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Boland EL, Van Dyken CM, Duckett RM, McCluskey AJ, Poon GMK. Structural complementation of the catalytic domain of pseudomonas exotoxin A. J Mol Biol 2014; 426:645-55. [PMID: 24211469 PMCID: PMC3997303 DOI: 10.1016/j.jmb.2013.11.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Revised: 10/28/2013] [Accepted: 11/04/2013] [Indexed: 12/17/2022]
Abstract
The catalytic moiety of Pseudomonas exotoxin A (domain III or PE3) inhibits protein synthesis by ADP-ribosylation of eukaryotic elongation factor 2. PE3 is widely used as a cytocidal payload in receptor-targeted protein toxin conjugates. We have designed and characterized catalytically inactive fragments of PE3 that are capable of structural complementation. We dissected PE3 at an extended loop and fused each fragment to one subunit of a heterospecific coiled coil. In vitro ADP-ribosylation and protein translation assays demonstrate that the resulting fusions-supplied exogenously as genetic elements or purified protein fragments-had no significant catalytic activity or effect on protein synthesis individually but, in combination, catalyzed the ADP-ribosylation of eukaryotic elongation factor 2 and inhibited protein synthesis. Although complementing PE3 fragments are catalytically less efficient than intact PE3 in cell-free systems, co-expression in live cells transfected with transgenes encoding the toxin fusions inhibits protein synthesis and causes cell death comparably as intact PE3. Complementation of split PE3 offers a direct extension of the immunotoxin approach to generate bispecific agents that may be useful to target complex phenotypes.
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Affiliation(s)
- Erin L Boland
- Department of Pharmaceutical Sciences, Washington State University, Pullman, WA 99164, USA
| | - Crystal M Van Dyken
- Department of Pharmaceutical Sciences, Washington State University, Pullman, WA 99164, USA
| | - Rachel M Duckett
- Department of Pharmaceutical Sciences, Washington State University, Pullman, WA 99164, USA
| | - Andrew J McCluskey
- Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA 02115, USA.
| | - Gregory M K Poon
- Department of Pharmaceutical Sciences, Washington State University, Pullman, WA 99164, USA.
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2
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Denton PW, Long JM, Wietgrefe SW, Sykes C, Spagnuolo RA, Snyder OD, Perkey K, Archin NM, Choudhary SK, Yang K, Hudgens MG, Pastan I, Haase AT, Kashuba AD, Berger EA, Margolis DM, Garcia JV. Targeted cytotoxic therapy kills persisting HIV infected cells during ART. PLoS Pathog 2014; 10:e1003872. [PMID: 24415939 PMCID: PMC3887103 DOI: 10.1371/journal.ppat.1003872] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2013] [Accepted: 11/22/2013] [Indexed: 11/18/2022] Open
Abstract
Antiretroviral therapy (ART) can reduce HIV levels in plasma to undetectable levels, but rather little is known about the effects of ART outside of the peripheral blood regarding persistent virus production in tissue reservoirs. Understanding the dynamics of ART-induced reductions in viral RNA (vRNA) levels throughout the body is important for the development of strategies to eradicate infectious HIV from patients. Essential to a successful eradication therapy is a component capable of killing persisting HIV infected cells during ART. Therefore, we determined the in vivo efficacy of a targeted cytotoxic therapy to kill infected cells that persist despite long-term ART. For this purpose, we first characterized the impact of ART on HIV RNA levels in multiple organs of bone marrow-liver-thymus (BLT) humanized mice and found that antiretroviral drug penetration and activity was sufficient to reduce, but not eliminate, HIV production in each tissue tested. For targeted cytotoxic killing of these persistent vRNA(+) cells, we treated BLT mice undergoing ART with an HIV-specific immunotoxin. We found that compared to ART alone, this agent profoundly depleted productively infected cells systemically. These results offer proof-of-concept that targeted cytotoxic therapies can be effective components of HIV eradication strategies.
