title: BCL-XL regulates TNF-alpha-mediated cell death independently of NF-kappaB, FLIP and IAPs.
abstract: 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.
authors.affiliation: Departament de Ciències Mèdiques Bàsiques, Universitat de Lleida, Lleida, Spain.
authors.forename: Raffaella
authors.initials: R
authors.lastname: Gozzelino
authors.forename: Carme
authors.initials: C
authors.lastname: Sole
authors.forename: Nuria
authors.initials: N
authors.lastname: Llecha
authors.forename: Miguel F
authors.initials: MF
authors.lastname: Segura
authors.forename: Rana S
authors.initials: RS
authors.lastname: Moubarak
authors.forename: Victoria
authors.initials: V
authors.lastname: Iglesias-Guimarais
authors.forename: M Jose
authors.initials: MJ
authors.lastname: Perez-Garcia
authors.forename: Stephanie
authors.initials: S
authors.lastname: Reix
authors.forename: Jisheng
authors.initials: J
authors.lastname: Zhang
authors.forename: Nahuai
authors.initials: N
authors.lastname: Badiola
authors.forename: Daniel
authors.initials: D
authors.lastname: Sanchis
authors.forename: Jose
authors.initials: J
authors.lastname: Rodriguez-Alvarez
authors.forename: Ramon
authors.initials: R
authors.lastname: Trullas
authors.forename: Victor J
authors.initials: VJ
authors.lastname: Yuste
authors.forename: Joan X
authors.initials: JX
authors.lastname: Comella
mesh_terms: 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*
chemical_list: 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