title: Adenine deoxynucleotides fludarabine and cladribine induce apoptosis in a CD95/Fas receptor, FADD and caspase-8-independent manner by activation of the mitochondrial cell death pathway.
abstract: The adenine deoxynucleosides cladribine (2CdA) and fludarabine (FAraA) are DNA-damaging agents that interfere with DNA repair and induce apoptosis in nonproliferating lymphoid cells. Although both drugs are clinically used for the treatment of indolent lymphoproliferative diseases, the pathways of apoptosis induction remain largely unknown. In the present work, we demonstrate that both drugs induce apoptosis independently of death receptor signaling but activate the mitochondrial cell death pathway. To dissect the signaling pathways, we employed Jurkat cells either deficient for FADD or caspase-8 or overexpressing Bcl-2. In Bcl-2 overexpressing cells, apoptosis and cytochrome c release were blocked whereas processing of caspase-9, -3 and -8 was partially inhibited. In contrast, neither the deficiency of FADD or caspase-8 nor the interference with death receptor signaling by neutralizing anti-CD95/Fas antibodies affected cell death. Inhibitor experiments revealed that caspase-8 is processed by caspase-3-like caspases. Moreover, cytochrome c release and processing of caspase-9 and -3 occurred to an equal extent in wild-type FADD -/- and caspase-8 -/- Jurkat cells. Likewise, apoptosis induction by cladribine or fludarabine was not hampered upon inhibition of caspase-8 in MOLT-3 and MOLT-4 cells or overexpression of a dominant-negative FADD mutant in BJAB cells. Thus, we conclude that apoptosis induced by nucleoside analogues is independent from death receptor signaling as well as from a proposed direct effect on APAF-1, but rather follows the mitochondrial signaling pathway of cytochrome c release and subsequent processing of caspase-9 and -3.
authors.affiliation: Department of Hematology, Oncology and Tumor Immunology, University Medical Center Charité, Campus Berlin-Buch, Humboldt University, Berlin, Germany.
authors.forename: Antje
authors.initials: A
authors.lastname: Klöpfer
authors.forename: Anne
authors.initials: A
authors.lastname: Hasenjäger
authors.forename: Claus
authors.initials: C
authors.lastname: Belka
authors.forename: Klaus
authors.initials: K
authors.lastname: Schulze-Osthoff
authors.forename: Bernd
authors.initials: B
authors.lastname: Dörken
authors.forename: Peter T
authors.initials: PT
authors.lastname: Daniel
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects*; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D017338:Cladribine / Q000494:pharmacology*; D053200:Fas-Associated Death Domain Protein; D006801:Humans; D008928:Mitochondria / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology; D014740:Vidarabine / Q000031:analogs & derivatives* / Q000494:pharmacology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C505533:FADD protein, human; D053200:Fas-Associated Death Domain Protein; D019253:Proto-Oncogene Proteins c-bcl-2; D017338:Cladribine; C505530:CASP8 protein, human; D053181:Caspase 8; D020169:Caspases; D014740:Vidarabine; C024352:fludarabine