title: Etoposide sensitizes neuroblastoma cells expressing caspase 8 to TRAIL.
abstract: TRAIL [TNF (tumour necrosis factor)-related apoptosis-inducing ligand] is a promising agent for clinical use since it kills a wide range of tumour cells without affecting normal cells. We provide evidence that pretreatment with etoposide significantly enhanced TRAIL-mediated apoptosis via up-regulation of DR5 (death receptor 5 or TRAIL-R2) expression in the caspase 8 expressing neuroblastoma cell line, SK-N-MC. In addition, sequential treatment with etoposide and TRAIL increased caspases 8, 9 and 3 activation, Mcl-1 cleavage and Bid truncation, which suggests that the ability of etoposide and TRAIL to induce apoptosis is mediated through activation of an intrinsic signalling pathway. Although TRAIL-R2 expression increased in IMR-32 cells in response to etoposide treatment, cell death was not increased by concurrent treatment with TRAIL compared with etoposide alone, because the cells lacked caspase 8 expression. Restoration of caspase 8 expression by exposure to IFNγ (interferon γ) sensitizes IMR-32 cells to TRAIL. Moreover, pretreatment with etoposide increased TRAIL-induced apoptosis in caspase 8 restored IMR-32 cells through activation of a caspase cascade that included caspases 8, 9 and 3. These results indicate that the etoposide-mediated sensitization of neuroblastoma cells to TRAIL is associated with an increase in TRAIL-R2 expression and requires caspase 8 expression. These observations support the potential use of a combination of etoposide and TRAIL in future clinical trials.
authors.affiliation: Department of Pediatrics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Hye Ryung
authors.initials: HR
authors.lastname: Kim
authors.forename: Myoung Woo
authors.initials: MW
authors.lastname: Lee
authors.forename: Dae Seong
authors.initials: DS
authors.lastname: Kim
authors.forename: Ha Yeong
authors.initials: HY
authors.lastname: Jo
authors.forename: Soo Hyun
authors.initials: SH
authors.lastname: Lee
authors.forename: Hee Won
authors.initials: HW
authors.lastname: Chueh
authors.forename: Hye Lim
authors.initials: HL
authors.lastname: Jung
authors.forename: Keon Hee
authors.initials: KH
authors.lastname: Yoo
authors.forename: Ki Woong
authors.initials: KW
authors.lastname: Sung
authors.forename: Hong Hoe
authors.initials: HH
authors.lastname: Koo
keywords: AzaC, 5-aza-2′ deoxycytidine; BCA, bicinchoninic acid; DD, death domain; DR5, death receptor 5; DcR, decoy receptor; FADD, Fas-associated death domain; FBS, fetal bovine serum; IFNγ, interferon γ; NF-κB, nuclear factor κB; PARP, poly(ADP-ribose) polymerase; TNF, tumour necrosis factor; TRAIL; TRAIL, TNF-related apoptosis-inducing ligand; caspase 8; death receptor; etoposide; inferferon γ; mitochondrial cascade