title: Thermotolerance induced at a mild temperature of 40°C alleviates heat shock-induced ER stress and apoptosis in HeLa cells.
abstract: Hyperthermia (39-45°C) has emerged as an alternate prospect for cancer therapy in combination with radiation and chemotherapy. Despite promising progress in the clinic, molecular mechanisms involved in hyperthermia-induced cell death are not clear. Hyperthermia causes protein denaturation/aggregation, which results in cell death by apoptosis and/or necrosis. Hyperthermia also induces thermotolerance, which renders cells resistant to subsequent exposure to lethal heat shock. This study investigates the role of both lethal (42-43°C) and mild (40°C) hyperthermia in regulating ER stress and ER stress-induced apoptosis in HeLa cells. The ability of mild thermotolerance induced at 40°C to alleviate either or both of these processes is also determined. Hyperthermia (42-43°C) induced ER stress, revealed by phosphorylation of PERK, eIF2α and IRE1α, cleavage of ATF6 and increased expression of BiP and sXBP1. Real-time PCR revealed that mRNA levels of ATF6, ATF4, BiP, sXBP1 and CHOP increased in cells exposed to hyperthermia. Moreover, hyperthermia caused disruption of calcium homeostasis and activated the calpain-calpastatin proteolytic system and ER resident caspase 4. Pre-exposure to mild hyperthermia (40°C) alleviated the induction of cytotoxicity and ER stress by hyperthermia (42-43°C) and protected cells against ER stress-induced apoptosis. ShRNA-mediated depletion of Hsp72 abrogated protective effects of mild thermotolerance (40°C) against heat-shock induced ER stress and sensitized cells to ER stress-mediated apoptosis. Our findings show that Hsp72 contributes to the protective effects of mild hyperthermia (40°C) against hyperthermia-induced ER stress and apoptosis.
authors.affiliation: Département des sciences biologiques, TOXEN, Université du Québec à Montréal, CP 8888, Succursale Centre-Ville, Montréal, Québec H3C 3P8, Canada.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Bettaieb
authors.affiliation: Département des sciences biologiques, TOXEN, Université du Québec à Montréal, CP 8888, Succursale Centre-Ville, Montréal, Québec H3C 3P8, Canada. Electronic address: averill.diana@uqam.ca.
authors.forename: Diana A
authors.initials: DA
authors.lastname: Averill-Bates
mesh_terms: D017209:Apoptosis; D002154:Calpain / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress; D050884:HSP72 Heat-Shock Proteins / Q000502:physiology; D006367:HeLa Cells; D018869:Heat-Shock Response; D006358:Hot Temperature; D006801:Humans
chemical_list: D050884:HSP72 Heat-Shock Proteins; D002154:Calpain; D020169:Caspases
keywords: Apoptosis; Calpain; Caspase; ER stress; Hsp72; Hyperthermia