title: A caspase-8-independent component in TRAIL/Apo-2L-induced cell death in human rhabdomyosarcoma cells.
abstract: Tumor necrosis factor related apoptosis inducing ligand (TRAIL) belongs to the Tumor necrosis factor (TNF) family of death-inducing ligands, and signaling downstream of TRAIL ligation to its receptor(s) remains to be fully elucidated. Components of the death-inducing signaling complex (DISC) and TRAIL signaling downstream of receptor activation were examined in TRAIL - sensitive and -resistant models of human rhabdomyosarcoma (RMS). TRAIL ligation induced DISC formation in TRAIL-sensitive (RD, Rh18, Rh30) and TRAIL-resistant RMS (Rh28, Rh36, Rh41), with recruitment of FADD and procaspase-8. In RD cells, overexpression of dominant-negative FADD (DNFADD) completely abolished TRAIL-induced cell death in contrast to dominant-negative caspase- 8 (DNC8), which only partially inhibited TRAIL-induced apoptosis, growth inhibition, or loss in clonogenic survival. DNC8 did not inhibit the cleavage of Bid or the activation of Bax. Overexpression of Bcl-2 or Bcl-xL inhibited TRAIL-induced apoptosis, growth inhibition, and loss in clonogenic survival. Bcl-2 and Bcl-xL, but not DNC8, inhibited TRAIL-induced Bax activation. Bcl-xL did not inhibit the early activation of caspase-8 (<4 h) but inhibited cleavage of Bid, suggesting that Bid is cleaved downstream of the mitochondria, independent of caspase-8. Exogenous addition of sphingosine also induced activation of Bax via a caspase-8-and Bid-independent mechanism. Further, inhibition of sphingosine kinase completely protected cells from TRAIL-induced apoptosis. Data demonstrate that in RMS cells, the TRAIL signaling pathway circumvents caspase-8 activation of Bid upstream of the mitochondria and that TRAIL acts at the level of the mitochondria via a mechanism that may involve components of the sphingomyelin cycle.
authors.affiliation: Division of Molecular Therapeutics, Department of Hematology-Oncology, St. Jude Children's Research Hospital, Memphis, Tennesse 38105, USA.
authors.forename: I
authors.initials: I
authors.lastname: Petak
authors.forename: R
authors.initials: R
authors.lastname: Vernes
authors.forename: K S
authors.initials: KS
authors.lastname: Szucs
authors.forename: M
authors.initials: M
authors.lastname: Anozie
authors.forename: K
authors.initials: K
authors.lastname: Izeradjene
authors.forename: L
authors.initials: L
authors.lastname: Douglas
authors.forename: D M
authors.initials: DM
authors.lastname: Tillman
authors.forename: D C
authors.initials: DC
authors.lastname: Phillips
authors.forename: J A
authors.initials: JA
authors.lastname: Houghton
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D053181:Caspase 8; D020169:Caspases / Q000187:drug effects / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D053200:Fas-Associated Death Domain Protein; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology; D008954:Models, Biological; D009154:Mutation / Q000187:drug effects / Q000235:genetics; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D012208:Rhabdomyosarcoma / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013109:Sphingomyelins / Q000378:metabolism; D013110:Sphingosine / Q000378:metabolism / Q000494:pharmacology; D053221:TNF-Related Apoptosis-Inducing Ligand; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism*; D051020:bcl-X Protein; D000099157:Sphingosine Kinase
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins; D053181:Caspase 8; D020169:Caspases; D053200:Fas-Associated Death Domain Protein; D008562:Membrane Glycoproteins; D017853:Phosphotransferases (Alcohol Group Acceptor); D019253:Proto-Oncogene Proteins c-bcl-2; D013109:Sphingomyelins; D013110:Sphingosine; D053221:TNF-Related Apoptosis-Inducing Ligand; D014409:Tumor Necrosis Factor-alpha; D051020:bcl-X Protein; D000099157:Sphingosine Kinase; C494811:BCL2L1 protein, human; C494814:BID protein, human; C505533:FADD protein, human; C505653:TNFSF10 protein, human; C505530:CASP8 protein, human