Channels formed by subnanomolar concentrations of the toxin aerolysin trigger apoptosis of T lymphomas

Nelson, Kim L.; Brodsky, Robert A.; Buckley, J. Thomas

doi:10.1046/j.1462-5822.1999.00009.x

Cited by 73 publications

(67 citation statements)

References 23 publications

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“…With other pore-forming toxins, such as the ␣-toxin from Staphylococcus aureus and aerolysin produced by Aeromonas hydrophila, cell death is triggered by two mechanisms, pore formation and apoptosis, depending on the cell type and on the dose of toxin (57,58). Overexpression of antiapoptotic protein could block aerolysin-induced apoptosis, although this effect is overcome if higher toxin concentrations are used, where cells die quickly and apoptotic pathway is not triggered (58).…”

Section: Discussionmentioning

confidence: 99%

Bacillus thuringiensis Cry1Ab Mutants Affecting Oligomer Formation Are Non-toxic to Manduca sexta Larvae

Jiménez-Juárez

Muñóz-Garay

Gómez

et al. 2007

Journal of Biological Chemistry

102

105

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Pore-forming toxins are biological weapons produced by a variety of living organisms, particularly bacteria but also by insects, reptiles, and invertebrates. These proteins affect the cell membrane of their target, disrupting permeability and leading eventually to cell death. The pore-forming toxins typically transform from soluble, monomeric proteins to oligomers that form transmembrane channels. The Cry toxins produced by Bacillus thuringiensis are widely used as insecticides. These proteins have been recognized as pore-forming toxins, and their primary action is to lyse midgut epithelial cells in their target insect. To exert their toxic effect, a prepore oligomeric intermediate is formed leading finally to membrane-inserted oligomeric pores. To understand the role of Cry oligomeric pre-pore formation in the insecticidal activity we isolated point mutations that affected toxin oligomerization but not their binding with the cadherin-like, Bt-R 1 receptor. We show the helix ␣-3 in domain I contains sequences that could form coiled-coil structures important for oligomerization. Some single point mutants in this helix bound Bt-R 1 receptors with similar affinity as the wild-type toxin, but were affected in oligomerization and were severally impaired in pore formation and toxicity against Manduca sexta larvae. These data indicate the pre-pore oligomer and the toxin pore formation play a major role in the intoxication process of Cry1Ab toxin in insect larvae. Bacillus thuringiensis (Bt)2 is a Gram-positive bacterium that produces insecticidal Cry toxins. Cry proteins are widely used for insect control in agriculture and forestry and against mosquitoes, due to their high specificity and safety for humans and for the environment (1, 2).Although Bt Cry toxins are widely used as insecticides their mode of action is still not completely understood. These Cry toxins are pore-forming toxins that induce cell death by forming ionic pores following insertion into the membrane, causing osmotic lysis of larvae midgut cells (1-3). However, recently an alternative model proposed that these toxins activate a signal pathway through Bt-R 1 receptor interaction, which results in insect cell death without the participation of lytic pores into the membrane (4). It is important to note that this alternative model was proposed based on the effect of Cry1Ab toxin to cultured Trichoplusia ni H5 insect cells expressing the Manduca sexta toxin receptor, Bt-R 1 .Nevertheless, in both models, receptor interaction with exposed regions in domains II and III of Cry1A toxins (1-4) is a key step that determines insect toxicity. In the case of Cry1A toxins, two receptors have been characterized in several lepidopteran species: cadherin-like proteins, known as Bt-R receptors (5) (Bt-R 1 in the case of M. sexta), and glycosylphosphatidylinositol-anchored proteins, as aminopeptidase-N or alkaline phosphatase (6, 7).In the pore-forming model, it is proposed that both receptors are important and participate in a sequential manner (3,8,9). After proteoly...

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Section: Discussionmentioning

confidence: 99%

Bacillus thuringiensis Cry1Ab Mutants Affecting Oligomer Formation Are Non-toxic to Manduca sexta Larvae

Jiménez-Juárez

Muñóz-Garay

Gómez

et al. 2007

Journal of Biological Chemistry

102

105

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“…These data could indicate that signal transdution induced by Cry toxin insertion into lipid rafts could be part of the mechanism of action of these toxins, but this remains to be demonstrated. It is important to mention that other pore forming toxins, such as the α-toxin from Staphylococcus aureus and aerolysin produced by Aeromonas hydrophila, induced cell death by two different mechanisms, pore-formation and apoptosis, depending on the cell type and on the dose of toxin [29,31]. Over-expression of antiapoptotic protein could block aerolysin-induced apoptosis, although this effect was overcome if higher toxin concentrations were used, where cells died quickly due to pore formation and apoptotic pathway was not triggered [31].…”

