title: Resistance to Fas-mediated apoptosis in EBV-infected B cell lymphomas is due to defects in the proximal Fas signaling pathway.
abstract: Post-transplant lymphoproliferative disorder is characterized by the outgrowth of EBV-infected B cell lymphomas in immunosuppressed transplant recipients. Using a panel of EBV-infected spontaneous lymphoblastoid cell lines (SLCL) derived from post-transplant lymphoproliferative disorder patients, we assessed the sensitivity of such lymphomas to Fas-mediated cell death. Treatment with either an agonist anti-Fas mAb or Fas ligand-expressing cells identifies two subsets of SLCL based on their sensitivity or resistance to Fas-driven apoptosis. Fas resistance in these cells cannot be attributed to reduced Fas expression or to mutations in the Fas molecule itself. In addition, all SLCL are sensitive to staurosporine-induced cell death, indicating that there is no global defect in apoptosis. Although all SLCL express comparable levels of Fas signaling molecules including Fas-associated death domain protein, caspase 8, and caspase 3, Fas-resistant SLCL exhibit a block in Fas-signaling before caspase 3 activation. In two SLCL, this block results in impaired assembly of the death-inducing signaling complex, resulting in reduced caspase 8 activation. In a third Fas-resistant SLCL, caspase 3 activation is hindered despite intact death-inducing signaling complex formation and caspase 8 activation. Whereas multiple mechanisms exist by which tumor cells can evade Fas-mediated apoptosis, these studies suggest that the proximal Fas-signaling pathway is impeded in Fas-resistant post-transplant lymphoproliferative disorder-associated EBV(+) B cell lymphomas.
authors.affiliation: Program in Immunology and Department of Surgery, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: A L
authors.initials: AL
authors.lastname: Snow
authors.forename: L J
authors.initials: LJ
authors.lastname: Chen
authors.forename: R R
authors.initials: RR
authors.lastname: Nepomuceno
authors.forename: S M
authors.initials: SM
authors.lastname: Krams
authors.forename: C O
authors.initials: CO
authors.lastname: Esquivel
authors.forename: O M
authors.initials: OM
authors.lastname: Martinez
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D017209:Apoptosis; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins / Q000032:analysis / Q000502:physiology; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D053200:Fas-Associated Death Domain Protein; D004854:Herpesvirus 4, Human; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D016393:Lymphoma, B-Cell / Q000473:pathology* / Q000821:virology; D016377:Organ Transplantation / Q000009:adverse effects; D019311:Staurosporine / Q000494:pharmacology; D019014:fas Receptor / Q000032:analysis / Q000502:physiology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D002352:Carrier Proteins; C505533:FADD protein, human; D053200:Fas-Associated Death Domain Protein; D047908:Intracellular Signaling Peptides and Proteins; D019014:fas Receptor; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; D019311:Staurosporine