BCL-XL regulates TNF-alpha-mediated cell death independently of NF-kappaB, FLIP and IAPs.
Upon activation, tumor necrosis factor alpha (TNF-alpha) receptor can engage apoptotic or survival pathways. Inhibition of macromolecular synthesis is known to sensitize cells to TNF-alpha-induced cell death. It is believed that this sensitization is due to the transcriptional blockade of genes regulated by NF-kappaB. Nevertheless, such evidence has remained elusive in the nervous system. Here, we show that TNF-alpha cannot normally induce apoptosis in PC12 cells or cortical neurons. However, cells treated with Actinomycin D (ActD) become susceptible to TNF-alpha-induced cell death through the activation of caspase-8, generation of tBid and activation of caspase-9 and -3. Analysis of several proteins involved in TNF-alpha receptor signaling showed no significant downregulation of NF-kappaB target genes, such as IAPs or FLIP, under such conditions. However, Bcl-x(L) protein levels, but not those of Bcl-2, Bax and Bak, are reduced by ActD or TNF-alpha/ActD treatments. Moreover, Bcl-x(L) overexpression fully protects cells against TNF-alpha/ActD-induced cell death. When endogenous levels of Bcl-x(L) are specifically downregulated by lentiviral-based RNAi, cells no longer require ActD to be sensitive to TNF-alpha-triggered apoptosis. Furthermore, Bcl-x(L) downregulation does not affect TNF-alpha-mediated NF-kappaB activation. Altogether, our results demonstrate that Bcl-x(L), and not Bcl-2, FLIP or IAPs, acts as the endogenous regulator of neuronal resistance/sensitivity to TNF-alpha-induced apoptosis in an NF-kappaB-independent manner.
Gozzelino
Raffaella
R
Departament de Ciències Mèdiques Bàsiques, Universitat de Lleida, Lleida, Spain.
Sole
Carme
C
Llecha
Nuria
N
Segura
Miguel F
MF
Moubarak
Rana S
RS
Iglesias-Guimarais
Victoria
V
Perez-Garcia
M Jose
MJ
Reix
Stephanie
S
Zhang
Jisheng
J
Badiola
Nahuai
N
Sanchis
Daniel
D
Rodriguez-Alvarez
Jose
J
Trullas
Ramon
R
Yuste
Victor J
VJ
Comella
Joan X
JX
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D017209:Apoptosis / Q000235:genetics; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D002478:Cells, Cultured; D003609:Dactinomycin / Q000494:pharmacology; D051034:Inhibitor of Apoptosis Proteins / Q000378:metabolism; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016716:PC12 Cells; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000633:toxicity*; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism*
D000900:Anti-Bacterial Agents; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D051034:Inhibitor of Apoptosis Proteins; D016328:NF-kappa B; D011500:Protein Synthesis Inhibitors; D014409:Tumor Necrosis Factor-alpha; D051020:bcl-X Protein; D003609:Dactinomycin; C505528:Casp8 protein, rat; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9