5'-untranslated sequence of ODC mRNA is extremely GC-rich, and computer predictions suggest a very stable secondary structure for this region, with an overall free energy of formation of -225.4 kcal/mol. In addition to the active ODC gene on chromosome 2, ODC gene-related sequences were isolated from human chromosome 7-specific libraries and shown to represent a processed ODC pseudogene.

Accumulation of ornithine decarboxylase mRNA accompanies activation of human and mouse monocytes/macrophages

Accumulation of ornithine decarboxylase (ODC) mRNA was investigated in human monocytes and mouse peritoneal macrophages. Treatment of both populations of mononuclear phagocytes with bacterial lipopolysaccharide induced a marked and rapid increase in the accumulation of the ODC gene transcript. A similar phenomenon, albeit less pronounced, was also observed following treatment of human monocytes with human recombinant interferon-gamma. These results suggest a role for ODC, and therefore polyamines, in the regulation of mononuclear phagocyte functions.

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.

Molecular biology of cell activation

This article summarizes common features of activation of different types of cells along different physiological lines such as proliferation, differentiation, and execution of function of terminally differentiated cells. The common basis of many of these phenomena includes (i) first messengers (growth factors, cytokines, neurotransmitters, etc.) acting on membrane receptors, (ii) second messengers (cAMP, IP3, DAG, Ca2+) spreading an activating signal inside the cell, and (iii) elevated expression of some genes (c-fos, c-myc, ornithine decarboxylase). The role of the genetic correlate in cell activation is emphasized, and it is concluded that the aforementioned genes (their protein products) should be called third messengers, whose function is mediation of long-term phenotypic changes.

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.

Polyamine depletion of cells reduces the infectivity of herpes simplex virus but not the infectivity of Sindbis virus

The effect of polyamines on the viral growth was examined using cell strains that could be effectively depleted of polyamines. In order to avoid the polyamines present in serum we used a polyamine auxotrophic Chinese hamster ovary cell line P22 growing in serum-free medium and Vero cells growing in low serum medium. The final yield of an enveloped RNA virus, Sindbis, in P22 cells was not decreased by depletion of cellular polyamines although the onset of the viral replication was delayed. In contrast the final yield of an enveloped DNA virus, Herpes simplex virus (HSV), was considerably reduced in Vero cells, depleted of polyamines by alpha-difluoromethylornithine, an inhibitor of polyamine synthesis. However, the number of HSV particles detected by electronmicroscopy was not decreased. Southern blot analysis of HSV-DNA from the polyamine depleted and the control cells showed changes in the relative abundance of the DNA fragments suggesting that impairment in DNA synthesis may have caused the decreased infectivity of HSV.

Cell-cycle-dependent expression of human ornithine decarboxylase

A human ornithine decarboxylase (ODC) gene probe has been isolated from a Jurkat T-cell cDNA expression library, sequenced, and used to analyze ODC mRNA levels in untransformed human lymphocytes and fibroblasts stimulated to proliferate by various mitogens. The partial cDNA sequence is 86% homologous to the mouse ODC cDNA, and Northern blots indicate that the human and mouse mRNA species are similar in size. ODC mRNA is barely detectable in quiescent human T lymphocytes and undetectable in density-arrested W138 fibroblasts. Following stimulation of T-lymphocyte proliferation with phytohemagglutinin, the ODC mRNA level rises to a peak around mid G1 phase and decreases as the cells enter S phase. Serum stimulation of density-arrested fibroblasts results in an elevation of the ODC mRNA level which persists throughout the cell cycle. Epidermal growth factor (20 ng/ml) but not insulin (10 mg/ml) or dexamethasone (55 ng/ml) stimulates ODC expression in quiescent W138 fibroblasts. Southern blots suggest that human cells have a single copy of the ODC gene.

Alterations in amounts and covalent modifications of low-molecular-weight chromosomal proteins in Chinese hamster ovary cells during polyamine depletion

The effect of polyamine depletion on phosphorylation and ADP-ribosylation of low-Mr chromosomal proteins was studied in intact, mutant Chinese hamster ovary cells (CHO-P22) devoid of ornithine decarboxylase activity. When starved of polyamines for 6 days, severe polyamine deficiency develops and the cells gradually stop growing. The rate of DNA synthesis was retarded to 16% of the control value and to 29% in density-inhibited cells. The synthesis of high-mobility-group (HMG) proteins was decreased by 65% in polyamine-depleted cells and by 40% in density-inhibited cells. The synthesis of core histones was decreased by 40% both in polyamine-depleted and density-inhibited cells. In polyamine-depleted cells the molar ratio of the higher-Mr HMG proteins (HMG 1 + 2) to the lower-Mr HMG proteins (HMG 14 + P) was about one-half of that found in cells grown in the presence of putrescine or in density-inhibited cells. In contrast to HMG proteins, no major differences were found in the content of core histones in these cell populations. In the perchloric acid-soluble fraction of nuclear proteins, 32P was incorporated mainly into histone H1, HMG P and a protein migrating more slowly than HMG 1 (protein P1). Specific changes in the 32P-labeling and migration of a number of protein bands, including histone H1, was observed in polyamine-depleted cells as compared to cells grown in the presence of putrescine or to density-inhibited cells. ADP-ribosylation experiments using [3H]adenosine showed a different pattern of label distribution; the higher-Mr HMG proteins from polyamine-depleted cells contained about one-half the amount of label found in the proteins from control cells. The lower-Mr HMG proteins and histone H1 were the preferentially labeled proteins in polyamine-depleted cells. Labeling of core histones with [32P]orthophosphate or [3H]adenosine did not differ markedly in the two cell populations. The results obtained using intact polyamine auxotrophic cells indicated that polyamine depletion is connected with more severe alterations in amounts and covalent modifications (phosphorylation and ADP-ribosylation) of HMG chromosomal proteins and histone H1 than core histones.

