title: Mild thermotolerance induced at 40 °C protects cells against hyperthermia-induced pro-apoptotic changes in Bcl-2 family proteins.
abstract: OBJECTIVE
  Despite clinical progress, mechanisms involved in cellular responses to low and high doses of hyperthermia are not entirely clear. This study investigates the role of Bcl-2 family proteins in control of the mitochondrial pathway of apoptosis during hyperthermia at 42-43 °C and the protective effect of a low dose adaptive survival response, mild thermotolerance induced at 40 °C.
  
  
  METHODS
  Levels of Bcl-2 family proteins were detected in HeLa cells by western blotting, caspase activation by spectrofluorimetry and apoptosis by chromatin condensation.
  
  
  RESULTS
  Hyperthermia (42-43 °C) decreased total and mitochondrial expression of anti-apoptotic proteins Bcl-2 and Bcl-xL, while expression of pro-apoptotic proteins Bax, Bak, Puma and Noxa increased. Hyperthermia perturbed the equilibrium between these anti- and pro-apoptotic Bcl-2 family proteins in favour of pro-apoptotic conditions. Hyperthermia also caused activation of caspases-9 and -3, and chromatin condensation. Disruption of the balance between Bcl-2 family proteins was reversed in thermotolerant (40 °C) cells, thus favouring cell survival. Bcl-2/Bcl-xL inhibitor ABT-737 sensitised cells to apoptosis, which indicates that Bcl-2 family proteins play a role in hyperthermia-induced apoptosis. The adaptive response of mild thermotolerance (40 °C) was still able to protect cells against hyperthermia (42-43 °C) when Bcl-2/Bcl-xL were inhibited.
  
  
  CONCLUSIONS
  These results improve knowledge about the role of Bcl-2 family proteins in cellular apoptotic responses to hyperthermia (42-43 °C), as well as the adaptive survival response induced by exposure to mild stresses, such as a fever temperature (40 °C). This study could provide rationale to explore the manipulation of Bcl-2 family proteins for increasing tumour sensitivity to hyperthermia.
authors.affiliation: Département des sciences biologiques (TOXEN), Université du Québec à Montréal , Montréal, Québec , Canada.
authors.forename: Audrey
authors.initials: A
authors.lastname: Glory
authors.forename: Ahmed
authors.initials: A
authors.lastname: Bettaieb
authors.forename: Diana A
authors.initials: DA
authors.lastname: Averill-Bates
mesh_terms: D000222:Adaptation, Physiological; D017209:Apoptosis; D001713:Biphenyl Compounds / Q000494:pharmacology; D006367:HeLa Cells; D006358:Hot Temperature; D006801:Humans; D006979:Hyperthermia, Induced / Q000009:adverse effects*; D008928:Mitochondria / Q000378:metabolism; D009596:Nitrophenols / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: C501332:ABT-737; D001713:Biphenyl Compounds; D009596:Nitrophenols; D010879:Piperazines; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D013449:Sulfonamides; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53
keywords: Apoptosis; Bcl-2 protein; hyperthermia; mitochondria; thermotolerance