Caspase-8, c-FLIP, and caspase-9 in c-Myc-induced apoptosis of fibroblasts

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Kristiina Järvinen1, Anneli Hotti, Leticia Santos

  • 1Haartman Institute, Department of Pathology, University of Helsinki and Helsinki University Central Hospital, P.O. Box 21, FI-00014 Helsinki, Finland.

Experimental Cell Research
|September 10, 2011
PubMed

Insights

c-Myc activation triggers apoptosis by down-regulating cellular FLICE inhibitory protein (c-FLIP), leading to caspase-8 activation. This intrinsic pathway, not death receptor signaling, drives c-Myc-induced cell death.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Apoptosis Research

Background:

  • c-Myc is a known regulator of apoptosis, primarily through caspase activation.
  • The precise mechanisms by which c-Myc activates caspases are not fully elucidated.
  • Cellular FLICE inhibitory protein (c-FLIP) is a key regulator of caspase-8 activity.

Purpose of the Study:

  • To investigate the role of c-FLIP in c-Myc-induced apoptosis.
  • To determine the specific caspase activation pathways initiated by c-Myc.
  • To differentiate between extrinsic and intrinsic apoptotic pathways in c-Myc-mediated cell death.

Main Methods:

  • Utilized MycER™ rat fibroblasts to study c-Myc activation.
  • Assessed caspase activation and cleavage using biochemical assays.
  • Quantified c-FLIP mRNA and protein expression levels.
  • Investigated the involvement of Fas and TNFR signaling pathways using neutralizing antibodies.
  • Examined the effect of ectopic c-FLIP(L) expression on c-Myc-induced apoptosis.

Main Results:

  • c-Myc activation led to early caspase-8 processing and activation, followed by effector caspases 3 and 7.
  • Down-regulation of c-FLIP expression preceded or coincided with caspase-8 activation.
  • Caspase-9 activation occurred late, after effector caspases.
  • Blocking Fas and TNFR signaling did not inhibit caspase-8 activation or cell death.
  • Ectopic c-FLIP(L) expression suppressed c-Myc-induced apoptosis.

Conclusions:

  • c-Myc induces apoptosis via an intrinsic pathway involving c-FLIP down-regulation and subsequent caspase-8 activation.
  • Extrinsic death receptor pathways (Fas, TNFR) are not the primary mediators of c-Myc-induced caspase-8 activation.
  • c-FLIP acts as a crucial inhibitor of c-Myc-driven apoptosis.

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