Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:4.1.1.17 (ornithine decarboxylase)
6,351 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We investigated the possibility that insulin could stimulate translation of ornithine decarboxylase (ODC) mRNA in a murine fibroblast cell line that expresses large numbers of human insulin receptors (HIR 3.5 cells). Within 3 h after exposure to 70 nM insulin, ODC enzyme activity increased approximately 50-fold and mRNA accumulation 3-fold in the HIR 3.5 cells but not in normal fibroblasts. Pretreatment of cells with cycloheximide completely inhibited insulin-stimulated ODC expression; actinomycin D partially inhibited this effect. To determine the influence of the 5' untranslated region (5'UTR) of ODC mRNA on insulin-regulated ODC expression, plasmids were constructed which contained sequences from the 5'UTR of a rat ODC mRNA interposed between the ferritin promoter and the coding region of the human growth hormone gene. These constructions were then expressed transiently in HIR 3.5 cells. Insulin stimulated a 2-4-fold change in growth hormone accumulation in the medium of cells transiently expressing plasmids containing the entire 5'UTR of ODC mRNA or just the 5'-most 115 bases, a G/C-rich conserved sequence predicted to form a stem-loop structure and shown previously to be responsible for constitutive inhibition of translation. There was a direct correlation between the extent of insulin stimulation and the predicted secondary structure of the added 5'UTR sequences. To determine whether this effect might be due to insulin activation of initiation factors responsible for melting mRNA secondary structure, we examined the effect of insulin on the phosphorylation states of two such factors, eucaryotic initiation factors eIF-4B and eIF-4E. Insulin stimulated the phosphorylation of both initiation factors; this stimulation was evident at 15 min and maximal by 60 min. These results suggest a potential general mechanism by which insulin could preferentially stimulate translation of mRNAs whose 5'UTRs exhibit significant secondary structure by activating initiation factors involved in melting such secondary structures.
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PMID:Insulin induction of ornithine decarboxylase. Importance of mRNA secondary structure and phosphorylation of eucaryotic initiation factors eIF-4B and eIF-4E. 198 89

Cowpea mosaic virus (CPMV) middle component RNA (M-RNA) encodes two proteins of 105 and 95 kDa, of which translation starts at nucleotide (nt) 161 and nt 512, respectively. In vitro translation of both proteins directed by T7 transcripts of M-RNA was stimulated fourfold by eukaryotic initiation factor 4F (eIF-4F), the cap-binding protein complex. The ratio of the synthesis of both proteins after translation was not influenced by eIF-4F or by any known eIF. Part of the CPMV 5' sequence was cloned downstream of the 5' untranslated region of ornithine decarboxylase (ODC); the latter untranslated sequence has a highly stable secondary structure, preventing efficient translation of ODC. Insertion of nt 161 to 512 of CPMV M-RNA upstream of the ODC initiation codon resulted in a marked increase in ODC translation, which indicates that the CPMV sequence contains an internal ribosome-binding site. The insertion conferred stimulation by eIF-4F on ODC translation, showing that eIF-4F is able to stimulate internal initiation.
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PMID:Cowpea mosaic virus middle component RNA contains a sequence that allows internal binding of ribosomes and that requires eukaryotic initiation factor 4F for optimal translation. 203 61

The mRNAs for two key enzymes in polyamine biosynthesis, ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (AdoMetDC), both long 5' untranslated regions (5'UTRs) that could be important in the regulation of enzyme levels by affecting the translation of these mRNAs. In order to test this hypothesis, ODC and AdoMetDC activities were measured in 3T3 cells and in 3T3 cells overexpressing eIF-4E (P2 cells). eIF-4E has been reported to be a limiting factor in the translation of mRNAs with extensive secondary structures in the 5'UTR. AdoMetDC activity was not greatly different in the two cell lines, but ODC activity was much greater in the P2 cells. These results were confirmed by transfecting these cells with plasmids containing a luciferase complementary DNA fused to follow the 5'UTR from ODC or AdoMetDC. The ODC 5'UTR construct produced a higher luciferase activity in the P2 cells. The high level of expression of ODC may be a critical factor in the transformed phenotype of the P2 cells since the ability of these cells to grow in soft agar was blocked by levels of the ODC inhibitor, alpha-difluoromethylornithine, that reduced the ODC activity to values comparable to those of the parent 3T3 cells. These results provide more evidence for a critical role of ODC activity in neoplastic transformation and for the importance of its translational regulation in cell growth and transformation.
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PMID:Overproduction of ornithine decarboxylase caused by relief of translational repression is associated with neoplastic transformation. 816 72

