title: Changes in endoplasmic reticulum luminal environment affect cell sensitivity to apoptosis.
abstract: To test the role of ER luminal environment in apoptosis, we generated HeLa cell lines inducible with respect to calreticulin and calnexin and investigated their sensitivity to drug-dependent apoptosis. Overexpression of calreticulin, an ER luminal protein, resulted in an increased sensitivity of the cells to both thapsigargin- and staurosporine-induced apoptosis. This correlated with an increased release of cytochrome c from the mitochondria. Overexpression of calnexin, an integral ER membrane protein, had no significant effect on drug-induced apoptosis. In contrast, calreticulin-deficient cells were significantly resistant to apoptosis and this resistance correlated with a decreased release of cytochrome c from mitochondria and low levels of caspase 3 activity. This work indicates that changes in the lumen of the ER amplify the release of cytochrome c from mitochondria, and increase caspase activity, during drug-induced apoptosis. There may be communication between the ER and mitochondria, which may involve Ca(2+) and play an important role in conferring cell sensitivity to apoptosis. Apoptosis may depend on both the presence of external apoptosis-activating signals, and, as shown in this study, on an internal factor represented by the ER.
authors.affiliation: Canadian Institutes of Health Research Group in Molecular Biology of Membrane Proteins, University of Alberta, Edmonton, Alberta, Canada, T6G 2H7.
authors.forename: K
authors.initials: K
authors.lastname: Nakamura
authors.forename: E
authors.initials: E
authors.lastname: Bossy-Wetzel
authors.forename: K
authors.initials: K
authors.lastname: Burns
authors.forename: M P
authors.initials: MP
authors.lastname: Fadel
authors.forename: M
authors.initials: M
authors.lastname: Lozyk
authors.forename: I S
authors.initials: IS
authors.lastname: Goping
authors.forename: M
authors.initials: M
authors.lastname: Opas
authors.forename: R C
authors.initials: RC
authors.lastname: Bleackley
authors.forename: D R
authors.initials: DR
authors.lastname: Green
authors.forename: M
authors.initials: M
authors.lastname: Michalak
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000502:physiology*; D037281:Calnexin; D037282:Calreticulin; D002460:Cell Line; D003001:Cloning, Molecular; D003574:Cytochrome c Group / Q000032:analysis; D004285:Dogs; D004721:Endoplasmic Reticulum / Q000502:physiology* / Q000648:ultrastructure; D005047:Etoposide / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000502:physiology; D051379:Mice; D008928:Mitochondria / Q000502:physiology; D018832:Molecular Chaperones / Q000502:physiology; D011817:Rabbits; D012261:Ribonucleoproteins / Q000235:genetics / Q000502:physiology*; D019311:Staurosporine / Q000494:pharmacology; D013601:T-Lymphocytes; D019284:Thapsigargin / Q000494:pharmacology; D014466:Ultraviolet Rays
chemical_list: D002135:Calcium-Binding Proteins; D037282:Calreticulin; D003574:Cytochrome c Group; D008565:Membrane Proteins; D018832:Molecular Chaperones; D012261:Ribonucleoproteins; D037281:Calnexin; D019284:Thapsigargin; D005047:Etoposide; D019311:Staurosporine; D002118:Calcium