Effect of Bax deficiency on death receptor 5 and mitochondrial pathways during endoplasmic reticulum calcium pool depletion-induced apoptosis.
Thapsigargin (TG), by inducing perturbations in cellular Ca(2+) homeostasis, can induce apoptosis, but the molecular mechanisms remain to be fully elucidated. We have recently reported that TG-induced apoptosis appears to involve the DR5-dependent apoptotic pathway that cross talks with the mitochondrial pathway via TG-induced Bid cleavage. In this study, we have utilized Bax-proficient and -deficient HCT116 human colon cancer cells to investigate the effect of Bax deficiency on TG-induced apoptosis and TG regulation of the DR5 and mitochondrial pathways. Our results indicate that Bax-deficient cells are less sensitive to undergo apoptosis following TG treatment. Our results further demonstrate that TG-induced apoptosis is coupled with DR5 upregulation and caspases 8 and 3 activation, as well as Bid cleavage in both Bax-proficient and -deficient cells, although caspase 3 activation was reduced in Bax-deficient cells. TG also promoted the release of cytochrome c into cytosol and caspase 9 activation in Bax-proficient cells but not in Bax-deficient cells. These findings suggest that although Bax is not absolutely required for death receptor (DR)-dependent signals, it appears to be a key molecule in TG-regulated mitochondrial events. Bax-deficient cells were relatively more resistant to Apo2L/TRAIL than the Bax-proficient counterparts. However, the combination of Apo2L/TRAIL and TG was more effective in mediating apoptosis in both Bax-proficient and -deficient cells and that was coupled with activation of caspases 8 and 3. Although both agents in combination also induced cytochrome c release into cytosol and caspase 9 activation in Bax-proficient cells, these events were abrogated in Bax-deficient cells. Our results thus suggest that the combination of Apo2L/TRAIL and TG appears to bypass the Bax deficiency-induced defects in the mitochondrial (intrinsic) pathway by engaging the DR5-dependent apoptotic signals (extrinsic pathway).
He
Qin
Q
Department of Pharmacology, State University of New York, Upstate Medical University, Syracuse, NY 13210, USA.
Montalbano
JoAnne
J
Corcoran
Chad
C
Jin
Weixin
W
Huang
Ying
Y
Sheikh
M Saeed
MS
D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D002118:Calcium / Q000378:metabolism*; D002273:Carcinogens / Q000494:pharmacology; D003110:Colonic Neoplasms / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000172:deficiency* / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism*; D053221:TNF-Related Apoptosis-Inducing Ligand; D019284:Thapsigargin / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D051028:bcl-2-Associated X Protein
D051017:Apoptosis Regulatory Proteins; C494826:BAX protein, human; D002273:Carcinogens; D008562:Membrane Glycoproteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor; D053221:TNF-Related Apoptosis-Inducing Ligand; C505639:TNFRSF10B protein, human; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D051028:bcl-2-Associated X Protein; D019284:Thapsigargin; D002118:Calcium