51
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Hoyt MA, McDonough S, Pimpl SA, Scheel H, Hofmann K, Coffino P. A genetic screen forSaccharomyces cerevisiae mutants affecting proteasome function, using a ubiquitin-independent substrate. Yeast 2008; 25:199-217. [DOI: 10.1002/yea.1579] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
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52
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Didier C, Merdes A, Gairin JE, Jabrane-Ferrat N. Inhibition of proteasome activity impairs centrosome-dependent microtubule nucleation and organization. Mol Biol Cell 2007; 19:1220-9. [PMID: 18094058 DOI: 10.1091/mbc.e06-12-1140] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Centrosomes are dynamic organelles that consist of a pair of cylindrical centrioles, surrounded by pericentriolar material. The pericentriolar material contains factors that are involved in microtubule nucleation and organization, and its recruitment varies during the cell cycle. We report here that proteasome inhibition in HeLa cells induces the accumulation of several proteins at the pericentriolar material, including gamma-tubulin, GCP4, NEDD1, ninein, pericentrin, dynactin, and PCM-1. The effect of proteasome inhibition on centrosome proteins does not require intact microtubules and is reversed after removal of proteasome inhibitors. This accrual of centrosome proteins is paralleled by accumulation of ubiquitin in the same area and increased polyubiquitylation of nonsoluble gamma-tubulin. Cells that have accumulated centrosome proteins in response to proteasome inhibition are impaired in microtubule aster formation. Our data point toward a role of the proteasome in the turnover of centrosome proteins, to maintain proper centrosome function.
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Affiliation(s)
- Christine Didier
- Institut de Sciences et Technologies du Médicament de Toulouse, Unité Mixte de Recherche 2587 Centre National de la Recherche Scientifique-Pierre Fabre, 31400 Toulouse, France
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53
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Kramer DL, Diegelman P, Jell J, Vujcic S, Merali S, Porter CW. Polyamine acetylation modulates polyamine metabolic flux, a prelude to broader metabolic consequences. J Biol Chem 2007; 283:4241-51. [PMID: 18089555 DOI: 10.1074/jbc.m706806200] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Recent studies suggest that overexpression of the polyamine-acetylating enzyme spermidine/spermine N(1)-acetyltransferase (SSAT) significantly increases metabolic flux through the polyamine pathway. The concept derives from the observation that SSAT-induced acetylation of polyamines gives rise to a compensatory increase in biosynthesis and presumably to increased flow through the pathway. Despite the strength of this deduction, the existence of heightened polyamine flux has not yet been experimentally demonstrated. Here, we use the artificial polyamine precursor 4-fluoro-ornithine to measure polyamine flux by tracking fluorine unit permeation of polyamine pools in human prostate carcinoma LNCaP cells. Conditional overexpression of SSAT was accompanied by a massive increase in intracellular and extracellular acetylated spermidine and by a 6-20-fold increase in biosynthetic enzyme activities. In the presence of 300 microM 4-fluoro-ornithine, SSAT overexpression led to the sequential appearance of fluorinated putrescine, spermidine, acetylated spermidine, and spermine. As fluorinated polyamines increased, endogenous polyamines decreased, so that the total polyamine pool size remained relatively constant. At 24 h, 56% of the spermine pool in the induced SSAT cells was fluorine-labeled compared with only 12% in uninduced cells. Thus, SSAT induction increased metabolic flux by approximately 5-fold. Flux could be interrupted by inhibition of polyamine biosynthesis but not by inhibition of polyamine oxidation. Overall, the findings are consistent with a paradigm whereby flux is initiated by SSAT acetylation of spermine and particularly spermidine followed by a marked increase in key biosynthetic enzymes. The latter sustains the flux cycle by providing a constant supply of polyamines for subsequent acetylation by SSAT. The broader metabolic implications of this futile metabolic cycling are discussed in detail.
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Affiliation(s)
- Debora L Kramer
- Department of Pharmacology and Therapeutics, Roswell Park Cancer Institute, Buffalo, New York 14263, USA
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54
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Porat Z, Landau G, Bercovich Z, Krutauz D, Glickman M, Kahana C. Yeast antizyme mediates degradation of yeast ornithine decarboxylase by yeast but not by mammalian proteasome: new insights on yeast antizyme. J Biol Chem 2007; 283:4528-34. [PMID: 18089576 DOI: 10.1074/jbc.m708088200] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mammalian antizyme (mAz) is a central element of a feedback circuit regulating cellular polyamines by accelerating ornithine decarboxylase (ODC) degradation and inhibiting polyamine uptake. Although yeast antizyme (yAz) stimulates the degradation of yeast ODC (yODC), we show here that it has only a minor effect on polyamine uptake by yeast cells. A segment of yODC that parallels the Az binding segment of mammalian ODC (mODC) is required for its binding to yAz. Although demonstrating minimal homology to mAz, our results suggest that yAz stimulates yODC degradation via a similar mechanism of action. We demonstrate that interaction with yAz provokes degradation of yODC by yeast but not by mammalian proteasomes. This differential recognition may serve as a tool for investigating proteasome functions.
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Affiliation(s)
- Ziv Porat
- Department of Molecular Genetics, The Weizmann Institute of Science, 1 Hertzel St., Rehovot 76100, Israel
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55
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Hsieh CH, Chen FD, Wang HE, Hwang JJ, Chang CW, Lee YJ, Gelovani JG, Liu RS. Generation of Destabilized Herpes Simplex Virus Type 1 Thymidine Kinase as Transcription Reporter for PET Reporter Systems in Molecular–Genetic Imaging. J Nucl Med 2007; 49:142-50. [DOI: 10.2967/jnumed.106.038943] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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56
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Keren-Paz A, Bercovich Z, Kahana C. Antizyme inhibitor: a defective ornithine decarboxylase or a physiological regulator of polyamine biosynthesis and cellular proliferation. Biochem Soc Trans 2007; 35:311-3. [PMID: 17371267 DOI: 10.1042/bst0350311] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
ODC (ornithine decarboxylase) is a central regulator of cellular polyamine synthesis. ODC is a highly regulated enzyme stimulated by a variety of growth-promoting stimuli. ODC overexpression leads to cellular transformation. Cellular ODC levels are determined at transcriptional and translational levels and by regulation of its degradation. Here we review the mechanism of ODC degradation with particular emphasis on AzI (antizyme inhibitor), an ODC homologous protein that appears as a central regulator of ODC stability, cellular polyamine homoeostasis and cellular proliferation.
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Affiliation(s)
- A Keren-Paz
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot, Israel
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57
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Xiao L, Rao JN, Zou T, Liu L, Marasa BS, Chen J, Turner DJ, Zhou H, Gorospe M, Wang JY. Polyamines regulate the stability of activating transcription factor-2 mRNA through RNA-binding protein HuR in intestinal epithelial cells. Mol Biol Cell 2007; 18:4579-90. [PMID: 17804813 PMCID: PMC2043536 DOI: 10.1091/mbc.e07-07-0675] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Maintenance of intestinal mucosal epithelial integrity requires polyamines that modulate the expression of various genes involved in cell proliferation and apoptosis. Recently, polyamines were shown to regulate the subcellular localization of the RNA-binding protein HuR, which stabilizes its target transcripts such as nucleophosmin and p53 mRNAs. The activating transcription factor-2 (ATF-2) mRNA encodes a member of the ATF/CRE-binding protein family of transcription factors and was computationally predicted to be a target of HuR. Here, we show that polyamines negatively regulate ATF-2 expression posttranscriptionally and that polyamine depletion stabilizes ATF-2 mRNA by enhancing the interaction of the 3'-untranslated region (UTR) of ATF-2 with cytoplasmic HuR. Decreasing cellular polyamines by inhibiting ornithine decarboxylase (ODC) with alpha-difluoromethylornithine increased the levels of ATF-2 mRNA and protein, whereas increasing polyamines by ectopic ODC overexpression repressed ATF-2 expression. Polyamine depletion did not alter transcription via the ATF-2 gene promoter but increased the stability of ATF-2 mRNA. Increased cytoplasmic HuR in polyamine-deficient cells formed ribonucleoprotein complexes with the endogenous ATF-2 mRNA and specifically bound to 3'-UTR of ATF-2 mRNA on multiple nonoverlapping 3'-UTR segments. Adenovirus-mediated HuR overexpression elevated ATF-2 mRNA and protein levels, whereas HuR silencing rendered the ATF-2 mRNA unstable and prevented increases in ATF-2 mRNA and protein. Furthermore, inhibition of ATF-2 expression prevented the increased resistance of polyamine-deficient cells to apoptosis induced by treatment with tumor necrosis factor-alpha and cycloheximide. These results indicate that polyamines modulate the stability of ATF-2 mRNA by altering cytoplasmic HuR levels and that polyamine-modulated ATF-2 expression plays a critical role in regulating epithelial apoptosis.