Section: Final Remarksmentioning

confidence: 99%

“…It is important to mention that other pore forming toxins, such as the α-toxin from Staphylococcus aureus and aerolysin produced by Aeromonas hydrophila, induced cell death by two different mechanisms, pore-formation and apoptosis, depending on the cell type and on the dose of toxin [29,31]. Over-expression of antiapoptotic protein could block aerolysin-induced apoptosis, although this effect was overcome if higher toxin concentrations were used, where cells died quickly due to pore formation and apoptotic pathway was not triggered [31]. In the case of aerolysin it was demonstrated that apoptosis was not directly triggered by binding of the toxin to its receptor, but rather it was caused by the production of a small number of channels in the membrane [31] indicating that the intracellular downstream effects were triggered by pore formation and membrane depolarization.…”

Section: Final Remarksmentioning

confidence: 99%

“…Over-expression of antiapoptotic protein could block aerolysin-induced apoptosis, although this effect was overcome if higher toxin concentrations were used, where cells died quickly due to pore formation and apoptotic pathway was not triggered [31]. In the case of aerolysin it was demonstrated that apoptosis was not directly triggered by binding of the toxin to its receptor, but rather it was caused by the production of a small number of channels in the membrane [31] indicating that the intracellular downstream effects were triggered by pore formation and membrane depolarization. The data presented in this work also indicate that pore formation induced by oligomeric toxin is required for Cry1A toxicity in vivo.…”

Section: Final Remarksmentioning

confidence: 99%

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The pre-pore from Bacillus thuringiensis Cry1Ab toxin is necessary to induce insect death in Manduca sexta

et al. 2008

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The insecticidal Cry toxins from Bacillus thuringiensis bacteria are pore-forming toxins that lyse midgut epithelial cells in insects. We have previously proposed that they form pre-pore oligomeric intermediates before membrane insertion.For formation of these oligomers coiled-coil structures are important, and helix α-3 from Cry toxins could form coiled-coils. Our data shows that different mutations in helix α-3 are affected in pore formation and toxicity. Mutants affected in toxicity bind Bt-R 1 receptor with a similar K D as the wild type toxin but do not form oligomers nor induce pore formation in planar lipid bilayers, indicating that the pre-pore oligomer is an obligate intermediate in the intoxication of Cry1Ab toxin and that interaction of monomeric Cry1Ab with Bt-R 1 is not enough to kill susceptible larvae.

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“…13,14 Instead, the interaction of toxins with cells involves complicated pathways, the end result of which is cell death. [15][16][17] The Cry proteins of Bacillus thuringiensis (Bt) represent more than 100 phylogenetically related toxins with varied entomopathogenic activities. 18 Like many other bacterial toxins, Cry toxins incorporate into lipid bilayer rafts as well as brush border membrane vesicles (BBMV).…”

Section: Introductionmentioning

confidence: 99%

Cytotoxicity of Bacillus thuringiensis Cry1Ab toxin depends on specific binding of the toxin to the cadherin receptor BT-R1 expressed in insect cells

et al. 2005

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The specific role of cadherin receptors in cytotoxicity involving Cry toxins of Bacillus thuringiensis and their interactions with cell membrane has not been defined. To elucidate the involvement of toxin-membrane and toxinreceptor interactions in cytotoxicity, we established a cellbased system utilizing High Five insect cells stably expressing BT-R 1 , the cadherin receptor for Cry1Ab toxin. Cry1Ab toxin is incorporated into cell membrane in both oligomeric and monomeric form. Monomeric toxin binds specifically to BT-R 1 whereas incorporation of oligomeric toxin is nonspecific and lipid dependent. Toxin oligomers in the cell membrane do not produce lytic pores and do not kill insect cells. Rather, cell death correlates with binding of the Cry1Ab toxin monomer to BT-R 1 , which apparently activates a Mg 2 þ -dependent cellular signaling pathway.

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Channels formed by subnanomolar concentrations of the toxin aerolysin trigger apoptosis of T lymphomas

Cited by 73 publications

References 23 publications

Bacillus thuringiensis Cry1Ab Mutants Affecting Oligomer Formation Are Non-toxic to Manduca sexta Larvae

Bacillus thuringiensis Cry1Ab Mutants Affecting Oligomer Formation Are Non-toxic to Manduca sexta Larvae

The pre-pore from Bacillus thuringiensis Cry1Ab toxin is necessary to induce insect death in Manduca sexta

Cytotoxicity of Bacillus thuringiensis Cry1Ab toxin depends on specific binding of the toxin to the cadherin receptor BT-R1 expressed in insect cells

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