A novel role of c-FLIP protein in regulation of ER stress response.
Cellular-Flice-like inhibitory protein (c-FLIP) is an apoptosis modulator known to inhibit the extrinsic apoptotic pathway thus blocking Caspase-8 processing in the Death Inducing Signalling Complex (DISC). We previously demonstrated that c-FLIP localizes at the endoplasmic reticulum (ER) and that c-FLIP-deficient mouse embryonic fibroblasts (MEFs) display an enlarged ER morphology. In the present study, we have addressed the consequences of c-FLIP ablation in the ER stress response by investigating the effects of pharmacologically-induced ER stress in Wild Type (WT) and c-FLIP-/- MEFs. Surprisingly, c-FLIP-/- MEFs were found to be strikingly more resistant than WT MEFs to ER stress-mediated apoptosis. Analysis of Unfolded Protein Response (UPR) pathways revealed that Pancreatic ER Kinase (PERK) and Inositol-Requiring Enzyme 1 (IRE1) branch signalling is compromised in c-FLIP-/- cells when compared with WT cells. We found that c-FLIP modulates the PERK pathway by interfering with the activity of the serine threonine kinase AKT. Indeed, c-FLIP-/- MEFs display higher levels of active AKT than WT MEFs upon ER stress, while treatment with a specific AKT inhibitor of c-FLIP-/- MEFs subjected to ER stress restores the PERK but not the IRE1 pathway. Importantly, the AKT inhibitor or dominant negative AKT transfection sensitizes c-FLIP-/- cells to ER stress-induced cell death while the expression of a constitutively active AKT reduces WT cells sensitivity to ER stress-induced death. Thus, our results demonstrate that c-FLIP modulation of AKT activity is crucial in controlling PERK signalling and sensitivity to ER stress, and highlight c-FLIP as a novel molecular player in PERK and IRE1-mediated ER stress response.
Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Sapienza University of Rome, 00161 Rome, Italy.
Silvia
S
Conti
Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Sapienza University of Rome, 00161 Rome, Italy.
Simonetta
S
Petrungaro
Department of Biosciences, Centre for Immune Regulation, University of Oslo, Blindernveien, 0371 Oslo, Norway.
Elettra Sara
ES
Marini
Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Sapienza University of Rome, 00161 Rome, Italy.
Silvia
S
Masciarelli
Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Sapienza University of Rome, 00161 Rome, Italy.
Luana
L
Tomaipitinca
Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Sapienza University of Rome, 00161 Rome, Italy.
Antonio
A
Filippini
Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Sapienza University of Rome, 00161 Rome, Italy.
Claudia
C
Giampietri
Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Sapienza University of Rome, 00161 Rome, Italy. Electronic address: elio.ziparo@uniroma1.it.
Elio
E
Ziparo
D000818:Animals; D017209:Apoptosis; D001343:Autophagy; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000172:deficiency / Q000378:metabolism*; D004622:Embryo, Mammalian / Q000166:cytology; D059865:Endoplasmic Reticulum Stress; D004789:Enzyme Activation; D005347:Fibroblasts / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction; D019892:eIF-2 Kinase / Q000378:metabolism
D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D008565:Membrane Proteins; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019892:eIF-2 Kinase; C486556:Ern2 protein, mouse
Apoptosis; Endoplasmic reticulum stress; Mouse embryonic fibroblast; UPR; c-FLIP