Downregulation of c-FLIP promotes caspase-dependent JNK activation and reactive oxygen species accumulation in tumor cells

Oncogene. 2008 Jan 3;27(1):76-84. doi: 10.1038/sj.onc.1210624. Epub 2007 Jun 25.


Nuclear factor-kappa B (NF-kappaB) inhibits cell death through suppression of the caspase cascade, the c-Jun N-terminal kinase (JNK) pathway, and reactive oxygen species (ROS) accumulation. To suppress this antiapoptotic function of NF-kappaB might be a promising strategy to increase susceptibility of tumor cells to stress-induced cell death. We have recently shown that tumor necrosis factor (TNF)alpha induces caspase-dependent and -independent JNK activation and ROS accumulation in cellular FLICE-inhibitory protein (c-Flip)(-/-) murine embryonic fibroblasts (MEFs). To apply this observation to tumor therapy, we knocked down c-FLIP by RNA interference in various tumor cells. Consistent with the results using c-Flip(-/-) MEFs, we found that TNFalpha stimulation induced caspase-dependent prolonged JNK activation and ROS accumulation, followed by apoptotic and necrotic cell death in various tumor cells. Furthermore, TNFalpha and Fas induced the cleavage of mitogen-activated protein kinase/ERK kinase kinase (MEKK)1, resulting in generation of a constitutive active form of MEKK1 leading to JNK activation in c-FLIP knockdown cells. Given that ROS accumulation and necrotic cell death enhance inflammation followed by compensatory proliferation of tumor cells, selective suppression of caspase-dependent ROS accumulation will be an alternative strategy to protect cells from ROS-dependent DNA damage and compensatory tumor progression.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • CASP8 and FADD-Like Apoptosis Regulating Protein / antagonists & inhibitors*
  • CASP8 and FADD-Like Apoptosis Regulating Protein / deficiency
  • CASP8 and FADD-Like Apoptosis Regulating Protein / genetics
  • CASP8 and FADD-Like Apoptosis Regulating Protein / physiology
  • Caspases / physiology*
  • Down-Regulation / genetics*
  • Enzyme Activation / physiology
  • Female
  • HCT116 Cells
  • HeLa Cells
  • Humans
  • JNK Mitogen-Activated Protein Kinases / metabolism*
  • RNA, Small Interfering / genetics
  • Reactive Oxygen Species / metabolism*
  • Tumor Necrosis Factor-alpha / physiology
  • Uterine Cervical Neoplasms / enzymology
  • Uterine Cervical Neoplasms / genetics
  • Uterine Cervical Neoplasms / metabolism*


  • CASP8 and FADD-Like Apoptosis Regulating Protein
  • CFLAR protein, human
  • RNA, Small Interfering
  • Reactive Oxygen Species
  • Tumor Necrosis Factor-alpha
  • JNK Mitogen-Activated Protein Kinases
  • Caspases