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Affiliation(s)
- Paul W. Denton
- Division of Infectious Diseases, Department of Medicine, UNC Center for AIDS Research, University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
| | - Julie M. Long
- Division of Infectious Diseases, Department of Medicine, UNC Center for AIDS Research, University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
| | - Stephen W. Wietgrefe
- Department of Microbiology, University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Craig Sykes
- Division of Pharmacotherapy and Experimental Therapeutics, UNC Eshelman School of Pharmacy, UNC Center for AIDS Research, University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
| | - Rae Ann Spagnuolo
- Division of Infectious Diseases, Department of Medicine, UNC Center for AIDS Research, University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
| | - Olivia D. Snyder
- Division of Infectious Diseases, Department of Medicine, UNC Center for AIDS Research, University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
| | - Katherine Perkey
- Department of Microbiology, University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Nancie M. Archin
- Division of Infectious Diseases, Department of Medicine, UNC Center for AIDS Research, University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
| | - Shailesh K. Choudhary
- Division of Infectious Diseases, Department of Medicine, UNC Center for AIDS Research, University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
| | - Kuo Yang
- Division of Pharmacotherapy and Experimental Therapeutics, UNC Eshelman School of Pharmacy, UNC Center for AIDS Research, University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
| | - Michael G. Hudgens
- Department of Biostatistics, UNC Center for AIDS Research, University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
| | - Ira Pastan
- Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Ashley T. Haase
- Department of Microbiology, University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Angela D. Kashuba
- Division of Pharmacotherapy and Experimental Therapeutics, UNC Eshelman School of Pharmacy, UNC Center for AIDS Research, University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
| | - Edward A. Berger
- Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - David M. Margolis
- Division of Infectious Diseases, Department of Medicine, UNC Center for AIDS Research, University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
| | - J. Victor Garcia
- Division of Infectious Diseases, Department of Medicine, UNC Center for AIDS Research, University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America
- * E-mail:
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Romaniuk SI, Kolybo DV, Komisarenko SV. Recombinant diphtheria toxin derivatives: Perspectives of application. RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY 2012; 38:639-52. [DOI: 10.1134/s106816201206012x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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Molecular decoys: antidotes, therapeutics and immunomodulators. Curr Opin Biotechnol 2008; 19:644-51. [PMID: 18977299 PMCID: PMC7127390 DOI: 10.1016/j.copbio.2008.10.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2008] [Revised: 09/17/2008] [Accepted: 10/03/2008] [Indexed: 12/27/2022]
Abstract
Receptor–ligand interactions are fundamental to the regulation of cell physiology, enabling the communication between cells and their environment via signal transduction. Receptors are also exploited by toxins and infectious agents to mediate pathogenesis. Over the past 20 years, however, this bi-partite paradigm for cellular regulation, that is, receptors and their ligands, has been revised to include an unforeseen participant namely, soluble receptors or molecular decoys. Decoys function as nature's modifiers of potent responses such as inflammation, stimulation of cell proliferation and triggering apoptosis. Decoys not only provide the means to fine tune the regulation of these phenomena; they also serve as potential leads for the development of recombinant anti-toxins, anti-viral agents and novel therapeutics for combating cancer and inflammatory disease.
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5
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Weng A, Melzig M, Bachran C, Fuchs H. Enhancement of Saporin Toxicity Against U937 Cells byGypsophilaSaponins. J Immunotoxicol 2008; 5:287-92. [DOI: 10.1080/15376510802312266] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Affiliation(s)
- A. Weng
- Institute of Pharmacy, Free University Berlin, Berlin, Germany
| | - M.F. Melzig
- Institute of Pharmacy, Free University Berlin, Berlin, Germany
| | - C. Bachran
- Zentralinstitut für Laboratoriumsmedizin und Pathobiochemie, Charité – Universitätsmedizin Berlin, Berlin
| | - H. Fuchs
- Zentralinstitut für Laboratoriumsmedizin und Pathobiochemie, Charité – Universitätsmedizin Berlin, Berlin
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He YW, Guo CX, Pan YF, Peng C, Weng ZH. Inhibition of hepatitis B virus replication by pokeweed antiviral protein in vitro. World J Gastroenterol 2008; 14:1592-7. [PMID: 18330954 PMCID: PMC2693758 DOI: 10.3748/wjg.14.1592] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
AIM: To explore the inhibitory effects of pokeweed antiviral protein seed (PAP-S) and PAP encoded by a eukaryotic expression plasmid on hepatitis B virus (HBV) replication in vitro.
