c-FLIP protein regulates autophagic flux by interacting with Beclin-1 and influencing its stability

c-FLIP protein is mostly known as an apoptosis modulator, but increasing data underline that c-FLIP has a complex role in cellular homeostasis, since it can differently influence the same pathway depending on its expression levels and its several isoforms. Few and controversial data are available regarding c-FLIP function within the molecular machinery responsible for the autophagic process. This issue has been addressed in the present work. We compared WT MEFs and c-FLIP-/- MEFs treated with autophagy-inducing stimuli and we found that autophagic flux is weaker in c-FLIP-/- MEFs than in WT cells. Therefore, we ran an analysis of specific markers of each autophagic phase and our data indicated that the absence of c-FLIP compromises the expression levels of pivotal factors in the nucleation of autophagosomes. As c-FLIP is a scaffold protein, we investigated and found a physical interaction between c-FLIP and Beclin-1, which is required for autophagosomes nucleation. Finally, a correlation between c-FLIP absence and Beclin-1 protein stability emerged thanks to a combination of bioinformatical tools and biochemistry assays, as we demonstrated that c-FLIP and Beclin-1 interaction is important to prevent Beclin-1 ubiquitination and degradation through the proteasomal pathway.