l-Ornithine decarboxylase (ODC) is essential for polyamine synthesis and growth in mammalian cells; it provides putrescine that is usually converted into the higher polyamines, spermidine and spermine. Many highly specific and potent inhibitors of ODC are based on the lead compound alpha-difluoromethylornithine (DFMO), which is an enzyme-activated irreversible inhibitor. DFMO is accepted as a substrate by ODC and is decarboxylated, leading to the formation of a highly reactive species that forms a covalent adduct with either cysteine-360 (90%) or lysine-69 (10%). Both modifications inactivate the enzyme. ODC activity is normally very highly regulated at both transcriptional and post-transcriptional levels according to the growth state of the cell and the intracellular polyamine content. Experimental over-production of ODC can be caused by either transfection with plasmids containing the ODC cDNA with part of the 5'-untranslated region (5'UTR) deleted under the control of a very strong viral promoter, or transfection of plasmids that cause the overproduction of eIF-4E, reported to be a limiting factor in the translation of mRNAs with extensive secondary structures in the 5'UTR. In both cases, unregulated overexpression of ODC transforms NIH 3T3 cells to a neoplastic state. Along with studies showing that many tumor promoters increase ODC activity and that a number of preneoplastic conditions and tumor samples show high levels of ODC, these results suggest that ODC may act as an oncogene in an appropriate background. This provides a rationale for the possible use of ODC inhibitors as chemopreventive agents.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Ornithine decarboxylase as a target for chemoprevention. 853 90

In mouse FM3A ornithine decarboxylase (ODC) overproducing cells (EXOD-1), the amount of ODC protein was approximately 100-fold that of normal cells. Since it is well known that the translational efficiency of ODC mRNA is very low and that eIF-4E is a limiting factor for the mRNA recognition and the scanning of 40 S ribosomal subunits, we measured the amount and phosphorylation of eIF-4E in EXOD-1 cells. An increase in the phosphorylation of eIF-4E, its association with p220 protein, and an enhancement of RNA helicase activity were observed in the cells. These results support the hypothesis that phosphorylation of eIF-4E enhances RNA helicase activity through eIF-4F (4A, 4E, and p220) complex formation.
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PMID:Enhancement of helicase activity and increase of eIF-4E phosphorylation in ornithine decarboxylase-overproducing cells. 865 16

pMV7-4E cells (4E-P2), derived from NIH-3T3 cells, overexpress eIF-4E and exhibit characteristics of transformation, possibly due to translational relief of mRNAs encoding proteins that regulate cell growth. Ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis, is induced in 4E-P2 cells, and this induction appears to be related to the transformed phenotype of these cells. ODC mRNA contains extensive secondary structure in its 5' untranslated region (5'UTR) and may be regulated by eIF-4E, which melts mRNA secondary structure. To better understand this regulation, cDNA constructs containing the wild-type 5'UTR of ODC or deletion mutants inserted ahead of the luciferase gene were transfected into 4E-P2 and 3T3 cells. Expression of luciferase was higher in 4E-P2 cells in all cases, suggesting that the secondary structure of the ODC 5'UTR inhibits expression in 3T3 cells, and this inhibition is overcome by the high eIF-4E levels in 4E-P2 cells. When a small open reading frame present in the 5'UTR of ODC was destroyed by a point mutation, this luciferase construct was expressed about 6-fold over that containing the wild-type 5'UTR in both cell lines, although both of these 5'UTRs contain the same predicted secondary structure. Thus, factors in addition to eIF-4E may be involved in the regulation of ODC. To examine the differences in ODC regulation by polyamines in normal and transformed cells, the effect of N1,N12-bis(ethyl)spermine (BE-3-4-3) on the synthesis and degradation of ODC was examined. ODC activity in 4E-P2 cells was 10 times less sensitive to reduction by BE-3-4-3 compared to 3T3 cells, suggesting that high ODC levels in eIF-4E-overexpressing cells are the result of decreased regulation by polyamines as well as relief of translational regulation by eIF-4E.
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PMID:Regulation of ornithine decarboxylase in a transformed cell line that overexpresses translation initiation factor eIF-4E. 876 19

pMV7-4E cells (4E-P2), which overexpress translation initiation factor eIF-4E, contain elevated levels of ornithine decarboxylase (ODC), the first and rate-limiting enzyme in polyamine biosynthesis. We have shown previously that this induction appears to be related to the transformed phenotype of these cells (L. M. Shantz and A. E. Pegg, Cancer Res., 54: 2313-2316, 1994). To test whether increased ODC activity is responsible for the transformation of 4E-P2 cells, a dominant-negative mutant of ODC was used to reduce the intracellular ODC activity in 4E-P2 cells, and the resulting phenotypic changes were examined. The mutant K69A/C360A contains mutations to alanine of two key active site residues, lysine 69 and cysteine 360, and is truncated at 425 amino acids. Combination of purified K69A/C360A and purified wild-type ODC resulted in a dose-dependent decrease in specific activity compared with wild-type ODC alone, with a 71% reduction at equimolar concentrations. This mutant was transfected into 4E-P2 cells, and stable clones that expressed the truncated K69A/ C360A were isolated. Several clones were tested for their ability to form transformed foci on a monolayer, grow in soft agar, and form tumors in nude mice. When ODC activity was reduced by 60%, the transformed phenotype of 4E-P2 cells was abolished, suggesting strongly that high ODC levels are critical to the transformation of these cells. In addition, K69A/C360A can be used to determine the ODC activity associated with transformation in both in vitro and in vivo systems.
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PMID:Expression of an ornithine decarboxylase dominant-negative mutant reverses eukaryotic initiation factor 4E-induced cell transformation. 891 47