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Affiliation(s)
- Lan Xiao
- *Cell Biology Group, Department of Surgery, and
- Baltimore Veterans Affairs Medical Center, Baltimore, MD 21201
| | - Jaladanki N. Rao
- *Cell Biology Group, Department of Surgery, and
- Baltimore Veterans Affairs Medical Center, Baltimore, MD 21201
| | - Tongtong Zou
- *Cell Biology Group, Department of Surgery, and
- Baltimore Veterans Affairs Medical Center, Baltimore, MD 21201
| | - Lan Liu
- *Cell Biology Group, Department of Surgery, and
- Baltimore Veterans Affairs Medical Center, Baltimore, MD 21201
| | - Bernard S. Marasa
- *Cell Biology Group, Department of Surgery, and
- Department of Pathology, University of Maryland School of Medicine, Baltimore, MD 21201
| | - Jie Chen
- *Cell Biology Group, Department of Surgery, and
- Baltimore Veterans Affairs Medical Center, Baltimore, MD 21201
| | - Douglas J. Turner
- *Cell Biology Group, Department of Surgery, and
- Baltimore Veterans Affairs Medical Center, Baltimore, MD 21201
| | - Huiping Zhou
- Department of Microbiology and Immunology, Virginia Commonwealth University, Richmond, VA 23298; and
| | - Myriam Gorospe
- Laboratory of Cellular and Molecular Biology, National Institute on Aging-Intramural Research Program, National Institutes of Health, Baltimore, MD 21224
| | - Jian-Ying Wang
- *Cell Biology Group, Department of Surgery, and
- Department of Pathology, University of Maryland School of Medicine, Baltimore, MD 21201
- Baltimore Veterans Affairs Medical Center, Baltimore, MD 21201
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58
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Chen J, Rao JN, Zou T, Liu L, Marasa BS, Xiao L, Zeng X, Turner DJ, Wang JY. Polyamines are required for expression of Toll-like receptor 2 modulating intestinal epithelial barrier integrity. Am J Physiol Gastrointest Liver Physiol 2007; 293:G568-76. [PMID: 17600044 DOI: 10.1152/ajpgi.00201.2007] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The Toll-like receptors (TLRs) allow mammalian intestinal epithelium to detect various microbes and activate innate immunity after infection. TLR2 and TLR4 have been identified in intestinal epithelial cells (IECs) as fundamental components of the innate immune response to bacterial pathogens, but the exact mechanism involved in control of TLR expression remains unclear. Polyamines are implicated in a wide variety of biological functions, and regulation of cellular polyamines is a central convergence point for the multiple signaling pathways driving different epithelial cell functions. The current study determined whether polyamines regulate TLR expression, thereby modulating intestinal epithelial barrier function. Depletion of cellular polyamines by inhibiting ornithine decarboxylase (ODC) with alpha-difluoromethylornithine decreased levels of TLR2 mRNA and protein, whereas increased polyamines by ectopic overexpression of the ODC gene enhanced TLR2 expression. Neither intervention changed basal levels of TLR4. Exposure of normal IECs to low-dose (5 microg/ml) LPS increased ODC enzyme activity and stimulated expression of TLR2 but not TLR4, while polyamine depletion prevented this LPS-induced TLR2 expression. Decreased TLR2 in polyamine-deficient cells was associated with epithelial barrier dysfunction. In contrast, increased TLR2 by the low dose of LPS enhanced epithelial barrier function, which was abolished by inhibition of TLR2 expression with specific, small interfering RNA. These results indicate that polyamines are necessary for TLR2 expression and that polyamine-induced TLR2 activation plays an important role in regulating epithelial barrier function.
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Affiliation(s)
- Jie Chen
- Department of Surgery, Baltimore Veterans Affairs Medical Center, 10 North Greene Street, Baltimore, MD 21201, USA.
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59
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Houten SM, Volle DH, Cummins CL, Mangelsdorf DJ, Auwerx J. In Vivo Imaging of Farnesoid X Receptor Activity Reveals the Ileum as the Primary Bile Acid Signaling Tissue. Mol Endocrinol 2007; 21:1312-23. [PMID: 17426284 DOI: 10.1210/me.2007-0113] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
We generated and characterized a firefly luciferase reporter mouse for the nuclear receptor farnesoid X receptor (FXR). This FXR reporter mouse has basal luciferase expression in the terminal ileum, an organ with well-characterized FXRalpha signaling. In vivo luciferase activity reflected the diurnal activity pattern of the mouse, and is regulated by both natural (bile acids, chenodeoxycholic acid) and synthetic (GW4064) FXRalpha ligands. Moreover, in vivo and in vitro analysis showed luciferase activity after GW4064 administration in the liver, kidney, and adrenal gland, indicating that FXRalpha signaling is functional in these tissues. Hepatic luciferase activity was robustly induced in cholestatic mice, showing that FXRalpha signaling pathways are activated in this disease. In conclusion, we have developed an FXR reporter mouse that is useful to monitor FXRalpha signaling in vivo in health and disease. The use of this animal could facilitate the development of new therapeutic compounds that target FXRalpha in a tissue-specific manner.
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Affiliation(s)
- Sander M Houten
- Institut de Génétique et Biologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique/Institut National de la Santé et de la Recherche Médicale/Université Louis Pasteur, Illkirch, France
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60
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Nasizadeh S, Thiman L, Persson L. Sequence elements essential for the rapid turnover of Crithidia fasciculata ornithine decarboxylase. Amino Acids 2007; 34:421-8. [PMID: 17514492 DOI: 10.1007/s00726-007-0552-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2007] [Accepted: 03/30/2007] [Indexed: 11/25/2022]
Abstract
Ornithine decarboxylase (ODC) has a very fast turnover in mammalian cells, but is a stable enzyme in T. brucei and other trypanosmatid parasites like Leishmania donovani. However, Crithidia fasciculata, which is a phylogenetically closely related trypanosomatid to L. donovani, has an ODC with a rapid turnover. Interestingly, C. fasciculata ODC, but not L. donovani ODC, is rapidly degraded also in mammalian systems. In order to obtain information on what sequences are important for the rapid degradation of C. fasciculata ODC, we produced a variety of C. fasciculata/L. donovani ODC hybrid proteins and characterized their turnover using two different mammalian expression systems. The results obtained indicate that C. fasciculata ODC contains several sequence elements essential for the rapid turnover of the protein and that these regions are mainly located in the central part of the enzyme.
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Affiliation(s)
- S Nasizadeh
- Department of Experimental Medical Science, Lund University, Lund, Sweden
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61
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Kahana C. Ubiquitin dependent and independent protein degradation in the regulation of cellular polyamines. Amino Acids 2007; 33:225-30. [PMID: 17404802 DOI: 10.1007/s00726-007-0519-y] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2006] [Accepted: 02/01/2007] [Indexed: 11/30/2022]
Abstract
Protein degradation mediated by the ubiquitin/proteasome system is the major route for the degradation of cellular proteins. In this pathway the ubiquitination of the target proteins is manifested via the concerted action of several enzymes. The ubiquinated proteins are then recognized and degraded by the 26S proteasome. There are few reports of proteins degraded by the 26S protesome without ubiquitination, with ornithine decarboxylase being the most notable representative of this group. Interestingly, while the degradation of ODC is independent of ubiquitination, the degradation of other enzymes of the polyamine biosynthesis pathway is ubiquitin dependent. The present review describes the degradation of enzymes and regulators of the polyamine biosynthesis pathway.
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Affiliation(s)
- C Kahana
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot, Israel.
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62
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Persson L. Ornithine decarboxylase and S-adenosylmethionine decarboxylase in trypanosomatids. Biochem Soc Trans 2007; 35:314-7. [PMID: 17371268 DOI: 10.1042/bst0350314] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The production of polyamines has been shown to be an effective target for a drug against the West African form of sleeping sickness caused by Trypanosoma brucei gambiense. T. brucei belongs to the group of protozoan parasites classed as trypanosomatids. Parasitic species of this group are the causative agents of various tropical diseases besides African sleeping sickness, e.g. Chagas' disease (Trypanosoma cruzi), cutaneous (Lesihmania spp.) and visceral (Leishmania donovani) leishmaniasis. The metabolism of polyamines in the parasites is a potential target for the development of new drugs for treatment of these diseases. The key steps in polyamine synthesis are catalysed by ODC (ornithine decarboxylase) and AdoMetDC (S-adenosylmethionine decarboxylase). In the present paper, some of the available information on ODC and AdoMetDC in trypanosomatids will be described and discussed.
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Affiliation(s)
- L Persson
- Department of Experimental Medical Science, Lund University, BMC F:13, S-221 84 Lund, Sweden.
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63
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Takeuchi J, Chen H, Coffino P. Proteasome substrate degradation requires association plus extended peptide. EMBO J 2006; 26:123-31. [PMID: 17170706 PMCID: PMC1782366 DOI: 10.1038/sj.emboj.7601476] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2006] [Accepted: 11/06/2006] [Indexed: 11/09/2022] Open
Abstract
To determine the minimum requirements for substrate recognition and processing by proteasomes, the functional elements of a ubiquitin-independent degradation tag were dissected. The 37-residue C-terminus of ornithine decarboxylase (cODC) is a native degron, which also functions when appended to diverse proteins. Mutating the cysteine 441 residue within cODC impaired its proteasome association in the context of ornithine decarboxylase and prevented the turnover of GFP-cODC in yeast cells. Degradation of GFP-cODC with C441 mutations was restored by providing an alternate proteasome association element via fusion to the Rpn10 proteasome subunit. However, Rpn10-GFP was stable, unless extended by cODC or other peptides of similar size. In vitro reconstitution experiments confirmed the requirement for both proteasome tethering and a loosely structured region. Therefore, cODC and degradation tags in general must serve two functions: proteasome association and a site, consisting of an extended peptide region, used for initiating insertion into the protease.
