title: Regulation of heat-induced apoptosis by Mcl-1 degradation and its inhibition by Hsp70.
abstract: Cellular stress eliminates irreversibly damaged cells by initiating the intrinsic death pathway. Cell stress is sensed by pro- and antiapoptotic members of the Bcl-2 protein family, which regulate the release of apoptogenic factors, such as cytochrome c, from mitochondria. Exposure of cells to hyperthermia results in the activation of the proapoptotic Bcl-2 family protein Bax, which plays an essential role in cytochrome c release. Heat directly affects Bax activity in vitro; however, antiapoptotic Bcl-2 family proteins, such as Bcl-xL, can suppress this activation, suggesting that a second heat-sensitive step must be breached before apoptosis ensues in cells exposed to hyperthermia. Here we show that heat shock causes the loss of Mcl-1 protein. Depletion of Noxa by short hairpin RNA protected cells from hyperthermia by preventing Mcl-1 degradation. Heat shock caused the dissociation of Noxa from Mcl-1, which allowed binding of the BH3-containing ubiquitin ligase Mule followed by Mcl-1 ubiquitination and degradation. Overexpression of Hsp70, which prevents heat-induced Bax activation, stabilized Mcl-1 protein levels in heat-shocked cells. This resulted from reduced Mule binding and ubiquitination as well as enhanced Mcl-1 expression compared with cells without Hsp70. Our results demonstrate that loss of Mcl-1 is a critical heat-sensitive step leading to Bax activation that is controlled by Hsp70.
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada.
authors.forename: A R
authors.initials: AR
authors.lastname: Stankiewicz
authors.forename: A M
authors.initials: AM
authors.lastname: Livingstone
authors.forename: N
authors.initials: N
authors.lastname: Mohseni
authors.forename: D D
authors.initials: DD
authors.lastname: Mosser
mesh_terms: D017209:Apoptosis / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000235:genetics; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006358:Hot Temperature; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D011485:Protein Binding / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D025521:Tumor Suppressor Proteins; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D018840:HSP70 Heat-Shock Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; C498702:PMAIP1 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D025521:Tumor Suppressor Proteins; D051028:bcl-2-Associated X Protein; C502830:HUWE1 protein, human; D044767:Ubiquitin-Protein Ligases