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 showthat 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, unlikeWTMEFs, KOMEFs 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