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Affiliation(s)
- Junko Takeuchi
- Department of Microbiology and Immunology, University of California, San Francisco, CA, USA
| | - Hui Chen
- Department of Microbiology and Immunology, University of California, San Francisco, CA, USA
| | - Philip Coffino
- Department of Microbiology and Immunology, University of California, San Francisco, CA, USA
- Department of Microbiology and Immunology, University of California, San Francisco, 513 Parnassus Ave, Microbiology room S430, San Francisco, CA 94143, USA. Tel.: +1 415 516 6515; Fax: +1 415 476 8201; E-mail:
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64
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Roberts SC, Jiang Y, Gasteier J, Frydman B, Marton LJ, Heby O, Ullman B. Leishmania donovani polyamine biosynthetic enzyme overproducers as tools to investigate the mode of action of cytotoxic polyamine analogs. Antimicrob Agents Chemother 2006; 51:438-45. [PMID: 17116678 PMCID: PMC1797743 DOI: 10.1128/aac.01193-06] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A number of anticancer and antiparasitic drugs are postulated to target the polyamine biosynthetic pathway and polyamine function, but the exact mode of action of these compounds is still being elucidated. To establish whether polyamine analogs specifically target enzymes of the polyamine pathway, a model was developed using strains of the protozoan parasite Leishmania donovani that overproduce each of the polyamine biosynthetic enzymes. Promastigotes overexpressing episomal constructs encoding ornithine decarboxylase (ODC), S-adenosylmethionine decarboxylase (ADOMETDC), or spermidine synthase (SPDSYN) revealed robust overproduction of the corresponding polyamine biosynthetic enzyme. Polyamine pools, however, were either unchanged or only marginally affected, implying that regulatory mechanisms must exist. The ODC, ADOMETDC, and SPDSYN overproducer strains exhibited a high level of resistance to difluoromethylornithine, 5'-{[(Z)-4-amino-2-butenyl]methylamino}-5'-deoxyadenosine, and n-butylamine, respectively, confirming previous observations that these agents specifically target polyamine enzymes. Conversely, augmented levels of polyamine biosynthetic enzymes did not affect the sensitivity of L. donovani promastigotes to pentamidine, berenil, and mitoguazone, drugs that were postulated to target the polyamine pathway, implying alternative and/or additional targets for these agents. The sensitivities of wild-type and overproducing parasites to a variety of polyamine analogs were also tested. The polyamine enzyme-overproducing lines offer a rapid cell-based screen for assessing whether synthetic polyamine analogs exert their mechanism of action predominantly on the polyamine biosynthetic pathway in L. donovani. Furthermore, the drug resistance engendered by the amplification of target genes and the overproduction of the encoded protein offers a general strategy for evaluating and developing therapeutic agents that target specific proteins in Leishmania.
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Affiliation(s)
- Sigrid C Roberts
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, OR 97239-3098, USA
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65
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Liu L, Guo X, Rao J, Zou T, Marasa B, Chen J, Greenspon J, Casero R, Wang JY. Polyamine-modulated c-Myc expression in normal intestinal epithelial cells regulates p21Cip1 transcription through a proximal promoter region. Biochem J 2006; 398:257-67. [PMID: 16706751 PMCID: PMC1550304 DOI: 10.1042/bj20060217] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Maintenance of intestinal mucosal epithelial integrity requires cellular polyamines that regulate expression of various genes involved in cell proliferation, growth arrest and apoptosis. Our previous studies have shown that polyamines are essential for expression of the c-myc gene and that polyamine-induced c-Myc plays a critical role in stimulation of normal IEC (intestinal epithelial cell) proliferation, but the exact downstream targets of induced c-Myc are still unclear. The p21Cip1 protein is a major player in cell cycle control, which is primarily regulated at the transcriptional level. The current study was designed to determine whether induced c-Myc stimulates normal IEC proliferation by repressing p21Cip1 transcription following up-regulation of polyamines. Overexpression of the ODC (ornithine decarboxylase) gene increased levels of cellular polyamines, induced c-Myc expression and inhibited p21Cip1 transcription, as indicated by repression of p21Cip1 promoter activity and a decrease in p21Cip1 protein levels. In contrast, depletion of cellular polyamines by inhibiting ODC enzyme activity with alpha-difluoromethylornithine decreased c-Myc, but increased p21Cip1 transcription. Ectopic expression of wild-type c-myc not only inhibited basal levels of p21Cip1 transcription in control cells, but also prevented increased p21Cip1 in polyamine-deficient cells. Experiments using different p21Cip1 promoter mutants showed that transcriptional repression of p21Cip1 by c-Myc was mediated through Miz-1- and Sp1-binding sites within the proximal region of the p21Cip1 promoter in normal IECs. These findings confirm that p21Cip1 is one of the direct mediators of induced c-Myc following increased polyamines and that p21Cip1 repression by c-Myc is implicated in stimulation of normal IEC proliferation.
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Affiliation(s)
- Lan Liu
- *Cell Biology Group, Department of Surgery, University of Maryland School of Medicine, Baltimore, MD 21201, U.S.A
- †Baltimore Veterans Affairs Medical Center, Baltimore, MD 21201, U.S.A
| | - Xin Guo
- *Cell Biology Group, Department of Surgery, University of Maryland School of Medicine, Baltimore, MD 21201, U.S.A
- †Baltimore Veterans Affairs Medical Center, Baltimore, MD 21201, U.S.A
| | - Jaladanki N. Rao
- *Cell Biology Group, Department of Surgery, University of Maryland School of Medicine, Baltimore, MD 21201, U.S.A
- †Baltimore Veterans Affairs Medical Center, Baltimore, MD 21201, U.S.A
| | - Tongtong Zou
- *Cell Biology Group, Department of Surgery, University of Maryland School of Medicine, Baltimore, MD 21201, U.S.A
- †Baltimore Veterans Affairs Medical Center, Baltimore, MD 21201, U.S.A
| | - Bernard S. Marasa
- *Cell Biology Group, Department of Surgery, University of Maryland School of Medicine, Baltimore, MD 21201, U.S.A
- ‡Department of Pathology, University of Maryland School of Medicine, Baltimore, MD 21201, U.S.A
| | - Jie Chen
- *Cell Biology Group, Department of Surgery, University of Maryland School of Medicine, Baltimore, MD 21201, U.S.A
- †Baltimore Veterans Affairs Medical Center, Baltimore, MD 21201, U.S.A
| | - Jose Greenspon
- *Cell Biology Group, Department of Surgery, University of Maryland School of Medicine, Baltimore, MD 21201, U.S.A
| | - Robert A. Casero
- §Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University, Baltimore, MD 21231, U.S.A
| | - Jian-Ying Wang
- *Cell Biology Group, Department of Surgery, University of Maryland School of Medicine, Baltimore, MD 21201, U.S.A
- †Baltimore Veterans Affairs Medical Center, Baltimore, MD 21201, U.S.A
- ‡Department of Pathology, University of Maryland School of Medicine, Baltimore, MD 21201, U.S.A
- To whom correspondence should be addressed (email )
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66
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Zou T, Mazan-Mamczarz K, Rao JN, Liu L, Marasa BS, Zhang AH, Xiao L, Pullmann R, Gorospe M, Wang JY. Polyamine depletion increases cytoplasmic levels of RNA-binding protein HuR leading to stabilization of nucleophosmin and p53 mRNAs. J Biol Chem 2006; 281:19387-94. [PMID: 16690610 DOI: 10.1074/jbc.m602344200] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Polyamines are essential for maintaining normal intestinal epithelial integrity, an effect that relies, at least in part, on their ability to keep low levels of nucleophosmin (NPM) and p53 mRNAs. The RNA-binding protein HuR associates with the p53 mRNA, as reported previously, and with the NPM mRNA, computationally predicted to be a target of HuR. Here, we show that HuR binds the NPM and p53 3'-untranslated regions and stabilizes these mRNAs in polyamine-depleted intestinal epithelial cells. Depletion of cellular polyamines by inhibiting ornithine decarboxylase with alpha-difluoromethylornithine dramatically enhanced the cytoplasmic abundance of HuR, whereas ectopic ornithine decarboxylase overexpression decreased cytoplasmic HuR; neither intervention changed whole-cell HuR levels. HuR was found to specifically bind the 3'-untranslated regions of NPN and p53 mRNAs. HuR silencing rendered the NPM and p53 mRNAs unstable and prevented increases in NPM and p53 mRNA and protein in polyamine-deficient cells. These results indicate that polyamines modulate cytoplasmic HuR levels in intestinal epithelial cells, in turn controlling the stability of the NPM and p53 mRNAs and influencing NPM and p53 protein levels.
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Affiliation(s)
- Tongtong Zou
- Cell Biology Group, Department of Surgery, University of Maryland School of Medicine, Baltimore 21201, USA
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67
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N/A, 李 茹, 陈 蔚. N/A. Shijie Huaren Xiaohua Zazhi 2006; 14:979-984. [DOI: 10.11569/wcjd.v14.i10.979] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
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68
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Hoyt MA, Zich J, Takeuchi J, Zhang M, Govaerts C, Coffino P. Glycine-alanine repeats impair proper substrate unfolding by the proteasome. EMBO J 2006; 25:1720-9. [PMID: 16601692 PMCID: PMC1440830 DOI: 10.1038/sj.emboj.7601058] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2005] [Accepted: 03/01/2006] [Indexed: 11/09/2022] Open
Abstract
Proteasome ATPases unravel folded proteins. Introducing a sequence containing only glycine and alanine residues (GAr) into substrates can impair their digestion. We previously proposed that a GAr interferes with the unfolding capacity of the proteasome, leading to partial degradation of products. Here we tested that idea in several ways. Stabilizing or destabilizing a folded domain within substrate proteins changed GAr-mediated intermediate production in the way predicted by the model. A downstream folded domain determined the sites of terminal proteolysis. The spacing between a GAr and a folded domain was critical for intermediate production. Intermediates containing a GAr did not remain associated with proteasomes, excluding models whereby retained GAr-containing proteins halt further processing. The following model is supported: a GAr positioned within the ATPase ring reduces the efficiency of coupling between nucleotide hydrolysis and work performed on the substrate. If this impairment takes place when unfolding must be initiated, insertion pauses and proteolysis is limited to the portion of the substrate that has already entered the catalytic chamber of the proteasome.
