Calnexin deficiency and endoplasmic reticulum stress-induced apoptosis.
In this study, we used calnexin-deficient cells to investigate the role of this protein in ER stress-induced apoptosis. We found that calnexin-deficient cells are relatively resistant to ER stress-induced apoptosis. However, caspase 3 and 8 cleavage and cytochrome c release were unchanged in these cells, indicating that ER to mitochondria "communication" during apoptotic stimulation is not affected in the absence of calnexin. The Bcl-2:Bax ratio was also not significantly changed in calnexin-deficient cells regardless of whether the ER stress was induced with thapsigargin or not. Ca(2+) homeostasis and ER morphology were unaffected by the lack of calnexin, but ER stress-induced Bap31 cleavage was significantly inhibited. Immunoprecipitation experiments revealed that Bap31 forms complexes with calnexin, which may play a role in apoptosis. The results suggest that calnexin may not play a role in the initiation of the ER stress but that the protein has an effect on later apoptotic events via its influence on Bap31 function.
Zuppini
Anna
A
CIHR Research Group in Molecular Biology of Membrane Proteins and Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada.
Groenendyk
Jody
J
Cormack
Lori A
LA
Shore
Gordon
G
Opas
Michal
M
Bleackley
R Chris
RC
Michalak
Marek
M
D017209:Apoptosis / Q000502:physiology*; D001483:Base Sequence; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D037281:Calnexin; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D006706:Homeostasis; D006801:Humans; D008565:Membrane Proteins; D008854:Microscopy, Electron; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019284:Thapsigargin / Q000494:pharmacology; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; C091247:BCAP31 protein, human; D002135:Calcium-Binding Proteins; D017931:DNA Primers; D008565:Membrane Proteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D037281:Calnexin; D019284:Thapsigargin; D002118:Calcium