Rapid tumor growth and metastasis require increased polyamine metabolism, which is coordinately regulated by ornithine decarboxylase (ODC) and the polyamine transporter. Both activities are stimulated by ras signalling and are dependent upon protein biosynthesis. T24ras oncogene expression in rat embryo fibroblasts (CREFT24) induces cellular transformation and malignancy, in part, by stimulating the rate-limiting translation initiation factor, eIF-4E. CREFT24 expressing antisense RNA to eIF-4E (AS4E) have markedly decreased tumor growth rates and metastatic capacity, without altered monolayer growth rates. Herein, we demonstrate that in AS4E, ODC is translationally suppressed resulting in decreased ODC activity. Additionally, exogenous polyamine uptake is suppressed in AS4E cells indicating that AS4E can neither generate nor import the polyamines necessary to support rapid tumor growth. These data provide evidence that eIF-4E is the link between ras-induced malignancy and increased polyamine metabolism and support the hypothesis that eIF-4E plays a pivotal role in mediating ras-induced malignancy.
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PMID:Translation of ODC mRNA and polyamine transport are suppressed in ras-transformed CREF cells by depleting translation initiation factor 4E. 936 73

PHAS-I is the prototype of a group of eIF4E-binding proteins that can regulate mRNA translation in response to hormones and growth factors. To investigate the importance of PHAS-I in the physiology of the intact animal, we disrupted the PHAS-I gene in mice. Tissues and cells derived from the knockout mice contained no detectable PHAS-I protein. A related protein, PHAS-II, and eIF4E were readily detectable in tissues from these animals, but neither appeared to be changed in a compensatory manner. Mice lacking PHAS-I appeared normal at birth. However, male knockout mice weighed approximately 10% less than controls at all ages, whereas female weights were similar to those of controls. Both males and females were fertile. Tissues from adult animals appeared to be normal by routine histological staining techniques, as were routine blood cell counts and chemistries. Fibroblasts derived from PHAS-I-deficient mouse embryos exhibited normal rates of growth and overall protein synthesis, responded normally to serum stimulation of ornithine decarboxylase activity and cell growth, and rapamycin inhibition of cell growth. Under these experimental conditions, PHAS-I is apparently not required for the normal development and reproductive behavior of female mice, but is required for normal body weight in male mice; the mechanisms responsible for this phenotype remain to be determined.
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PMID:Disruption of the gene encoding the mitogen-regulated translational modulator PHAS-I in mice. 939 87

Gastrin via its G-protein coupled specific receptor induces transcription of c-fos and c-jun genes through a ras-MAPK pathway. Ornithine Decarboxylase (ODC), a growth regulated proto-oncogene, was chosen to investigate gastrin effects on translation initiation of mRNAs exhibiting a 5'UnTranslated Region (5'UTR) responsible for translation repression in quiescent cells. In AR4-2J tumoral cells, we first demonstrated that gastrin increases ODC mRNA translation. Transient transfections with various CAT chimeric constructs suggested a direct involvement of the 5'UTR in this observation. Translation of this group of mRNAs is enhanced by the availability of the cap-binding protein (eIF4E) that is increased after phosphorylation of its specific binding protein eIF4E-BP1. We found that AR4-2J cells over-expressed eIF4E protein which was not modulated by gastrin treatment. Rapamycin which inhibits 4E-BP1 phosphorylation, completely prevents gastrin-mediated increase of ODC translation indicating that 4E-BP1 could be involved in regulating ODC translation. Implication of 4E-BP1 in mediating gastrin effects is corroborated by the capacity of the ligand to affect 4E-BP1 phosphorylation. These results indicate that gastrin enhances ornithine decarboxylase mRNA translation through a rapamycin sensitive pathway and provide the first evidence in the control of 4E-BP1 phosphorylation after occupancy of a G protein-coupled receptor.
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PMID:Gastrin induces phosphorylation of eIF4E binding protein 1 and translation initiation of ornithine decarboxylase mRNA. 961 31


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