Lifeguard Inhibits Fas Ligand-mediated Endoplasmic Reticulum-Calcium Release Mandatory for Apoptosis in Type II Apoptotic Cells

J Biol Chem. 2016 Jan 15;291(3):1221-34. doi: 10.1074/jbc.M115.677682. Epub 2015 Nov 18.


Death receptors are members of the tumor necrosis factor receptor superfamily involved in the extrinsic apoptotic pathway. Lifeguard (LFG) is a death receptor antagonist mainly expressed in the nervous system that specifically blocks Fas ligand (FasL)-induced apoptosis. To investigate its mechanism of action, we studied its subcellular localization and its interaction with members of the Bcl-2 family proteins. We performed an analysis of LFG subcellular localization in murine cortical neurons and found that LFG localizes mainly to the ER and Golgi. We confirmed these results with subcellular fractionation experiments. Moreover, we show by co-immunoprecipitation experiments that LFG interacts with Bcl-XL and Bcl-2, but not with Bax or Bak, and this interaction likely occurs in the endoplasmic reticulum. We further investigated the relationship between LFG and Bcl-XL in the inhibition of apoptosis and found that LFG protects only type II apoptotic cells from FasL-induced death in a Bcl-XL dependent manner. The observation that LFG itself is not located in mitochondria raises the question as to whether LFG in the ER participates in FasL-induced death. Indeed, we investigated the degree of calcium mobilization after FasL stimulation and found that LFG inhibits calcium release from the ER, a process that correlates with LFG blockage of cytochrome c release to the cytosol and caspase activation. On the basis of our observations, we propose that there is a required step in the induction of type II apoptotic cell death that involves calcium mobilization from the ER and that this step is modulated by LFG.

Keywords: CD95 (APO-1/Fas); apoptosis; calcium; endoplasmic reticulum (ER); neuron.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis*
  • Calcium Signaling*
  • Cell Line
  • Cells, Cultured
  • Cerebral Cortex / cytology
  • Cerebral Cortex / metabolism
  • Endoplasmic Reticulum / metabolism*
  • Fas Ligand Protein / antagonists & inhibitors*
  • Fas Ligand Protein / genetics
  • Fas Ligand Protein / metabolism
  • Female
  • Golgi Apparatus / metabolism
  • HEK293 Cells
  • Humans
  • Membrane Proteins / antagonists & inhibitors
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Mice, Inbred C57BL
  • Nerve Tissue Proteins / antagonists & inhibitors
  • Nerve Tissue Proteins / chemistry
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism*
  • Neurons / cytology
  • Neurons / metabolism*
  • Peptide Fragments / antagonists & inhibitors
  • Peptide Fragments / chemistry
  • Peptide Fragments / genetics
  • Peptide Fragments / metabolism
  • Protein Interaction Domains and Motifs
  • Protein Transport
  • RNA Interference
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism


  • FASLG protein, human
  • Fas Ligand Protein
  • Fasl protein, mouse
  • Membrane Proteins
  • Nerve Tissue Proteins
  • Peptide Fragments
  • Recombinant Proteins
  • lifeguard protein, mouse