Abstract
Sorafenib is a multikinase inhibitor that induces apoptosis in human leukemia and other malignant cells. Recently, we demonstrated that sorafenib diminishes Mcl-1 protein expression by inhibiting translation through a MEK1/2-ERK1/2 signaling-independent mechanism and that this phenomenon plays a key functional role in sorafenib-mediated lethality. Here, we report that inducible expression of constitutively active MEK1 fails to protect cells from sorafenib-mediated lethality, indicating that sorafenib-induced cell death is unrelated to MEK1/2-ERK1/2 pathway inactivation. Notably, treatment with sorafenib induced endoplasmic reticulum (ER) stress in human leukemia cells (U937) manifested by immediate cytosolic-calcium mobilization, GADD153 and GADD34 protein induction, PKR-like ER kinase (PERK) and eukaryotic initiation factor 2alpha (eIF2alpha) phosphorylation, XBP1 splicing, and a general reduction in protein synthesis as assessed by [35S]methionine incorporation. These events were accompanied by pronounced generation of reactive oxygen species through a mechanism dependent upon cytosolic-calcium mobilization and a significant decline in GRP78/Bip protein levels. Interestingly, enforced expression of IRE1alpha markedly reduced sorafenib-mediated apoptosis, whereas knockdown of IRE1alpha or XBP1, disruption of PERK activity, or inhibition of eIF2alpha phosphorylation enhanced sorafenib-mediated lethality. Finally, downregulation of caspase-2 or caspase-4 by small interfering RNA significantly diminished apoptosis induced by sorafenib. Together, these findings demonstrate that ER stress represents a central component of a MEK1/2-ERK1/2-independent cell death program triggered by sorafenib.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, Non-P.H.S.
MeSH terms
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Animals
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Benzenesulfonates / pharmacology*
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Calcium Signaling / drug effects
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Caspase 2 / metabolism
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Caspases, Initiator / metabolism
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Cell Death / drug effects
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Cell Line, Tumor
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DNA-Binding Proteins / metabolism
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Dose-Response Relationship, Drug
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Endoplasmic Reticulum / drug effects*
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Endoplasmic Reticulum / pathology*
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Endoplasmic Reticulum Chaperone BiP
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Enzyme Activation / drug effects
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Enzyme Induction / drug effects
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Eukaryotic Initiation Factor-2 / metabolism
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Extracellular Signal-Regulated MAP Kinases / metabolism
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Humans
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Mice
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Mitogen-Activated Protein Kinase Kinases / metabolism
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Niacinamide / analogs & derivatives
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Nuclear Proteins / metabolism
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Phenylurea Compounds
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Phosphorylation / drug effects
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Protein Biosynthesis / drug effects
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Protein Folding
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Protein Kinase Inhibitors / pharmacology*
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Pyridines / pharmacology*
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RNA Splicing / drug effects
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Reactive Oxygen Species / metabolism
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Regulatory Factor X Transcription Factors
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Sorafenib
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Transcription Factors
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X-Box Binding Protein 1
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eIF-2 Kinase / antagonists & inhibitors
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eIF-2 Kinase / metabolism
Substances
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Benzenesulfonates
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DNA-Binding Proteins
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Endoplasmic Reticulum Chaperone BiP
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Eukaryotic Initiation Factor-2
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HSPA5 protein, human
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Hspa5 protein, mouse
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Nuclear Proteins
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Phenylurea Compounds
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Protein Kinase Inhibitors
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Pyridines
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Reactive Oxygen Species
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Regulatory Factor X Transcription Factors
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Transcription Factors
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X-Box Binding Protein 1
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XBP1 protein, human
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Xbp1 protein, mouse
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Niacinamide
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Sorafenib
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PERK kinase
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eIF-2 Kinase
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Extracellular Signal-Regulated MAP Kinases
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Mitogen-Activated Protein Kinase Kinases
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CASP4 protein, human
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Caspase 2
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Caspases, Initiator