c-Flip KO fibroblasts display lipid accumulation associated with endoplasmic reticulum stress.
c-Flip proteins are well-known apoptosis modulators. They generally contribute to tissue homeostasis maintenance by inhibiting death-receptor-mediated cell death. In the present manuscript, we show that c-Flip knock-out (KO) mouse embryonic fibroblasts (MEFs) kept in culture under starvation conditions gradually modify their phenotype and accumulate vacuoles, becoming progressively larger according to the duration of starvation. Large vacuoles are present in KO MEFs though not in WT MEFs, and are Oil Red-O positive, which indicates that they represent lipid droplets. Western blot experiments reveal that, unlike WT MEFs, KO MEFs express high levels of the lipogenic transcription factor PPAR-γ. Lipid droplet accumulation was found to be associated with endoplasmic reticulum (ER) stress activation and autophagic modulation valuated by means of BIP increase, LC3 lipidation and AMP-activated protein kinase (AMPK) phosphorylation, and p62 accumulation. Interestingly, XBP-1, an ER stress-induced lipogenic transcription factor, was found to preferentially localize in the nucleus rather than in the cytoplasm of KO MEFs. These data demonstrate that, upon starvation, c-Flip affects lipid accumulation, ER stress and autophagy, thereby pointing to an important role of c-Flip in the adaptive response and ER stress response programs under both normal and pathological conditions.
Istituto Pasteur-Fondazione Cenci Bolognetti, Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Section of Histology and Medical Embryology, Sapienza University of Rome, Rome, Italy. Electronic address: claudia.giampietri@uniroma1.it.
Claudia
C
Giampietri
Istituto Pasteur-Fondazione Cenci Bolognetti, Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Section of Histology and Medical Embryology, Sapienza University of Rome, Rome, Italy.
Simonetta
S
Petrungaro
Istituto Pasteur-Fondazione Cenci Bolognetti, Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Section of Histology and Medical Embryology, Sapienza University of Rome, Rome, Italy.
Silvia
S
Conti
Istituto Dermopatico dell'Immacolata IDI-IRCCS, Rome, Italy.
Antonio
A
Facchiano
Istituto Pasteur-Fondazione Cenci Bolognetti, Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Section of Histology and Medical Embryology, Sapienza University of Rome, Rome, Italy.
Antonio
A
Filippini
Istituto Pasteur-Fondazione Cenci Bolognetti, Department of Anatomy, Histology, Forensic Medicine and Orthopedics, Section of Histology and Medical Embryology, Sapienza University of Rome, Rome, Italy.
Elio
E
Ziparo
D000818:Animals; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000235:genetics*; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free; D004268:DNA-Binding Proteins / Q000378:metabolism; D004622:Embryo, Mammalian; D059865:Endoplasmic Reticulum Stress / Q000235:genetics*; D005347:Fibroblasts / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D050356:Lipid Metabolism / Q000235:genetics*; D050155:Lipogenesis / Q000235:genetics; D051379:Mice; D047495:PPAR gamma / Q000378:metabolism; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors / Q000378:metabolism; D000071717:X-Box Binding Protein 1
D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506387:Cflar protein, mouse; D016895:Culture Media, Serum-Free; D004268:DNA-Binding Proteins; D047495:PPAR gamma; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605544:Xbp1 protein, mouse
Autophagy; ER stress; Lipid droplets; Mouse embryonic fibroblasts; c-Flip