METHODS: HepG2 2.2.15 cells in cultured medium were treated with different concentrations of PAP-S. HBsAg, HBeAg and HBV DNA in supernatants were determined by ELISA and fluorescent quantitative PCR respectively. MTT method was used to assay for cytotoxicity. HepG2 were cotransfected with various amounts of PAP encoded by a eukaryotic expression plasmid and replication competent wild-type HBV 1.3 fold over-length plasmid. On d 3 after transfection, HBsAg and HBeAg were determined by using ELISA. Levels of HBV core-associated DNA and RNA were detected by using Southern and Northern blot, respectively.
RESULTS: The inhibitory effects of PAP-S on HBsAg, HBeAg and HBV DNA were gradually enhanced with the increase of PAP concentration. When the concentration of PAP-S was 10 &mgr;g/mL, the inhibition rates of HBsAg, HBeAg and HBV DNA were 20.9%, 30.2% and 50%, respectively. After transfection of 1.0 &mgr;g and 2.0 &mgr;g plasmid pXF3H-PAP, the levels of HBV nucleocapside-associated DNA were reduced by 38.0% and 74.0% respectively, the levels of HBsAg in the media by 76.8% and 99.7% respectively, and the levels of HBeAg by 72.7% and 99.3% respectively as compared with controls. Transfection with 2 &mgr;g plasmid pXF3H-PAP reduced the levels of HBV nucleocapside-associated RNA by 69.0%.
CONCLUSION: Both PAP-S and PAP encoded by a eukaryotic expression plasmid could effectively inhibit HBV replication and antigen expression in vitro, and the inhibitory effects were dose-dependent.
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Kennedy PE, Bera TK, Wang QC, Gallo M, Wagner W, Lewis MG, Berger EA, Pastan I. Anti-HIV-1 immunotoxin 3B3(Fv)-PE38: enhanced potency against clinical isolates in human PBMCs and macrophages, and negligible hepatotoxicity in macaques. J Leukoc Biol 2006; 80:1175-82. [PMID: 16923920 DOI: 10.1189/jlb.0306139] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Highly active antiretroviral therapy (HAART) against human immunodeficiency virus type 1 (HIV-1) infection dramatically suppresses viral load, leading to marked reductions in HIV-1 associated morbidity and mortality. However, infected cell reservoirs and low-level replication persist in the face of suppressive HAART, leading invariably to viral rebound upon cessation of treatment. Toxins engineered to target the Env glycoprotein on the surface of productively infected cells represent a complementary strategy to deplete these reservoirs. We described previously highly selective killing of Env-expressing cell lines by CD4(178)-PE40 and 3B3(Fv)-PE38, recombinant derivatives of Pseudomonas aeruginosa exotoxin A containing distinct targeting moieties against gp120. In the present report, we compare the in vitro potency and breadth of these chimeric toxins against multiple clinical HIV-1 isolates, replicating in biologically relevant primary human target cell types. In PBMCs, 3B3(Fv)-PE38 blocked spreading infection by all isolates examined, with greater potency than CD4(178)-PE40. 3B3(Fv)-PE38 also potently inhibited spreading HIV-1 infection in primary macrophages. Control experiments demonstrated that in both target cell types, most of the 3B3(Fv)-PE38 activity was due to selective killing of infected cells, and not merely to neutralization by the antibody moiety of the chimeric toxin. High-dose treatment of rhesus macaques with 3B3(Fv)-PE38 did not induce liver toxicity, whereas equivalent dosage of CD4(178)-PE40 induced mild hepatotoxicity. These findings highlight the potential use of 3B3(Fv)-PE38 for depleting HIV-infected cell reservoirs persisting in the face of HAART.