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Affiliation(s)
- Martin A Hoyt
- Department of Microbiology and Immunology, University of California, San Francisco, CA, USA
| | - Judith Zich
- Department of Microbiology and Immunology, University of California, San Francisco, CA, USA
| | - Junko Takeuchi
- Department of Microbiology and Immunology, University of California, San Francisco, CA, USA
| | - Mingsheng Zhang
- Department of Microbiology and Immunology, University of California, San Francisco, CA, USA
| | - Cedric Govaerts
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, CA, USA
| | - Philip Coffino
- Department of Microbiology and Immunology, University of California, San Francisco, CA, USA
- Department of Microbiology and Immunology, UCSF, 513 Parnassus Avenue, San Francisco, CA 94143-0414, USA. Tel.: +1 415 476 1783; E-mail:
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69
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Yamaguchi Y, Takatsuka Y, Matsufuji S, Murakami Y, Kamio Y. Characterization of a Counterpart to Mammalian Ornithine Decarboxylase Antizyme in Prokaryotes. J Biol Chem 2006; 281:3995-4001. [PMID: 16354653 DOI: 10.1074/jbc.m507545200] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The degradation of mammalian ornithine decarboxylase (ODC) (EC 4.1.1.17) by 26 S proteasome, is accelerated by the ODC antizyme (AZ), a trigger protein involved in the specific degradation of eukaryotic ODC. In prokaryotes, AZ has not been found. Previously, we found that in Selenomonas ruminantium, a strictly anaerobic and Gram-negative bacterium, a drastic degradation of lysine decarboxylase (LDC; EC 4.1.1.18), which has decarboxylase activities toward both L-lysine and L-ornithine with similar K(m) values, occurs upon entry into the stationary phase of cell growth by protease together with a protein of 22 kDa (P22). Here, we show that P22 is a direct counterpart of eukaryotic AZ by the following evidence. (i) P22 synthesis is induced by putrescine but not cadaverine. (ii) P22 enhances the degradation of both mouse ODC and S. ruminantium LDC by a 26 S proteasome. (iii) S. ruminantium LDC degradation is also enhanced by mouse AZ replacing P22 in a cell-free extract from S. ruminantium. (iv) Both P22 and mouse AZ bind to S. ruminantium LDC but not to the LDC mutated in its binding site for P22 and AZ. In this report, we also show that P22 is a ribosomal protein of S. ruminantium.
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Affiliation(s)
- Yoshihiro Yamaguchi
- Laboratory of Applied Microbiology, Department of Microbial Biotechnology, Graduate School of Agricultural Science, Tohoku University, Aoba-ku, Sendai, Japan
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70
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Lan L, Hayes CS, Laury-Kleintop L, Gilmour SK. Suprabasal induction of ornithine decarboxylase in adult mouse skin is sufficient to activate keratinocytes. J Invest Dermatol 2005; 124:602-14. [PMID: 15737202 DOI: 10.1111/j.0022-202x.2005.23620.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
To study the effects of de novo induction of ornithine decarboxylase (ODC) activity in adult, quiescent skin, we generated transgenic mice in which the suprabasal expression of an inducible form of the ODC protein fused to a modified estrogen receptor ligand-binding domain (ODCER) is driven by an involucrin promoter. After topical treatment with the inducing agent 4-hydroxytamoxifen (4OHT), ODC activity and putrescine levels were dramatically increased in the epidermis but not in the dermis of transgenic mice. 4OHT treatment stimulated both proliferation as measured by bromodeoxyuridine incorporation in basal epidermal cells and differentiation shown by increased expression of differentiation markers. Furthermore, induction of ODC activity did not rescue primary epidermal keratinocyte cultures isolated from ODCER2 mice from a calcium-triggered DNA synthesis block, as measured by [3H]thymidine incorporation. In vivo induction of epidermal ODC enzyme activity significantly stimulated the vascularization of ODCER transgenic skin. Increased expression of interleukin-1beta and keratin 6, markers of keratinocyte activation seen in wound healing, was also observed in 4OHT-treated transgenic skin. These results suggest that de novo suprabasal induction of ODC activity in adult mouse skin activates keratinocytes and stimulates vascularization in the dermal layer in a manner similar to skin undergoing wound healing.
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Affiliation(s)
- Li Lan
- Lankenau Institute for Medical Research, Wynnewood, Pennsylvania, USA
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71
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Asher G, Bercovich Z, Tsvetkov P, Shaul Y, Kahana C. 20S proteasomal degradation of ornithine decarboxylase is regulated by NQO1. Mol Cell 2005; 17:645-55. [PMID: 15749015 DOI: 10.1016/j.molcel.2005.01.020] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2004] [Revised: 01/02/2005] [Accepted: 01/25/2005] [Indexed: 01/18/2023]
Abstract
Ornithine decarboxylase (ODC), a key enzyme in the biosynthesis of polyamines, is a very labile protein. ODC is a homodimeric enzyme that undergoes ubiquitin-independent proteasomal degradation via direct interaction with antizyme, a polyamine-induced protein. Binding of antizyme promotes the dissociation of ODC homodimers and marks ODC for degradation by the 26S proteasomes. We describe here an alternative pathway for ODC degradation that is regulated by NAD(P)H quinone oxidoreductase 1 (NQO1). We show that NQO1 binds and stabilizes ODC. Dicoumarol, an inhibitor of NQO1, dissociates ODC-NQO1 interaction and enhances ubiquitin-independent ODC proteasomal degradation. We further show that dicoumarol sensitizes ODC monomers to proteasomal degradation in an antizyme-independent manner. This process of NQO1-regulated ODC degradation was recapitulated in vitro by using purified 20S proteasomes. Finally, we show that the regulation of ODC stability by NQO1 is especially prominent under oxidative stress. Our findings assign to NQO1 a role in regulating ubiquitin-independent degradation of ODC by the 20S proteasomes.
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Affiliation(s)
- Gad Asher
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel
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72
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Hoyt MA, Zhang M, Coffino P. Probing the ubiquitin/proteasome system with ornithine decarboxylase, a ubiquitin-independent substrate. Methods Enzymol 2005; 398:399-413. [PMID: 16275346 DOI: 10.1016/s0076-6879(05)98033-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Ornithine decarboxylase (ODC) is an unusual proteasome substrate-ubiquitin conjugation plays no part in its turnover. It can therefore be used as a probe to distinguish proteasome-mediated actions that do or do not depend on the activity of the ubiquitin system. A 37 residue region of ODC suffices for proteasome interactions, and within this sequence functionally critical residues have been identified. Because no posttranslational modifications are required for substrate preparation, ODC and derived constructs can be readily generated as substrates for either in vitro or in vivo studies. This chapter describes methodologies that allow the use of ODC as a reporter to examine the ubiquitin-proteasome system, both in reconstituted in vitro systems and in living cells.
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Affiliation(s)
- Martin A Hoyt
- Department of Microbiology and Immunology, University of California-San Francisco, San Francisco, CA 94143-0414, USA
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73
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Bercovich Z, Kahana C. Degradation of antizyme inhibitor, an ornithine decarboxylase homologous protein, is ubiquitin-dependent and is inhibited by antizyme. J Biol Chem 2004; 279:54097-102. [PMID: 15491992 DOI: 10.1074/jbc.m410234200] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ornithine decarboxylase (ODC) is the most notable example of a protein degraded by the 26 S proteasome without ubiquitination. Instead, ODC is targeted to degradation by direct binding to a polyamine-induced protein termed antizyme (Az). Antizyme inhibitor (AzI) is an ODC-related protein that does not retain enzymatic activity yet binds Az with higher affinity than ODC. We show here that like ODC, AzI is also a short-lived protein that undergoes proteasomal degradation. However, in contrast to ODC degradation, the degradation of AzI is ubiquitin-dependent and does not require interaction with Az. Moreover, Az binding actually stabilizes AzI by inhibiting its ubiquitination. Substituting the C terminus of AzI with that of ODC, which together with Az constitutes the complete degradation signal of ODC, does not subvert AzI degradation from the ubiquitin-dependent mode to the Az-dependent mode, suggesting dominance of the ubiquitination signal. Our results suggest opposing roles of Az in regulating the degradation of AzI and ODC.
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Affiliation(s)
- Zippi Bercovich
- Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel
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74
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Zhang M, MacDonald AI, Hoyt MA, Coffino P. Proteasomes Begin Ornithine Decarboxylase Digestion at the C Terminus. J Biol Chem 2004; 279:20959-65. [PMID: 15016805 DOI: 10.1074/jbc.m314043200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Proteasomes denature folded protein substrates and thread them through a narrow pore that leads to the sequestered sites of proteolysis. Whether a protein substrate initiates insertion from its N or C terminus or in a random orientation has not been determined for any natural substrate. We used the labile enzyme ornithine decarboxylase (ODC), which is recognized by the proteasome via a 37-residue C-terminal tag, to answer this question. Three independent approaches were used to assess orientation as follows. 1) The 461-residue ODC protein chain was interrupted at position 305. The C-terminal fragment was degraded by purified proteasomes, but because processivity requires continuity of the polypeptide chain, the N-terminal fragment was spared. 2) A proteasome-inhibitory viral sequence prevented degradation when introduced near the C terminus but not when inserted elsewhere in ODC. 3) A bulky tightly folded protein obstructed in vivo degradation most effectively when positioned near the C terminus. These data demonstrate that the proteasome initiates degradation of this native substrate at the C terminus. The co-localization of entry site and degradation tag to the ODC C terminus suggests that recognition tags determine the site for initiating entry. Flexibility of a polypeptide terminus may promote the initiation of degradation.
