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A caspase-8-independent component in TRAIL/Apo-2L-induced cell death in human rhabdomyosarcoma cells

I Petak1, R Vernes, K S Szucs

  • 1Division of Molecular Therapeutics, Department of Hematology-Oncology, St. Jude Children's Research Hospital, Memphis, Tennesse 38105, USA.

Cell Death and Differentiation
|May 23, 2003
PubMed

Insights

Tumor necrosis factor related apoptosis inducing ligand (TRAIL) triggers cell death pathways in rhabdomyosarcoma. TRAIL signaling in these cancer cells involves mitochondria and potentially the sphingomyelin cycle, bypassing direct caspase-8 activation of Bid.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Oncology

Background:

  • Tumor necrosis factor related apoptosis inducing ligand (TRAIL) is a key mediator of programmed cell death.
  • The precise downstream signaling mechanisms of TRAIL, particularly in cancer, require further elucidation.
  • Rhabdomyosarcoma (RMS) is a pediatric cancer where TRAIL sensitivity varies.

Purpose of the Study:

  • To investigate the TRAIL signaling pathway in TRAIL-sensitive and TRAIL-resistant human rhabdomyosarcoma (RMS) cells.
  • To identify key components and mechanisms involved in TRAIL-induced apoptosis in RMS.
  • To explore the role of caspase-8, Bid, and mitochondrial pathways in TRAIL signaling.

Main Methods:

  • Analysis of death-inducing signaling complex (DISC) formation upon TRAIL ligation.
  • Overexpression of dominant-negative FADD (DNFADD) and caspase-8 (DNC8) to assess their roles.
  • Evaluation of Bcl-2 and Bcl-xL effects on TRAIL-induced apoptosis.
  • Investigation of Bid cleavage, Bax activation, and sphingosine signaling.

Main Results:

  • TRAIL induced DISC formation with FADD and procaspase-8 recruitment in both sensitive and resistant RMS cells.
  • DNFADD abolished TRAIL-induced cell death, while DNC8 only partially inhibited it.
  • Bcl-2 and Bcl-xL inhibited TRAIL-induced apoptosis and Bax activation.
  • Bid cleavage and Bax activation occurred independently of caspase-8, suggesting a mitochondrial involvement.
  • Sphingosine addition activated Bax independently of caspase-8 and Bid; sphingosine kinase inhibition blocked TRAIL-induced apoptosis.

Conclusions:

  • TRAIL signaling in RMS cells bypasses direct caspase-8 activation of Bid upstream of mitochondria.
  • TRAIL-induced apoptosis in RMS appears to be mediated at the mitochondrial level.
  • Components of the sphingomyelin cycle may play a crucial role in TRAIL-mediated apoptosis in RMS.

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