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Affiliation(s)
- Paul E Kennedy
- Laboratory of Viral Diseases, NIAID, National Institutes of Health Building 4, Room 237 Bethesda, MD 20892, USA
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Abstract
The main results of the research performed in the last 30 years on ribosome-inactivating proteins (RIPs) are reviewed, with emphasis on the new, controversial and uncertain aspects. The nature, distribution, mechanism of action and properties of these proteins are briefly reported, together with their possible applications. A pattern appears of a still largely unexplored subject, whose role in nature is probably important, and not limited to the biology of plants, since RIPs have been found also in other organisms.
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Affiliation(s)
- Fiorenzo Stirpe
- Dipartimento di Patologia Sperimentale, Università di Bologna, I-40125 Bologna, Italy.
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Lueders KK, De Rosa SC, Valentin A, Pavlakis GN, Roederer M, Hamer DH. A potent anti-HIV immunotoxin blocks spreading infection by primary HIV type 1 isolates in multiple cell types. AIDS Res Hum Retroviruses 2004; 20:145-50. [PMID: 15018701 DOI: 10.1089/088922204773004851] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Although several immunotoxins that selectively kill HIV-1-infected cells have been described, their clinical utility is limited by low potency against spreading viral infection. We show here that changing the carboxyterminal sequence of an anti-HIV-1 envelope immunotoxin to the consensus endoplasmic reticulum retention sequence KDEL substantially improves its ability to block infection of peripheral blood mononuclear cells by primary HIV-1 isolates without increasing nonspecific toxicity. Polychromatic flow cytometry of peripheral blood mononuclear cells (PBMC) infected with an HIV-1-GFP reporter virus demonstrated that the improved immunotoxin is active against a variety of primary cell types including memory T cells, NK-T cells, and monocyte/macrophages. The subnanomolar potency of this agent suggests that it could be clinically useful either as an adjuvant to highly active antiretroviral therapy (HAART) in drug-resistant patients or to reduce the reservoir of latently infected cells that is implicated in HIV-1 persistence.
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Affiliation(s)
- Kira K Lueders
- Laboratory of Biochemistry, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
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Tomatsu M, Kondo T, Yoshikawa T, Komeno T, Adachi N, Kawasaki Y, Ikuta A, Tashiro F. An apoptotic inducer, aralin, is a novel type II ribosome-inactivating protein from Aralia elata. Biol Chem 2004; 385:819-27. [PMID: 15493877 DOI: 10.1515/bc.2004.107] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
We recently found that aralin, a novel cytotoxic protein consisting of two subunits, from Aralia elata selectively induces apoptosis in transformed cells as compared to normal cells. Here we report that aralin is a lectin specific for galactose (Gal) and its derivatives, and possesses RNA N-glycosidase activity as a new type II ribosome-inactivating protein (RIP). The RNA N-glycosidase activity of aralin was detected in cell-free and whole cell systems by the generation of an R-fragment from 28S rRNA. Coinciding with appearance of the R-fragment in aralin-treated cells, significant inhibition of protein synthesis was observed prior to the onset of apoptosis. Aralin-evoked cell death was efficiently repressed by the addition of Gal and its derivatives. Interestingly, melibiose preferentially protected normal cells from apoptosis as compared with transformed cells. Using rhodamine-coupled aralin, the aralin receptor could be clearly detected around the cell surface of transformed cells, but to a lesser extent on normal cells. Receptor binding was suppressed by Gal. These results indicate that aralin is incorporated into cells via its Gal-containing cell surface receptor and induces apoptosis through its RIP activity. Moreover, the expression level and/or structural changes of the aralin receptor may affect the sensitivity toward aralin.
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Affiliation(s)
- Makoto Tomatsu
- Akita Research Institute of Food and Brewing, Arayamachi, Akita 010-1623, Japan.