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Affiliation(s)
- Mingsheng Zhang
- Department of Microbiology and Immunology, University of California-San Francisco, 513 Parnassus Avenue, San Francisco, CA 94143, USA
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75
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Roberts SC, Tancer MJ, Polinsky MR, Gibson KM, Heby O, Ullman B. Arginase plays a pivotal role in polyamine precursor metabolism in Leishmania. Characterization of gene deletion mutants. J Biol Chem 2004; 279:23668-78. [PMID: 15023992 DOI: 10.1074/jbc.m402042200] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The polyamine pathway of protozoan parasites has been successfully targeted in anti-parasitic therapies and is significantly different from that of the mammalian host. To gain knowledge into the metabolic routes by which parasites synthesize polyamines and their precursors, the arginase gene was cloned from Leishmania mexicana, and Deltaarg null mutants were created by double targeted gene replacement and characterized. The ARG sequence exhibited significant homology to ARG proteins from other organisms and predicted a peroxisomal targeting signal (PTS-1) that steers proteins to the glycosome, an organelle unique to Leishmania and related parasites. ARG was subsequently demonstrated to be present in the glycosome, whereas the polyamine biosynthetic enzymes, in contrast, were shown to be cytosolic. The Deltaarg knockouts expressed no ARG activity, lacked an intracellular ornithine pool, and were auxotrophic for ornithine or polyamines. The ability of the Deltaarg null mutants to proliferate could be restored by pharmacological supplementation, either with low putrescine or high ornithine or spermidine concentrations, or by complementation with an arginase episome. Transfection of an arg construct lacking the PTS-1 directed the synthesis of an arg that mislocalized to the cytosol and notably also complemented the genetic lesion and restored polyamine prototrophy to the Deltaarg parasites. This molecular, biochemical, and genetic dissection of ARG function in L. mexicana promastigotes establishes: (i) that the enzyme is essential for parasite viability; (ii) that Leishmania, unlike mammalian cells, expresses only one ARG activity; (iii) that the sole vital function of ARG is to provide polyamine precursors for the parasite; and (iv) that ARG is present in the glycosome, but this subcellular milieu is not essential for its role in polyamine biosynthesis.
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Affiliation(s)
- Sigrid C Roberts
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland 97239-3098, USA
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76
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Wallace HM, Fraser AV, Hughes A. A perspective of polyamine metabolism. Biochem J 2003; 376:1-14. [PMID: 13678416 PMCID: PMC1223767 DOI: 10.1042/bj20031327] [Citation(s) in RCA: 676] [Impact Index Per Article: 32.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2003] [Revised: 09/16/2003] [Accepted: 09/18/2003] [Indexed: 01/30/2023]
Abstract
Polyamines are essential for the growth and function of normal cells. They interact with various macromolecules, both electrostatically and covalently and, as a consequence, have a variety of cellular effects. The complexity of polyamine metabolism and the multitude of compensatory mechanisms that are invoked to maintain polyamine homoeostasis argue that these amines are critical to cell survival. The regulation of polyamine content within cells occurs at several levels, including transcription and translation. In addition, novel features such as the +1 frameshift required for antizyme production and the rapid turnover of several of the enzymes involved in the pathway make the regulation of polyamine metabolism a fascinating subject. The link between polyamine content and human disease is unequivocal, and significant success has been obtained in the treatment of a number of parasitic infections. Targeting the polyamine pathway as a means of treating cancer has met with limited success, although the development of drugs such as DFMO (alpha-difluoromethylornithine), a rationally designed anticancer agent, has revolutionized our understanding of polyamine function in cell growth and provided 'proof of concept' that influencing polyamine metabolism and content within tumour cells will prevent tumour growth. The more recent development of the polyamine analogues has been pivotal in advancing our understanding of the necessity to deplete all three polyamines to induce apoptosis in tumour cells. The current thinking is that the polyamine inhibitors/analogues may also be useful agents in the chemoprevention of cancer and, in this area, we may yet see a revival of DFMO. The future will be in adopting a functional genomics approach to identifying polyamine-regulated genes linked to either carcinogenesis or apoptosis.
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Affiliation(s)
- Heather M Wallace
- Department of Medicine and Therapeutics, University of Aberdeen, Polwarth Building, Foresterhill, Aberdeen AB25 2ZD, Scotland, UK.
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77
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Zhao X, Jiang X, Huang CC, Kain SR, Li X. Generation of a destablilized form of enhanced green fluorescent protein. Methods Enzymol 2003; 302:438-44. [PMID: 12876791 DOI: 10.1016/s0076-6879(99)02038-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Affiliation(s)
- X Zhao
- CLONTECH Laboratories, Inc., Palo Alto, California 94303-4230, USA
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78
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Hoyt MA, Zhang M, Coffino P. Ubiquitin-independent mechanisms of mouse ornithine decarboxylase degradation are conserved between mammalian and fungal cells. J Biol Chem 2003; 278:12135-43. [PMID: 12562772 DOI: 10.1074/jbc.m211802200] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The polyamine biosynthetic enzyme ornithine decarboxylase (ODC) is degraded by the 26 S proteasome via a ubiquitin-independent pathway in mammalian cells. Its degradation is greatly accelerated by association with the polyamine-induced regulatory protein antizyme 1 (AZ1). Mouse ODC (mODC) that is expressed in the yeast Saccharomyces cerevisiae is also rapidly degraded by the proteasome of that organism. We have now carried out in vivo and in vitro studies to determine whether S. cerevisiae proteasomes recognize mODC degradation signals. Mutations of mODC that stabilized the protein in animal cells also did so in the fungus. Moreover, the mODC degradation signal was able to destabilize a GFP or Ura3 reporter in GFP-mODC and Ura3-mODC fusion proteins. Co-expression of AZ1 accelerated mODC degradation 2-3-fold in yeast cells. The degradation of both mODC and the endogenous yeast ODC (yODC) was unaffected in S. cerevisiae mutants with various defects in ubiquitin metabolism, and ubiquitinylated forms of mODC were not detected in yeast cells. In addition, recombinant mODC was degraded in an ATP-dependent manner by affinity-purified yeast 26 S proteasomes in the absence of ubiquitin. Degradation by purified yeast proteasomes was sensitive to mutations that stabilized mODC in vivo, but was not accelerated by recombinant AZ1. These studies demonstrate that cell constituents required for mODC degradation are conserved between animals and fungi, and that both mammalian and fungal ODC are subject to proteasome-mediated proteolysis by ubiquitin-independent mechanisms.
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Affiliation(s)
- Martin A Hoyt
- Department of Microbiology and Immunology, University of California, San Francisco, California 94143-0414, USA
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79
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Zhang M, Pickart CM, Coffino P. Determinants of proteasome recognition of ornithine decarboxylase, a ubiquitin-independent substrate. EMBO J 2003; 22:1488-96. [PMID: 12660156 PMCID: PMC152902 DOI: 10.1093/emboj/cdg158] [Citation(s) in RCA: 166] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Ornithine decarboxylase (ODC) is regulated by its metabolic products through a feedback loop that employs a second protein, antizyme 1 (AZ1). AZ1 accelerates the degradation of ODC by the proteasome. We used purified components to study the structural elements required for proteasomal recognition of this ubiquitin-independent substrate. Our results demonstrate that AZ1 acts on ODC to enhance the association of ODC with the proteasome, not the rate of its processing. Substrate-linked or free polyubiquitin chains compete for AZ1-stimulated degradation of ODC. ODC-AZ1 is therefore recognized by the same element(s) in the proteasome that mediate recognition of polyubiquitin chains. The 37 C-terminal amino acids of ODC harbor an AZ1-modulated recognition determinant. Within the ODC C terminus, three subsites are functionally distinguishable. The five terminal amino acids (ARINV, residues 457-461) collaborate with residue C441 to constitute one recognition element, and AZ1 collaborates with additional constituents of the ODC C terminus to generate a second recognition element.
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Affiliation(s)
- Mingsheng Zhang
- Department of Microbiology and Immunology, University of California, San Francisco, CA 94143, USA
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80
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Chen H, MacDonald A, Coffino P. Structural elements of antizymes 1 and 2 are required for proteasomal degradation of ornithine decarboxylase. J Biol Chem 2002; 277:45957-61. [PMID: 12359729 DOI: 10.1074/jbc.m206799200] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The antizymes constitute a conserved gene family with at least three mammalian orthologs. As described previously, in a degradation system utilizing rabbit reticulocyte lysate, antizyme 1 (AZ1) accelerates proteasomal ornithine decarboxylase (ODC) degradation, but antizyme 2 (AZ2) does not. To examine the relationship between antizyme structure and function, we further characterized the properties of AZ1 and AZ2 and protein chimeras composed of elements of the two. AZ1 binds to ODC with about a 3-fold higher potency than AZ2, but this cannot account for their distinct degradative activities. The dissimilar degradative capacity of AZ1 and AZ2 is also observed using purified proteasomes. A series of reciprocal AZ1/AZ2 chimeras was used to determine the sequence elements needed to direct ODC degradation. An element contained within amino acids 130-145 of AZ1 is essential for this function. Constructs in which amino acids 130-145 were exchanged between the antizymes confirmed the critical nature of this region. Within this region, amino acids 131 and 145 proved responsible for the functional difference between the two forms of AZ.
