A fundamental question regarding autophagosome formation is how the shape of the double-membraneautophagosomal vesicle is generated. Here we show that in mammalian cells assembly of an actin scaffold inside the isolationmembrane (the autophagosomal precursor) is essential forautophagosomalmembraneshaping. Actin filaments are depolymerized shortly after starvation and actin is assembled into a network within theisolationmembrane. When formation of actin puncta is disrupted by an actin polymerization inhibitor or by knocking down the actin-capping protein CapZβ, isolation membranes and omegasomes collapse into mixed-membrane bundles. Formation of actin puncta is PtdIns(3)P dependent, and inhibition of PtdIns(3)P formation by treating cells with the PI(3)K inhibitor 3-MA, or by knocking down Beclin-1, abolishes the formation of actin puncta. Binding of CapZ to PtdIns(3)P, which is enriched in omegasomes, stimulates actin polymerization. Our findings illuminate the mechanism underlying autophagosomalmembraneshaping and provide key insights into how autophagosomes are formed.
- Mi N*, Chen Y, Wang S, Chen M, Zhao M, Yang G, Ma M, Su Q, Luo S, Shi J, Xu J, Guo Q, Gao N, Sun Y, Chen Z*, Yu L*. (2015) CapZ regulates autophagosomal membrane shaping by promoting actin assembly inside the isolation membrane. Nature Cell Biology, 17(9):1112-1123.
