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The endogenous caspase-8 inhibitor c-FLIPL regulates ER morphology and crosstalk with mitochondria

E S Marini1, C Giampietri1, S Petrungaro1

  • 1Istituto Pasteur-Fondazione Cenci Bolognetti, DAHFMO - Section of Histology and Medical Embryology, Sapienza University of Rome, Rome, Italy.

Cell Death and Differentiation
|December 16, 2014
PubMed

Insights

The cellular FLICE-inhibitory protein (c-FLIP(L)) regulates endoplasmic reticulum (ER) morphology and ER-mitochondria connections. Loss of c-FLIP(L) disrupts ER structure by enhancing caspase-8 activity.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Apoptosis Signaling

Background:

  • Caspase-8, a key initiator of extrinsic apoptosis, is found in intracellular membrane complexes.
  • The long isoform of cellular FLICE-inhibitory protein (c-FLIP(L)) inhibits caspase-8 activation.
  • Mitochondria-associated membranes (MAMs) are critical sites for lipid transfer and signaling.

Purpose of the Study:

  • To investigate the role of c-FLIP(L) localization at the ER and MAMs.
  • To determine the impact of c-FLIP(L) on ER morphology and ER-mitochondria crosstalk.
  • To elucidate the mechanism by which c-FLIP(L) regulates caspase-8 activity and downstream targets.

Main Methods:

  • Utilized c-FLIP knockout mouse embryonic fibroblasts (MEFs).
  • Assessed ER morphology, ER Ca(2+) release, and ER-mitochondria tethering.
  • Investigated caspase-8 activation and processing of reticulon-4 (RTN4).
  • Reintroduced c-FLIP(L) and employed caspase inhibition for rescue experiments.

Main Results:

  • c-FLIP(L) localizes to the ER and MAMs.
  • Loss of c-FLIP(L) in MEFs led to disrupted ER morphology, reduced ER Ca(2+) release, and decreased ER-mitochondria tethering.
  • c-FLIP ablation enhanced basal caspase-8 activation and promoted caspase-mediated cleavage of RTN4.
  • Reintroduction of c-FLIP(L) or caspase inhibition restored normal ER morphology and ER-mitochondria juxtaposition.

Conclusions:

  • c-FLIP(L) functions as a crucial regulator at MAMs signaling platforms.
  • Caspase-8, influenced by c-FLIP(L), modulates ER morphology and ER-mitochondria communication via RTN4.
  • c-FLIP(L) plays a vital role in maintaining ER structure and function through its interaction with caspase-8 at the MAMs.

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