Ambra1 interplay with cullin E3 ubiquitin ligases defines the temporal dynamics of autophagy

Autophagy controls cell homeostasis by timely removing damaged organelles and harmful protein aggregates. While several key autophagy genes have been identified, how this pathway is rapidly and transiently induced in response to stress remains unclear. Here we report that the dynamic interaction of the E3 ubiquitin ligases Cullin-4 and Cullin-5 with the proautophagic molecule AMBRA1 controls the timing of autophagy execution. In normal conditions, Cullin-4, through its adaptor DDB1, associates with AMBRA1 to curtail its protein abundance. Autophagy stimuli trigger DDB1 dissociation via ULK1 activation, leading to AMBRA1 accumulation. AMBRA1 is so enabled to interact and inhibit the Cullin-5/Elongin-B/SOCS3 complex to stabilize the mTOR inhibitor DEPTOR, thus establishing an autoregulatory feedback loop that shortens the onset of autophagy response. Autophagy is finally terminated when Cullin-4/DDB1 reassociate to AMBRA1 driving its degradation. Overall, our findings show that Cullin-mediated degradation of autophagy regulators determines how autophagy is temporally tuned in response to stress.