A novel mechanism of resistance to alpha-difluoromethylornithine induced by cycloheximide. Growth with abnormally low levels of putrescine and spermidine

Treatment of the chemically transformed fibroblasts BP-A31 and other cell lines with low concentrations of cycloheximide (CHM) for 72 h followed by the removal of the protein synthesis inhibitor leads to the proliferation of alpha-difluoromethylornithine (DFMO)-resistant phenotypes. These drug-resistant cells contain almost no ornithine decarboxylase (ODC) activity and concomitantly very low levels of putrescine and spermidine. Southern blot analysis and measurements of ODC activity and intracellular polyamine levels showed that the described mechanism of inducing resistance to DFMO triggered by CHM does not involve ODC gene amplification, altered transport of the drug or reduced affinity of the enzyme for DFMO.

Effects of certain 5'-substituted adenosines on polyamine synthesis: selective inhibitors of spermine synthase

A number of nucleosides related to S-adenosylmethionine were tested for their inhibitory action on three enzymes involved in the biosynthesis of polyamines. The particular objective of the experiments was to determine whether any of the compounds could be used as selective inhibitors of the synthesis of spermine by spermine synthase. None of the nucleosides examined were potent inhibitors of S-adenosylmethionine decarboxylase. 5'-[(3-Aminopropyl)amino]-5'-deoxyadenosine dihydrochloride was quite a strong inhibitor of spermidine synthase (I50 of 7 microM) but was more than an order of magnitude less active than S-adenosyl-1,8-diamino-3-thiooctane, which is a mechanism-based inhibitor of this enzyme. 5'-[(3-Aminopropyl)amino]-5'-deoxyadenosine also inhibited spermine synthase with an I50 of 17 microM, but more selective inhibition of spermine synthase was produced by 9-[6(RS),8-diamino-5,6,7,8-tetradeoxy-beta-D-ribo-octofuranosyl]-9 H-purin-6- amine (I50 of 12 microM) and by dimethyl(5'-adenosyl)sulfonium perchlorate (I50 of 8 microM) since these compounds were much less active against spermidine synthase. Both 9-[6(RS),8-diamino-5,6,7,8-tetradeoxy-beta-D-ribo-octofuranosyl]-9 H-purin-6- amine and dimethyl(5'-adenosyl)sulfonium perchlorate were able to reduce the synthesis of spermine in SV-3T3 cells, but there was a compensatory increase in the concentration of spermidine, and there was no effect on cell growth. These results and those from experiments in which these spermine synthesis inhibitors were combined with inhibitors of spermidine synthase and ornithine decarboxylase indicated that the cells compensated for the inhibition of the aminopropyltransferases by increasing the production of decarboxylated S-adenosylmethionine and putrescine.(ABSTRACT TRUNCATED AT 250 WORDS)

The chemotherapeutic potential of polyamine antimetabolites

The polyamines, putrescine, spermidine and spermine are small cationic molecules essential for DNA synthesis and cell replication. Because the cytotoxicity of most anti-cancer drugs can be attributed to inhibitory effects on DNA synthesis and cell replication it led to speculation that inhibition of polyamine synthesis could be a useful tool in the control of neoplastic growth. In 1978 alpha-difluoromethylornithine (DFMO), a powerful inhibitor of ornithine decarboxylase, the rate limiting enzyme in polyamine synthesis, was synthesized by Metcalf. Since then numerous investigators have tested the potential of DFMO and other polyamine antimetabolites as chemotherapeutic agents in experimental animals and cell cultures. The accumulated knowledge is now being evaluated in the treatment of human proliferative disorders and cancer.

Phosphorylation of a low Mr high mobility group protein in Chinese hamster ovary cells

Phosphorylation of high mobility group (HMG) chromatin proteins was studied both in intact Chinese hamster ovary cells (strain CHO-P22) and in vitro conditions using isolated HMG proteins from the same cells and purified protein kinases. Prominent phosphorylation of serine in a low Mr HMG protein designated as HMG P was observed in unsynchronized cells. Of the three protein kinases tested, only nuclear type II protein kinase phosphorylated HMG P in vitro. The phosphorylated amino acid was phosphoserine. Cyclic nucleotide dependent protein kinases did not phosphorylate HMG P but phosphorylated HMG 14 with a preference for cGMP-dependent protein kinase. 32P-labeling of HMG 17 was not observed in intact cells or in vitro.