ARF1-mediated actin polymerization produces movement of artificial vesicles

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Abstract
Vesicular trafficking and actin dynamics on Golgi membranes are both regulated by ADP-ribosylation factor 1 (ARF1) through the recruitment of various effectors, including vesicular coats. Actin assembly on Golgi membranes contributes to the architecture of the Golgi complex, vesicle formation, and trafficking and is mediated by ARF1 through a cascade that leads to Arp2/3 complex activation. Here we addressed the role of Golgi actin downstream of ARF1 by using a biomimetic assay consisting of liposomes of defined lipid composition, carrying an activated form of ARF1 incubated in cytosolic cell extracts. We observed actin polymerization around the liposomes resulting in thick actin shells and actin comet tails that pushed the ARF1 liposomes forward. The assay was used to characterize the ARF1-dependent pathway, leading to actin polymerization, and confirmed a dependency on CDC42 and its downstream effector N-WASP. Overall, this study demonstrates that actin polymerization driven by the complex multicomponent signaling cascade of the Golgi apparatus can be reproduced with a biomimetic system. Moreover, our results are consistent with the view that actin-based force generation at the site of vesicle formation contributes to the mechanism of fission. In addition to its well established function in coat recruitment, the ARF1 machinery also might produce movement- and fission-promoting forces through actin polymerization.