NF-κB activation fails to protect cells to TNFα-induced apoptosis in the absence of Bcl-xL, but not Mcl-1, Bcl-2 or Bcl-w.
TNFα can promote either cell survival or cell death. The activation of NF-κB plays a central role in cell survival while its inhibition makes TNFα-triggered cytotoxicity possible. Here, we report that the overexpression of a non-degradable mutant of the inhibitor of NF-κB (super-repressor (SR)-IκBα) sensitizes HeLa cells towards TNFα-induced apoptosis, involving caspases activation and cytocrome C release from the mitochondria. Interestingly, we describe that the specific knockdown of Bcl-xL, but not that of Bcl-2, Bcl-w or Mcl-1, renders cells sensitive to TNFα-induced apoptosis. This cytotoxic effect occurs without altering the activation of NF-κB. Then, the activation of the NF-κB pathway is not sufficient to protect Bcl-xL-downregulated cells from TNFα-induced cell death, meaning that TNFα is not able to promote cell survival in the absence of Bcl-xL. In addition, Bcl-xL silencing does not potentiate the cytotoxicity afforded by the cytokine in SR-IκBα-overexpressing cells. This indicates that TNFα-induced apoptosis in SR-IκBα-overexpressing cells relies on the protein levels of Bcl-xL. We have corroborated these findings using RD and DU-145 cells, which also become sensitive to TNFα-induced apoptosis after Bcl-xL knockdown despite that NF-κB remains activated. Altogether, our results point out that the impairment of the anti-apoptotic function of Bcl-xL should make cells sensitive towards external insults circumventing the TNFα-triggered NF-κB-mediated cytoprotective effect. Hence, the specific inhibition of Bcl-xL could be envisaged as a promising alternative strategy against NF-κB-dependent highly chemoresistant proliferative malignancies.
Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, Barcelona, Spain.
Elisenda
E
Casanelles
Raffaella
R
Gozzelino
Fernando
F
Marqués-Fernández
Victoria
V
Iglesias-Guimarais
Mercè
M
Garcia-Belinchón
María
M
Sánchez-Osuna
Carme
C
Solé
Rana S
RS
Moubarak
Joan X
JX
Comella
Victor J
VJ
Yuste
D017209:Apoptosis / Q000235:genetics; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D020868:Gene Silencing; D006367:HeLa Cells; D006801:Humans; D020672:I-kappa B Proteins / Q000494:pharmacology; D008928:Mitochondria; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; C494811:BCL2L1 protein, human; C491073:BCL2L2 protein, human; D020672:I-kappa B Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D014409:Tumor Necrosis Factor-alpha; D051020:bcl-X Protein; D000072000:NF-KappaB Inhibitor alpha