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McHugh L, Hu S, Lee BK, Santora K, Kennedy PE, Berger EA, Pastan I, Hamer DH. Increased affinity and stability of an anti-HIV-1 envelope immunotoxin by structure-based mutagenesis. J Biol Chem 2002; 277:34383-90. [PMID: 12119300 DOI: 10.1074/jbc.m205456200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
HIV-infected cells are selectively killed by an immunotoxin in which a truncated form of Pseudomonas exotoxin A is joined to the variable region of a broadly neutralizing antibody (3B3) that recognizes the viral envelope glycoprotein (Env). To improve the efficacy of this molecule, we used three-dimensional structural information and phage selection data to design 23 single and multiple point mutations in the antibody variable region sequences that contact Env. Substituting an aromatic residue for an aspartate in the third complementarity-determining region of V(H) increased the potency of the immunotoxin by approximately 10-fold in a cell-killing assay. Detailed analysis of one such mutant, N31H/Q100eY, revealed both a higher affinity for monomeric and cell surface Env and an increased stability against aggregation compared with the starting immunotoxin. Conversion to a disulfide-linked two-chain format further stabilized the protein. N31H/Q100eY retained the ability to bind to Env from multiple viral isolates, to inhibit Env-mediated cell fusion, and to limit spreading viral infection in peripheral blood mononuclear cells. Such site-directed mutants may increase the utility of immunotoxins for reducing or eradicating persistent HIV-1 infection in humans.
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Affiliation(s)
- Louise McHugh
- Laboratory of Biochemistry, National Cancer Institute/National Institutes of Health, 37 Convent Drive, Bethesda, MD 20892, USA
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12
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Campos EC, Schiavi C, Bolognesi A, Bellusci C, Lubelli C, Duca A, Polito L, Poulas K, Tzartos SJ, Stirpe F. Selective lesions of rabbit extraocular muscles injected with the anti-AChR immunotoxin saporin-mAb 73. Curr Eye Res 2002; 24:58-65. [PMID: 12187496 DOI: 10.1076/ceyr.24.1.58.5430] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
PURPOSE To evaluate the effects on extraocular muscles of a skeletal muscle-specific immunotoxin, saporin-mAb 73, as an alternative to botulinum toxin to induce a permanent correction of oculo-facial dystonias or some forms of ocular motility disorders. METHODS An immunotoxin was prepared with a monoclonal antibody (mAb 73) against acetylcholine receptors of skeletal muscle, linked to saporin, a type 1 ribosome-inactivating protein (RIP) from Saponaria officinalis. Sixteen New Zealand white rabbits were treated with a single injection of immunotoxin directly into the medial rectus muscle of one eye. Four different dosages of 2, 5, 20, or 50 ng saporin-mAb 73 were used. The rabbits were sacrificed at two, 7 and 14 days post-injection. The medial rectus muscle and the retractor bulbi muscle of both the injected and the fellow eyes were taken and serial sections were examined by light microscopy in a blinded manner. RESULTS Saporin-mAb 73, even at the dosage of 2 ng, brought about focal damage in the extraocular muscles of rabbits without histological changes in adjacent muscles. The histological examination revealed necrotic/apoptotic lesions restricted to the sites of inoculation and largely infiltrated by macrophages. No evident inflammatory reaction was detected at any time and neutrophils were substantially absent. At 14 days after injection, necrosis/apoptosis was still evident and the sclerotic reaction was minimal. CONCLUSIONS The immunotoxin saporin-mAb 73 injections into the extraocular muscles of rabbits caused focal damage to the muscles. There was no significant inflammatory reaction and muscle fiber loss was present even at the lower doses. Although the lesions were followed for only 14 days, our results suggest that saporin-mAb 73 has potential to cause safe focal muscle damage but longer-term follow-up are needed to investigate the persistence of muscle weakness.
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Affiliation(s)
- Emilio C Campos
- Ophthalmology Unit, University of Bologna, School of Medicine, Bologna, Italy.
