ARPIN基因敲除HEK293细胞

Arp2/3 complex nucleates branched actin networks that drive cell motility and intracellular trafficking. Coronins, a family of seven proteins in humans, inhibit Arp2/3 complex in vitro and reduce branch density in cells. Coro7, a distant member of this family, features two β-propeller domains (β1β2) and C-terminal Central-Acidic (CA) domains and remains poorly studied. Here, cryo-EM and biochemical data show that CA binds subunit Arp3 of free Arp2/3 complex with ~1 µM affinity, inhibiting polymerization like Arpin, while displacing Arp3's autoinhibitory C-terminal tail and promoting the active, short-pitch conformation, like WASP-family nucleation-promoting factors. Full-length Coro7, however, does not inhibit Arp2/3 complex polymerization but effectively induces debranching, whereas the isolated β1β2 or CA domains do not. In cells, Coro7 depletion disrupts ER-Golgi transport, which is rescued by full-length Coro7 but not by truncated variants. These results suggest that Coro7 functions as an Arp2/3 complex branch disassembly factor implicated in actin-dependent ER-Golgi trafficking.

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 its interacting partners and identified both Tankyrase 1 and 2 (TNKS) using a yeast two-hybrid screening and coimmunoprecipitation with full-length Arpin as bait. Arpin interacts with ankyrin repeats of TNKS through a C-terminal-binding site on its acidic tail, which overlaps with the Arp2/3-binding site. Arpin was found to dissolve the liquid-liquid phase separation of TNKS upon overexpression. 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 migration persistence of the Arpin knockout cells using random plasmid integration or compensating knock-ins at the locus. Arpin mutations impairing interactions with either Arp2/3 or TNKS were insufficient to fully abolish Arpin activity. Only the mutation that affected both interactions rendered Arpin completely inactive, suggesting the existence of two independent pathways, whereby Arpin controls the migration persistence.