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Affiliation(s)
- Hui Chen
- Department of Microbiology and Immunology, University of California, San Francisco, San Francisco, California 94143-0414, USA
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81
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Morehead TA, Gurnon JR, Adams B, Nickerson KW, Fitzgerald LA, Van Etten JL. Ornithine decarboxylase encoded by chlorella virus PBCV-1. Virology 2002; 301:165-75. [PMID: 12359457 DOI: 10.1006/viro.2002.1573] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Sequence analysis of the 330-kb genome of chlorella virus PBCV-1 revealed an open reading frame, A207R, which encodes a protein with 37-41% amino acid identity to ornithine decarboxylase (ODC) from many eukaryotic organisms. The a207r gene was cloned and the protein was expressed as a His-A207R fusion protein in Escherichia coli. The recombinant protein catalyzes pyridoxal 5'-phosphate-dependent decarboxylation of ornithine to putrescine, the first step in the polyamine biosynthetic pathway. The enzyme has a pH optimum of 9.0 and a temperature optimum of 42 degrees C, and it requires dithiothreitol for maximal activity. The enzyme has a K(m) for ornithine of 0.78 mM and a specific activity of 100 micromol/min/mg protein. PBCV-1 ODC is quite sensitive to the competitive inhibitor L-arginine and the irreversible inhibitor difluoromethylarginine but it is less sensitive to the irreversible inhibitor difluoromethylornithine. The a207r gene is expressed both early and late in PBCV-1 infection and is highly conserved among the chlorella viruses. The 42-kDa PBCV-1 ODC (372 amino acids) is the smallest ODC in the databases and, to our knowledge, is the first virus-encoded ODC.
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Affiliation(s)
- Tiara A Morehead
- Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska 68583-0722, USA
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82
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Gandre S, Kahana C. Degradation of ornithine decarboxylase in Saccharomyces cerevisiae is ubiquitin independent. Biochem Biophys Res Commun 2002; 293:139-44. [PMID: 12054575 DOI: 10.1016/s0006-291x(02)00194-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Ornithine decarboxylase (ODC), the first rate-limiting enzyme in the polyamine biosynthesis is one of the most rapidly degraded proteins in eukaryotic cells. Mammalian ODC is a notable exception to the widely accepted dogma that ubiquitination is always required for targeting a protein to degradation by the 26S proteasome. However, while it is well established that in mammalian cells degradation of ODC is ubiquitin independent, the requirement of ubiquitination for degradation of ODC in yeast cells remained undetermined. We have investigated ODC degradation in three mutant strains of Saccharomyces cerevisiae in which ubiquitin-dependent protein degradation activity is severely compromised. While yeast ODC was rapidly degraded in all these mutant strains the degradation of N-end rule substrates was inhibited. A mutant mouse ODC that fails to interact with Az was rapidly degraded in yeast cells but was stable in mammalian cells suggesting that interaction with a mammalian Az like yeast protein is not necessary for the degradation of ODC in yeast cells. Deletion analysis revealed that sequences from its unique N-terminus are involved in targeting yeast ODC to rapid degradation in yeast cells.
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Affiliation(s)
- Shilpa Gandre
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel
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83
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Babal P, Ruchko M, Ault-Ziel K, Cronenberg L, Olson JW, Gillespie MN. Regulation of ornithine decarboxylase and polyamine import by hypoxia in pulmonary artery endothelial cells. Am J Physiol Lung Cell Mol Physiol 2002; 282:L840-6. [PMID: 11880311 DOI: 10.1152/ajplung.00347.2001] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In rat lung and cultured lung vascular cells, hypoxia decreases ornithine decarboxylase (ODC) activity and increases polyamine import. In this study, we used rat cultured pulmonary artery endothelial cells to explore the mechanism of hypoxia-induced reduction in ODC activity and determined whether this event was functionally related to the increase in polyamine import. Two strategies known to suppress proteasome-mediated ODC degradation, lactacystin treatment and use of cells expressing a truncated ODC incapable of interacting with the proteasome, prevented the hypoxia-induced decrease in ODC activity. Interestingly, though, cellular abundance of the 24-kDa antizyme, a known physiological accelerator of ODC degradation, was not increased by hypoxia. These observations suggest that an antizyme-independent ODC degradation pathway contributes to hypoxia-induced reductions of ODC activity. When reductions in ODC activity in hypoxia were prevented by the proteasome inhibitor strategies, hypoxia failed to increase polyamine transport. The induction of polyamine transport in hypoxic pulmonary artery endothelial cells thus seems to require decreased ODC activity as an initiating event.
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MESH Headings
- Animals
- Blotting, Western
- Carbon Radioisotopes
- Cattle
- Cells, Cultured
- Endothelium, Vascular/cytology
- Endothelium, Vascular/enzymology
- Enzyme Activation/physiology
- Gene Expression Regulation, Enzymologic
- Hypertension, Pulmonary/metabolism
- Hypoxia/metabolism
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/enzymology
- Ornithine Decarboxylase/genetics
- Ornithine Decarboxylase/metabolism
- Polyamines/pharmacokinetics
- Proteins/analysis
- Proteins/metabolism
- Pulmonary Artery/cytology
- Pulmonary Artery/enzymology
- Putrescine/pharmacokinetics
- RNA, Messenger/analysis
- Rats
- Rats, Sprague-Dawley
- Spermidine/pharmacokinetics
- Spermine/pharmacokinetics
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Affiliation(s)
- Pavel Babal
- Department of Pharmacology, College of Medicine, University of South Alabama, Mobile, AL 36688, USA
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84
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Roberts SC, Scott J, Gasteier JE, Jiang Y, Brooks B, Jardim A, Carter NS, Heby O, Ullman B. S-adenosylmethionine decarboxylase from Leishmania donovani. Molecular, genetic, and biochemical characterization of null mutants and overproducers. J Biol Chem 2002; 277:5902-9. [PMID: 11734561 DOI: 10.1074/jbc.m110118200] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The polyamine biosynthetic enzyme, S-adenosylmethionine decarboxylase (ADOMETDC) has been advanced as a potential target for antiparasitic chemotherapy. To investigate the importance of this protein in a model parasite, the gene encoding ADOMETDC has been cloned and sequenced from Leishmania donovani. The Delta adometdc null mutants were created in the insect vector form of the parasite by double targeted gene replacement. The Delta adometdc strains were incapable of growth in medium without polyamines; however, auxotrophy could be rescued by spermidine but not by putrescine, spermine, or methylthioadenosine. Incubation of Delta adometdc parasites in medium lacking polyamines resulted in a drastic increase of putrescine and glutathione levels with a concomitant decrease in the amounts of spermidine and the spermidine-containing thiol trypanothione. Parasites transfected with an episomal ADOMETDC construct were created in both wild type and Delta adometdc parasites. ADOMETDC overexpression abrogated polyamine auxotrophy in the Delta adometdc L. donovani. In addition, ADOMETDC overproduction in wild type parasites alleviated the toxic effects of 5'-(((Z)-4-amino-2-butenyl)methylamino)-5'-deoxyadenosine (MDL 73811), but not pentamidine, berenil, or methylglyoxyl bis(guanylhydrazone), all inhibitors of ADOMETDC activities in vitro. The molecular, biochemical, and genetic characterization of ADOMETDC establishes that it is essential in L. donovani promastigotes and a potential target for therapeutic validation.
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Affiliation(s)
- Sigrid C Roberts
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97201-3098, USA
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85
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Pitkänen LT, Heiskala M, Andersson LC. Expression of a novel human ornithine decarboxylase-like protein in the central nervous system and testes. Biochem Biophys Res Commun 2001; 287:1051-7. [PMID: 11587527 DOI: 10.1006/bbrc.2001.5703] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Ornithine decarboxylase (ODC) is the key enzyme of polyamine synthesis. The physiological activity of ODC is associated with cell proliferation, and high ODC activities are encountered in rapidly growing cancer cells. We have cloned a cDNA for a novel human protein that is 54% identical to ODC and 45% identical to antizyme inhibitor (AZI). mRNA for ODC-paralogue (ODC-p) was found only in the central nervous system and testes, suggesting a role in terminal differentiation rather than cell proliferation. ODC-p occurs at least in eight alternatively spliced forms. In vitro translated ODC-p did not decarboxylate ornithine, whereas, in vivo, one splice variant exerted modest ODC-like activity upon expression in COS-7 cells. ODC-p has a unique mutation in cysteine 360, where this ornithine decarboxylase reaction-directing residue is substituted by a valine. This substitution might lead to an enzymatic reaction that differs from typical ODC activity. ODC-p might also function as a brain- and testis-specific AZI.
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Affiliation(s)
- L T Pitkänen
- Department of Pathology, University of Helsinki, Helsinki, Finland
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86
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Shantz LM, Feith DJ, Pegg AE. Targeted overexpression of ornithine decarboxylase enhances beta-adrenergic agonist-induced cardiac hypertrophy. Biochem J 2001; 358:25-32. [PMID: 11485548 PMCID: PMC1222028 DOI: 10.1042/0264-6021:3580025] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
These studies were designed to determine the consequences of constitutive overexpression of ornithine decarboxylase (ODC) in the heart. Induction of ODC is known to occur in response to agents that induce cardiac hypertrophy. However, it is not known whether high ODC levels are sufficient for the development of a hypertrophic phenotype. Transgenic mice were generated with cardiac-specific expression of a stable ODC protein using the alpha-myosin heavy-chain promoter. Founder lines with >1000-fold overexpression of ODC in the heart were established, resulting in a 50-fold overaccumulation of putrescine, 4-fold elevation in spermidine, a slight increase in spermine and accumulation of large amounts of cadaverine compared with littermate controls. Despite these significant alterations in polyamines, myocardial hypertrophy, as measured by ratio of heart to body weight, did not develop, although atrial natriuretic factor RNA was slightly elevated in transgenic ventricles. However, stimulation of beta-adrenergic signalling by isoproterenol resulted in severe hypertrophy and even death in ODC-overexpressing mice without further altering polyamine levels, compared with only a mild hypertrophy in littermates. When beta1-adrenergic stimulation was blocked by simultaneous treatment with isoproterenol and the beta1 antagonist atenolol, a significant, although reduced, hypertrophy was still present in the hearts of transgenic mice, suggesting that both beta1 and beta2 adrenergic receptors contribute to the hypertrophic phenotype. Therefore these mice provide a model to study the in vivo co-operativity between high ODC activity and activation of other pathways leading to hypertrophy in the heart.