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Senchenkov A, Han TY, Wang H, Frankel AE, Kottke TJ, Kaufmann SH, Cabot MC. Enhanced ceramide generation and induction of apoptosis in human leukemia cells exposed to DT(388)-granulocyte-macrophage colony-stimulating factor (GM-CSF), a truncated diphtheria toxin fused to human GM-CSF. Blood 2001; 98:1927-34. [PMID: 11535531 DOI: 10.1182/blood.v98.6.1927] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
DT(388)-GM-CSF, a targeted fusion toxin constructed by conjugation of human granulocyte-macrophage colony-stimulating factor (GM-CSF) with the catalytic and translocation domains of diphtheria toxin, is presently in phase I trials for patients with resistant acute myeloid leukemia. HL-60/VCR, a multidrug-resistant human myeloid leukemia cell line, and wild-type HL-60 cells were used to study the impact of DT(388)-GM-CSF on metabolism of ceramide, a modulator of apoptosis. After 48 hours with DT(388)-GM-CSF (10 nM), ceramide levels in HL-60/VCR cells rose 6-fold and viability fell to 10%, whereas GM-CSF alone was without influence. Similar results were obtained in HL-60 cells. Examination of the time course revealed that protein synthesis decreased by about 50% and cellular ceramide levels increased by about 80% between 4 and 6 hours after addition of DT(388)-GM-CSF. By 6 hours this was accompanied by activation of caspase-9, followed by activation of caspase-3, cleavage of caspase substrates, and chromatin fragmentation. Hygromycin B and emetine failed to elevate ceramide levels or induce apoptosis at concentrations that inhibited protein synthesis by 50%. Exposure to C(6)-ceramide inhibited protein synthesis (EC(50) approximately 5 microM) and decreased viability (EC(50) approximately 6 microM). Sphingomyelinase treatment depleted sphingomyelin by about 10%, while increasing ceramide levels and inhibiting protein synthesis. Diphtheria toxin increased ceramide and decreased sphingomyelin in U-937 cells, a cell line extremely sensitive to diphtheria toxin; exposure to DT(388)-GM-CSF showed sensitivity at less than 1.0 pM. Diphtheria toxin and conjugate trigger ceramide formation that contributes to apoptosis in human leukemia cells through caspase activation and inhibition of protein synthesis.
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Affiliation(s)
- A Senchenkov
- John Wayne Cancer Institute at Saint John's Health Center, Santa Monica, CA, USA
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Poma A, Cesare P, Marcozzi G, Spanò L. NUCLEAR DAMAGE INDUCED BY LIPOSOMES CONTAINING FITC-LABELLED SAPORIN ON HUMAN MELANOMA CELLS IN VITRO. J Liposome Res 2001; 11:91-102. [DOI: 10.1081/lpr-100103172] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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15
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Epinat JC, Gilmore TD. In vitro-translated diphtheria toxin A chain inhibits translation in wheat germ extracts: analysis of biologically active, caspase-3-resistant diphtheria toxin mutants. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1472:34-41. [PMID: 10572923 DOI: 10.1016/s0304-4165(99)00101-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The diphtheria toxin A chain (DTA) is a potent cytocidal agent that inactivates elongation factor 2. This activity of DTA inhibits protein synthesis and rapidly leads to cell death through apoptosis. In this paper, we have developed a simple in vitro assay for DTA activity in which in vitro-translated DTA is used to inhibit the translation of proteins in wheat germ extracts. Inhibition of translation by DTA is dependent on cofactor NAD+, and the analysis of an attenuated DTA mutant indicates that this in vitro assay accurately reflects the in vivo activity of DTA. We have also identified aspartic acid at residue 8 (Asp-8) of DTA as a site of cleavage by the cell-death protease caspase-3. Cleavage of DTA by caspase-3 inactivates its ability to inhibit translation in wheat germ extracts. Conservative mutations at Asp-8 render DTA resistant to cleavage by caspase-3, but only slightly affect the ability of DTA to inhibit translation in vitro. Moreover, caspase-3-resistant DTA mutants are toxic in cells in tissue culture. The in vitro assay that we describe here will be useful for the rapid analysis of DTA activity and the development of DTA mutants with altered biological properties that may be of therapeutic value. Lastly, these studies serve as a prototype for the creation of caspase-resistant effector molecules.
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Affiliation(s)
- J C Epinat
- Department of Biology, Boston University, MA 02215-2406, USA
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