title: Dynamic effect of heat shock pretreatment on apoptotic responses to TNF-alpha in liver cells.
abstract: The heat shock (HS) response is a protective mechanism for cells to protect themselves against subsequent lethal stress. HS upregulated heat shock protein (HSP) expression reduced apoptosis following tumor necrosis factor-alpha (TNF-alpha) stimulation. However, vector-mediated overexpression of HSP70 failed to provide similar protection but rather sensitized cells to TNF-alpha induced apoptosis. This may be due to the fact that the kinetics of vector-mediated HSP overexpression is totally different from that of HSP upregulation by HS. We hypothesized that the response depends on the timing of TNF-alpha challenge relative to HSP expression dynamics after HS. Therefore, we investigated the correlation between the dynamic change of HSP expression and the levels of apoptosis induced by TNF-alpha after HS. Hepatoma cells were subjected to mild heat shock at 42 degrees C for 2 h followed by varied recovery times and then treated with TNF-alpha to induce apoptosis. The results from quantitative apoptosis assays using the TUNEL reaction reveal an optimal HS protection window centered around 5 h post-HS against TNF-alpha induced apoptosis. In addition, we found a window extending up to 2 h after HS where HS sensitized cells to TNF-alpha stress. Importantly, the correlation between apoptosis and HSP expression kinetics demonstrates that both high levels of HSPs and proper timing between HS and TNF-alpha stress were critical for optimal protection. Our study establishes a dynamic experimental model for further investigation of HS as a potential clinical approach to target tissue survival or death.
authors.affiliation: Department of Biomedical Engineering, The City College of the City University of New York, New York, NY 10031, USA.
authors.forename: Sihong
authors.initials: S
authors.lastname: Wang
authors.forename: Pohun C
authors.initials: PC
authors.lastname: Chen
authors.forename: Francois
authors.initials: F
authors.lastname: Berthiaume
authors.forename: Mehmet
authors.initials: M
authors.lastname: Toner
authors.forename: Arul
authors.initials: A
authors.lastname: Jayaraman
authors.forename: Martin L
authors.initials: ML
authors.lastname: Yarmush
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D006360:Heat-Shock Proteins / Q000378:metabolism*; D018869:Heat-Shock Response / Q000187:drug effects / Q000502:physiology*; D022781:Hepatocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D006358:Hot Temperature; D051381:Rats; D014409:Tumor Necrosis Factor-alpha / Q000008:administration & dosage*
chemical_list: D006360:Heat-Shock Proteins; D014409:Tumor Necrosis Factor-alpha