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Affiliation(s)
- L M Shantz
- Department of Cellular and Molecular Physiology H166, P.O. Box 850, The Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, Hershey, PA 17033, USA.
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87
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Lövkvist Wallström E, Takao K, Wendt A, Vargiu C, Yin H, Persson L. Importance of the 3' untranslated region of ornithine decarboxylase mRNA in the translational regulation of the enzyme. Biochem J 2001; 356:627-34. [PMID: 11368794 PMCID: PMC1221878 DOI: 10.1042/0264-6021:3560627] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Translational regulation of ornithine decarboxylase (ODC), which catalyses the first step in the biosynthesis of polyamines, appears to be an important mechanism in the strong feedback control as well as in the hypotonic induction of the enzyme. However, the exact mechanisms are not yet understood. The ODC mRNA has long 5' and 3' untranslated regions (UTRs) which may be involved in the translational control of the enzyme. In the present study we have used a series of stable transfectants of Chinese Hamster ovary cells expressing ODC mRNAs with various truncations in the 5' and 3' UTRs to investigate the importance of these regions. It is demonstrated that neither the 5' UTR nor the 3' UTR appears to be involved in the polyamine-mediated feedback control of ODC synthesis. The hypotonic induction of ODC, on the other hand, was shown to be highly dependent on the presence of the 3' UTR, but not on the 5' UTR, of ODC mRNA. Cells expressing ODC mRNAs lacking the 3' UTR showed no, or only a very slight, induction of ODC whether the 5' UTR was present or not, whereas the cell lines expressing ODC mRNAs containing the 3' UTR (with or without the 5' UTR) markedly induced ODC after a hypotonic shock. The present finding of a role for the ODC mRNA 3' UTR in the hypotonic induction of ODC is the first demonstration of a specific effect of the 3' UTR in the regulation of ODC.
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Affiliation(s)
- E Lövkvist Wallström
- Department of Physiological Sciences, Lund University, Sölvegatan 19, S-223 62 Lund, Sweden
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88
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Bhatnagar P, Glasheen BM, Bains SK, Long SL, Minocha R, Walter C, Minocha SC. Transgenic manipulation of the metabolism of polyamines in poplar cells. PLANT PHYSIOLOGY 2001; 125:2139-53. [PMID: 11299393 PMCID: PMC88869 DOI: 10.1104/pp.125.4.2139] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2000] [Revised: 11/15/2000] [Accepted: 01/10/2001] [Indexed: 05/18/2023]
Abstract
The metabolism of polyamines (putrescine, spermidine, and spermine) has become the target of genetic manipulation because of their significance in plant development and possibly stress tolerance. We studied the polyamine metabolism in non-transgenic (NT) and transgenic cells of poplar (Populus nigra x maximowiczii) expressing a mouse Orn decarboxylase (odc) cDNA. The transgenic cells showed elevated levels of mouse ODC enzyme activity, severalfold higher amounts of putrescine, a small increase in spermidine, and a small reduction in spermine as compared with NT cells. The conversion of labeled ornithine (Orn) into putrescine was significantly higher in the transgenic than the NT cells. Whereas exogenously supplied Orn caused an increase in cellular putrescine in both cell lines, arginine at high concentrations was inhibitory to putrescine accumulation. The addition of urea and glutamine had no effect on polyamines in either of the cell lines. Inhibition of glutamine synthetase by methionine sulfoximine led to a substantial reduction in putrescine and spermidine in both cell lines. The results show that: (a) Transgenic expression of a heterologous odc gene can be used to modulate putrescine metabolism in plant cells, (b) accumulation of putrescine in high amounts does not affect the native arginine decarboxylase activity, (c) Orn biosynthesis occurs primarily from glutamine/glutamate and not from catabolic breakdown of arginine, (d) Orn biosynthesis may become a limiting factor for putrescine production in the odc transgenic cells, and (e) assimilation of nitrogen into glutamine keeps pace with an increased demand for its use for putrescine production.
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Affiliation(s)
- P Bhatnagar
- Department of Plant Biology, University of New Hampshire, Durham, New Hampshire 03824, USA
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89
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Abstract
Proteins that are degraded by the proteasome are first modified by a set of enzymes that attach multiple copies of ubiquitin to substrate lysines, but a tiny minority, including the polyamine-synthesizing enzyme ornithine decarboxylase, is handled differently. This enzyme is targeted for destruction by another protein--antizyme. Why does ornithine decarboxylase have its own dedicated destruction mechanism, how does it work, and is it the only protein to be targeted to the proteasome in this way?
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Affiliation(s)
- P Coffino
- Department of Microbiology and Immunology and Department of Medicine, University of California, San Francisco, San Francisco, California 94143-0414, USA.
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90
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Abstract
Ornithine decarboxylase (ODC) is among the small set of proteasome substrates that is not ubiquitinated. It is instead degraded in conjunction with the protein antizyme (AZ). ODC and AZ are participants in a regulatory circuit that restricts pools of polyamines, the downstream products of ODC enzymatic activity. Functional studies using directed mutagenesis have identified regions of ODC and AZ required for the process of ODC degradation. Within ODC, there is a region that is required for AZ binding which lies on the surface of an alpha-beta barrel forming one domain of the ODC monomer. A carboxy-terminal ODC domain is needed for both AZ-dependent and AZ-independent degradation. Within AZ, the carboxy-terminal half molecule is sufficient for binding to ODC, but an additional domain found within the AZ amino terminus must be present for stimulation of ODC degradation by the proteasome. Recently, the AZs have been found to consist of an ancient gene family. Within vertebrate species, multiple isoforms are found, with distinct functions that remain to be sorted out. Although AZ homologs have been found in some yeast species, homology searches have failed to identify an AZ homolog in Saccharomyces cerevisiae. Nevertheless, the close parallel between polyamine-induced ODC degradation in S. cerevisiae and in animal cells suggests that this organism will also be found to harbor an AZ-like protein.
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Affiliation(s)
- P Coffino
- Department of Microbiology and Immunology and Department of Medicine, University of California, San Francisco 94143-0414, USA.
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91
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Abstract
O-linked N-acetylglucosamine (O-GlcNAc) is a highly dynamic and abundant modification found on nuclear and cytoplasmic proteins of nearly all eukaryotes. O-GlcNAc addition is required for life at the single cell level and is analogous to protein phosphorylation in most respects. In a previous study (M.S. Jiang, G.W. Hart, A subpopulation of estrogen receptors are modified by O-linked N-acetylglucosamine. J. Biol. Chem. 270 (1997) 2421-2428), we demonstrated that a subpopulation of the murine estrogen receptor-alpha (mER-alpha) is modified by O-GlcNAc at Thr(575). Here we mutated mER-alpha to convert Thr(575) and Ser(576) to Val and Ala, respectively. Surprisingly, this glycosylation-site mutant is still extensively modified by O-GlcNAc. Analyses of glycopeptides identified two additional sites of modification on mER-alpha, at Ser(10) and Thr(50) near the N-terminus. The major glycosylation sites are within or near PEST regions, suggesting that O-GlcNAc may regulate mER-alpha turnover.
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Affiliation(s)
- X Cheng
- Department of Biological Chemistry, School of Medicine, Johns Hopkins University, 725 N Wolfe St., Baltimore, MD 21205-2185, USA
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92
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Mziaut H, Korza G, Ozols J. The N terminus of microsomal delta 9 stearoyl-CoA desaturase contains the sequence determinant for its rapid degradation. Proc Natl Acad Sci U S A 2000; 97:8883-8. [PMID: 10922050 PMCID: PMC16790 DOI: 10.1073/pnas.97.16.8883] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Stearoyl-CoA desaturase (SCD) is a key regulator of membrane fluidity, turns over rapidly, and represents a model for selective degradation of short-lived proteins of the endoplasmic reticulum (ER). The mechanism whereby specific ER proteins are targeted for degradation in the midst of stable proteins coexisting in the same membrane is unknown. To investigate the intracellular fate of SCD and to identify the determinants involved in the rapid turnover of SCD, we created chimeras of SCD tagged at the C terminus with the green fluorescent protein (GFP). The fusion proteins were expressed in Chinese hamster ovary cells and exhibited an ER localization. Unlike native GFP, the SCD-GFP construct was unstable and had a half life of a few hours. Truncated fusion proteins consisting of residues 27-358 and 45-358 of SCD linked to the N terminus of GFP were stable. To investigate the general applicability of the N terminus of SCD in the destabilization of proteins, we fused residues 1-33 of SCD to the N terminus of GFP. The resulting chimera was extremely short lived. To investigate the effect of membrane sidedness on the fusion protein degradation, we attached a lumenal targeting signal to the N terminus of SCD 1-33-GFP. The construct was localized to the lumen of ER and was metabolically stable, indicating that SCD degradation signal functions on the cytosolic rather than the lumenal side of the ER. These results demonstrate that the N-terminal segment of some 30 residues of SCD constitutes a motif responsible for the rapid degradation of SCD.
