ToxSci Advance Access published online on June 4, 2008
Toxicological Sciences, doi:10.1093/toxsci/kfn110
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Satratoxin G-Induced Apoptosis in PC-12 Neuronal Cells is Mediated by PKR and Caspase-Independent
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* Center for Integrative Toxicology
Department of Microbiology and Molecular Genetics
Department of Food Science and Human Nutrition
# Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI 48824-1224, USA
1 To whom correspondence should be addressed at 234 G.M. Trout Building, Michigan State University, East Lansing, MI 48824, Fax: 517-353-8963. Email: pestka{at}msu.edu.
Received April 11, 2008; revision received May 25, 2008; accepted May 25, 2008
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Abstract |
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Satratoxin G (SG) is a macrocyclic trichothecene mycotoxin produced by Stachybotrys chartarum, a mold suggested to play an etiologic role in damp building–related illnesses. Acute intranasal exposure of mice to SG specifically induces apoptosis in olfactory sensory neurons of the nose. The PC-12 rat pheochromocytoma cell model was used to elucidate potential mechanisms of SG-induced neuronal cell death. Agarose gel electrophoresis revealed that exposure to SG at 10 ng/ml or higher for 48 h induced DNA fragmentation characteristic of apoptosis in PC-12 cells. SG-induced apoptosis was confirmed by microscopic morphology, hypodiploid fluorescence and annexin V-FITC uptake. mRNA expression of the proapoptotic genes p53, double stranded RNA-activated protein kinase (PKR), BAX and caspase-activated DNAse (CAD) was significantly elevated from 6 to 48 h after SG treatment. SG also induced apoptosis and proapoptotic gene expression in neural growth factor-differentiated PC-12 cells. Although SG induced caspase-3 activation, caspase inhibition did not impair apoptosis. Moreover, SG induced nuclear translocation of apoptosis-inducing factor (AIF), a known contributor to caspase-independent neuronal cell death. SG-induced apoptosis was not affected by inhibitors of oxidative stress or mitogen-activated protein kinases but was suppressed by the PKR inhibitor C16 and by PKR siRNA transfection. PKR inhibition also blocked SG-induced apoptotic gene expression and AIF translocation but not caspase-3 activation. Taken together, SG-induced apoptosis in PC-12 neuronal cells is mediated by PKR via a caspase-independent pathway possibly involving AIF translocation.