Heat shock inhibits radiation-induced activation of NF-kappaB via inhibition of I-kappaB kinase.
Radiation stimulates signaling cascades that result in the activation of several transcription factors that are believed to play a central role in protective response(s) to ionizing radiation (IR). It is also well established that heat shock alters the regulation of signaling cascades and transcription factors and is a potent radiosensitizing agent. To explore the hypothesis that heat disrupts or alters the regulation of signaling factors activated by IR, the effect of heat shock on IR-induced activation of NF-kappaB was determined. Irradiated HeLa cells demonstrated transient increases in NF-kappaB DNA binding activity and NF-kappaB protein nuclear localization. In addition, irradiated cells demonstrated increased I-kappaB phosphorylation and decreased I-kappaBalpha cytoplasmic protein levels, corresponding temporally with the increase of NF-kappaB DNA binding. Heat shock prior to IR inhibited the increase in NF-kappaB DNA binding activity, nuclear localization of NF-kappaB, and the phosphorylation and subsequent degradation of I-kappaB. I-kappaB kinase (IKK) immunoprecipitation assays demonstrated an increase in IKK catalytic activity in response to IR that was inhibited by pretreatment with heat. Kinetic experiments determined that heat-induced inhibition of NF-kappaB activation in response to IR decayed within 5 h after heating. Furthermore, pretreatment with cycloheximide, to block de novo protein synthesis, did not alter heat shock inhibition of IR induction of NF-kappaB. These experiments demonstrate that heat shock transiently inhibits IR induction of NF-kappaB DNA binding activity by preventing IKK activation and suggests a mechanism independent of protein synthesis.
Curry
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HA
Section of Cancer Biology, Radiation Oncology Center, Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Clemens
R A
RA
Shah
S
S
Bradbury
C M
CM
Botero
A
A
Goswami
P
P
Gius
D
D
D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D006367:HeLa Cells; D018869:Heat-Shock Response; D006801:Humans; D051550:I-kappa B Kinase; D020672:I-kappa B Proteins; D007259:Infrared Rays; D007700:Kinetics; D016328:NF-kappa B / Q000096:biosynthesis / Q000378:metabolism / Q000528:radiation effects*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors*; D015398:Signal Transduction
D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D016328:NF-kappa B; D017346:Protein Serine-Threonine Kinases; C496559:CHUK protein, human; D051550:I-kappa B Kinase; C496560:IKBKB protein, human; C496565:IKBKE protein, human