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Affiliation(s)
- H Mziaut
- Department of Biochemistry, University of Connecticut Health Center, Farmington, CT 06030-3305, USA
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93
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Starkova NN, Koroleva EP, Rotanova TV. Intracellular proteolysis: Signals of selective protein degradation. RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY 2000. [DOI: 10.1007/bf02759152] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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94
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Murakami Y, Matsufuji S, Hayashi SI, Tanahashi N, Tanaka K. ATP-Dependent inactivation and sequestration of ornithine decarboxylase by the 26S proteasome are prerequisites for degradation. Mol Cell Biol 1999; 19:7216-27. [PMID: 10490656 PMCID: PMC84714 DOI: 10.1128/mcb.19.10.7216] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The 26S proteasome is a eukaryotic ATP-dependent protease, but the molecular basis of its energy requirement is largely unknown. Ornithine decarboxylase (ODC) is the only known enzyme to be degraded by the 26S proteasome without ubiquitinylation. We report here that the 26S proteasome is responsible for the irreversible inactivation coupled to sequestration of ODC, a process requiring ATP and antizyme (AZ) but not proteolytic activity. Neither the 20S proteasome (catalytic core) nor PA700 (the regulatory complex) by itself contributed to this ODC inactivation. Analysis with a C-terminal mutant ODC revealed that the 26S proteasome recognizes the C-terminal degradation signal of ODC exposed by attachment of AZ, and subsequent ATP-dependent sequestration of ODC in the 26S proteasome causes irreversible inactivation, possibly unfolding, of ODC and dissociation of AZ. These processes may be linked to the translocation of ODC into the 20S proteasomal inner cavity, centralized within the 26S proteasome, for degradation.
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Affiliation(s)
- Y Murakami
- Department of Biochemistry 2, Jikei University School of Medicine, Minato-ku, Tokyo 105-8461, Japan.
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95
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Abstract
Green fluorescent protein (GFP) is a powerful tool for cell-based assays owing to the intrinsic fluorescence of this protein that allows real-time analysis of molecular events in living cells. A number of GFP variants have been developed with optimal properties for both high-throughput screening and high-content screening. The author discusses advances in basic GFP technology, including the discovery of fluorescent proteins from divergent bioluminescent species, as well as the development of various GFP biosensors suited to the drug discovery process.
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96
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Cubría JC, Ordóñez C, Reguera RM, Tekwani BL, Balaña-Fouce R, Ordóñez D. Early alterations of polyamine metabolism induced after acute administration of clenbuterol in mouse heart. Life Sci 1999; 64:1739-52. [PMID: 10353628 DOI: 10.1016/s0024-3205(99)00112-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
An acute treatment of mice with clenbuterol, a beta-adrenergic agonist, produced a marked increase of polyamines levels in heart, particularly during the early phase of administration of the drug. A single dose of 1.5 mg/kg caused as much as a 10 fold induction in activity of ornithine decarboxylase (ODC) and 3 to 4 fold increase in levels of putrescine, spermidine and spermine in mouse heart. Maximum changes were observed 3 to 4 hours post-administration of clenbuterol. This treatment did not produce any change in S-adenosylmethionine decarboxylase activity. The induction of cardiac ODC by clenbuterol was also dose dependent with a peak at about 5 micromol/kg. Co-administration of difluoromethylornithine, an irreversible inhibitor of ODC, or propranolol, a nonspecific beta-antagonist, with clenbuterol completely prevented the induction of ODC activity as well as the increase in polyamine levels in heart. However, pretreatment with alprenolol or metoprolol, the specific beta1 and beta2-antagonists, respectively, produced only partial prevention. The cardiac ODC from controls as well as clenbuterol treated mice exhibited similar affinity (Km) for its substrate, ornithine, while maximum enzyme activity (Vmax) was about 14 fold higher in clenbuterol treated mouse heart than in the control. Clenbuterol produced no change in the level of specific ODC mRNA or the protein, but the enzyme from the drug-treated mouse heart was considerably more stable than the control. Pretreatment of mice with either cycloheximide or actinomycin D followed by administration of clenbuterol could not prevent the induction in ODC activity suggesting that de novo biosynthesis of the enzyme protein or ODC mRNA was not responsible for induction of ODC activity. Post-translational changes in ODC may be responsible for an early increase of ODC activity due to clenbuterol treatment.
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Affiliation(s)
- J C Cubría
- Departamento de Fisiología, Farmacología y Toxicología (INTOXCAL), Universidad de León, Spain
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97
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Abstract
The polyamines spermine, spermidine, and putrescine are small organic molecules one or more of which are present in all living organisms. Many natural products contain polyamine residues. Polyamines are synthesized by a highly regulated pathway from arginine or ornithine and also can be transported in and out of cells. Polyamines are degraded to a variety of compounds the functions of which are largely unknown. Polyamines influence the transcriptional and translational stages of protein synthesis, stabilize membranes, and, in mammalian systems, modulate neurophysiological functions and may act as intracellular messengers. However, at the molecular level the mode of action of the polyamines is largely unknown.
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98
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Su K, Roos MD, Yang X, Han I, Paterson AJ, Kudlow JE. An N-terminal region of Sp1 targets its proteasome-dependent degradation in vitro. J Biol Chem 1999; 274:15194-202. [PMID: 10329728 DOI: 10.1074/jbc.274.21.15194] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The transcription factor Sp1 is important for the expression of many cellular genes. Previously, it was shown that reduced O-glycosylation of Sp1 is associated with increased proteasome susceptibility. Sp1 undergoes proteasome-dependent degradation in cells stressed with glucose deprivation and adenylate cyclase activation, and this process is blocked in cells treated with glucosamine. In this study, using a reconstituted in vitro system, we identified the principal structural determinant in Sp1 that targets Sp1 for proteasome-dependent degradation. We found by using deletion analysis that the N-terminal 54 amino acids of Sp1 is required for Sp1 degradation. This element can act as an independent processing signal by directing degradation of an unrelated protein. Recognition of this Sp1 element by the proteasome-dependent system is saturable, and ubiquitination of this element is not required for recognition. Time course experiments revealed that Sp1 degradation is a two-step process. First, a discrete endoproteolytic cleavage occurs downstream of the target region immediately C-terminal to Leu56. The Sp1 sequence C-terminal to the cleavage site is subsequently degraded, whereas the N-terminal peptide remains intact. The identification of this Sp1 degradation-targeting signal will facilitate the identification of the critical proteins involved in the control of Sp1 proteasome-dependent degradation and the role of OGlcNAc in this process.
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Affiliation(s)
- K Su
- Departments of Medicine and Cell Biology, Division of Endocrinology and Metabolism, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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99
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Kern AD, Oliveira MA, Coffino P, Hackert ML. Structure of mammalian ornithine decarboxylase at 1.6 A resolution: stereochemical implications of PLP-dependent amino acid decarboxylases. Structure 1999; 7:567-81. [PMID: 10378276 DOI: 10.1016/s0969-2126(99)80073-2] [Citation(s) in RCA: 122] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
BACKGROUND Pyridoxal-5'-phosphate (PLP) dependent enzymes catalyze a broad range of reactions, resulting in bond cleavage at C alpha, C beta, or C gamma carbons of D and L amino acid substrates. Ornithine decarboxylase (ODC) is a PLP-dependent enzyme that controls a critical step in the biosynthesis of polyamines, small organic polycations whose controlled levels are essential for proper growth. ODC inhibition has applications for the treatment of certain cancers and parasitic ailments such as African sleeping sickness. RESULTS The structure of truncated mouse ODC (mODC') was determined by multiple isomorphous replacement methods and refined to 1.6 A resolution. This is the first structure of a Group IV decarboxylase. The monomer contains two domains: an alpha/beta barrel that binds the cofactor, and a second domain consisting mostly of beta structure. Only the dimer is catalytically active, as the active sites are constructed of residues from both monomers. The interactions stabilizing the dimer shed light on its regulation by antizyme. The overall structure and the environment of the cofactor are compared with those of alanine racemase. CONCLUSIONS The analysis of the mODC' structure and its comparison with alanine racemase, together with modeling studies of the external aldimine intermediate, provide insight into the stereochemical characteristics of PLP-dependent decarboxylation. The structure comparison reveals stereochemical differences with other PLP-dependent enzymes and the bacterial ODC. These characteristics may be exploited in the design of new inhibitors specific for eukaryotic and bacterial ODCs, and provide the basis for a detailed understanding of the mechanism by which these enzymes regulate reaction specificity.
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Affiliation(s)
- A D Kern
- Department of Chemistry and Biochemistry, University of Texas at Austin 78712, USA
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100
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Li X, Zhao X, Fang Y, Jiang X, Duong T, Fan C, Huang CC, Kain SR. Generation of destabilized green fluorescent protein as a transcription reporter. J Biol Chem 1998; 273:34970-5. [PMID: 9857028 DOI: 10.1074/jbc.273.52.34970] [Citation(s) in RCA: 619] [Impact Index Per Article: 23.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The green fluorescent protein (GFP) is a widely used reporter in gene expression and protein localization studies. GFP is a stable protein; this property allows its accumulation and easy detection in cells. However, this stability also limits its application in studies that require rapid reporter turnover. We created a destabilized GFP for use in such studies by fusing amino acids 422-461 of the degradation domain of mouse ornithine decarboxylase (MODC) to the C-terminal end of an enhanced variant of GFP (EGFP). The fusion protein, unlike EGFP, was unstable in the presence of cycloheximide and had a fluorescence half-life of 2 h. Western blot analysis indicated that the fluorescence decay of EGFP-MODC-(422-461) was correlated with degradation of the fusion protein. We mutated key amino acids in the PEST sequence of EGFP-MODC-(422-461) and identified several mutants with variable half-lives. The suitability of destabilized EGFP as a transcription reporter was tested by linking it to NFkappaB binding sequences and monitoring tumor necrosis factor alpha-mediated NFkappaB activation. We obtained time course induction and dose response kinetics similar to secreted alkaline phosphatase obtained in transfected cells. This result did not occur when unmodified EGFP was used as the reporter. Because of its autofluorescence, destabilized EGFP can be used to directly correlate gene induction with biochemical change, such as NFkappaB translocation to the nucleus.
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Affiliation(s)
- X Li
- Laboratories, Inc., Palo Alto, California 94303, USA.
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