Arpin regulates migration persistence by interacting with both tankyrases and the Arp2/3 complex

During cell migration, protrusion of the leading edge is driven by the polymerization of Arp2/3-dependent branched actin networks. Migration persistence is negatively regulated by the Arp2/3 inhibitory protein Arpin. To better understand Arpin regulation in the cell, we looked for interacting partners and identified both Tankyrase 1 and 2 (TNKS) using a yeast two hybrid screen and co-immunoprecipitation with full-length Arpin as a bait. Arpin interacts with ankyrin repeats of TNKS through a C-terminal binding site on its acidic tail overlapping with the Arp2/3 binding site. To uncouple the interactions of Arpin with TNKS and Arp2/3, we introduced point mutations in the Arpin tail and attempted to rescue the increased persistence of the Arpin knock-out using random plasmid integration or compensating knock-in at the ARPIN locus. Arpin mutations impairing either Arp2/3- or TNKS-interaction were insufficient to fully abolish Arpin activity. Only the mutation that affects both interactions rendered Arpin completely inactive, suggesting the existence of two independent pathways, by which Arpin controls migration persistence. Arpin was found to dissolve liquid-liquid phase separation of TNKS upon overexpression. Together these data suggest that TNKS might be mediating the function of Arpin rather than regulating Arpin.