Cytotoxicity of anthrax lethal toxin to human acute myeloid leukemia cells is nonapoptotic and dependent on extracellular signal-regulated kinase 1/2 activity

Elias Kassab, Manal Darwish, Zahra Timsah, ShiHui Liu, Stephen H. Leppla, Arthur E. Frankel, Ralph J. Abi-Habib

Research output: Contribution to journalArticle

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Abstract

In this study, we attempt to target the mitogen-activated protein kinase (MAPK) pathway in acute myeloid leukemia (AML) cells using a recombinant anthrax lethal toxin (LeTx). LeTx consists of protective antigen (PrAg) and lethal factor (LF). PrAg binds cells, is cleaved by furin, oligomerizes, binds three to four molecules of LF, and undergoes endocytosis, releasing LF into the cytosol. LF cleaves MAPK kinases, inhibiting the MAPK pathway. We tested potency of LeTx on a panel of 11 human AML cell lines. Seven cell lines showed cytotoxic responses to LeTx. Cytotoxicity of LeTx was mimicked by the specific mitogen-activated protein/extracellular signal-regulated kinase kinase 1/2 (MEK1/2) inhibitor U0126, indicating that LeTx-induced cell death is mediated through the MEK1/2- extracellular signal-regulated kinase (ERK1/2) branch of the MAPK pathway. The four LeTx-resistant cell lines were sensitive to the phosphatidylinositol 3-kinase inhibitor LY294002. Co-treatment of AML cells with both LeTx and LY294002 did not lead to increased sensitivity, showing a lack of additive/synergistic effects when both pathways are inhibited. Flow cytometry analysis of MAPK pathway activation revealed the presence of phospho-ERK1/2 only in LeTx-sensitive cells. Staining for Annexin V/propidium iodide and active caspases showed an increase in doublepositive cells and the absence of caspase activation following treatment, indicating that LeTx-induced cell death is caspase-independent and nonapoptotic. We have shown that a majority of AML cell lines are sensitive to the LF-mediated inhibition of the MAPK pathway. Furthermore, we have demonstrated that LeTx-induced cytotoxicity in AML cells is nonapoptotic and dependent on phospho-ERK1/2 levels.

Original languageEnglish (US)
Pages (from-to)25-32
Number of pages8
JournalTranslational Oncology
Volume6
Issue number1
DOIs
StatePublished - 2013

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Mitogen-Activated Protein Kinase 3
Mitogen-Activated Protein Kinase 1
Myeloid Cells
Acute Myeloid Leukemia
Caspases
Mitogen-Activated Protein Kinases
Cell Line
2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
Cell Death
Phosphatidylinositol 3-Kinase
Furin
MAP Kinase Kinase Kinases
Antigens
Propidium
Annexin A5
Mitogen-Activated Protein Kinase Kinases
Extracellular Signal-Regulated MAP Kinases
Endocytosis
Mitogens
Cytosol

ASJC Scopus subject areas

  • Oncology
  • Cancer Research

Cite this

Cytotoxicity of anthrax lethal toxin to human acute myeloid leukemia cells is nonapoptotic and dependent on extracellular signal-regulated kinase 1/2 activity. / Kassab, Elias; Darwish, Manal; Timsah, Zahra; Liu, ShiHui; Leppla, Stephen H.; Frankel, Arthur E.; Abi-Habib, Ralph J.

In: Translational Oncology, Vol. 6, No. 1, 2013, p. 25-32.

Research output: Contribution to journalArticle

Kassab, Elias ; Darwish, Manal ; Timsah, Zahra ; Liu, ShiHui ; Leppla, Stephen H. ; Frankel, Arthur E. ; Abi-Habib, Ralph J. / Cytotoxicity of anthrax lethal toxin to human acute myeloid leukemia cells is nonapoptotic and dependent on extracellular signal-regulated kinase 1/2 activity. In: Translational Oncology. 2013 ; Vol. 6, No. 1. pp. 25-32.
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AB - In this study, we attempt to target the mitogen-activated protein kinase (MAPK) pathway in acute myeloid leukemia (AML) cells using a recombinant anthrax lethal toxin (LeTx). LeTx consists of protective antigen (PrAg) and lethal factor (LF). PrAg binds cells, is cleaved by furin, oligomerizes, binds three to four molecules of LF, and undergoes endocytosis, releasing LF into the cytosol. LF cleaves MAPK kinases, inhibiting the MAPK pathway. We tested potency of LeTx on a panel of 11 human AML cell lines. Seven cell lines showed cytotoxic responses to LeTx. Cytotoxicity of LeTx was mimicked by the specific mitogen-activated protein/extracellular signal-regulated kinase kinase 1/2 (MEK1/2) inhibitor U0126, indicating that LeTx-induced cell death is mediated through the MEK1/2- extracellular signal-regulated kinase (ERK1/2) branch of the MAPK pathway. The four LeTx-resistant cell lines were sensitive to the phosphatidylinositol 3-kinase inhibitor LY294002. Co-treatment of AML cells with both LeTx and LY294002 did not lead to increased sensitivity, showing a lack of additive/synergistic effects when both pathways are inhibited. Flow cytometry analysis of MAPK pathway activation revealed the presence of phospho-ERK1/2 only in LeTx-sensitive cells. Staining for Annexin V/propidium iodide and active caspases showed an increase in doublepositive cells and the absence of caspase activation following treatment, indicating that LeTx-induced cell death is caspase-independent and nonapoptotic. We have shown that a majority of AML cell lines are sensitive to the LF-mediated inhibition of the MAPK pathway. Furthermore, we have demonstrated that LeTx-induced cytotoxicity in AML cells is nonapoptotic and dependent on phospho-ERK1/2 levels.

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