Unleashing the Ambra1-Beclin 1 complex from dynein chains: Ulk1 sets Ambra1 free to induce autophagy

The Beclin 1-VPS34 complex plays a crucial role in the induction of the autophagic process by generating PtdIns(3)P-rich membranes, which act as platforms for ATG protein recruitment and autophagosome nucleation. Several cofactors, such as Ambra1, ATG14 and UVRAG, are necessary for Beclin 1 complex activity. However, the mechanism by which Beclin 1 complex activity is: stimulated by autophagic stimuli has not yet been fully elucidated. Recently, we reported that autophagosome formation in mammalian cells is primed by Ambra1 release from the dynein motor complex. We found that Ambra1 specifically binds the dynein motor complex under normal conditions through a direct interaction with DLC1. When autophagy is induced, Ambra1-DLC1 are released from the dynein complex in an ULK1-dependent manner, and relocalize to the endoplasmic reticulum, thus enabling autophagosome nucleation. In addition, we found that both DLC1 downregulation and Ambra1 mutations in its DLC1-binding sites strongly enhance autophagosome formation. Ambra1 is therefore not only a cofactor of Beclin 1 in favoring its kinase-associated activity, but also a crucial upstream regulator of autophagy initiation.