title: Overexpression of heat shock protein 72 attenuates NF-κB activation using a combination of regulatory mechanisms in microglia.
abstract: Overexpression of the inducible heat shock protein 70, Hsp72, has broadly cytoprotective effects and improves outcome following stroke. A full understanding of how Hsp72 protects cells against injury is elusive, though several distinct mechanisms are implicated. One mechanism is its anti-inflammatory effects. We study the effects of Hsp72 overexpression on activation of the transcription factor NF-κB in microglia combining experimentation and mathematical modeling, using TNFα to stimulate a microglial cell line stably overexpressing Hsp72. We find that Hsp72 overexpression reduces the amount of NF-κB DNA binding activity, activity of the upstream kinase IKK, and amount of IκBα inhibitor phosphorylated following TNFα application. Simulations evaluating several proposed mechanisms suggest that inhibition of IKK activation is an essential component of its regulatory activities. Unexpectedly we find that Hsp72 overexpression reduces the initial amount of the RelA/p65 NF-κB subunit in cells, contributing to the attenuated response. Neither mechanism in isolation, however, is sufficient to attenuate the response, providing evidence that Hsp72 relies upon multiple mechanisms to attenuate NF-κB activation. An additional observation from our study is that the induced expression of IκBα is altered significantly in Hsp72 expressing cells. While the mechanism responsible for this observation is not known, it points to yet another means by which Hsp72 may alter the NF-κB response. This study illustrates the multi-faceted nature of Hsp72 regulation of NF-κB activation in microglia and offers further clues to a novel mechanism by which Hsp72 may protect cells against injury.
authors: Department of Mechanical Engineering, University of California, Santa Barbara, Santa Barbara, California, United States of America ; Department of Biosystems Science and Engineering, ETH-Zurich, Basel, Switzerland.
authors: Patrick W
authors: PW
authors: Sheppard
authors: Department of Anesthesia, Stanford University, Stanford, California, United States of America.
authors: Xiaoyun
authors: X
authors: Sun
authors: Department of Biosystems Science and Engineering, ETH-Zurich, Basel, Switzerland.
authors: Mustafa
authors: M
authors: Khammash
authors: Department of Anesthesia, Stanford University, Stanford, California, United States of America.
authors: Rona G
authors: RG
authors: Giffard
mesh_terms: D000818:Animals; D002460:Cell Line; D019295:Computational Biology; D004247:DNA / Q000378:metabolism; D050884:HSP72 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D051550:I-kappa B Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D020672:I-kappa B Proteins / Q000235:genetics / Q000378:metabolism; D055641:Mathematical Concepts; D051379:Mice; D017628:Microglia / Q000378:metabolism*; D008959:Models, Neurological; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D051996:Transcription Factor RelA / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D050884:HSP72 Heat-Shock Proteins; D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606205:Nfkbia protein, mouse; D012333:RNA, Messenger; C498144:Rela protein, mouse; D051996:Transcription Factor RelA; D014409:Tumor Necrosis Factor-alpha; D000072000:NF-KappaB Inhibitor alpha; D004247:DNA; D051550:I-kappa B Kinase